,,the ,,international ,,scientific ,,series ,,volume ,,lv ,,the ,,international ,,scientific ,,series ,,earthquakes ,,and ,,other ,,earth ,,movements ,,by ,,john ,,milne ,,professor ,,of ,,mining ,,and ,,geology ,,in ,,the ,,imperial ,,college ,,of ,,engineering1 ,,tokio1 ,,japan ,,with ,,thirty-,,eight ,,figures ,,new ,,york ,d4 ,,appleton ,,and ,,company #a1 #c1 ,,and #e ,,bond ,,street #ahhf ,,preface4 ,in the following pages it has been my object to give a systematic account of various ,earth ,movements4 ,these comprise ,earthquakes1 or the sudden violent movements of the ground2 ,earth ,tremors1 or minute movements which escape our attention by the smallness of their amplitude2 ,earth ,pulsations1 or movements which are overlooked on account of the length of their period2 and lastly1 ,earth ,oscillations1 or movements of long period and large amplitude which attract so much attention from their geological importance4 ,it is difficult to separate these ,earth ,movements from each other1 because they are phenomena which only differ in degree1 and which are intimately associated in their occurrence and in their origin4 ,because ,earthquakes are phenomena which have attracted a universal attention since the earliest times1 and about them so many observations have been made1 they are treated of at considerable length4 ,as very much of what might be said about the other ,earth ,movements is common to what is said about ,earthquakes1 it has been possible to make the description of these phenomena comparatively short4 ,the scheme which has been adopted will be understood from the following table3-- ,i4 ,,earthquakes4 #a4 ,introduction4 #b4 ,seismometry4 7a7 ,theoretically4 #c4 ,earthquake ,motion4 7b7 ,as deduced from experiments4 7c7 ,as deduced from actual ,earthquakes4 #d4 ,earthquake ,effects4 7a7 ,on land4 7b7 ,in the ocean4 #e4 ,determination of ,earthquake origins4 7a7 ,in space4 #f4 ,distribution of ,earthquakes4 7b7 ,in time 7geological time1 historical time1 annual1 seasonal1 diurnal1 c47 #g4 ,cause of ,earthquakes4 #h4 ,earthquake prediction and warning4 ,,ii4 ,,earth ,,tremors4 ,,iii4 ,,earth ,,pulsations4 ,,iv4 ,,earth ,,oscillations4 ,in some instances the grouping of phenomena according to the above scheme may be found inaccurate1 as1 for example1 in the chapters referring to the effects and causes of ,earthquakes4 ,this arises from the fact that the relationship between ,earthquakes and other ,earth phenomena are not well understood4 ,thus the sudden elevation of a coast line and an accompanying earthquake may be related1 either as effect and cause1 or vice vers1 or they may both be the effect of a third phenomenon4 ,much of what is said respecting ,earthquake motion will show how little accurate knowledge we have about these disturbances4 ,had ,i been writing in ,england1 and1 therefore1 been in a position to make references to libraries and persons who are authorities on subjects connected with ,seismology1 the following pages might have been made more complete1 and inaccuracies avoided4 ,a large proportion of the material embodied in the following pages is founded on experiments and observations made during an eight years' residence in ,japan1 where ,i have had the opportunity of recording an earthquake every week4 ,the writer to whom ,i am chiefly indebted is ,mr4 ,robert ,mallet4 ,not being in a position to refer to original memoirs1 ,i have drawn many illustrations from the works of ,professor ,karl ,fuchs and ,m4 ,s4 di ,rossi4 ,these1 and other writers to whom reference has been made1 are given in an appendix4 ,for seeing these pages through the press1 my thanks are due to ,mr4 ,thomas ,gray1 who1 when residing in ,japan1 did so much for the advancement of observational ,seismology4 ,for advice and assistance in devising experiments1 ,i tender my thanks to my colleagues1 ,professor ,t4 ,alexander1 ,mr4 ,t4 ,fujioka1 and to my late colleague4 ,professor ,john ,perry4 ,for assistance in the actual observation of ,earthquakes1 ,i have to thank my friends in various parts of ,japan1 especially ,mr4 ,j4 ,bissett and ,mr4 ,t4 ,talbot1 of ,yokohama4 ,for assistance in obtaining information from ,italian sources ,i have to thank ,dr4 ,f4 ,du ,bois1 from ,german sources ,professor ,c4 ,netto1 and from ,japanese sources ,mr4 ,b4 ,h4 ,chamberlain4 ,for help in carrying out experiments1 ,i am indebted to the liberality of the ,british ,association1 the ,geological ,society of ,london1 the ,meteorological and ,telegraph departments of ,japan1 and to the officers of my own institution1 the ,imperial ,college of ,engineering4 ,and1 lastly1 ,i offer my sincere thanks to those gentlemen who have taken part in the establishment and working of the ,seismological ,society of ,japan1 and to my publishers1 whose liberality has enabled me to place the labours of residents in the ,far ,east before the ,european public4 ,,john ,,milne4 ,,tokio1 ,,japan2 ,june #cj1 #ahhc ,,contents4 ,,chapter ,i4 ,,introduction4 ,,page ,relationship of man to nature--,the aspect of a country is dependent on geological phenomena--,earthquakes an important geological phenomenon--,relationship of seismology to the sciences and arts--,earth movements other than earthquakes--,seismological literature--7,writings of ,perrey1 ,mallet1 ,eastern writings1 the ,philosophical ,transactions of the ,royal ,society1 the #8,gentleman's ,magazine1' the ,bible1 ,herodotus1 ,pliny1 ,hopkins1 ,von ,hoff1 ,humboldt1 ,schmidt1 ,seebach1 ,lasaulx1 ,fuchs1 ,palmieri1 ,bertelli1 ,seismological ,society of ,japan7--,seismological terminology #a ,,chapter ,,ii4 ,,seismometry4 ,nature of earthquake vibrations--,many instruments called seismometers only seismoscopes--,eastern seismoscopes1 columns1 projection seismometers--,vessels filled with liquid--,palmieri's mercury tubes--,the ship seismoscope--,the cacciatore--,pendulum instruments of ,kreil1 ,wagner1 ,ewing1 and ,gray--,bracket seismographs--,west's parallel motion instrument--,gray's conical pendulums1 rolling spheres1 and cylinders--,verbeck's ball and plate seismograph--,the principle of ,perry and ,ayrton--,vertical motion instruments--,record receiver--,time-recording apparatus--,the ,gray and ,milne seismograph #ab ,,chapter ,,iii4 ,,earthquake ,,motion ,,discussed ,,theoretically4 ,ideas of the ancients 7the views of ,travagini1 ,hooke1 ,woodward1 ,stukeley1 ,mitchell1 ,young1 ,mallet7--,nature of elastic waves and vibrations--,possible causes of disturbance in the earth's crust--,the time of vibration of an earth particle--,velocity and acceleration of a particle--,propagation of a disturbance as determined by experiments upon the elastic moduli of rocks--,the intensity of an earthquake--,area of greatest overturning moment--,earthquake waves--,reflexion1 refraction1 and interference of waves--,radiation of a disturbance #da ,,chapter ,,iv4 ,,earthquake ,,motion ,,as ,,deduced ,,from ,,experiment4 ,experiments with falling weights--,experiments with explosives--,results obtained from experiments--,relative motion of two adjacent points--,the effect of hills and excavations upon the propagation of vibrations--,the intensity of artificial disturbances--,velocity with which earth vibrations are propagated--,experiments of ,mallet--,experiments of ,abbot--,experiments in ,japan--,mallet's results--,abbot's results--,results obtained in ,japan #eg ,,chapter ,v4 ,,earthquake ,,motion ,,as ,,deduced ,,from ,,observation ,,on ,,earthquakes4 ,result of feelings--,the direction of motion--,instruments as indicators of direction--,duration of an earthquake--,period of vibration--,the amplitude of earth movements--,side of greatest motion--,intensity of earthquakes--,velocity and acceleration of an earth particle--,absolute intensity of an earthquake--,radiation of an earthquake--,velocity of propagation #fg ,,chapter ,,vi4 ,,effects ,,produced ,,by ,,earthquakes ,,upon ,,buildings4 ,the destruction of buildings is not irregular--,cracks in buildings--,buildings in ,tokio--,relation of destruction to earthquake motion--,measurement of relative motion of parts of a building shaken by an earthquake--,prevention of cracks--,direction of cracks--,the pitch of roofs--,relative position of openings in a wall--,the last house in a row--,the swing of buildings--,principle of relative vibrational periods #if ,,chapter ,,vii4 ,,effects ,,produced ,,upon ,,buildings 7continued74 ,types of buildings used in earthquake countries--,in ,japan1 in ,italy1 in ,south ,america1 in ,caraccas--,typical houses for earthquake countries--,destruction due to the nature of underlying rocks--,the swing of mountains--,want of support on the face of hills--,earthquake shadows--,destruction due to the interference of waves--,earthquake bridges--,examples of earthquake effects--,protection of buildings--,general conclusions #abb ,,chapter ,,viii4 ,,effects ,,of ,,earthquakes ,,on ,,land4 #a4 ,cracks and fissures--,materials discharged from fissures--,explanation of fissure phenomena4 #b4 ,disturbances in lakes1 rivers1 springs1 wells1 fumaroles1 c4--,explanation of these latter phenomena4 #c4 ,permanent displacement of ground--,on coast lines--,level tracts--,among mountains--,explanation of these movements #adf ,,chapter ,,ix4 ,,disturbances ,,in ,,the ,,ocean4 ,sea vibrations--,cause of vibratory blows--,sea waves3 preceding earthquakes2 succeeding earthquakes--,magnitude of waves--,waves as recorded in countries distant from the origin--,records on tide gauges--,waves without earthquakes--,cause of waves--,phenomena difficult of explanation--,velocity of propagation--,depth of the ocean--,examples of calculations--,comparison of velocities of earthquake waves with velocities which ought to exist from the known depth of the ocean #afc ,,chapter ,x4 ,,determination ,,of ,,earthquake ,,origins4 ,approximate determination of an origin--,earthquake-hunting in ,japan--,determinations by direction of motion--,direction indicated by destruction of buildings--,direction determined by rotation--,cause of rotation--,the use of time observations--,errors in such observations--,origin determined by the method of straight lines--,the method of circles1 the method of hyperbolas1 the method of co-ordinates--,haughton's method--,difference in time between sound1 earth1 and water waves--,method of ,seebach #ahg ,,chapter ,,xi4 ,,the ,,depth ,,of ,,an ,,earthquake ,,centrum4 ,the depth of an earthquake centrum--,greatest possible depth of an earthquake--,form of the focal cavity #bac ,,chapter ,,xii4 ,,distribution ,,of ,,earthquakes ,,in ,,space ,,and ,,time4 ,general distribution of earthquakes--,occurrence along lines--,examples of distribution--,italian earthquake of #ahgc--;,in ,tokio--,extension of earthquake boundaries--,seismic energy in relation to geological time2 to historical time--,relative frequency of earthquakes--,synchronism of earthquakes--,secondary earthquakes #bbf ,,chapter ,,xiii4 ,,distribution ,,of ,,earthquakes ,,in ,,time 7continued7 #bcd ,,chapter ,,xiv4 ,,distribution ,,of ,,earthquakes ,,in ,,time 7continued74 ,the occurrence of earthquakes in relation to the position of the heavenly bodies--,earthquakes and the moon--,earthquakes and the sun2 and the seasons2 the months--,planets and meteors--,hours at which earthquakes are frequent--,earthquakes and sun spots--,earthquakes and the aurora #bej ,,chapter ,,xv4 ,,barometrical ,,fluctuations ,,and ,,earthquakes--,,fluctuations ,,in ,,temperature ,,and ,,earthquakes #bff ,,chapter ,,xvi4 ,,relation ,,of ,,seismic ,,to ,,volcanic ,,phenomena4 ,want of synchronism between earthquakes and volcanic eruptions--,synchronism between earthquakes and volcanic eruptions--,conclusion #bgj ,,chapter ,,xvii4 ,,the ,,cause ,,of ,,earthquakes4 ,modern views respecting the cause of earthquakes--,earthquakes due to faulting--,to explosions of steam--,to volcanic evisceration--,to chemical degradation--,attractive influence of the heavenly bodies--,the effect of oceanic tides--,variation in atmospheric pressure--,fluctuation in temperature--,winds and earthquakes--,rain and earthquakes--,conclusion #bgg ,,chapter ,,xviii4 ,,prediction ,,of ,,earthquakes4 ,general nature of predictions--,prediction by the observation of unusual phenomena 7,alteration in the appearance and taste of springs2 underground noises2 preliminary tremors2 ,earthquake prophets--warnings furnished by animals1 c47--,earthquake warning #big ,,chapter ,,xix4 ,,earth ,,tremors4 ,artificially produced tremors--,observations of ,kater1 ,denman1 ,airy1 ,palmer1 ,paul--,natural tremors--,observations of ,zllner1 ,m4 d',abbadie1 ,g4 ,h4 and ,h4 ,darwin--,experiments in ,japan--,with seismoscopes1 microphones1 pendulums--,work in ,italy--,bertelli1 ,count ,malvasia1 ,m4 ,s4 di ,rossi--,instruments employed in ,italy--,tromometers1 microseismographs1 microphones--,results obtained in ,italy--,in ,japan--,cause of microseismic motion #cjf ,,chapter ,,xx4 ,,earth ,,pulsations4 ,definition of an earth pulsation--,indications of pendulums--,indications of levels--,other phenomena indicating the existence of earth pulsations--,disturbances in lakes and oceans--,phenomena resultant on earth pulsations--,cause of earth pulsations #cbf ,,chapter ,,xxi4 ,,earth ,,oscillations4 ,evidences of oscillation--,examples of oscillation--,temple of ,jupiter ,serapis--,observations of ,darwin--,causes of oscillation #cdd ,,appendix #cdi ,,index #cei ,,earthquakes4 ,,chapter ,i4 ,,introduction4 ,relationship of man to nature--,the aspect of a country is dependent on geological phenomena--,earthquakes an important geological phenomenon--,relationship of seismology to the sciences and arts--,earth movements other than earthquakes--,seismological literature--7,writings of ,perrey1 ,mallet1 ,eastern writings1 the ,philosophical ,transactions of the ,royal ,society1 the #8,gentleman's ,magazine1' the ,bible1 ,herodotus1 ,pliny1 ,hopkins1 ,von ,hoff1 ,humboldt1 ,schmidt1 ,seebach1 ,lasaulx1 ,fuchs1 ,palmieri1 ,bertelli1 ,seismological ,society of ,japan7--,seismological terminology4 ,in bygone superstitious times lightning and thunder were regarded as supernatural visitations4 ,but as these phenomena became better understood1 and men learned how to avoid their destructive power1 the superstition was gradually dispelled4 ,thus it is with ,earthquakes3 the more clearly they are understood1 the more confident in the universality of law will man become1 and the more will his mental condition be advanced4 ,in his #8,history of ,civilisation in ,england1' ,buckle has laid considerable stress upon the manner in which earthquakes1 volcanoes1 and other of the more terrible forms in which the workings of nature reveal themselves to us1 have exerted an influence upon the imagination and understanding2 and just as a sudden fright may affect the nerves of a child for the remainder of its life1 we have in the annals of seismology records which indicate that earthquakes have not been without a serious influence upon the mental condition of whole communities4 ,to a geologist there are perhaps no phenomena in nature more interesting than earthquakes1 the study of which is called ,seismology4 ,coming1 as shocks often will1 from a region of volcanoes1 the study of these disturbances may enable us to understand something about the nature and working of a volcano4 ,as an earthquake wave travels along from strata to strata1 if we study its reflections and changing velocity in transit1 we may often be led to the discovery of certain rocky structures buried deep beneath our view1 about which1 without the help of such waves1 it would be hopeless ever to attain any knowledge4 ,by studying the propagation of earthquake waves the physicist is enabled to confirm his speculations respecting the transmission of disturbances in elastic media4 ,for the physicist earthquakes are gigantic experiments which tell him the elastic moduli of rocks as they exist in nature1 and when properly interpreted may lead him to the proper comprehension of many ill-understood phenomena4 ,it is not impossible that seismological investigation may teach us something about the earth's magnetism1 and the connection between earthquakes and the #8earth currents' which appear in our telegraph wires4 ,these and numerous other kindred problems fall within the domain of the physicist4 ,it is of interest to the meteorologist to know the connections which probably exist between earthquakes and the fluctuations of the barometer1 the changes of the thermometer1 the quantity of rainfall1 and like phenomena to which he devotes his attention4 ,next we may turn to the more practical aims of seismology and ask ourselves what are the effects of earthquakes upon buildings1 and how1 in earthquake-shaken countries1 the buildings are to be made to withstand them4 ,here we are face to face with problems which demand the attention of engineers and builders4 ,to attain what we desire1 observation1 common sense1 and subtle reasoning must be brought to bear upon this subject4 ,in the investigation of the principle on which earthquake instruments make their records1 in the analysis of the results they give1 in problems connected with astronomy1 with physics1 and with construction1 seismology offers to the mathematician new fields for investigation4 ,a study of the effects which earthquakes produce on the lower animals will not fail to interest the student of natural history4 ,a study like seismology1 which leads us to a more complete knowledge of earth-heat and its workings1 is to be regarded as one of the corner-stones of geology4 ,the science of seismology invites the co-operation of workers and thinkers in almost every department of natural science4 ,we have already referred to the influence exerted by earthquakes over the human mind4 ,how to predict earthquakes1 and how to escape from their dangers1 are problems which1 if they can be solved1 are of extreme interest to the world at large4 ,in addition to the sudden and violent movements which we call earthquakes1 the seismologist has to investigate the smaller motions which we call earth tremors4 ,from observations which have been made of late years1 it would appear that the ground on which we dwell is incessantly in a state of tremulous motion4 ,a further subject of investigation which is before the seismologist is the experimental verification of the existence of what may be called #8earth-pulsations4' ,these are motions which mathematical physicists affirmed the existence of1 but which1 in consequence of the slowness of their period1 have hitherto escaped observation4 ,the oscillations1 or slow changes in the relative positions of land and sea1 might also be included2 but this has already been taken up as a separate branch of geology4 ,these four classes of movements are no doubt interdependent1 and seismology in the widest sense might conveniently be employed to include them all4 ,in succeeding chapters we will endeavour to indicate how far the first three of these branches have been prosecuted1 and to point out that which remains to be accomplished4 ,it is difficult1 however1 to form a just estimate of the amount of seismological work which has been done1 in consequence of the scattered and uncertain nature of many of the records4 ,seismology1 as a science1 originated late1 chiefly owing to the facts that centres of civilisation are seldom in the most disturbed regions1 and that earthquake-shaken countries are widely separated from each other4 ,as every portion of the habitable globe appears to have been shaken more or less by earthquakes1 and as these phenomena are so terrible in their nature1 we can readily understand why seismological literature is extensive4 ,in the annals of almost every country which has a written history1 references are made to seismic disturbances4 ,an idea of the attention which earthquakes have received may be gathered from the fact that ,professor ,alexis ,perrey1 of ,dijon1 who has published some sixty memoirs on this subject1 gave1 in #ahef1 a catalogue of #a1hcg works devoted to seismology4#a ,in #aheh ,mr4 ,robert ,mallet published in the ,reports of the ,british ,association a list of several hundred works relating to earthquakes4 ,sixty-five of these works are to be found in the ,british ,museum4 ,so far as literature is concerned1 earthquakes have received as much attention in the ,east as in the ,west4 ,in ,china there are many works treating on earthquakes1 and the attention which these phenomena received may be judged of from the fact that in ,a4,d4 #acf the ,government appointed a commission to inquire into the subject4 ,even the isolated empire of ,japan can boast of at least sixty-five works on earthquakes1 seven of which are earthquake calendars1 and twenty-three earthquake monographs4#b ,besides those treating especially of earthquakes1 there are innumerable references to such disturbances in various histories1 in the transactions of learned societies1 and in periodicals4 ,to attempt to give a complete catalogue of even the books which have been written would be to enter on a work of compilation which would occupy many years1 and could never be satisfactorily finished4 ,in the #8,philosophical ,transactions of the ,royal ,society1' which were issued in the eighteenth century1 there are about one hundred and eighty separate communications on earthquakes2 and in the #8,gentleman's ,magazine' for #agee there are no less than fifty notes and articles on the same subject4 ,the great interest shown in earthquakes about the years #agej-fj in ,england1 was chiefly due to the terrible calamity which overtook ,lisbon in #agee1 and to the fact that about this time several shocks were experienced in various parts of the ,british ,islands4 ,in #agej1 which may be described as the earthquake year of ,britain1 #8a shock was felt in ,surrey on ,march #ad2 on the #ahth of the same month the whole of the south-west of ,england was disturbed4 ,on ,april #b1 ,chester was shaken2 on ,june #g1 ,norwich was disturbed2 on ,august #bc1 the inhabitants of ,lancashire were alarmed2 and on ,september #cj ludicrous and alarming scenes occurred in consequence of a shock having been felt during the hours of ,divine service1 causing the congregations to hurry into the open air4'#c ,as might be expected1 these occurrences gave rise to many articles and notes directing attention to the subject of earthquakes4 ,seismic literature has not1 however1 at all times been a measure of seismic activity3 thus1 in ,japan1 the earthquake records for the twelfth and sixteenth centuries scarcely mention any shocks4 ,at first sight it might be imagined that this was owing to an absence of earthquakes2 but it is sufficiently accounted for by the fact that at that time the country was torn with civil war1 and matters more urgent than the recording of natural phenomena engaged the attention of the inhabitants4 ,professor ,rockwood1 who has given so much attention to seismic disturbances in ,america1 tells us that during the recent contest between ,chili and ,peru a similar intermission is observable4 ,we see1 therefore1 that an absence of records does not necessarily imply an absence of the phenomena to be recorded4 ,perhaps the earliest existing records of earthquakes are those which occur in the ,bible4 ,the first of these1 which we are told occurred in ,palestine1 was in the reign of ,ahab 7,b4,c4 #iah-hig74d ,one of the most terrible earthquakes mentioned in the ,bible is that which took place in the days of ,uzziah1 king of ,judah 7,b4,c4 #haa-gei71 which shook the ground and rent the ,temple4 ,the awful character of this1 and the deep impression produced on men's minds1 may be learned from the fact that the time of its occurrence was subsequently used as an epoch from which to reckon dates4 ,the writings of ,herodotus1 ,pliny1 ,livy1 c41 c41 show the interest which earthquakes attracted in early ages4 ,these writers chiefly devoted themselves to references and descriptions of disastrous shocks1 and to theories respecting the cause of earthquakes4 ,the greater portion of the ,japanese notices of earthquakes is simply a series of anecdotes of events which took place at the time of these disasters4 ,we also find references to superstitious beliefs1 curious occurrences1 and the apparent connection between earthquake disturbances and other natural phenomena4 ,in these respects the literature of the ,east closely resembles that of the ,west4 ,the earthquake calendars of the ,east1 however1 form a class of books which can hardly be said to find their parallel in ,europe2#e while1 on the other hand1 the latter possesses types of books and pamphlets which do not appear to have a parallel elsewhere4 ,these are the more or less theological works--#8,moral ,reflections on ,earthquakes1' #8,sermons' which have been preached on earthquakes1 #8,prayers' which have been appointed to be read4#f ,speaking generally1 it may be said that the writings of the ancients1 and those of the ,middle ,ages1 down to the commencement of the nineteenth century1 tended to the propagation of superstition and to theories based on speculations with few and imperfect facts for their foundation4 ,among the efforts which have been made in modern times to raise seismology to a higher level1 is that of ,professor ,perrey1 of ,dijon1 who commenced in #ahdj a series of extensive catalogues embracing the earthquakes of the world4 ,these catalogues enabled ,perrey1 and subsequently ,mallet in his reports to the ,british ,association1 to discuss the periodicity of earthquakes1 with reference to the seasons and to other phenomena1 in a more general manner than it had been possible for previous workers to accomplish4 ,the facts thus accumulated also enabled ,mallet to discuss earthquakes in general1 and the various phenomena which they present were sifted and classified for inspection4 ,another great impetus which observational seismology received was ,mr4 ,mallet's report upon the ,neapolitan earthquake of #aheg1 in which new methods of seismic investigation were put forth4 ,these have formed the working tools of many subsequent observers1 and by them1 as well as by his experiments on artificially produced disturbances1 ,mallet finally drew the study of earthquakes from the realms of speculation by showing that they1 like other natural phenomena1 were capable of being understood and investigated4 ,in addition to ,perrey and ,mallet1 the nineteenth century has produced many writers who have taken a considerable share in the advancement of seismology4 ,there are the catalogues of ,von ,hoff1 the observations of ,humboldt1 the theoretical investigations of ,hopkins1 the monographs of ,schmidt1 ,seebach1 ,lasaulx1 and others2 the books of ,fuchs1 ,credner1 ,vogt1 ,volger2 the records and observations of ,palmieri1 ,bertelli1 ,rossi1 and other ,italian observers4 ,to these1 which are only a few out of a long list of names1 may be added the publications of the ,commission appointed for the observation of earthquakes by the ,natural ,history ,society of ,switzerland1 and the volumes which have been published by the ,seismological ,society of ,japan4 ,before concluding this chapter it will be well to define a few of the more ordinary terms which are used in describing earthquake phenomena4 ,it may be observed that the ,english word earthquake1 the ,german erdbeben1 the ,french tremblement de terre1 the ,spanish terremoto1 the ,japanese jishin c41 all mean1 when literally translated1 earth-shaking1 and are popularly understood to mean a sudden and more or less violent disturbance4 ,seismology 7 an earthquake1 a discourse7 in its simplest sense means the study of earthquakes4 ,to be consistent with a ,greek basis for seismological terminology1 some writers have thrown aside the familiar expression #8earthquake1' and substituted the awkward word #8seism4' ,the source from which an earthquake originates is called the #8origin1' #8focal cavity1' or #8centrum4' ,the point or area on the surface of the ground above the origin is called the #8epicentrum4' ,the line joining the centrum and epicentrum is called the #8seismic vertical4' ,the radial lines along which an earthquake may be propagated from the centrum are called #8wave paths4' ,the angle which a wave path1 where it reaches the surface of the earth1 makes with that surface is called the #8angle of emergence' of the wave4 ,this angle is usually denoted by the letter e4 ,as the result of a simple explosion at a point in a homogeneous medium1 we ought1 theoretically1 to obtain at points on the surface of the medium equidistant from the epicentrum1 equal mechanical effects4 ,these points will lie on circles called #8isoseismic' or #8coseismic' circles4 ,the area included between two such circles is an #8isoseismic area4' ,in nature1 however1 isoseismic lines are seldom circles4 ,elliptical or irregular curves are the common forms4 ,the isoseismic area in which the greatest disturbance has taken place is called the #8meizoseismic area4' ,seebach calls the lines enclosing this area #8pleistoseists4' ,these last-mentioned lines are wholly due to ,mallet and ,seebach4 ,many words are used to distinguish different kinds of earthquakes from each other4 ,all of these appear to be very indefinite and to depend upon the observer's feelings1 which1 in turn1 depend upon his nervous temperament and his situation4 ,in ,south ,america small earthquakes1 consisting of a series of rapidly recurring vibratory movements not sufficiently powerful to create damage1 are spoken of as trembelores4 ,the terremotos of ,south ,america are earthquakes of a destructive nature1 in which distinct shocks are perceptible4 ,it may be observed that shocks which at one place would be described as terremoto would at another and more distant place probably be described as trembelores4 ,the succussatore are the shocks where there is considerable vertical motion4 ,the terrible shock of ,riobamba 7,february #d1 #agig71 which is said to have thrown corpses from their graves to a height of #ajj feet1 was an earthquake of this order4 ,the vorticosi are shocks which have a twisting or rotatory motion4 ,another method of describing earthquakes would be to refer to instrumental records4 ,when the vibrations of the ground have only been along the line joining the observer and the epicentrum1 the disturbance might be called #8euthutropic4' ,a disturbance in which the prominent movements are transverse to the above direction might be called #8diagonic4' ,if motions in both of these directions occur in the records1 the shock might be said to be #8diastrophic4' ,if there be much vertical movement1 the shock might be said to be #8anaseismic4' ,some disturbances could only be described by using two or three of these terms4 ,,chapter ,,ii4 ,,seismometry4 ,nature of earthquake vibrations--,many instruments called seismometers only seismoscopes--,eastern seismoscopes1 columns1 projection seismometers--,vessels filled with liquid--,palmieri's mercury tubes--,the ship seismoscope--,the cacciatore--,pendulum instruments of ,kreil1 ,wagner1 ,ewing1 and ,gray--,bracket seismographs--,west's parallel motion instrument--,gray's conical pendulums1 rolling spheres1 and cylinders--,verbeck's ball and plate seismograph--,the principle of ,perry and ,ayrton--,vertical motion instruments--,record receivers--,time-recording apparatus--,the ,gray and ,milne seismograph4 ,before we discuss the nature of earthquake motion1 the determination of which has been the aim of modern seismological investigation1 the reader will naturally look for an account of the various instruments which have been employed for recording such disturbances4 ,a description of the earthquake machines which have been used even in ,japan would form a bulky volume4 ,all that we can do1 therefore1 is to describe briefly the more prominent features of a few of the more important of these instruments4 ,in order that the relative merits of these may be better understood1 we may state generally that modern research has shown a typical earthquake to consist of a series of small tremors succeeded by a shock1 or series of shocks1 separated by more or less irregular vibrations of the ground4 ,the vibrations are often both irregular in period and in amplitude1 and they have a duration of from a few seconds to several minutes4 ,we will illustrate the records of actual earthquakes in a future chapter1 but in the meantime the idea that an earthquake consists of a single shock must be dismissed from the imagination4 ,to construct an instrument which at the time of an earthquake shall move and leave a record of its motion1 there is but little difficulty4 ,contrivances of this order are called seismoscopes4 ,if1 however1 we wish to know the period1 extent1 and direction of each of the vibrations which constitutes an earthquake1 we have considerable difficulty4 ,instruments which will in this way measure or write down the earth's motions are called seismometers or seismographs4 ,many of the elaborate instruments supplemented with electro-magnetic and clockwork arrangements are1 when we examine them1 nothing more than elaborate seismoscopes which have been erroneously termed seismographs4 ,the only approximations to true seismographs which have yet been invented are without doubt those which during the past few years have been used in ,japan4 ,it would be a somewhat arbitrary proceeding1 however1 to classify the different instruments as seismoscopes1 seismometers1 and seismographs1 as the character of the record given by certain instruments is sometimes only seismoscopic1 whilst at other times it is seismometric1 depending on the nature of the disturbance4 ,many instruments1 for instance1 would record with considerable accuracy a single sudden movement1 but would give no reliable information regarding a continued shaking4 ,eastern ,seismoscopes4--,the earliest seismoscope of which we find any historical record is one which owes its origin to a ,chinese called ,chko4 ,it was invented in the year ,a4,d4 #acf4 ,a description is given in the ,chinese history called #8,gokanjo1' and the translation of this description runs as follows3-- #8,in the first year of ,yka1 ,a4,d4 #acf1 a ,chinese called ,chko invented the seismometer shown in the accompanying drawing4 ,this instrument consists of a spherically formed copper vessel1 the diameter of which is eight feet4 ,it is covered at its top1 and in form resembles a wine-bottle4 ,its outer part is ornamented by the figures of different kinds of birds and animals1 and old peculiar-looking letters4 ,in the inner part of this instrument a column is so suspended that it can move in eight directions4 ,also1 in the inside of the bottle1 there is an arrangement by which some record of an earthquake is made according to the movement of the pillar4 ,on the outside of the bottle there are eight dragon heads1 each of which holds a ball in its mouth4 ,underneath these heads there are eight frogs so placed that they appear to watch the dragon's face1 so that they are ready to receive the ball if it should be dropped4 ,all the arrangements which cause the pillar to knock the ball out of the dragon's mouth are well hidden in the bottle4' ,illustration3 ,,fig4 #a4 #8,when an earthquake occurs1 and the bottle is shaken1 the dragon instantly drops the ball1 and the frog which receives it vibrates vigorously2 any one watching this instrument can easily observe earthquakes4' ,with this arrangement1 although one dragon may drop a ball1 it is not necessary for the other seven dragons to drop their balls unless the movement has been in all directions2 thus we can easily tell the direction of an earthquake4 #8,once upon a time a dragon dropped its ball without any earthquake being observed1 and the people therefore thought the instrument of no use1 but after two or three days a notice came saying that an earthquake had taken place at ,rsei4 ,hearing of this1 those who doubted the use of this instrument began to believe in it again4 ,after this ingenious instrument had been invented by ,chko1 the ,chinese ,government wisely appointed a secretary to make observations on earthquakes4' ,not only is this instrument of interest on account of its antiquity1 but it is also of interest on account of the close resemblance it bears to many of the instruments of modern times4 ,another earthquake instrument also of ,eastern origin is the magnetic seismoscope of ,japan4 ,on the night of the destructive earthquake of #ahee1 which devastated a great portion of ,tokio1 the owner of a spectacle shop in ,asakusa observed that a magnet dropped some old iron nails and keys which had been attached to it4 ,from this occurrence the owner thought that the magnet had1 in consequence of its age1 lost its powers4 ,about two hours afterwards1 however1 the great earthquake took place1 after which the magnet was observed to have regained its powers4 ,this occurrence led to the construction of the seismoscope1 which is illustrated in a book called the #8,ansei-,kembun-,roku1' or a description of the earthquake of #ahee1 and examples of the instrument are still to be seen in ,tokio4 ,these instruments consist of a piece of magnetic iron ore1 which holds up a piece of iron like a nail4 ,this nail is connected1 by means of a string1 with a train of clockwork communicating with an alarm4 ,if the nail falls a catch is released and the clockwork set in motion1 and warning given by the ringing of a bell4 ,it does not appear that this instrument has ever acted with success4 ,columns4--,one of the commonest forms of seismoscope1 and one which has been very widely used1 consists of a round column of wood1 metal1 or other suitable material1 placed1 with its axis vertical1 on a level plane1 and surrounded by some soft material such as loose sand to prevent it rolling should it be overturned4 ,the fall of such a column indicates that a shaking or shock has taken place4 ,attempts have been made by using a number of columns of different sizes to make these indications seismometric1 but they seldom give reliable information either as to intensity or direction of shock4 ,the indications as to intensity are vitiated by the fact that a long-continued gentle shaking may overturn a column which would stand a very considerable sudden shock1 while the directions in which a number of columns fall seldom agree owing to the rotational motion imparted to them by the shaking4 ,besides1 the direction of motion of the earthquake seldom remains in the same azimuth throughout the whole disturbance4 ,an extremely delicate1 and at the same time simple form of seismoscope may be made by propping up strips of glass1 pins1 or other easily overturned bodies against suitably placed supports4 ,in this way bodies may be arranged1 which1 although they can only fall in one direction1 nevertheless fall with far less motion than is necessary to overturn any column which will stand without lateral support4 ,projection ,seismometers4--,closely related to the seismoscopes and seismometers which depend on the overturning of bodies4 ,mallet has described two sets of apparatus whose indications depend on the distance to which a body is projected4 ,in one of these1 which consisted of two similar parts arranged at right angles1 two metal balls rest one on each side of a stop at the lower part of two inclined _/ like troughs4 ,in this position each of the balls completes an electric circuit4 ,by a shock the balls are projected or rolled up the troughs1 and the height to which they rise is recorded by a corresponding interval in the break of the circuits4 ,the vertical component of the motion is measured by the compression of a spring which carries the table on which this arrangement rests4 ,in the second apparatus two balls are successively projected1 one by the forward swing1 and the other by the backward swing of the shock4 ,attached to them are loose wires forming terminals of the circuits4 ,they are caught in a bed of wet sand in a metal trough forming the other end of the circuit4 ,the throw of the balls as measured in the sand1 and the difference of time between their successive projections as indicated by special contrivances connected with the closing of the circuits1 enables the observer to calculate the direction of the wave of shock1 its velocity1 and other elements connected with the disturbance4 ,it will be observed that the design of this apparatus assumes the earthquake to consist of a distinct isolated shock4 ,oldham1 at the end of his account of the ,cachar earthquake of #ahfi1 recommends the use of an instrument based on similar principles4 ,in his instrument four balls like bullets are placed in notches cut in the corners of the upper end of a square stake driven into the ground4 ,vessels filled with liquid4--,another form of simple seismoscope is made by partially filling a vessel with liquid4 ,the height to which the liquid is washed up the side of the vessel is taken as an indication of the intensity of the shock1 and the line joining the points on which maximum motion is indicated1 is taken as the direction of the shock4 ,if earthquakes all lasted for the same length of time1 and consisted of vibrations of the same period1 such instruments might be of service4 ,these instruments have1 however1 been in use from an early date4 ,in #agdb we find that bowls of water were used to measure the earthquakes which in that year alarmed the inhabitants of ,leghorn4 ,about the same time the ,rev4 ,s4 ,chandler1 writing about the shock at ,lisbon1 tells us that earthquakes may be measured by means of a spherical bowl about three or four feet in diameter1 the inside of which1 after being dusted over with ,barber's puff1 is filled very gently with water4 ,mallet1 ,babbage1 and ,de la ,bche have recommended the same sort of contrivance1 but1 notwithstanding1 it has justly been criticised as #8ridiculous and utterly impracticable4'#g ,an important portion of ,palmieri's well-known instrument consists of horizontal tubes turned up at the ends and partially filled with mercury4 ,to magnify the motion of the mercury1 small floats of iron rest on its surface4 ,these are attached by means of threads to a pulley provided with indices which move in front of a scale of degrees4 ,we thus read off the intensity of an earthquake as so many degrees1 which means so many millimetres of washing up and down of mercury in a tube4 ,the direction of movement is determined by the azimuth of the tube which gives the maximum indication1 several tubes being placed in different azimuths4 ,this form of instrument appears to have been suggested by ,mallet1 who gives an account of the same in #ahdf4 ,inasmuch as the rise and fall of the mercury in such tubes depend on its depth and on the period of the earthquake together with its duration1 we see that although the results obtained from a given instrument may give us means of making approximate comparisons as to the relative intensity of various earthquakes1 it is very far from yielding any absolute measurement4 ,another method which has been employed to magnify and register the motions of liquid in a vessel has been to float upon its surface a raft or ship from which a tall mast projected4 ,by a slight motion of the raft1 the top of the mast vibrated through a considerable range4 ,this motion of the mast as to direction and extent was then recorded by suitable contrivances attached to the top of the mast4 ,a very simple form of liquid seismoscope consists of a circular trough of wood with notches cut round its side4 ,this is filled with mercury to the level of the notches4 ,at the time of an earthquake the maximum quantity of mercury runs over the notches in the direction of greatest motion4 ,this instrument1 which has long been used in ,italy1 is known as a ,cacciatore1 being named after its inventor4 ,it is a prominent feature in the collection of apparatus forming the well-known seismograph of ,palmieri4 ,pendulum instruments4--,mallet speaks of pendulum seismoscopes and seismographs as #8the oldest probably of seismometers long set up in ,italy and southern ,europe4' ,in #ahda we find these being used to record the earthquake disturbances at ,comrie in ,scotland4 ,these instruments may be divided into two classes3 first1 those which at the time of the shock are intended to swing1 and thus record the direction of movement2 and second1 those which are supposed to remain at rest and thus provide #8steady points4' ,to obtain an absolutely #8steady point' at the time of an earthquake1 has been one of the chief aims of all recent seismological investigations4 ,with a style or pointer projecting down from the steady point to a surface which is being moved backward and forward by the earth1 such a surface has written upon it by its own motions a record of the ground to which it is attached4 ,conversely1 a point projecting upwards from the moving earth might be caused to write a record on the body providing the steady point1 which in the class of instruments now to be referred to is supposed to be the bob of a pendulum4 ,it is not difficult to get a pendulum which will swing at the time of a moderately strong earthquake1 but it is somewhat difficult to obtain one which will not swing at such a time4 ,during the past few years1 pendulums varying between forty feet in length and carrying bobs of eighty pounds in weight1 and one-eighth of an inch in length1 and carrying a gun-shot1 have been experimented with under a great variety of circumstances4 ,sometimes the supports of these pendulums have been as rigid as it is possible to make a structure from brick and mortar1 and at other times they have intentionally been made loose and flexible4 ,the indices which wrote the motions of these pendulums have been as various as the pendulums themselves4 ,a small needle sliding vertically through two small holes1 and resting its lower end on a surface of smoked glass1 has on account of its small amount of friction been perhaps one of the favourite forms of recording pointers4 ,the free pendulums which have been employed1 and which were intended to swing1 have been used for two purposes3 first1 to determine the direction of motion from the direction of swing1 and second1 to see if an approximation to the period of the earth's motion could be obtained by discovering the pendulum amongst a series of different lengths which was set in most violent motion1 this probably being the one which had its natural period of swing the most nearly approximating to the period of the earthquake oscillations4 ,inasmuch as all pendulums when swinging have a tendency to change the plane of their oscillation1 and also as we now know that the direction of motion during an earthquake is not always constant1 the results usually obtained with these instruments respecting the direction of the earth's motion have been unsatisfactory4 ,the results which were obtained by series of pendulums of different lengths were1 for various reasons1 also unsatisfactory4 ,of pendulums intended to provide a steady point1 from which the relative motion of a point on the earth's surface could be recorded1 there has been a great variety4 ,one of the oldest forms consisted of a pendulum with a style projecting downwards from the bob so as to touch a bed of sand4 ,sometimes a concave surface was placed beneath the pendulum1 on which the record was traced by means of a pencil4 ,probably the best form was that in which a needle1 capable of sliding freely up and down1 marked the relative horizontal motion of the earth and the pendulum bob on a smoked glass plate4 ,it generally happens that at the time of a moderately severe earthquake the whole of these forms of apparatus are set in motion1 due partly to the motion of the point of support of the pendulum1 and partly to the friction of the writing point on the plate4 ,among these pendulums may be mentioned those of ,cavallieri1 ,faura1 ,palmieri1 ,rossi1 and numerous others4 ,it is possible that the originators of some of these pendulums may have intended that they should record by swinging4 ,if this is so1 then so far as the determination of the actual nature of earthquake motion is concerned1 they belong to a lower grade of apparatus than that in which they are here included4 ,a great improvement in pendulum apparatus is due to ,mr4 ,thomas ,gray of ,glasgow1 who suggested applying so much frictional resistance to the free swing of a pendulum that for small displacements it became #8dead beat4' ,by carrying out this suggestion1 pendulum instruments were raised to the position of seismographs4 ,the manner of applying the friction will be understood from the following description of a pendulum instrument which is also provided with an index which gives a magnification of the motion of the earth4 ,b ,b ,b ,b is a box #aac cm4 high and #cj cm4 by #ah cm4 square4 ,inside this box a lead ring ,r1 #ag cm4 in diameter and #c cm4 thick1 is suspended as a pendulum from the screw ,s4 ,this screw passes through a small brass plate ,p ,p1 which can be moved horizontally over a hole in the top of the box4 ,these motions in the point of suspension allow the pendulum to be adjusted4 ,illustration3 ,,fig4 #b4 ,projecting over the top of the pendulum there is a wooden arm ,w carrying two sliding pointers ,h ,h1 resting on a glass plate placed on the top of the pendulum4 ,these pointers are for the purpose of giving the frictional resistance before referred to4 ,if this friction plate is smoked1 the friction pointers will write upon it records of large earthquakes independently of the records given by the proper index1 which only gives satisfactory records in the case of shocks of ordinary intensity4 ,crossing the inside of the pendulum ,r there is a brass bar perforated with a small conical hole at ,m4 ,a stiff wire passes through ,m and forms the upper portion of the index ,i1 the lower portion of which is a thin piece of bamboo4 ,fixed upon the wire there is a small brass ball which rests on the upper side of a second brass plate also perforated with a conical hole1 which plate is fixed on the bar ,o ,o crossing the box4 ,if at the time of an earthquake the upper part of the index ,i remains steady at ,m1 then by the motion at ,o1 the lower end of the index which carries a sliding needle at ,g1 will magnify the motion of the earth in the ratios ,m ,o3 ,o ,g4 ,in this instrument ,o ,g is about #ag cm4 ,the needle ,g works upon a piece of smoked glass4 ,in order to bring the glass into contact with the needle without disturbance1 the glass is carried on a strip of wood ,k1 hinged at the back of the box1 and propped up in front by a loose block of wood ,y4 ,when ,y is removed the glass drops down with ,k out of contact with the needle4 ,the box is carried on bars of wood ,c ,c1 which are fixed to the ground by the stakes ,a ,a4 ,the great advantage of a pendulum seismograph working on a stationary plate is1 that the record shows at once whether the direction of motion has been constant1 or whether it has been variable4 ,the maximum extent of motion in various directions is also easily obtained4 ,the disadvantage of the instrument is1 that at the time of a large earthquake1 owing perhaps to a slight swing in the pendulum1 the records may be unduly magnified4 ,on such occasions1 however1 fairly good records may be obtained from the friction pointers1 provided that the plates on which they work have been previously smoked4 ,it might perhaps be well to use two of these instruments1 one having a comparatively high frictional resistance1 and hence #8dead beat' for large displacements4 ,many attempts have been made to use a pendulum seismograph in conjunction with a record-receiving surface1 which at the time of the earthquake should be kept in motion by clockwork4 ,in this way it was hoped to separate the various vibrations of the earthquake1 and thus avoid the greater or less confusion which occurs when the index of the pendulum writes its backward and forward motion on a stationary plate4 ,hitherto all attempts in this direction1 in which a single multiplying index was used1 have been unsuccessful because of the moving plate dragging the index in the direction of its motion for a short distance1 and then allowing it to fall back towards its normal position4 ,in connection with this subject we may mention the pendulum seismographs of ,kreil1 ,wagener1 ,ewing1 and ,gray4 ,in the bob of ,kreil's pendulum there was clockwork1 which caused a disc on the axis of the pendulum to continuously rotate4 ,on this continually revolving surface a style fixed to the earth traced an unbroken circle4 ,at the time of an earthquake1 by the motion of the style1 the circle was to be broken and lines drawn4 ,the number and length of these lines were to indicate the length and intensity of the disturbance4 ,gray's pendulum consisted of a flat heavy disc carrying on its upper surface a smoked glass plate4 ,this1 which formed the bob of the pendulum1 was supported by a pianoforte steel wire4 ,when set ready to receive an earthquake1 the wire was twisted and the bob held by a catch so arranged that at the time of the earthquake the catch was released1 and the bob of the pendulum allowed to turn slowly by the untwisting of the supporting wire4 ,resting on the surface of this rotating disc were two multiplying indices arranged to write the earth's motions as two components4 ,in the instruments of ,wagener and ,ewing1 the clockwork and moving surface do not form part of the pendulum1 but rest independently on a support rigidly attached to the earth4 ,in ,wagener's instrument one index only is used1 while in ,ewing's two are used for writing the record of the motion4 ,a difficulty which is apparent in all pendulum machines is that when the bob of such a pendulum is deflected it tends to fall back to its normal position4 ,to make a pendulum perfect it therefore requires some compensating arrangement1 so that the pendulum1 for small displacements1 shall be in neutral equilibrium1 and the errors due to swinging shall be avoided4 ,several methods have been suggested for making the bob of an ordinary pendulum astatic for small displacements4 ,one method proposed by ,gray consists in fixing in the bob of a pendulum a circular trough of liquid1 the curvature of this trough having a proper form4 ,another method which was suggested1 was to attach a vertical spiral spring to a point in the axis of the pendulum a little below the point of suspension1 and to a fixed point above it1 so that when the pendulum is deflected it would introduce a couple4 ,professor ,ewing has suggested an arrangement so that the bob of the pendulum shall be partly suspended by a stretched spiral spring1 and at the same time shall be partly held up from below by a vertically placed strut1 the weight carried by the strut being to the weight carried by the spring in the ratio of their respective lengths4 ,as to how these arrangements will act when carried into practice yet remains to be seen4 ,another important class of instruments are inverted pendulums4 ,these are vertical springs made of metal or wood loaded at their upper end with a heavy mass of metal4 ,an arrangement of this sort1 provided at its upper end with a pencil to write on a concave surface1 was employed in #ahda to register the earthquakes at ,comrie in ,scotland4 ,in ,japan they were largely employed in series1 each member of a series having a different period of vibration4 ,the object of these arrangements was to determine which of the pendulums1 with a given earthquake1 recorded the greatest motion1 it being assumed that the one which was thrown into the most violent oscillation would be the one most nearly approximating with the period of the earthquake4 ,the result of these experiments showed that it was usually those with a slow period of vibration which were the most disturbed4 ,bracket ,seismographs4--,a group of instruments of recent origin which have done good work1 are the bracket seismographs4 ,these instruments appear to have been independently invented by several investigators3 the germ from which they originated probably being the well-known horizontal pendulum of ,professor ,zllner4 ,in ,japan they were first employed by ,professor ,w4 ,s4 ,chaplin4 ,subsequently they were used by ,professor ,ewing and ,mr4 ,gray4 ,they consist essentially of a heavy weight supported at the extremity of a horizontal bracket which is free to turn on a vertical axis at its other end4 ,when the frame carrying this axis is moved in any direction excepting parallel to the length of the gate-like bracket1 the weight causes the bracket to turn round a line known as the instantaneous axis of the bracket corresponding to this motion of the fixed axis4 ,any point in this line may therefore be taken as a steady point for motions at right angles to the length of the supporting bracket4 ,two of these instruments placed at right angles to each other have to be employed in conjunction1 and the motion of the ground is written down as two rectangular components4 ,in ,professor ,ewing's form of the instrument1 light prolongations of the brackets form indices which give magnified representations of the motion1 and the weights are pivoted round a vertical axis through their centre4 ,in the accompanying sketch ,b is a heavy weight pivoted at the end of a small bracket ,c ,a ,k1 which bracket is free to turn on a knife-edge1 ,k1 above1 and a pivot ,a1 below1 in the stand ,s4 ,at the time of an earthquake ,b remains steady1 and the index ,p1 forming a continuation of the bracket1 magnifies the motion of the stand1 in the ratio of ,a ,c 3 ,c ,n4 ,illustration3 ,,fig4 #c4 ,in an instrument called a double-bracket seismograph1 invented by ,mr4 ,gray1 we have two brackets hinged to each other1 and one of them to a fixed frame4 ,the planes of the two brackets are placed at right angles1 so as to give to a heavy mass supported at the end of the outer bracket two degrees of horizontal freedom4 ,in all bracket machines1 especially those which carry a pivoted weight1 it is doubtful whether the weight provides a truly steady point relatively to the plate on which the record is written for motion parallel to the direction of the arm4 ,illustration3 ,,fig4 #d4 ,parallel motion ,instrument4--,a machine which writes its record as two components1 and which promises great stability1 is one suggested by ,professor ,c4 ,d4 ,west4 ,like the bracket machines it consists of two similar parts placed at right angles to each other1 and is as follows3 ,a bar of iron ,a is suspended from both sides on pivots at ,c ,c by a system of light arms hinging with each other at the black dots1 between the upper and lower parts of the rigid frame ,b ,c4 ,the arms are of such a length that for small displacements parallel to the length of the bar1 ,c ,c practically move in a straight line1 and the bar is in neutral equilibrium4 ,a light prolongation of the bar d works the upper end of the light index e1 passing as a universal joint through the rigid support ,f4 ,a second index e from the bar at right angles also passes through ,f4 ,the multiplying ends of these indices are coupled together to write a resultant motion on a smoked glass plate ,s4 ,conical ,pendulums4--,another group of instruments which have also yielded valuable records are the conical pendulum seismographs4 ,the idea of using the bob of a conical pendulum to give a steady point in an earthquake machine was first suggested and carried into practice by ,mr4 ,gray4 ,the seismograph as employed consists of a pair of conical pendulums hung in planes at right angles to each other4 ,the bob of each of these pendulums is fixed a short distance from the end of a light lever1 which forms the writing index1 the short end resting as a strut against the side of a post fixed in the earth4 ,the weight is carried by a thin wire or thread1 the upper end of which is attached to a point vertically above the fixed end of the lever4 ,rolling ,spheres and ,cylinders4--,after the conical pendulum seismographs1 which claim several important advantages over the bracket machines1 we come to a group of instruments known as rolling sphere seismographs4 ,here1 again1 we have a class of instruments for the various forms of which we are indebted to the ingenuity of ,mr4 ,gray4 ,the general arrangement and principle of one of these instruments will be readily understood from the accompanying figure4 ,s is a segment of a large sphere with a centre near ,c4 ,slightly below this centre a heavy weight ,b1 which may be a lead ring1 is pivoted4 ,at the time of an earthquake ,c is steady1 and the earth's motions are magnified by the pointer ,c ,a ,n in the proportion of ,c ,a 3 ,a ,n4 ,the working of this pointer or index is similar to that of the pointer in the pendulum4 ,illustration3 ,,fig4 #e4 ,closely connected with the rolling sphere seismographs1 are ,gray's rolling cylinder seismographs4 ,these are two cylinders resting on a surface plate with their axes at right angles to each other4 ,near to the highest point in each of these cylinders1 this point remaining nearly steady when the surface plate is moved backwards and forwards1 there is attached the end of a light index4 ,these indices are again pivoted a short distance from their ends on axes connected with the surface plate4 ,in order that the two indices may be brought parallel1 one is cranked at the second pivot4 ,ball and ,plate ,seismograph4--,another form of seismograph1 which is closely related to the two forms of apparatus just described1 is ,verbeck's ball and plate seismograph4 ,this consists of a surface plate resting on three hard spheres1 which in turn rests upon a second surface plate4 ,when the lower plate is moved1 the upper one tends to remain at rest1 and thus may be used as a steady mass to move an index4 ,the ,principle of ,perry and ,ayrton4--,an instrument which is of interest from the scientific principle it involves is a seismograph suggested by ,professors ,perry and ,ayrton1 who propose to support a heavy ball on three springs1 which shall be sufficiently stiff to have an exceedingly quick period of vibration4 ,by means of pencils attached to the ball by levers1 the motions of the ball are to be recorded on a moving band of paper4 ,the result would be a record compounded of the small vibrations of the springs superimposed on the larger1 slower1 wave-like motions of the earthquake1 and1 knowing the former of these1 the latter might be separated by analysis4 ,although our present knowledge of earthquake motion indicates that the analysis of such a record would often present us with insuperable difficulties1 this instrument is worthy of notice on account of the novelty of the principle it involves1 which1 the authors truly remark1 has in seismometry been a #8neglected' one4 ,instruments to record ,vertical ,motion4--,the instruments which have been devised to record vertical motion are almost as numerous as those which have been devised to record horizontal motion4 ,the earliest form of instrument employed for this purpose was a spiral spring stretched by weight1 which1 on account of its inertia1 was supposed at the time of a shock to remain steady4 ,no satisfactory results have ever been obtained from such instruments1 chiefly on account of the inconvenience in making a spring sufficiently long to allow of enough elongation to give a long period of vibration4 ,similar remarks may be applied to the horizontally placed elastic rods1 one end of which is fixed to a wall1 whilst the opposite end is loaded with a weight4 ,such contrivances1 furnished with pencil on the weight to write a record upon a vertical surface1 were used in #ahdb at ,comrie1 and we see the same principle applied in a portion of ,palmieri's apparatus4 ,contrivances like these neither give us the true amplitude of the vertical motion1 insomuch as they are readily set in a state of oscillation2 nor do they indicate the duration of a disturbance1 for1 being once set in motion1 they continue that motion in virtue of their inertia long after the actual earthquake has ceased4 ,they can only be regarded as seismoscopes4 ,illustration3 ,,fig4 #f4 ,the most satisfactory instrument which has yet been devised for recording vertical motion is ,gray's horizontal lever spring seismograph4 ,this instrument will be better understood from the accompanying sketch4 ,a vertical spring ,s is fixed at its upper end by means of a nut n1 which rests on the top of the frame ,f1 and serves to raise or lower the spring through a short distance as a last adjustment for the position of the cross-arm ,a4 ,the arm ,a rests at one end on two sharp points1 p1 one resting in a conical hole and the other in a ,v-slot2 it is supported at ,b by the spring ,s1 and is weighted at ,c with a lead ring ,r4 ,over a pin at the point ,c a stirrup of thread is placed which supports a small trough1 t4 ,the trough t is pivoted at a1 has attached to it the index i 7which is hinged by means of a strip of tough paper at h1 and rests through a fine pin on the glass plate g71 and is partly filled with mercury4 ,another method of obtaining a steady point for vertical motion is that of ,dr4 ,wagener1 who employs a buoy partly immersed in a vessel of water4 ,this was considerably improved upon by ,mr4 ,gray1 who suggested the use of a buoy1 which1 with the exception of a long thin style1 was completely sunk4 ,among the other forms of apparatus used to record vertical motion may be mentioned vessels provided with india-rubber or other flexible bottoms1 and partially filled with water or some other liquid4 ,as the vessel is moved up and down1 the bottom tends to remain behind and provides a more or less steady point4 ,pivoted to this is a light index1 which is again pivoted to a rigid frame in connection with the earth4 ,instruments of this description have yielded good records4 ,record ,receivers4--,a large number of earthquake machines having been referred to1 it now remains to consider the apparatus on which they write their motions4 ,the earlier forms of seismographs1 as has already been indicated1 recorded their movements in a bed of sand2 others wrote their records by means of pencils on sheets of paper4 ,where we have seismographs which magnify the motion of the earth1 it will be observed that methods like the above would involve great frictional resistances1 tending to cause motion in the assumed steady points of the seismographs4 ,one of the most perfect instruments would be obtained by registering photographically the motions of the recording index by the reflection of a ray of light4 ,such an instrument would1 however1 be difficult to construct and difficult to manipulate4 ,one of the best practical forms of registering apparatus is one in which the record is written on a surface of smoked glass4 ,this can afterwards be covered with a coat of photographer's varnish1 and subsequently photographed by the #8blue process' so well known to engineers4 ,to obtain a record of all the vibrations of an earthquake it is necessary that the surface on which the seismograph writes should at the time of an earthquake be in motion4 ,of record-receiving machines there are three types4 ,first1 there are those which move continuously4 ,the common form of these is a circular glass plate like an old form of chronograph1 driven continuously by clockwork4 ,on this the pointers of the seismograph rest and trace over and over again the same circles4 ,at the time of an earthquake they move back and forth across the circles1 which are theoretically fine lines1 and leave a record of the earthquake4 ,instead of a circular plate1 a drum covered with smoked paper may be used1 which1 after the earthquake1 possesses the advantage1 after unrolling1 of presenting the record in a straight line1 instead of a record written round the periphery of a circle1 as is the case with the circular glass plates4 ,such records are easily preserved1 but they are more difficult to photograph4 ,the second form of apparatus is one which is set in motion at the time of a shock4 ,this may be a contrivance like one of those just described1 or a straight smoked glass plate on a carriage4 ,by means of an electrical or a mechanical contrivance called a #8starter1' of which many forms have been contrived1 the earthquake is caused to release a detent and thus set in motion the mechanism which moves the record receiver4 ,the great advantage of continuously-moving machines is that the beginning and end of the shock can usually be got with certainty1 while all the uncertainty as to the action of the #8starter' is avoided4 ,self-starting machines have1 of course1 the advantage of simplicity and cheapness1 while there is no danger of the record getting obliterated by the subsequent motion of the plate under the index4 ,time-recording ,apparatus4--,of equal importance with the instruments which record the motion of the ground1 are those instruments which record the time at which such motion took place4 ,the great value of time records1 when determining the origin from which an earthquake originates1 will be shown farther on4 ,the most important result which is required in connection with time observations1 is to determine the interval of time taken by a disturbance in travelling from one point to another4 ,on account of the great velocity with which these disturbances sometimes travel1 it is necessary that these observations should be made with considerable accuracy4 ,the old methods of adapting an apparatus to a clock which1 when shaken1 shall cause the clock to stop1 are of little value unless the stations at which the observations are made are at considerable distances apart4 ,this will be appreciated when we remember that the disturbance may possibly travel at the rate of a mile per second1 that its duration at any station may often extend over a minute1 and that one set of apparatus at one station may stop1 perhaps1 at the commencement of the disturbance1 and the other near the end4 ,a satisfactory time-taking apparatus will therefore require1 not only the means for stopping a clock1 but also a contrivance which1 at the same instant that the clock is stopped1 shall make a mark on a record which is being drawn by a seismograph4 ,in this way we find out at which portion of the shock the time was taken4 ,illustration3 ,,fig4 #g4 ,palmieri stops a clock in his seismograph by closing an electric circuit4 ,mallet proposes to stop a clock by the falling of a column which is attached by a string to the pendulum of the clock4 ,so long as the column is standing the string is loose and the pendulum is free to move2 but when the column falls1 the string is tightened and the pendulum is arrested4 ,the difficulty which arises is to obtain a column that will fall with a slight disturbance4 ,the best form of contrivance for causing a column to fall1 and one which may also be used in drawing out a catch to relieve the machinery of a record receiver1 is shown in the accompanying sketch4 ,s is the segment of a sphere about #de cm4 radius1 with a centre slightly above ,c4 ,l is a disc of lead about #g cm4 in diameter resting upon the segment4 ,above this there is a light pointer1 ,p1 about #cj cm4 long4 ,on the top of the pointer a small cylinder of iron1 ,w1 is balanced1 and connected by a string with the catch to be relieved4 ,when the table on which ,w ,p ,s rests is shaken1 rotation takes place near to ,c1 the motion of the base ,s is magnified at the upper end of the pointer1 and the weight overturned4 ,this catch may be used to relieve a toothed bar axled at one end1 and held up above a pin projecting from the face of the pendulum bob4 ,when this falls it catches the projecting pin and holds the pendulum4 ,another way of relieving the toothed bar is to hold up the opposite end to that at which it is axled by resting it on the extremity of a horizontal wire fixed to the bob of a conical pendulum--for example1 one of the indices of a conical pendulum seismograph4 ,the whole of this apparatus1 which may be constructed at the cost of a few pence1 can be made small enough to go inside an ordinary clock case4 ,the difficulty which arises with all these clock-stopping arrangements is that it is difficult for observers situated at distant stations to re-start their clocks so that their difference in time shall be accurately known4 ,even if each observer is provided with a well-regulated chronometer1 with which he can make comparisons1 the rating of these instruments is for all ordinary persons an extremely troublesome operation4 ,in order to avoid this difficulty the author has of late years used a method of obtaining the time without stopping the clock4 ,to do this a clock with a central seconds hand is taken1 and the hour and minute hands are prolonged and bent out slightly at their extremities at right angles to the face1 the hour hand being slightly the longest4 ,each hand is then tipped with a piece of soft material like cork1 which is smeared with a glycerine ink4 ,a light flat ring1 with divisions in it corresponding to those on the face of the clock1 is so arranged that at the time of a shock it can be quickly advanced to touch the inked pads on the hands of the clock and then withdrawn4 ,this is accomplished by suitable machinery1 which is relieved either by an electro-magnet or some other contrivance which will withdraw a catch4 ,in this way an impression in the form of three dots is received on the disc1 and the time known without either stopping or sensibly retarding the clock4 ,for ordinary observers1 if a time-taker is not used in conjunction with a record receiver1 as good results as those obtained by ordinary clock-stopping apparatus are obtainable by glancing at an ordinary watch4 ,subsequently the watch by which the observation was made should be compared with some good time-keeper1 and the local time at which the shock took place is then approximately known4 ,from what has now been said it will be seen that for a complete seismograph we require three distinct sets of apparatus--an apparatus to record horizontal motion1 an apparatus to record vertical motion1 and an apparatus to record time4 ,the horizontal and vertical motions must be written on the same receiver1 and if possible side by side1 whilst the instant at which the time record is made a mark must be made on the edge of the diagram which is being drawn by the seismograph4 ,such a seismograph has been constructed and is now erected in ,japan4 ,it is illustrated in the accompanying diagram4 ,the ,gray and ,milne ,seismograph4--,in this apparatus two mutually rectangular components of the horizontal motion of the earth are recorded on a sheet of smoked paper wound round a drum1 ,d1 kept continuously in motion by clockwork1 ,w1 by means of two conical pendulum seismographs1 ,c4 ,the vertical motion is recorded on the same sheet of paper by means of a compensated-spring seismograph1 ,s ,l ,m ,b4 ,the time of occurrence of an earthquake is determined by causing the circuit of two electro-magnets to be closed by the shaking4 ,one of these magnets relieves a mechanism1 forming part of a time-keeper1 which causes the dial of the timepiece to come suddenly forwards on the hands and then move back to its original position4 ,the hands are provided with ink-pads1 which mark their positions on the dial1 thus indicating the hour1 minute1 and second when the circuit was closed4 ,the second electro-magnet causes a pointer to make a mark on the paper receiving the record of the motion4 ,this mark indicates the part of the earthquake at which the circuit was closed4 ,illustration3 ,,fig4 #h4 ,the duration of the earthquake is estimated from the length of the record on the smoked paper and the rate of motion of the drum4 ,the nature and period of the different movements are obtained from the curves drawn on the paper4 ,mr4 ,gray has since greatly modified this apparatus1 notably by the introduction of a band of paper sufficiently long to take a record for twenty-four hours without repetition4 ,the record is written in ink by means of fine siphons4 ,in this way the instrument1 which is extremely sensitive to change of level1 can be made to show not only earthquakes1 but the pulsations of long period which have recently occupied so much attention4 ,,chapter ,,iii4 ,,earthquake ,,motion ,,discussed ,,theoretically4 ,ideas of the ancients 7the views of ,travagini1 ,hooke1 ,woodward1 ,stukeley1 ,mitchell1 ,young1 ,mallet7--,nature of elastic waves and vibrations--,possible causes of disturbance in the ,earth's crust--,the time of vibration of an earth particle--,velocity and acceleration of a particle--,propagation of a disturbance as determined by experiments upon the elastic moduli of rocks--,the intensity of an earthquake--,area of greatest overturning moment--,earthquake waves--,reflexion1 refraction1 and interference of waves--,radiation of a disturbance4 ,ideas of ,early ,writers4--,one of the first accounts of the varieties of motion which may be experienced at the time of an earthquake is to be found in the classification of earthquakes given by ,aristotle4#h ,it is as follows3-- #a4 ,epiclint1 or earthquakes which move the ground obliquely4 #b4 ,brast1 with an upward vertical motion like boiling water4 #c4 ,chasmati1 which cause the ground to sink and form hollows4 #d4 ,rhect1 which raise the ground and make fissures4 #e4 ,ost1 which overthrow with one thrust4 #f4 ,palmati1 which shake from side to side with a sort of tremor4 ,from the sixth group in this classification we see that this early writer did not regard earthquakes as necessarily isolated events1 but that some of them consisted of a succession of backward and forward vibratory motions4 ,he also distinguishes between the total duration of an earthquake and the length of1 and intervals between1 a series of shocks4 ,aristotle had1 in fact1 some idea of what modern writers upon ordinary earthquakes would term #8modality4' ,the earliest writer who had the idea that an earthquake was a pulse-like motion propagated through solid ground appears to have been ,francisci ,travagini1 who1 in #afgi1 wrote upon an earthquake which in #affg had overthrown ,ragusa4 ,the method in which the pulses were propagated he illustrated by experiments4 ,hooke1 who1 in #afij1 delivered discourses on earthquakes before the ,royal ,society1 divides these phenomena according to the geological effects they have produced2 thus there is a genus producing elevations1 a genus producing sinkings1 a genus producing conversions and transportations1 and a genus which produces what1 in modern language1 we should term metamorphic action4 ,woodward1 in his #8,natural ,history1' written in #afie1 speaks of earthquakes as being agitations and concussions produced by water in the interior of the earth coming in contact with internal fires4 ,stukeley observed that an earthquake was #8a tremor of the earth1' to be explained as a vibration in a solid4 ,the ,rev4 ,john ,mitchell1 writing in #agfj1 says that the motion of the earth in earthquakes is partly tremulous and partly propagated by waves4 ,from these few examples1 to which might be added many more1 it will be seen that an earthquake disturbance has usually been regarded as a concussion1 vibration1 trembling1 or undulatory movement4 ,further1 it can be seen in narratives of earthquakes that it had been often observed that these tremblings and shakings continued over a certain period of time4 ,although it had been noticed that large areas were almost simultaneously affected by these disturbances1 no definite idea appears to have existed as to how earthquake motion was propagated4 ,usually it was assumed that the disturbance spread through subterranean channels4 ,the first true conception of earthquake motion and the manner of its propagation is due to ,dr4 ,thomas ,young1 who suggested that earthquake motion was vibratory1 and it might be #8propagated through the earth nearly in the same manner as a noise is conveyed through the air4' ,the same idea was moulded into a more definite form by ,gay ,lussac4 ,the first accurate definition of an earthquake is due to ,mr4 ,robert ,mallet1 who1 after collecting and examining many facts connected with earthquake phenomena1 and reasoning on these1 with the help of known laws connected with the production and propagation of waves of various descriptions1 formulated his views as follows3-- ,an earthquake is #8the transit of a wave or waves of elastic compression in any direction from vertically upwards to horizontally1 in any azimuth1 through the crust and surface of the earth1 from any centre of impulse or from more than one1 and which may be attended with sound and tidal waves1 dependent upon the impulse and upon circumstances of position as to sea and land4' ,in brief1 so far as motion in the earth is concerned4 ,mallet defined an earthquake as being a motion due to the transit of waves of elastic compression4 ,in many cases it is possible that this is strictly true1 but in succeeding pages it will be shown that earthquake motion may also be due to the transit of waves of elastic distortion4 ,to obtain a true idea of earthquake motion is a matter of cardinal importance1 as it forms the key-stone of many investigations4 ,if we know the nature of the motion produced by an earthquake1 we are aided in tracking it to its origin1 and in reasoning as to how it was produced4 ,if our knowledge of the nature of the motion of an earthquake is incorrect1 it will be impossible for us intelligently to construct buildings to withstand the effects of these disturbances4 ,we have thus to consider1 in this portion of seismology1 a point of great scientific importance1 and shall deal with it at some length4 ,nature of ,elastic ,waves and ,vibrations4--,when it is stated that an earthquake consists of elastic waves of compression and distortion1 the student of physics has a clear idea of what is meant and a knowledge of the mechanical laws which govern such disturbances4 ,the ordinary reader1 however1 and the majority of the inhabitants of earthquake countries1 who of all people have the greatest interest in this matter1 may not have so clear a conception1 and it will1 therefore1 not be out of place to give some general explanation on this point4 ,the ordinary idea of a wave is that it is a disturbance similar to that which we often see in water4 ,waves like these must not1 however1 be confounded with elastic waves4 ,a disturbance produced in water1 say1 for instance1 by dropping a stone into a pond1 is propagated outwards by the action of gravity4 ,first1 a ridge of water is raised up by the stone passing beneath the surface4 ,as this ridge falls towards its normal position in virtue of its weight1 it raises a second ridge4 ,this second ridge raises a third ridge1 and so on4 ,the water moves vertically up and down1 whilst the wave itself is propagated horizontally4 ,to understand what is meant by elastic waves1 it is first necessary to understand what is meant by the term elastic4 ,in popular language the term elastic is confined to substances like india-rubber1 and but seldom to rock-like materials1 through which earthquake waves are propagated4 ,india-rubber is called elastic because after we remove a compressive force it has a tendency to spring back to its original shape4 ,the elastic force of the india-rubber is in this case the force which causes it to resist a change of form4 ,now1 a piece of rock may1 up to a certain point1 like the india-rubber1 be compressed1 and when the compressing force is removed it will also tend to resume its original form4 ,however1 as the rock offers more resistance to the compressing force than the india-rubber offers1 we say that it is the more elastic4 ,it may be here observed that a substance like granite offers great resistance1 not only to compression or a change of volume1 but also to a change of form or shape2 whereas a substance like air1 which is also elastic1 only offers resistance to compression1 but not to a change of shape4 ,with these ideas before us we will now proceed to consider how1 after a body has been suddenly compressed or distorted1 this disturbance is propagated through the mass4 ,for the elastic body let us take a long spiral spring hung from the ceiling of a room and kept slightly stretched by a weight4 ,if we give this weight an upward tap from below1 say with a hammer1 we shall observe a pulse-like wave which runs up the spring until it reaches the ceiling of the room4 ,here it will1 so to speak1 rebound1 like a billiard ball from the end of a table1 and run towards the weight from which it started4 ,whilst this is going on we may also observe that the weight is moving up and down4 ,here1 then1 we have two distinct things to observe--one being the transmission of motion up to the ceiling1 which we may liken to the transmission of an earthquake wave between two distant localities on the earth's surface1 and the other being the up and down motion of our weight1 which we may compare to the backward and forward swinging which we experience at the time of an earthquake4 ,these two motions--namely1 the pulse-like wave produced by the transmission of motion1 and the backward and forward oscillation of the weight or of any point on the spring--must be carefully distinguished from each other4 ,first1 we will consider the backward and forward motion of the weight4 ,the distance through which the weight moves depends upon the force of the blow4 ,the number of up and down oscillations it makes1 say in a second1 depends upon the stiffness of the spring4 ,the weight1 supposing it to be always the same1 will move more quickly at the end of a stiff spring than at the end of a flaccid one2 that is to say1 its velocity is quicker4 ,as in any given spring the number of up and down oscillations are always the same in a given interval of time1 if these oscillations are of great extent1 the weight must move more quickly with large than with small oscillations4 ,at the time of an earthquake the manner in which we are moved backward and forward is very similar to the manner in which the weight is moved4 ,if we stand on a hard rock-like granite1 we are to a great extent placed as if we were attached to a stiff quickly-vibrating spring4 ,if1 however1 we are on a soft rock1 it is more like being on a loose flaccid spring4 ,all that has thus far been considered has been a backward and forward kind of motion1 where there is a rectilinear compression and extension amongst the particles on which we stand4 ,we might1 however1 imagine our rock1 which for the moment we will consider to be a square column1 to be twisted1 and thus have its shape altered4 ,when the twisting force is taken off it seems evident that the column would endeavour to untwist itself or regain its original form4 ,now the force which a body offers against a change of volume may be very different from that which it offers against a change of form4 ,in disturbances which take place in the rocky crust of our earth1 it would seem possible that we may have vibrations set up which are either compressions and extensions or twistings and distortions4 ,these may take place separately or simultaneously1 or we may have resultant motions due to their combination4 ,the following are examples of possible causes which might give rise to these different orders of disturbance3-- #a4 ,imagine a large area stretched by elevation until it reaches the limit of its elasticity and cracks4 ,after cracking1 in consequence of its elasticity1 it will fly back over the whole area like a broken spring1 and each point in the area will oscillate round its new position of equilibrium4 ,in this case there will be no waves of distortion excepting near the end of the crack1 where waves are transmitted in a direction parallel to the fissure4 #b4 ,the ground is broken and slips either up1 down1 or sideways1 as we see to have taken place in the production of faults4 ,here we get distortion in the direction of the movement1 and waves are produced by the elastic force of the rock1 causing it to spring back from its distorted form4 ,in a case like this the production of a fissure running north and south might give rise to north and south vibrations1 which would be propagated end on towards the north and south1 but broadside on towards the east and west4 ,with disturbances of this kind1 on account of the want of homogeneousness in the materials in which they are produced1 we should expect to find waves of compression and extension4 #c4 ,a truly spherical cavity is suddenly formed by the explosion of steam in the midst of an elastic medium4 ,in this case all the waves will be those of compression1 each particle moving backward and forward along a radius4 ,should the cavity1 instead of being truly spherical1 be irregular1 it is evident that1 in addition to the normal vibration of compression1 transverse waves of distortion will be more or less pronounced1 depending upon the nature of the cavity4 ,the combination of these two sets of vibrations may cause a point in the earth to move in a circle1 an ellipse1 the form of a figure eight1 and in other curves similar to these1 which are produced by apparatus designed to show the combination of harmonic motion4 ,from these examples it will be seen that we have therefore to consider two kinds of vibrations--one produced by compression or the alteration of volume1 and the other produced by an alteration in shape4 ,now the resistance which a body offers1 either to a change in its volume or in its shape1 is called its elasticity1 and the law which governs the backward and forward motion of a particle under the influence of this elasticity may be expressed as follows3 ,if ,t be the time of vibration1 or the time taken by a particle to make one complete backward and forward swing1 ,d the density of the material of which this particle forms a part1 and ,e the proper modulus of elasticity of the material1 then1 ,t #b ,d_/,e ,from this formula1 ,t #b ,d_/,e1 we see that the time of vibration of the earth during an earthquake1 or the rate at which we are shaken backwards and forwards1 varies directly as the square root of the density of the material on which we stand1 and inversely as the square root of a number proportional to its elasticity4 ,velocity and ,acceleration of an ,earth ,particle4--,another important point1 which the practical seismologist has often brought to his notice1 is the question of the velocity with which an earth particle moves4 ,according to the formula1 ,t #b ,d_/,e1 we should expect that a particle would make each semi-vibration in an equal time1 and from a knowledge of the density and elastic moduli of a body this time might be calculated4 ,although the time of a semi-oscillation may be constant1 we must bear in mind that1 like the bob of a pendulum during each of its swings1 the particle starts from rest1 increases in velocity until it reaches the middle portion of its half swing1 from which it gradually decreases in speed until it reaches zero1 when it again commences a similar motion in the opposite direction4 ,these pendulum-like vibrations are sometimes spoken of as simple harmonic motions4 ,if we know the distance through which an earthquake moves in making a single swing1 and the time taken in making this swing1 on the assumption that the motion is simple harmonic we can easily calculate the maximum velocity with which the particle moves4 ,thus1 if an earth particle takes one second to complete a semi-oscillation1 half of which1 or the amplitude of the motion1 equals a1 the maximum velocity equals a4 ,again1 assuming the earth vibrations to be simple harmonic1 the maximum acceleration or rate of change in velocity will come about at the ends of each semi-oscillation2 and if ,v be the maximum velocity of the particle1 and a the amplitude or half semi-oscillation1 then the ,v#b maximum acceleration equals ------4 a ,later on it will be shown1 as the result of experiment1 that certain of the more important earth oscillations in an earthquake are not simple harmonic motion4 ,nevertheless the above remarks will be of assistance in showing how the velocity and other elements connected with the motion of an earth particle1 which are required by the practical seismologist1 may be calculated1 irrespective of assumptions as to the nature of the motion4 ,propagation of a ,disturbance4--,we may next consider the manner in which a disturbance1 in which there are both vibrations of compression and of distortion1 is propagated4 ,the first or normal set of vibrations are propagated in a manner similar to that in which sound vibrations are propagated4 ,from a centre of disturbance these movements approach an observer at a distant station1 so to speak1 end on4 ,the other vibrations have a direction of motion similar to that which we believe to exist in a ray of light4 ,these would approach the observer broadside on4 ,if the disturbance passed through a formation like a series of perfectly laminated slates1 each of these two sets of vibration might be subdivided1 and we should then obtain what ,mallet has termed ordinary and extraordinary normal and transverse vibrations4 ,in consequence of the difference in the elastic forces on which the propagation of these two kinds of vibration depends1 the normal vibrations are transmitted faster than the transversal ones--that is to say1 if an earthquake originated from a blow1 the first thing that would be felt at a point distant from the origin of the shock would be a backward and forward motion in the direction to and from the origin1 and then1 a short interval afterwards1 a motion transversal1 or at right angles to this1 would be experienced4 ,from the mathematical theory of vibratory motions it is possible to calculate the velocity with which a disturbance is propagated4 ,as the result of these investigations it has been shown that normal vibrations travel more quickly than transverse vibrations4 ,deductions from experiments on small specimens are1 however1 invalidated by the fact that the specimens used for experiments are1 of course1 nearly homogeneous1 whilst the earthquake passes through a mass which is heterogeneous and more or less fissured4 ,mallet1 by experiments #8on the compressibility of solid cubes of these rocks1 obtained the mean modulus of elasticity1' with the result that #8nearly seven-eighths of the full velocity of wave-transit due to the material1 if solid and continuous1 is lost by reason of the heterogeneity and discontinuity of the rocky masses as they are found piled together in nature4' ,the full velocities of wave-transit1 as calculated by ,mallet from a theorem given by ,poisson1 were-- ,for slate and quartz transverse to lamination1 #i1fia feet per second4 in line of lamination1 #e1dae ,this more rapid transmission in a direction transverse to the lamination1 ,mr4 ,mallet observes1 may be more than counterbalanced by the discontinuity of the mass transverse to the same direction4 ,the ,intensity of an ,earthquake4--,the intensity of an earthquake is best estimated by the intensity of the forces which are brought to bear on bodies placed on the earth's surface4 ,these forces are evidently proportional to the rate of change of velocity in the body1 and1 as the destructive effect will be proportional to the maximum forces1 we may consistently indicate the intensity of an earthquake by giving the maximum acceleration to which bodies were subject during the disturbance4 ,on the assumption that the motion of a point on the earth's surface is simple harmonic1 the maximum acceleration is directly as the maximum velocity and inversely as the amplitude of v#b motion1 or as ---------- where v indicates velocity and a amplitude4 a ,the next question of importance is to determine the manner in which earthquake energy becomes dissipated--that is1 to compare together the intensity of an earthquake as recorded at two or more points at different distances from the origin4 ,first let us imagine the origin of our earthquake to be surrounded by concentric shells1 each of which is the breadth of the vibration of a particle4 ,going outwards from the centre1 each successive shell will contain a greater number of particles1 this number increasing directly as the square of the distance from the origin4 ,let the blow have its origin at the centre1 and give a vibratory movement to the particles in one of the shells near the centre4 ,this shell may be supposed to possess a certain amount of energy1 which will be measured by its mass and the square of the velocity of its particles4 ,in transferring this energy to the neighbouring shell which surrounds it1 because it has to set in motion a greater number of particles than it contains itself1 the energy in any one particle of the second layer will be less than the energy in any one particle in the first layer2 the total energy in the second shell1 however1 will be equal to the total energy in the first shell4 ,neglecting the energy lost during the transfer1 if the energy in a particle of the first shell at any particular phase of the motion be ,k#a1 and the energy in a particle of the second shell ,k#b1 these quantities are to each other inversely as the masses of the shells--that is1 inversely as the squares of the mean radii of the shells4 ,k#b r#ab ,in symbols1 ---------- ------------------ 7#a7 ,k#a r#bb ,assuming that energy is dissipated1 ,k#b r#ab r#ab ---------- ------------------ f ------------------ 7#b7 ,k#a r#bb r#bb where f #a is the rate of dissipation of energy which is assumed to be constant4 ,area of greatest ,overturning ,moment4--,although the rate of dissipation of the impulsive effects of an earthquake may follow a law like that just enumerated1 it must be remembered that if the depth of the origin is comparable with the radius of the area which is shaken1 the maximum impulsive effect as exhibited by the actual destruction on the surface may not be immediately above the origin where buildings have simply been lifted vertically up and down1 but at some distance from this point1 where the impulsive effort has been more oblique4 ,at the epicentrum we have the maximum of the true intensity as measured by the acceleration of a particle1 or the height to which a body might be projected1 but it will be at some distance from this where we shall have the maximum intensity as exhibited by an overturning effort4 ,this will be rendered clear by the following diagram4 ,in the accompanying diagram let ,o be the origin of a shock1 and ,o ,c the seismic vertical equal to r4 ,let the direct or normal shock emerge at ,c1 ,c#a1 ,c#b1 and at the angles #a1 #b1 c4 ,assuming that the displacement of an earth particle at ,c equals ,c ,b1 and at ,c#a equals c#a b#a1 and at ,c#b equals c#b b#b1 c41 and let these displacements ,c ,b1 c#a b#a1 c#b b#b1 c41 for the sake of argument1 vary inversely as r1 r#a1 r#b1 c4 ,illustration3 ,,fig4 #i4 ,the question is to determine where the horizontal component ,c ,a of these normal motions is a maximum4 ,first observe that the triangle ,o ,c c is similar to a1 b1 c4 h ,also r ----------1 and therefore the normal component c#a sin sin b#a at ,c#a is equal to ,c ----------4 h ,also c#a a#a c#a b#a1 cos 4 sin cos c sin #b ,c#a a ,c ------------------------ -------- --------------1 h h #b and sin #b is greatest when #b #ij or #de4 ,that is to say1 the horizontal component reaches a maximum where the angle of emergence equals #de4 ,this question has been discussed on the assumption that the amplitude of an earth particle varies inversely as its distance from the origin of the shock4 ,should we1 however1 assume that this amplitude varies inversely as the square of the distance from the origin1 we are led to the result that the area of greatest disturbance is nearer to the point where the angle of emergence is #ee #dd #i4 ,both of these methods are referred to by ,mallet1 but the first is considered as probably the more correct4 ,earthquake ,waves4--,hitherto we have chiefly considered earthquake vibrations2 now we will say a few words about earthquake waves4 ,if we strike a long iron rod at one end1 we can imagine that1 as in the long spring1 a pulse-like motion is transmitted4 ,if the rod be struck quickly1 the pulses will rapidly succeed each other1 and if struck slowly the pulses will be at longer intervals4 ,each individual pulse1 however1 will travel along the rod at the same rate1 and hence the distance between any two will remain constant2 but that distance will depend on the interval between the blows producing these pulses being equal to the distance travelled by one pulse before the next blow is struck4 ,from this we see that an irregular disturbance will produce an irregular succession of motions2 some will be like long undulations in a wide deep ocean1 whilst others will be like ripples in a shallow bay4 ,again1 consider the bar to be struck one blow only1 and then left to itself4 ,the bar will propagate a series of pulses along its length1 due to the out and in vibration of its end4 ,these will succeed each other at regular intervals1 and will be mixed up with the pulses we have previously considered4 ,from this we see that in an earthquake1 if it be produced by one blow1 the motion will be isochronous in its character2 but if it be due to a succession of blows at regular intervals1 the motion will be the resultant of a series of isochronous motions1 and will be periodical4 ,if the impulses are irregular1 you have a motion which is the resultant of a number of isochronous motions due to each impulse1 but these compounded together in a different manner at each instant during the earthquake1 and giving as a result a motion which is in no sense isochronous4 ,this approaches more nearly to the actual motions we feel as earthquakes4 ,if we can imagine the ground shaken by an earthquake1 made of a transparent material which transmitted less light when compressed1 and we could look down upon a long extent of this at the time of an earthquake1 we should see a series of dark bands indicating strips of country which were compressed4 ,the distances between these bands might be irregular4 ,keeping our attention on one particular band1 this would be seen to travel forward in a direction from the source4 ,if we kept our eye on one particular point1 it would appear to open and shut1 becoming light and dark alternately4 ,as to the existence of these elastic waves in actual earthquakes we have no direct experimental evidence4 ,the only kind of wave with which we are familiar is a true surface undulation1 which1 although having the appearance of a water-wave1 may nevertheless represent a district of compression4 ,,chapter ,,iv4 ,,earthquake ,,motion ,,as ,,deduced ,,from ,,experiment4 ,experiments with falling weights--,experiments with explosives--,results obtained from experiments--,relative motion of two adjacent points--,the effect of hills and excavations upon the propagation of vibrations--,the intensity of artificial disturbances--,velocity with which earth vibrations are propagated--,experiments of ,mallet--,experiments of ,abbot--,experiments in ,japan--,mallet's results--,abbot's results--,results obtained in ,japan4 ,experiments with ,falling ,weights4--,a series of experiments1 as the nature of the disturbance produced in the surface of the earth when a heavy weight is allowed to fall on it1 was begun in ,november #ahhj by ,mr4 ,t4 ,gray and the author4 ,these experiments were carried out at the ,akabane ,engineering ,works in ,tokio4 ,the weight used was a ball of iron weighing about a ton1 which in the different experiments was allowed to fall from heights varying between ten and thirty-five feet4 ,the position of the place where the ball was allowed to fall was such that in one direction the vibrations were transmitted up the side of a steep hill1 in another direction across a pond with perpendicular sides1 and in another direction across a level plain the material of which consisted for the most part of hardened mud extending to a very considerable depth4 ,the vibrations produced by the fall of the ball were transmitted through this hard mud with considerable intensity to a distance of between #cjj and #djj feet4 ,the object of the experiment was to find the nature of the vibrations produced in the crust of the earth by such a blow1 the velocity of transmission through this comparatively soft material1 the effect of hills and excavations in cutting off such disturbances1 and the law according to which the amplitude of the vibrations diminishes with the distance from the source4 ,a considerable variety of apparatus was used during these experiments1 but the most reliable results were obtained from the records of a rolling sphere seismograph1 which wrote the vibrations on a stationary plate1 and from the records of two bracket seismographs1 similar to ,professor ,ewing's horizontal lever seismographs1 which gave a record of the vibrations as two rectangular components on a moving plate of smoked glass4 ,illustration3 ,,fig4 #aj4 ,the general result as to the nature of the disturbance was that two distinct sets of vibrations were set up by the blow4 ,in one set the direction of motion was along a line joining the point of observation with the point from which the disturbance emanated2 in the other set the direction of motion was at right angles to that line4 ,the nature of the resultant motion will be gathered from fig4 #aj1 which is taken from the records drawn by the rolling sphere seismograph at a distance of #ej feet1 #ajj feet1 and #bjj feet respectively from the point where the ball struck the ground4 ,the direct or normal vibrations reached the instrument first1 and were followed at an interval depending on the distance of the instrument from the origin by the transverse vibrations4 ,from the records of these two sets of vibrations as separated by the bracket seismographs1 combined with the known rate of motion of the glass plate1 the velocity of transmission was found to be1 for normal vibrations #ddf-dch feet per second1 and for transverse vibrations #ceg-cec feet per second4 ,the effect of the hill in cutting off the disturbance seemed to be slight1 but the direction of the vibrations which ascended the side was mostly transverse4 ,the pond1 on the other hand1 seemed completely to cut off the disturbance1 which1 however1 gradually crept round the side1 so that only a comparatively small triangular area was in shadow4 ,the amplitude of the vibrations diminished directly as the distance increased for some distance from the origin1 but at greater distance the rate of diminution seemed to be slower4 ,the transverse vibration seemed to die out less quickly than the normal vibrations4#i ,these experiments were afterwards very considerably extended by the author4 ,in these later experiments charges of from one to two pounds of dynamite were placed in bore-holes of various depths and exploded by means of electricity4 ,the results obtained confirmed the conclusions already arrived at from the former experiments4 ,the experiments on velocity1 however1 seemed to indicate that the higher the initial impulse the greater was the velocity4 ,the velocity of propagation of the transverse vibrations seemed to approach more and more to that of the directed vibrations as the distance from the origin of disturbance increased4 ,fig4 #aa shows the nature of the record obtained from the explosion of two pounds of dynamite at the bottom of a bore-hole eight feet deep4 ,these records show the interval of time which elapsed between the arrival of the normal and the transverse vibrations at points distant #ajj1 #bej1 and #djj feet from the bore-hole4 ,in the case of the #ajj-;feet station it will be observed that the motion towards the origin is greater than that from the origin4 ,it is also to be noticed that the period of vibration becomes greater as the distance from the origin increases4 ,illustration3 ,,fig4 #aa4--,records obtained at three stations of the motion of the ground produced by the explosion of #b lbs4 of dynamite4 ,the ,intensity of ,artificial ,disturbances4--,the data which we have at our disposal for determining the intensity of an earth particle which has been caused to vibrate by the explosion of a charge of dynamite are a series of records similar to that given on p4 #fj4 ,these disturbances are practically surface movements1 and may be compared with the movements of an earthquake which spreads over an area the radius of which is great as compared with its depth4 ,to find the mean acceleration of an earth particle1 which quantity has been taken to represent intensity1 during any simple backward or forward motion of the earth1 it will be first necessary to determine the amplitude of this motion and its maximum velocity1 the mean ,v#b acceleration being equal to ------4 #b;,a ,illustration3 ,,fig4 #ab4 ,the second and third movements in a shock invariably exhibited the greatest intensity1 and to a distance of #djj feet from the origin1 where about three pounds of dynamite had been exploded in a bore-hole about six feet deep1 these intensities decreased directly as the distance from the origin4 ,the less intense movements also decreased directly as the distance from the origin to a certain point1 but after that they decreased more slowly4 ,a mean result of the more prominent vibrations in four sets of experiments is shown in the curve1 fig4 #ab1 where the horizontal measurements represent distance from the origin in feet1 and the vertical measurements mean acceleration in thousands of millimetres per second4 ,this curve approximates to an equi-angular hyperbola4 ,the area between the curve and its asymptotes is proportional to the whole energy of the shock4 ,the area of the diagram is proportional to the energy given up to the ground by the explosion of three pounds of dynamite4 ,if we call the unit shock the effect produced by the explosion of one pound of dynamite1 the above artificial earthquake had an intensity equal to three4 ,the only other investigations which have been made in this interesting branch of observational seismology are those by ,mr4 ,robert ,mallet1#aj and those by ,general ,henry ,l4 ,abbot4#aa ,mallet's ,results4--,the velocity with which earth vibrations were transmitted as deduced by ,mr4 ,mallet were as follows3-- ,feet per second ,in sand #hbdiae ,in contorted stratified rock1 quartz1 and slate at ,holyhead #a1jhhffi ,in discontinuous and much shattered granite #a1cjfdbe ,in more solid granite #a1ffdegd ,a striking result which was obtained by ,mallet in his experiments at ,holyhead was that the transit velocity increases with an increase in the intensity of the initial shock4 ,thus with a charge of #ab1jjj pounds of powder the transit rate was #a1cgc feet per second1 whilst with #b1ajj pounds the transit rate was #a1jii feet per second4 ,in these experiments tremors were observed as preceding and following the main shock4 ,abbot's ,results4--,the important results obtained by ,general ,abbot are contained in the following table3-- ,a4 ,no4 of ,observation ,b4 ,distance to ,station in miles ,c4 ,type of ,seismometer ,d4 ,velocity in feet per second ---------------------------------------- ---------------------- ,a ,date ,cause of ,shock ,b ,c ,d ---------------------------------------- ---------------------- #a ,aug4 #ah1 #ahgf #bjj lbs4 of dynamite #e ,b #e1bhj #b ,sept4 #bd1 #ahgf ,hallet's ,point ,explosion #eacd ,a #c1hgc #c #hccj ,b #h1cjj #d #iccc ,a #d1eba #e #abgfi ,b #e1cji #f ,oct4 #aj1 #ahgf #gj lbs4 dynamite #acfj ,a #a1bdj #g ,sept4 #f1 #ahgg #djj #aafi ,a #c1dbh #h #aafi ,b #h1had #i ,sept4 #ab1 #ahgg #bjj #acdj ,a #f1gcj #aj #acdj ,b #h1gcj #aa #gj #acdj ,a #e1eei #ab #acdj ,b #h1dae ---------------------------------------- ---------------------- ,a seismometer of type ,a means that the telescope used in observing the tremor produced on the surface of a vessel of mercury by the passage of the shock had a magnification of #f1 whilst a telescope of the type ,b had a magnification of #ab4 ,the mean velocity given by six observations with type ,a is #d1bbe feet per second1 while that given by the same number with type ,b is #g1dge feet per second4 ,illustration3 ,,fig4 #ac4 ,if we assume that the first tremor observed in the mercury is to determine the true rate of transmission1 ,general ,abbot tells us that we must reject all observations made with type ,a1 inasmuch as they do not reveal the velocity of the leading tremor4 ,however1 he also tells us that a still higher power above #ab might have detected still earlier tremors4 ,when gunpowder was the explosive1 the observers noted that the disturbance observed in the mercury took a much longer time to reach a maximum than it did when dynamite was employed4 ,it was also observed that explosions fired beneath deep water gave a higher velocity than similar explosions which took place beneath shallow water4 ,in the latter case much of the energy was probably expended in throwing a jet of water into the air4 ,another point which was observed appears to have been that the rate varied with the initial shock4 ,thus3-- ,feet per second #djj lbs4 of dynamite gave #h1had #bjj #h1gcj #gj powder 7deep7 gave #h1dae ,also it is probable that the rate of a wave diminished with its advance4 ,for1 ,feet per second #bjj lbs4 of dynamite gave for #a mile #h1gcj #e miles #e1bej #ej1jjj #h #h1cjj #ac #e1cjj ,general ,abbot's general conclusions are3-- #a4 ,a high magnifying power of telescope is essential in seismometric observations4 #b4 ,the more violent the initial shock the higher is the velocity of transmission4 #c4 ,this velocity diminishes as the general wave advances4 #d4 ,the movements of the earth's crust are complex1 consisting of many short waves first1 increasing and then decreasing in amplitude2 and with a detonating explosive the interval between the first wave and the maximum wave1 at any station1 is shorter than with a slow burning explosive4 ,results obtained in ,japan4--,from some experiments made by the author in the grounds of the ,meteorological ,department in ,tokio1 the following results were obtained3-- ,a4 ,velocity in feet per second for the first #bjj ft4 7,a to ,b7 ,b4 ,velocity in feet per second for the second #bjj ft4 7,b to ,c7 ,c4 ,velocity in feet per second for #djj ft4 7,a to ,c7 ,d4 ,number of ,cartridges of ,dynamite 7#f #a lb47 ---------------------------------------- - ,no4 of ,explosion ,a ,b ,c ,d ---------------------------------------- - ,i4 #dfd #ahf #bfe #hc ,vertical ,,iii4 -- #baa -- #aja vibrations ,,iv4 #ceb #bcd #bha #ga ,v4 #cdc #bcb #bgg #ej ,normal ,,vi4 -- -- #djg #ajj vibrations ,,vii4 -- -- #eaf #abe ,transverse ,,viii4 -- -- #cdd #abe vibrations ---------------------------------------- - ,the general results to be deduced from the above appear to be3-- #a4 ,for vertical motion4 7a7 ,for the first #bjj feet4 ,the velocity depends upon the initial force--the greater the charge of dynamite the greater the velocity4 7b7 ,for the second #bjj feet4 ,the above law only appears in experiments ,,iv4 and ,v41 but it must be remembered that the origins of ,i4 and ,,iii4 were farther removed from ,a than ,,iv4 and ,v4 ,the speed of the wave during the second #bjj feet is always less than during the first #bjj feet4 #b4 ,for normal vibrations4 ,here the speed between ,a and ,c is all that was measured1 but we again see that the greater the initial force1 or the nearer we are to the origin of the disturbance1 the greater is the velocity4 ,this velocity is greater than the velocity of the vertical or transverse vibrations4 #c4 ,for transverse vibrations4 ,if we assume that the vertical vibrations are a component of the transverse motions we see the same law as before--namely1 that the nearer we are to the origin of the disturbance the greater is the speed with which that disturbance is propagated4 ,it will be observed that the chief law here enunciated respecting the decrease in speed of earth vibrations is the same as that pointed out by ,general ,abbot1 from which it only differs by its being in all cases proved without the introduction of personal errors1 for the same explosion1 along the same line of ground and for different kinds of vibrations4 ,,chapter ,v4 ,,earthquake ,,motion ,,as ,,deduced ,,from ,,observation ,,on ,,earthquakes4 ,result of feelings--,the direction of motion--,instruments as indicators of direction--,duration of an earthquake--,period of vibration--,the amplitude of earth movements--,side of greatest motion--,intensity of earthquakes--,velocity and acceleration of an earth particle--,absolute intensity of an earthquake--,radiation of an earthquake--,velocity of propagation4 ,result of ,feelings4--,as the result of our experiences1 and by observations upon the movements produced in various bodies1 we can say that an ordinary earthquake consists of a number of backward and forward motions of the ground following each other in quick succession4 ,sometimes these commence and die out so gently that those who have endeavoured to time the duration of an earthquake have found it difficult to say when the shock commenced and when it ended4 ,this was a difficulty which ,mr4 ,james ,bissett in ,yokohama1 and the author in ,tokio1 had to contend against when1 in #ahgh1 they commenced to time shocks between these two places4 ,sometimes these motions gradually increase to a maximum and then die out as gradually as they commenced4 ,sometimes the maximum comes suddenly1 and at other times during an earthquake our feelings distinctly tell us that there are several maxima4 ,these have been the experiences of many observers1 and have been recorded by writers since the earliest times4 ,mallet devotes a chapter to a consideration of the tremulous motion that precedes and follows a shock1 and he tells us that a single shock is an absolute impossibility4 ,in speaking of earthquakes1 he says3 #8,the almost universal succession of phenomena recorded in earthquakes is1 first a trembling1 then a severe shock1 or several in quick succession1 and then a trembling gradually but rapidly becoming insensible4' ,a quantitative and exact knowledge of the nature of earthquake motion has only been attained of late years4 ,the chief results which investigators have aimed at have been the measurement of the amplitude1 the period1 the direction1 and the duration of the motions which constitute an earthquake4 ,attention has also been given to the velocity with which a disturbance is propagated4 ,the ,direction of ,motion4--,one of the most ordinary observations which are made about an earthquake is its direction4 ,if we were to ask the inhabitants of a town which had been shaken by an earthquake the direction of the motion they experienced1 it is not unlikely that their replies would include all the points of the compass4 ,many1 in consequence of their alarm1 have not been able to make accurate observations4 ,others have been deceived by the motion of the building in which they were situated4 ,some tell us that the motion had been north and south1 whilst others say that it was east and west4 ,a certain number have recognised several motions1 and amongst the rest there will be a few who have felt a wriggling or twisting4 ,leaving out exceptional cases1 the general result obtained from personal observation as to the direction of an earthquake of moderate intensity is extremely indefinite1 and the only satisfactory information to be obtained is that derived from instruments or from the effects of the earthquake exhibited in shattered buildings and bodies which had been overturned or projected4 ,by the direction in which walls1 columns1 and other objects had been overthrown or fractured1 ,mallet was enabled to determine the position of the origin of the ,neapolitan earthquake4 ,similar phenomena have many times been taken advantage of by other investigators of earthquake phenomena4 ,effects produced upon structures are1 however1 only to be observed as the results of a destructive earthquake1 at which time cities may be regarded as collections of seismometers4 7,see chapter on ,effects in ,buildings47 ,to determine the direction of movement during a small earthquake1 the most satisfactory method appears to be an appeal to instruments4 ,instruments as ,indicators of ,direction4--,the relative values of different kinds of instruments1 such as columns1 pendulums1 and the like1 as indicators of direction have already been discussed4 ,by the use of pendulum seismographs it has been shown that during an earthquake the ground may move in one1 two1 or several directions 7see p4 #ba72 and it is1 generally speaking1 only in those cases where we experience a decided shock in the disturbance that we can determine with any confidence the direction in which the motion has been propagated4 ,such directions are usually indicated by the major axis of certain more or less elliptical figures which have been drawn1 which in themselves appear to indicate the combination of two rectilinear movements4 ,results similar to those indicated by the records of pendulum seismographs have also been obtained upon moving plates with a double bracket seismograph4 ,thus1 in the earthquake which shook ,tokio at #f ,a4,m4 on ,july #e1 #ahha1 there were indications of the following motions3-- ,near the commencement of the shock the motion was ,n4 #aab ,e4 ,one and a half second after this1 the direction of motion appears to have been ,n4 #ej ,e4 ,in three-fourths of a second more it gradually changed to a direction ,n4 #ade ,e41 and after a similar interval to ,n4 #fb ,e4 ,half a second after this it was ,n4 #acb ,e41 and four seconds later the motion was again in the original direction--namely1 ,n4 #aab ,e4 ,these particular directions of motion have been selected because they were so definitely indicated4 ,the commonest type of earthquake which is experienced in ,japan1 and probably also in other earthquake-shaken districts1 is the compound or diastrophic form4 ,that earthquakes often have motions compounded of two sets of vibrations1 has also been proved by the analysis of the records obtained from two component seismographs4 ,from an analysis of a record of this description1 ,professor ,ewing has shown that in the earthquake felt in ,tokio on ,march #aa1 #ahha1 there were approximate circular 7somewhat spiral7 movements4 ,this leads us to the consideration of the twisting and wriggling motions which are said to be experienced by some observers4 ,motions like these1 which by the ,italians and ,mexicans are called vorticosi1 are usually supposed to be the cause of objects like chimneys and gravestones being rotated4 ,these phenomena1 it will be seen from what is said in the chapter upon the effects produced in buildings1 can be more easily explained upon the supposition of a simple rectilinear movement4 ,that at the time of an earthquake there may be motion in more than one direction has been recognised since the time of ,aristotle2 and it is possible that two sets of rectilinear motion1 as1 for instance1 the normal and transverse movements1 may have led observers to imagine that there has been a twisting motion taking place1 and this especially when the two sets of movements have quickly succeeded each other4 ,persons inside flexible buildings may possibly have experienced more or less of a rotatory motion1 although the shock was rectilinear2 the building assuming such a motion in consequence of its construction and its position with regard to the direction of the shock4 ,in the case of destructive earthquakes1 especially at points situated practically above the origin1 the universal testimony1 ,mallet tells us1 is that a twisting1 wriggling motion in different planes1 attended by an up-and-down movement of greater range1 is experienced4 ,to such disturbances the word sussultatore is sometimes applied4 ,mallet has given many elliptical and other closed curves to illustrate the nature of such motions4 ,duration of an ,earthquake4--,when reading accounts of earthquakes it is often difficult to determine the length of time a shaking was continuous4 ,in ,japan1 in ,a4,d4 #gde1 there was a shaking which is said to have lasted sixty hours2 and in ,a4,d4 #igg there were a series of shakings lasting #cjj days4 ,often we meet with records of disturbances which have lasted from twenty to seventy days4 ,at ,san ,salvador1 in #ahgi1 more than #fjj shocks were felt within ten days2 in #ahej1 at ,honduras1 there were #ajh shocks in a week2 in #agdf1 at ,lima1 #bjj shocks were felt in twenty-four hours2 at the island of ,st4 ,thomas1 in #ahfh1 #bhc shocks were felt during about ten hours4 ,disturbances like these1 which succeed each other with sufficient rapidity to cause an almost continual trembling in the ground1 may be regarded as collectively forming one great seismic effort which may last a minute1 an hour1 a day1 a week1 or even several years4 ,strictly speaking1 they are a series of separate earthquakes1 the resultant vibrations of which more or less overlap4 ,whenever a large earthquake occurs it is generally succeeded by a large number of smaller shocks4 ,the seismic disturbance as regards time is1 as ,mallet remarks1 very often #8like an occasional cannonade during a continuous but irregular rattle of musketry4' ,in the ,new ,zealand earthquake of #ahdh1 shocks continued for nearly five weeks1 and during a large portion of the time there were at least #a1jjj shocks per day4#ab ,the earthquake of ,lisbon1 which in five minutes destroyed the whole town1 was followed by a series of disturbances lasting over several months4 ,after ,basle had1 on ,october #ah1 #acef1 been laid in ruins1 it is stated shocks followed each other for a period of a year4 ,the ,calabrian earthquake was continued with considerable strength for a year1 and it is said that the earth did not come completely to rest for ten years4 ,during this cannonade the heavy shocks announced1 as they do in most earthquake countries at the present day1 a series of weaker disturbances4 ,in certain exceptional cases this order of events has been inverted1 and slight shocks have announced the coming of heavy ones4 ,fuchs gives an example of this in the earthquake of ,broussa1 when the first shock was on ,february #bh1 #ahee4 ,on ,march #i and #bc there were heavier shocks1 but the heaviest did not arrive until ,march #bh4 ,under certain conditions it is possible to have a sensible vibration produced in the ground which is practically of unlimited duration2 thus1 for instance1 it has been noticed that the falling of water at certain large waterfalls1 by its continuous rhythmical impact on the rocks1 produces in them tremors which are to be observed at great distances4 ,of this the author convinced himself at the ,falls of ,niagara1 where he observed the reflected and ever-moving image of the sun in a pool of water4 ,under favourable circumstances almost continual condensation of steam might take place in volcanic foci1 each condensation giving rise to a blow sufficiently powerful to produce vibrations in the surrounding ground4 ,those who have stood near a large geyser1 like the one in ,iceland1 when it makes an ineffectual effort to erupt1 will recognise how powerful such a cause might be4 ,humboldt has remarked shocks on ,vesuvius and ,pichincha which were periodic1 occurring twenty to thirty seconds before each ejection of vapour and ashes4 ,earthquakes like these may be of vast extent1 gradually spreading further and further outwards4 ,this spreading of earth vibrations may be observed at a large factory containing heavy machinery or a steam hammer4 ,after the machinery comes to rest1 it is probably some time before the ground returns to rest4 ,examples of disturbances of this nature are spoken of under the head of ,earth ,tremors4 ,the record of the duration of an ordinary earthquake as observed at a given point is dependent upon the sensibility of our instruments4 ,continuous motions perceptible to our senses without the aid of instruments usually last from thirty seconds to about two or three minutes4 ,in ,japan the shocks1 as timed by watches1 usually last from twenty to forty seconds4 ,occasionally a continuous shaking is felt for more than one and a half minutes1 and cases have been recorded where the motion has continued for as much as four minutes and thirty-three seconds4 ,seismometers having a multiplication of #f to #ab usually indicate that motion continues longer than is perceptible to the senses4 ,period of ,vibration4--,when an earthquake contains several prominent vibrations which might be called the shocks of the disturbance1 our feelings tell us that these have occurred at unequal intervals4 ,about the time which is taken for the complete backward and forward oscillation of the ground which constitutes the shock a little has already been said4 ,this was deduced from the records of disturbances as drawn by seismographs4 ,from the same sources we can readily obtain the period of all the prominent vibrations in a disturbance4 ,in any given earthquake there are irregularities in period1 and different earthquakes differ from each other4 ,about the early attempts to determine the period of earth vibrations something has been said in the chapter on ,earthquake ,instruments4 ,in the earthquake of ,march #aa 7referred to on p4 #gj7 we find that both components commenced with a series of small vibrations1 about five or six to the second2 next came the shock1 consisting of two complete vibrations executed in two seconds4 ,in this it is to be observed that the motion eastwards was performed much more quickly than the motion westwards4 ,next1 by reference to the east and west component1 it is seen that there are a number of large vibrations1 about one per second1 on which a number of smaller motions are superposed4 ,as the motion proceeds1 these become less and less definitely pronounced and more irregular in their intervals1 until finally the motion dies away4 ,this earthquake1 as recorded at the author's house in ,tokio1 lasted about one and a half minute4 ,the same earthquake1 as recorded by ,professor ,ewing at a station situated about one and a half mile distant1 but on flat ground1 appears to have lasted four and a half minutes4 ,the largest wave had a period of #jg second4 ,in the earthquake of ,march #h1 #ahha1 there were on an average #ad vibrations per second4 ,these vibrations were executed in a direction transverse to the line joining the observing station and the locality from which the disturbance must have originated as determined by time observations4 ,it can1 therefore1 be assumed that these vibrations1 having so slow a period1 were transverse motions1 this slowness or sluggishness being due to the fact that the modulus for distortion is less than the modulus which governs the propagation of normal vibrations4 ,the ,amplitude of ,earth ,movements4--,in making estimates of the distances through which we are moved backward and forward at the time of an earthquake1 if we judge by our feelings1 we may often be misled4 ,if a person is out of doors and walking1 an earthquake may take place sufficiently strong to cause chimneys to fall and unroof houses1 which1 so far as the actual shaking of the ground is concerned1 will be passed by unnoticed4 ,on the other hand1 to persons indoors1 especially on an upper story1 it is impossible even for a tremor to pass by without creating considerable alarm by the angular movement that has been taken up by the building4 ,many observers have endeavoured to make actual measurements of the maximum extent through which the earth moves at the time of an earthquake4 ,among the reports of the ,british ,association for #ahda is the report of a committee which had been appointed #8for obtaining instruments and registers to record shocks of earthquakes in ,scotland and ,ireland'4 ,we read that in one earthquake which had been measured the displacement of the ground had been half an inch1 and in another it had been less than half an inch4 ,the instruments used to make these observations depended upon the inertia of pendulums which at the time of the disturbance were supposed to remain at rest4 ,observations similar to these have been made in ,japan4 ,one long series were made by ,mr4 ,e4 ,knipping for ,dr4 ,gr4 ,wagener4 ,they extended from ,november #ahgh to ,april #ahhj1 and were as follows3-- ,number of ,maximum horizontal ,earthquakes motion of the ground #aj #j to #jae mm4 #g #ae #je #h #e #be #b #be more ,with his apparatus for vertical motion ,dr4 ,wagener also made observations on the absolute vertical motion4 ,this seldom reached #jb mm4 ,the greatest value was that observed for the destructive shock of ,feb4 #bb1 #ahhj1 which was #ef mm4 ,by means of a number of instruments distributed at various localities round ,tokio1 the chief of which were pendulums with friction pointers to render them #8dead beat1' and with magnifying apparatus to show the actual motion of the ground1 the author arrived at results similar to those obtained by ,dr4 ,wagener--namely1 that the earth's maximum horizontal motion at the time of a small earthquake was usually only the fraction of a millimetre1 and it seldom exceeded three or four millimetres4 ,when we get a motion of five or six millimetres1 we usually find that brick and stone chimneys have been shattered4 ,the results obtained for vertical motion were also very small4 ,in ,tokio it is seldom that vertical motion can be detected1 and when it is recorded it is seldom more than a millimetre4 ,these results1 which were put forward some years ago1 have since received confirmation by the use of a variety of instruments in the hands of different observers4 ,mallet1 in his account of the ,neapolitan earthquake of #aheg1 approximated to the amplitude of an earth particle by observing the width1 at the level of the centre of gravity1 of fissures formed through and remaining in great masses of very inelastic masonry4 ,taking stations situated on or very nearly on the same line passing through the seismic vertical 7epicentrum71 ,mallet observed the amplitude increased as some function of the distance1 as will be seen from the following table3-- ---------------------------------------- --------------------- ,station ,polla ,la ,sala,certosa,tramutola,sarconi ---------------------------------------- --------------------- ,distance from ,seismic ,vertical in #cde #aafj #afej #bjfj #bfg geographical miles ,amplitude in inches #be #ce #dj #de #dge ---------------------------------------- --------------------- ,the possibility of a law such as this having an existence for places at a distance from the seismic vertical comparable with the vertical depth of the centrum will be shown farther on4 ,with regard to the maximum displacement of an earth particle4 ,mallet was of opinion that there was evidence to show that it had in some cases been over one foot4 ,m4 ,abella1 in an earthquake which occurred in the ,philippines in #ahha1 made a rough observation of the motion of the earth to a distance of about two metres4 ,this1 as might be expected1 was beyond the elastic limits of the material1 and caused fissures to be formed1 which were seen to open and shut4 ,intensity of ,earthquakes4--,in speaking of the strength of an earthquake1 we usually employ terms like #8weak1' #8strong1' #8violent1' c4 ,although these expressions1 accompanied by illustration of the effects which an earth quake has produced1 convey a general idea of the strength of a shock as felt at some particular locality1 our ideas nevertheless wanting in definiteness2 and if we endeavour to compare one shock with another1 as a whole1 our want of exactness is augmented4 ,we have seen that ,palmieri's seismograph indicates intensity by a certain number of degrees1 which1 to a certain extent1 is a measure of the violence of the motion as indicated at a particular locality4 ,the degrees1 as before stated1 refer to the height to which in consequence of the shaking1 a certain quantity of mercury was washed in a tube1 which is a function of the depth of mercury in the tube1 and also of the duration of the disturbance4 ,from this it seems possible that a very slow motion of small amplitude1 continuing over a sufficient period of time1 might1 if it agreed with the period of the mercury1 indicate an earthquake of many degrees of intensity1 whilst residents in the neighbourhood might not have noticed the disturbance2 and1 on the other hand1 a short but intense shock creating considerable destruction might have been recorded as of only a few degrees of intensity4 ,although objections like these might be raised to such a method of recording intensity1 in practice it would appear that such results are not pronounced1 and the indications of the instrument usually give us approximate indications of relative intensity4 ,in writing about the ,neapolitan earthquake of #aheg1 ,mallet says that #8area alone affords no test of seismic energy4' ,the area over which a shock is felt will depend not only upon the initial force of the disturbance1 but also upon the focal depth of a shock1 the form and position of that focus1 the duration of the disturbance1 and the nature and arrangement of the materials which are shaken4 ,from observations in ,japan1 it is clearly shown that massive mountain ranges exert a considerable influence upon the extension of seismal disturbances4 ,on one side of a large range of mountains large cities might be laid in ruins1 whilst on the other side the disturbance creating this destruction might not be noticed4 ,velocity and ,acceleration of an ,earth ,particle4--,we now pass on to methods of determining the intensity of an earthquake which are less arbitrary than those which have just been discussed4 ,these methods have already been discussed when speaking of artificial disturbances1 where it was shown that the intensity of an earthquake as measured by its destructive effects greatly depended upon the suddenness with which the backward and forward motions of the ground were commenced or ended4 ,amongst the earlier investigators of seismic phenomena who observed that there existed a connection between the distance to which bodies had been projected during an earthquake and the suddenness or initial velocity with which the ground had been moved beneath them1 was ,professor ,wenthrop of ,cambridge1 ,massachusetts1 who noted that bricks from his chimneys had1 by the ,new ,england earthquake of #agee1 been thrown thirty feet4 ,from this and the known height of the chimney1 he calculates that the bricks had been projected with an initial velocity of twenty-one feet per second4#ac ,the calculations made by ,mallet respecting the maximum velocity of an earth particle at the time of the ,neapolitan earthquake in #aheg depended upon the overthrow1 projection1 and fracture of bodies4 ,the principles which guided him in making the calculations will be understood from the following illustration4 ,illustration3 ,fig4 #ad4 ,if a column1 ,a ,b ,c ,d1 receive a shock or be suddenly moved in the direction of the arrow1 the centre of gravity1 ,g1 of this column will revolve round the edge1 and tend to describe the path ,g ,o4 ,if it passes ,o1 the column will fall4 ,the work done in such a case as this is equal to lifting the column through the height o h4 ,if ,g ,a a1 the angle ,g ,a h 1 and the weight of the body ,w1 then the above work equals ,wa 7#a - cos 74 ,this must equal the work acquired--that is to say1 the kinetic energy of rotation of the body1 or ,w w#b ,k#b ,wa 7#a - cos 7 ----------------------4 #b g ,where w is the angular velocity of the body at starting1 ,k the radius of gyration round ,a1 and g the velocity acquired by a falling body in one second4 ,whence w#b ,k#b #b ga 7#a - cos 71 but w1 the angular velocity1 is equal to the statical couple applied1 divided by the moment of inertia1 or1 ,va cos w --------------------1 ,k#b squaring and substituting ,k#b #a - cos ,v#b #b;g ------ ------------------1 a cos#b ,k#b and since the length of the corresponding pendulum is l ------1 a #a - cos ,v#b #b;gl ------------------4 cos#b ,to apply this to any given case we must find the value of l or of ,k#b ------4 a ,mallet finds these values for the cube1 solid and hollow rectangular parallelopipeds1 solid and hollow cylinders1 c4 ,in these formul we have a direct connection between the dimensions and form of a body and the velocity with which the ground must move beneath it to cause its overthrow4 ,illustration3 ,,fig4 #ae4 ,not only is the case discussed for horizontal forces1 but also for forces acting obliquely4 ,similar reasonings are applied to the productions of fractures in walls1 but as there is uncertainty in our knowledge of the co-efficient of force necessary to produce fracture through joints across beds of masonry1 the deductions ought not to be applied as the measures of velocity4 ,where the fractures occur at the base or in horizontal planes1 or in those of the continuous beds of the masonry1 or through homogeneous bodies1 the uncertainty is not so great1 and for cases like these ,mallet gives several illustrations4 ,the distance to which bodies had been projected1 as1 for example1 ornaments from the tops of pedestals1 coping-stones from the edges of roofs1 were also used as means of determining the angle at which the shock had emerged1 or1 if this be known1 for determining the velocity4 ,thus by a shock in the direction ,o ,c1 a ball1 ,a1 on the top of a pedestal would describe a trajectory to the point ,c4 ,let the angle which ,o ,c makes with the horizon be e1 the vertical height through which the ball has fallen be b1 and the horizontal distance of projection be a2 then a#b b a tan e ------------------------1 #d;,h cos#b e ,h being the height due to the velocity of projection4 ,whence #b;,h #d;,h7,h b7 - a#b ,tan e ---------------------------------------- ------------4 a a#b g ,v#b ---------------------------------------- ----------------------4 #b cos#b e 7b - a tan e7 ,for the back motion or subnormal wave in the direction ,c ,o1 #b;,h #d;,h7,h b7 - a#b ,tan e ---------------------------------------- ------------4 a a#b g ,v#b ---------------------------------------- ----------------------4 #b cos#b e 7b a tan e7 ,a serious error which may enter into calculations of this description when practically applied has been pointed out when speaking of columns as seismometers4 ,it was then shown that such bodies before being overthrown may often be caused to rock1 and therefore that their final overthrow may not have any direct connection with the impulse of the succeeding shock4 ,another point to which attention must be drawn respecting the above calculations is that if there was no friction or adherence between the projected body and its pedestal1 in consequence of its inertia it would be left behind by the forward motion of the shock1 and simply drop at the foot of its support4 ,in the case of frictional adherence it would be carried forward by the velocity acquired before this adherence was broken1 and thrown in a direction opposite to that given in the figure--that is to say1 in the direction of the shock4#ad ,the ,absolute ,intensity of the ,force exerted by an ,earthquake4--,no doubt it has occurred to many who have experienced an earthquake that the power which gave birth to such a disturbance must have been enormously great4 ,the estimates which we shall make of the absolute amount of energy represented by an earthquake cannot1 on account of the nature of the factors with which we deal1 be regarded as accurate4 ,they may1 however1 be of assistance in forming estimates of quantities about which we have at present no conception4 ,one method of obtaining the result we seek is that which was employed by ,mallet in his calculations respecting the ,neapolitan earthquake4 ,although disbelieving in the general increment of temperature as we descend in the earth at an average rate of #a ,f4 for every fifty or sixty feet of descent1 for want of better means4 ,mallet assumes this law to be true1 and1 knowing from a variety of observations the depth of various parts of the cavity from which the disturbance sprang1 he calculates the temperatures of this cavity in various parts as due to its depth beneath the surface4 ,next1 it is assumed that steam was suddenly admitted into this cavity1 which might exert the greatest possible pressure due to the maximum temperature4 ,this was calculated as being about #fhd atmospheres4 ,next1 he determined the column of limestone necessary to balance such a pressure1 which is about #h1eej feet in height4 ,as the least thickness of strata above this cavity was #af1gjj feet1 the pressure of #fhd atmospheres was not sufficient to blow away its cover1 but if suddenly admitted or generated in the cavity it might have produced the wave of impulse by the sudden compression of the walls of the cavity4 ,the pressure of #fhd atmospheres is equivalent to about #deh tons on the square inch1 and1 as the total area of the walls of the cavity is calculated at twenty-seven square miles1 the total accumulated pressure would be more than #fdj1ebh millions of tons4 ,mallet1 however1 shows that it is probable that the temperature of the focal cavity was much greater than that due to the hypogeal increment1 and that therefore the pressure may have been greater4 ,the capability of producing the earthquake impulse1 however1 depends on the suddenness with which the steam is flashed off4 ,according to the experiments of ,boutigny and others1 ,mallet tells us that the most sudden production of steam would take place at a temperature of #ejj-eej ,c41 which is but a few degrees below that calculated for the mean focal depth4 ,assuming the above calculated pressure to be true1 and knowing the co-efficient of compression of the materials on which it acted1 the volume of the wave at a given moment near the instant of starting--that is1 at the focus--can be calculated1 and from this the wave amplitude on reaching the surface may be deduced4 ,proceeding backwards1 if we have observed the wave amplitude1 calculated the depth of the focus1 and know the co-efficient of expansion1 then the total compression may be calculated and the temperature due to the pressure producing this may be arrived at4 ,in this way earthquakes may be used as a means of calculating subterranean temperature at depths that can never be attained experimentally4 ,a method of proceeding which is probably more definite than that adopted by ,mallet would be the application of the method indicated when speaking of the intensity of artificial disturbances4 ,if for a given earthquake the origin of which is known we have determined by seismographs the mean acceleration of an earth particle at two or more stations at different distances from that origin1 we are enabled to construct a curve of intensity the area between which and its asymptotes was shown to be a measure of the total intensity of the shock4 ,comparing this area with that of a unit disturbance produced1 say1 by the explosion of a pound of dynamite1 one may approximately calculate in terms of this unit the initial intensity of the earthquake4 ,radiation of an ,earthquake4--,the tremors preceding the more violent movements of an earthquake may be due1 as ,mallet has suggested1#ae to the free surface waves reaching a distant point before the direct vibrations4 ,the fact that earth vibrations produced by striking a blow on or near the surface of the ground are wholly obliterated in reaching a cutting or valley1 there being no underground waves of distortion to crop up on the opposite side of the valley1 indicates that the disturbance is one that travels on the surface2 the same fact is illustrated when we endeavour to transmit vibrations through the side of a hill into a tunnel4 ,in the tunnel1 although the distance may be small1 no sensible effects are produced1 whilst the same disturbance may be recorded at a long distance from its origin on the surface of the ground outside the tunnel4 ,lastly1 we may refer to the experiences of miners underground4 ,occasionally it has happened that miners when deep underground1 as in the ,marienberg in the ,saxon ,erzgebirge1 have felt shocks which have not been noticed on the surface4 ,these observations are rare1 and it is possible that they may be explained by the caving in of subterranean excavations4 ,the usual experience is1 that if a shock is felt underground it is also felt on the surface1 as for example in the lead mines in ,derbyshire at the time of the ,lisbon disturbance 7#agee74 ,the most frequent observation1 however1 is that a shock may be felt on the surface while it is not remarked by the miners beneath the surface1 as at ,fahlun and ,presburg in ,november1 #ahbc4 ,at the ,comstock ,lode in ,colorado about twelve years ago many earthquakes were felt4 ,on one particular day twenty-four were counted4 ,superintendent ,charles ,foreman told the author when he visited ,virginia ,city in #ahhb1 that special observations were made to determine whether these shocks were felt as severely deep down in the mines as on the surface1 where they were on the verge of being destructive4 ,the universal testimony of many observers was that in most cases they were not felt at all underground1 and when a shock was felt it was extremely feeble4 ,at ,takashima ,colliery1 in ,japan1 it is seldom that shocks are felt underground4 ,the explanation of these latter observations appears to be either that1 in consequence of a smaller amplitude of motion in the solid rocks beneath the surface as compared with the extent of motion on the surface1 the disturbances are passed by unnoticed1 or else the disturbance is1 at a distance from its origin1 practically confined to the surface4 ,velocity of ,propagation of an ,earthquake4--,although many have written upon earthquakes and have endeavoured to give to us the velocity with which they were propagated1 the subject is one about which we have as yet but little exact information4 ,the importance of this branch of investigation is undoubtedly great4 ,by knowing the velocity with which an earthquake has travelled in various directions we are assisted in determining the locality of its origin2 we may possibly make important deductions respecting the nature of the medium through which it has passed2 perhaps also we may learn something regarding the intensity of the disturbance which created the earthquake4 ,in the ,report of the ,british ,association for #ahea ,mallet gives the table on next page1 in which are placed together the approximate rates of transit of shocks of several earthquakes which he discusses4 ,some of these1 it will be observed1 are records of disturbances which must have passed through or across the bed of the ocean4 ,in ,mallet's ,british ,association ,report for #aheh1 he gives data compiled by ,mr4 ,david ,milne#af respecting the ,lisbon earthquakes of #agee and #agfa1 from which data the tables of velocities 7p4 #hi7 have been calculated1 omitting those which ,mr4 ,mallet has marked as uncertain4 ,the distances are marked in degrees of seventy ,english miles each1 and the time is reduced to ,lisbon time4 ---------------------------------------- ------------------------ ,approx4 rate in ,formation constituting ,occasion and ,place feet ,range on surface as far ,authority per as known or conjectured second ---------------------------------------- ------------------------ ,rev4 ,john ,mitchell's #a1gfj ,sea bottom1 probably on ,mitchell guesses from the slates1 secondary and ,lisbon earthquakes crystalline rocks ,von ,humboldt's #a1gfj ,from observations in ,humboldt guesses from ,south to various ,south ,american ,america #b1dfd rocks in great part volcanic ,lisbon ,earthquake of #agfa4 ,lisbon to ,corunna #a1iid ,transition1 carboniferous #8,annual and granitoid ,register' ,lisbon to ,cork #e1bbh ,transition1 carboniferous crystalline slates and granitoid1 probably1 under sea bottom ,lisbon to ,santa ,cruz #c1bfa ,the same with many alterations ,antilles4 ,pointe ,pitre to #f1ehf ,probably volcanic rocks ,stier and ,cayenne 7doubtful7 under sea bottom ,perrey's memoran- dum1 ,dijon ,india4 ,cutch to ,calcutta1 #a1agc ,alluvial1 secondary1 #8,royal #ahai granitoid and later ,asiatic igneous rocks ,journal' ,india1 ,nepauls1 and basin of the ,ganges1 #ahcd3-- ,rungpur to ,arrah #b1cad ,deep alluvia1 with #8,royal ,monghyr to ,gorackpur #c1ebj occasional transition1 ,asiatic ,rungpur to ,monghyr #iij carboniferous1 granitoid1 ,journal' ,rungpur to ,calcutta #a1baj and later igneous rocks ,ships #8,rambler' and #a1jef ,sea bottom resting on #8,nautical #8,millwood1' at sea1 unknown rock ,magazine' #ahea2 between lat4 #af #cj ,n4,l41 #ed #cj ,w41 and lat4 #bc #cj ,n4,l41 #eh #j ,w4 ---------------------------------------- ------------------------ ,,the ,,lisbon ,,earthquake ,,on ,,november #a1 #agee4 ---------------------------------------- ------------- ,moment ,distance,velocity ,localities observed from in feet of shock presumed per origin second ---------------------------------------- ------------- h4 m4 ,presumed focus of shock1 #i #bc -- -- lat4 #cj1 long4 #aa ,w4 ,a ship at sea in lat4 #ch1 #i #bd #j #cj #c1jia long4 #aj #dg ,w4 ,colares #i #cj #a #cj #a1cbe ,lisbon #i #cb #a #cj #a1jcj ,oporto #i #ch #b #cj #a1jcj ,ayamont #i #ej #d #j #iaf ,cadiz #i #dh #e #j #a1bcf ,tangier and ,tetuan #i #df #e #cj #a1dgh ,madrid #i #dc #f #j #a1hee ,funchal #aj #a #h #cj #a1chb ,portsmouth #aj #c #ab #cj #a1dca ,havre #aj #bc #ac #j #a1cci ,reading #aj #bg #ac #cj #a1cjd ,yarmouth #aj #db #ae #j #a1agd ,amsterdam #aj #f #ag #j #b1ddd ,loch ,ness #aj #db #ah #j #a1dji ---------------------------------------- ------------- ,,the ,,lisbon ,,earthquake ,,of ,,march #ca1 #agfa4ag ---------------------------------------- ------------- ,moment ,distance,velocity ,localities observed from in feet of shock presumed per origin second ---------------------------------------- ------------- h4 m4 ,presumed focus1 lat4 #dc1 #aa #ea -- -- long4 #aa ,w4 ,ship at sea in lat4 #dc1 many leagues from coast #aa #eb #j #cj #c1jia of ,portugal ,ship in lat4 #dd #h and #aa #ed #a #de #c1fjg about #hj leagues from coast ,corunna #aa #ea #b #cj #b1egf ,ship lat4 #dd #h and #hj leagues ,,nnw4 of ,cape #aa #eh #c #cj #c1jia ,finisterre ,lisbon noon #d #cj #c1jia ,madeira #ab #f #aj #j #d1abb ,cork #ab #aa #i #cj #b1icg ---------------------------------------- ------------- ,these tables1 owing to the nature of the materials which ,mallet had at his disposal1 are but rude approximations to the truth4 ,two interesting facts are1 however1 observable3 the first being that the velocities for the earthquake of #agfa are much higher than those obtained for the earthquake of #agee2 and1 secondly1 that in both cases the velocities as determined from the observations of ships at sea closely approximate to each other1 in all cases being nearly the same as that with which a sound wave would travel through water4 ,the great differences in transit velocity obtained for different earthquakes is a point worthy of attention4 ,seebach's velocity is a true transit velocity1 and its determination is dependent on the assumption that the shock radiated from the centrum and not from the epicentrum1 ,seebach's method is explained when speaking about the determination of origins4 ,some interesting observations on the velocity with which the earthquake of ,october #g1 #ahgd1 was propagated1 are given by ,m4 ,s4 di ,rossi4#ah ,one assumption is that the disturbance radiated from an origin to surrounding points of observation1 whilst another is that the disturbance followed natural fractures1 the direction of which is derived from the crest of certain mountain ranges4 ,these velocities are as follows1 ,maradi being at or near the origin of the disturbance3-- ---------------------------------------- ------------------------ ,velocity in feet per second ,velocity in feet per second by with direct radiation propagation along mountain chains ---------------------------------------- ------------------------ ,modigliana #hbj ,by the ,valley of ,marenzo #a1jhj ,bologna #fef ,saveno #a1jhj ,forli #hgd ,montone #a1jhj ,modena #eah ,panaro #a1jhj #ihd ,firenze #bgc ,sieve #edj ,compiobbi #cbh #edj ---------------------------------------- ------------------------ ,another set of interesting results are those of ,p4 ,serpieri on the earthquake of ,march #ab1 #ahgc4 ,the curious manner in which this shock radiated is described in the chapter on the ,geographical ,distribution of ,earthquakes 7see p4 #bca74 ,two large areas appear to have been almost simultaneously struck1 so that1 there being no time for elastic yielding1 the velocities calculated between places situated on either of the areas are exceedingly great4#ai ,from ,ragusa to ,venice the velocity was #b1gcd feet per second ,spoleto #d1aja ,perugia to ,orvieto #fja ,ancona #a1fdj ,rome #a1fdj or1 #b1ahf ,the following are examples of approximate earthquake velocities which have been determined in ,japan4 ,the ,tokio ,earthquake of ,october #be1 #ahha4--;,from records respecting this earthquake it appears to have been felt over the whole of ,yezo and the northern and eastern coast of ,nipon1 a little farther south than ,tokio4 ,it was severest at ,nemuro and ,hakodate1 and at the former place a little damage was done4 ,from these facts1 together with the indications of instruments recording direction of movement and a general inspection of the time records1 it seems that the disturbance must have originated beneath the sea on the east coast of ,yezo at a very long distance to the north-east of ,tokio1 from which place it passed in a practically direct line on to ,yokohama4 ,as the disturbance was felt at ,yokohama twenty-one seconds later than at ,tokio1 and the distances between these two places is about sixteen geographical miles1 for this portion of its course the disturbance must have travelled at a rate of at least #d1cjj feet per second4 ,if we assume that the shock1 after having reached ,hakodate1 travelled on at the same rate as it did between ,tokio and ,yokohama in order to reach ,saporo1 where the shaking was felt eighteen seconds after ,hakodate1 it must have had about thirteen geographical miles to travel after ,hakodate was shaken before ,saporo felt its effect4 ,drawing from ,hakodate a tangent to the eastern side of a circle of thirteen miles radius described round ,saporo1 the origin of the disturbance must be on the line bisecting this tangent at right angles4 ,as it also lies on a line drawn through ,tokio and ,yokohama1 it lies in a position about #da ,n4 lat4 and #add #ae ,e4 long41 which is a position somewhat nearer to ,nemuro than ,hakodate1 as we should anticipate4 ,if this be taken as approximately indicating the origin1 then the shock1 after reaching ,hakodate from the ,hakodate homoseist1 travelled about #bah miles to reach ,tokio in #abh seconds1 which gives a velocity of #aj1bai feet per second4 ,the method here followed is equivalent to that of the hyperbola and one direction 7see p4 #bjd74 ,the hyperbola is described on the assumption that the velocity deduced from the time taken to travel between ,tokio and ,yokohama is correct1 and also that the earth waves travelled with approximately the same velocity in the vicinity of ,saporo as near ,tokio4 ,the probability1 however1 is that they travelled more quickly4 ,if this be so1 then the origin is thrown somewhat to the south-east and the velocity between the ,hakodate homoseist and ,tokio reduced4 ,thus1 if the velocity in the ,saporo district be double that observed in the ,tokio district1 the origin is shifted about twenty-eight miles to the south-west1 and the last-mentioned velocity is reduced to about #i1jjj feet per second4 ,if we work by the method of circles1 and assume the velocity to have been constant in all directions1 then this velocity must have been about #f1jjj feet per second4 ,if we assume that the indications of direction obtained from seismographs and other sources give to us by this intersection a proper origin1 the velocity in some directions may have been as much as #ag1jjj feet per second4 ,an origin thus determined1 or even if determined by the method of circles1 is in discord with the fact that places like ,nemuro1 in the north-east of ,yezo1 were nearer to the origin than any of the other places which have been mentioned4 ,the conclusion which we are therefore led to with regard to this shock1 assuming of course that the time observations are tolerably correct1 is that the velocity of propagation was variable1 being greater when measured between points near to the origin than between points at a distance4 ,the velocities estimated vary between #d1jjj and #i1jjj feet per second4 ,in the case of the earthquake which has just been discussed1 we have an example of a disturbance which must have passed between ,tokio and ,yokohama in what was almost a straight line from the origin4 ,as this direction ought to give the maximum time of transit if all earthquakes are propagated with the same velocity1 the following table is given of the interval between the time of observation of several shocks at these two stations3-- ,,from ,,yokohama ,,to ,,tokio4 ,,from ,,tokio ,,to ,,yokohama4 #ahhj ,december #bjth #cf seconds #ahhb ,october #beth #ba seconds #ahha ,january #gth #ad-ca #ahhc ,february #fth #bc ,march #hth #fj ,march #a #ec #agth4 #ff #fc ,november #aeth #ca #hth #bg #ahhb ,february #afth #bb #aath #bf ,as these are observations which have been made with the assistance of a telegraphic signal daily employed to correct and rate the clocks from which the observations were obtained1 they may be regarded as being tolerably1 correct4 ,the disturbance of ,february #f1 the two shocks of ,march #a1 appear1 like that of ,october #be1 to have passed in almost a direct line from an origin in the ,n4,n4,e1 through ,tokio on to ,yokohama4 ,their velocities of propagation as calculated from the above intervals are approximately #c1ijj1 #a1ijj1 and #a1djj feet per second4 ,the shock of ,february #af appears to have had its origin near to a point in ,yedo ,bay about eight miles east of ,yokohama4 ,assuming this to be the case1 the shock between the ,yokohama homoseist and ,tokio travelled at the rate of #b1ded feet per second1 but between the ,tokio homoseist and ,chiba at the rate of #gej feet per second2 that is to say1 the velocity of propagation rapidly decreased as the disturbance spread outwards4 ,at ,yokohama it was recorded at #e4ca4ed1 at ,tokio at #e4cb4af1 and at ,chiba at #e4cc4dh4 ,these times are given in ,tokio mean time4 ,the shock of ,march #aa1 which was recorded at ,tokio at #g4ea4bb ,p4,m4 and at ,yokohama at #g4ea4cc ,p4,m41 appears1 from the indications of instruments which were exceptionally definite in their records1 to have originated in the ,n4,e4 corner of ,yedo ,bay1 about nineteen miles ,s4,s4,w4 from ,chiba4 ,this shock was rather severe1 fracturing several chimneys4 ,from the ,tokio homoseist it appears to have travelled on to ,yokohama at the rate of about #b1bjj feet per second4 ,assuming these observations to be approximately accurate1 if we take them with the records of previous observers they lead us to the following conclusions3-- #a4 ,different earthquakes1 although they may travel across the same country1 have very variable velocities1 varying between several hundreds and several thousands of feet per second4 #b4 ,the same earthquake travels more quickly across districts near to its origin than it does across districts which are far removed4 #c4 ,the greater the intensity of the shock the greater is the velocity4 ,,chapter ,,vi4 ,,effects ,,produced ,,by ,,earthquakes ,,upon ,,buildings4 ,the destruction of buildings is not irregular--,cracks in buildings--,buildings in ,tokio--,relation of destruction to earthquake motion--,measurement of relative motion of parts of a building shaken by an earthquake--,prevention of cracks--,direction of cracks--,the pitch of roofs--,relative position of openings in a wall--,the last house in a row--,the swing of buildings--,principle of relative vibrational periods4 ,the subject of this chapter is1 from a practical point of view1 one of the most important with which a seismologist has to deal4 ,we cannot prevent the occurrence of earthquakes1 and unless we avoid earthquake-shaken regions1 we have not the means of escaping from them4 ,what we can do1 however1 is in some degree to protect ourselves4 ,by studying the effects produced by earthquakes upon buildings of different construction and variously situated1 we are taught how to avoid or at least to mitigate calamities which1 in certain regions of the world1 are continually repeated4 ,the subject is an extensive one1 and what is here said about it must be regarded only as a contribution to the work of future writers who may give it the attention it deservedly requires4 ,the ,destruction produced by ,earthquakes is not irregular4--,if we were suddenly placed amongst the ruins of a large city which had been shattered by an earthquake1 it is doubtful whether we should at once recognise any law as to the relative position of the masses of dbris and the general destruction with which we are surrounded4 ,the results of observation have1 however1 shown us that1 amongst the apparently chaotic ruin produced by earthquakes1 there is in many cases more or less law governing the position of bodies which have fallen1 the direction and position of cracks in walls1 and the various other phenomena which result from such destructive disturbances4 ,mallet1 at the commencement of his first volume1 describing the ,neapolitan earthquake of #aheg1 discusses the general effect produced by various shocks upon differently constructed buildings4 ,first he shows that1 if we have a rectangular building1 the walls at right angles to the shock will be more likely to be overthrown than those which are parallel to it4 ,experience teaches a similar lesson4 ,thus ,darwin1 when speaking of the earthquake at ,concepcion in #ahce1bj tells us that the town was built in the usual ,spanish fashion1 with all the streets running at right angles to each other4 ,one set ranged ,s4,w4 by ,w4 and ,n4,e4 by ,e4 and the other ,n4,w4 by ,n4 and ,s4,e4 by ,s4 ,the walls in the former direction certainly stood better than those in the latter4 ,the undulations came from the ,s4,w4 ,in ,caraccas it is said that every house has its laga securo1 or safe side1 where the inhabitants place their fragile property4 ,this laga securo is the north side1 and it was chosen because about two out of every three destructive shocks traversed the city from west to east1 so that the walls in these sides of a building have been stricken broadside on4#ba ,cracks in ,buildings4--,results like the above come from destructive earthquakes rather than from movements such as those we have to deal with ordinarily4 ,when a building is subjected to a slight movement it is assumed that the walls at right angles to the direction of the shock move backwards and forwards as a whole1 and there is little or no tendency for them to be fractured at their weaker parts1 these weaker parts being those over the various openings4 ,the walls1 however1 which are parallel to the direction of the movement are1 so to speak1 extended and contracted along their length1 and in consequence they may be expected to give way over the various openings4 ,this tendency for extension and contraction of a wall along its length may be supposed1 for instance1 to be due to the different portions of a wall1 owing to differences in dimensions and elasticity1 having different periods of natural vibration1 or possibly for two portions of a long line of wall to be simultaneously affected by portions of waves in different phases4 ,as an illustration of the giving way of a building in the manner here suggested we may take the case of a large brick structure which was recently being erected in ,tokio4 ,this building1 at the time of the earthquake1 was only some fourteen or fifteen feet above the surface of the ground4 ,the length of the building stretched from ,n4,w4 to ,s4,e41 and it was intersected by many walls at right angles to this direction4 ,through all the walls of this building there were many arched openings4 ,in the central part of the transverse walls1 which walls were fully five feet in thickness1 the arches which joined them together were #d feet #d inches in thickness4 ,the arches therefore formed a comparatively lightly constructed link between heavy masses of brickwork4 ,on ,march #c1 #ahgi1 at #d4dc ,p4,m41 an earthquake was felt throughout ,tokio1 the strength of which1 as judged by our feelings1 was above that of an average shock4 ,as registered by one of ,palmieri's instruments1 it had a direction ,s4,s4,w4 to ,n4,n4,e4 and an intensity of #aa4 ,on the same day there were several smaller shocks having the same direction1 and these were succeeded by others on the #ith of the month4 ,immediately after these shakings it was discovered that almost every arch in the internal walls of the building here referred to had been cracked across the crown in a direction about ,n4 #dj ,w4 ,all the other arches of the building1 of which there were a great number in walls at right angles to the direction of the shock1 were found not to have sustained any injury4 ,to this statement1 however1 there was one exception1 which was subsequently proved to have been due to a settlement taking place4 ,after examining these cracks the only cause to which they could be attributed was the series of shakings which they had just experienced4 ,it seemed as if the heavy walls right and left of the arches had been in vibration without synchronism in their periods1 and as a consequence the arches which connected them had been torn asunder4 ,although the time at which the cracks were formed and the peculiar positions in which they were only to be found pointed distinctly to their origin1 to be certain that they were not due to settlement of the foundations1 horizontal lines were ruled upon the brickwork and from time to time subsequently observed4 ,the points to which the various cracks extended were also marked and observed4 ,beneath the walls as foundations there were beds of concrete about three feet thick and about ten feet in width4 ,these had been under the pressure of the partially built walls for two years before the arches had been put in4 ,as these foundations were unusually strong1 being intended to carry so very much greater weight than that to which they had been subjected1 if any settlement had been detected it would have been a matter of surprise4 ,some weeks after the formation of these cracks it was observed that they gradually closed4 ,this was probably due to the gradual falling inwards of the two broken portions of the arch1 their position when open being one of instability4 ,illustration3 ,,fig4 #af4--;,cracks in a corner house1 ,belluno1 ,june #bi1 #ahgc 7,bittner74 ,had this building been more complete at the time of the shock1 and the heavy walls been tied together at higher points1 although the archways would have been points of weakness1 it is quite possible that fracture would not have taken place4 ,this illustration shows us that when a building is shaken in a definite direction there will be some rule as to the positions in which fractures occur4 ,as another example1 we may take the observations of ,alexander ,bittner upon the buildings of ,belluno after the shock of ,june #bi1 #ahgc 7see ,beitrge zur ,kenntniss des ,erdbebens von ,belluno am #bi ,juni1 #ahgc1 p4 #dj4 ,von ,alexander ,bittner4 ,aus dem ,,lxix4 ,bande der ,sitzungsb4 der ,k4 ,akad4 der ,wissensch41 ,,ii4 ,abth41 ,april-,heft4 ,jahrg4 #ahgd74 ,speaking generally1 he remarks that #8,houses similarly situated have suffered in corresponding walls and corners in a similar manner4 ,in ,belluno there is a certain kind of damage which is repeated everywhere1 making a peculiar system of splits in the ,s4,w4 and ,n4,e4 corners of the houses4' ,this is well shown in the accompanying sketch1 which evidently illustrates the effect of a shock oblique to the direction of two walls at right angles to each other4 ,illustration3 ,,fig4 #ag4--;,brick buildings in ,tokio1 showing fractures4 ,buildings in ,tokio4--,for the purpose of finding out what has been the effect produced by earthquakes upon the buildings of ,tokio1 and at the same time for ascertaining whether blocks of buildings ranging in different directions suffered to the same extent1 the author examined1 in company with ,mr4 ,josiah ,conder1 a large number of foreign-built houses in the district of the ,ginza4 ,the chief reason for choosing this was because it was the only district where a large number of similar buildings could be found4 ,by examining houses or buildings of different constructions1 the effects produced upon them by earthquakes are very often likely to show so many differences that it becomes almost an impossibility to determine what the general effect has been--unsymmetrical construction involving unsymmetrical ruin4 ,a number of similarly constructed buildings in one locality may be regarded as a number of seismographs1 the effect upon any one of them being judged of by the average of the general effect which has been produced upon the whole4 ,the general form of two of these houses which were examined is shown in fig4 #ag4 ,in this figure the general character of the fractures which have been produced can also be seen4 ,the houses are built of brick1 and are in many cases faced with a thin coat of white plaster4 ,projecting from the level of the upper floor there is a balcony fronted by a low balustrade4 ,this is supported by small beams which at their outer extremity are carried on a row of cylindrical columns4 ,this forms a covered way in front of each row of houses4 ,the roofs are covered with thick tiles4 ,it will be observed that the arches of the upper windows spring sharply from their abutments1 and at their crown they carry a heavy key-stone4 ,the lower openings1 which have a span of #i feet1 have evidently been constructed in imitation of the open front of an ordinary ,japanese house4 ,these archways curve out gently from their abutments4 ,the outside walls have a thickness of #ac inches4 ,the results obtained from a careful examination of #agd houses in streets running ,n4,e4 and #aef houses in streets running ,n4,w41 all of these houses being similar1 were as follows3-- #a4 ,in the upper windows nearly all the cracks ran from the springing1 which formed an angle with the abutment4 #b4 ,in the lower arches1 which curved into the abutments1 not a single crack was observed at the springway4 ,the cracks in these arches were near the crown1 where beams projected to carry the balcony4 ,in many instances the cracks proceeded from such beams1 even if there were no arch beneath4 ,that cracks should occur in peculiar positions1 as is here indicated1 is shown in the illustrations which accompany the accounts of many earthquakes4 #c4 ,the houses which were most cracked were in the streets running parallel to the direction in which the greater number and most powerful set of shocks cross the city4 ,the results showed that1 in order to avoid the effects of small shocks1 all walls containing principal openings should be placed as nearly as possible at right angles to the direction in which the shocks of the districts usually travel4 ,the blank walls1 or those containing unimportant openings1 would then be parallel to the direction of the shocks--that is1 presuming our building to be made up of two sets of walls at right angles to each other4 ,another point of importance would be to build archways curving into the supporting buttresses2 the archways over doors and windows which we find in earthquake countries do not appear to be in any way different from those which are built in countries free from earthquakes4 ,in the one country these structures have simply to withstand vertical pressures applied statically2 in the other1 they have to withstand more or less horizontal stresses1 applied suddenly4 ,relation of ,destruction to ,earthquake ,motion4--,the relations which exist between the overturning and projection of bodies and the motion of the ground have already been discussed4 ,it may be interesting to call attention to the fact that in the formul showing three relationships1 it was the shape rather than the weight of a body which determined whether it should be overturned or projected by a motion at its base4 ,as an interesting proof that light bodies may be overturned as easily as heavy ones4 ,mallet refers to the overturning of several large haystacks as one of the results of the ,neapolitan earthquake4 ,if masses of material are displaced or fractured1 then ,mallet remarks that the maximum velocity will exceed #b;gh1 where h is the amplitude of the wave4 ,should the maximum velocity be less than this quantity1 the masses which are acted upon will be simply raised and lowered1 and there will be no relative displacements even if the emergence of the wave be nearly or quite vertical4 ,when we get a vertical wave acting upon an irregular mass of masonry1 the heavier portions of the masonry1 by their inertia1 tend to descend relatively to the remaining portions1 and in this way vertical fissures will be produced4 ,for this reason it would not be advisable to use heavy materials above archways1 heavy roofs1 or heavy floors4 ,the vertical fissures1 ,mallet remarks1 would have their widest opening at the base4 ,in considering cases of fracture produced by earthquake motion1 it must be remembered that these are due to stresses applied suddenly1 and that if the same amount of stress had been slowly applied to a building1 fractures might not have occurred4 ,if a disturbance is horizontal1 and has a direction parallel to the length of a wall1 the wall is carried forward at its foundations4 ,this motion is opposed by the inertia of the upper portion of the wall and the various loads it carries4 ,the wall being elastic1 distortion takes place1 and cracks1 which are widest at the top1 will be formed4 ,in a uniform wall the two most prominent fissures ought to be near the ends4 ,if the horizontal backward and forward movement has a direction oblique to the plane of the wall1 the wall will be either overthrown1 fractured1 or have a triangular fragment thrown off towards the origin from the end last reached4 ,should the wave emerge steeply1 diagonal fissures at right angles to the direction of transit will be formed1 or else triangular pieces will be projected4 ,the accompanying figures are reduced from ,mallet's #8,account of the ,neapolitan ,earthquake of #aheg4' ,illustration3 ,,fig4 #ah4--;,cathedral ,church1 ,potenza 7,mallet74 ,taking a b as the general direction of the fractures in fig4 #ah1 then c d will represent the direction in which the shock emerged1 which is at an angle of #bcbj to the horizon4 ,it might be argued that the direction of these fractures was due to the direction in which surface undulations had travelled1 or to the relative strengths and proportions of different portions of the building4 ,the directions of cracks in a building are undoubtedly due to a complexity of causes1 but for buildings situated in the region of shock the impulsive effect of the shock is probably the most important function to be considered4 ,the method of applying the directions of emergence1 deduced from observations on fractures1 to determine the origin of a disturbance will be referred to in ,chapter ,x4 ,illustration3 ,,fig4 #ai4--,the ,cathedral1 ,paterno 7,mallet74 ,neapolitan ,earthquake of #aheg4 ,mallet observed that1 although two ends of a building might be nearly the same1 the fissures and joints do not occur at equal distances from the ends1 nor are they equally opened4 ,the end where the joints are the most opened is that which was first acted upon1 and this phenomenon may be sufficiently well pronounced to indicate the direction in which we must look to find the origin of a disturbance4 ,amongst possible explanations for this disposition of fractures in a wall4 ,mallet suggests that they may be due to real differences in the two semiphases of the wave of shock1 the second semiphase being described with a somewhat slower velocity than the first4 ,this1 it will be observed1 is contrary to the indications of seismographs4 ,fig4 #ai1 of the cathedral at ,paterno1 shows the effect of a subnormal shock striking a wall obliquely and projecting one of its corners4 ,,measurements ,,of ,,the ,,relative ,,motion ,,of ,,parts ,,of ,a ,,building ,,at ,,the ,,time ,,of ,,an ,,earthquake4 ,in #ahhj a series of observations was made in ,tokio to determine whether at the time of an earthquake the various parts of the arched openings which we see in many buildings synchronised in their vibrations1 or1 for want of synchronism1 were caused to approach and recede from each other4 ,the arches experimented on were heavy brick arches forming the two corridors of the ,imperial ,college of ,engineering4 ,the direction of one set of these corridors is ,n4 #dj ,e4 and that of the other ,n4 #ej ,w4 ,the thickness of the walls in which these arches are placed is #a ft4 #aa in4 ,they are built of ,japanese bricks bound together with ordinary lime4 ,the span of the arches is #h ft4 #c in41 and the height of the arch from the springing-line to the crown #d ft4 #a in4 ,the height of the abutments is #g ft4 #a in4 ,the voussoirs of the arch are formed of a light grey soft volcanic rock1 and on their faces show a depth of #ab inches4 ,the width of the intermediate columns between the arches is #d ft4 #f in4 ,to determine whether at the time of an earthquake there was any variation in the dimensions of these arches1 a light stiff deal rod1 about #b in4 by in4 in cross section1 was placed across the springing-line of the arch4 ,one end of this was firmly fixed to the top of one abutment by means of a spike2 on the other end1 which was to indicate any horizontal movement if the abutments approached each other1 there was fixed a pointer made out of a piece of steel wire4 ,this rested on a piece of smoked glass fixed to the ledge on which the loose end of the rod was resting4 ,if the abutments approached or receded from each other a line would be drawn measuring the extent of the motion4 ,as a further indication of motion1 a second smoked glass plate was fixed on the transverse rod1 which plate was marked on by a pointer attached to a vertical rod hanging down from the crown of the arch4 ,as a general result of these experiments it may be said that the portions of the building which were examined usually either did not move at all1 or else they practically synchronised in their movements4 ,when they did move1 the extent of motion was small1 and the small differences in movement which were observed were in every probability far within the elastic limits of the structure4 ,observations on ,cracks4--,to determine whether the walls of a building which have once been cracked1 when subjected to a series of shocks1 similar to those which they experienced before being cracked1 still continued to give way1 the extremities of a considerable number of cracks in the ,n4,e4 end of the museum buildings of the ,engineering ,college were marked with pencil4 ,although since the time of marking there had been many severe shocks1 these cracks did not visibly extend4 ,these marks were made on the outside wall of the building4 ,on the inside1 one of these same cracks showed itself as a fissure about inch in width4 ,across this crack a horizontal steel wire pointer was placed4 ,one end of this wire was fixed in the wall2 the other end1 which was pointed1 rested on the surface of a smoked glass plate placed on the other side of the crack4 ,after small earthquakes there was no indication of motion having taken place1 but after a shock on ,february #ba1 as indicated by a line upon the smoked glass plate1 it was seen that the sides of the crack had approached and receded from each other through a distance of about #a_/af inch4 ,by similar contrivances placed on cracks in a neighbouring building exactly similar results were obtained1 namely1 that during small earthquakes the two sides of the crack had retained their relative positions1 but at the time of a large shock this position had been changed4 ,in this building it was also observed that the cracks in many instances increased their length4 ,by attaching levers to the end of the pointers to multiply any motion that might take place1 no doubt the indications would be more frequent and more definite4 ,it would also be easier to note the relative distances of motion in two directions1 namely1 how far the cracks had closed and how far they had opened4 ,as to whether motion would occur or not1 much would no doubt depend upon the direction of the earthquake4 ,prevention of ,fractures4--,one conclusion which may perhaps be drawn from these observations is1 that a cracked building at the time of an earthquake shows a certain amount of flexibility4 ,whether a building which had been designed with cracks or joints between those parts which were likely to have different periods of vibration would be more stable1 so far as earthquake shakings are concerned1 than a similar building put up in an ordinary manner1 is a matter to be decided by experiment4 ,certainly some of the cracks which have been examined indicate that if they had not existed1 the strain upon the portion of the building where they occur would have been extremely great4 ,direction of ,cracks4--,in looking at the cracks produced by small earthquakes it is interesting to note the manner of their extension4 ,the basements of the buildings which have been most carefully examined are1 for a height of two or three feet1 built of large rectangular blocks of a greyish-coloured volcanic rock4 ,in these parts the cracks pass in and out between the joints of the stone1 indicating that the stones have evidently been stronger than the mortar which bound them together1 and as a consequence the latter had to give way4 ,above this basement when the cracks enter the brickwork1 they no longer exclusively confine themselves to the joints1 but run in an irregular line through all they meet with1 sometimes across the bricks and sometimes through the mortar joints4 ,in places where they have traversed the brickwork1 we can say that the mortar has been stronger than the bricks4 ,this traversing of the bricks rather than the joints is1 ,i think1 the general rule for the direction of the cracks in the brickwork of ,tokio buildings4 ,the ,pitch of ,roofs4--,from observation of the effects produced by earthquakes1 it appears to us that the houses which lost the greater number of tiles appear to be those with the steepest pitch1 and those where the tiles were simply laid upon the roof and not in any manner fastened down4 ,it would seem that destruction of this sort might to a great extent be obviated by giving the roofs a less inclination and fixing the tiles with nails4 ,it was also noticed that the greatest disturbance amongst the tiles was upon the ridges of the roofs4 ,destruction of this sort might be overcome by giving especial attention to these portions during the construction of the roof4 ,illustration3 ,,fig4 #bj4 ,,fig4 #ba4 ,relative ,position of ,openings in ,walls4--,from what has been said about the fractures in the buildings of ,tokio it will have been seen that1 with but few exceptions1 they have all taken place above openings like doorways and windows4 ,if architecture demands that openings like arches should be placed one above another in heavy walls of this kind1 as in fig4 #ag1 there will be lines of weakness running through the openings parallel to the dotted lines4 ,as arches are only intended to resist vertical thrusts1 special construction must be adopted to make them strong enough to resist horizontal pulls4 ,for instance1 a flat arch would offer more resistance to horizontal pulls than an arch put together with ordinary voussoirs1 there being in the former case more friction to prevent the component parts sliding over each other4 ,or again1 above each arch an iron girder or wooden lintel might be inserted in the brick or stone arch4 ,it was suggested to me by my colleague1 ,mr4 ,perry1 that the best form calculated to give a wall uniform strength1 would be to build it so that the openings of each tier would occupy alternate positions1 that is to say1 along lines parallel to the struts and ties of a girder4 ,in this way we should have our materials so arranged that they would offer the same resistance to horizontal as to vertical movements4 ,such a wall is shown in fig4 #bj3 the dotted lines running through the openings1 and all similar lines parallel to the former1 representing lines of weakness4 ,if we compare this with fig4 #ba1 we shall see that in the case of a horizontal movement a b or of a vertical movement c d1 we should rather expect to find fractures in a house built like fig4 #ba than in one built like fig4 #bj4 ,if1 however1 these two buildings were shaken by a shock which had an angle of emergence of about #de in the direction e f1 the effects might be reversed4 ,usually1 however1 and always in a town like ,tokio which is visited by shocks originating at a distance1 the movements are practically horizontal ones1 and1 therefore1 buildings erected on the principles illustrated by fig4 #bj should be much superior1 so far as resisting earthquakes is concerned1 to buildings constructed in the ordinary manner1 as in fig4 #ba4 ,fractures following a vertical line of weakness are shown in the accompanying drawing1 fig4 #bb1 of the ,church of ,st4 ,augustin1 at ,manilla1 shattered by the earthquakes of #ahhj4 ,the last ,house in a ,row4--,when an earthquake shock enters a line of buildings1 and proceeds in a direction coincident with that of the buildings1 we should expect that the last of these houses1 being unsupported on one side1 would be in the position of the last person in ,tyndall's row of boys4 ,from this it would seem that the end house in a row would show the greatest tendency to fly away from its neighbours4 ,if the last house stood upon the edge of a deep canal or a cliff1 there would be a layer of ground1 equal in thickness to the depth of the canal or to the height of the cliff1 as the case may be1 which would also be in a position to be thrown forward4 ,the effect which is sometimes produced upon an end building is shown in fig4 #bc1 which is taken from the photograph of a house shattered in #ahfh at ,san ,francisco4 ,illustration3 ,,fig4 #bb4--;,church of ,st4 ,augustin1 ,manilla4 ,earthquakes of ,july #ah-bj1 #ahhj4 ,the ,swing of ,buildings4--,the distance through which buildings are moved at the time of an earthquake depends partly on their construction and partly on the extent1 nature1 and duration of the movement communicated to them at their foundations4 ,by violent shocks buildings may be completely overthrown4 ,in the case of small earthquakes1 the upper portion of a house may frequently move through a much greater distance than the ground at its foundation4 ,for instance1 during the ,yokohama earthquake of ,february1 #ahhj1 when the maximum amplitude of the earth's motion was probably under of an inch1 from the slow swing of long ,japanese pictures1 from three to six feet in length1 which oscillated backwards and forwards on the wall1 it is very probable that the extent through which the upper portion of houses moved was very considerable4 ,in some instances these pictures seem to have swung as much as two feet1 and from the manner in which they swung they evidently synchronised with the natural swing of the house4 ,illustration3 ,,fig4 #bc4--,webber ,house1 ,san ,francisco4 ,oct4 #ba1 #ahfh4 ,from this it would seem that such a house must have rocked from side to side one foot out of its normal perpendicular position4 ,that the motion was great is testified by nearly all who tried to stand at the time of the shock1 it having been impossible to walk steadily across the floor of a room in an upper story4 ,the houses here referred to are either those which are purely ,japanese1 or else those which are framed of wood and built on ,european models1 a class of building which is very common in ,tokio and ,yokohama4 ,perry and ,ayrton calculated the period of a complete natural vibration of different structures4 ,for a square house whose outer and inner sections were respectively #cj and #bf feet1 and whose height was #cj feet1 the period calculated would be about #jf second4 ,at the time of the above earthquake many houses seem to have moved like inverted pendulums4 ,on the morning after the shock my neighbour1 who was living upstairs in a tall wooden house with a tile roof1 told me that he endeavoured to count the vibrations1 and was of the impression that to make a complete swing it took about #b seconds4 ,assuming now that the distance through which the top of a wooden house moved was about #a foot1 and the number of vibrations which it made per second was about #e1 then the greatest velocity of a point on the top of such a house must have been about #f feet per second4 ,mallet1 who made observations upon the vibrations of various structures1 tells us that ,salisbury spire moves to and fro in a gale more than #c inches4 ,a well-constructed brick and mortar wall1 #dj feet high and #a foot #f inches thick1 was observed to vibrate in a gale #b feet transversely before it fell4 ,an octagonal chimney with a heavy granite capping1 #afj feet high1 was observed instrumentally to vibrate at the top nearly #e inches4#bb ,at the time of a severe earthquake it does not seem impossible but that a building may be swung completely over4 ,the accompanying illustration1 fig4 #bd1 taken from a photograph1#bc apparently indicates a movement of description4 ,illustration3 ,,fig4 #bd4--,stud ,mill at ,haywards1 ,california4 ,oct4 #ba1 #ahfh4 ,principle of relative ,vibrational ,period4--,if a lath or thin pole loaded at one end with a weight fixed to the ground1 so as to stand vertically1 be shaken by an earthquake it will be caused to rock to and fro like an inverted pendulum4 ,the period of its swing will be chiefly dependent on its dimensions1 its elasticity1 and its load4 ,in a building we have to consider the vibration of a number of parts1 the periods of which1 if they were independent of each other1 would be different4 ,on account of this difference in period1 whilst one portion of a building is endeavouring to move towards the right1 another is pulling towards the left1 and1 in consequence1 either the bonds which join them or else they themselves are strained or broken4 ,this was strikingly illustrated by many of the chimneys in the houses at ,yokohama1 which by the earthquake of ,february #bj1 #ahhj1 were shorn off just above the roof4 ,the chimneys were shafts of brick1 and probably had a slower period of vibration than the roof through which they passed1 this latter vibrating with the main portion of the house1 which was framed of wood4 ,a particularly instructive example of this kind which came under my notice is roughly sketched in fig4 #be4 ,illustration3 ,,fig4 #be4 ,this is a chimney standing alone1 which1 for the sake of support1 was strapped by an iron band to an adjoining building4 ,it would seem that at the time of the shock1 the building moving one way and the chimney another1 the swing of the heavy building gave the chimney a sharp jerk and cut it off4 ,the upper portion1 being then loose upon the lower part1 rotated under the influence of the oscillations in manner similar to that in which gravestones are rotated4 ,mallet made observations similar to these in ,italy4 ,he tells us that a buttress may often not have time to transmit its stability to a wall4 ,the wall and the buttress have different periods of vibration1 and therefore they exert impulsive actions on each other4 ,effects like these were strikingly observable in many of the rural ,italian churches where the belfry tower is built into one of the quoins of the main rectangular building4 ,not only have we to consider the relative vibrations of the various parts of a building amongst themselves1 but we have to consider the relation of the natural vibrations of any one of them or the vibration of the building as a whole1 with regard to the earth1 the vibrations of which it must be remembered are not strictly periodic4 ,some of the more important results dependent upon the principle of #8relative vibrational periods' may be understood from the following experiments3-- ,illustration3 ,,fig4 #bf4 ,in fig4 #bf ,a1 ,b1 and ,c are three flat springs made out of strips of bamboo1 and loaded at the top with pieces of lead4 ,at the bottom they are fixed into a piece of board ,d ,e1 and the whole rests on a table ,f ,g4 ,the legs of this table being slightly loose1 by placing the fingers on the top of it1 a quick short backward and forward movement can be produced4 ,the weights on ,a and ,b are the same1 but they are larger than the weight on ,c4 ,consequently the periods of ,a and ,b are the same1 but different to the period of ,c4 ,the dimensions of these springs are as follows3 height1 #ah inches2 ,a and ,b each carry weights equal to #cbj grammes1 and they make one vibration per second2 ,c has a weight of #aii grammes1 and makes #jge vibrations per second4 ,first ,experiment4--,it will be found that by giving the table a gentle backward and forward movement1 the extent of which movement may be so small that it will be difficult to detect it with the eye1 either ,a and ,b may be made to oscillate violently whilst ,c remains still2 or vice vers1 ,c may be caused to oscillate whilst ,a and ,b remain still4 ,in the one case the period of shaking will have been synchronous with the natural period of ,a and ,b1 whilst in the latter it will have been synchronous with that of ,c4 ,this would seem to show us that if the natural period of vibration of a house1 or of parts of it1 at any time agree with the period of the shock1 it may be readily thrown into a state of oscillation which will be dangerous for its safety4 ,second ,experiment4--,bind ,a and ,b together with a strip of paper pasted between them4 7,the paper used was three-eighths of an inch broad and would carry a weight of nearly three pounds47 ,if the table be now shaken as before1 ,a and ,b will always have similar movements1 and tend to remain at the same distance apart1 and as a consequence the strip of paper will not be broken4 ,from this experiment it would seem that so long as the different portions of a building have almost the same periods of vibration1 there will be little or no strain upon the tie-rods or whatever contrivance may be used in connecting the different parts4 ,third ,experiment4--,join ,a and ,c1 or ,b and ,c with a strip of paper in a manner similar to the last experiment4 ,if the table be now shaken with a period approximating either to that of ,a and ,b1 or with that of ,c1 the paper will be suddenly snapped4 ,this indicates that if we have different portions of a building of such heights and thicknesses that their natural periods of vibration are different1 the strain upon the portions which connect such parts is enormous1 and it would seem1 as a consequence1 that either the vibrators themselves1 or else their connections1 must1 of a necessity1 give way4 ,this was very forcibly illustrated in the ,yokohama earthquake of ,february #ahhj by the knocking over of chimneys4 ,the particular case of the chimneys is1 however1 better illustrated by the next experiment4 ,fourth ,experiment4--,take a little block of wood three-quarters of an inch square and about one inch high1 and place it on the top of ,a1 ,b1 or ,c4 ,it will be found that1 although the spring on which it stands is caused to swing backwards and forwards through a distance of three inches1 the little block will retain its position4 ,this little block we may regard as the upper part of a chimney standing on a vibrating stack1 and we see that1 so long as this upper portion is light1 it has no tendency to fall4 ,fifth ,experiment4--,repeat the fourth experiment1 having first placed a small leaden cap on the top of the block representing the chimney4 7,the cap used only weighed a few grammes47 ,when vibration commences it will be found that the block quickly falls4 ,this would seem to indicate that chimneys with heavy tops are more likely to fall than light ones4 ,sixth ,experiment4--,bind ,a and ,b together with a strip of paper and stand the little block upon the top of either4 ,it will be found that the block will stand as in the fourth experiment4 ,seventh ,experiment4--,bind ,a and ,c1 or ,b and ,c together1 and place the block upon the top of either of them4 ,when vibration commences1 although the paper may not be broken1 the little block will quickly fall4 ,eighth ,experiment4--,take two pencils or pieces of glass tube and place them under the board ,d ,e4 ,if the table ,f ,g be now shaken in the direction ,d ,e1 it will be found that the springs will not vibrate4 ,in a similar manner if a house or portion of a house were carried on balls or rollers1 as has already been suggested1 it would seem that the house might be saved from much vibration4 ,ninth ,experiment4--,set any of the springs in violent vibration by gently shaking ,d ,e instead of the table1 and then suddenly cease the actuating motion4 ,it will be observed that at the moment of cessation the board and the springs will have a sudden and very decided motion of translation in the same direction as that in which the springs were last moving1 and although the springs were at the time swinging through a considerable arc1 all motion will suddenly cease4 ,this shows1 that if a house is in a state of vibration the strain at the foundations must be very great4 ,it would not be difficult to devise other experiments to illustrate other phenomena connected with the principle of relative vibrational periods1 but these may perhaps be sufficient to show to those who have not considered this matter its great importance in the construction of buildings4 ,perhaps the greater portion of what is here said may by many be regarded as self-evident truisms hardly worth the trouble of demonstration4 ,their importance1 however1 seems to be so great that ,i hope that their discussion has not been altogether out of place4 ,i may remark that in the rebuilding of chimneys in ,yokohama the principles here enunciated were taken advantage of by allowing the chimneys to pass freely through the roofs without coming in contact with any of the main timbers4 ,in putting up buildings to resist the effects of an earthquake1 besides the idea of making everything strong because the earthquake is strong1 there are several principles which1 like the one just enunciated1 might advantageously be followed which as yet appear to have received but little attention4 ,,chapter ,,vii4 ,,effects ,,produced ,,upon ,,buildings 7continued74 ,types of buildings used in earthquake countries--,in ,japan1 in ,italy1 in ,south ,america1 in ,caraccas--,typical houses for earthquake countries--,destruction due to the nature of underlying rocks--,the swing of mountains--,want of support on the face of hills--,earthquake shadows--,destruction due to the interference of waves--,earthquake bridges--,examples of earthquake effects--,protection of buildings--,general conclusions4 ,types of buildings used in earthquake countries4--,in ,japan there are excellent opportunities of studying various types of buildings4 ,the ,japanese types1 of course1 form the majority of the buildings4 ,the ordinary ,japanese house consists of a light framework of #d or #e inch scantling1 built together without struts or ties1 all the timbers crossing each other at right angles4 ,the spaces are filled in with wattle-work of bamboo1 and this is plastered over with mud4 ,this construction stands on the top of a row of boulders or of square stones1 driven into the surface soil to a distance varying from a few inches to a foot4 ,the whole arrangement is so light that it is not an uncommon thing to see a large house rolled along from one position to another on wooden rollers4 ,in buildings such as these after a series of small earthquake shocks1 we could hardly expect to find more fractures than in a wicker basket4 ,the larger buildings1 such as temples and pagodas1 are also built of timber4 ,these are built up of such a multitude of pieces and framed together in such an intricate manner that they also are capable of yielding in all directions4 ,the ,european buildings are1 of course1 made of brick and stone with mortar joints4 ,some of these1 as the buildings of the ,ginza in ,tokio1 are not designed for great strength4 ,on the other hand1 others have thick and massive walls and are equal in strength to those we find in ,europe4 ,the third type of buildings are those which are built in blocks2 and these blocks being bound together with iron rods traversing the walls in various directions are especially designed to withstand earthquakes4 ,a system somewhat similar to this has been patented in ,america1 and examples of these so-called earthquake-proof buildings are to be found in ,san ,francisco4 ,speaking of ,japanese buildings1 ,mr4 ,r4 ,h4 ,brunton1 who has devoted especial attention to them says that1#bd #8to imagine that slight buildings1 such as are seen here 7i4e4 in ,japan71 are the best calculated to withstand an earthquake shock is an error of the most palpable kind4' ,after describing the construction of a ,japanese house in pretty much the same terms as we have used1 he says #8that with its unnecessarily heavy roof and weak framework it is a structure of all others the worst adapted to withstand a heavy shock4' ,he tells us1 further1 that these views are sustained by the truest principles of mechanics4 ,in order to render buildings to some extent proof against earthquakes1 some of the heavy roofs in ,tokio have been so constructed that they are capable of sliding on the walls4 ,mr4 ,brunton mentions a design for a house1 the upper part of which is to rest on balls1 which roll on inverted cups fixed on the lower part of the building1 which is to be firmly embedded in the earth4 ,a similar design was1 at the suggestion of ,mallet1 used to support the tables carrying the apparatus of some of the lighthouses erected in ,japan by ,mr4 ,brunton4 ,the very existence of these designs seems to indicate that the ordinary ,european house1 however solidly and strongly it may be built1 is not sufficient to meet the conditions imposed upon it4 ,what is required1 is something that will give way--an approximation to the timber frame of a ,japanese house1 so strongly condemned by ,mr4 ,brunton and others4 ,the crucial test of the value of the ,japanese structure1 as compared with the modern buildings of brick and stone1 is undoubtedly to be found by an appeal to the buildings themselves4 ,so far as my own experience has gone1 ,i must say that ,i have never seen any signs in the ,japanese timber buildings which could be attributed to the effects of earthquakes1 and ,his ,excellency ,yamao ,yozo1 ,vice ,minister of ,public ,works1 who has made the study of the buildings of ,japan a speciality1 told me that none of the temples and palaces1 although many of them are several centuries old1 and although they have been shaken by small earthquakes and also by many severe ones1 show any signs of having suffered4 ,the greatest damage wrought by large earthquakes appears to have resulted from the influx of large waves or from fires4 ,in every case where an earthquake has been accompanied by great destruction1 by consulting the books describing the same1 it can be seen1 from the illustrations in these books portraying conflagrations1 that this destruction was chiefly due to fire4 ,when we remember that nearly all ,japanese houses are constructed of materials that are readily inflammable1 it is not hard to imagine how destruction of this kind has come about4 ,to a ,japanese1 living as he does in a house which has been compared to a tinder-box1 fire is one of his greatest enemies1 and in a city like ,tokio it is not at all uncommon to see during the winter months many fires which sweep away from #ajj to #ejj houses4 ,in one winter ,i was a spectator of three fires1 each of which was said to have destroyed upwards of #aj1jjj houses4 ,although it would appear that the smaller earthquakes of ,japan produce no visible effect upon the native buildings1 it is nevertheless probable that small effects may have been produced1 the observation of which is rendered difficult by the nature of the structure4 ,if we look at buildings of foreign construction1 by which are meant buildings of brick and stone1 the picture before us is quite different1 and everywhere the effects of earthquakes are palpable even to the most casual observer4 ,of these effects numerous examples have already been given4 ,not only are these buildings damaged by the cracking of walls and the overturning of chimneys1 but they also appear to be affected internally4 ,for instance1 in the timbers of the roof of the museum attached to the ,imperial ,college of ,engineering in ,tokio1 there are a number of diagonal faces acting as struts or ties intended to prevent more or less horizontal movements taking place4 ,those which are rigidly joined together with bolts and angle irons have apparently suffered from their rigidity1 being twisted and bent into various forms4 ,the buildings in ,tokio1 which are strongly put together1 being especially designed to withstand earthquakes1 appear to have suffered but little4 ,i know only one example which at the time of the severe shock of #ahhj had several of its chimneys damaged4 ,the ordinary houses in ,italy1 though built of stone and mortar1 are but poorly put together1 and1 as ,mallet has remarked1 are in no way adapted to withstand the frightful shakings to which they are subjected from time to time4 ,in the large towns1 like ,naples1 ,rome1 and ,florence1 where happily earthquakes are of rare occurrence1 although the building may be better than that found in the country1 the height of the houses and the narrowness of the streets are sufficient to create a shudder1 when we think of the possibility of the occurrence of a moderately severe earthquake4 ,in ,south ,america1 although many buildings are built with brick and stone1 the ordinary houses1 and even the larger edifices1 are specially built to withstand earthquakes4 ,in ,mr4 ,james ,douglas's account of a #8,journey ,along the ,west ,coast of ,south ,america1' we read the following#be3 #8,the characteristic building material of ,guayaquil is bamboo1 which grows to many inches in thickness1 and which1 when cut partially through longitudinally at distances of an inch or so1 and once quite through1 can be opened out into fine elastic boards of serviceable width4 ,houses1 and even churches1 of a certain primitive beauty are built of such reeds1 so bound together with cords that few nails enter into the construction1 and which1 therefore1 yield so readily to the contortions of the earth during an earthquake as to be comparatively safe4' ,here we have a house1 which1 so far as earthquakes are concerned1 is an exaggerated example of the principles which are followed in the construction of an ordinary ,japanese dwelling4 ,another plan adopted in ,south ,america can be gathered from the same author's writings upon ,lima1 about which he says1 #8,to build high houses would be to erect structures for the first earthquake to make sport of1 and1 therefore1 in order to obtain space1 safety1 and comfort1 the houses of the wealthy surround court after court1 filled with flowers1 and cooled with fountains1 connected one with another with wide passages which give a vista from garden to garden4' ,history would indicate that houses of this type have been arrived at as the results of experience1 for it is said that when the inhabitants of ,south ,america first saw the ,spaniards building tall houses1 they told them they were building their own sepulchres4#bf ,in ,jamaica1 we find that even as early as #afib experience had taught the ,spaniards to construct low houses1 which withstood shakings better than the tall ones4#bg ,in ,caraccas1 which has been called the city of earthquakes1 it is said that the earthquakes cause an average yearly damage amounting to the equivalent of a per capita tax of four dollars4 ,to reduce this impost to a minimum much attention is paid to construction4 #8,projecting basement corners 7giving the house a slightly pyramidal appearance7 have been found better than absolutely perpendicular walls2 mortised corner-stones and roof beams have saved many lives when the central walls have split from top to bottom2 vaults and key-stone arches1 no matter how massive1 are more perilous than common wooden lintels1 and there are not many isolated buildings in the city4 ,in many streets broad iron girders1 riveted to the wall1 about a foot above the house door1 run from house to house along the front of an entire square4 ,turret-like brick chimneys1 with iron top ornaments1 would expose the architect to the vengeance of an excited mob2 the roofs are flat1 or flat terraced2 the chimney flues terminate near the eaves in a perforated lid4'#bh ,typical houses for earthquake countries4--,from what has now been said about the different buildings found in earthquake countries1 it will be seen that if we wish to put up a building able to withstand a severe shaking1 we have before us structures of two types4 ,one of these types may be compared with a steel box1 which1 even were it rolled down a high mountain1 would suffer but little damage2 and the other1 with a wicker basket1 which would equally withstand so severe a test4 ,both of these types may be1 to some extent1 protected by placing them upon a loose foundation1 so that but little momentum enters them at their base4 ,one suggestion is to place a building upon iron balls4 ,another method would be to place them upon two sets of rollers1 one set resting upon the other set at right angles4 ,the ,japanese1 we have seen1 place their houses on round stones4 ,the solid type of building is expensive1 and can only be approached partially1 whilst the latter is cheap1 and can be approached closely4 ,in the case of a solid building it would be a more difficult matter to support it upon a movable foundation than in the case of a light framework4 ,such a building is usually firmly fixed on the ground1 and consequently at the time of an earthquake1 as has already been shown by experiment1 must be subjected to stresses which are very great4 ,in consequence also of the greater weight of the solid structure1 more momentum will enter it at its base than in the case of the light structure4 ,also1 we must remember that the rigidity favours the transmission of momentum1 and with rigid walls we are likely to have ornaments1 coping-stones1 and the comparatively freer portions forming the upper part of a building displaced2 whilst1 with flexible walls absorbing momentum in the friction of their various parts1 such disturbances would not be so likely4 ,mr4 ,t4 ,ronaldson1 referring to this1 says1 that in #ahfh1 at ,san ,francisco1 the ornamental stone work in stone and cement buildings was thrown from its position1 whilst similar ornaments in neighbouring brick buildings stood4 ,to reduce the top weight of a building1 hollow bricks might be employed4 ,to render a building more homogeneous and elastic1 the thickness of bricks might be reduced4 ,inasmuch as the elasticity of brick and timber are so different1 the two ought to be employed separately4 ,for internal decorations plaster mouldings might be replaced by papier mch and carton-pierre1 the elastic yielding of which is comparatively great4#bi ,houses1 whether of brick and stone1 or of timber1 ought to be broad and low1 and the streets three or four times as wide as the houses4 ,the flatter the roofs the better4 ,one of the safest houses for an earthquake country would probably be a one-storied strongly framed timber house1 with a light flattish roof made of shingles or sheet-iron1 the whole resting on a quantity of small cast-iron balls carried on flat plates bedded in the foundations4 ,the chimneys might be made of sheet-iron carried through holes free of the roof4 ,the ornamentation ought to be of light materials4 ,at the time of severe earthquakes many persons seek refuge from their houses by leaving them4 ,in this case accidents frequently happen from the falling of bricks and tiles4 ,others rush to the doorways and stand beneath the lintels4 ,persons with whom the author has conversed have suggested that strongly constructed tables and bedsteads in their rooms would give protection4 ,to see persons darting beneath tables and bedsteads would undoubtedly give rise to humiliating and ludicrous exhibitions4 ,this latter idea is not without a value1 and most certainly1 if applied in houses of the type described1 would be valuable4 ,the great danger of fire may partially be obviated by3 the use of #8earthquake lamps1' which are so constructed that before they overturn they are extinguished4 ,it is said that in ,south ,america some of the inhabitants are ready at any moment to seek refuge in the streets1 and they have coats prepared1 stocked with provisions and2 other necessaries1 which1 if occasion demands1 will enable them to spend the night in the open air4 ,these coats1 called #8earthquake coats1' might also1 with properly constructed houses1 be rendered unnecessary4 ,destruction due to the nature of the underlying rocks4--,that the nature of the ground on which a building stands is intimately related with the severity of the blow it receives is a fact which has often been demonstrated4 ,one cause of destruction is due to placing a building on foundations which are capable of receiving the full effects of a shock1 and transmitting it to the buildings standing on them4 ,for instance1 the reason why a soft bed might possibly make a good foundation1 is1 as has been pointed out by ,messrs4 ,perry and ,ayrton1 because the time of transmission of momentum is increased2 in fact1 the soft bed is very like a piece of wood interposed between a nail and the blows of a hammer--it lengthens the duration of impact4 ,for this reason we are told that a quaking bog will make a good foundation4 ,when a shock enters loose materials its waves will be more crowded1 and it is possible that a line of buildings may rest on more than one wave during a shock4 ,there are many examples on record of the stability of buildings which rested on beds of particular material at the time of destructive earthquakes4 ,as the observations which have been made by various writers on this subject appear to point in a contrary direction1 ,i give the following examples3-- ,in the great ,jamaica earthquake of #afib1 the portions of ,port ,royal which remained standing were situated on a compact limestone foundation2 whilst those on sand and gravel were destroyed 7#8,geological ,observer1' p4 #dbf74 ,again1 on p4 #adh of the same work1 we read1 #8,according to the observations made at ,lisbon1 in #agcg1 by ,mr4 ,sharpe1 the destroying effects of this earthquake were confined to the tertiary strata1 and were most violent on the blue clay1 on which the lower part of the city is constructed4 ,not a building on the secondary limestone or on the basalt was injured4' ,in the great earthquakes of ,messina1 those portions of the town situated on alluvium1 near the sea1 were destroyed1 whilst the high parts of the town1 on granite1 did not suffer so much4 ,similar observations were made in ,calabria1 when districts consisting of gravel1 sand1 and clay became1 by the shaking1 almost unrecognisable1 whilst the surrounding hills of slate and granite were but little altered4 ,at ,san ,francisco1 in #ahfh1 the chief destruction was in the alluvium and made ground4 ,at ,talcahuano1 in #ahce1 the only houses which escaped were the buildings standing on rocky ground2 all those resting on sandy soil were destroyed4 ,from the results of observations like these1 it would seem the harder rocks form better foundations than the softer ones4 ,the explanation of this1 in many cases1 appears to lie in the fact that the soft strata were in a state of unstable equilibrium1 and by shaking1 they were caused to settle4 ,observations like the following1 however1 point out another reason why soft strata may sometimes afford a bad foundation4 #8,humboldt observed that the ,cordilleras1 composed of gneiss and mica-slate1 and the country immediately at their foot1 were more shaken than the plains4'#cj #8,some writers have asserted that the wave-like movements 7of the ,calabrian earthquake in #aghc7 which were propagated through recent strata from west to east1 became very violent when they reached the point of junction with the granite1 as if a reaction was produced when the undulatory movement of the soft strata was suddenly arrested by the more solid rocks4' ,dolomieu when speaking of this earthquake says1 the usual effect #8was to disconnect from the sides of the ,apennines all those masses 7of sand and clay7 which either had not sufficient bases for their bulk1 or which were supported only by lateral adherence4' ,these intensified actions taking place at and near to lines of junction between dissimilar strata is probably due to the phenomena of reflection and refraction4 ,when referring to the question as to whether buildings situated on loose materials suffered more or less than those on solid rocks1 ,mallet1 in his description of the ,neapolitan earthquake of #aheg1 remarks3 #8,we have in this earthquake1 towns such as ,saponara and ,viggiano1 situated upon solid limestone1 totally prostrated2 and we have others such as ,montemarro1 to a great extent based upon loose clays1 totally levelled4 ,we have examples of almost complete immunity in places on plains of deep clay as that of ,viscolione1 and in places on solid limestone1 like ,castelluccio1 or perched on mountain tops like ,petina4'#ca ,after reading the above1 we see that the probable reason why1 in several cases1 beds of soft materials have not made good foundations1 consists in the fact that they have either been of small extent or else have been observed only in the neighbourhood of lines which divided them from other formations1 which lines are always those of great disturbances4 ,at the end of his description of the ,neapolitan earthquake of #aheg1 ,mallet says that more buildings were destroyed on the rock than on the loose clay4 ,this1 however1 he remarks1 is hardly a fact from which we can draw any valuable deductions1 because it so happened that more buildings were constructed on the hills than on the loose ground4#a ,professor ,d4 ,s4 ,martin1 writing on the earthquake of ,new ,england in #ahgd1 remarks that in ,long ,island the shock was felt where there was gneiss between the drift4 ,around portions to the east the observations were few and far between4 ,he also remarks that generally the shocks were felt more strongly and frequently on rocky than on soft ground4#cb ,from these examples1 it would appear that the hard ground1 which usually means the hills1 forms a better foundation than the softer ground1 which is usually to be found in the valleys and plains4 ,other examples1 however1 point to a different conclusion4 ,for instance1 a civil engineer1 writing about the ,new ,zealand earthquake of #ahee1 when all the brick buildings in ,wellington were overthrown1 says that #8it was most violent on the sides of the hills at those places1 and least so in the centre of the alluvial plains4'#cc ,in this example it must be noticed that the soft alluvium here referred to was of large extent1 and not loose material resting on the flanks of rocks1 from which it was likely to be shaken down1 as in most of the previous examples4 ,the results of my own observations on this subject point as much in one direction as in the other4 ,in ,tokio1 from instrumental observations upon the slopes and tops of hills1 the disturbance appears to be very much less than it is in the plains4 ,thus1 at my house1 situated on the slope of a hill about #ajj feet in height1 for the earthquake of ,march #aa1 #ahhb1 ,i obtained a maximum amplitude of motion of from three to four millimtres only1 whilst ,professor ,ewing1 with a similar instrument1 situated on the level ground at about a mile distant1 found a motion of fully seven millimtres4 ,this calculation has been confirmed by observations on other earthquakes4 ,thus1 for instance1 in the destructive earthquake of #ahee1 when a large portion of ,tokio was devastated1 it was a fact1 remarked by many1 that the disturbance was most severe on the low ground and in the valleys1 whilst on the hills the shock had been comparatively weak4 ,as another illustration1 ,i may mention that within three-quarters of a mile from my house in ,tokio there is a prince's residence which has so great a reputation for the severity of the shakings it receives that its marketable value has been considerably depreciated1 and it is now untenanted4 ,in ,hakodadi1 which is a town situated very similarly to ,gibraltar1 partly built on the slope of a high rocky mountain and partly on a level plain1 from which the mountain rises1 the rule is similar to that for ,tokio1 namely1 that the low1 flat ground is shaken more severely than the high ground4 ,at ,yokohama1 sixteen miles south-west from ,tokio1 the rule is reversed1 as was very clearly demonstrated by the earthquake of ,february #ahhj1 when almost every house upon the high ground lost its chimney1 whilst on the low ground there was scarcely any damage done2 the only places on the low ground which suffered were those near to the base of the hills4 ,the evidence as to the relative value of hard ground as compared with soft ground1 for the foundation of a building1 is very conflicting4 ,sometimes the hard ground has proved the better foundation and sometimes the softer1 and the superiority of one over the other depends1 no doubt1 upon a variety of local circumstances4 ,these latter observations open up the inquiry as to the extent to which the intensity of an earthquake may be modified by the topography of the disturbed area4 ,the swing of mountains4--,if an earthquake wave is passing through ground the surface of which is level1 so long as this ground is homogeneous1 as the wave travels further and further we should expect its energy to become less and less1 until1 finally1 it would insensibly die out4 ,if1 however1 we have standing upon this plain a mountain1 judging from ,mallet's remarks1 this mountain would be set in a state of vibration much in the same way as a house is set in vibration1 and it would tend to oscillate backward and forward with a period of vibration dependent upon the nature of its materials1 size1 and form4 ,the upper portion of this mountain would1 in consequence1 swing through a greater arc than the lower portion1 and buildings situated on the top of it would swing to and fro through a greater arc than those which were situated near its foot4 ,this explanation why buildings situated on the top of a mountain should suffer more than those situated on a plain1 is one which was offered by ,mallet when writing of the ,neapolitan earthquake4 ,he tells us that towns on hills are #8rocked as on the top of masts1' and if we accept this explanation it would1 in fact1 be one reason why the houses situated on the ,bluff at ,yokohama suffered more than those situated in the settlement4 ,this explanation is given on account of the great authority it claims as a consequence of its source4 ,it is not clear how the statement can be supported1 as different portions of the mountain receive momentum in opposite directions at the same time4 ,want of support on the faces of hills4--,when a wave of elastic compression is propagated through a medium1 we see that the energy of motion is being continually transmitted from particle to particle of that medium4 ,a particle1 in moving forwards1 meets with an elastic resistance of the particles towards which it moves1 but1 overcoming these resistances1 it causes these latter particles to move1 and in turn to transmit the energy to others further on4 ,so long as the medium in which this transfer of energy is continuous1 each particle has a limit to its extent of motion1 dependent on the nature of the medium4 ,when1 however1 the medium1 which we will suppose to be the earth1 is not continuous1 but suddenly terminates with a cliff or scarp1 the particles adjacent to this cliff or scarp1 having no resistance offered to their forward motion1 are shot forward1 and1 consequently1 the ground here is subjected to more extensive vibrations than at those places where it was continuous4 ,this may be illustrated by a row of marbles lying in a horizontal groove2 a single marble rolled against one end of this row will give a concussion which will run through the chain1 like the bumping of an engine against a row of railway cars1 and as a result1 the marble at the opposite end of the row1 being without support1 will fly off4 ,tyndall illustrates the same thing with his well known row of boys1 each one standing with his arms stretched out and his hands resting upon the shoulders of the boy before him4 ,a push being given to the boy at the back1 the effect is to transmit a push to the first boy1 who1 being unsupported1 flies forward4 ,in the case of some earthquakes1 most disastrous results have occurred which seem only to admit of an explanation such as this4 ,a remarkable instance of this kind occurred when the great earthquake of #aheg #8swept along the ,alps from ,geneva to the east-north-east1 and its crest reached the edge of the deep glen between ,zermatt and ,visp4 ,then the upper part of the wave-movement1 a thousand or two thousand feet in depth from the surface1 came to an end2 the forward pulsation acted like the breaker of the sea1 and heavy falls of rock encumbered the western side of the valley4' ,earthquake shadows4--,if a mountain stands upon a plain through which an elastic wave is passing1 which is almost horizontal1 the mountain is1 so to speak1 in the shadow of such a wave4 ,if we only consider the normal motion of this wave1 we see that the only motion which the mountain can obtain will be a wave of elastic distortion produced by a shearing force along the plain of the base4 ,should1 however1 the wave approach the mountain from below1 and emerge into it at a certain angle1 only the portion of the mountain on the side from which the wave advanced could remain in shadow1 whilst the portion on the opposite side would be thrown into a state of compression and extension4 ,portions in shadow1 however1 would be subject to waves of elastic distortion4 ,in a manner similar to this we may imagine that certain portions of the bluff1 so far as the advancing wave was concerned1 were in shadow1 and thus saved from the immediate influence of the direct shock4 ,a hypothetical case of such a shadow is shown in the accompanying section1 illustrating the contour of the ground at ,yokohama4 ,the situation which might be in the shadow of one shock1 however1 it is quite possible might not be in that of another4 ,we must also remember that a place in shadow for a direct shock might be affected by reflected waves1 and also by the transverse vibrations of the direct shock4 ,these effects are over and above the effects produced by the waves of elastic distortion just referred to4 ,it might be asked whether whole countries1 like ,england1 which are but seldom shaken1 are in shadow4 ,illustration3 ,,fig4 #bg4--;,hypothetical section at ,yokohama4 ,destruction due to the interference of waves4--,referring to the section of the ground at ,yokohama 7,fig4 #bg71 it will be seen that both the settlement and the bluff stand upon beds of gravel capping horizontal beds of grey tuff4 ,the gravel of that portion of the settlement on the seaboard originally formed the line of a shingle beach4 ,that portion of the settlement back from the sea stands upon ground which was originally marshy4 ,in the central portions of the settlement this bed of gravel is very thick1 perhaps #ajj feet or so1 but as you near the edge of the bluff it probably becomes thinner1 until it finally dies out upon the flanks of the scarps4 ,on the top of the bluff1 the beds of gravel will1 in every probability1 be generally thinner than they are upon the lower level4 ,the beds of tuff1 which is a soft grey-coloured clay-like rock1 produced by the solidification of volcanic mud1 appear1 when walking on the seaboard1 to be horizontally stratified4 ,if there is a dip inland1 it is in all probability very slight4 ,here and there the beds slightly faulted4 ,taken as a whole we may consider these beds as being tolerably homogeneous1 and an earthquake in passing through them would meet with but little reflection or refraction4 ,at the junction of these beds with the overlying gravels1 both reflection and refraction would comparatively be very great4 ,on entering the gravel1 as the wave would be passing into a less elastic medium1 the direction of the wave would be bent towards the perpendicular to the line of junction1 and the angle of emergence at the surface would consequently be augmented4 ,at the surface certain reflection would also take place1 but the chief reflections would be those at the junction of the tuff and the alluvium4 ,under the settlement it is probable that all the reflections which took place would be single4 ,thus wave fronts like ,a#a advancing in a direction parallel to the line a#a2 would be reflected in a direction a#b and give rise to a series of reflected waves ,a#b4 ,these are shown by thicker lines4 ,similarly all the neighbouring waves to the right and left of ,a#a would give rise to a series of reflected waves4 ,if the lines drawn representing wave fronts are districts of compression1 then1 where two of the lines cross each other1 there would be double energy in producing compression4 ,similarly1 districts of rarefaction might accord1 and1 again1 compression of one wave might meet with the rarefaction of another and a neutralisation of effect take place4 ,a diagram illustrating concurrence and interference of this description is given in ,le ,conte's #8,elements of ,geology1' p4 #aae4 ,the interference which has been spoken of1 however1 is not the greatest which would occur4 ,the greatest would probably be beneath the bluff and the scarps which run down to join the level ground below4 ,this would be the case because it is a probability that there might not only be cases of interference of single reflected waves1 but also of waves which had been not only twice but perhaps thrice reflected4 ,for example1 a wave like ,b#a 7which is parallel to ,a#a of the first supposition71 advancing in a direction parallel to b#a might be reflected along the line b#b giving rise to waves like ,b#b1 which in turn might be reflected along b#c giving rise to waves like ,b#c4 ,the number of districts where there would be concurrence and interference would1 in consequence of the number of times waves might be reflected1 be augmented4 ,here the violence of the shock would1 at certain points1 be considerably increased1 but as a general result energy must be lost1 so that even if some of the reflected waves found their way into the portion we have regarded as being in shadow1 their intensity would not be so great as if they had entered it directly4 ,the shaking down of loose materials from the sides of hills may be partially explained on the assumption of an increased disturbance due to interference4 ,earthquake bridges4--,in certain parts of ,south ,america there appear to exist tracts of ground which are practically exempt from earthquake shocks1 whilst the whole country around is sometimes violently shaken4 ,it would seem as if the shock passes beneath such a district as water passes beneath a bridge1 and for this reason these districts have been christened #8bridges4' ,this phenomenon appears to depend upon the nature of the underlying soil4 ,when an elastic wave passes from one bed of rock to another of a different character1 a certain portion of the wave is reflected1 while the remainder of it is transmitted and refracted1 and #8bridges' we may conceive of as occurring where the phenomenon of total reflection occurs4 ,in the instances given of soft materials having proved good foundations1 it was assumed that they had chiefly acted as absorbers of momentum4 ,they have also acted as reflecting surfaces1 and where no effects have been felt by those residing on them1 this may have been the result of total reflection1 and the soft beds thus have played the part of bridges4 ,fuchs gives an example taken from the records of the ,syrian earthquake of #ahcg1 where not only neighbouring villages suffered differently1 but even neighbouring houses4 ,in one case a house was entirely destroyed1 whilst in the next house nothing was felt4 ,in ,japan1 at a place called ,choshi1 about #ee miles east of the capital1 earthquakes are but seldom felt1 although the surrounding districts may be severely shaken4 ,from descriptions of this place it would appear that there is a large basaltic boss rising in the midst of alluvial strata4 ,the immunity from earthquakes in this district has probably given rise to the myth of the ,kanam rock1 which is a stone supposed to rest upon the head of a monstrous catfish 7,namadzu71 which by its writhings causes the shakings so often felt in this part of the world4#cd ,prof4 ,d4 ,s4 ,martin1 writing on the earthquake of ,new ,england in #ahgd1 says that it was felt at four points2 it was felt in the heart of ,brooklyn all within a circle of half a mile across2 #8and this fact would suggest that a ridge of rock perhaps approaches the surface at that point1 though none is known to appear4'#ce ,the subject of special districts1 which are more or less protected from severe shakings1 will be again referred to1 and it will be seen that after a seismic survey has been made even of a country like ,japan1 where there are on the average at least two earthquakes per day1 it is possible to choose a place to build in as free from earthquakes as ,great ,britain4 ,general examples of earthquake effects4--,the following examples of earthquake effects are drawn from ,mallet's account of the ,neapolitan earthquake of #aheg4 ,at a town called ,polla there was great destruction4 ,judging from the fissures in the parts that remained standing it seemed that the emergence of the shock had been more vertical in the upper part of the town than in the lower1 proving that whatever had been the angle below1 the hill had itself vibrated1 which1 being horizontal1 had modified the angle of the fissures4 ,diano suffered but little1 partly because it was well built1 and partly on account of its situation1 which was such that before the shock reached it the disturbance had to pass from beds of clay into nearly vertically placed beds of limestone4 ,also a great portion of the shock was cut off by the ,vallone del ,raccio to the north and north-west of the town4 ,here the effects of the partial extinction of the wave on the #8free outlaying stratum' were visible in the masses of projected rock4 ,castellucio did not suffer because its well buttressed knoll was end on to the direction of shock1 and on account of a barrier of vertical breccia beds protecting it upon the east4 ,pertosa stands on a mound4 ,the destruction was least in the southern part of the town4 ,from the relation of the beds of breccia on which the town stands1 and the direction of the wave path1 it is evident that the southern part of the town received the force of the shock through a greater thickness of the breccia beds than the other parts did4 ,petina1 standing on a level limestone spur jutting out from a mountain slope1 suffered nothing1 whilst ,anletta five miles to the south-west1 and ,pertosa six miles distant1 were in great part prostrated4 7#a7 ,the terrace did not vibrate1 and 7#b7 between ,petina and ,anletta there is almost #f1jjj feet of piled up limestone1 so that any shock emergent at a steep angle had to pass up transversely through these beds4 ,protection of buildings4--,in addition to giving proper construction to our buildings1 choosing proper foundations and positions for them1 something might possibly be done to ward off the destructive effects of an earthquake4 ,we read that the ,temple of ,diana at ,ephesus was built on the edge of a marsh1 in order to ward off the effect of earthquakes4 ,pliny tells us that the ,capitol of ,rome was saved by the ,catacombs1 and ,elise ,reclus#cf says that the ,romans and ,hellenes found out that caverns1 wells1 and quarries retarded the disturbance of the earth1 and protected edifices in their neighbourhood4 ,the tower of ,capua was saved by its numerous wells4 ,vivenzis asserts that in building the ,capitol the ,romans sunk wells to weaken the effects of terrestrial oscillations4 ,humboldt relates the same of the inhabitants of ,san ,domingo4 ,quito is said to receive protection from the numerous caons in the neighbourhood1 whilst ,lactacunga1 fifteen miles distant1 has often been destroyed4 ,similarly1 it is extremely probable that many portions of ,tokio have from time to time been protected more or less from the severe shocks of earthquakes by the numerous moats and deep canals which intersect it4 ,although we are not prepared to say how far artificial openings of this description are effectual in warding off the shocks of earthquakes1 from theoretical considerations1 and from the fact that their use has been discovered by persons who1 in all probability1 were without the means of making theoretical deductions1 the suggestions which they offer are worthy of attention4 ,general conclusions4--,the following are a few of the more important results which may be drawn from the preceding chapter3-- #a4 ,in choosing a site for a house find out by the experience of others or experimental investigation the localities which are least disturbed4 ,in some cases this will be upon the hills1 in others in the valleys and on the plains4 #b4 ,a wide open plain is less likely to be disturbed than a position on a hill4 #c4 ,avoid loose materials resting on harder strata4 #d4 ,if the shakings are definite in direction1 place the blank walls parallel to such directions1 and the walls with many openings in them at right angles to such directions4 #e4 ,avoid the edges of scarps or bluffs1 both above and below4 #f4 ,so arrange the openings in a wall1 that for horizontal stresses the wall shall be of equal strength for all sections at right angles4 #g4 ,place lintels over flat arches of brick or stone4 #h4 ,to withstand destructive shocks either rigidly follow one or other of the two systems of constructing an earthquake-proof building4 ,the light building on loose foundations is the cheaper and probably the better4 #i4 ,let all portions of a building have their natural periods of vibration nearly equal4 #aj4 ,if it is a necessity that one portion of a building should have a very different period of vibration to the remainder1 as for instance a brick chimney in a wooden house1 it would seem advisable either to let these two portions be sufficiently free to have an independent motion1 or else they must be bound together with great strength4 #aa4 ,avoid heavy topped roofs and chimneys4 ,if the foundations were free the roof might be heavy4 #ab4 ,in brick or stone work use good cement4 #ac4 ,let archways curve into their abutments4 #ad4 ,let roofs have a low pitch1 and the tiles1 especially those upon the ridges1 be well secured4 ,,chapter ,,viii4 ,,effects ,,of ,,earthquakes ,,on ,,land1 #a4 ,cracks and fissures--,materials discharged from fissures--,explanation of fissure phenomena4 #b4 ,disturbances in lakes1 rivers1 springs1 wells1 fumaroles1 c4--,explanation of these latter phenomena4 #c4 ,permanent displacement of ground--,on coast lines--,level tracts--,among mountains--,explanation of these movements4 ,cracks and fissures formed in the ground4--,almost all large earthquakes have produced cracks in the ground4 ,the cracks which were found in the ground at ,yokohama 7,february #bb1 #ahhj7 were about two or three inches wide1 and from twenty to forty yards in length4 ,they could be best seen as lines along a road running near the upper edge of some cliffs which overlook the sea at that place4 ,the reason that cracks should have occurred in such a position rather than in others was probably owing to the greater motion at such a place1 due to the face of the cliff being unsupported1 and there being no resistance opposed to its forward motion4 ,it often happens that earthquake cracks are many feet in width4 ,at the ,calabrian earthquake of #aghc1 one or two of the crevasses which were formed were more than #ajj feet in width and #bjj feet in depth4 ,their lengths varied from half a mile to a mile4#cg ,besides these large cracks1 many smaller ones of one or two feet in breadth and of great length were formed4 ,in the large fissures many houses were engulfed4 ,subsequent excavations showed that by the closing of the fissures these had been jammed together to form one compact mass4 ,these cracks are usually more or less parallel1 and at the same time parallel to some topographical feature1 like a range of mountains4 ,for example1 the cracks which were formed by the ,mississippi earthquake of #ahab ran from north-east to south-west parallel to the ,alleghanies4 ,by succeeding shocks these crevasses are sometimes closed and sometimes opened still wider4 ,their permanency will also depend upon the nature of the materials in which they are made4 ,during an earthquake large cracks may suddenly open and shut4 ,during the convulsions of #afib which destroyed ,port ,royal1 it is said that many of the fissures which were formed1 opened and shut4 ,in some of these1 people were entirely swallowed up and buried4 ,in others they were trapped by the middle1 and even by the neck1 where if not killed instantaneously they perished slowly4 ,subsequently their projecting parts formed food for dogs4#ch ,the earthquake which1 ,july #ah1 #ahhj1 shook the ,philippines caused many fissures to be found1 which in some places were so numerous that the ground was broken up into steps4 ,near to the village of ,san ,antonio the soil was so disturbed that the surface of a field of sugar-canes was so altered that in some cases the top of one row of full grown plants was on a level with the roots of the next4 ,into one such fissure a boat disappeared1 and into another1 a child4 ,subsequently the child was excavated1 and its body1 which was found a short distance below the surface1 was completely crushed4#ci ,at the time of the ,riobamba earthquake1 not only were men engulfed1 but animals1 like mules1 also sank into the fissures which were formed4 ,the fissures which were formed at the time of the ,owen's ,valley earthquake in #ahgb extended for miles nearly parallel to the neighbouring ,sierras4 ,in some places the ground between the fissures sank twenty or thirty feet1 and at one place about three miles east of ,independence1 a portion of the road was carried eighteen feet to the south by a fissure4#dj ,speaking generally1 it may be said that all large earthquakes are accompanied by the formation of fissures4 ,the ,japanese have a saying that at the time of a large earthquake persons must run to a bamboo grove4 ,the object of this is to escape the danger of being engulfed in fissures1 the ground beneath a bamboo grove being so netted together with fine roots that it is almost impossible for it to be rent open4 ,materials discharged from fissures4--,together with the opening of cracks in the earth it often has happened that water1 mud1 vapours1 gases1 and other materials1 have been ejected4 ,at the time of the ,mississippi earthquake water1 mixed with sand and mud1 was thrown out with such violence that it spurted above the tops of the highest trees4 ,in ,italy such phenomena have often been repeated4 ,from the fissures which were formed in #afib at the time of the earthquakes in ,sicily1 water issued which in some instances was salt4#da ,by the ,cachar earthquake 7,january #aj1 #ahfi7 numerous fissures were formed parallel to the banks of a river1 from this water and mud were ejected4 ,dr4 ,oldham1 who describes this earthquake1 says that the first shot of dry mud or sand was mistaken for smoke or steam4 ,the water was foul1 and hotter than surface water at the time1 but only slightly so2 and the sulphurous smell was nothing more than you would perceive in stirring up the mud at the bottom of any stagnant pool which had lain undisturbed for some time4#db ,in #agee1 when ,tauris was destroyed1 boiling water issued from the cracks which were formed4 ,similar phenomena were witnessed at a place eight miles from ,la ,banca in ,mexico1 in the year #ahbj4 ,part of this hot water was pure and part was muddy4 ,sometimes the water which has been ejected has been so muddy that the mud has been collected to form small hills4 ,this was the case at the time of the ,riobamba earthquake4 ,the mud in this case consisted partly of coal1 fragments of augite1 and shells of infusoria4 ,at the time of the ,jamaica earthquake men who had fallen into crevices were in some cases thrown out again by issuing water4 ,sometimes1 as has already been mentioned1 vapour1 gases1 and even flames issue from fissures4 ,vapour of sulphur appears to be exceedingly common4 ,kluge says that many fish were killed in consequence of the sulphurous vapours which rose in the sea near to the coast of ,new ,zealand in #ahee4 ,on ,december #ad1 #agig1 an insupportable smell of sulphur was observed to have accompanied the earthquake which at that time shook ,cumana1 which was greatest when the disturbance was greatest4 ,sulphurous fumes which were combustible were belched out of the earth at the time of the ,jamaica earthquake in #afib4 ,the smell which accompanied this was so powerful that it caused a general sickness which swept away about #c1jjj persons4#dc ,from the fissures formed at ,concepcion in #ahce1 water1 which was black and ftid1 issued4#dd ,the earthquakes of ,new ,england in #agbg were accompanied by the formation of fissures1 from which sand and water boiled out in sufficient quantity to form a quagmire4 ,in some places ash and sulphur are said to have been ejected4 ,at one house the stink of sulphur accompanying the earthquake was so great that the family could not bear to remain in doors4#de ,emanations of gas sometimes appear to have burst out from submarine sources4 ,thus the earthquake at ,lima1 in ,march1 #ahfe1 was accompanied with great agitation of the water and an odour of sulphuretted and carburetted hydrogen4 ,this former gas was developed to such an extent that the white paint of the ,u4,s4 ship #8,lancaster' was blackened4#df ,with the smell1 flames have sometimes been observed1 as1 for instance1 at the time of the ,lisbon earthquake4 ,at the time of the earthquakes of #ahaa and #ahac1 in the ,mississippi valley1 steam and smoke issued from some of the fissures which were formed4 ,instances are recorded where stones have been shot up from fissures unaccompanied by water1 as1 for instance1 at the earthquake of ,pasto 7,january1 #ahcd74 ,it is imagined that the propelling power must have been the sudden expansion of escaping gases4 ,it has been suggested that flames seen above fissures might perhaps be due to the burning of materials like sulphur4 ,mr4 ,d4 ,forbes1 who examined the effects of the earthquakes of ,mendoza1 which were felt for a distance of #a1bjj miles1 says that where the hard rock came to the surface there were no traces of fissures1 these being entirely confined to the alluvium4 ,the rumours of fire and smoke having appeared at some of the fissures were without foundation1 the presumed smoke being nothing but dust4#dg ,in addition to flames lights appear often to have been observed1 the origin of which cannot be easily explained4 ,the earthquake of ,november #bb1 #agea1 at ,genoa is said to have been accompanied by a light like that of a prodigious fire which seemed to arise out of the ground4#dh ,explanation of fissure phenomena4--,the manner in which fissures are formed has already been explained when referring to the want of support in the face of hills 7page #acf74 ,similar remarks may be applied to the banks of rivers and all depressions1 whether natural or artificial1 which have a steep slope4 ,at such places the wave of shock emerges on a free surface1 which1 being unsupported in the direction of its motion1 tends to tear itself away from the material behind1 and form a fissure parallel to the face of the free surface4 ,the distance of the fissure from the face of the free surface will1 theoretically1 be equal to half the amplitude of the wave of motion1 one half tending to move forwards1 and the other half backwards4 ,the reason that water and other materials rush forth from fissures has been explained by ,schler as being due to cracks having been opened through impervious strata1 which1 before the earthquake1 by their continuity prevented the rising of subterranean water under hydrostatic pressure4#di ,kluge explains the coming up of the waters as being due to the same causes which he considers may be the origin of disturbances in the sea4 ,the most reasonable explanations of the eruption of water1 mud1 sand1 and gas through fissures are those given by ,oldham and ,mallet in their account of the ,cachar earthquake4 ,in the case of a horizontal shock passing through a bed of ooze or water-bearing strata1 the elastic wave will tend to pack up the water during the forward motion to such an extent that it will flow or spout up through any aperture communicating with the surface4 ,by the repetition of these movements causing ejections1 sand or mud cones1 like those produced by a volcanic eruption1 may be formed1 and by a similar action water may be shot violently up out of wells1 as was the case in ,jamaica in #afib4 ,if an emergent wave acts through a water-bearing bed upon a superincumbent layer of impervious material1 this upper layer is1 during the upward motion1 by its inertia suddenly pressed down upon the latter4 ,this pressure is equal to that which would raise the upper layer to a height equal to the amplitude of the motion of an earth particle1 and with a velocity at least equal to the mean velocity of the earth particle resolved in the vertical direction4 ,for a moment the water-bearing strata receive an enormous squeeze1 and the water or mud starts up through any crevice which may be formed leading to the surface4 ,from this we see that liquids may rise far beyond the level due to hydrostatic pressure4#ej ,volger has attributed the origin of lights or flames appearing above fissures to the friction which must take place between various rocky materials at the time when the fissures are opened4 ,as confirmatory of this he refers to instances where similar phenomena have been observed at the time of landslips4 ,at the time of these landslips the heat developed by friction has been sufficiently intense to convert water into steam1 the tension of which threw mud and earth into the air like the explosion of a mine4#ea ,the gas eruptions which occasionally take place with earthquakes are probably due to the opening of fissures communicating with reservoirs or strata charged with products of natural distillation1 or chemical action1 which previously had accumulated beneath impervious strata4 ,of the existence of such gases we have abundant evidence4 ,in coal mines we have fire damp which escapes in increased quantities with a lowering of the barometrical pressure4 ,in volcanic regions we have many examples of natural springs of carbon dioxide4 ,these various gases sometimes escape in quantity1 or erupt without the occurrence of earthquakes4 ,rossi mentions an instance where a few years ago quantities of fish were killed by the eruption of gas in the ,tiber1 near ,rome4 ,another instance is one which occurred at ,follonica on ,april #f1 #ahgd4 ,on the morning of that day many of the streets and roads were covered with the dead bodies of rats and mice4 ,it seemed as if it had rained rats4 ,from the facts that the bodies of the creatures seemed healthy1 that the destruction had happened suddenly1 and not come on gradually like an epidemic1 it was supposed that they had been destroyed by an emanation of carbon dioxide4 ,the fact that many of them lay in long lines suggested the idea that they had been endeavouring to escape at the time of the eruption4#eb ,if we can suppose sudden developments of gas like this to have occasionally accompanied earthquakes1 we may sometimes have the means of accounting for the sickness which has been felt4 ,disturbances in lakes4--,it has often been observed that1 at the time of large earthquakes1 lakes have been thrown into violent agitation1 and their waters have been raised or lowered4 ,at the time of the great ,lisbon earthquake1 not only were the waters of ,european lakes thrown into a state of oscillation1 but similar effects were produced in the great lakes of ,north ,america4 ,in some instances1 as in the case of small ponds1 these movements may be produced by the horizontal backward and forward motion of the ground4 ,at other times they are probably due to an actual tipping of a portion of their basins4 ,movements like these latter will be again referred to in the chapter on ,earth ,pulsations4 ,on ,january #bg1 #ahef1 there was a shock of earthquake at ,bailyborough1 ,ireland1 which occasioned an adjacent lough to overflow its banks and rush into the town with great impetuosity4 ,in returning it swept away two men1 leaving behind a great quantity of pike and eels of a prodigious growth4#ec ,disturbances in rivers4--,just as lakes have been disturbed1 so also have there been sudden disturbances in rivers4 ,sometimes these have overflowed their banks1 whilst at other times they have been suddenly dried up4 ,in certain cases the reason that a portion of a river should have become dry has been very apparent1 as1 for instance1 at the time of the ,zenkoji earthquake in ,japan in #ahdg1 when the ,shikuma-gawa became partly dry in consequence of the large masses of earth which had been shaken down from overhanging cliffs damming a portion of its course1 and thus forming1 first1 lakes1 and subsequently1 new water-courses4 ,as another example1 out of the many which might be quoted1 may be mentioned the sudden drying up of the river ,aboat1 a tributary of the ,magat1 in the ,philippine ,islands1 on ,july #bg1 #ahha1 shortly after a severe shock of earthquake4 ,the water of this river ceased to flow for two hours1 after which it reappeared with considerable increase of volume and of a reddish colour4 ,signor ,e4 ,a4 ,casariego1 who describes this1 remarks that the phenomenon could easily be explained through the slipping down of the steep banks in narrow parts of its upper valley1 by which means its flow had been obstructed until the water had time to accumulate and pass over or demolish the obstruction4 ,after the earthquake of ,belluno 7,june #bi1 #ahgc71 the torrent ,tesa1 which is ordinarily limpid1 became very muddy4#ed ,similar phenomena have been observed even in ,britain1 as1 for instance1 in #aghg1 when1 at the time of a shock which was felt in ,glasgow1 there was a temporary stoppage in the waters of the ,clyde4 ,again1 in #aaaj1 there was a dreadful earthquake at ,shrewsbury and ,nottingham1 and the ,trent became so low at ,nottingham that people walked over it4 ,the earthquake of #aaeh1 which was felt in many parts of ,england1 was accompanied by the drying up of the ,thames1 which was so low that it could be crossed on foot even at ,london4#ee ,facts analogous to these are mentioned in the accounts of many large earthquakes4 ,sometimes rivers only come muddy or change their colour4 ,in an account of the ,lisbon earthquake we read that some of the rivers near ,neufchtel suddenly became muddy4#ef ,at other times large waves are formed4 ,thus the earthquake of ,kansas 7,april #bd1 #ahfg7 apparently created a disturbance in the rivers at ,manhattan1 which rolled in a heavy wave from the north to the south bank4#eg ,sometimes curious phenomena have happened with regard to rivers without the occurrence of earthquakes4 ,thus1 for instance1 on ,november #bg1 #ahch1 there was a simultaneous stoppage of the ,teviot1 ,clyde1 and ,nith4 ,in these rivers similar phenomena have been observed in previous years4 ,again1 on ,january #a1 #agee1 there was a sudden sinking of the river ,frooyd1 near ,pontypool4 ,this appears to have been due to the water sinking into chasms which were suddenly opened4#eh ,effects produced in springs1 wells1 fumaroles1 c4--,springs also are often affected by earthquakes4 ,sometimes the character of their waters change2 those which were pure become muddy1 whilst those which were hot have their temperature altered4 ,sometimes springs have been dried up1 whilst at other times new springs have been formed4 ,this latter was the case in ,new ,england 7,october #bg1 #agbg74 ,in some places springs were formed1 whilst at other places they were either entirely or partly dried up4#ei ,at and near ,lisbon1 in #agee1 some fountains became muddy1 others decreased1 others increased1 and others dried up4 ,at ,montreux1 ,aigle1 and other places1 springs became turbid4 ,the baths at ,toplitz1 in ,bohemia1 which were discovered in ,a4,d4 #gfb1 were seriously affected by the same earthquake4 ,previous to the earthquake it is said that they had always given a constant supply of hot water4 ,at this time1 however1 the chief spring sent up vast quantities of water and ran over4 ,one hour before this it had grown turbid and flowed muddy4 ,after this it stopped for about one minute1 but recommenced to flow with prodigious violence1 driving before it considerable quantities of reddish ochre4 ,finally1 it settled back to its original clear state and flowed as before4#fj ,in #ahee1 at the earthquake of ,wallis1 many new springs burst forth1 and some of these in ,nicolai ,thale were so rich in iron that they quickly formed a deposit of ochre4 ,at the time of the ,belluno earthquake 7,june #bi1 #ahgc71 a hot spring1 ,la ,vena d',oro1 suddenly became red4#fa ,the following examples of like changes are taken from the writings of ,fuchs4#fb ,in #agch the hot springs of ,st4 ,euphema rose considerably in their temperature4 ,during the earthquake of ,october1 #ahdh1 the hot springs of ,ardebil1 which usually had a temperature of from #dd to #df ,c41 rose so high that their temperature was sufficient to cause scalding4 ,at the time of the earthquake of ,wallis1 in #ahee1 the temperature of hot springs rose #g1 and the quantity of water increased three times4 ,during the earthquake of #ahce in ,chili1 the springs of ,cauquenes fell from #aah to #ib ,f4 ,subsequently1 however1 they again rose4 ,fumaroles are similarly disturbed4 ,thus1 at the time of the earthquakes of ,martinique 7,september1 #ahge71 the fumaroles there showed an abnormal activity4#fc ,wells often appear to be acted upon in the same manner as springs4 ,at the time of the ,california earthquake 7,april1 #ahee71 the level of the water in certain wells was raised ten to twelve feet4 ,a consequence of the earthquake at ,neufchtel1 in #agdi1 was to fill some of the wells with mud4#fd ,at ,constantinople1 on ,september #b1 #aged1 wells became dry4#fe ,explanation of the above phenomena4--,that the water in springs and wells should be caused to rise at the time of an earthquake1 admits of explanation on the supposition of compressions taking place similar to those which cause the rise of water in fissures4 ,that the water in wells and springs should be rendered turbid1 is partly explained on the supposition of more or less dislocation taking place in the earthy or rocky cavities in which they are contained or through which they flow4 ,at the time of a large earthquake it is extremely probable that there is a general disturbance in the lines of circulation of subterranean waters and gases throughout the shaken area4 ,by these disturbances1 new waters may be brought to the surface1 two or more lines of circulation may be united1 and the flow of a spring or supply of a well be augmented4 ,fissures1 through which waters reached the surface1 may be closed1 wells may become dry1 or springs may cease to flow1 hot springs may have their temperature lowered by the additions of cold water from another source1 and1 in a similar manner1 waters may be altered in their mineralisation4 ,an important point to be remembered in this consideration is the mutual dependence of various underground water supplies1 and the area over which any given supply may circulate4 ,a well in the higher part of ,lincoln ,heath is said to be governed by the river ,trent1 which is ten miles distant2 when the river rises the well rises in proportion1 and when the river falls the water in the well falls4#ff ,the change which is usually observed in hot springs is1 that before or with earthquakes they increase in temperature1 but afterwards sink back to their normal state4 ,this increase in temperature may possibly be due to communication being opened with new or deeper centres of volcanic activity1 or a temporarily increased rate of flow4 ,that the water issuing from newly formed fissures or springs should be hot1 might be explained on the supposition of its arising from a considerable depth1 or from some volcanic centre4 ,it might also be attributed to the heat developed by friction at the opening of the fissures4 ,these changes which earthquakes produce upon the underground circulation of waters are phenomena deserving especial attention4 ,although we know much about the circulation of surface water1 it is but little that we yet know about the movement of the streams hidden from view1 from which these surface waters have their sources4 ,earthquakes may be regarded as gigantic experiments on the circulatory system of the earth1 which1 if properly interpreted1 may yield information of scientific and utilitarian value4 ,the sudden elevations1 depressions1 or lateral shifting of large tracts of country at the time of destructive earthquakes are phenomena with which all students of geology are familiar4 ,in most cases these displacements have been permanent2 and evidences of many of the movements which occurred within the memory of man1 remain as witnesses of the terrible convulsions with which they were accompanied4 ,movements on coast lines and level tracts4--,at the time of the great earthquake of ,concepcion1 on ,february #bj1 #ahce1 much of the neighbouring coast line was suddenly elevated four or five feet above sea level4 ,this1 however1 subsequently sank until it was only two feet4 ,a rocky flat1 off the island of ,santa ,maria1 was lifted above high-water mark1 and left covered with #8gaping and putrefying mussel-shells1 still attached to the bed on which they had lived4' ,the northern end of the island itself was raised ten feet and the southern extremity eight feet4#fg ,by the earthquake of #ahci1 the island of ,lemus1 in the ,chonos ,archipelago1 was suddenly elevated eight feet4#fh ,of movements like these1 especially along the western shores of ,south ,america1 ,darwin1 who paid so much attention to this subject1 has given many examples4 ,in #ahbb1 the shore near ,valparaiso was suddenly lifted up1 and ,darwin tells us that he heard it confidently asserted #8that a sentinel on duty1 immediately after the shock1 saw a part of a fort which previously was not within the line of his vision1 and this would indicate that the uplifting was not vertical4'#fi ,that the large areas of land should be shifted permanently in horizontal directions1 as well as vertically1 we should anticipate from the observations which we are able to make upon large fissures which are caused by earthquakes4 ,another remarkable example of sudden movement in the rocky crust is that which took place during the earthquakes of #ahaa-ab in the valley of the ,mississippi1 near to the mouth of the ,ohio1 which was convulsed to such a degree1 that lakes1 twenty miles in extent1 were formed in the course of an hour4 ,this country1 which is called the #8sunk country1' extends some seventy to eighty miles north and south1 and thirty miles east and west4#gj ,in the #8,gentleman's ,magazine' we read of the little territory of ,causa ,nova1 in ,calabria1 being sunk twenty-nine feet into the earth by an earthquake1 without throwing down a house4 ,the inhabitants1 being warned by a noise1 escaped into the fields1 and only five were killed4#ga ,other examples of these permanent dislocations of strata are to be found in almost every text-book on geology4 ,geological changes produced4--,passing over the accounts of earth movements which are more or less fictitious1 and confining our attention to the well authenticated facts1 we see at once the important part which earthquakes have played as agents working geological changes4 ,even in the nineteenth century long tracts of coast1 as in ,chili and ,new ,zealand1 have been raised1 whilst other areas1 like the ,delta of the ,indus1 have been sunk4 ,sir ,h4 ,bartle ,frere1 speaking about the disturbance which took place in his latter region in #ahai1 remarks that all the canals drawn from the ,fullalee ,river ceased to run for about three days1 probably indicating a general upheaval of the lower part of the canal4 ,in consequence of the earthquakes in former times it is not unlikely that water-courses have ceased to flow1 water has decreased in wells1 and districts have been depopulated4#gb ,sometimes these changes have taken place gradually and sometimes with violence4 ,mountains have been toppled over1 valleys have been filled1 cities have been submerged or buried4 ,with the records of these convulsions before us1 we see that seismic energy yet exhibits a terrible activity in changing the features of the globe4 ,reason of these movements4--,to formulate a single reason for these catastrophes would be difficult4 ,where they are of the nature of landslips1 or materials have been dislodged from mountain sides1 the cause is evidently the sudden movement of this ground acting upon strata not held together in a sufficiently stable condition4 ,a similar explanation may be given for the sudden elevations or depressions of strata in a district removed from the centre where the disturbance had its origin4 ,the seismic effort exhibits itself in a certain area round its origin as a sudden push1 and by this push1 strata are fractured and caused to move relatively to each other4 ,at or near to the origin of an earthquake it might be argued that it was the sudden falling of rocky strata towards a position of stable equilibrium that caused the shaking1 and in such a case the movements referred to may be regarded as the cause rather than the effect of an earthquake4 ,a subject closely connected with the sudden dislocation of strata1 is the production of secondary or consequent earthquakes1 due to the disturbance of ground in a critical state 7see p4 #bdh74 ,,chapter ,,ix4 ,,disturbances ,,in ,,the ,,ocean4 ,sea vibrations--,cause of vibratory blows--,sea waves3 ,preceding earthquakes2 ,succeeding earthquakes--,magnitude of waves--,waves as recorded in countries distant from the origin--,records on tide gauges--,waves without earthquakes--,cause of waves--,phenomena difficult of explanation--,velocity of propagation--,depth of the ocean--,examples of calculations--,comparison of velocities of earthquake waves with velocities which ought to exist from the known depth of the ocean4 ,sea vibrations4--,whilst residing in ,japan ,i have had many opportunities of conversing with persons who had experienced earthquakes when on board ships1 and it has often happened that these same earthquakes have been recorded on the shore4 ,for example1 at the time of every moderately severe earthquake which has shaken ,yokohama1 the same disturbance has been felt on board the ships lying in the adjoining harbour4 ,in some cases the effect had been as if the ship was grounding2 in others1 as if a number of sharp jerks were being given to the cable4 ,the effect produced upon a man-of-war lying in the ,yokohama harbour on the evening of ,march #aa1 #ahha1 was described to me as a #8violent irresistible shaking4' ,vessels eighty miles at sea have recorded and timed shocks which were felt like sudden blows4 ,these were accompanied by a noise described as a #8dull rattle like thunder4' ,in none of the cases here quoted was any disturbance of the water observed4 ,the great earthquake of ,lisbon was felt by vessels on the ,atlantic1 fifty miles away from shore4 ,on ,february #aj1 #agaf1 the vessels in the harbour of ,new ,pisco were so violently shaken that both ropes and masts were broken1 and yet no motion in the water was observed4 ,some have described these shocks like those which would be produced by the sudden dropping of large masses of ballast in the hold of the vessel4 ,other cases are known where rigging was damaged1 and even cannon have been jerked up and down from the decks on which they rested4 ,cause of vibratory blows4--,from the rattling sound which has accompanied some of these submarine shocks1 many of which1 it may be remarked1 have never been recorded as earthquakes upon neighbouring shores1 it does not seem improbable that they may have been the result of the sudden condensation of volumes of steam produced by submarine volcanic eruptions4 ,as confirmatory of this supposition we have the fact1 that many of the marine disturbances which might be called #8sea-quakes1' have been observed in places which are close to1 or in the line of1 volcanic vents4 ,thus1 ,m4 ,daussy1 who has paid special attention to this subject1 has collected evidence to show that a large number of shocks have been felt by vessels in that portion of the ,atlantic between ,cape ,palamas1 on the west coast of ,africa1 and ,cape ,st4 ,roque1 on the east coast of ,south ,america4#gc ,some of the vessels only felt shocks and tremblings1 but others saw smoke1 and some even collected floating ashes4 ,in considering the submarine shocks of this particular area1 we must bear in mind that it lies in the line of ,iceland1 the west coast of ,scotland1 the ,azores1 ,canaries1 ,cape de ,verd ,islands1 ,st4 ,helena1 and other places1 all of which1 if not at present in volcanic activity1 shew evidence of having been so within recent times4 ,the connection between volcanic action and earthquakes will be again referred to4 ,sea waves4--,although in the above-mentioned instances sea waves have not been noticed1 it is by no means uncommon to find that destructive earthquakes have been accompanied by waves of an enormous size1 which1 if the earthquake has originated beneath the sea1 have1 subsequently to the shaking1 rolled in upon the land1 to create more devastation than the actual earthquake4 ,it may1 however1 be mentioned that a few exceptional cases exist when it is said that the sea wave has preceded the earthquake1 as1 for example1 at ,smyrna1 on ,september #h1 #aheb4 ,again1 at the earthquake in ,st4 ,thomas1 in #ahfh1 it is said that the water receded shortly before the first shock4 ,when it returned1 after the second shock1 it was sufficient to throw the ,u4,s4 ship #8,monagahela' high and dry4#gd ,another ,american ship1 the #8,wateree1' was also lost in #ahfh by being swept a quarter of a mile inland by the sea wave which inundated ,arequippa4 ,much of the great destruction which occurred at the time of the great ,lisbon earthquake was due to a series of great sea waves1 thirty to sixty feet higher than the highest tide1 which swamped the town4 ,these came in about an hour after the town had been shattered by the motion of the ground4 ,the first motion in the waters was their withdrawal1 which was sufficient to completely uncover the bar at the mouth of the ,tagus4 ,at ,cadiz1 the first wave1 which was the greatest1 is said to have been sixty feet in height4 ,fortunately the devastating effect which this would have produced was partially warded off by cliffs4 ,at the time of the ,jamaica earthquake 7#afib7 the sea drew back for a distance of a mile4 ,in ,south ,america sea waves are common accompaniments of large earthquakes1 and they are regarded with more fear than the actual earthquakes4 ,on ,october #bh1 #agbd1 ,lima was destroyed1 and on the evening of that day the sea rose in a wave eighty feet over ,callao4 ,out of twenty-three ships in the harbour1 nineteen were sunk1 and four others were carried far inland4 ,the first movement which is usually observed is a drawing back of the waters1 and this is so well known to precede the inrush of large waves1 that many of the inhabitants in ,south ,america have used it as a timely warning to escape towards the hills1 and save themselves from the terrible reaction which1 on more than one occasion1 has so quickly followed4 ,at ,caldera1 near to ,copiapo1 on ,may #i1 #ahgg1 which was the time when ,iquique was devastated1 the first motion which was observed in the sea was that it silently drew back for over #bjj feet1 after which it rose as a wave over five feet high4 ,at some places the water came in as waves from twenty to eighty feet in height4 ,at ,talcahuano1 on the coast of ,chili1 in #ahce1 there was a repetition of the phenomena which accompanied the destruction of ,penco in #agcj and #agea4 ,about forty minutes after the first shock1 the sea suddenly retired4 ,soon afterwards1 however1 it returned in a wave twenty feet high1 the reflex of which swept everything towards the sea4 ,these phenomena were repeated three times4#ge ,when ,callao and ,lima were destroyed1 in #agdf1 the sea first drew back1 then came in as waves1 four or five minutes after the earthquake4 ,altogether1 between ,october #bh and ,february #bd1 #dea shocks were counted4 ,at one time the sea came in eighty feet above its usual level4 ,one account says that the large waves came in forty-one and a half hours after the first shock1 and seventeen and a half hours after comparative tranquillity had prevailed4#gf ,at the eruption of ,monte ,nuovo1 near ,naples1 in ,september #bg1 #aech1 the water drew back forty feet1 so that the whole gulf of ,baja became dry4 ,in #afif1 at the time of the ,catanian earthquake1 the sea is said to have gone back #b1jjj fathoms4 ,instances are recorded where the sea has receded several miles4 ,the time taken for the flowing back of the sea is usually very different4 ,sometimes it has only been five or six minutes1 whilst at other times over half an hour1 and there are records where the time is said to have been still longer4 ,thus1 at the earthquake of ,santa 7,june #ag1 #afgh71 the sea is stated to have gone as far back as the eye could reach1 and did not rise again for twenty-four hours1 when it flooded everything4 ,in #afij at ,pisco the sea went back two miles1 and did not return for three hours4 ,when it returns it does so with violence1 and examples of the heights to which it may reach have been given4 ,the greatest sea wave yet recorded1 according to ,fuchs1 is one which1 on ,october #f1 #agcg1 broke on the coast of ,lupatka1 #baj feet in height4 ,there are1 however1 cases known where the sea has returned as gradually as it went out4 ,thus1 on ,december #d1 #ahed1 when ,acapulco was destroyed1 the sea is said to have returned as gently as it went out4 ,when sea waves have travelled long distances from their origin1 as1 for instance1 whenever a ,south ,american wave crosses the ,pacific to ,japan1 the phenomena which are observed are like those which were observed at ,acapulco2 the sea falls and rises1 at intervals of from ten minutes to half an hour1 to heights of from six to ten feet1 without the slightest appearance of a wave4 ,its phenomenon is like that of an unusually high tide1 which repeats itself several times per hour4 ,even if we watch distant rocks with a telescope1 although the surface of the ocean may be as smooth as the surface of a mirror1 there is not the slightest visible evidence of what is popularly called a wave4 ,the sea being once set in motion it continues to move as waves of oscillation for a considerable time4 ,in #ahgg1 as observed in ,japan1 the motion continued for nearly a whole day4 ,the period and amplitude of the rise and fall were variable1 usually it quickly reached a maximum1 and then died out gradually4 ,as observed in a self-recording tide gauge at ,san ,francisco1 the disturbance lasted for about four days4 ,a diagram of this is here given4 ,in its general appearance it is very similar to the records of other earthquake waves4 ,the large waves represent the usual six hours rise and fall of the tides2 usually these are fairly smooth curves4 ,superimposed on the large waves are the smaller zigzag curves of the earthquake disturbance1 lasting with greater or less intensity for several days4 ,as these curves are drawn to scale--horizontally for hours1 and vertically one fifth inch to the foot1 to show the extent of the rise and fall--they will be easily understood4 ,sometimes1 as in the present example1 the first movement in the waters is that of an incoming wave4 ,in many instances1 however1 this observation may be due to the slow and more gentle phenomena of the previous drawing out of the water1 which in a steep waste1 or when the water is rough1 would be difficult to observe1 not having been remarked4 ,the distance to which these sea waves have extended has usually been exceedingly great4 ,illustration3 ,,fig4 #bh4--,record of ,tide ,gauge at ,port ,point1 ,san ,francisco4 ,showing ,earthquake ,waves of ,may #ahgg4 ,the sea wave of the ,iquique earthquake of ,may #i1 #ahgg1 like many of its predecessors1 was felt across the basin of the whole ,pacific1 from ,new ,zealand in the south1 to ,japan and ,kamschatka in the north4 ,and but for the intervention of the ,eurasian and ,american continents would have made itself appreciable over the surface of the whole of our globe4 ,at places on the ,south ,american coast1 it has been stated that the height of the waves varied from twenty to eighty feet4 ,at the ,samoa ,islands the heights varied from six to twelve feet4 ,in ,new ,zealand the sea rose and fell from three to twenty feet4 ,in ,australia the heights to which the water oscillated were similar to those observed in ,new ,zealand4 ,in ,japan it rose and fell from five to ten feet4 ,in this latter country1 the phenomena of sea waves which follow a destructive earthquake on the ,south ,american coast are so well known that old residents have written to the local papers announcing the probability of such occurrences having taken place some twenty-five hours previously in ,south ,america4 ,in this way news of great calamities has been anticipated1 details of which only arrived some weeks subsequently4 ,just as the destructive earthquakes of ,south ,america have announced themselves in ,japan1 in a like manner the destructive earthquakes of ,japan have announced themselves upon the tide gauges of ,california4 ,similarly1 but not so frequently1 disturbances shake the other oceans of the world4 ,for example1 the great earthquake of ,lisbon propagated waves to the coasts of ,america1 taking on their journey nine and a half hours4 ,sea waves without earthquakes4--,sometimes we get great sea waves like abnormal tides occurring without any account of contemporaneous earthquakes4 ,although earthquakes have not been recorded1 these ill understood phenomena are usually attributed to such movements4 ,several examples of these are given by ,mallet4 ,thus1 at #aj ,a4,m4 on ,march #b1 #ahef1 the sea rose and fell for a considerable distance at many places on the coast of ,yorkshire4 ,at ,whitby1 the tide was described ebbing and flowing six times per hour1 and this to such a distance that a vessel entering the harbour was alternately afloat and aground4 ,in #agfa1 on ,july #ag1 a similar phenomena was observed at the same place4 ,a like occurrence took place at ,kilmore1 in the county of ,wexford1 on ,september #af1 #ahfd1 when the water ebbed and flowed seven times in the course of two hours and a half4 ,these tides1 which appear to have taken about five minutes to rise and five minutes to fall1 were seen by an observer approaching from the west as six distinct ridges of water4 ,the general character of the phenomena appears to have been very similar to that which was produced at the same place by the ,lisbon earthquake of #agee2 and the opinion of those who saw and wrote about their occurrence was that it was due to an earthquake disturbance4 ,such phenomena are not uncommon on the ,wexford coast1 where they are popularly known as #8death waves1' probably in consequence of the lives which have been lost by these sudden inundations4 ,they have also been observed in other parts of ,ireland1 the north-east coast of ,england1 and in many parts of the globe4 ,they will be again referred to under the head of earth pulsations4 ,cause of sea waves4--,mallet1 who in his report to the ,british ,association in #aheh1 writes upon this last-mentioned occurrence at considerable length1 whilst admitting that many may have originated from earthquakes1 he thinks it scarcely probable that an earthquake blow1 sufficiently powerful to have produced waves like those observed at ,kilmore1 should not have been felt generally throughout the south of ,ireland4 ,he1 therefore1 suggests that sometimes waves like the above might be produced by an underwater slippage of the material forming the face of a submarine bank1 the slope of which by degradation and deposition1 produced by currents1 had reached an angle beyond the limits of repose of the material of which it was formed4 ,mallet does not insist upon the existence of these submarine landslips1 but only suggests their existence as a means of explaining certain abnormal sea waves which do not appear to have been accompanied by earthquakes4 ,in the generality of cases sea waves are accompanied by earthquakes1 but it may often happen that the connection between the two is difficult to clearly establish4 ,one simple explanation for the origin of waves occurring with earthquakes1 is1 that in consequence of the earthquake a large volume of water suddenly finds its way into cavities which have been opened1 the disturbance produced by the inrush giving rise to waves4 ,a second explanation is1 that the land along a shore is caused by an earthquake to oscillate upwards1 the water running off to regain its level4 ,a supposition like this is negatived by the fact that these disturbances are felt far away from the chief disturbance1 on small islands4 ,also1 it may be added1 that the whole disturbance appears to approach the land from the sea1 and not in the opposite direction4 ,thus1 in the earthquake of ,oahu 7,february #ah1 #ahga71 it was remarked that the shock was first felt by the ships farthest from the land4#gg ,another suggestion is that the waves are due to a sudden heaving up of the bottom of the ocean4 ,if this lifting took place slowly1 then the first result would be that the water situated over the centres of disturbance would flow away radially in all directions from above the area of disturbance4 ,if1 however1 the submarine upheaval took place with great rapidity1 say by the sudden evolution of a large volume of steam developed by the entry of water into a volcanic vent1 as the water was heaped above the disturbed area1 water might run in radially towards this spot4 ,supposing a primary wave to be formed in the ocean by any such causes1 then the falling of this will cause a second wave to be formed1 existing as a ring round the first one4 ,the combined action of the first and second wave will form a third one1 and so the disturbance1 starting from a point1 will radiate in broadening circles4 ,during the up and down motion of these waves1 the energy which is imparted to any particle of water will1 on account of the work which it has to do in displacing its neighbours1 by frictional resistance1 gradually grow less and less1 until it finally dies away4 ,the waves which are the result of this motion will also grow less and less4 ,if a series of sea waves were produced by a single disturbance1 we see that these will be of unequal magnitude4 ,now1 for small waves1 the velocity with which they travel depends upon the square root of their lengths2 but with large waves1 like earthquake waves1 the velocity depends upon the square root of the depth of water1 and these latter travel more quickly than the former4 ,if1 therefore1 we have a series of disturbances of unequal magnitude producing sea waves1 which1 from the series of shocks which have been felt upon shores subsequently invaded by waves1 seems in all probability often to have been the case1 it is not unlikely that the waves of an early disturbance may be overtaken and interfered with by a series which followed4 ,these considerations help us to understand the appearance of the records on our tide gauges1 and also the phenomena observed by those who have recorded tidal waves as they swept inwards upon the land4 ,for instance1 we understand the reason why sea waves1 as observed at places at different distances from the origin of a disturbance1 should be of different heights4 ,we also see an explanation for the fact that small waves should sometimes appear to be interpolated between large ones1 and that these should occur at varying intervals4 ,the fact that whenever a wave is produced1 a certain quantity of water must be drawn from the level which surrounds it1 in order that it should be formed1 explains the phenomena that the sea is often observed first to draw back4 ,out in the open ocean it is drawn from the hollow between two waves4 ,as has been pointed out by ,darwin1 it is like the drawing of the water from the shore of a river by a passing steamer4 ,the difference in the height of waves1 as observed at places lying close to each other1 is probably due to the configuration of the coast1 the interference of outlying islands1 reefs1 c4--causes which would produce similar effects in the height of tide4 ,as a wave approaches shallow water it gradually increases in height1 its front slope becomes steep1 and its rear slope gentle1 until finally it topples over and breaks4 ,this increasing in height of waves is no doubt connected with the destruction of ,talcahuano and ,callao1 which are situated at the head of shallow bays4 ,valparaiso1 which is on the edge of deep water1 has never been overwhelmed4#gh ,another case tending to produce anomalies in the character of waves would be their reflection and mutual interference1 the reflections due to the configuration of the ocean bed and coast lines4 ,the complete phenomena which may accompany a violent submarine disturbance are as follows3-- ,by the initial impulse of explosion or lifting of the ground1 a #8great sea wave' is generated1 which travels shorewards with a velocity dependent upon its size and the depth of the ocean4 ,at the same instant1 a #8sound wave' may be produced in the air1 which travels at a quicker rate than the #8great sea wave4' ,a third wave which is produced1 is an #8earth wave1' which will reach the shore with a velocity dependent on the intensity of the impulse and the elasticity of the rocks through which it is propagated4 ,this latter1 which travels the fastest1 may carry on its back a small #8forced sea wave4' ,on reaching the shore and passing inland1 this #8earth wave' will cause a slight recession of the water as the #8forced sea wave' slips from its back4 ,as these #8forced sea waves' travel they will give blows to ships beneath which they may pass1 being transmitted from the bottom of the ocean to the bottom of the ships like sound waves in water4 ,at the time of small earthquakes1 produced1 for example1 by the explosion of small quantities of water entering volcanic fissures1 or by the sudden condensation of steam from such a fissure entering the ocean1 aqueous sound waves are produced1 which cause the rattling and vibrating jars so often noticed on board ships4 ,phenomena difficult of explanation4--,although we can in this way explain the origin and phenomena of sea waves1 we must remember1 as ,kluge has pointed out1 that it is not the simple backward and forward movement of the ground which produces sea waves1 and that the majority of earthquakes which have occurred in volcanic coasts have been unaccompanied by such phenomena4 ,out of #ae1jjj earthquakes observed on coast lines1 only #abd were accompanied by sea waves4#gi ,out of #a1jih earthquakes catalogued by ,perrey for the west coast of ,south ,america1 only nineteen are said to have been accompanied by movements in the waters4 ,according to the #8,geographical ,magazine' 7,august #ahgg1 p4 #bjg71 it would seem that out of seventy-one severe earthquakes which have occurred since the year #aejj upon the ,south ,american coast many have been accompanied by sea waves4 ,darwin also remarks1 when speaking of ,south ,america1 that almost every large earthquake has been accompanied by considerable agitation in the neighbouring sea4#hj ,on ,april #b1 #ahea1 when many towns in ,chili were destroyed1 the sea was not disturbed4 ,at the time of the great earthquake of ,new ,zealand 7,june #bc1 #ahee71 although all the shocks came from the sea1 yet there was no flood4 ,the small shock of ,february #ad1 however1 was accompanied by a motion in the sea4 ,to these examples1 which have been chiefly drawn from the writings of ,fuchs1 must be added the fact that the greater number of disturbances which are felt in the north-eastern part of ,japan1 although they emanate from beneath the sea1 do not produce any visible sea waves4 ,they are1 however1 sufficient to cause a vibratory motion on board ships situated near their origin4 ,another point referred to by ,fuchs1 as difficult of explanation1 is1 that the water1 when it draws back1 often does so with extreme slowness1 and farther1 in some instances1 it has not returned to its original level4 ,that the sea might be drawn back for a period of fifteen or thirty minutes is intelligible1 when we consider the great length of the waves which are formed4 ,cases where it has retired for several hours or days1 and when its original level is altered1 appear only to be explicable on the assumption of more or less permanent changes in the levels of the ground4 ,for example1 in the earthquake of #ahee which shook ,new ,zealand1 the whole southern portion of the northern island was raised several feet4 ,these sudden alterations in the levels of coast lines have already been referred to4 ,other points which are difficult to understand are the occurrence of disturbances in the sea at the time of feeble earthquakes1 and with earthquakes occurring in distant places4 ,as examples of such occurrences1 ,fuchs quotes the following3 #8,on ,may #af1 #ahej1 at #d4bh ,a4,m41 an earthquake took place in ,pesth1 and at #g4cj a motion was observed in the sea at ,livorno4 ,again1 at the time of the earthquake of ,december #ai1 #ahej1 which shook ,heliopolis1 a flood suddenly came in upon ,cherbourg4' ,may not these phenomena be the result of an earth pulsation1 which produced an earthquake at one point1 and a sea wave at another8 ,equally difficult to understand are the observations when the disturbance in the sea has occurred several hours after an earthquake2 as1 for instance1 at ,batavia1 in #aheb1 when there was an interval of two hours2 and to this must be added the observations where the motion of the sea has preceded that of the earthquake--as1 for instance1 in #aheb1 at ,smyrna4 ,whilst recognising the fact that it is possible to suggest explanations for many of these anomalies1 we must also bear in mind that they are1 generally speaking1 exceptional1 and1 in some instances1 may possibly be due to errors in observations4 ,velocity of propagation of sea waves1 and depth of the ocean4--,it has long been known to physical science that the velocity with which a given wave is propagated along a trough of uniform depth1 holds a relation to the depth of the trough4 ,if v is the velocity of the wave1 and h the depth of the trough1 this relation may be expressed as follows3-- v#b 7v7 h ---------- or h 7------7#b g 7k7 ,where g #cbai and k #efga4 ,it will be observed that these two formul 7the first of which is known as ,russell's formula1 and the second as ,airy's7 are practically identical4 ,the apparent difference is in the average value assigned to the constant4 ,for large waves such as we have to deal with1 it would be necessary1 if we were desirous of great accuracy1 to increase the value of h by some small fraction of itself4 ,we might also make allowance for the different values of g1 according to our position on the earth's surface4 ,with these formul at our disposal it is an easy matter1 after having determined the velocity with which a wave was propagated1 to determine the average depth of the area over which it was transmitted4 ,in making certain earthquake investigations the reverse problem is sometimes useful--namely1 determining the velocity with which a sea wave has advanced upon a shown line1 from a knowledge of the depth of the water in which it has been propagated4 ,calculations of the average depths of the ,pacific1 dependent on the velocity with which earthquake waves have been propagated1 have been made by many investigators4 ,in most cases1 however1 in consequence of having assumed the wave to have originated on a coast line1 when the evidence clearly showed it to have originated some distance out at sea1 the calculations which have been made are open to criticism4 ,the average depths which ,i obtained for various lines across the ,pacific appear to be somewhat less than the average depth as given by actual soundings4 ,we must1 however1 remember that the common error in actual soundings is that they are usually too great1 it being difficult in deep-sea sounding to determine when the lead actually reaches the bottom4 ,until oceans have been more thoroughly surveyed with the improved forms of sounding apparatus1 we shall not be able to verify the truth of the results which have been given to us by earthquake waves4 ,,examples ,,of ,,calculations ,,on ,,sea ,,waves4 #a4 ,the wave of #ahed4--,this wave originated near ,japan1 and it was recorded on tide gauges at ,san ,francisco1 ,san ,diego1 and ,astoria4 ,on ,december #bc1 at #i4ae4 ,a4,m41 a strong shock was felt at ,simoda in ,japan1 which1 at #aj o'clock1 was followed by a large wave thirty feet in height4 ,the rising and falling of the water continued until noon4 ,half an hour after1 the movement became more violent than before4 ,at #b4ae ,p4,m4 this agitation decreased1 and at #c ,p4,m4 it was comparatively slow4 ,altogether there were five large waves4 ,on ,december #bc and #be1 unusual waves were recorded upon the self-registering tide gauges at ,san ,francisco1 ,san ,diego1 and ,astoria4 ,at ,san ,francisco three sets of waves were observed4 ,the average time of oscillation of one of the first set was thirty-five minutes1 whilst one of the second and third sets was almost thirty-one minutes4 ,at ,san ,diego three series of waves were also shown1 but with average times of oscillation of from four to two minutes shorter than the waves at ,san ,francisco4 ,the ,san ,francisco waves appear to indicate a recurrence of the same phenomena4 ,the record at ,san ,diego shows what was probably the effect of a series of impulses1 the heights increasing to the third wave1 then diminishing1 then once more renewed1 after which it died away4 ,the result of calculations based on these data were3-- ---------------------------------------- --------------------- ,distance ,time ,velocity ,depth of geographical of in feet ocean in miles transmissionper sec4 fathoms ---- ---------------------------------------- ---------------- h4 m4 ,simoda to ,san #diag #ab #ac #ede #bajj ,diego ,simoda to ,san #debg #ab #ci #ebh #bejj or #bbcj ,francisco ---------------------------------------- --------------------- ,the difference for the depths in the ,san ,francisco path depends whether the length of the waves is reckoned at #baj or #bag miles4 ,the length of the waves on the ,san ,diego path were #ahf or #aib miles4#ha ,the wave of #ahfh4--,on ,august #aa1 #ahfh1 a sea wave ruined many cities on the ,south ,american coast1 and #be1jjj lives were lost4 ,this wave1 like all the others1 travelled the length and breadth of the ,pacific4 ,in ,japan1 at ,hakodate1 it was observed by ,captain ,t4 ,blakiston1 ,r4,a41 who very kindly gave me the following account3 ,on ,august #ae1 at #aj4cj ,a4,m41 a series of bores or tidal waves commenced1 and lasted until #c ,p4,m4 ,in ten minutes there was a difference in the sea level of ten feet1 the water rising above high water and falling below low water mark with great rapidity4 ,the ordinary tide is only two and a half to three feet4 ,the disturbance producing these waves originated between ,iquique and ,arica1 in about lat4 #ah4bh ,s4 at about #e ,p4,m4 on ,august #ac4 ,in ,greenwich time this would be about #ac;h4 #im4 #djs4 ,august #ac4 ,the arrival of the wave at ,hakodate in ,greenwich time would be about #ad;h4 #gm4 #fs4 ,august #ad3 that is to say1 the wave took about #bd;h4 #egm4 to travel about #h1gjj miles1 which gives us an average rate of about #eaa feet per second4 ,these waves were felt all over the ,pacific4 ,at the ,chatham ,islands they rushed in with such violence that whole settlements were destroyed4 ,at the ,sandwich ,islands the sea oscillated at intervals of ten minutes for three days4 ,comparing this wave with the one of #ahgg we see that one reached ,hakodate with a velocity of #eaa feet per second1 whilst the other travelled the same distance at #eab feet per second4 ,an account of this earthquake wave has been given by ,f4 von ,hochstetter 7#8ber das ,erdbeben in ,peru am #ac4 ,august #ahfh und die dadurch veranlassten ,fluthwellen im ,pacifischen ,ocean1' ,sitzungsberichte der ,kaiserl4 ,akademie der ,wissenschaften1 ,wien #eh4 ,bd41 #b4 ,abth4 #ahfh74 ,from an epitome of this paper given in #8,petermann's ,geograph4 ,mittheil4' #ahfi1 p4 #bbb1 ,i have drawn up the following table of the more important results obtained by ,f4 von ,hochstetter4 ,the wave is assumed to have originated near ,arica4 ---------------------------------------- ------------------ ,distance ,time ,velocity ,depth of sea miles taken by in feet ocean in from ,arica wave per second feet ---------------------------------------- ------------------ h4 m4 ,valdivia #a1dbj #e #j #dgi #g1adj ,chatham ,islands #e1ebj #ae #ai #fjh #aa1dgb ,lyttleton #f1abj #ai #ah #ecc #h1hch ,newcastle #g1chj #bb #bh #ech #i1jjf ,apia 7,samoa7 #e1gfj #af #b #fjd #aa1cdf ,rapa #d1jeg #aa #aa #faa #aa1eih ,hilo #e1djj #ad #be #eee #i1efh ,honolulu #e1ehj #ab #cg #gdf #ag1bib ---------------------------------------- ------------------ ,calculations on the same disturbance are also given by ,j4 ,e4 ,hilgard4#hb ,assuming the origin of the wave to have been at ,arica1 his results are as follows3 ---------------------------------------- -------------------- ,nautical ,distance ,time of miles ,mean depth from ,africa transmission per hour of ocean ---------------------------------------- -------------------- miles h4 m4 feet ,san ,diego #d1jcj #aj #ee #cfi #ab1ajj ,fort ,point #d1dhj #ab #ef #cdh #aj1hjj ,astoria #e1jjj #ah #ea #bfe #f1bjj ,kodiak #f1bjj #bb #jj #bhb #g1jjj ,rapa #d1jeg #aj #ed #cgb #ab1bjj ,chatham ,islands #e1ebj #ae #ja #cfh #ab1ajj ,hawaii #e1dfj #ad #aj #che #ac1bjj ,honolulu #e1ehj #ab #ah #ded #ah1ejj ,samoa #e1gfj #ae #ch #cfh #ab1ajj ,lyttelton #f1abj #ai #ja #cbb #i1bjj ,newcastle #i1chj #bb #aj #ccb #i1hjj ,sydney #g1ddj #bc #da #cad #h1hjj ---------------------------------------- -------------------- ,the wave of #ahgg4--,two sets of calculations have been made upon the wave of #ahgg by ,dr4 ,e4 ,geinitz of ,rostock4#hc ,the following table is taken from ,dr4 ,geinitz's second paper1 in which there are several modifications of his first results4 ,the origin of the disturbance is assumed to have been near ,iquique4 ---------------------------------------- ---------------------- ,distance ,velocity ,mean ,observation from ,arrival ,time in feet depth of stations ,iquique of wave taken per ocean geol4 by wavesecond in miles fathoms ---------------------------------------- ---------------------- h4 m4 h4 m4 ,taiohc 7,marquesa ,islands7 #d1jhf #h #dj ,a4,m4 #ab #ae #efch #a1fdg ,apia 7,samoa7 #e1gdj #ab #j #ae #cj #fajd #a1icj ,hilo 7,sandwich #e1ebf #aj #bd #ad #j #ffgi #b1caj ,islands7 ,kahuliu #e1fbh #aj #cj #ad #e #fgeb #b1cfa ,honolulu #e1gab #aj #ej #ad #be #ffig #b1cai ,wellington 7,new #e1feg #b #dj ,p4,m4 #ah #ae #ebdb #a1dcj ,zealand7 ,lyttelton #e1fda #b #dh #ah #bc #eaih #a1djj ,newcastle 7,australia7 #f1hjj #b #cb #ah #g #fccj #b1jge ,sydney #f1ghb #b #ce #ah #aj #fcad #b1jfe ,kamieshi 7,japan7 #h1gij #g #bj #bb #ee #fdij #b1ahb ,hakodate #h1gfj #i #be #be #j #eibe #a1hah ,kadsusa #h1ici #i #ej #be #ae #fjdi #a1hie ---------------------------------------- ---------------------- ,the mean depths represent a mean of two sets of calculations1 one made with the aid of ,airy's formula1 and the other by ,scott-,russell's formula4 ,the result of my own investigation about this disturbance1 the origin of which1 by several methods of calculation1 is shown to have been beneath the ocean1 near #ga #e west long41 and #ba #bb south lat41 are given on next page4 ,dr4 ,geinitz considers that his calculated depths of the ocean and those obtained by actual soundings are in accordance1 a result which is diametrically opposed to that which ,i have obtained4 ,this difference between my calculations and those of ,dr4 ,geinitz1 ,hochstetter1 and others1 chiefly rests on the origin we have assigned for the sea waves4 ,dr4 ,geinitz1 for instance1 although he says that the origin of the #ahgg earthquake was not on the continent but to the west in the ocean1 bases all his calculations on the assumption that the centrum was at or near to ,iquique1 and the time at which that city was disturbed was the time at which the waves commenced to spread across the ocean4 ,this time is #h4be ,p4,m4 ,at this time1 however1 it appears that the waves must have been more than double the distance between the true origin and ,iquique1 from ,iquique on their way towards the opposite side of the ,pacific4 ,introducing this element into the various calculations which have been made respecting the depth of the ,pacific ,ocean as derived from observations on earthquake waves--which element1 insomuch as the waves appear to have come in to inundate the land some time after the shock1 needs to be introduced--we reduce the velocity of transit of the earthquake wave and1 consequently1 the resultant depths of the ocean4 ,key3 ,a ,distance from the origin in miles 7calculated in great circles7 ,b ,velocity in feet per second ---------------------------------------- -------------------------- ,arrival ,time ,depth ,interval of wave taken of the ,height between ,longitude in by ,a ,b ocean of waves in ,greenwichwave in feet waves minutes mean time ---------------------------------------- -------------------------- day h4 m4h4 m4 ,origin of wave #ga #e ,w4 #i #ab #ei ,san ,francisco#abb #cb #aj #b #bhac #bid1eghdih #g1gba #i in4 ,callao #gg #ae #i #ag #i #d #aj #fehbca #a1feg ,iquique #gj #ad #i #ac #ba #j #bb #hgcdh #c1ggj #bj ft4 #bb ,cobija #gj #ba #i #ac #ai #j #bj #hjceb #c1heg #cj ,mejillones #gj #ce #i #ac #bg #j #bh #ajhcci #c1ehg #ce #ae or #de ,chanaral #ga #cd #i #ae #bf #b #bg #deebgb #b1cji #aj ,coquimbo #ga #bd #i #ae #ae #b #af #ejhcbh #c1cfc #cj ,valparaiso #ga #ch #i #af #af #c #ag #fiecaj #c1jjj ,concepcion #gc #e #i #af #eb #c #ec #ibhcej #c1hbd #ab to #ae ,honolulu #aeg #ee #aj #c #ebad #ece1fidefa #i1hjg #cd to #be #ed ft4 ,hilo #aee #c #aj #c #ead #fe1ejfefcaj1bag #cj or #c or #ae #h #ah or #bg ,kahuliu #aef #dc #aj #c #abad #ace1faaegiaj1dcg ,samoa #aga #da ,w4#aj #c #egad #ehe1ggceff #i1igb #ab ft4 #aj ,taurauga #agf #aa ,e4#aj #h #aeai #afe1faedbg #e1fig ,wellington #agd #cj #aj #g #bbah #bce1egddde #f1afh #aa #aj ,akaroa #agb #ei #aj #g #bhah #bie1edbddj #f1jca ,lyttelton #agb #de #aj #g #biah #cje1eehdda #f1jee ,kameishi #adj #ej #aj #ab #cgbc #chh1hddedi #i1cgh #f #ae ,hakodate #adj #ej #aj #ad #gbe #hh1ggheab #h1afi #g #bj ---------------------------------------- -------------------------- ,in ,dr4 ,geinitz's paper there are also some slight differences in the times at which the earthquake phenomena were observed at various localities4 ,these1 however1 are but of minor importance4 ,at the end of the paper by ,dr4 ,geinitz two interesting tide gauge records are introduced1 one from ,sydney and the other from ,newcastle4 ,these appear to show a marked difference in the periods of the sea waves at these two places4#hd ,comparison of velocities of wave-transit which have been actually observed1 with velocities which ought to exist from what we know of the depth of the ,pacific by actual soundings4--,from a chart given in #8,petermann's ,geograph4 ,mittheilungen1' ,band xxiii4 p4 #afd1 #ahgg1 it is possible to draw approximate sections on lines in various directions across the bed of the ,pacific4 ,from the origin of the shock to ,japan 7,kameishi7 the line would be as follows3-- about #g1dda miles #ae1jjj feet deep #a1ajj #ah1jjj #afj #bg1jjj #hj #ab1jjj #fj #f1jjj ,on account of the ,tuscarora and ,belkap ,deeps this would be the most irregular line over which the wave had to travel4 ,from the origin to ,new ,zealand 7,wellington7 the line would be about #e1bgd miles #ae1jjj feet deep4 #cjj #ab1jjj ,from the origin to ,samoa the line would be about #e1ggc miles #ae1jjj feet deep4 ,from the origin to the ,sandwich ,islands 7,honolulu7 the line would be almost #f1fcd miles #ae1jjj feet deep and #fj #ab1jjj ,by ,scott-,russell's rule1 or1 what is almost identically the same1 by ,airy's general formula1 we can calculate how long it would take such waves as we have been speaking about to travel over the different portions of each of these lines1 and by adding these times together we obtain the time taken to travel across any one line4 ,i have made these calculations1 but as ,i get in every case answers which are too small1 ,i think it unnecessary to give them4 ,the actual times taken to travel the distances just referred to were1 ,to ,japan 7,kameishi7 #bc hr4 #ch min4 ,new ,zealand 7,wellington7 #ah #bc ,samoa #ad #eh ,sandwich ,islands 7,honolulu7 #ad #ec ,from ,san ,francisco to ,simoda the line is almost #c1efg miles1 #c1jjj fathoms deep1 #hdj miles1 #b1ejj fathoms deep1 and #abj miles #a1jjj fathoms deep4 ,this gives an average depth of about #b1hed fathoms4 ,bache calculated the depth at #b1ejj fathoms4 ,if we are to consider that1 because the sea wave at ,simoda came in some time after the land shock had been felt1 the origin of this earthquake1 instead of being at ,simoda1 was some distance out at sea1 this calculated depth would be reduced4 ,,chapter ,x4 ,,determination ,,of ,,earthquake ,,origins4 ,approximate determination of an ,origin--,earthquake-hunting in ,japan--,determinations by direction of motion--,direction indicated by destruction of buildings--,direction determined by rotation--,cause of rotation--,the use of time observations--,errors in such observations--,origin determined by the method of straight lines--,the method of circles1 the method of hyperbolas1 the method of co-ordinates--,haughton's method--,difference in time between sound1 earth1 and water waves--,method of ,seebach4 ,one of the most practical problems which can be suggested to the seismologist is the determination of the district or districts in any given country from which earthquake disturbances originate4 ,with a map of a country before us1 shaded with tints of different intensity to indicate the relative frequency of seismic disturbance in various districts1 we at once see the localities where we might dwell with the least disturbance1 and those we should seek if we wish to make observational seismology a study4 ,before erecting observatories for the systematic investigation of earthquakes in a country1 it would be necessary for us1 in some way or other1 to examine the proposed country to find out the most suitable district4 ,the special problem of determining approximately the origin or origins of a set of earthquakes would be given to us4 ,having made this preliminary investigation1 the next point is1 by means of observatories so arranged that they could always work in conjunction with each other1 to determine the origins more accurately4 ,by knowing the origin from which a set of shocks spring we know the general direction in which we may expect the most violent disturbances1 and we can arrange our seismometers accordingly4 ,approximate determination of origins4--,in #ahhj ,i obtained a tolerably fair idea of the distribution of seismic energy throughout ,japan1 by compiling the facts obtained from some hundreds of communications received from various parts of the country respecting the number of earthquakes that had been felt4 ,the communications were replies to letters sent to various residents in the country and to a large number of public officers4 ,by taking these records1 in conjunction with the records made by instruments1 it was ascertained that in ,japan alone there were certainly #a1bjj shocks felt during the year1 that is to say1 three or four shocks per day4 ,the greater number of these shocks were felt along the eastern coast1 commencing at ,tokio1 in the south1 and going northwards to the end of the main island4 ,these shocks were seldom felt on the west coast4 ,it appeared as if the central range of mountains formed a barrier to their progress4 ,similarly1 ranges of mountains to the south-west of ,tokio prevented the shocks from travelling southwards4 ,proceeding in this way the conclusion was arrived at that the west coast1 the southern part of ,japan1 and the islands of ,shikoku and ,kiushiu1 had their own local earthquakes4 ,earthquake-hunting4--,these preliminary enquiries having shown that the northern part of ,japan was a better district for seismological observations than the southern half1 the next step was to subject the northern half to a closer analysis4 ,this analysis was commenced by sending to all the important towns1 from thirty to one hundred miles distant from ,tokio1 bundles of postcards4 ,these were entrusted to the local government offices with a request that each week one of these cards would be returned to ,tokio stating the number of shocks felt4 ,in this way it was quickly discovered that the majority of shakings emanated from the north and east1 and seldom1 if ever1 passed a heavy range of mountains to the south4 ,the barricade of postcards was then extended farther northwards1 with the result of surrounding the origin of certain shocks amongst the mountains1 whilst others were traced to the sea shore4 ,by systematically pursuing earthquakes it was seen that many shocks had their origin beneath the sea--they shook all the places on the north-east coast1 but it was seldom that they crossed through the mountains1 forming the backbone of the island1 to disturb the places on the west coast4 ,the actual results obtained in three months by this method of working are shown in the accompanying map1 which embraces the northern half of the main island of ,nipon and part of ,yezo4 ,the shaded portion of the map indicates the mountainous districts1 which are traversed by ranges varying in height from about #b1jjj and #g1jjj feet4 ,the dotted lines show the boundaries of the more important groups of earthquakes which were recorded4 ,i4 is the western boundary of earthquakes1 which at places to the eastward are usually felt somewhat severely4 ,some of these have been felt the most severely at or near ,hakodadi1 whilst farther south their effects have been weak4 ,occasionally the greatest effect has been near to ,kameishi4 ,sometimes these earthquakes terminate along the western boundaries of ,,iii4 or ,,iv41 not being able to pass the high range of mountains which separate the plain of ,musashi from ,kofu4 ,illustration3 ,,fig4 #bi4--,northern ,japan4 ,mountainous districts shaded with oblique lines4 ,,ii4 is the boundary of a shock confined to the plain which surrounds ,kofu4 ,these earthquakes are evidently quite local4 ,many of the disturbances have evidently originated beneath the ocean1 having come in upon the land in the direction of the arrows ,a or ,b4 ,,iii4 ,this line indicates the boundary of a group of shocks which are often experienced in ,tokio4 ,these may come in the directions ,d1 ,e1 or ,f4 ,it is probable that some of them originate to the eastward of ,yokohama1 on or near to the opposite peninsula4 ,,iv4 ,v4 and ,,vi4 ,the earthquakes bounded by these lines probably originate in the directions ,c or ,d4 ,,vii4 ,the earthquakes bounded by this line probably come from the direction ,e4 ,,viii4 ,this line gives us the boundary of earthquakes which may come from the direction ,b4 ,the above boundaries sometimes do not extend so far to the westward as they are shown4 ,at other times1 groups like ,v4 and ,,vi4 extend farther to the south-west4 ,these earthquake boundaries1 which so clearly show the effects of high mountains in preventing the extension of motion1 have been drawn up1 not from single earthquakes1 but from a large series of earthquakes which have been plotted upon blank maps1 and are now bound together to form an atlas4 ,to give an idea of the material upon which ,i have been working1 ,i may state that between ,march #a and ,march #aj1 #ahhb1 ,i received records of no less than thirty-four distinct shocks felt in districts between ,hakodate and ,tokio1 and for each of these it is quite possible to draw a map4 ,in addition to the boundaries of disturbances given in the accompanying map1 other boundaries might be drawn for shocks which were more local in their character4 ,the groups which contained the greatest number of shocks are ,,iii41 ,,iv41 ,v41 ,,vi41 and ,,vii4 ,by work of this description it was found that a very important group of earthquakes might be studied by a line of stations commencing at ,saporo in the north1 passing through ,hakodate1 down the east coast of the main island1 to ,tokio or ,yokohama in the south4 ,a further aid to the study of this group1 together with the study of an important local group1 might be effected with the help of a few additional stations properly distributed on the plain of ,musashi1 which surrounds ,tokio4 ,with this example before us it will be recognised that the choice of sites for a connected set of seismological observatories will often be more or less a special problem4 ,if earthquake stations were to be placed in different directions around ,tokio without preliminary investigation1 it is quite possible that some of them might be so situated that they would seldom if ever work in conjunction with the remaining observatories1 and therefore be of but little value4 ,and this remark must equally apply to districts in other portions of the globe4 ,the method is crude1 and1 so far as actual earthquake origins are concerned1 it only yields results which are approximate4 ,the crudeness and the want of absoluteness in the results is1 however1 more than counterbalanced by the certainty with which we are enabled to express ourselves with regard to such results as are obtained4 ,even when working with the best instruments we have at our command1 unless we are employing some elaborate system1 this method of working gives a most valuable check upon our instrumental records1 and enables us to interpret them with greater confidence4 ,determination of earthquake origins from the direction of motion4--,if we assume that an earthquake is propagated from a centre as a series of waves1 in which normal vibrations are conspicuous1 and obtain at two localities1 not in the same straight line with the origin1 and sufficiently far separated from each other1 the direction of movement of these normal motions1 by drawing lines parallel to these directions through our two stations1 the lines would intersect at a point above the required origin4 ,if instead of two points we had three1 or1 better still1 a large number1 the results we should obtain ought to be still more certain4 ,unfortunately1 it seems that earthquakes seldom originate from a given point1 and1 further1 normal motions are not always 7sufficiently7 prominent4 ,sometimes1 as has already been shown in the chapters on earthquake motion1 they may be non-existent4 ,it is probable1 however1 that difficulties of this sort are more usually associated with non-destructive earthquakes4 ,mallet regards the destructive effects of an earthquake as almost solely due to normal motions4 ,if this be true1 for destructive earthquakes1 the problem is shorn of many of its difficulties4 ,in cases where normal vibrations are not prominent1 where we have only transverse vibrations1 motions due to the interference of normal or transverse motions1 or directions of motions due to the topographical or geological nature through which the disturbance has passed1 the determination of the origin of an earthquake by observations on the direction in which the ground has been moving appears to be a problem which is practically without a solution4 ,we will1 therefore1 only consider the determination of the origin of those earthquakes which have predominating directions in their movements1 which directions we will consider as normal ones4 ,the question which is1 then1 before us1 is the determination of the direction of these normal movements4 ,first of all we may take the evidence of our senses4 ,in exceptional cases these have given results which closely approximate to the truth1 but in the majority of cases such results are not to be relied upon1 as the inhabitants of a town will1 for the same shock1 give directions corresponding to all points of the compass4 ,much1 no doubt1 depends upon the situation of the observer1 and much1 perhaps1 upon his temperament4 ,if he is sitting in a room alone1 and is accustomed to making observations on an earthquake1 on feeling the earthquake1 if he concentrates his attention on the direction in which he is being moved1 his observations may be of value4 ,if1 however1 he is not so situated1 and his attention is not thus concentrated1 his opinions1 unless the motion has been very decided in its character1 are usually of but little worth4 ,direction determined from destruction of buildings4--,when an observer first sees a town that has been partially shattered by an earthquake1 all appears to be confusion1 and it is difficult to imagine that in such apparent chaos we are able to discover laws4 ,if1 however1 we take a general view of this destruction and compare together similarly built buildings1 it is possible to discover that similar and similarly situated structures have suffered in a similar manner4 ,by carefully analysing the destruction we are enabled to infer the direction in which the destroying forces have acted4 ,it was chiefly by observing the cracks in buildings1 and the direction in which bodies were overthrown or projected1 that ,mallet determined the origin of the ,neapolitan earthquake4 ,from the observations given in ,chapter ,,vii4 it would appear that1 with destructive earthquakes1 walls which are transverse to the direction of motion are most likely to be overturned1 whilst1 with small earthquakes1 these walls are the least liable to be fractured4 ,from a critical examination of the general nature of the damage done on the buildings of a town1 earthquake observers have shown that the direction of a shock may often be approximately determined4 ,the direction in which a body having a regular form like a prismatic gravestone or a cylindrical column is overturned sometimes gives the means by which we can determine the direction from which a movement came4 ,the rotation of bodies4--,it has often been observed that almost all large earthquakes have caused objects like tombstones1 obelisks1 chimneys1 c41 to rotate4 ,one of the most natural and at the same time most simple explanations is to suppose that during the shock there had been a twisting1 or backward and forward screw-like motion in the ground4 ,amongst the ,italians and the ,mexicans earthquakes producing an effect like this are spoken of as #8vorticosi4' ,in the ,calabrian earthquake1 not only were bodies like obelisks twisted on their bases1 but straight rows of trees seem to have been left in interrupted zigzags4 ,these latter phenomena have been explained upon the assumption of the interference of direct waves and reflected waves1 the consequence of which being that points in close proximity might be caused to move in opposite directions4 ,reflections such as these would be most likely to occur near to the junction of strata of different elasticity1 and it may be remarked that it is often near such places that much twisting has been observed4 ,another way in which it is possible for twisting to have taken place would be by the interference of the normal and transverse waves which probably always exist in an earthquake shock1 or by the meeting of the parts of the normal wave itself1 one having travelled in a direct line from the origin1 whilst the other1 travelling through variable material1 has had its direction changed4 ,mallet1 however1 has shown that the rotation may have been in many cases brought about without the supposition of any actual twisting motion of the earth--a simple backward and forward motion being quite sufficient4 ,if one block of stone rests upon another1 and the two are shaken backwards and forwards in a straight line1 and if the vertical through the centre of gravity of the upper block does not coincide with the point where there is the greatest friction between the blocks1 rotation must take place4 ,if the vertical through the centre of gravity falls on one side of the centre of friction1 the rotation would be in one direction1 whilst1 if on the other side1 the rotation would be in the opposite direction4 ,although the above explanation is simple1 and also in many cases probably true1 it hardly appears sufficient to account for all the phenomena which have been observed4 ,thus1 for instance1 if the stones in the ,yokohama cemetery1 at the time of the earthquake of #ahhj1 had been twisted in consequence of the cause suggested by ,mallet1 we should most certainly have found that some stones had turned in one direction whilst others had been twisted in another4 ,by a careful examination of the rotated stones1 ,i found that every stone--the stones being in parallel lines--had revolved in the same direction1 namely in a direction opposite to that of the hands of a watch4 ,as it would seem highly improbable that the centre of greatest friction in all these stones of different sizes and shapes should have been at the same side of their centres of gravity1 an effect like this could only be explained by the conjoint action of two successive shocks1 the direction of one being transverse to the other4 ,although fully recognising the sufficiency of two transverse shocks to produce the effects which have been observed in ,yokohama1 ,i will offer what appears to me to be the true explanation of this phenomenon3 it was first suggested by my colleague1 ,mr4 ,gray1 and appears to be simpler than any with which ,i am acquainted4 ,illustration3 ,,fig4 #cj4 ,if any columnar-like object1 for example a prism which the basal section is represented by ,a ,b ,c ,d 7see fig4 #cj71 receives a shock at right angles to ,b ,c1 there will be a tendency for the inertia of the body to cause it to overturn on the edge ,b ,c4 ,if the shock were at right angles to ,d ,c1 the tendency would be to overturn on the edge ,d ,c4 ,if the shock were in the direction of the diagonal ,c ,a1 the tendency would be to overturn on the point ,c4 ,let us1 however1 now suppose the impulse to be in some direction like ,e ,g1 where ,g is the centre of gravity of the body4 ,for simplicity we may imagine the overturning effect to be an impulse given through ,g in an opposite direction--that is1 in the direction ,g ,e4 ,this force will tend to tip or make the body bear heavily on ,c1 and at the same time to whirl round ,c as an axis1 the direction of turn being in the direction of the hands of a watch4 ,if1 however1 the direction of impulse had been ,e ,g1 then1 although the turning would still have been round ,c1 the direction would have been opposite to that of the hands of a watch4 ,to put these statements in another form1 imagine ,g ,e to be resolved into two components1 one of them along ,g ,c and the other at right angles1 ,g ,f4 ,here the component of the direction ,g ,c tends to make the body tip on ,c1 whilst the other component along ,g ,f causes revolution4 ,similarly ,g ,e may be resolved into its two components ,g ,c and ,g ,f1 the latter being the one tending to cause revolution4 ,from this we see that if a body has a rectangular section1 so long as it is acted upon by a shock which is parallel to its sides or to its diagonals1 there ought not to be any revolution4 ,if we divide our section ,a ,b ,c ,d up into eight divisions by lines through these directions1 we shall see that any shock the direction of which passes through any of the octants which are shaded will cause a positive revolution in the body--that is to say1 a revolution corresponding in its direction to that of the movements of the hands of a watch2 whilst if its direction passes through any of the remaining octants the revolution will be negative1 or opposite to that of the hands of a watch4 ,from the direction in which any given stone has turned1 we can therefore give two sets of limits between one of which the shock must have come4 ,further1 it will be observed that the tendency of the turning is to bring a stone1 like the one we are discussing1 broadside on to the shock2 therefore1 if a stone with a rectangular cross section has turned sufficiently1 the direction of a shock will be parallel to one of its faces1 but if it has not turned sufficiently it will be more nearly parallel to its faces in their new position than it was to its faces when in their original position4 ,if a stone receives a shock nearly parallel with its diagonal1 on account of its instability it may turn either positively or negatively according as the friction on its base or some irregularity of surface bearing most influence4 ,similarly1 if a stone receives a shock parallel to one of its faces1 the twisting may be either positive or negative1 but the probability is that it would only turn slightly2 whereas in the former case1 where the shock was nearly parallel to a diagonal1 the turning would probably be great4 ,determination of direction from instruments4--,when speaking about earthquakes it was shown1 as the result of many observations1 that the same earthquake in the space of a few seconds1 although it may sometimes have only one direction of motion1 very often has many directions of motion4 ,in certain cases1 therefore1 our records1 if we assume the most permanent motions to be normal ones1 give definite and valuable results4 ,in other cases it is necessary to carefully analyse the records1 comparing those taken at one station with those taken at another4 ,one remarkable fact which has been pointed out in reference to artificial earthquakes produced by exploding charges of gunpowder or dynamite1 and also with regard to certain earthquakes1 is that the greatest motion of the ground is inwards1 towards the point from which the disturbance originated4 ,should this prove the rule1 it gives a means of determining1 not only the direction of earthquake1 but the side from which it came4 ,determination of earthquake origins by time observations4--,the times at which an earthquake was felt at a number of stations are among the most important observations which can be made for the determination of an earthquake origin4 ,the methods of making time observations1 and the difficulties which have to be overcome1 have already been described4 ,when determining the direction from which a shock has originated1 or determining the origin of the shock by means of time observations1 it has been usual to assume that the velocity of propagation of the shock has been uniform from the origin4 ,the errors involved in this assumption appear to as follows3-- #a4 ,we know from observations on artificial earthquakes that the velocity of propagation is greater between stations near to the origin of the shock than it is between more remote stations2 and also the velocity of propagation varies with the initial force which produced the disturbance4 ,if our points of observation are sufficiently close together as compared with their distance from the origin of the disturbance1 it is probable that errors of this description are small and will not make material differences in the general results4 #b4 ,we have reasons for believing that the transit velocity of an earthquake is dependent on the nature of the rocks through which it is propagated4 ,errors which arise from causes of this description will1 however1 be practically eliminated if our observation points are situated on an area sufficiently large1 so that the distribution of the causes tending to alter the velocity of a shock balance each other4 ,it must be remarked1 that causes of this description may also produce an alteration in the direction of our shock4 ,other errors which may sometimes enter into our results1 when determining the origin of shocks by means of observations on velocities1 are the assumptions that the disturbance has travelled along the surface from the epicentrum and not in a direct line from the centrum4 ,again1 it is assumed that the origin is a point1 whereas it may possibly be a cavity or a fissure4 ,lastly1 if we desire extreme accuracy1 we must make due allowance for the sphericity of the earth and the differences of elevation of the observing stations4 ,i4 ,the method of straight lines4--,given a number of pairs of points ,a#j1 ,a#a1 ,b#j1 ,b#a1 ,c#j1 ,c#a1 c41 at each of which the shock was felt simultaneously1 to determine the origin4 ,theoretically if we bisect the line which joins ,a#j and ,a#a by a line at right angles to ,a#j1 ,a#a1 and similarly bisect the lines ,b#j1 ,b#a1 ,c#j1 ,c#a1 all these bisecting lines a#j1 a#a1 b#j1 b#a1 c#j1 c#a1 c41 ought to intersect in a point1 which point will be the epicentrum or the point above the origin4 ,this method will fail1 first1 if ,a#j1 ,a#a1 ,b#j1 ,b#j1 ,c#j1 ,c#a form a continuous straight line1 or if they form a series of parallel lines4 ,hopkins gives a method based on a principle similar to the one which is here employed--namely1 given that a shock arrives simultaneously at three points to determine1 the centre4 ,in this case1 the relative positions of the three points1 where the time of arrival was simultaneous1 must be accurately known1 and these three points must not lie in a straight line1 or the method will fail4 ,for practical application the problem must be restricted to the case of three points which do not lie nearly in the same straight line4 ,,ii4 ,the method of circles4--,given the times t#j1 t#a1 t#b1 c41 at which a shock arrived at a number of places ,a#j1 ,a#a1 ,a#b1 c41 to determine the position from which the shock originated4 ,suppose ,a#j to be the place which the shock reached first1 and that it reached ,a#a1 ,a#b1 ,a#c1 c41 successively afterwards4 ,let t#a - t#j a t#b - t#j b t#c - t#j c1 c4 ,with ,a#a1 ,a#b1 ,a#c1 c4 as centres1 describe circles with radii proportional to the known qualities a1 b1 c1 c41 and also a circle which passes through ,a#j and touches these circles4 ,the centre of the last circle will be the epicentrum4 ,the radii proportional to a1 b1 c1 c4 may be represented by the quantities ax1 bx1 cx1 c41 where x is the velocity of propagation of the shock4 ,it will be observed that the times at which the shock arrived at three places might alone be sufficient4 ,if1 instead of taking the times of arrival of a shock1 the arrival of a sea wave be taken1 the result would be a closer approximate to the absolute truth4 ,it will be observed that this method is not a direct one1 but is one of trial4 ,if1 however1 an imaginary case be taken1 and three given points of observation1 ,a#j1 ,a#a1 ,a#b1 be plotted on a piece of paper1 it will be found that it is not a difficult matter to determine two numbers proportional to a and b which will allow you to draw two circles so that they may be touched by a third circle drawn through ,a#j4 ,this problem has practically been applied in the case of the arrival of a sea wave at a number of places on the ,south ,american coast1 at the time of the earthquake of ,may #i1 #ahgg4 ,this is illustrated as follows4 ,the places which were chosen were ,huanillos1 ,tocopilla1 ,cobija1 ,iquique1 ,mejillones4 ,in the following table the first column gives the times at which the sea wave arrived at each of these places in ,iquique time2 in the second column the difference between these times and the time at which it reached ,huanillos is given2 in the third column the distances through which a sea wave1 propagated at the rate of #cej feet per second1 could travel during the intervals noted in the second column is given4 ---------------------------------------- ---- ,arrival ,time after ,distance at of sea arrival at#cej feet per wave ,huanillos second ---------------------------------------- ---- h4 m4 minutes miles ,huanillos #h #cj #j #j ,tocopilla #h #cb #b #h ,cobija #h #ch #h #cb ,iquique #h #dj #aj #dj ,mejillones #h #df #af #fd ---------------------------------------- ---- ,the distances marked in the third column are used as radii of the circles drawn round the places to which they respectively refer4 ,the centre of the circle drawn to touch the circles of the first column1 and at the same time to pass through ,huanillos1 is marked ,c4 ,the position from which the shock originated appears therefore to have occurred very near to a place lying in ,long4 #g #ae ,w4 and ,lat4 #ba #bb ,s4 ,illustration3 ,,fig4 #ca4 ,the actual operations which were gone through in making the accompanying map were as follows4 ,first1 the places with which we had to deal were represented on a map in orthographical projection1 the centre of projection being near to the centre of the map4 ,this was done so that the measurements which were made upon the map might be more correct than those we should obtain from an ordinary chart where this portion of the world was not the centre of projection4 ,next1 a number was taken as equal to the velocity with which the sea wave had travelled4 ,the first velocity taken was about #djj feet per second--this being about the velocity with which1 theoretically1 it must have travelled in an ocean having a depth equal to that indicated upon the charts--also it seemed to have travelled at this rate from the various times of arrival as recorded at places along the coast4 ,circles were then drawn round ,tocopilla1 ,cobija1 ,iquique1 and ,mejillones with radii equal to #b1 #h1 #aj1 and #ae1 each multiplied by 7#fj #djj74 ,it was then seen by trial that it was impossible to draw a single circle which should touch four circles and also pass through ,huanillos4 ,these four circles were1 in fact1 too large4 ,four new but smaller circles1 which are shown in the map1 were next drawn1 their radii being respectively equal to the numbers #b1 #h1 #aj1 and #af1 each multiplied by 7#fj #cej71 and it was found that a circle1 with a centre ,c1 could be drawn which would practically touch the four circles1 and at the same time would pass through ,huanillos4 ,,iii4 ,the method of hyperbolas4--,the method which ,i call that of hyperbolas is only another form of the method of circles4 ,it is1 however1 useful in special cases1 as1 for instance1 where we have the times of arrival of earthquakes at only two stations4 ,between ,tokio and ,yokohama1 at which places ,i frequently obtain tolerably accurate time records1 the method has been applied on several occasions with advantage4 ,in the preceding example let us suppose that the only time records which we had were for ,huanillos and ,mejillones1 and that the wave was felt at the latter place sixteen minutes or #ifj seconds after it was experienced at the former4 ,calling these places ,h and ,m respectively1 round ,m draw a circle equal to the #ifj multiplied by the velocity with which the wave was propagated4 ,it is then evident that the origin of this disturbance must be the centre of a circle which passes through ,h and touches the circle drawn round ,m4 ,join ,h ,m1 cutting the circle round ,m in ,y4 ,bisect ,y ,h in ,v4 ,it is evident that ,v is one possible origin for the disturbance4 ,next1 from ,m1 in the direction of ,h1 draw any line ,m ,z ,p2 join ,z ,h2 bisect ,z ,h at right angles by the line ,o ,p ,n4 ,because ,,ph ,,pz1 it is evident that ,p is a second possible origin4 ,proceeding in this way a series of points lying to the right and left of ,v on the curve ,r ,v ,t may be found1 and we may therefore say that the origin lies somewhere in the curve ,r ,v ,t4 ,by increasing or decreasing our velocity we vary the position of the curve ,r ,v ,t1 and1 instead of a line on which our origin may be1 we obtain a band4 ,as the assumed velocity increases1 the circle round ,m becomes larger1 and has its limit when it passes through ,h1 where the two arms of the curve ,r ,v ,t will close together and form a prolongation of the line ,m ,y ,h as the assumed velocity diminishes4 ,the circle round ,m becomes smaller until it coincides with the point ,m4 ,at such a moment the curve ,r ,v ,t opens out to form a straight line bisecting ,m ,h at right angles4 ,the curve ,r ,v ,t is a hyperbola with a vertex ,v and foci ,h and ,m4 ,inasmuch as ,,pm - ,,ph a constant quantity4 ,if we have the time given at which the shock or wave arrived at a third station as at ,iquique1 it is evident that a second hyperbola ,r ,v ,t might be drawn with ,iquique and ,huanillos as foci1 and that the mutual intersection of these two hyperbolas with a third hyperbola1 having for its foci ,iquique and ,mejillones1 would give the origin of the wave4 ,the obtaining of a mutual intersection would depend on the assumed velocity1 and the accuracy of the result1 like that of the method of circles1 would depend upon the trials we made4 ,the method here enunciated may be carried farther by describing hyperboloids instead of hyperbolas1 the mutual intersection of which surfaces would1 in the case of an earth wave1 give the actual origin or centrum rather than the point above the origin or epicentrum4 ,,iv4 ,the method of co-ordinates4--,given the times at which a shock arrived at five or more places1 the position of which we have marked upon a map1 or chart1 to determine the position on the map of the centre of the shock1 its depth1 and the velocity of propagation4 ,commencing with the place which was last reached by the shock1 call these places p1 p#a1 p#b1 p#c1 and p#d1 and let the times taken to reach these places from the origin be respectively t1 t#a1 t#b1 t#c1 and t#d4 ,through p draw rectangular co-ordinates1 and with a scale measure the co-ordinates of p#a1 p#b1 p#c1 and p#d1 and let these respectively be a#a1 b#a2 a#b1 b#b2 a#c1 b#c2 a#d1 b#d4 ,then if x1 y1 and z be the co-ordinates of the origin of the shock1 d1 d#a1 d#b1 d#c1 and d#d1 the respective distances of p1 p#a1 p#b1 p#c1 and p#d from this origin1 and v the velocity of the shock1 we have #a4 x#b y#b z#b d#b v#b t#b #b4 7a#a - x7#b 7b#a - y7#b z#b v#b t#ab #c4 7a#b - x7#b 7b#b - y7#b z#b v#b t#bb #d4 7a#c - x7#b 7b#c - y7#b z#b v#b t#cb #e4 7a#d - x7#b 7b#d - y7#b z#b v#b t#db ,because we know the actual times at which the waves arrived at the places p1 p#a1 p#b1 p#c1 p#d1 we know the values t--t#a1 t--t#b1 t--t#c1 t--t#d4 ,call these respectively m1 p1 q1 and r4 ,suppose t known1 then t#a t - m t#b t - p t#c t - q t#d t - r4 ,subtracting equation ,no4 #a from each of the equations #b1 #c1 #d1 and #e1 we obtain1 a#ab b#ab - #b;a#a x - #b;b#a y v#b 7t#ab - t#b7 v#b 7m#b - #bt m7 a#bb b#bb - #b;a#b x - #b;b#b y v#b 7t#bb - t#b7 v#b 7p#b - #bt p7 a#cc b#cb - #b;a#c x - #b;b#c y v#b 7t#cb - t#b7 v#b 7q#b - #bt q7 a#db b#db - #b;a#d x - #b;b#d y v#b 7t#db - t#b7 v#b 7r#b - #bt r7 ,now let v#b u1 and #bv#b t w4 ,then #a4 #b;a#a x #b;b#a y u m#b - n m a#ab b#ab #b4 #b;a#b x #b;b#b y u p#b - n p a#bb b#bb #c4 #b;a#c x #b;b#c y u q#b - n q a#cb b#cb #d4 #b;a#d x #b;b#d y u r#b - n r a#db b#db ,we have here four simple equations containing the four unknown quantities x1 y1 u1 and w4 x and y determine the origin of the shock4 ,the absolute velocity v equals u4 ,from v and w we obtain t4 ,substituting x1 y1 v1 and t in the first equation we obtain z4 ,we have here assumed that the points of observation have all about the same elevation above sea level4 ,if it is thought necessary to take these elevations into account1 a sixth equation may be introduced4 ,if the propagation of the wave is considered as a horizontal one1 as would be done when calculating the position of the epicentrum or point above the origin1 by means of the times of arrival of a sea wave1 the ordinate z of the first five equations would be omitted4 ,working in this way the resulting four equations1 viz4 #b;a#a x #b;b#a y um#b - wm#b a#ab b#ab c4 c4 c4 remained unchanged4 ,applying this method to the same example as that used as illustration for the two previous methods1 we obtain for the co-ordinates of ,mejillones1 ,iquique1 ,cobija1 ,tocopilla1 and ,huanillos1 measured in geographical miles1 and the times in ,iquique time at which the wave reached each1 as given in the following table2 ox and oy being1 drawn through ,mejillones4 ---------------------------------------- ------------------- ,co-ordinates ,time of arrival ---------------------------------------- ------------------ ,,ox ,,oy h4 m4 ,mejillones a or #j b or #j #h #df p4 m4 ,iquique a#a or #aej b#a or #if #h #dj ,cobija a#b or #cf b#b or #ad #h #ch ,tocopilla a#c or #ff b#c or #ca #h #cb ,huanillos a#d or #ajb b#d or #eh #h #cj ---------------------------------------- ------------------ ,from this data we find the co-ordinates x and y of this origin to be #heh and #efg2 whilst the velocity of propagation #de feet per second4 ,measuring these ordinates upon the map1 we obtain a centre lying very near ,long4 #ga #e ,w4 and ,lat4 #ba #bb ,s41 a position which is very near to that which has already been obtained by other methods4 ,if instead of ,huanillos we substitute the ordinates and time of arrival of the sea wave for ,pabalon de ,pica1 another point for the origin will be obtained lying farther out at sea4 ,to obtain the best result1 the method to be taken will evidently be1 first to reject those places at which it seems likely that some mistake has been made with the time observations1 and then with the remaining places to form as many equations as possible1 and from these to obtain a mean value4 ,this is a long and tedious process1 and as the time observations of this particular earthquake are probably one and all more or less inaccurate1 it is hardly worth while to follow the investigation farther4 ,in this example1 as in the preceding ones1 it will be observed that it has been sea waves that have been dealt with1 rather than earth vibrations4 ,it is evident1 however1 that these latter vibrations may be dealt with in a similar manner4 ,in these determinations it will also have been observed that it is assumed that the disturbance has radiated from a centre1 and1 therefore1 approached the various stations in different directions4 ,if we assume that we have three stations very near to each other as compared with their distances from the origin1 so that we can assume that the wave fronts at the various stations were parallel1 the determination of the direction in which the wave advanced appears to be much simplified4 ,the determination of the direction in which a wave has passed across three stations was first given by ,professor ,haughton4 ,haughton's method4--,given1 the time of an earthquake shock at three places1 to determine its horizontal velocity and coseismal line4 ,the solution of this is contained in the formula a 7t#b - t#a7 sin tan ---------------------------------------- ---------------------------------------- ----------------------------4 c 7t#c - t#b7 a 7t#b - t#a cos ,when ,a1 ,b1 and ,c are three stations at which a shock is observed at the times t#a1 t#b1 and t#c2 a1 b1 and c are the distances between ,a1 ,b1 and ,c1 and is the angle made by the coseismal lines x ,a x1 y ,b y1 and the line ,a ,b1 which are assumed to be parallel4 ,this ,i applied in the case of the ,iquique earthquake1 but owing to the smallness of the angles between the three stations ,a1 ,b1 and ,c1 the result was unsatisfactory4 ,the problem ought to be restricted1 first1 to places which are a long distance away from a centre1 and1 secondly1 to places which are not nearly in a straight line4 ,this problem may be solved more readily by geometrical methods4 ,plot the three stations ,a1 ,b1 and ,c on a map1 join the two stations between which there was the greatest difference in the time observation4 ,let these1 for example1 be ,a and ,c4 ,divide the line ,a ,c at point ,d1 so that ,a ,d 3 ,d ,c as the interval between the shock felt at ,a and ,b is to the interval between the shock felt at ,b and ,c4 ,the line ,b ,d will be parallel to the direction in which the wave advanced4 ,the difference in time of the arrival of two disturbances4--,in the various calculations which have been made to determine an origin based on the assumption of a known or of a constant velocity1 we have only dealt with a single wave1 which may have been a disturbance in the earth or in the water4 ,a factor which has not yet been employed in this investigation is the difference in time between the arrival of two disturbances2 one propagated1 for instance1 through the earth1 and the other1 for example1 through the ocean4 ,the difference in the times of the arrival of two waves of this description is a quantity which is so often recorded that it is well not to pass it by unnoticed4 ,to the waves mentioned we might also add sound waves1 which so frequently accompany destructive earthquakes1 and1 in some localities1 as1 for instance1 in ,kameishi1 in ,north ,japan1 are also commonly associated with earthquakes of but small intensity4 ,it was by observing the difference in time between the shaking and the sound in different localities that ,signor ,abella was enabled to come to definite conclusions regarding the origin of the disturbances which affected the province of ,neuva ,viscoya in the ,philippines1 in #ahha2 the places where the interval of time was short1 or the places where the two phenomena were almost simultaneous1 being1 in all probability1 nearer to the origin than when the intervals were comparatively large4 ,i myself applied the method with considerable success when seeking for the origin of the ,iquique earthquake of #ahgg4 ,the assumptions made in that particular instance were1 first1 that the velocity of the disturbance through the earth was known1 and1 secondly1 that the velocity with which a sea wave was propagated was also known4 ,a method similar to the above was first suggested by ,hopkins4 ,it depended on the differences of velocity with which normal and transversal waves are propagated4#he ,seebach's method4--,to determine the true velocity of an earthquake1 the time of the first shock1 and the depth of the centre4 ,illustration3 ,,fig4 #cb4 ,let the straight line ,m1 m#a1 m#b1 m#c represent the surface of the earth shaken by an earthquake4 ,for small earthquakes1 to consider the surface of the earth as a plane will not lead to serious errors4 ,if an earthquake originates at ,c1 then to reach the surface at ,m it traverses a distance h in the time t4 ,to reach the surface at ,m#a it traverses a distance h x#a in a time t#b4 ,if v equals the velocity of propagation1 h h x#a then t ------1 t#a --------------------------1 v v h x#b t#b --------------------------1 c4 v ,seebach now says that if we have given the position of ,m or epicentrum of the shock1 and draw through it rectangular axes like ,m m#c and ,m ,t#c1 and lay down on ,m m#c in miles the distances from ,m of the various stations which have been shaken1 and in equal divisions for minutes lay down on ,m ,t#c the differences of time at which ,m1 m#a1 m#b1 c4 were shaken1 then ,m#a ,t#a1 ,m#b ,t#b1 c4 are the co-ordinates of points on an hyperbola4 ,the degree of exactness with which this hyperbola is in any given case constructed is a check upon the accuracy of the time observations and the position of the epicentrum4 ,the apex of the hyperbola is the epicentrum4 ,the intersection of the asymptote with the ordinate axis is the time point of the first shock1 which1 because the scale for time and for space were taken as equal1 gives the absolute position of the centrum4 ,this intersection is shown by dotted lines4 ,knowing the position of the centrum1 we can directly read from our diagram how far the disturbance has been propagated in a given time4 ,,chapter ,,xi4 ,,the ,,depth ,,of ,,an ,,earthquake ,,centrum4 ,the depth of an earthquake centrum--,greatest possible depth of an earthquake--,form of the focal cavity4 ,depth of centrum4--,the first calculations of the depth at which an earthquake originated were those made by ,mallet for the ,neapolitan earthquake of #aheg4 ,these were made on the assumption that the earth wave radiated in straight lines from the origin1 and1 therefore1 at points at different distances from the epicentrum it had different angles of emergence4 ,these angles of emergence were chiefly calculated from the inclination of fissures produced in certain buildings1 which were assumed to be at right angles to the direction of the normal motion4 ,if we have determined the epicentrum of an earthquake and the muzoseismal circle1 and make either the assumption that the angle of emergence in this circle has been #de or #ed #dd #i 7see page #ed71 it is evidently an easy matter by geometrical construction to determine the depth of the centrum4 ,hfer followed this method when investigating the earthquake of ,belluno4 ,other methods of calculation which have been employed are based on time observations1 as1 for instance1 the method of ,seebach1 the method of co-ordinates1 the method of hyperboloids or spheres 7see pages #bjj-bab74 ,by means of a number of lines parallel to twenty-six angles of emergence1 drawn in towards the seismic vertical1 ,mallet found that twenty-three of these intersected at a depth of #g geographical miles4 ,the maximum depth was #h geographical miles1 and the minimum depth #b geographical miles4 ,the mean depth was taken at a depth of #e geographical miles where1 within a range of #ab1jjj feet1 eighteen of the wave paths intersected the seismic vertical4 ,the point where these wave paths start thickest is at a depth not greater than three geographical miles1 and this is considered to be the vertical depth of the focal cavity itself4 ,for the ,yokohama earthquake of #ahhj1 from the indications of seismometers1 and by other means1 certain angles of emergence were obtained1 leading to the conclusion that the depth of origin of that earthquake might be between #a and #e miles4 ,possibly1 perhaps1 the earthquake may have originated from a fissure the vertical dimensions of which was comprised between these depths4 ,a source of error in a calculation of this description is that the vertical motions may have been a component of transverse motions or perhaps due to the slope of surface waves4 ,the following table of the depths at which certain earthquakes have originated has been compiled from the writings of several observers4 ---------------------------------------- ---------------------- ,in feet ---------------------------------------- ------------------- ,minimum ,mean ,maximum ,rhineland #ahdf 7,schmidt7 #abg1cji ,sillien #aheh 7,schmidt7 #hf1agc ,middle ,germany #ahgb 7,seebach7 #dg1bbe #eh1iab #gj1hda ,herzogenrath #ahgc 7,lasaulx7 #af1eec #cf1eaf #ef1dgg ,neapolitan #aheg 7,mallet7 #af1gje #cd1icj #di1cei ,yokohama #ahhj 7,milne7 #g1ibj #ag1bfj #bf1djj ---------------------------------------- ------------------- ,a table similar to this has been compiled by ,lasaulx4#hf ,with the exception of the determination for the two last disturbances these calculations have been made with the assistance of the method of ,seebach1 which depends1 amongst other things1 on the assumptions of exact time determinations1 direct transmission of waves from the centrum1 and a constant velocity of propagation4 ,admitting that our observations of time are practically accurate1 it appears that the other assumptions may often lead to errors of such magnitude that our results may be of but little value4 ,from what has been said respecting the velocity with which earth disturbances are propagated1 it seems that these velocities may vary between large limits1 being greatest nearest to the origin4 ,if we refer to ,seebach's method1 we shall see that a condition of this kind would tend to make the differences in time between various places1 as we recede from the epicentrum1 greater than that required for the construction of the hyperbola4 ,the curve which is obtained would1 in consequence1 have branches steeper than that of the hyperbola1 and the resultant depth1 obtained by the intersection of the asymptotes of this curve with the seismic vertical1 indicates an origin which may be much too great4 ,another point worthy of attention1 which is common to the method of ,mallet as well as to that of ,seebach1 is the question whether the shock radiates directly from the origin1 or is propagated from the origin more or less vertically to the surface1 and then spreads horizontally4 ,we know that earthquakes1 both natural and artificial1 may be propagated as undulations on the surface of the ground1 and that the vertical motion of the latter1 as testified by the records of well-constructed instruments1 has no practical connection with the depth from which the disturbance originated4 ,in cases like these1 the direction of cracks in buildings1 and other phenomena usually accredited to a normal radiation1 may in reality be due to changes in inclination of the surface on which the disturbed objects rested4 ,when our points of observation are at a distance from the epicentrum of the disturbance which1 as compared with the depth of the same1 is not great1 calculations or observations based on the assumption of a direct radiation of the disturbance may possibly lead to results which are tolerably correct4 ,the calculations of ,mallet for the ,neapolitan earthquake appear to have been made under such conditions4 ,for smaller earthquakes1 and for places at a distance from the seismic vertical of a destructive earthquake1 the results which are deduced from the observations on shattered buildings1 and all observations based upon the assumption of direct radiation1 we must accept with caution4 ,another error which may enter into calculations of this description is one which has been discussed by ,mallet at some length4 ,this is the effect which the form and the position of the focal cavity may have upon the transmission of waves4 ,should the impulse originate from a point or spherical cavity1 then we might1 in a homogeneous medium perhaps1 regard the isoseismals as concentric circles1 and expect to find that equal effects had been produced at equal distances from the epicentrum4 ,should1 however1 this cavity be a fissure1 it is evident that even in a homogeneous medium the inclination of the plane of such a cavity will have considerable effect upon the form of the waves which would radiate from its two walls4 ,for example1 let it be assumed that the first impulse of an earthquake is due to the sudden formation of a fissure1 rent open from its centre1 and that the waves leave the walls at all points normal to its surface4 ,then1 as ,mallet points out1 it is evident that the disturbance will spread out in ellipsoidal waves1 the greatest axis of which will be perpendicular to the plane of the fissure4 ,by taking a number of cases of fissures lying in various directions and drawing the ellipsoidal waves which would result from an elastic pressure1 like that of steam suddenly admitted into such cavities1 the differences in effect which would be simultaneously produced by these waves on reaching the surface can be readily understood4 ,the following example of an investigation on this subject will serve as an example to illustrate the general nature of the many other cases which might be taken4 ,illustration3 ,,fig4 #cc4 ,let a disturbance simultaneously originate from all points of the fissure f f4 ,this will spread outwards in ellipsoidal shells to the surface of the earth e e4 ,the major axis of these ellipsoidal shells will be the direction of greatest effect4 ,in the direction c d the waves will plunge into the earth1 and places to the right side of the fissure will1 to use an expression due to ,stokes1 when speaking of analogous phenomena connected with sound1 be in earthquake shadow4 ,the same expression has been employed1 somewhat differently1 when speaking of the effects produced on buildings4 ,for places1 like s and p1 situated at equal distances from the seismic vertical1 it is evident that the intensity of the shock will be different1 and also its time of arrival4 ,it will also be observed that the isoseismals will take the form of ovals or distorted ellipses1 the larger or fuller end of which being to the left of the fissure4 ,other cases1 like those just given1 which are discussed by ,mallet in his account of the ,neapolitan earthquake1 are where the fissure forms the division between materials of different elasticities4 ,in the hard and more elastic material the waves will be more crowded1 the velocity of a wave particle will be greater1 and the transit will be quicker than in the less elastic medium4 ,the result is that the distance of equal effect from the seismic vertical will be greatest in the direction of the more compressible material4 ,unless these considerations are kept carefully before the mind when investigating the depth and1 we may add1 the position and form of the centrum of an earthquake1 serious errors may arise4 ,greatest depth of an earthquake origin4--,a curious but instructive calculation which ,mallet made was a determination of the greatest possible depth at which an earthquake may occur4 ,this calculation is based upon the idea that the impulsive effect of an earthquake has an intimate relationship with the height of neighbouring volcanoes1 the column of lava supported on a volcanic cone being a measure of the internal pressure tending to rupture the adjacent crust of the earth4 ,mitchell1 in #agjj1 virtually propounded this idea1 when he suggested that the velocity of propagation of an earthquake was related to the height of such a column4#hg ,mallet showed that there was probably considerable truth in such a supposition by appealing to the results of actual observation4 ,the pressure gauge of the ,neapolitan district would be ,vesuvius1 the height of which has in round numbers varied between #c1ejj to #d1jjj feet4 ,one of the most destructive earthquakes in this district--namely1 the one of #aheg--projected bodies with an initial velocity of about fifteen feet per second4 ,the ,riobamba earthquake1 which projected bodies with an initial velocity of eighty feet per second1 appears to have been the most violent earthquake1 so far as its impulsive effort is concerned1 of which we have any record4 ,it occurred amongst the ,andes1 where there are volcanoes from #af1jjj to #ba1jjj feet in height4 ,comparing these two earthquakes together1 we see that the ,riobamba shock had a destructive power #ecc times that of the ,neapolitan shock1 and we also see that the ,riobamba volcanoes were about #ecc times higher than ,vesuvius4 ,the accordance in these quantities is certainly interesting1 and tends to substantiate the idea that volcanoes are barometrical-like pressure gauges of a district4 ,carrying the argument still further4 ,mallet says that if the depth of origin of earthquakes were the same1 then the area of disturbance would1 for like formations and configuration of surface1 be a measure of the earthquake effort1 and also some function of the velocity of the wave4 ,from this we may generally infer #8that earthquakes1 like that of ,lisbon1 which have a very great area of sensible disturbance1 have also a very deep seismal focus1 and also the greatest depth of seismal focus within our planet is probably not greater than that ascertained for this ,neapolitan earthquake1 multiplied by the ratio that the velocity of the ,riobamba wave bears to that of its wave1 or1 what is the same thing1 by the ratio of the altitudes of the volcanoes of the ,andes to that of ,vesuvius4' ,now1 as the depth of the ,neapolitan shock may be taken at #cd1icj feet1 the greatest probable depth of origin of any earthquake impulse occurring in our planet is limited to #eccc #d1icj feet1 or #cjfd geographical miles4 ,ingenious as this argument is1 we can hardly admit it without certain qualifications4 ,first1 we are called upon to admit the identity of the originating cause of the volcano and the earthquake--as to what may be the originating cause of earthquakes we have yet to refer1 but certainly in the case of particular earthquakes1 as1 for instance1 those which occur in countries like ,scotland1 ,scandinavia1 and portions of ,siberia1 the direct connection between these phenomena are not at first sight very apparent4 ,secondly1 even if we admit the identity of the origin of these phenomena1 it is not difficult to imagine that the fluid pressure brought to bear upon certain portions of the crust of the earth may possibly in many instances be infinitely greater than that indicated by the height of the column of liquid lava in the throat of a volcano1 the true height of which we are unable to obtain4 ,further1 in certain instances such a column only appears to be a measure of the pressure upon the crust of the earth in the immediate vicinity of the cone4 ,thus1 in the ,sandwich ,islands1 we have lava standing in the throat of the volcano of ,mauna ,loa #aj1jjj feet higher than it stands in the crater ,kilauea1 only twenty miles distant4 ,that these columns should be measures of the same pressure1 originating in a general subterranean liquid layer with which they are connected1 is a supposition difficult to satisfactorily substantiate4 ,another measure of the impulsive efforts which subterranean forces may exert upon the crust above them is evidently the height to which volcanoes eject materials4 ,cotopaxi is said to have hurled a #bjj-ton block of stone nine miles4 ,sir ,w4 ,hamilton tells us that in #aggi ,vesuvius shot up a column of ashes #aj1jjj feet in height2 and ,judd tells us that this same mountain in #ahgb threw up vapours and rock fragments to the enormous height of #bj1jjj feet4 ,this would indicate an initial velocity of #a1aca feet per second4 ,notwithstanding ,mallet's calculation that thirty miles is the limiting depth for the origin of an earthquake1 the origin of the ,owen's ,valley earthquake of ,march #ahgb was estimated as being at least fifty miles4#hh ,form of the focal cavity4--,among the various problems which are put before those who study the physics of the interior of our earth it would at first sight appear that there was none more difficult than the attempt to determine the form of the cavity1 if it be a cavity1 from which an earthquake originates4 ,almost all investigators of seismology have recognised that the birthplace of an earthquake is not a point1 and have made suggestions about its general nature4 ,the ordinary supposition is that the earthquake originates from a fissure1 and if the focus of a disturbance could be laid bare to us it would have the appearance of a fault such as we so often see exposed on the faces of cliffs4 ,a strong argument1 tending to demonstrate that some of the shakings which are felt in ,japan are due to the production of such fissures1 is the fact that the vibrations which are recorded are transverse to a line joining the point of observation and the district from which1 by time observations1 we know the shock to have originated4 ,the most probable explanation of this phenomena appears to be that one mass of rock has been sliding across another mass1 giving rise to shearing strains1 and producing waves of distortion4 ,the first seismologist who attacked the problem of finding out the dimensions and position of such a fissure was ,mallet1 when working on the ,neapolitan earthquake of #aheg4 ,the reasons that the origin should1 in the first place1 have been a fissure1 rather than any other form of cavity1 was that such a supposition seemed to be a priori the most probable1 and1 further1 that it afforded a better explanation of the various phenomena which were observed1 than that obtained from any other assumption4 ,the method on which ,mallet worked to determine the form and position of the assumed fissure1 which method was subsequently more or less closely followed by other investigators1 was as follows3-- ,from an observation of the various phenomena produced upon the surface of the disturbed area1 a map of isoseismals was constructed4 ,these were seen1 as has been the case with many earthquakes1 not to distribute themselves in circles round the epicentrum1 but as distorted oval or elliptical figures1 the major axes of which roughly coincided with each other4 ,further1 the epicentrum1 did not lie in the centre of these ovals1 but was near to the narrow end where they converged4 ,this at once showed1 if the reasoning respecting the manner in which waves are propagated from an inclined fissure be correct1 that the fissure was at right angles to the major axis of the curves1 dipping from their narrow end downwards1 in the direction of their larger widespread ends4 ,the next weapon which ,mallet employed to attack this problem was the sound which was heard at different points round about the focus4 ,these sounds appear to have been of the nature of sudden explosive reports accompanied by rushing1 rolling sounds4 ,the form of the area in which these sounds were heard was closely similar to that of the first two isoseismals4 ,except in the central area of great disturbance1 no sound was heard to accompany the shock4 ,those at the northern and southern extremity of the sound area all described what they heard as a #8low1 grating1 heavy1 sighing rush1 of twenty to sixty seconds' duration4' ,those in the middle and towards the east and west boundaries of this area described a sound of the same tone1 but shorter and more abrupt1 and accompanied with more rumbling4 ,the nature of the arguments which were followed in discussing the sound observations will be found in the chapter relating to these phenomena4 ,a portion of the argument which it is difficult to follow relates to the maximum rate at which it can be supposed possible for a fissure to be rent in rocks1 which rate depends on the density and elasticity of these rocks and other constant factors4 ,next it was observed that the paths of the waves drawn on the surface1 although generally intersecting in a point1 did not do so absolutely1 but along a line passing through the main focus some #g miles in length4 ,this1 coupled with the observations of sounds1 led to the supposition that the centre of disturbance1 considered horizontally1 originated along a curved line passing through the chief focus and the various intersections of the wave paths4 ,the last phenomena brought forward to assist in the solution of this interesting problem were a study of the tremulous movements that preceded and followed the shock1 and their relation to the sound phenomena4 ,if the earthquake originated by the formation of a fissure1 after the rending has gone on for a certain time the focal cavity is enlarged to a certain extent1 and the great shock takes place4 ,this would be followed by concluding tremulous waves4 ,a succession of phenomena like those accompanied the shock about which ,mallet writes4 ,by observations such as these1 coupled with what has been said about the maximum and mean depths of the focal cavity1 ,mallet came to the conclusion that the focal cavity was a fissure1 the rending open of which produced the earthquake4 ,the vertical dimensions of this cavity were not more than #ec miles1 but were probably limited to three miles4 ,from the intersection of the wave paths upon the surface and the observed emergences1 this fissure followed horizontally a curve of double flexure1 about nine geographical miles in length4 ,the area of this fissure was twenty-seven geographical miles4 ,the time of rending it open in ,apennine limestone would be about #g seconds1 which should be the same as the period during which tremors were felt4 ,the time actually recorded was six or eight seconds4 ,briefly1 this is1 then1 the line of reasoning which was followed by ,mallet in an investigation the results of which are as interesting as they are startling4 ,since the line of investigation has been opened1 and the existence of new problems has been indicated1 other investigators1 although not exactly following ,mallet's method in all their details1 have1 when endeavouring to attain the same ends1 employed similar weapons4 ,thus1 for example1 ,seebach1 when determining the depth and nature of the origin of the earthquake of ,middle ,germany1 reasoned somewhat as follows3-- ,had the origin been more or less of a spherical cavity1 then the region of most violent disturbance upon the surface would1 according to a theorem we have already mentioned1 have been upon or near a circle of about #hh miles in radius round the epicentrum4 ,this region1 however1 was found by observation to lie along a curved band about forty miles in length1 altogether on one side of the epicentrum4 ,to explain this anomaly ,seebach followed ,mallet1 and assumed that the origin was not a spherical cavity1 but a fissure4 ,the depth and strike of this fissure was determined by the observation that the area of greatest disturbance was along a curved line lying radial to the epicentrum4 ,such a condition it was assumed indicated that the fissure of origin must be inclined towards this area of greatest disturbance4 ,a line was then drawn from this area to the centrum4 ,a second line at right angles to this one gave the dip of the fissure4 ,hfer1 when working on the earthquake of ,belluno1 came to the conclusion that the disturbance originated from two faults meeting each other at an angle of #fj4 ,in this determination he was chiefly influenced by the form of a certain homoseist which was of the form of an elongated ellipse met on one side by a second ellipse1 the principal axes of the two ellipses giving the strike of the two faults4 ,,chapter ,,xii4 ,,distribution ,,of ,,earthquakes ,,in ,,space ,,and ,,time4 ,general distribution of earthquakes--,occurrence along lines--,examples of distribution--,italian earthquake of #ahgc--;,in ,tokio--,extension of earthquake boundaries--,seismic energy in relation to geological time2 to historical time--,relative frequency of earthquakes--,synchronism of earthquakes--,secondary earthquakes4 ,general distribution of earthquakes4--,the records of earthquakes collected by various seismologists lead us to the conclusion that at some time or other every country and every ocean in the world has experienced seismic disturbances4 ,in some countries earthquakes are felt daily1 and from what will be said in the chapter on earth pulsations it is not unlikely that every large earthquake might with proper instrumental appliances be recorded at any point on the land surfaces of our globe4 ,the area over which any given earthquake extends is indeterminate4 ,the area over which an earthquake is sensible is sometimes very great4 ,the ,lisbon shock of #agee is estimated as having been sensible over an area of #c1cjj miles long and #b1gjj miles wide1 but in the form of tremors and pulsations it may have shaken the whole globe4 ,the regions in which earthquakes are frequent are indicated in the accompanying map1 which1 to a great extent1 is a reproduction of a map drawn by ,mallet4 ,the regions coloured with the darkest tint are those where great earthquakes are the most frequent4 ,the actual number of earthquakes which have been felt in the differently coloured areas are given1 when speaking of the relation of seismic energy to season4 ,when looking at this chart it must be remembered that if we were to make a detailed map of any one of the different countries where earthquakes are frequent1 we should find in it all the differences that we observe in the general chart4 ,for instance1 one portion of ,japan1 where perhaps sixty shocks are felt per year1 would be coloured with a dark tint1 whilst other portions of the same country1 where there is only one slight shaking felt every few years1 would be left almost uncoloured4 ,the black dots indicating the position of volcanic vents are even more general in their signification than the tinted areas4 ,professor ,haughton gives for the world a list of #djg volcanoes1 #bbe of which are active4 ,these numbers are the same as those given by ,a4 von ,humboldt4 ,of the active volcanoes #agb are on the margin of the ,pacific1 and of the total number eight are in ,japan4 ,from my own observations in ,japan independently of the ,kurile ,islands1 ,i have enumerated fifty-three volcanoes which are either active or have been active within a recent period4 ,in a few years' time this list will probably be increased4 ,i mention this fact to show how very imperfect our knowledge is respecting the number of volcanic vents existing on our globe4 ,if we were in a position to indicate the volcanoes which had been in eruption during the last #d1jjj years1 the probability is that they would number several thousands rather than four or five hundred4 ,an inspection of the map shows that earthquakes chiefly occur in volcanic and mountainous regions4 ,the most earthquake-shaken regions of the world form the boundaries of the ,pacific ocean4 ,it may be remarked that these boundaries slope beneath the neighbouring ocean at a much steeper angle than the boundaries of countries where earthquakes occur but seldom4 ,the coasts of ,south ,america1 ,kamschatka1 the ,kuriles1 ,japan1 and the ,sandwich ,islands1 for example1 have slopes beneath the ,pacific from one in twenty to one in thirty4 ,the coasts of ,australia1 ,scandinavia1 and the eastern parts of ,south ,america1 where earthquakes are practically unknown1 have slopes from one in fifty to one in two hundred and fifty4 ,many earthquakes have taken place in mid-ocean4 ,in the ,atlantic ,ocean ,m4 ,perrey has given about #adj instances of such occurrences4 ,the majority of the earthquakes which shake ,japan appear to have their origin in the neighbouring ocean4 ,if we could draw a map of earthquake origins1 it is probable that the greater number of the marks indicating these origins would be found to be suboceanic and along lines parallel to the shores of continents and islands which rise steeply from the bed of deep oceans4 ,in countries like ,switzerland and ,india1 our marks would hold a relationship to the mountains of these countries4#hi ,looking at the broad features of the globe1 we see on its surface many vast depressions4 ,some of these saucer-like hollows form land surfaces1 as in central ,asia4 ,the majority of these1 however1 are occupied by the oceans4 ,active volcanoes chiefly occur near the rim of the hollows which have the steepest slopes4 ,the majority of earthquakes probably have their origin on or near the bottom of these slopes4 ,to these1 however1 there are exceptions1 as for instance the earthquakes in the ,alps1 in the hills of ,scotland1 and the shakings which are occasionally felt in countries like ,egypt4 ,the earthquakes which shake the borders of the ,pacific have their origins in1 and their effects are almost exclusively felt on1 the sides of the bounding ridge facing this ocean4 ,in ,japan it is the eastern sides of the islands which suffer1 the western side being almost as free from these convulsions as ,england4 ,similar remarks may be made about the eastern side of ,south ,america1 especially the southern portion of the continent4 ,at ,buenos ,ayres1 for example1 there has been no disturbance since ,mendoza was destroyed1 some twenty years ago4 ,in ,british ,guiana slight shocks are occasionally felt in the low delta which forms the settled portion of the colony1 but they are extremely rare4 ,disturbances in lines or zones4--,it has often been observed that disturbances are propagated along the length of mountains or valleys1 and it is but seldom that earthquakes cross them transversely4 ,thus the valleys of the ,rhone1 the ,rhine1 and the ,danube are lines along which disturbances travel4 ,the major axes of the elliptical areas of disturbances which have shaken ,india have a general direction parallel to the valley of the ,ganges along the flanks of the ,himalayas4 ,the disturbances which have shaken ,london appear to have been chiefly east and west1 or along the valley of the ,thames4 ,in ,south ,america the line of disturbance is along the western sides of the ,andes4 ,another line is along the northern coast of the continent through ,andalusia and ,caraccas towards the ,antilles and ,trinidad4 ,the shocks of the ,pyrenees are chiefly felt along the southern side of these mountains4 ,in the middle and on the northern side they are but seldom felt4 ,this propagation in lines or zones may in certain cases be apparent rather than real4 ,thus the north and south ranges of mountains in ,japan are mountains almost simultaneously shaken along their eastern flanks1 giving the impression that an earthquake had originated simultaneously from a fissure parallel to this line1 or else1 starting at one end1 had run down their lengths4 ,time observations have1 however1 shown that such disturbances had their origin at some distance in the ocean1 and1 travelling inwards1 had reached all points on the flanks of these mountains almost simultaneously4 ,the same explanation will probably hold for the so-called linear disturbances of western ,south ,america4 ,all earthquake disturbances have probably a tendency to radiate from their source1 and are only prevented from doing so by meeting with heavy mountainous districts1 which by their mass and structure absorb the energy communicated to them4 ,much energy is also lost by emergence on the open flanks of a range of mountains4 ,rather than say that high mountains often bound the extension of an earthquake1 or that earthquakes appear to run along the flanks of such mountains1 we might say that earthquakes have boundaries parallel to the strike of the rocks in a given district1 that such a direction is the one in which the propagation is the easier4 ,rossi is of opinion that volcanic fractures play an important part in governing the distribution of seismic disturbances4 ,when a volcano is formed1 a series of starlike fractures are formed round the central crater4 ,secondary craters may indicate the line of these fissures4 ,the mountains about ,rome are regarded as typical of this radial structure4 ,the more distant the secondary craters are from the centre of the system1 the smaller will they be1 and also the younger4 ,if two fissures intersect we get a larger crater at the junction4 ,earthquakes are propagated along the direction of these fissures1 whilst the rising and falling of these lips throw off transverse waves4 ,rossi adduces observations which appear to meet with explanation on such suppositions4 ,suess1 who has written upon the earthquakes of lower ,austria1 shows how the majority of the disturbances have had their origin along certain lines which form a break in the continuity of the ,alps4 ,one line runs north-east from ,bruck towards ,vienna4 ,near ,wiener ,neustadt1 where the greatest number and heaviest shocks have occurred1 this line is met by a north-north-west line crossing the ,danube and following the valley of the river ,kamp4#ij ,hoeffer has drawn similar lines from the head of the ,adriatic1 one set running north-north-east to intersect near ,litschau1 and the other north-north-west to intersect near ,frankfort in the valley of the ,rhine4#ia ,examples of distribution4--,a curious example of the distribution of seismic movement is that of the earthquake of ,march #ab1 #ahgc1 worked out by ,professor ,p4 ,a4 ,serpieri4 ,this earthquake appears to have been simultaneously felt on the ,dalmatian coast and in central ,italy1 in a region lying north-east from ,rome and south-east from ,florence4 ,in both of these areas the motion was from south-east to north-west4 ,the shock then radiated from the central ,italian regions1 so that at places on the western shore of the ,adriatic it was felt after it had been felt on the ,dalmatian coast4 ,many explanations might be offered for this peculiar distribution of seismic activity4 ,possibly the shock originated at a great depth beneath the bed of the southern part of the ,adriatic1 and by following existing lines of weakness simultaneously reached the surface of the earth in central ,italy and ,dalmatia4 ,in ,tokio1 which is built partly on a flat plain1 partly in valleys denuded from a low tableland1 and partly on the spurs of the tableland itself1 the distribution of earthquakes is a subject yet requiring attention4 ,sometimes it has happened that persons in one house have been sufficiently alarmed to escape into the open air1 whilst others1 not more than a mile distant1 have not been aware that the city had been shaken4 ,illustration3 ,,fig4 #cd4 ,areas almost simultaneously struck from ,s4,e4 to ,n4,w4 graphic ,subsequent radial disturbance graphic ,extension of earthquake boundaries4--,natural obstructions which may be sufficient to retard small earthquakes may in certain instances not be found sufficient to retard the larger disturbances4 ,thus the shocks of ,calabria are usually only felt on the western side of the ,apennines1 but instances have occurred when they have crossed this barrier4 ,in #ahja the earthquake of ,cumana crossed a branch of the coast range4 ,sometimes earthquake boundaries give way1 and countries which they sheltered subsequently become exposed to all disturbances4 ,the true explanation of this is probably in a shifting of the centre of seismic activity4 ,thus up to ,december #ad1 #agig1 although ,cumana was often devastated1 the peninsula of ,araya was not hurt4 ,on this date ,araya commenced to suffer1 and has continued to suffer ever since4 ,fuchs gives an example of the movement of a seismic centre in the case of the ,calabrian earthquake4 ,the first shock commenced near ,oppiedo1 the second shock commenced four or five miles farther to the north1 and the third shock had its origin five or six miles still farther1 near to ,girifalco4 ,,chapter ,,xiii4 ,,distribution ,,of ,,earthquakes ,,in ,,time 7continued74 ,seismic energy in relation to geological time4--,if we admit that seismic energy is only a form of volcanic energy1 it must also be admitted that any cause tending to produce a general decrease in the amount of the latter will also produce an alteration in the amount of the former4 ,the nebular hypothesis of ,laplace tells us that the solar system is the result of the whirling of a heated gaseous mass1 which as it cooled continually contracted and consequently whirls the faster4 ,with this hypothesis before us1 we understand why all the planets and their satellites have a similarity in the directions of their movements1 why they revolve nearly in the same plane1 in orbits nearly circular1 why some have a flattened figure and are surrounded by rings or belts1 why the exterior planets should have a greater velocity of rotation1 a greater number of satellites1 and a less density as compared with the interior planets1 the similarity of the elements in meteoric stones1 the sun1 the stars1 and those found upon our earth1 and lastly why there should be an increase in temperature as we descend into our earth4#ib ,this increase in temperature as we descend into the earth as deduced from many observations appears to be about #a ,f4 for every fifty or sixty feet of descent4 ,to explain this and other kindred phenomena it is assumed that the earth was once very much hotter than it is at present1 and to reach its present stage it has been gradually cooling4 ,as the laws of cooling are perfectly known1 to calculate how many years it must have taken a body like our earth to cool down to its present temperature is a definite problem4 ,sir ,william ,thomson1 starting with the temperature of #g1jjj ,f41 when all the rocks of the earth must have been molten and a skin or crust upon the surface1 such as is so quickly produced upon the surface of molten lava1 finds by calculation that the time taken to reach the present temperature must have been about one hundred million years4 ,into this period he and other physicists desire to compress the history of all the stratified deposits4 ,geologists find this period too short4 ,others seeking to reconcile the views of physicists and geologists endeavour to show that the various agencies engaged in degrading rocks and accumulating sediments in former ages are not to be judged of by the agencies we now see around us2 in former times they were more active4 ,at one period the elastic tides in the earth may have been so great that they resulted in the fracturing off from our planet its satellite the moon1 and subsequently the moon1 acting on the waters of the earth1 may1 even as late as #aej1jjj years ago1 have produced every three hours tides #aej feet in height4 ,whatever may be the value of the figures here quoted1 reasonings like these bring us to the conclusions that the various agencies which we now know to be acting upon our earth were once far more potent than they are at present1 and if the moon1 as a producer of elastic tides1 has any influence upon the occurrence of earthquakes1 it must have had a much greater influence in bygone times4 ,we might speak similarly with regard to the internal heat of the earth4 ,from the present heat gradient of our globe it is possible to calculate how much heat flows from the earth every year4 ,this is equivalent to a quantity which would raise a layer of water #fg centimetres thick1 covering the whole of our globe1 from a temperature of #j to #ajj ,c4 ,similarly1 we might calculate the quantity of heat which would be lost when the average heat gradient1 instead of being #a ,f4 for fifty feet of descent1 was #a ,f4 for twenty-five feet of descent4 ,we might also calculate how many years ago it was since such a gradient existed4 ,the general result which we should arrive at would be that in past ages the loss of heat was more rapid than it is at present4 ,now the contraction of a body as it cools is for low temperatures proportional to its loss of heat1 and this law is also probably true for contraction as it takes place from high temperatures4 ,contraction being more rapid1 it is probable that phenomena like elevations and depressions would be more rapid than they are at present1 and generally all changes due to plutonic action1 as has already been pointed out by ,sir ,william ,thomson1 must have been more active4 ,we have1 therefore1 every reason to imagine that earthquakes which belong to the category of phenomena here referred to were also numerous and occurred on a grander scale during the earlier stages of the world's history than they do at present1 and seismic and volcanic energy1 when considered in reference to long periods of time1 is probably a decreasing energy4 ,in making this statement we must not overlook the fact that in geological time1 as testified by the records of our rocks1 volcanic action1 and with it probably seismic action1 has been continually shifting1 first appearing in one area and then in another1 and even in the same area we have evidence to show that these have periods of activity and repose successively succeeding each other4 ,thus in ,britain1 during the ,palozoic times1 we have many evidences of an intense volcanic activity4 ,during the ,mesozoic or ,secondary period volcanic energy appears to have subsided1 to wake up with renewed vigour in the ,cainozoic or ,tertiary period4 ,during this latter period it is not at all improbable that ,scotland was in past times as remarkable for its earthquakes as ,japan is at the present day4 ,later on it will also be shown that earthquakes are concomitant phenomena1 with those elevatory processes which we have reason to believe are slowly going on in certain portions of the earth's crust4 ,if1 therefore1 we are able by the examination of the rocks which constitute the accessible portions of our globe to determine which periods were characterised by elevation1 we may assume that such periods were also periods of seismic activity4 ,amongst these periods we have those in which various mountain ranges appeared4 ,thus the ,grampians1 and the mountains of ,scandinavia1 were probably produced before the deposition of the ,old ,red sandstone4 ,the ,urals were upheaved prior to ,permian times4 ,the chief upheaval in the ,alps took place after ,eocene times4 ,the ,rigi and other sub-,alpine mountains were formed after the deposition of the ,miocene beds4 ,about this same time the ,himalayas were upheaved4#ic ,the earthquakes which from time to time shake those newer mountains apparently indicate that the process of mountain-making is hardly ended4 ,seismic energy in relation to historical time4--,the distribution of seismic energy with regard to historical time is a subject which has been very carefully examined by ,mallet1 who collected together a catalogue of between six and seven thousand earthquakes1 embraced between the periods ,b4,c4 #afjf and ,a4,d4 #ahej4 ,the earthquake of ,b4,c4 #afjf was on the occasion of the delivery of the law at ,mount ,sinai4 ,between ,b4,c4 #afjd and ,b4,c4 #aehf an earthquake probably occurred in ,arabia1 when ,korah1 ,dathan1 and ,abiram were swallowed up4 ,another biblical record is that of ,b4,c4 #aeff1 when the walls of ,jericho were overthrown4 ,the earliest records from ,china is in ,b4,c4 #eie2 in ,japan ,b4,c4 #bhe2 in ,india ,a4,d4 #hid4 ,by using the number of earthquakes which have been recorded in each century as ordinates1 ,mallet constructed a curve1 which apparently shows a continual increase in seismic energy1 especially during recent times4 ,this1 ,mallet remarks1 contradicts all the analogies of the physics of the globe1 and points out that the rapid increase in the number of earthquakes in latter years is chiefly due to the greater number of records which have been made1 and the increase of the area of observation4 ,no doubt many of the records made by the ancients have been lost4 ,if we compare ,mallet's records1 as he invites us to do1 with the great outlines of human progress1 we see that the two increase simultaneously1 and we come to the conclusion that1 taken as a whole1 during the historical period the seismic activity of the world has been tolerably constant4 ,these conclusions1 based on the evidence at our command1 are not to be confuted4 ,if1 however1 instead of considering the seismic energy of the whole world1 we consider the seismic energy of particular areas1 it seems reasonable to expect that in certain instances sometimes a decrease and sometimes an increase in this energy might be discovered1 especially1 perhaps1 in areas which are highly volcanic4 ,in ,france we know that volcanic activity ceased at a period closely bordering on historical times1 and it is not unlikely that seismic activity may have ceased at a corresponding time4 ,in a country like ,japan1 it is possible that in one district seismic energy may be on the increase1 whilst in another upon the decrease4 ,in a country like ,england1 it is probable that the seismic state is constant1 and1 whatever changes may be now occurring1 they are taking place at so slow a rate that1 even if our records of the historical period were complete1 we could hardly be expected to find these changes sufficiently marked to be observable4 ,for purposes of reference1 and also for examining the present question1 the table1 page #bdj1 has been compiled4 ,the earthquakes given are chiefly those which have been recorded in histories as being more or less destructive4 ,in the second column of this table will be seen the number of earthquakes which have occurred in ,japan during each century1 the centuries being marked in the first column4 ,in columns #c to #ah inclusive are given the number of earthquakes which have occurred during different centuries in the various countries and districts mentioned at the head of each column4 ,these latter1 which are taken from the writings of ,mallet1 are given for the sake of comparison with the ,japanese earthquakes4 ,if we commence with the seventh century in the column for ,japan1 we see that a great increase in the number of earthquakes1 as we come towards the present time1 is not so observable as it is in the other columns4 ,key3 #a ,centuries #b ,japan #c ,scandinavia and ,iceland #d ,british ,isles and ,northern ,isles #e ,spanish ,peninsula #f ,france1 ,belgium1 ,holland #g ,rhine ,basin #h ,switzerland and ,rhine ,basin #i ,danube ,basin #aj ,italy1 ,sicily1 ,sardinia1 and ,malta #aa ,supplemental table for ,italy1 ,sardinia1 and ,malta #ab ,turco-,hellenic ,territory1 ,syria1 gean ,isles1 and ,levant #ac ,united ,states and ,canada #ad ,mexico and ,central ,america #ae ,antilles #af ,cuba #ag ,chili and ,la ,plata ,basin #ah ,northern ,zone of ,asia #ai ,approximate ,intensity in the ,kioto ,district of ,japan ---------------------------------------- ----------- #a #b #c #d #e #f #g #h #i #ajaa #abacad #aeaf #agahai ---------------------------------------- ----------- ,i4 #a -- ---- ---- -- -- ---- ------ ---- ------ ,,ii4 -- -- ---- ---- -- -- ---- ------ ---- ------ ,,iii4 #a -- ---- ---- -- -- ---- ------ ---- ------ ,,iv4 -- -- ---- ---- -- -- #f-- #bc---- ---- ------ ,v4 #a -- ---- #a-- -- -- #e-- #ai---- ---- ------ ,,vi4 #a -- ---- #f-- -- #c-- #bg---- ---- ------ ,,vii4 #ab -- ---- ---- -- #a-- #h---- ---- ----#ae ,,viii4 #aa -- ---- ---- -- #b #a #ab---- ---- ----#ag ,,ix4 #dj -- ---- #ba-- #ai #f-- #g---- ---- ----#fj ,x4 #ag -- ---- #b-- #bai #c #c #e---- ---- ----#bd ,,xi4 #bj -- #h #c #af-- #i #g #e #ah---- ---- ----#bh ,,xii4 #ah -- #aa #d #ab-- #h #ahbb #bc---- ---- ----#bj ,,xiii4 #af #ae #c #i-- #c #aebf #ac---- ---- ----#af ,,xiv4 #ai #d #h #ba-- #ah #bjea #h---- ---- ----#be ,,xv4 #cfbh #a #d #ad-- #ab #ahdg #aa---- ---- ----#bi ,,xvi4 #ag #haj #faaj #eb #ce #cb #e #bb-- #f #a #d #e--ag ,,xvii4 #bf #adaj #iabiabj #caaba #i #ecaj #g #af #d #i--aa ,,xviii4#caaaa #fcicbcggaada #hhdchbjabdhhbd #he #b #ajcb #h ,,xix4 #bgaacaajhebaahaagcadecijhhaideacjadeeja gjeg #h ---------------------------------------- ----------- ,the explanation for this probably lies in the fact that ,japan has practised civilised arts for a longer period than many of the ,european and other countries mentioned in the table4 ,in ,japan1 no doubt1 the records of later years have been more perfect than they were in early times1 but this1 although so potent an effacer of what was probably the true state of natural phenomena in the case of ,europe1 has not quite obliterated the truth in ,japan2 for instead of an apparent increase of seismic energy since early times it shows a slight decrease4 ,to draw up a table of earthquakes such as the one which has just been given1 and then1 after the inspection of it1 draw conclusions as to whether there has been an increase or decrease in seismic energy1 is1 however1 hardly a just method of reasoning4 ,the earthquakes1 taken as they are1 for the whole of ,japan1 represent a collection of places some of which are #a1jjj miles apart4 ,when we consider that many earthquakes which occurred at one end of this line were never felt at the other end1 in order to justly estimate the periodicity of seismic phenomena it would seem that we ought either to take some particular seismic area or else the whole world4 ,the particular area which has been taken is that of ,kioto in ,central ,japan1 and the earthquakes which have been felt there are enumerated in the table4 ,in order to show the variation in seismic activity of this district a curve has been plotted1 fig4 #ce1 with ordinates equal to the values given for the ,kioto earthquakes during succeeding centuries4 ,the upper points of these ascending and descending lines are joined by a free curve4 ,the lower points are similarly joined4 ,the points of bisection of ordinates drawn between these two curves are taken as points in a curve to show the true secular change in seismic energy4 ,illustration3 ,,fig4 #ce4--;,curve of ,seismic ,intensity for ,kioto4 ,by looking at this wavy line it will be seen that the intervals between maxima and minima are closer together in early times than they are later on4 ,thus1 between the eighth century and the ninth century1 points of maximum and minimum seismic efforts occurred at times a century apart1 whilst later on1 from the eleventh to the fifteenth century1 they were at intervals of #cjj years apart4 ,by inspecting either the wavy line or the resultant curve1 it will be seen that since the ninth century down to the present time there has been a decided decrease in seismic energy4 ,from the ninth century down to the fifteenth century this decrease is represented by a regular curve4 ,at this point1 however1 the decrease becomes slightly more rapid1 and is represented by a second curve4 ,if1 instead of calculating ordinates for my curve1 in which intensity has been considered1 simply the number of earthquakes are counted1 a similar result is obtained4 ,from this it appears that the rate at which seismic energy decreased during the last #ejj years was about the same as that at which it decreased during the #ejj years previous to this period4 ,if the lists for the ,italian and ,turco-,hellenic districts could be similarly analysed1 and the earthquakes of any particular district picked out from the others1 it is very probable that a similar decrease or alteration in seismic energy might be observed4 ,provided that we have at our disposal records of the various earthquakes which have occurred in any given district during a sufficiently long period of time1 one conclusion that we may expect to arrive at is that we shall be able to trace some variation in the seismic activity of that district4 ,for the ,kioto area1 it has been shown that there is a diminution in seismic activity1 ,in other districts1 however1 there may possibly be an increase4#id ,relative frequency of earthquakes4--,a question which is of great interest to those who dwell in shaken districts is as to how often disturbances may be expected to occur4 ,from a general examination of this question1 considering the earthquakes of the whole world4 ,mallet arrived at the following conclusions3-- #a4 ,while the smallest or minimum paroxysmal intervals may be a year or two1 the average interval is from five to ten years of comparative repose4 #b4 ,the shorter intervals are in connection with periods of fewer earthquakes--not always with those of least intensity1 but usually so4 #c4 ,the alternations of paroxysm and of repose appear to follow no absolute law deducible from these curves4 #d4 ,two marked periods of extreme paroxysm are observable in each century1 one greater than the other--that of greatest number and intensity occurring about the middle of each century1 the other towards the end of each4 ,the form of the curves which ,mallet has drawn seem to indicate that seismic energy came in sudden bursts1 and then subsided1 gradually gathering strength for another exhibition4 ,this is continually seen in the shocks experienced in various seismic areas--a large shock1 or the maximum of the activity dying out by repeated small shocks on succeeding days4 ,mr4 ,i4 ,hattori1 writing on the large earthquakes of ,japan1 remarks that on the average there has been one large earthquake every ten years4 ,they1 however1 occur in groups1 as shown in the following table4 ------------------------------- ,no4 of shocks ,period ,interval ------------------------------- #f ,a4,d4 #hbg-hcf #aj years #f #hhj-hij #aj #d #ajdj-ajdc #d #e #adic-aejg #e #d #aeaj-aeac #d #e #afde-afej #f #e #affb-affd #c #d #ahec-ahef #d ------------------------------- ,dr4 ,e4 ,naumann1 who has also written on the earthquakes in ,japan1 remarks that if periods of seismic activity do not occur every #dij years1 there is a repetition of the cycle after #ihj years1 but there is much variability4 ,a period of #fh years is very marked4 ,on the average1 large earthquakes have occurred every #ei years4 ,fuchs gives some interesting examples of the repetition of earthquakes at definite intervals1 of which the following are examples4 ,sometimes earthquakes appear to have repeated themselves after #ajj years4 ,one remarkable example of this is that of ,lima1 on ,june #ag1 #aegh1 which was repeated on the same day in the year #afgh4 ,in ,copiapo it is believed that earthquakes occur every twenty-three years1 and examples of such repetitions are found in the years #aggc1 #agif1 and #ahai4 ,in ,canada1 near to ,quebec1 earthquakes lasting forty days are said to occur every twenty-five years4 ,the plateau of ,ardebil is said to be regularly shaken by earthquakes every two years4 ,a4 ,caldcleugh1 writing on the earthquake of ,chili1 in #ahce1ie remarks that the ,spaniards first had the idea that a great earthquake occurs every century4 ,afterwards they thought the period was every fifty years4 ,as a matter of fact1 however1 there were large earthquakes in #ahab1 at ,caracas2 in #ahah1 at ,copiapo2 in #ahbb1 at ,santiago2 in #ahbg1 at ,bogota2 in #ahbh1 at ,lima2 in #ahbi1 at ,santiago2 and in #ahcb1 at ,huasco4 ,the average period of seismic disturbances in any country probably depends upon the subterranean volcanic activity of that country4 ,when the activity is great the large earthquakes may occur at short intervals2 but when the activity is small1 as in ,england1 shocks of moderate intensity may not be felt more than once or twice per century4 ,a general idea of the relative frequency of the large earthquakes in various parts of the world may be easily obtained by an inspection of the table on page #bdj4 ,between the years #ahej and #aheg ,kluge found that in the world there had been #d1fbj earthquakes1 which is1 upon the average1 nearly two per day4 ,this estimate of the frequency of earthquakes of sufficient intensity to be recorded without the aid of instruments is1 however1 much below the truth4 ,in ,japan alone there probably occurs1 as a daily average1 a number at least equal to that which has been just given for the whole world4 ,boussingault considered that1 in the ,andes1 earthquakes were occurring every instant of time4#if ,to state definitely how many earthquakes are felt in the world on the average every day is1 from the data which we have at our command1 an impossibility4 ,perhaps there may be ten1 perhaps there may be #ajj4 ,the question is one which remains to be decided by statistics which have yet to be compiled4 ,after a large earthquake1 smaller shocks usually occur at short intervals4 ,at first the succession of disturbances are separated from each other by perhaps only a few minutes or hours4 ,later on1 the intensity of these shocks usually decreases1 and the intervals between them become greater and greater1 until1 finally1 after perhaps a few months1 the seismic activity of the area assumes a quiescent state4 ,the great earthquake which overtook ,concepcion on ,february #bj1 #ahce1 was followed by a succession of shocks like those just referred to1 there being registered1 between the date of the destructive shock and ,march #d1 #cjj smaller disturbances4 ,during the twenty-four hours succeeding the destruction of ,lima 7,october #bh1 #agdf71 #bjj shocks were counted1 and up to the #bdth of ,february in the following year #dea shocks were felt4 ,at ,st4 ,thomas1 in #ahfh1 #bhc shocks were counted in nine and a quarter hours4 ,similar examples might be taken from the description of almost all destructive earthquakes of which we have records4 ,for a large earthquake to occur1 and not to be accompanied by a train of succeeding earthquakes1 is exceptional4 ,sometimes we find that a large number of small earthquakes have occurred without a large one being felt4 ,seismic storms of this description have happened1 even in ,england--for instance1 in the year #agej1 which appears to have been a year of earthquakes for many portions of the globe4 ,in this year1 which is known as the #8earthquake year1' shocks were felt in ,england as follows3 ,on ,march #ad1 in ,surrey2 ,march #ah1 in south-west of ,england2 ,april #b1 at ,chester2 ,june #g1 at ,norwich2 ,august #bc1 in ,lincolnshire2 ,september #cj1 ,northamptonshire4 ,synchronism of earthquakes4--,one of the first writers who drew attention to the fact that two shocks of earthquakes have been felt simultaneously at distant places was ,david ,milne1 who published a list of these occurrences4#ig ,in two instances1 ,february and ,march #agej1 shocks were simultaneously felt in ,england and ,italy4 ,in ,september #ahcc shocks appear to have been simultaneously felt in ,england and ,peru4 ,these and many other similar examples are discussed by ,mallet1 who thinks with ,milne that these coincidences are in every probability matters of accident4 ,according to ,fuchs1 ,calabria and ,sicily appear often to have had earthquakes at the same time1 as for instance in #aafi1 #aece1 #afch1 when the town ,euphemia sank1 and in the years #aggj1 #aggf1 #aghj1 and #aghc4 ,a remarkable example of coincidence occurred on ,november #af1 #ahbg1 when a terrible earthquake was felt in ,columbia1 and at the same time a shock occurred on the ,ochotsk plains1 nearly antipodal to each other4 ,kluge also gives a large number of instances of simultaneous earthquakes2 thus1 on ,january #bc1 #ahee1 on the same day that ,wellington1 ,new ,zealand1 so severely suffered1 there was a heavy earthquake in the ,siebengeberge1 and also in ,north ,america4 ,to this might be added the fact that the last destructive earthquake in ,japan occurred within a few days of this time4 ,sometimes neighbouring countries where earthquakes are common are equally remarkable by their utter want of synchronism4 ,for example1 ,southern ,italy and ,syria are said never to be shaken simultaneously4 ,secondary earthquakes4--,although it is possible that the simultaneous occurrence of earthquakes in distant regions may sometimes be a matter of chance1 it must also be remarked that the shaking produced by one earthquake may be sufficient to cause ground which is in a critical state to give way1 and thus the first disturbance becomes the originator of a second earthquake4 ,admitting that an earthquake1 as it radiates from its centre1 may act in such a manner1 we see that a feeble disturbance might be the ultimate cause in the production of a destructive earthquake1 just as the disturbance of a stone upon the face of a scarp might1 by its impact upon other stones1 cause many tons of material to be dislodged4 ,it is also easy to conceive how the seismic activity of two districts may be dependent upon each other4 ,inasmuch as these secondary shocks are direct effects of primary disturbances1 they might have been treated in a previous chapter4 ,as examples of consequent or secondary earthquakes ,fuchs tells us that when small earthquakes take place in ,constantinople and ,asia ,minor1 earthquakes are felt in ,bukharest1 ,galazy1 and ,kronstadt4 ,the great ,lisbon earthquake also appears to have given rise to several consequent disturbances4 ,one was in ,derbyshire1 occurring at #aa a4m4 ,it was sufficiently violent to cause plaster to fall from the sides of a room and a chasm to open on the surface of the ground4 ,some miners working underground were so alarmed that they endeavoured to escape to the surface4 ,during twenty minutes there were three distinct disturbances4 ,another shock was felt at ,cork4#ih ,although these disturbances own a consequence of the ,lisbon earthquake they might properly perhaps be attributed to the pulsations produced by the shock at ,lisbon1 which spread through ,england and other countries without being felt4 ,the shocks which men felt in ,new ,zealand and ,new ,south ,wales in #ahfh were probably secondary shocks1 due to the disturbance at ,arequipa and other places on the ,south ,american coast4 ,these so-called secondary earthquakes1 although in many instances they may be due to earth pulsations produced by earthquake1 or to the immediate sensible shaking of a large earthquake1 may perhaps1 in certain instances1 be attributed to some widespread disturbance beneath the crust of the earth4 ,the occurrence of periods where all earthquake countries suffer1 unusual disturbances indicate the probability of such underground phenomena4 ,,chapter ,,xiv4 ,,distribution ,,of ,,earthquakes ,,in ,,time 7continued74 ,the occurrence of earthquakes in relation to the position of the heavenly bodies--,earthquakes and the moon--,earthquakes and the sun2 and the seasons2 the months--,planets and meteors--,hours at which earthquakes are frequent--,earthquakes and sun spots--,earthquakes and the aurora4 ,the position of the heavenly bodies and the occurrence of earthquakes4--,since the earliest times1 in searching for the cause of various natural phenomena1 man has turned his energies towards the heavens4 ,one of the earliest observations was the connection that exists between the season of the year and the motions of the heavenly bodies4 ,tides were seen to be influenced by the moon4 ,in later times it has been discovered that periods of maximum magnetic disturbances occur every ten or eleven years with the sun spots1 and ,herr ,kreil1 of ,vienna1 tells us our satellite1 the moon1 has also an influence upon the magnet4 ,from day to day we see the bond connecting our planet with the sun1 the moon1 and other heavenly bodies which are outside us gradually becoming closer4 ,inasmuch as many phenomena1 like the motion of the tides1 the rise and fall of the barometer1 fluctuations in temperature1 are all more or less directly connected with the relative position of our planet with regard to the sun and moon1 any coincidence between the phases of these bodies and the occurrence of earthquakes more or less involves a time relationship with the other phenomena resultant on lunar and solar influences4 ,earthquakes and the position of the moon4--,many earthquake investigators have attempted to show the connection between earthquakes and the phases of the moon4 ,the first and most successful worker in this branch of seismology was ,professor ,alexis ,perrey1 of ,dijon1 who1 after many years of arduous labour in tabulating and examining catalogues of earthquakes1 showed that earthquakes were more likely to occur at the following periods than at others4 #a4 ,they are more frequent at new or full moon 7syzygies7 than at half moon 7quadratures74 #b4 ,they are more frequent when the moon is nearest the earth 7perigee7 than when she is farthest off 7apogee74 #c4 ,they are more frequent when the moon is on the meridian than when she is on the horizon4 ,these results were obtained by ,perrey after analysing his catalogues by three different and independent methods1 and they were confirmed by the report of a committee appointed by the ,academy of ,sciences4 ,it must1 however1 be remarked that in several instances anomalies occur1 and also that the difference between the number of earthquakes at any two periods is not a very large one4 ,thus1 for instance1 the annual catalogues compiled by ,perrey from #ahdd to #ahdg1 the earthquakes in perigee are to those in apogee as #dg 3 #ci4 ,between the years #ahdc and #ahgb ,perrey finds that #c1bij shocks occurred at the moon's perigee1 and #c1jae at the apogee4#ii ,between #agfa and #ahjj earthquakes occurred as follows3-- ,in ,perigee #ebf ,apogee #dfe ,the following table shows the results which enabled ,perrey to deduce his first law4 ,dividing the period of lunation into quarters1 with the time of syzygies and quadratures as the centres of these quarters1 he found that the earthquakes were distributed as follows4 ---------------------------------------- ----------------- ,difference in ,totals ,syzygies ,quadratures favour of the ,syzygies ---------------------------------------- ----------------- #ahdc-ahdg #a1fjd #hejdh #geceb #fiif #ahdh-aheb #b1jdi #a1jecec #iiedg #ehjf #ahec-aheg #c1jah #a1ecdac #a1dhchg #ejbf #aheh-ahfb #c1adj #a1fjbii #a1ecgda #feih #ahfc-ahfg #b1hde #a1dfcdb #a1chaeh #hahd #ahfh-ahgb #d1eic #b1cccdh #b1beieb #gcif #ahdc-ahgb #ag1bdi #h1hchjc #h1dajig #dbgjf ---------------------------------------- ----------------- ,the reported earthquakes between #agea and #ahdc are shown to conform with the same rule4#ajj ,julius ,schmidt1 astronomer at ,athens1 found for the earthquakes of ,eastern ,europe and adjacent countries for the years #aggf to #ahgc that there were more earthquakes when the moon was in perigee4 ,other maxima were at new moon1 and two days after the first quarter4 ,there was a diminution at full moon1 and a minimum on the day of the last quarter4 ,as one example of results which are antagonistic to the general results obtained by ,perrey may be quoted the results of an examination by ,professor ,w4 ,s4 ,chaplin of the earthquake recorded at the meteorological observatory in ,tokio4 ,the list of earthquakes1 #adc in number1 extending over a period of three years1 was recorded by one of ,palmieri's instruments4 ,the results were as follows3-- #a4 ,there have been maxima of earthquakes when the moon was two and nine hours east and seven hours west4 ,at the upper transit there is a minimum4 #b4 ,considering the moon's position with regard to the sun1 at conjunction there were #cb1 at opposition #cg1 and at quadrature #gd4 ,east of the meridian the maximum was at least four hours4 #c4 ,when the moon was north of the equator these were #fh1 when south #hb4 #d4 ,a maximum of earthquakes seven and eleven days after the moon's perigee4 ,the fact that these results were obtained for the earthquakes of a special small seismic area renders them more interesting4#aja ,frequency of earthquakes in relation to the position of the sun4--,the question as to whether there is a connection between the frequency of earthquakes and the relative position of the sun is to a great extent identical with the question as to the relative frequency of earthquakes in the various seasons4 ,it is a subject which we find referred to by writers in the earliest ages4 ,pliny and ,aristotle thought that earthquakes occurred chiefly in spring and autumn4 ,in later times it has been a subject which has been most carefully considered by ,merian1 von ,hoff1 ,perrey1 ,mallet1 ,volger1 ,kluge1 and others who have devoted attention to seismology4 ,in a rsum of the earthquakes of ,europe1 and of the adjacent parts of ,asia and ,africa1 from ,a4,d4 #cjf-ahdc1 ,mallet gives the following results3-- ---------------------------------------- ------------------------ ,for ,nineteenth ,century ,for the whole period ---------------------------------------- ------------------------ ,winter ,solstice #agg ,solstices #bec ,solstices ,spring ,equinox #aea #cjf #agj #djc ,summer ,solstice #abi ,equinoxes #aej ,equinoxes ,autumnal ,equinox #afd #cae #aei #cbi ---------------------------------------- ------------------------ ,the above periods were called by ,perrey critical epochs1 because as a general result of his researches he found that at such periods there was a greater frequency of earthquakes4 ,fuchs1 quoting from ,kluge's tables1 extending from #ahej-aheg1 tells us that the recorded earthquakes occurred as follows3-- ,in the ,northern ,hemisphere-- ,equinoxes #acbd ,solstices #abjb ,in the ,southern ,hemisphere-- ,equinoxes #cja ,solstices #bfa ,earthquakes are1 therefore1 more frequent at the equinoxes1 and this especially at the autumnal equinox4 ,in the northern hemisphere1 at the solstices1 the greater number of shocks occur about the winter solstices1 whilst in the southern hemisphere1 about the summer solstices4 ,exceptions1 however1 are found in ,central ,america and the ,west ,indies1 in the ,caucasus1 and the gean ,sea4 ,the idea that earthquakes had a periodicity dependent upon the position of the heavenly bodies is by no means confined to ,europe4 ,in a ,japanese work called #8,jishin ,setsu' 7an opinion about earthquakes7 by a priest called ,tensho1 it is stated that the relative positions and movements of the twenty-eight constellations with respect to the moon cause earthquakes4 ,this ,tensho asserts after careful calculation1 and ,falb tells us that all future earthquakes can be predicted4 ,in the ,kuriles and ,kamschatka1 ,sicily1 and in parts of ,south ,america1 it is said that the equinoxes are regarded as dangerous seasons4 ,frequency of earthquakes in relation to the seasons and months4--,what is here said respecting the relative frequency of earthquakes at the different seasons and months is little more than an extension and critical examination of the results which have been given respecting the frequency of earthquakes in regard to the position of the sun4 ,that there is a difference between the number of earthquakes which are felt at one season of the year as compared with those felt at another is a fact which1 as seismoscopic observations are extended1 is becoming more and more recognised4 ,some of the more important results which were arrived at by ,mallet from #e1hgi observations made in the northern hemisphere1 and #bbc in the southern hemisphere1 may be expressed as follows3-- ---------------------------------------- ------------------------ ,maxima ,minima ---------------------------------------- ------------------------ ,northern ,hemisphere ,january1 also a slight ,may1 ,june1 and rise in ,august and ,july ,october ,southern ,hemisphere ,november1 also ,may ,march1 extending and ,june over one month1 also ,august ---------------------------------------- ------------------------ ,julius ,schmidt1 of ,athens1 who so carefully examined the earthquakes of eastern ,europe1 came to the following conclusions3-- ,for the earthquakes between #abjj and #ahgc1 a maximum on ,september #bf and ,january #ag2 a minimum on ,december #c and ,june #ac4 ,for the earthquakes between #ahgc and #ahgd1 a maximum on ,march #a and ,october #a2 a minimum on ,july #g and ,december #ae4 ,for all the earthquakes of eastern ,europe1 a maximum on ,january #c2 a minimum on ,july #h1 or there was a maximum at perihelion and aphelion4 ,when the months are grouped together according to the seasons1 spring1 summer1 autumn1 and winter1 we find that in the northern hemisphere the minimum is in summer and the maximum in winter1 whilst in the southern hemisphere 7giving the proper months corresponding to its seasons7 we find two maxima1 one at the commencement of winter1 and the other at midsummer1 whilst the minima are in spring and autumn4 ,illustration3 ,,fig4 #cf4--;,curves of ,monthly ,seismic ,intensity 7,mallet74 ,in the following table the difference in the number of earthquakes felt at different seasons is given more in detail4 ,in examining this table1 we must remember that for countries like ,peru1 ,chili1 and ,new ,zealand1 lying in the southern hemisphere1 the records given for the months ,april to ,september correspond to the winter months of those countries4 ,the ,roman numerals indicate the centuries between which the records date4 ---------------------------------------- -------------------------- ,october ,april to to ,march ,september ---------------------------------------- -------------------------- #a4 ,scandinavia and ,iceland1 xii-xix #abi #ia #b4 ,british and ,northern ,isles1 xi-xix #abc #id #c4 ,belgium1 ,france1 and ,holland1 iv-xix #cie #bgb #d4 ,rhone ,basin1 xvi-xix #aae #fi #e4 ,switzerland and ,rhine ,basin1 ix-xix #cbg #bje #f4 ,danube ,basin1 v-xix #adg #abh #g4 ,spanish ,peninsula1 xi-xiv #aad #hg #h4 ,italy1 ,sicily1 ,sardinia1 and ,malta1 ,northern iv-xix #fej #eha ,regions #i4 ,turco-,hellenic ,territory1 ,syria1 gean ,isles1 and ,levant1 iv-xix #bad #bbb #aj4 ,northern ,zone of ,asia1 xviii-xix #df #cf #aa4 ,japan 7,tokio area71 #ahgb-ahhj 7small earthquakes7 #bac #aeg #ab4 ,japan ,b4,c4 #bie-;,a4,d4 #ahgb 7large earthquakes7 #afe #ahh #ac4 ,algeria and ,northern ,africa #bf #bj #ad4 ,united ,states and ,canada1 xvii-xix #hf #dh #ae4 ,java1 ,sumatra1 and neighbouring ,islands1 #ahgc-d-g-h #aid #ahb ,central #af4 ,mexico and ,central ,america1 xvi-xix #bf #bf ,regions #ag4 ,west ,indies 7,mallet71 xvi-xix #ajh #aad #ah4 ,west ,indies1 xvi-xix #bif #cdc #ai4 ,cuba1 xvi-xix #bh #bc #bj4 ,chili1 and ,la ,plata ,basin1 xvi-xix #hi #hi ,southern #ba4 ,peru1 ,columbia1 ,basin of ,amazons1 ,regions xvi-xix #ejf #eda #bb4 ,new ,zealand1 #ahfi-ahgi #aff #agf ---------------------------------------- -------------------------- ,neglecting those records which show as many earthquakes for the winter months as for the summer months1 we see at a glance that generally the greater number of shocks have happened during the colder seasons4 ,in the southern hemisphere1 so far as the records go1 this is not true4 ,in the northern regions1 out of fourteen examples there are two exceptions4 ,in the central regions there are two cases where the greatest number of earthquakes have been recorded in the winter months1 and two cases where the greatest number have been recorded for the summer4 ,altogether1 out of twenty-two examples1 there are only six exceptions to the rule4 ,these exceptions altogether occur among records many of which are ancient1 and are1 therefore1 more open to error than lists which have been compiled in modern times4 ,because small earthquakes are seldom noticed by persons out in the open air1 it might be expected that the number of earthquakes observed in warm countries at one portion of the year would be equal to those observed in any other season4 ,such an argument1 however1 would hardly apply to most of the records which are quoted1 as they refer to destructive disturbances4 ,if1 however1 we take the records made in tropical countries from the table just given1 we see that in such countries there have been almost as many observations of earthquakes at one season as at any other4 ,another fact which might be adduced against the rule that the greater number of earthquakes occur during the winter months would be the comparison of a table of earthquakes recorded previous to the nineteenth century4 ,by doing this we see that for certain countries the winter rule is inverted1 and that the greater number of shocks are felt during the summer4 ,notwithstanding these objections to ,perrey's conclusions1 the balance of evidence is in favour of his general result1 and we may conclude that during the colder portions of the year we may expect more shakings than during the warmer portions4 ,comparing the number of earthquakes of winter and autumn to those of summer and spring1 they are to each other in the proportion of #d 3 #c4 ,a fairer way to examine this question1 and to determine what is probably the present state of seismic activity in our globe1 would be only to consider the earthquakes which have taken place in comparatively recent times1 laying especial stress upon those observations which have been made with the assistance of automatic instruments1 or those which have been collected by persons interested in these investigations4 ,for this purpose the following table1 showing the distribution of earthquakes in different countries during the nineteenth century1 has been compiled4 ,the arrangement is mensual4 ,where the number of earthquakes in any month is above the average1 the number is printed in large type2 where below the average1 in small type4 ,,earthquakes ,,of ,,the ,,nineteenth ,,century1 ,,chiefly ,,from ,,perrey4 ,key3 ,jan ,january ,feb ,february ,mar ,march ,apr ,april ,may ,may ,jun ,june ,jul ,july ,aug ,august ,sep ,september ,oct ,october ,nov ,november ,dec ,december ,ave ,average per month ---------------------------------------- -------------------------------------- ,jan,feb,mar,apr,may,jun,jul,aug,sep,oct ,nov,dec,ave ---------------------------------------- ------------------------- ,scandinavia and ,iceland #ag #aa #aa #g #g #f #h #h #aj #aj #aa #f #ic ,british ,isles and ,northern ,isles #i #i #aj #g #h #f #e #aa #ab #h #aa #ab #i ,france1 ,belgium1 ,holland #bg #ag #ba #ac #ac #h #ae #ag #ae #ag #ba #beag ,basin of the ,rhone #ab #ab #h #c #c #b #b #d #f #f #h #ad #ff ,basin of the ,rhine and ,switzerland #ae #ag #ac #ab #aa #f #ab #aa #aj #ag #bd #bead ,basin of the ,danube #ad #ae #i #h #ab #h #af #aa #aa #af #aj #abaah ,spanish ,peninsula #aj #e #f #g #d #f #aj #e #i #aa #g #e #g ,italian ,peninsula1 ,sicily1 ,sardinia1 and ,malta #dd #dd #dh #dc #dj #cd #da #df #bg #de #bf #cici ,turco-,hellenic ,territory1 ,syria1 gean ,islands1 and ,levant #bb #bj #aj #aj #af #ae #ad #bb #ad #ag #ab #adaf ,northern ,zone of ,asia #d #f #f #d #d #c #e #g #f #c #d #e #dg #ahgf-ahha1 ,japan 7,tokio area7 #ci #da #da #cj #cc #cj #bg #ba #aj #bh #cd #dccad ,japan 7large earthquakes7 -- #e #c #c #a -- #e #d -- -- #a #e #b ,algeria and ,north'rn ,africa #e #b #f #g #c #b #b #e #a #d #h #a #ch ,united ,states and ,canada #d #d #c #c #c -- #d #f #c #b #g #e #ch ,java1 ,sumatra1 c41 #ahgc-d-e-g and #i #ce #cj #ch #cc #bb #cf #bg #dj #bd #ce #cj #bfca ,mexico and ,central ,america #c #b #b #b #f #b #b #a #a #c #b #c #be ,antilles #i #h #ai #ab #ab #aj #i #af #ab #aj #ac #abaah ,cuba #d #c #b #c #c #d #e #b #f #e #f #d #d ,chili and ,la ,plata #ad #aj #ad #h #ai #aa #af #ae #af #i #bg #haci ,peru1 ,columbia1 ,basins of ,amazons1 xvi-xix #ib #hc #ib #bgajf #gi #id #ic #ig #gg #gb #ijhg ,new ,zealand1 #ahfi-gi #ca #bg #cg #bc #bb #ca #bg #cf #cg #ba #bg #bcbhe ,jan4 #ahej1 ,dec4 #aheg ,northern ,hemisphere #aecafbadcafaabfabdadaaefaedagaaeaafhaej ,southern ,hemisphere #ge #dc #fa #ff #df #db #ec #ci #ed #ee #eg #dfec #ahba-ahcj ,northern ,hemisphere #ca #cf #ca #bi #cc #cc #bj #ca #bd #da #bf #cdcj ,southern ,hemisphere #b -- #a #a #c #a #c #b #c #b #a #a #af ---------------------------------------- ------------------------- ,a glance at this table shows that for most countries in the northern hemisphere the rule that there are generally more earthquakes during the winter months--that is1 from ,october to ,march--holds good4 ,for countries which lie comparatively near to the ,equator1 and also for those countries in the southern hemisphere1 the rule is not so clear4 ,when examining this table it must be remembered that it does not enable us to judge of the relative frequency of earthquakes in different countries1 inasmuch as the periods over which the records were taken are different in different cases4 ,to the above table might be added the records of ,p4 ,merian1 who examined the earthquakes felt in ,basle up to #ahca4 ,as a result he found that during the winter months eighty shocks had been felt1 whilst during the summer only forty4 ,taking the records for the two hemispheres from #ahej-aheg1 compiled by ,kluge1#ajb in the northern hemisphere we have in the months between ,october and ,march #idh shocks against #hfb in the remainder of the year4 ,in the same months in the southern hemisphere we have for the corresponding periods the numbers #ccg and #cjj1 and thus both hemispheres would appear to follow the same rule4 ,if1 however1 we examine the table we see that the two seasons are not so pronounced for the southern hemisphere as they are for the northern1 and that there may be two or three periods of maximum disturbance as has been previously indicated4 ,earthquakes and the planets and meteors4--,just as the moon and the sun may exert an attractive influence upon the earth and cause earthquakes to predominate at certain seasons rather than at others1 several investigators of seismic phenomena have thought that the planets might act in a similar manner4 ,m4 ,j4 ,delauney1 from a study of ,perrey's tables of earthquakes from #agej-ahdb1 found two groups of maxima each with a period of about twelve years1 one commencing in #agei and the other in #agef4 ,two other groups with twenty-eight year periods respectively commence in #agef and #aggc4 ,these groups coincide with the times when ,jupiter and ,saturn reach the mean longitudes of #bfe and #ace4 ,from this ,delauney concludes that earthquakes have a maximum when the planets are in the mean longitudes just mentioned4 ,the increased number of earthquakes1 especially in ,november1 are attributed to the passage of the earth through swarms of meteors1 and in like manner supposes the influence of ,jupiter and ,saturn to be due to their passing through meteor streams situated in mean longitudes #ace and #bfe4 ,as a consequence of this he predicts an increase of earthquakes in the years #ahhf1 #ahia1 #ahih1 #aijj1 c4#ajc ,dr4 ,e4 ,naumann1 who critically examined the large earthquakes of ,japan1 showed that there was an approximate coincidence between many of the disturbances and the thirty-three year period of meteoric showers4#ajd ,humboldt states that a great shower of meteors was seen at ,quito before the great earthquake of ,riobamba 7,feb4 #d1 #agig74 ,the earthquakes of #agff and #agii at ,cumana are also said to have been accompanied with meteoric showers4 ,mallet gives a list of large earthquakes which occurred at the times when meteors were observed4#aje ,the hours at which earthquakes are most frequent4--,from the examination of a catalogue of over #b1jjj earthquakes which occurred in various parts of the world between the years #ahej and #aheg1 made by ,kluge1 it is found that both for the northern and southern hemispheres the observations which were made during the night generally exceed those which were made during the day4 ---------------------------------------- ---------- ,number of ,earthquakes ---------------------------------------- ---------- ,day ,night ,in the ,northern ,hemisphere #ich #aeib ,in the ,southern ,hemisphere #bib #ceg ---------------------------------------- --------- ,in the northern hemisphere the greatest number were observed between #aj ,p4,m4 and #ab ,p4,m4 7#cfj shocks71 and the fewest between #ab and #b ,p4,m4 7#aci shocks74 ,in the southern hemisphere1 the greatest number were observed at night between #ab and #a1 and the smallest number between #a and #b and #d and #e in the afternoon4#ajf ,these distinctions1 however1 are less distinctly marked as we approach the ,equator4 ,schmidt found for the earthquakes of the ,orient between #aggd and #ahgc1 that shocks had been most frequent about half-past two ,a4,m41 and less frequent about #a ,p4,m4 ,with regard to these conclusions1 which have been reached with much labour1 we might be inclined to think that they are partially to be explained on the supposition that more observations are made during the night than during the day--the personal experience of residents in an earthquake country being1 that many earthquakes which occur during the day are passed by unnoticed1 whilst those which occur during the night are recorded by thousands of observers4 ,such a view is certainly confirmed by the instrumental records obtained in ,japan4 ,from #ahgb to #ahhj inclusive there were #bfa shocks recorded1 #acb of which occurred between the hours of #f ,p4,m4 and #f ,a4,m4 ,earthquakes and sun spots4--,of late years considerable attention has been drawn to a coincidence between the occurrence of sun spots1 magnetic disturbances1 rainfall1 and other natural phenomena4 ,these periods of sun spots occur about every eleven years1 and appear to be coincident with the periodical return of the planet ,jupiter4 ,in ,japan1 ,dr4 ,e4 ,naumann sought for a coincidence between these periods of sun spots and earthquakes1 but without any marked results4 ,schmidt1 who carefully compared his lists of earthquakes with the appearance of sun spots1 came to the conclusion that there was no marked coincidence4 ,the occurrence of earthquakes had sometimes synchronised with sun spots1 whilst at other times there had been a maximum of sun spots and no earthquakes4 ,m4 ,r4 ,wolf#ajg apparently considers that earthquakes1 like volcanic eruptions and the appearance of the aurora1 are coincident with sun spots4 ,kluge1 however1 came to the conclusion that when there are few sun spots1 earthquakes1 like volcanic eruptions and magnetic disturbances1 have been at a maximum4 ,m4 ,a4 ,poey1 who examined a catalogue of the earthquakes of ,mexico and the ,antilles1 extending from #afcd to #ahgj1 shows by a table that earthquakes have come in groups1 first at the maxima and then at the minima period of sun spots4 ,out of thirty-eight groups1 seventeen being at the maximum and seventeen at the minimum1 the remaining four are exceptions to the rule1 being between the maximum and minimum4 ,phenomena which are dependent upon heat occur with the minima of sun spots1 and those dependent upon cold with the maxima4#ajh ,earthquakes and the aurora4--,the possible connection between earthquakes and the aurora is a subject which has attracted some attention4 ,bou has especially made a careful examination of this subject4#aji ,he comes to the conclusion that if we compare the monthly periods of earthquake frequency and the aurora there is an agreement between the two4 ,comparing ,perrey's tables of earthquakes from the fourth to the nineteenth century1 with tables of the aurora1 one-third of both phenomena have occurred1 not only in the same day1 but often at the same hour4 ,between #ahcd and #ahdg1 #deg earthquakes are given and #cea notices of the aurora4 ,out of these3-- #dh occur on the same day1 #e occur in the same hour1 #cj approximate to the same time4 ,the nearer together that these phenomena have occurred the stronger have they been4 ,professor ,m4 ,s4 di ,rossi brings forward many examples where there has been a coincidence between the appearance of the aurora and earthquakes4 ,on #aci nights out of #baa days the aurora was seen in some parts of ,italy1 and ninety-three times earthquakes were felt4 ,on forty-six occasions earthquakes and aurora took place together4#aaj ,in considering the probability of a connection existing between these two phenomena1 we must bear in mind that the aurora is at no great height above the surface of our earth1 and1 further1 that it can be partially imitated4 ,the fact that in earthquake countries1 like ,japan1 the aurora is practically never seen1 would indicate that we can neither regard this imperfectly understood phenomenon either as an effect or cause of earthquakes4 ,that earthquakes and the appearance of the aurora in certain countries should not sometimes coincide is an impossibility4 ,dr4 ,stukeley1 who1 it must be remembered1 attempted to correlate the phenomena of earthquakes and electricity1 when writing of the disturbances which shook ,england in #ahdi and #ahej1 says that the weather had been unusually warm1 the aurora borealis frequent and of unusually bright colours1 whilst the whole year was remarkable for its fire-balls1 lightnings1 and corruscations4#aaa ,the aurora was observed before the commencement of the ,maestricht earthquakes in #ageaaab2 whilst at the time of the shock flashes of light like lightning were observed in the sky4 ,glimmering lights were seen in the sky before the ,new ,england earthquakes 7,nov4 #ah1 #agee71 and again1 before the disturbances which occurred in the same region in #agbg1 peculiar flashes of light were seen4 ,preceding the ,sicilian earthquake of #afib strange lights were seen in the sky4 ,ignis fatui have also been observed with earthquakes4 ,at the time of auroral displays ,bertelli has observed microseismical disturbances1 and ,m4 ,s4 di ,rossi1 who has made similar observations1 thinks that there is an intimate connection between the aurora and earthquakes2 the aurora either occurring in a period of earthquakes1 or else taking the place of earthquakes4 ,,chapter ,,xv4 ,,barometrical ,,fluctuations ,,and ,,earthquakes--,,fluctuations ,,in ,,temperature ,,and ,,earthquakes4 ,changes in the barometer and earthquakes4--,mallet1 who collected together a number of examples of earthquakes which have occurred with a fall of the barometer1 and a number which have happened with a rise1 concludes that there are as many instances of the one as of the other4 ,at the great earthquake of ,calabria1 in #aghc1 the barometer was very low4 ,the earthquake of the ,rhine 7,february #bc1 #ahbh7 was preceded by a gradual fall of the barometer1 which reached its lowest point upon that day4 ,after the earthquake the barometer again rose4 ,the earthquake of ,february #bb1 #ahhj1 in ,japan1 was accompanied by exactly similar phenomena4 ,caldcleugh1 who observed the heavy shocks in ,chili 7,february #bj1 #ahce71 noticed that on ,february #ag and #ah the barometer fell #e_/aj inches4 ,similar phenomena were observed before the succeeding smaller shocks4 ,after the shocks the barometer again rose4 ,principal ,dawson1 speaking of the earthquakes of ,canada1 observes that some of the shocks have been accompanied with a low barometer4 ,p4 ,merian1 who examined the connection between the ,swiss earthquakes and atmospheric pressure1 found that out of twenty-two earthquakes observed in ,basle between #agee and #ahcf1 thirteen of these were local shocks1 of which eight were accompanied with sudden changes of pressure4 ,of the remaining nine1 which were only felt slightly in ,basle1 no change in atmospheric pressure was observed4 ,of thirty-six earthquakes which1 between #ahbf and #ahcf1 were felt in ,switzerland1 thirty were chiefly confined to ,switzerland1 and ten of these occurred with a low or falling barometer4 ,humboldt is of opinion that earthquakes only occur with changes in barometric pressure in those countries where earthquakes are few2 and he gives examples where the regular variations of the barometer have gone on without interruption at the time of earthquakes4 ,frederick ,hoffmann1 who examined fifty-seven earthquakes which occurred at ,palermo between #aghh and #ahch1 came to the following result3-- ,the barometer was sinking in #bj cases rising in #af at a minimum in #g maximum in #c undetermined in #aa #aac ,the observations of ,m4 ,s4 di ,rossi apparently show that the earthquakes in ,italy chiefly occur with a barometrical depression and with sudden jumps in atmospheric pressure4 ,schmidt1 who examined the earthquakes of the ,orient1 which occurred between #aheh and #ahgc1 says that they were rare with a high barometer1 but numerous when the barometer was low4 ,from an examination of a table of #cif earthquakes 7,may #h1 #ahge-;,dec4 #ahha7 felt in ,tokio1 furnished to me by ,mr4 ,arai ,ikunosuke1 the director of the meteorological department1 ,i obtained the following results3-- ,the barometer was rising in #afi cases falling in #aed steady in #gc below the monthly mean in #ahi above in #aib ,from this it would appear that in ,japan at least the movements of the barometer do not show any marked connection with the occurrence of earthquakes4 ,when considering this question we must remember the marked effects which a lowering of the barometer produces upon certain volcanoes and solfataras4 ,the volumes of steam emitted from ,stromboli and from some of the solfataras in ,tuscany hold a marked connection with atmospheric pressure as the quantity of fire damp given off from coal seams--these being greatest when the barometer is low4 ,at certain changes of the weather it is said that the volcano of ,vulture1 near ,melfi1 emits noises4 ,these phenomena at once place volcanic phenomena and barometrical pressure in direct relationship4 ,changes in temperature4--,if1 with an earthquake1 it should happen that there is a change in the height of the barometer1 we should naturally expect that this might be accompanied with the changes in the temperature1 in the wind1 and in other atmospheric phenomena which are more or less connected with the height of the barometer4 ,many times it has been observed that after an earthquake there has been a sudden fall in the temperature4 ,such was the case with the ,yokohama earthquakes of #ahhj4 ,cotte endeavours to show that the earthquakes of ,lisbon produced a change upon the temperature of all ,europe4 ,in the year which followed this earthquake storms were more common than usual4 ,kluge has collected together a large number of examples when there has been a fall of temperature at the time of an earthquake4#aad ,at ,kiachta1 in ,siberia1 at the time of the earthquake of ,december #bg1 #ahef1 the thermometer fell from #ab to #be ,r4 ,we must1 however1 remember that there are many cases known where the thermometer rose4 ,m4 ,s4 di ,rossi remarks that we have the highest records of temperature in the years richest in earthquakes4 ,thus1 in #ahgc1 at the time of the earthquakes in ,central and ,northern ,italy1 an abnormal high temperature was remarked4 ,japanese writers have remarked upon the unusual heat which has shaken their countries4 ,the temperature of subterranean waters have been known to increase before earthquakes4 ,,chapter ,,xvi4 ,,relation ,,of ,,seismic ,,to ,,volcanic ,,phenomena4 ,want of synchronism between earthquakes and volcanic eruptions--,synchronism between earthquakes and volcanic eruptions--,conclusion4 ,connection between earthquakes and volcanic eruptions4--,insomuch as it is a recognised fact that regions which are characterised by their seismic activity are chiefly those which are also characterised by the number of their volcanoes1 it is generally assumed that these two phenomena have an intimate relation4 ,the residents in a volcanic country1 when seeking for the origin of an earthquake1 invariably turn towards the volcanoes which surround them4 ,if a neighbouring volcano is in a state of activity1 it is often regarded as a safeguard against seismic convulsions1 in other cases it is looked upon as being the cause of such disturbances4 ,in certain instances both of these views have apparently been corroborated4 ,when we consider that an earthquake and a volcanic eruption may both be the result of some great internal convulsion1 and that first one and then the other may take place in the same neighbourhood1 it is natural to expect that when these internal forces have expended themselves in the production of one of these phenomena1 it is not so likely that they should exhibit themselves in the other4 ,the inhabitants of ,sicily and ,naples1 we are told1 regard eruptions of ,etna and ,vesuvius as safeguards against earthquakes4 ,a similar belief is to be found in portions of ,south ,america with regard to the volcanoes for which that country is so celebrated4 ,from an examination of the records of the large earthquakes and the volcanic eruptions which have taken place in ,japan during the last #b1jjj years1 ,dr4 ,naumann found that there was often an approximate coincidence between the times of the occurrence of these phenomena1 suggesting the idea that the efforts which had been sufficient to establish the volcano had at the same time been sufficient to shake the ground4 ,of destructive earthquakes which have occurred at the time of volcanic eruptions1 and of examples when these phenomena have occurred at widely separated intervals1 the records are extremely numerous4 ,want of synchronism between earthquakes and volcanic eruptions4--,many of the great earthquakes of ,south ,america do not appear to have been connected with volcanic eruptions4 ,the great earthquakes of the world1 like those of ,calabria and ,lisbon1 which took place in regions which are not volcanic1 have not1 ,fuchs tells us1 taken place in conjunction with volcanic outbursts4 ,in ,japan1 as in the ,sandwich ,islands and in many other parts of the globe1 the small earthquakes which occur almost daily do not appear to show any marked connection with volcanic disturbances4 ,in #ahha1 during the eruption of ,natustake1 a volcano lying about a hundred miles north of ,tokio1 there was neither an increase nor a decrease in the earthquakes which were felt in ,tokio4 ,similar remarks apply to the state of seismic activity of #ahgf-gg1 when ,oshima1 a volcanic island about seventy miles to the south of ,tokio1 was in eruption4 ,in the ,sandwich ,islands ,mauna ,loa seems to have its eruptions independently of the disturbances which shake these islands4#aae ,synchronism of earthquakes and volcanic eruptions4--,although many examples like the above may be quoted1 which apparently show an utter want of connection between earthquakes and volcanoes1 we must not overlook that class of earthquakes which almost invariably accompany all great volcanic disturbances4 ,in fact the sudden explosions which take place at volcanic foci1 as1 for instance1 at the commencement of an eruption1 are enumerated as one of the causes which produce earthquakes4 ,earthquakes like these usually continue until the pressure of the steam and lava have found for themselves an opening4 ,as compared with the total number of earthquakes which are recorded1 they form but an insignificant portion4 ,the direct connection which exists between these phenomena has1 no doubt1 done very much to spread the popular belief that all earthquakes may be connected with volcanic eruptions4 ,as examples where this connection has existed we might quote from almost all the volcanic countries in the world4 ,thus1 ,fuchs tells us that on ,october #f1 #agcg1 almost the whole of ,kamschatka and the ,kurile ,islands were disturbed by movements which were simultaneous with the outbreak of the great volcano ,klutschenskja of ,north ,kamschatka4 ,one of the earliest records of a severe earthquake and a volcanic eruption occurring simultaneously is found in the accounts of the destruction of ,herculaneum and ,pompeii4 ,the throwing up of ,monte ,nuovo in the neighbourhood of ,pozzuoli was accompanied with a dreadful earthquake4#aaf ,in #ahfh the earthquake of ,arequipa was accompanied by the opening of the volcano ,misti1 on its north side4 ,the distance to the volcano is about fourteen miles4 ,at the time of the eruptions of ,kilauea in #aghi the ground shook and rocked so that persons could not stand4 ,the first eruption of the volcano ,irasu1 in ,costa ,rica 7#aghc71 was accompanied by violent earthquakes4#aag ,the smoke and flames which are said to have issued from the side of ,mount ,fojo at the time of the ,lisbon earthquake are regarded by some as having been volcanic4 ,others thought that the phenomena1 rather than being on the side of ,fojo1 which showed no traces of volcanic action1 had taken place in the ocean4 ,at the time of the great earthquake at ,concepcion 7#ahce71 whilst the waves were coming in1 two great submarine eruptions were observed4 ,one1 behind the ,isle of ,quiriquina1 appeared like a column of smoke4 ,the other1 in the bay of ,san ,vicente1 appeared to form a whirlpool4 ,the sea-water became black1 and had a sulphurous smell1 there being a vast eruption of gas in bubbles4 ,many fish were killed4#aah ,with this same earthquake1 near to ,juan ,fernandez1 about one mile from the shore1 the sea appeared to boil1 and a high column of smoke was thrown into the air4 ,at night flames were seen4 ,in #ahfa1 when ,mendoza was destroyed and #aj1jjj inhabitants killed1 a volcano at the foot of which ,mendoza is situated burst into eruption4 ,the earthquake of #ahbb at ,valdivia was accompanied by eruptions of the neighbouring mountains1 which only lasted a few minutes4 ,at the time of the ,leghorn shocks 7,january #af-bg1 #agdb7 some fishermen observed a part of the sea to rage violently1 to raise itself to a great height1 and then rush landwards4#aai ,in #agig1 when ,riobamba was destroyed1 the neighbouring volcanoes were not affected1 but ,mount ,pasto1 #abj miles distant1 suddenly ceased to throw out its usual column of water4 ,on the night of ,december #aj1 #ahgd1 a strong shock was felt in ,new ,england1 whilst at #d4de ,a4,m4 on ,december #aa a shock was felt in the ,pic du ,midi1 in the ,pyrenees4 ,in the middle of ,december there were volcanic outbursts in ,iceland4#abj ,it is possible that these occurrences might be the results of some widespread disturbance beneath the crust of the earth1 or perhaps even of widely extended earth pulsations4 ,the probability1 however1 is that these coincidences are accidental4 ,when we remember that in a small area like the northern half of ,japan alone there are periods when there are at least two shocks per day on the average1 it is impossible for these coincidences not to exist4 ,less frequently coincidences between the larger disturbances must occur4 ,over and above these accidental coincidences1 it would appear that in the world's history periods have occurred when earthquakes were unusually frequent1 and at such times distant countries have suffered simultaneously4 ,this approximate coincidence in period1 which has been referred to when speaking of the distribution of destructive earthquakes in historical time1 does not imply an exact synchronism in the single shocks4 ,small earthquakes1 or1 more properly speaking1 local tremblings1 are a necessary accompaniment of almost all volcanic eruptions4 ,tremors of this description are seldom1 however1 felt beyond the crater1 or at the most upon the flanks of the mountain where the eruption is going on4 ,they are due to the explosive action of steam bursting through the molten lava4 ,volcanic eruption succeeding earthquakes4--,sometimes it has happened that an earthquake1 or a series of earthquakes1 have terminated with the formation of volcanic vents4 ,as an example of a volcanic outburst terminating a seismic disturbance1 may be mentioned the appearance of a new volcano in the centre of ,lake ,ilopango1 as a sequel to the shocks which had disturbed that neighbourhood in #ahgi4aba ,in #agej there were continuous shakings lasting over three months at ,manilla4 ,these terminated with an eruption of a small island in the middle of a neighbouring lake4 ,three days after the commencement of this eruption1 four other small islands rose in the same lake4#abb ,antonio d',ulloa1 when speaking of the ,andes1 remarks that after a volcanic eruption the shocks cease4#abc ,conclusion4--,looking at this question generally1 insomuch as the greatest number of volcanic eruptions appear1 according to ,fuchs1 to have taken place in summer1 whilst the greatest number of its earthquakes have apparently taken place in winter1 it would seem that the two phenomena are without any direct connection1 unless it be that both are different effects of a common cause4 ,regarded in this manner1 an earthquake may be looked upon as an uncompleted effort to establish a volcano4 ,to use the words of ,mallet1 #8,the forces of explosion and impulse are the same in both2 they differ only in degree of energy1 or on the varying sorts and degrees of resistance opposed to them4'#abd ,although we have many examples of earthquakes having occurred without volcanic eruptions1 and1 on the other hand1 of volcanic eruptions without earthquakes1 volcanoes may still be regarded as #8safety-valves of the earth's crust1' which1 by giving relief to internal stresses1 guard us against the effects of earthquakes4 ,that many earthquakes are felt at ,copiapo is attributed to the fact that in the neighbouring mountains there are no volcanic vents4 ,we must not1 however1 overrate the protective influence of volcanoes4 ,in the ,sandwich ,islands we see the columns of liquid lava in neighbouring mountains standing at different heights1 indicating a want of subterranean connection between these vents4 ,in consequence of this it would seem that enormous pressures might be generated in the neighbourhood of one of these mountains without finding relief at the other4 ,when we have conditions like these1 it would seem that the eruption of a volcano may have little or no influence in protecting neighbouring districts4 ,this may possibly be the explanation of the fact that in #ahce ,concepcion was destroyed1 notwithstanding there being an unusual activity in the volcanic vents of the neighbouring mountains4 ,,chapter ,,xvii4 ,,the ,,cause ,,of ,,earthquakes4 ,modern views respecting the cause of earthquakes--,earthquakes due to faulting--,to explosions of steam--,to volcanic evisceration--,to chemical degradation--,attractive influence of the heavenly bodies--,the effect of oceanic tides--,variation in atmospheric pressure--,fluctuation in temperature--,winds and earthquakes--,rain and earthquakes--,conclusion4 ,as the results of modern inquiries respecting the cause of earthquakes1 we see many investigators chiefly attributing these phenomena to special causes4 ,a few attribute them to several causes4 ,it seems to us that they might be attributed to very many causes which often act in a complex manner4 ,the primary causes are telluric heats1 solar heat1 and variations in gravitating influences4 ,these may be the principal1 and sometimes the immediate1 cause of an earthquake4 ,the secondary causes are those dependent upon the primary causes1 such as expansions and contractions of the earth's crust1 variations in temperature1 barometrical pressure1 rain1 wind1 the attractive influences of the sun and moon in producing tides in the ocean or the earth's crust1 variations in the distribution of stress upon the earth's surface caused by processes of degradation1 the alterations in the position of isogeothermal surfaces1 c4 ,the part which may be played by these various causes in the production of oscillations1 pulsations1 and tremors will be referred to4 ,earthquakes consequent on faulting4--,in the chapter on ,earth ,oscillations1 the causes producing the phenomena of elevation and depression are briefly indicated4 ,by the variations in stress accompanying elevations and depressions1 cracks are produced4 ,inasmuch as compression would crush the rocks constituting the earth's crust1 we must conclude with ,captain ,dutton that these cracks are formed by tension4 ,by elevation1 the upper rigid crust of the earth is stretched1 and fissures are produced4 ,the sudden formation of these fissures or faults gives rise to earthquakes1 and perhaps also to volcanic vents4 ,that earthquake and volcanic regions are situated on areas where there is evidence of rapid elevation is strikingly illustrated round the shores of the ,pacific4 ,lasaulx considered that the earthquake of ,herzogenrath was more or less intimately connected with the great mountain fissure--the ,feldbiss--which crosses the coal region of the ,wurm4#abe ,the sudden elevation or sinking of large areas at the time of an earthquake may be a consequence of these dislocations4 ,it has already been pointed out that the earthquake region of ,japan is the one where we have evidence of recent and rapid elevation4 ,that certain earthquakes of this region may possibly be the result of faulting we have the evidence of our senses and of our instruments4 ,the sudden blows and jolts which are sometimes felt are indicative of the sliding of one mass of rock across another4 ,should the ground be simply torn asunder1 this tearing would give rise to a series of waves of distortion1 vibrating in directions parallel to the plane of the fissure4 ,supposing this motion to be propagated to a number of surrounding stations1 it would be recorded at each of these as having the same direction4 ,to those situated on a line forming a continuation of the strike of the fissure1 the vibrations would advance so to speak end on1 whilst to those stations lying in a line perpendicular to the strike of the fissure1 the motion would advance broadside on4 ,motions like these latter have been recorded in ,tokio1 where earthquakes which from time observations were known to have come from the faulted and rising region to the south have been registered as a series of east and west motions1 or vibrations transverse to this line of propagation4 ,it must1 however1 be here mentioned that the registration of only transverse motion may possibly be due to the extinction of normal motion1 although this is not generally regarded as probable4 ,it would therefore appear that certain earthquakes and faults are closely related phenomena1 the former being an immediate effect of the latter4 ,faults are due to earth oscillations1 and to a variety of causes producing disturbances in the equilibrium of the earth's crust2 the principal cause of all these phenomena being alterations in the distribution of heat1 and the attractive force of gravity4 ,earthquakes consequent on the explosion of steam4--,humboldt regarded volcanoes and earthquakes as the results of a common cause1 which he formulated as #8the reaction of the fiery interior of the earth upon its rigid crust4' ,certain investigators1 who have endeavoured to reduce ,humboldt's explanation to definite limits1 have suggested that earthquakes may be due to sudden outbursts of steam beneath the crust of the earth1 and its final escape through cracks and fissures4 ,admitting that steam may accumulate by separating out from the cooling interior of our globe1 its sudden explosion might be brought about by its own expansive force1 or by the movements in the bubbling mass from which it originated4 ,others1 however1 rather than regard the steam as being a primeval constituent of the earth's interior1 imagine it arises from the gradual percolation of water from the surface of the earth down to volcanic foci1 into which it is admitted against opposing pressures1 by virtue of capillary action4 ,mallet1 in his account of the ,neapolitan earthquake1 shows that the whole of the observed phenomena can be accounted for by the admission of steam into a fissure1 which by the expansive force exerted on its walls was rent open4 ,just as at the ,geysers we hear the thud and feel the trembling produced by the sudden evolution and condensation of steam1 so may steam by its sudden evolution and condensation in the ground beneath us give rise to a series of shocks of varying intensity1 accompanied by intermediate vibratory motions--that is to say1 a motion which1 as judged of by our feelings1 is not unlike many earthquakes4 ,often it may happen that the result of the explosion may be the production of a fault1 or at least a fissure2 and thus in the resulting movements we may have a variety of vibrations1 some being those of compression and distortion1 produced by the blow of the explosion1 and others being those of distortion alone1 produced by the shearing action which may have taken place by the opening of the fault4 ,sometimes one set of these vibrations may be prominent1 and sometimes the other4 ,thus1 when we say that an earthquake has shown evidence by the nature of its vibrations that it was produced by a fault1 this by no means precludes the possibility that an explosion of steam may also have been connected with the production of the disturbance4 ,mallet threw out the suggestion that the opening of fissures beneath the ocean might admit water to volcanic foci4 ,during the time that the water was in the spheroidal state1 the preliminary tremors1 so common to many earthquakes1 would be produced4 ,these would be followed by the explosion1 or series of explosions1 constituting the shock or shocks of the earthquakes4 ,the chief reasons for believing that the earthquakes of ,north-,eastern ,japan are partly due to explosive efforts are3-- #a4 ,that the greater number of disturbances1 perhaps ninety per cent41 originate beneath the sea1 where we may imagine that the ground1 under the superincumbent hydrostatic pressure1 is continuously being saturated with moisture4 #b4 ,many of the diagrams show that the prominent vibrations1 of which there are usually from one to three1 in a given disturbance have the same character as those produced by an explosive like dynamite1 the greatest and probably the most rapid motions being inwards towards the origin4 ,it may here be remarked that a very large proportion of the destructive earthquakes of the world have originated beneath the sea1 as has often been testified by the succeeding sea waves4 ,also1 it must be observed1 that earthquake countries1 like volcanic countries1 are chiefly those which have a coast line sloping at a steep angle beneath the sea--that is to say1 earthquakes are frequent along coasts bordered by deep water4 ,the earthquakes which occur at volcanic foci constitute another class of disturbances which may be accredited to the explosive efforts of steam4 ,earthquakes due to volcanic evisceration4--,by the ejection of ashes and lava from volcanic vents1 there is an extensive evisceration of the neighbouring ground4 ,when we look at a volcano like ,fujiyama1 #ac1jjj feet in height1 and at least fifty miles in circumference1 and remember that the mass of cinders and slag of which it is composed came from beneath the area on which it rests1 the point to be wondered at is1 that earthquakes1 consequent on the collapse of subterranean hollows1 are not more frequent than they are4 ,at the time of a single eruption of a volcano1 the quantity of lava ejected amounts to many thousand millions of cubic feet4 ,in #aghc the quantity of lava ejected from ,skaptas ,joknee1 in ,iceland1 was estimated as surpassing #8in magnitude the bulk of ,mont ,blanc4'#abf ,admitting that hollow spaces are the results of these eruptions1 and that in consequence of this evisceration the ground is rendered unstable1 the instability being increased by the additional load placed above the eviscerated area1 it would seem that from time to time earthquakes are inevitable4 ,facts1 however1 teach us that volcanoes act as safety valves1 and that1 as a rule1 at or shortly after an eruption1 earthquakes cease4 ,the relationship of earthquakes to volcanic eruptions would therefore indicate1 notwithstanding the arguments put forward to show that an area loaded by a volcano has in consequence of the evisceration and the load a quaquaversal dip1 that evisceration does not take place beneath volcanoes as is usually supposed1 and we may conclude that it is but few earthquakes which have an origin due to these causes4 ,earthquakes and evisceration by chemical degradation4--,a powerful agent1 which tends to the formation of subterranean hollows1 is chemical degradation4 ,the effects of this have been often measured by quantitative analysis of the solid materials which are daily carried away by many of our springs4 ,in limestone districts this is very great4 ,prof4 ,ramsay estimates that the mineral matter discharged annually by the hot springs of ,bath is equivalent in bulk to a column #adj feet in height and #i feet in diameter4 ,at ,san ,filippo1 in ,tuscany1 the solid matter discharged from the springs has formed a hill a mile and a quarter long1 a third of a mile broad1 and #bej feet in thickness4#abg ,many other examples of subterranean chemical degradation will be found in text-books of geology4 ,by this chemical action large cavernous hollows are produced4 ,beneath a volcano it is probable that liquid material immediately takes the place of that which is ejected1 and that hollows are not formed as in the case of chemical degradation4 ,if a cavern becomes too large1 it eventually collapses4 ,of the falling in of large excavations we have examples in large mines4 ,as a consequence1 not only is a trembling produced1 but also a noise1 which is so like that produced by certain earthquakes that the ,south ,american miners have but one word1 #8bramido1' to express both4#abh ,boussingault1 who was an advocate for the theory that many earthquakes are produced by the sinking of the ground1 calls attention to the fact that we have evidences of the subsidence of great mountains1 like the ,andes1 the districts around which are so well known for their earthquakes4 ,capac ,urcu is one of these mountains which legends tell us has decreased in height4 ,the variation in the height of mountains is a subject which deserves attention4 ,that mountains may possibly be hollow1 we have the remarkable results attained by ,captain ,herschel1 who found that the attractive force of gravity in the neighbourhood of the ,himalayas was not so great as it ought to have been had these mountains been solid4 ,the ,rev4 ,o4 ,fisher gives another explanation of this phenomenon4 ,palmieri considers that the terrible earthquake which devastated ,casamicciola 7#ahha7 was due to the hot springs having gradually eaten out cavernous spaces beneath the town4 ,the extremely local character of this shock was certainly favourable to such a view4 ,the earthquake which1 in #ahdj1 caused ,mount ,cernans1 in the ,jura1 to fall1 is also attributed to the solvent action of waters in undermining its foundations4 ,this undermining action was in great measure probably due to a large spring1 which1 twenty-five years previously1 had disappeared1 and which subsequently may possibly have been slowly disintegrating the foundations of the mountain4 ,earthquakes of this order would be principally confined to districts where there are rocks which are more or less soluble1 as1 for instance1 rock salt1 gypsum1 and limestone4 ,earthquakes and the attractive influences of the heavenly bodies4--,the most important attractions exercised upon our planet are those due to the sun and moon4 ,to these influences we owe the tides in our ocean1 and possibly elastic tides in the earth's crust4 ,some theorists would also insist upon liquid tides in the fluid interior of our earth4 ,the nature of the earth's interior is1 however1 a question on which there is a diversity of opinion4 ,one doctrine1 which1 until recent years1 received much support1 was that the interior of the earth was a reservoir of molten matter contained within a thin crust4 ,hopkins showed that the least possible thickness of such a crust must be from #hjj or #a1jjj miles1 otherwise the motions of precession and nutation would be subject to interference4 ,m4 ,delauney objected to the views of ,hopkins1 on the supposition that the fluid interior of the earth had a certain viscosity4 ,sir ,william ,thomson arrives at the conclusion that the earth on the whole must be more rigid than a continuous solid globe of glass4 ,mr4 ,george ,h4 ,darwin's investigations on the bodily tides of viscous or semi-elastic spheroids tend to strengthen the arguments of ,sir ,william ,thomson4 ,some philosophers hold the view that the central portion of the earth1 although intensely hot1 is solid by pressure1 whilst the outer crust is solid by cooling4 ,between the two there is a shell of liquid or viscous molten matter4 ,another argument is1 that although the interior of the globe may be solid1 it is only retained in that condition by an immense pressure1 on the relief of which it is liquefied--it is potentially liquid4 ,as these views1 and the arguments for and against them1 are to be found in all modern text-books of geology1 we will at once proceed to consider the effect of solar and lunar attractive influences in producing earthquakes upon a globe which is either solid1 partially solid1 or which has an interior wholly liquid4 ,effect of the attractive influences of the sun and moon4--,in #ahed ,m4 ,f4 ,zantedeschi put forward the view--that it is probable there is a continual tendency of the earth to protuberance in the direction of the radii vectores of the two luminaries which attract it4 ,in consequence of these protuberances1 pendulums ought at one time to swing more slowly than at others4 ,zantedeschi remarks that the periods of earthquakes appear to confirm such a view1 insomuch as they occur more often at the syzygies1 or epoch of the spring tides1 than at neap tides--an observation found in the works of ,georges ,baglivi 7#agjc7 and ,joseph ,toaldo 7#aggj74abi ,prof4 ,perrey1 of ,dijon1 who did so much for seismology1 held the view that the preponderance in the number of earthquakes felt at particular seasons was possibly due to the attractive influence of the sun and moon producing a tide in the fluid interior of the earth1 which1 acting on the solid crust1 produced fractures4 ,rudolf ,falb1 whose writings have of late years attracted considerable attention1 brings forward views which may be regarded as amplifications of those suggested by ,perrey4 ,according to ,falb1 the inner portion of the earth must be regarded as fluid4 ,in the crust above this fluid reservoir are cracks and channels1 into which1 by the attraction of the moon and sun1 the fluid is drawn4 ,on entering these cracks cooling takes place1 together with explosions of gas and subterranean volcanic disturbances4 ,the attractions producing the internal tides required by ,falb are chiefly dependent upon the following factors3-- #a4 ,the nearness and distance of the sun from the earth 7,january #a and ,july #a74 #b4 ,the position of the moon with regard to the earth1 which in every twenty-seven days is once near and once distant4 #c4 ,the phases of the moon--whether full or new moon 7syzygies71 or whether first or last quarter 7quadratures74 #d4 ,the equinoxes1 the position of the sun in the equator1 and the relative position of the earth4 #e4 ,the position of the moon relative to the equator4 #f4 ,the concurrence of the #8centrifugal force' of the earth with the last quarter of the moon4 #g4 ,the entrance of the moon on the ecliptic--the so-called nodes4 ,assuming that earthquakes are wholly consequent on these attractions1 it at once becomes possible to predict their occurrence4 ,this ,falb does1 and when his predictions have been fulfilled he has certainly gained notoriety4 ,he commenced by the predictions of great storms4 ,in #ahgc he predicted the destructive earthquake of ,belluno1 which earned for himself a eulogistic poem1 which he has republished in his #8,gedanken und ,studien ber ,vulkanismus4' ,after this1 in #ahgd1 he predicted the eruption of ,etna4 ,he also explained why1 in ,b4,c4 #djjj1 there should have been a great flood1 and for ,a4,d4 #fdjj he predicts a repetition of such an occurrence4 ,when we approach the question of the extent to which the attraction of the sun and moon may influence the production of earthquakes1 a question which we have to answer is1 whether it is likely that the attractive power of the moon is so great that it could draw up the crust the earth beyond its elastic limits4 ,we know what it can do with water4 ,it can lift up a hemispherical shell #h1jjj miles in diameter about two or three feet higher at its crown than it lifts the earth4 ,even supposing the solid crust to be lifted #ajj times the apparent rise of the tide1 is it likely that a hemispherical arch #h1jjj miles in diameter when it is raised #bjj feet at its crown could by any possibility suffer fracture8 ,if an arch is #ab1jjj miles in length1 all that we here ask is1 whether the materials which compose the arch are sufficiently elastic to allow themselves to be so far stretched that the crown may be raised #bjj feet4 ,the result which we should arrive at is apparently so obvious that actual calculation seems hardly necessary4 ,if we regard the earth as being solid1 the question resolves itself into the inquiry as to whether a column of rock1 which is equal in length to the diameter of the earth1 or about #h1jjj miles1 can be elongated #bjj feet without a fracture4 ,this is equivalent to asking whether a piece of rock one yard in length can be stretched one seventy thousandth of a foot4 ,considering that this is a quantity which is scarcely appreciable under the most powerful of our microscopes1 we must also regard this as a question which it is hardly necessary to enter into calculations about before giving it an answer4 ,to vary the method of treating such a question1 may we not ask what is the utmost limit to which it would be possible to raise up or stretch the crust of the earth without danger of a fracture8 ,thus1 for instance1 to what extent might a column of rock be elongated without danger of its being broken8 ,from what we know of the tenacity of materials like brick and their moduli of elasticity1 it would seem possible to stretch a bar of rock #h1jjj miles in length for approximately half a mile before expecting it to break4 ,as to whether there is a wave1 the height of which is equal to half this quantity1 running round our earth as successive portions of its surface pass beneath the attracting influences of the sun and moon1 is a phenomenon which1 if it exists1 would probably long ago have met with a practical demonstration4 ,the deformation which a solid globe or spherical shell would experience under the attractive influences of the sun and moon has been investigated by ,lam1 ,thomson1 ,darwin1 and other physicists and mathematicians4 ,a conclusion that we are led to as one result of these valuable investigations is1 that if the interior of the earth be fluid1 and covered with a thin shell1 then enormous elastic tides must be produced4 ,a consequent phenomenon1 dependent on the existence of these tides1 would be a marked regularity in the occurrence of earthquakes4 ,as this marked regularity does not exist1 we must conclude that earthquakes are not due to the attractive influences of the sun and moon acting upon the thin crust of the earth covering a fluid interior4 ,the periodicity of earthquakes corroborates the conclusions of ,sir ,william ,thomson1 who remarks that if the earth were not extremely rigid the enormous elastic tides which must result would be sufficient to lift the waters of the ocean up and down so that the oceanic tide would be obliterated4 ,assuming that the earth has the rigidity assigned to it by mathematical and physical investigators1 we nevertheless have travelling round our earth1 following the attractions of the moon and sun1 a tidal stress4 ,this stress1 imposed upon an area in a critical state1 may cause it to give way1 and thus be the origin of an earthquake4 ,earthquakes ought therefore to be more numerous when these stresses are the greatest4 ,the periods of maximum stress or greatest pull exerted by the moon and sun will occur when these bodies are nearest to our planet--that is1 in perigee and perihelion1 and again when they are acting in conjunction or at the syzygies4 ,that earthquakes are slightly more numerous at these particular periods than at others is a strong reason for believing that the attractions of the moon and sun enter into the list of causes producing these phenomena4 ,had there been a strongly marked distinction in the number of earthquakes occurring at these particular seasons as compared with others1 we might have attributed earthquakes to the existence of elastic tides of a sensible magnitude4 ,as the facts stand1 it appears that the maximum pulls exerted by the moon and sun are only sufficient to cause a slight preponderance in the number of earthquakes felt at particular seasons1 and therefore that these pulls only result in earthquakes when the distorting effort has been exerted on an area which1 by volcanic evisceration1 the pressure of included gases1 and other causes1 is on the verge of yielding4 ,earthquakes and the tides4--,if we assume that earthquakes are in many cases due to the overloading of an area and its consequent fracture1 such loading may occur by the rising of the tide4 ,a belief that the earthquakes of ,japan were attributable to the tides may be found in the diary of ,richard ,cocks under the date ,november #g1 #afah1 who remarks3-- #8,and1 as we retorned1 about ten aclock1 hapned a greate earthquake1 which caused many people to run out of their howses4 ,and about the lyke hower the night following hapned an other1 this countrey being much subject to them4 ,and that which is comunely markd1 they allwais hapen at a hie water 7or full sea72 so it is thought it chauseth per reason is much wind blowen into hollow caves under ground at a loe water1 and the sea flowing in after1 and stoping the passage out1 causeth these earthquakes1 to fynd passage or vent for the wind shut up4'#acj ,although we may not acquiesce in ,cock's views respecting the imprisoned wind1 it would seem that a comparison of the occurrence of earthquakes and the state of the tide would be a legitimate research4 ,inasmuch as the stresses which are brought to bear upon an area by the rising of the tide are so very much greater than those due to barometrical changes1 it is not unlikely that a marked connection would be found4 ,but it must be remembered that because researches1 so far as they have gone1 tend to show that earth movements are more frequent when an area is relieved of a load1 it is not unlikely that the greatest number of earthquakes may be found to occur at low water4 ,prof4 ,w4 ,s4 ,chaplin attempted to make this investigation in ,japan1 but not being able to obtain the necessary information respecting the tides1 was compelled to relinquish this interesting work4 ,every foot of rise in a tide is equivalent to a load being placed on the area over which the tide takes place of sixty-two pounds to the square foot4 ,this load is not evenly distributed1 but stops abruptly at a coast line4 ,lastly1 it may be observed that many coast lines are not simultaneously subjected to stresses consequent upon this load4 ,japan1 for instance1 may be regarded as an arch placed horizontally4 ,the area near the crown of this arch is loaded by the tidal wave crossing the ,pacific before the areas near the abutment1 and farther there is a horizontal pressure at the crown which1 if ,japan were like a raft1 would tend1 as the tide advanced1 to straighten its bow-like form1 but as the wave passed its abutments to increase its curvature4 ,prof4 ,g4 ,darwin has calculated the amount of rise and fall of a shore line due to tidal loads 7see p4 #ccf1 #8,earth ,pulsations'74 ,the result of these calculations apparently indicates that these loads may have a considerable influence upon the stability of an area in a more or less critical condition4 ,mr4 ,j4 ,carruthers suggests that tidal action may hold a general but indirect relationship to volcanic and seismic action by the retardation it causes on the earth's rotation4 ,by this retardation the polar axis tends to lengthen1 and tensile stresses are induced1 resulting in fracture4 ,the fluid interior of the earth1 being no longer restrained1 would move polewards1 and1 leaving equatorial portions unsupported1 this would gradually collapse4 ,the primary fractures would be north and south1 while the secondary fractures would be east and west4#aca ,that the rise of the tide is accompanied by a greater percolation of water to volcanic foci1 which1 in consequence1 assume a greater state of activity1 is a theory which was advanced many years ago4 ,to determine how far tides may directly be connected with earthquakes1 the necessary records have yet to be examined4 ,variations in atmospheric pressure4--,when we consider the immense load which1 by a sudden rise of the barometer1 is placed upon the area over which this rise takes place1 it is not difficult to imagine that this rise may occasionally be the final cause which makes the crust of the earth to give way4 ,a barometric rise of an inch is equivalent to a load of about seventy-two pounds being put upon every square foot of area over which this rise takes place4 ,on the other hand1 a fall in the barometric column indicates that a load has been removed1 and whatever elastic effort may be exerted by subterranean forces in endeavouring to escape1 being met by less resistance1 they may burst these bonds1 and an earthquake will result4 ,for reasons such as these the final cause of earthquakes has often been attributed to variations in atmospheric pressure4 ,in ,japan there are practically as many earthquakes with a high barometer as with a low one4 ,the extent to which barometric fluctuations have acted as final causes in the production of earthquakes may be judged of by a comparison of the times of barometric variation and the times at which earthquakes have occurred4 ,three important laws of barometric variation are the following3-- #a4 ,in the world generally the average barometric pressure is highest in winter4 7,exceptions occur near ,iceland and in the ,north ,pacific47 #b4 ,the summer and winter monthly mean barometer differs least near the equator and over the great oceans4 ,they differ most over the great continents and generally with increasing latitude4 #c4 ,the greatest number of barometrical fluctuations usually take place in winter4 ,inasmuch as there are generally more earthquakes in winter than in summer1 the first of these laws would indicate that this might be due to the greater load which acts upon the crust of the earth at that season4 ,the second law would indicate that the distinction between the winter and summer earthquakes ought to be most marked in high latitudes1 which1 if we refer to the table on p4 #beg1 we observe to be borne out by the results of observation4 ,the countries where there are as many earthquakes in winter as in summer are chiefly those in low latitudes4 ,the number of these countries from which we have records are1 however1 few4 ,facts opposed to the idea that earthquakes may be caused by an increase of barometric pressure are the results of observations like those of ,schmidt and ,rossi1 which show that earthquakes chiefly occur with a low barometer4 ,assuming that these latter observations will be found by future investigators to be generally true1 we must conclude that the relief of atmospheric pressure has an influence upon the occurrence of earthquakes4 ,such a conclusion would partially accord with the third barometrical law1 or the fact that there are more occasions on which we get a low barometer during the winter months4 ,other writers who have examined this question are ,volger1 ,kluge1 ,andrs1 and ,poly4 ,the latter investigator sought a connection between earthquakes and revolving storms1 in the centres of which there is usually an abnormal decrease of atmospheric pressure4 ,if an area over which such a sudden change in pressure took place was in a critical state1 it is not difficult to see that storms such as ,poly refers to might sometimes be accompanied by earthquakes4 ,fluctuations in temperature4--,inasmuch as fluctuations in temperature are governed by the sun1 it may at once be said that there is a connection between earthquakes and readings of the thermometer4 ,certainly earthquakes occur mostly during the cold months or in winter4 ,similarly1 as changes in temperature are so closely connected with barometric fluctuations1 and these are said to have a direct influence upon the yielding of the earth's crust1 seismic phenomena are indirectly linked to fluctuations in temperature4 ,a rise in temperature is usually accompanied by a fall in the barometer1 and this in turn may be a condition favourable for the occurrence of an earthquake4 ,if we regard solar heat as an agent causing expansions or contractions in the earth's crust1 then fluctuations in temperature become an immediate cause of earthquakes4 ,the probability1 however1 is that solar heat has little or no connection with the final cause producing earthquakes1 although at the same time coincidences between the occurrence of earthquakes and unusual fluctuations in temperature may from time to time be observed4 ,winds and earthquakes4--,although it may be admitted that high winds exert enormous pressures upon mountain ranges1 and might occasionally give rise to stresses causing rocky masses in unstable equilibrium to give way1 the coincidences which have been established between the occurrence of storms and earthquakes can usually only be regarded as occurrences which have synchronised by chance4 ,storms are usually accompanied with a barometric depression1 and the relation of diminutions in atmospheric pressure to earthquakes has been discussed4 ,rain and earthquakes4--,it has already been shown that earthquakes have occasionally been found to coincide with rain and rainy seasons4 ,whether the saturation of the ground with moisture or the percolation of the same to volcanic foci may be a direct effect producing earthquakes it is difficult to say4 ,the probability1 however1 is that1 rain being dependent on phenomena like changes in temperature1 barometric fluctuations1 and winds1 we must regard it and the earthquakes which happen to coincide with these precipitations of moisture as congruent effects of more general causes4 ,conclusion4--,although it would be an easy matter to discuss the relationship of earthquakes and other phenomena1 we must conclude that the primary cause of earthquakes is endogenous to our earth1 and that exogenous phenomena1 like the attraction of the sun and moon and barometric fluctuations1 play but a small part in the actual production of these phenomena1 their greatest effect being to cause a slight preponderance in the number of earthquakes at particular seasons4 ,they may1 therefore1 sometimes be regarded as final causes4 ,the majority of earthquakes are due to explosive efforts at volcanic foci4 ,the greater number of these explosions take place beneath the sea1 and are probably due to the admission of water through fissures to the heated rocks beneath4 ,a smaller number of earthquakes originate at actual volcanoes4 ,some earthquakes are produced by the sudden fracture of rocky strata or the production of faults4 ,this may be attributable to stresses brought about by elevatory pressure4 ,lastly1 we have earthquakes due to the collapse of underground excavations4 ,,chapter ,,xviii4 ,,prediction ,,of ,,earthquakes4 ,general nature of predictions--,prediction by the observation of unusual phenomena 7alteration in the appearance and taste of springs2 underground noises2 preliminary tremors2 earthquake prophets--warnings furnished by animals1 c47--,earthquake warning4 ,general nature of predictions4--,ever since seismology has been studied1 one of the chief aims of its students has been to discover some means which would enable them to foretell the coming of an earthquake1 and the attempts which have been made by workers in various countries to correlate these occurrences with other well-marked phenomena may be regarded as attempts in this direction4 ,ability to herald the approach of these calamities would unquestionably be an inestimable boon to all who dwell in earthquake-shaken countries1 and the attempts which have been made both here and in other places are extremely praiseworthy4 ,in almost all countries where earthquakes are of common occurrence these movements of the earth have been more or less connected with certain phenomena which1 in the popular mind1 are supposed to be associated with an approach of an earthquake4 ,if predictions were given in general terms1 and they only referred to time1 inasmuch as on the average there are in the world several shakings per day1 we should always find that predictions were verified4 ,we might even go further and predict that on certain days earthquakes would occur in certain countries1 and still find that in many instances our supposed power of foresight had not deceived us4 ,thus1 for instance1 in ,japan1 where on the average there are probably one or two shakings every day1 if prognostications were never correct there would be a violation of the laws of chance4 ,what is required from those who undertake to forewarn us of an earthquake is an indication not only of the time at which the disturbance will happen1 but also an indication of the area in which it is to occur4 ,those who dwell in an area where there are certain well-defined periods during which seismic activity is at a maximum--if ten or fourteen days should have passed without a shock--might1 in many instances1 find that a prophecy that there would be an earthquake within the next few days would prove itself correct4 ,also1 if a severe shock had taken place1 a prophecy that there would be a second or third smaller disturbance within a short period would also meet with verification4 ,certain persons with whom ,i am intimate appear to have persuaded themselves that they can foretell the coming of an earthquake by the sultry state of the atmosphere or a certain oppressiveness they feel1 and an instinctive feeling arises that an earthquake is at hand4 ,it is said that a few minutes before many of the shocks which shook ,new ,england between #ahbg and #ahdg people could foretell the coming disturbance by an alteration in their stomach4#acb ,no doubt many who dwell in earthquake countries1 and have been alarmed by earthquakes1 are at times subject to nervous expectancy4 ,the author has had such sensations himself1 due1 perhaps1 to a knowledge that it was the earthquake season1 that there had been no disturbance for some weeks1 and a consequent increasing state of nervous presentments4 ,in consequence of this1 not only has he carefully prepared his instruments for the coming shock1 but he has written and telegraphed to friends to do the same4 ,sometimes these guesses have proved correct4 ,one remarkable instance was a few hours prior to the severe shock of ,february #bb1 #ahhj1 when he communicated with his friends in ,yokohama and asked them to see that their instruments were in good order4 ,oftener1 however1 his prognostications have been incorrect4 ,the point in connection with this subject which he wishes to be remarked is1 that the instances where earthquakes occurred shortly after the receipt of his letters are carefully remembered1 and often mentioned1 but the instances in which earthquakes did not occur appear to be entirely forgotten4 ,he is led to mention these facts because they appear to be an experimental proof of what has taken place in bygone times1 and what still takes place1 especially amongst savages--namely1 that the record of that which is remarkable survives1 whilst that which is of every-day occurrence quickly dies4 ,had the records of all prognostications been preserved1 the probability is that we should find that they had1 in the majority of cases1 been incorrect1 whilst it would have been but in very few instances they had been fulfilled4 ,prediction by the observation of natural phenomena4--,the above remarks may perhaps help us to understand the prognostications of the ancient philosophers about which ,professor ,antonio ,favaro1 of ,padua1 has written4#acc ,cicero in the #8,de ,divinatione1' speaking on this subject1 says that #8,god has not predicted so much as the divine intelligence of man4'--#8,non ,deus prvidet tantum1 sed et divini in genii viri4' ,favaro regards these predictions1 however1 as the result of observations of nature which show it is possible that indications of coming earthquakes had been announced by variations in the gas given out from subterranean sources1 the change in colour1 taste1 level1 temperature of the water in springs1 c4 ,in #ahdc a bishop of ,ischia forewarned his people of a conning earthquake1 and thus was instrumental in the saving of many lives4 ,naturally1 in an age of superstition1 the bishop would be regarded as a prophet1 but ,favaro considers that the prognostication was probably due to a knowledge of premonitory signs as exhibited in changes in the characters of mineral waters4 ,the shock of #ahea1 at ,melfi1 was in this way predicted by the ,capuchin fathers1 who observed that a lake near their door became frothy and turbulent4 ,underground noises have led persons to the belief that an earthquake was at hand4 ,it was in this way that ,viduari1 a prisoner at ,lima1 predicted the destruction of that city4 ,before the earthquake of #ahfh1 so severely felt at ,iquique1 the inhabitants were terrified by loud subterranean noises4 ,that underground noises have preceded earthquakes by considerable intervals appears to be a fact1 but1 at the same time1 it must be remembered that similar noises have often occurred without an earthquake having taken place4 ,farmers predicted the earthquake of ,st4 ,remo1 in #ahca1 by underground noises4 ,on the day before the earthquake which1 in #ahgc1 shook ,mount ,baldo1 the inhabitants of ,puos1 a village north of ,lake ,santa ,croce1 heard underground noises4 ,before the earthquakes which1 in #aghc1 shook ,calabria and ,sicily1 fish are said to have appeared in great numbers on the coast of ,sicily1 and the whirlpool of ,charybdis assumed an unusual excited state4 ,it is said that ,pherecydes predicted the earthquakes of ,lacedemon and ,helm out1 by the taste of the water in the very deep well at the castle of ,lovain4#acd ,the writer of an article on the ,lisbon earthquake says that #8after the #bdth ,i felt apprehensive1 as ,i observed the same prognostics as on the afternoon of ,october #ca1 that is1 the weather was severe1 the wind northerly1 a fog came from the sea1 the water in a fountain ran of a yellow clay colour1 and' he adds1 #8from midnight to the morning of the #beth ,i felt five shocks4'#ace ,at the present time ,rudolf ,falb1 following a theory based upon the attractive influences of the sun and moon1 tells us the time at which we are to expect earthquakes4 ,that occasionally there are signs attendant on earthquakes1 although we cannot give them a physical explanation1 we cannot doubt4 ,also we know that in certain areas earthquakes are more likely to occur at one season than at another4 ,should earthquakes be foretold with the assistance of knowledge of this description1 the predictions at once become the result of the application of certain natural laws1 and are not to be regarded as predictions in the popularly accepted sense of that term1 any more than the arrival of a friend is predicted by the previous receipt of a telegram announcing his coming4 ,rather than accredit the ancients and those of more modern times who1 in consequence of their feelings1 have recorded the coming of an earthquake1 with a knowledge of premonitory signs1 we might in many instances regard the records of those prognostications as the survival of accidental guesses1 and1 as such1 examples of the survival of the useless4 ,the effect of accidental occurrences of this description upon an uneducated mind1 in engendering superstition1 is a subject which has often been dwelt upon1 and the difficulty of eradicating the same--as may be judged of by the following accident which came under the observation of ,mr4 ,t4 ,b4 ,lloyd and the author1 in #ahgc1 when travelling in ,newfoundland--will be easily appreciated4 ,at the time to which ,i refer1 my companion was bringing a canoe down the rapids below the ,grand ,pond in a country which is practically uninhabited1 and where an ,indian trapper would perhaps be the only person met with1 and this not more than once a year4 ,whilst shooting the rapids one of the ,indians1 ,reuben ,soulian1 shot at a deer passing up one bank of the river4 ,that the deer had been hit was testified by a trail of blood which bespattered the rocks4 ,subsequently several more shots were fired1 and it was believed by all that the deer was killed4 ,soulian quickly followed the animal to the spot where it was supposed to have fallen4 ,some time after he returned1 having failed to find any trace of the animal4 ,he was greatly agitated1 but eventually became melancholy1 saying that the sudden disappearance of the animal was a sure sign that some of his relations had suddenly died4 ,about two hours afterwards ,mr4 ,lloyd's party met with a party of ,indians coming up the river1 the first they had seen for four weeks1 who told them that ,soulian's sister had just died on the coast4 ,in the northern part of ,south ,america certain shocks are anticipated by preliminary vibrations which cause a little bell attached to a ,t-shaped frame 7cruz sonante7 to ring4 ,there are1 however1 persons 7trembloron7 who are supposed to be endowed with seismic foresight1 whose verdicts are much relied upon4 ,in ,caraccas it is said that nearly every street in the river suburb has an earthquake ,cassandra or two4 ,some of these go so far not only as to predict the coming seisms1 but also the vicissitudes of particular streets4#acf ,earthquake prophets are1 however1 by no means confined to the new world1 and many examples of them may be found in the histories of countries where earthquakes have been felt4 ,the story of the crazy lifeguardsman who prophesied an earthquake to take place in ,london on ,april #d1 #afia1 is an example4 ,the ,rev4 ,sig4 ,pasquel ,e4 ,perdini1 writing on the earthquakes at ,leghorn in #agdb1 says that #8a ,milanese astrologer predicted this earthquake for ,january #bg1 by which 8misfortune0 the faith and credit given to the astrologer gained him more reverence and honour than the prophets and holy gospel4' ,before the time at which he predicted a second shock1 people removed away from ,leghorn4 ,warnings furnished by animals4--,a study of the warnings furnished by animals is also interesting4 ,several of the natives in ,caraccas possess oracular quadrupeds1 such as dogs1 cats1 and jerboas1 which anticipate coming dangers by their restlessness4 ,before the catastrophe of #ahab1 at ,caraccas1 a ,spanish stallion broke out from its stable and escaped to the highlands1 which was regarded as the result of the prescience of a coming calamity4 ,before the disturbances of #ahbb and #ahce1 which shook ,chili1 immense flocks of sea birds flew inland1 as if they had been alarmed by the commencement of some suboceanic disturbance4 ,before this last shock it is also related that all the dogs escaped from the city of ,talcahuano4 ,earthquake warning4--,what has here been said respecting the prediction of earthquakes is necessarily imperfect--many of the signs which are popularly supposed to enable persons to foretell the coming of an earthquake having already been mentioned in previous chapters4 ,that we shall yet be able to prepare ourselves against the coming of earthquakes1 by the applications of laws governing these disturbances1 is not an unreasonable hope4 ,with an electric circuit which is closed by a movement of the ground1 we are already in a position to warn the dwellers in surrounding districts that a movement is approaching4 ,an earthquake which travelled at the rate of four seconds to the mile might1 if it were allowed to close a circuit which fired a gun at a station fifteen miles distant1 give the inhabitants at that place a minute's warning to leave their houses4 ,the inhabitants of ,australia and the western shores of the ,pacific might1 by telegraphic communication1 receive eighteen to twenty-five hours' warning of the coming of destructive sea waves resulting from earthquakes in ,south ,america4 ,although warnings like these might have their value1 that which is chiefly required is to warn the dwellers at and near an earthquake centre of coming disturbances4 ,what the results of the observations on earth tremors will lead to is problematical4 ,should microseismic observation enable us to say when and where the minute movements of the soil will reach a head1 a valuable contribution to the insurance of human safety in earthquake regions will have been attained4 ,as to whether the movements of tromometers are destined to become barometric-like warnings of increased activity beneath the earth crust1 or whether they are only due to vibrations of the earth crust produced by variations in atmospheric pressure1 has yet to be investigated4 ,other phenomena which may probably forewarn us of the coming of an earthquake are phenomena resultant on the stresses brought to bear upon the rocky crust previous to its fracture1 or phenomena due to changes in the position and condition of heated materials beneath the earth's surface4 ,amongst these may be mentioned electrical disturbances1 which appear to be so closely related to seismic phenomena4 ,at the time of earthquakes telegraph lines have been disturbed1 but as to what may happen before an earthquake we have as yet but little information4 ,the subject of earthquake warning is of importance to many countries1 and is deserving of attention4 ,as our knowledge of earth movements1 and their attendant phenomena1 increases1 there is but little doubt that laws will gradually be formulated1 and in the future1 as telluric disturbances increase1 a large black ball gradually ascending a staff may warn the inhabitants on the land of a coming earthquake1 with as much certainty as the ball upon a pole at many seaports warns the mariner of coming storms4 ,,chapter ,,xix4 ,,earth ,,tremors4 ,artificially produced tremors--,observations of ,kater1 ,denman1 ,airy1 ,palmer1 ,paul--,natural tremors--,observations of ,zllner1 ,m4 d',abbadie1 ,g4 ,h4 and ,h4 ,darwin--,experiments in ,japan--,with seismoscopes1 microphones1 pendulums--,work in ,italy--,bertelli1 ,count ,malvasia1 ,m4 ,s4 di ,rossi--,instruments employed in ,italy--,tromometers1 microseismographs1 microphones--,results obtained in ,italy--in ,japan--,cause of microseismic motion4 ,during the past few years considerable attention has been drawn towards the study of small vibratory motions of the ground1 which to the unaided senses are usually passed by without recognition4 ,these motions are called earth tremors4 ,their discovery appears to have been due to accident1 and not to the results of inductive reasoning4 ,no sooner had philosophers contrived astronomical and other instruments for the purpose of making refined measurements and observations than they at once discovered that they had an enemy to contend against in the form of microscopic earthquakes4 ,artificially produced tremors4--,artificial disturbances of this description exist in all our towns1 and near a railway line they are perceptible with every passing train4 ,those who have used microscopes of high power will readily appreciate how small a disturbance of the ground is visible in the apparent movement of the object under examination4 ,captain ,kater found that he could not perform his pendulum experiments in ,london on account of the vibrations produced by the rolling of carriages4 ,captain ,denman1 who made some observations on artificially produced tremors1 found that a goods train produced an effect #a1ajj feet distant in marshy ground over sandstone4 ,vertically1 however1 above a tunnel through the sandstone1 the effects only extended #ajj feet4 ,a remarkable example of the trouble which artificially produced earth vibrations have occasioned those who make astronomical observations occurred some twenty years ago at the ,greenwich ,observatory4 ,when determining the collimation error of the transit circle by means of the reflexion of a star in a tray of mercury1 it was found that on certain nights the surface of the mercury was in such a state of trembling that the observers were unable to complete their observations until long after midnight4 ,after obtaining a series of dates on which these disturbances occurred1 it was found that they coincided with public and bank holidays1 on which days crowds of the poorer classes of ,london flocked to ,greenwich ,park1 and there amused themselves with running and rolling down the hill on which the observatory is situated4 ,on these occasions it was found that the disturbances in the mercury were such that observations could not be made until two or three hours after the crowds had been turned out of the neighbouring park4#acg ,to obviate this difficulty ,sir ,george ,airy suspended his dish of mercury in a system of india-rubber bands1 and in this way succeeded in eating the intruders up4 ,lieutenant-,colonel ,h4 ,s4 ,palmer1 ,r4,e41 when engaged with the transit of ,venus expedition in ,new ,zealand1 in #ahgd1 was troubled with vibrations produced from a neighbouring railway4 ,to escape the enemy he intrenched his instruments by placing them in pits4 ,with pits #c feet deep he found himself sufficiently protected4 ,the distance from the line was about #djj yards1 and the soil through which the disturbances were propagated was a coarse pebbly gravel4#ach ,before the ,united ,states ,naval ,observatory was established at ,washington1 ,professor ,h4 ,m4 ,paul was deputed to make a tremor survey to discover stable ground4 ,the results of these experiments were exceedingly interesting4 ,by watching the reflected image of a star in a dish of mercury a passing train would be noticed at the distance of a mile4 ,its approach could be detected by the trembling of the image before its coming could be heard4 ,at one point of observation the disturbance appeared to be cut off by a ravine4 ,the strata was gravel and clay4#aci ,these few examples of artificially produced tremors1 to which many more might be added1 have been given because they teach us something respecting their nature4 ,hitherto earth tremors have only been regarded as intruders1 which it was necessary to escape from or destroy4 ,from what has been said they appear to be a superficial disturbance which is propagated to an enormous distance4 ,this distance appears to depend upon the propagating medium1 upon the intensity of the initial disturbance1 and upon its duration4 ,in the observation of these artificial disturbances1 which are accessible to every one1 and which hitherto have been so neglected1 we have undoubtedly a fruitful source of study4 ,natural tremors4--,next let us turn to those microscopical disturbances of our soil which are due to natural causes4 ,thus far they seem to have been recorded wherever instruments suitable for their detection have been erected1 and it is not improbable that they are common to the surface of the whole globe4 ,some of the more definite observations which have been made upon earth tremors were those made in connection with experiments on the deviation of the vertical due to the attractive influence of the moon and sun4 ,professor ,zllner1 who invented the horizontal pendulum which he used in the attempt to measure the change in level due to lunar and solar attraction1 found his instruments so sensitive that the readings were always changing4 ,the most interesting observations which were made upon small disturbances of the soil were those of ,m4 d',abbadie1 who carried on his experiments at ,abbadia1 in ,subernoa1 near ,hendaye1 #djj mtres distant from the ,atlantic1 and #fb mtres above sea level4 ,the soil was a loamy rock4 ,here ,m4 d',abbadie constructed a concrete cone #h mtres in height1 which was pierced down the centre by a vertical hole or well1 which was continued two mtres below the cone into the solid rock4 ,at the bottom of this hole or well a pool of mercury was formed which reflected the image of cross wires placed at the top of the hole4 ,these cross wires and their reflection were observed by means of a microscope4 ,the observations consisted in noting the displacement and azimuth of the reflected image relatively to the real image of the wires4 ,after allowing this structure five years to settle1 ,m4 d',abbadie commenced his observations4 ,to find the surface of the mercury tranquil was a rare occurrence4 ,sometimes the mercury appeared to be in violent motion1 although both the air and neighbouring sea were perfectly calm4 ,at times the reflected image would disappear as if the mercury had been disturbed by a microscopic earthquake4 ,the relative positions of the images were in part governed by the state of the tide4 ,altogether the movements were so strange that ,m4 d',abbadie did not venture any speculations as to their cause1 but he remarks that the cause of the changes he observed were sometimes neither astronomical nor thermometrical4 ,these observations1 the principal object of which was to determine changes in level rather than earth vibrations1 were carried on between the years #ahfh and #ahgb4adj ,observations at ,cambridge4--,another instructive set of observations were those which were made in the years #ahhj-ahhb1 by ,george and ,horace ,darwin1 in the ,cavendish ,laboratory1 at ,cambridge4 ,the main object in these experiments was to determine the disturbing influence of gravity produced by lunar attraction4 ,the result which was obtained1 however1 showed that the soil at ,cambridge was in such an incessant state of vibration that whatever pull the moon may have exerted upon the instrument which was employed was masked by the magnitude of the effects produced by the earth tremors1 and the experiments had1 in consequence1 to be abandoned4 ,the principle of this instrument was similar to one devised by ,sir ,william ,thomson1 and put up by him in his laboratory at ,glasgow4 ,as erected by the brothers ,darwin1 at ,cambridge1 it was briefly as follows3 ,a pendulum1 which was a massive cylinder of pure copper1 was hung by a copper wire1 about four feet long1 inside a hollow cylindrical tube rising from a stone support4 ,a small mirror was then hung by two silk fibres1 one of which was fastened to the bob and the other to the stone basement4 ,a ray of light sent from a lamp on to the mirror was reflected to a scale seven feet distant1 and by this magnification any motion of the bob relatively to the stone support was magnified #ej1jjj times4 ,in several ways the apparatus was insulated from all accidental disturbances4 ,the spot of light was observed from another room by means of a telescope4 ,this instrument was so delicate that even at the distance of sixteen feet the shifting of your weight from one foot to the other caused the spot of light to run along the scale4 ,so sensitive was the instrument that1 notwithstanding its being cut off from the surrounding soil by a trench filled with water and the whole instrument being immersed in water to damp out the small vibrations1 it would seem that the ground was in a constant state of tremor2 in fact1 so persistent and irregular were these movements that it seemed impossible to separate them from the perturbations due to the attraction of the moon4#ada ,as a result of observations like these1 the world had gradually forced upon it the fact that the ground on which we live is probably everywhere in what is practically an incessant state of vibration4 ,this led those who were interested in the study of earth movements to establish special apparatus for the purpose of recording these motions with the hope of eventually discovering the laws by which they were governed4 ,experiments in ,japan4--,the simpler forms of apparatus which have been used in ,japan may be described as delicate forms of seismoscopes1 which1 in addition to recording earth tremors1 also record the occurrence of small earthquakes4 ,a simple contrivance which may be used for the purpose of recording small earthquakes can be made with a small compass needle4 ,if a light1 small sensitive compass needle be placed on a table1 it will be found that a small piece of iron like a nail may be pushed so near to it that the needle assumes a position of extremely unstable equilibrium4 ,if the table now receives the slightest tap or shake this condition is overcome1 and the needle flies to the iron and there remains4 ,by making the support of the needle and the iron the poles of an electric circuit it is possible to register the time at which motion took place with considerable accuracy4 ,with crude apparatus like this a large number of small earth disturbances have been recorded4 ,another form of apparatus1 employed in ,japan1 has been a delicately constructed circuit closer4 ,the motions of this instrument were recorded by causing an electro-magnet to deflect a pencil which was tracing a circle on a revolving dial4 ,the revolving dial was a disc of wood covered with paper fixed to the hour-hand axle of a common clock4 ,a third form of apparatus used in ,japan consisted of a small piece of sheet lead about the size of a threepenny piece suspended by a short loop from a rigid support4 ,projecting from the lead a fine wire1 about two inches in length1 passed freely through a hole in a metallic plate4 ,by the slightest motion of the support the small pendulum of lead was set into a state of tremor and caused its pointer to come in contact with one or other side of the hole in the metal plate and thus to close an electric circuit4 ,a more refined kind of apparatus which has been employed in ,japan was similar to that used by the ,darwins at ,cambridge4 ,this was so arranged that any deflection of the mirror was permanent until the instrument was reset1 and in this way the maximum disturbance which had taken place between each observation was recorded4 ,in addition to these and other contrivances1 experiments were made with microphones4 ,the microphones used were small doubly pointed pencils of carbon about three centimetres long1 saturated with mercury1 and supported vertically in pivot holes bored in other pieces of carbon1 which were the terminals of an electric circuit4 ,these microphones were screwed down on the top of stakes driven deeply into the ground4 ,they were covered with a glass shade thickly greased at its base4 ,the stakes were in the ground at the bottom of a small pit--about two feet square and two feet deep--which was lined with a box4 ,the box was covered with a lid1 and earth to the depth of nine inches or one foot4 ,one of these pits was in the middle of a lawn in the front of my house1 and the other was at the foot of a hill at the back of the house4 ,the wires from the microphone passed through the side of the box into a bamboo tube and thence up to my dining-room and bed-room4 ,in one of the circuits there were three ,daniell's cells1 a telephone1 and a small galvanometer4 ,i used the galvanometer because ,i found that when there was sufficient motion in the microphone to produce a sound in the telephone a motion in the needle of a galvanometer was produced4 ,if in any case motion took place in the magnetic needle during my absence1 it was held deflected by a small piece of iron with which it was brought into contact by the movement4 ,the sensitiveness of the arrangement may be judged of from the fact that if a person walked on the grass within six feet of the microphone1 each step caused a creak in the telephone1 and the needle of the galvanometer was caused to swing and come in contact with the iron4 ,dogs running on the grass had no effect4 ,a small stone one or two inches in diameter thrown from the house so that it fell near to the microphone pit caused a sharp creak in the telephone and a movement in the needle4 ,the nature of the records ,i received from this contrivance may be judged of from the following extract from my papers4 h4 m4 #ahgi4 ,nov4 #abth #g #j ,p4,m4 contact of needle #g #b difficult to set the needle #g #c needle swings and telephone creaks #g #d #g #e #g #f #g #aj #c more swings #g #aa again ,here ,i went out1 took away the covering1 and examined the microphone4 ,nothing wrong was to be observed4 ,all that ,i saw was one small ant4 ,i do not think that this could have caused the disturbance1 because it could not get near the instrument4 ,on the succeeding nights ,i experienced similar disturbances1 and it seemed as if they might possibly have been the prelude to several small shocks which occurred about this time 7,november #ae1 #af1 and #ag74 ,on ,november #ag1 at #h ,a4,m41 the needle was found in contact1 and again at #e ,p4,m41 and at #f ,p4,m4 the shock of a small earthquake was felt which caused a rattling sound in the telephone for about one minute after the motion had appeared to cease4 ,the needle swung considerably1 but did not come in contact4 ,the great objection to these observations is that it is possible that the movements and sounds which ,i have recorded might1 with the exception of one case when the shaking was actually felt1 possibly have been produced by causes other than that of the movement of the ground4 ,to determine this ,i subsequently put up two distinct sets of apparatus to determine whether the motions of each were synchronous4 ,so far as ,i went this appeared only to be sometimes the case3--but this is a question difficult to determine1 unless a recorder of time be added to the apparatus4 ,the greatest objection to observations of this sort is that the sensibility of the instrument is not constant4 ,after a current has been running for several days it is no longer sensible to slight shocks1 it appears as if its resistance had been increased4 ,to overcome this it is necessary to resharpen the carbon points and bore out the pivot holes every three or four days4 ,farther1 the battery varies4 ,this might to some extent be overcome by using a battery with large plates4 ,these two causes tend to reduce the sensitiveness of the galvanometer-like recorder--the deflection of the needle gradually becoming less and less1 and therefore day by day needing a greater swing to bring it into contact with the iron4 ,for reasons such as these this instrument1 to be used successfully1 appears to require considerable attention4 ,another form of microphone employed by the author consisted of an aluminium wire standing vertically on a metallic plate1 its upper end passing loosely through a hole in an aluminium wire standard4 ,the upper end of the vertical wire was loaded with lead4 ,this contrivance possesses all the sensitiveness of an ordinary microphone1 whilst1 if it receives a sudden impulse1 there is a sudden break in the current1 and the vertical wire is thrown from one side to the other of the hole in the standard4 ,after many months of tiresome observation with instruments of this description1 and after eliminating all motions which might have been produced by accidental causes1 the general result obtained showed that in ,tokio there were movements of the soil to be detected every day1 and sometimes many times per day1 which to ordinary persons were passed by unnoticed4 ,work in ,italy4--,the most satisfactory observations which have been made upon microseismic disturbances are those which have been made during the last ten years in ,italy4 ,the father of systematical microseismical research appears to have been ,father ,timoteo ,bertelli1 of ,florence4 ,in #ahgj ,father ,bertelli suspended a pendulum in a cellar1 and observed it with a microscope4 ,as the result of his observations it was announced that he had perceived the earthquakes which shook ,romagna1 although to the ordinary observer in ,florence these shakings had not been perceptible4 ,in #ahgc ,bertelli1 by means of microscopes fixed in several azimuths1 made #e1ejj observations on free pendulums4 ,he also made observations on reflections from the surface of mercury4#adb ,one result of these observations was to show that microseismic motions increased with a fall of the barometer4 ,similar observations were made at ,bologna by ,m4 le ,conte ,malvasia1 and also by ,m4 ,s4 di ,rossi1 near ,rome4 ,on ,january #ad1 #ae1 and ,february #be these three observers at their respective stations simultaneously observed great disturbances4 ,similar investigations were made at ,nice by ,m4 le ,baron ,prost4 ,although doubt was cast upon ,bertelli's observations they appear to have been the origin of a series of microseismical observations1 a distinguished leader in which is ,professor ,rossi1 who1 in #ahgd1 found that large earthquakes were almost always preceded or accompanied with microseismical storms4 ,in #ahgh ,professor ,rossi worked upon these small disturbances with the assistance of the microphone and telephone1 and his first results were published by ,professor ,palmieri4 ,many of ,professor ,rossi's observations were made in the grotto of ,roca de ,papa1 #gjj mtres high and eighteen mtres under the soil4 ,here over #f1jjj observations were made by means of microscopes1 on pendulums of different lengths1 suspended in tubes cut in the solid rock4 ,instruments employed in ,italy4--,it is impossible to describe in detail the various forms of apparatus which have been used by the ,italian investigators4 ,a description of one or two of the more important instruments may not1 however1 be out of place1 inasmuch as they will assist the reader to understand the manner in which the various results respecting the laws governing microseismic movements have been arrived at4 ,the most important of these instruments is the ,normal ,tromometer of ,bertelli and ,rossi4 ,this consists of a pendulum #a metres long1 carrying1 by means of a very fine wire1 a weight of #ajj grammes4 ,to the base of the bob a vertical stile is attached1 and the whole is enclosed in a tube terminated1 at its base1 by a glass prism of such a form that when looked through horizontally the motion of the stile can be seen in all azimuths4 ,in front of this prism a microscope is placed4 ,inside the microscope there is a micromatic scale1 so arranged that it can be turned to coincide with the apparent direction of oscillation of the point of the stile4 ,in this way not only can the amplitude of the motion of the stile be measured1 but also its azimuth4 ,the extent of vertical motion is measured by the up and down motion of the stile due to the elasticity of the supporting wire4 ,this instrument is shown in the accompanying drawing4 ,illustration3 ,,fig4 #cg4--,normal ,tromometer4 ,b1 bob of pendulum2 ,p1 prism2 ,m1 microscope2 ,s1 rim of scale4 ,another apparatus is the ,microseismograph of ,professor ,rossi4 ,here we have an arrangement which gives automatic records of slight motions4 ,it consists of four pendulums1 each about three feet long1 suspended so that they form the corners of a square platform4 ,in the centre of this platform a fifth1 but rather longer1 pendulum is suspended4 ,the four pendulums are each connected just above their bobs to the central pendulum with loose silk threads4 ,fixed to the centre of each of these threads1 and held vertically by a light spring1 is a needle1 so adjusted that each thread is depressed to form an obtuse angle of about #aee4 ,these needles form the terminals of an electric circuit1 the other termination of which is a small cup of mercury placed just below the lower end of the needle4 ,by a horizontal swing of one of the pendulums this arrangement causes the needle to move vertically1 but with a slightly multiplied amplitude4 ,by this motion the needle comes in contact with the mercury1 and an electro-magnet with a lever and pencil is caused to make a mark on a band of paper moved by clockwork4 ,the five pendulums being of different lengths allows the apparatus to respond #8to seismic waves of different velocities4'#adc ,lastly1 we have ,professor ,rossi's ,microphone4 ,this consists of a metallic swing arranged like the beam of a balance4 ,by means of a movable weight at one end of the beam this is so adjusted that it falls down until it comes in contact with a metallic stop4 ,this can be so adjusted that a slight tap will cause the beam to slightly jump from the stop4 ,the beam and the stop form two poles of an electric circuit1 in which there is a telephone4 ,the slightest motion in a vertical direction causes a fluctuation in the current passing between the stop and the beam1 and a consequent noise is heard in the telephone4 ,with instruments analogous to these1 observations have been made by various observers in all portions of ,italy1 extending over a period of ten years4 ,every precaution appears to have been taken to avoid accidental disturbances1 and the experiments have been repeated in a variety of forms4 ,results obtained in ,italy4--,the results which from time to time have been announced are of the greatest interest to those who study the physics of the earth's crust1 and they appear to be leading to the establishment of laws of scientific value4 ,it would seem that the soil of ,italy is in incessant movement1 there being periods of excessive activity usually lasting about ten days4 ,such periods are called seismic storms4 ,these storms are separated by periods of relative calm4 ,these storms have their greater regularity in winter1 and sharp maximums are to be observed in spring and autumn4 ,in the midst of such a period or at its end there is usually an earthquake4 ,usually these storms are closely related to barometric depressions4 ,to distinguish these movements from those which occur under high pressure1 the latter are called baro seismic movements1 and the former vulcano seismic movements4 ,the relation of these storms to barometric fluctuation has been observed to have been very marked during the time of a volcanic eruption4 ,at the commencement of a storm the motions are usually small1 and one storm1 lasting two or three days1 may be joined to another storm4 ,in such a case the action may be a local one4 ,it has been observed that a barometrical depression tended to bring a storm to a maximum1 whilst an increase of pressure would cause it to disappear4 ,sometimes these actions are purely local1 but at other times they may affect a considerable tract of land4 ,if a number of pendulums of different length are observed at the same place1 there is a general similarity in their movements1 but it is also evident that the free period of the pendulum more or less disturbs the character of the record4 ,the greatest amplitude of motion in a set of pendulums is not reached simultaneously by all the pendulums1 and at every disturbance the movement of one will predominate4 ,from this ,rossi argues that the character of the microseismical motions is not constant4 ,bertelli observed that the direction of oscillation of the pendulums is different at different places1 but each place will have its particular direction dependent upon the direction of valleys and chains of mountains in the neighbourhood4 ,rossi shows that the directions of movement are perpendicular to the direction of lines of faults1 the lips of these fractures rising and falling1 and producing two sets of waves1 one set parallel to the line of fracture1 and the other perpendicular to such a direction4 ,these movements1 according to ,bertelli1 have no connection with the wind1 rain1 change of temperature1 and atmospheric electricity4 ,illustration3 ,,fig4 #ch4 ,the disturbances1 as recorded at different towns1 are not always strictly synchronous1 but succeed each other at short intervals4 ,if1 however1 we take monthly curves of the disturbances as recorded at different towns in ,italy1 we see that these are similar in character4 ,the maximum of disturbance occurs about the winter solstice1 and the minimum about the summer solstice1 and in this respect they exhibit a perfect accordance with the curves drawn by ,mallet to show the periodicity of earthquakes4 ,the accompanying curves taken from one of ,bertelli's original memoirs not only show this general result but also show the close accord there is between the results obtained at different towns during successive months4 ,at ,florence1 before a period of earthquakes there is an increase in the amplitude and frequency of vertical movements4 ,these vertical movements do not appear to coincide with the barometrical disturbances1 but they appear to be connected with the seismic disturbances4 ,they are usually accompanied with noises in the telephone1 but as the microphone is so constructed as to be more sensitive to vertical motion than to horizontal motion1 this is to be expected4 ,this vertical motion would appear to be a local action1 inasmuch as the accompanying motions of an earthquake which originates at a distance are horizontal4 ,storms of microseismical motions appear to travel from point to point4 ,sometimes a local earthquake is not noticed in the tromometer1 whilst one which occurred at a distance1 although it may be small1 is distinctly observed4 ,to explain this1 ,bertelli suggests the existence of nodes4 ,similar conclusions were arrived at by ,rossi when experimenting on different portions of the sides of ,vesuvius4 ,galli noticed an augmentation in microseismic activity when the sun and moon are near the meridian4 ,grablovitz found from ,bertelli's observations a maximum two or three days before the syzygies1 and a minimum three days after these periods4 ,he also found that the principal large disturbances occurred in the middle of periods separating the quadrature from the syzygies1 the apogee from perigee1 and the lunistigi period from the nodes1 whilst the smallest disturbances happened in the middle of periods opposed to these4 ,p4 ,c4 ,melzi says that the curves of microseismical motions1 earthquakes1 lunar and solar motions1 show a concordance with each other4 ,with the microphone ,rossi hears sounds which he describes as roarings1 explosions1 occurring isolated or in volleys1 metallic and bell-like sounds1 ticking1 c41 which1 he says1 revealed natural telluric phenomena4 ,sometimes these have been intolerably loud4 ,at ,vesuvius the vertical shocks corresponded with a sound like volleys of musketry1 whilst the undulatory shocks gave the roaring4 ,some of these sounds could be imitated artificially by rubbing together the conducting wires in the same manner in which the rocks must rub against each other in an earthquake4 ,other sounds were imitated by placing the microphone on a vessel of boiling water1 or by putting it on a marble slab and scratching and tapping the under side of it4 ,these1 then1 are some of the more important results which have been arrived at by the study of microseismic motions4 ,one point which seems worthy of attention is that they appear to be more law-abiding than their more violent relations1 the earthquakes1 and as phenomena in which natural laws are to be traced they are certainly deserving our attention4 ,as to whether they will ever become the means of forewarning ourselves against earthquakes is yet problematical4 ,their systematic study1 however1 will enable us to trace the progress of a microseismic storm from point to point1 and it is not impossible that we may yet be enabled to foretell where the storm may reach its climax as an earthquake4 ,these1 ,i believe1 are the views of ,professor di ,rossi1 who is at the present time engaged in the establishment of a system of microseismic observations throughout ,italy4 ,before the earthquake of ,san ,remo 7,dec4 #f1 #ahgd7 ,rossi's tromometer was in a state of agitation1 and similar disturbances were observed at ,livorno1 ,florence1 and ,bologna4 ,since ,february #ahhc ,i have observed a tromometer in ,japan1 and such results as have been obtained accord with results obtained in ,italy4 ,the increase in microseismical activity with a fall of the barometer is very marked4 ,other peculiarities in the behaviour of the instrument will be referred to under #8,earth ,pulsations4' ,cause of microseismic movements4--,as to the cause of tromometric movements1 we have a field for speculation4 ,possibly they may be due to slight vibratory motions produced in the soil by the bending and crackling of rocks produced by their rise upon the relief of atmospheric pressure4 ,if this were so we should expect similar movements to be produced at the time of an increase of pressure4 ,rossi suggests that they may be the result of an increased escape of vapour from the molten materials beneath the crust of the earth1 consequent upon a relief of pressure4 ,the similarity of some of the sounds which are heard with the microphone to those produced by boiling water are suggestive of this1 and ,rossi quotes instances when underground noises like those which we should expect to hear from a boiling fluid have been heard before earthquakes without the aid of microphones4 ,one instance was that of ,viduari1 a prisoner in ,lima1 who1 two days before the shock of #ahbd1 repeatedly predicted the same in consequence of the noises he heard4 ,a possible cause of disturbances of this order may be small but sudden fluctuations in barometric pressure1 which are visible during a storm4 ,during a small typhoon on ,september #ae1 #ahha1 when in the ,kurile ,islands1 ,i observed that the needle of an aneroid worked back and forth with a period of from one to three seconds4 ,this continued for several hours4 ,with every gust of wind the needle suddenly rose and then immediately fell4 ,at times it trembled4 ,these movements were observed in the open air4 ,the extent of these sudden variations was approximately from #jc to #je inches4 ,beckoning an increase of barometrical pressure of one hundredth of an inch as equivalent to a load of twenty million pounds on the square mile1 during this storm there must have been the equivalent of loads of from #fj to #ajj million pounds to the square mile continually placed on and removed from a considerable tract of the earth's surface4 ,if the period of application of these stresses approximately coincide with the natural vibrational period of the area affected1 it would surely seem1 especially when we reflect upon the effect of an ordinary carriage1 that tremors of considerable magnitude ought to be produced4 ,an inspection of the following few observations taken from my note-book for the same typhoon will suggest that even the large and slower variations are capable of producing tremulous motions4 ,time ,barometer h4 m4 reading #ab #e ,p4,m4 #bijb #ab #aj #bije #ab #ab #bijg #ab #ac #bije #ab #be #biaj #ab #ej #bijj #a #aj #bijj #a #bj #bijg ,,chapter ,,xx4 ,,earth ,,pulsations4 ,definition of an earth pulsation--,indications of pendulums--,indications of levels--,other phenomena indicating the existence of earth pulsations--,disturbances in lakes and oceans--,phenomena resultant on earth pulsations--,cause of earth pulsations4 ,the object of the present chapter is to show that from time to time it is very probable that slow but large wave-like undulations travel over or disturb the surface of the globe4 ,these movements1 which have escaped our attention on account of their slowness in period1 for want of another term ,i call earth pulsations4 ,the existence of movements such as these may be indicated to us by changes in the level of bodies of water like seas and lakes1 by the movements of delicate levels1 by the displacement of the bob of a pendulum relatively to some point on the earth above which it hangs1 and by other phenomena which will be enumerated4 ,indication of pendulums4--,pendulums which have been suspended for the purposes of seismometrical observations have1 both by observers in ,italy and ,japan1 been seen to have moved a short distance out from1 and then back to1 their normal position4 ,this motion has simply taken place on one side of their central position1 and is not due to a swing4 ,the character of these records is such that we might imagine the soil on which the support of the pendulum had rested to have been slowly tilted1 and slowly lowered4 ,they are the most marked on those pendulums provided with an index writing a record of its motions on a smoked glass plate1 which index is so arranged that it gives a multiplied representation of the relative motion between it and the earth4 ,as motions of this sort might be possibly due to the action of moisture in the soil tilting the support of the pendulum1 and to a variety of other accidental causes1 we cannot insist on them as being certain indications that there are slow tips in the soil1 but for the present allow them to remain as possible proof of such phenomena4 ,evidence of displacement of the vertical1 which are more definite than the above1 are those made by ,bertelli1 ,rossi1 ,count ,malvasia1 and other ,italian observers1 who1 whilst recording earth tremors1 have spent so much time in watching the vibrations of stiles of delicate pendulums by means of microscopes4 ,as a result of these observations we are told that the point about which the stile of a pendulum oscillates is variable4 ,these displacements take place in various azimuths1 and they appear to be connected with changes of the barometer4 ,i have made similar observations in ,japan4 ,from this1 and from the fact that it is found that a number of different pendulums differently situated on the same area give similar evidence of these movements1 it would hardly seem that these phenomena could be attributed to causes like changes in temperature and moisture4 ,m4 ,s4 di ,rossi lays stress on this point1 especially in connection with his microseismograph1 where there are a number of pendulums of unequal length which give indications of a like character4 ,the direction in which these tips of the soil take place--which phenomena are noticeable in seismic as well as microseismic motions--,rossi states are related to the direction of certain lines of faulting4 ,indications of levels4--,bubbles of delicate levels can be easily seen to change their position with meteorological variations2 but ,rossi also tells us that they change their position1 sometimes not to return for a long time1 during a microseismic storm4 ,here again we have another phenomenon pointing to the fact that microseismic disturbances are the companions of slow alterations in level4 ,one of the most patient observers of levels has been ,m4 ,plantamour1 who commenced his observations in #ahgh1 at ,scheron1 on the ,lake of ,geneva4 ,he used two levels1 one placed north and south1 and the other east and west4 ,during the summer of #ahgh the east end rose1 but at the end of ,september a depression set in4 ,the diurnal movements had their maximum and minimum at #f and #g4de ,a4,m4 and ,p4,m4 ,the total amplitude was #dhi4 ,the variations of the east and west level appeared to be due to the temperature1 but the movements of the north and south level were dependent upon an unknown cause4 ,between ,october #a1 #ahgi1 and ,september #cj1 #ahhj1 the east end fell rapidly1 from the middle of ,november up to ,december #bf1 amounting to #hhga4 ,it then rose #fee to ,january #e1 and then fell again4 ,on ,january #bh it reached #hiie1 after which it rose4 ,between ,october #d1 #ahgi1 and ,january #bh1 #ahhj1 the movement was #ieh1 against #bhjh of the previous year4 ,these movements were not due alone to temperature4 ,the north and south level1 which was not influenced by the cold of the winter1 moved #def4 ,in the previous year #dhi4add ,from ,february #ag to ,june #e1 #ahhc1 the author observed in ,tokio the bubbles of two delicate levels1 one placed north and south1 and the other east and west4 ,they were placed under glass cases on the head of a stone column4 ,the column1 which is inside a brick building1 rests on a concrete foundation1 and is about ten years old4 ,it is in no way connected with the building4 ,the temperature of the room has a daily variation of about #a ,fahr4 ,in both these levels diurnal changes are very marked4 ,occasionally they are enormously great4 ,thus1 on ,march #be1 the readings of the south end of the north south level were as follows3-- ,time ,readings4 h4 m4 #beth4 #d #jj ,p4,m4 #ajde #d #e #ajc #d #aj #ajb #d #be #aja #d #cj #ajj #d #dj #ih #d #db #iie #d #de #ajj #d #ej #aja #d #ee #aja #e #jj #ajj #bfth4 #g #jj ,a4,m4 #aje ,usually this level moves through about three divisions per day4 ,from ,march #be to ,may #d it travelled from #ih to #abg4 ,since then1 to ,june #e1 it has descended to #aaf4 ,during this period the east west level has been comparatively quiet4 ,one division of the north south level equals about #b of arc4 ,many of these changes may be due to changes in temperature1 variations in moisture1 and other local actions4 ,some of them1 however1 are hardly explicable on such assumptions4 ,the fact that the general direction in change of the vertical1 as indicated by a tromometer standing on the same column with the levels1 showed that the change which was taking place was rather in the column than in the instruments4 ,the fact also that at the time of a barometrical depression a pulse-like surge can be seen in the levels1 having a period averaging about three seconds and sometimes amounting to about one second of arc1 is a phenomenon hardly to be attributed to sudden fluctuations in moisture or temperature1 but indicates real changes in level4#ade ,in addition to variation in the bubbles of levels which come on more or less gradually1 we have many recorded instances of sudden alterations taking place in these instruments4 ,examples of what may have been a slow oscillating motion of the earth's crust are referred to by ,mr4 ,george ,darwin in a ,report to the ,british ,association in #ahhb4 ,one of them was made by ,m4 ,magnus ,nyrn1 at ,pulkova1 who1 when engaged in levelling the axis of a telescope1 observed spontaneous oscillation in the bulb of the level4 ,this was on ,may #aj 7,april #bh71 #ahgg4 ,the complete period was about #bj seconds1 the amplitude being #ae and #b4 ,one hour and fourteen minutes before this he observes that there had been a severe earthquake at ,iquique1 the distance to which in a straight line was #aj1fjj kilomtres1 and on an arc of a great circle1 #ab1ejj kilomtres4 ,on ,september #bj 7#h71 in #ahfg1 ,mr4 ,wagner had observed at ,pulkova oscillations of #c1 seven minutes before which there had been an earthquake at ,malta4 ,on ,april #d 7,march #bc71 #ahfh1 an agitation of the level had been observed by ,mr4 ,gromadzki1 five minutes before which there had been an earthquake in ,turkestan4 ,similar observations had been made twice before4 ,these1 however1 had not been connected with any earthquakes--at least1 ,mr4 ,darwin remarks--with certainty4 ,phenomena analogous to the pendulum and level observations4--,as examples of phenomena which are analogous to those made on pendulums and levels1 the following may be noticed4 ,on ,march #bj1 #ahha1 at #i ,p4,m4 a watchmaker in ,buenos ,ayres observed that all his clocks oscillating north and south suddenly began to increase their amplitude1 until some of them became twice as great as before4 ,similar observations were made in all the other shops4 ,no motion of the earth was detected4 ,subsequently it was learnt that this corresponded with an earthquake in ,santiago and ,mendoza4#adf ,another remarkable example illustrating the like phenomena is furnished by the observations which were made on ,december #ba1 #ahfj1 by means of a barometer in ,san ,francisco1 which oscillated1 with periods of rest1 for half an hour4 ,no shock was felt1 nor is it likely that it was a local accident1 as it could not be produced artificially4 ,on the following day1 however1 a violent earthquake was experienced at ,santiago4#adg ,at the time or shortly after the great ,lisbon earthquake1 curious phenomena were observed in distant countries1 which only appear to be explicable on the assumption of the existence of earth pulsations4 ,thus at ,amsterdam and other towns1 chandeliers in churches were observed to swing4 ,at ,haarlem water was thrown over the sides of tubs1 and it is expressly mentioned that no motion was perceived in the ground4 ,at the ,hague a tallow chandler was surprised at the clashing noise made by his candles1 and this the more so because no motion was felt underfoot4 ,unusual disturbances in bodies of water4--,at the time of large earthquakes it would appear that earth pulsations are produced1 which exhibit themselves in countries where the actual shaking of the earthquake is not felt1 by disturbances in bodies of waters like lakes and seas4 ,some remarkable examples of these disturbances are to be found in the records of the great ,lisbon earthquake4 ,this earthquake1 as a violent movement of the ground1 was chiefly felt in ,spain1 ,portugal1 northern ,italy1 the south of ,france and ,germany1 northern ,africa1 ,madeira1 and other ,atlantic islands4 ,in other countries further distant1 as1 for instance1 ,great ,britain1 ,holland1 ,scandinavia1 and ,north ,america1 although the records are numerous1 the only phenomena which were particularly observed was the slow oscillations of the waters in lakes1 ponds1 canals1 c4 ,in some instances the observers especially remark that there was no motion in the soil4 ,pebley ,dam1 in ,derbyshire1 which is a large body of water covering some thirty acres1 commenced to oscillate from the south4 ,a canal near ,godalming flowed eight feet over the walk on the north side4 ,coniston ,water1 in ,cumberland1 which is about five miles long1 oscillated for about five minutes1 rising a yard up its shores4 ,near ,durham a pond1 forty yards long and ten broad1 rose and fell about one foot for six or seven minutes4 ,there were four or five ebbs and flows per minute4 ,loch ,lomond rose and fell through about two and a half feet every five minutes1 and all the other lochs in ,scotland seem to have been similarly agitated4 ,at ,shirbrun ,castle1 in ,oxfordshire1 where the water in some moats and ponds was very carefully observed1 it was noticed that the floods began gently1 the velocity then increased1 till at last with great impetuosity they reached their full height4 ,here the water remained for a little while1 until the ebb commenced1 at first gently1 but finally with great rapidity4 ,at two extremities of a moat about #ajj yards long1 it was found that the sinkings and risings were almost simultaneous4 ,the motions in a pond a short distance from the moat were also observed1 and it was found that the risings and sinkings of the two did not agree4 ,during these motions there were several maxima4 ,these few examples of the motions of waters1 without any record of the motions of the ground1 at the time of the ,lisbon earthquake1 must be taken as examples of a very large number of similar observations of which we have detailed accounts4 ,like agitations1 it must also be remembered1 were perceived in ,north ,america and in ,scandinavia1 and if the lakes of other distant countries had been provided with sufficiently delicate apparatus1 it is not unlikely that similar disturbances would have been recorded4 ,besides these movements in the waters of seas and lakes1 at or about the time of great earthquakes1 we have records of like movements1 which take place as independent phenomena4 ,thus we read that on ,october #bb1 #agee1 the waters of ,lake ,ontario rose and fell five and a half feet several times in the course of half an hour4#adh ,on ,march #ca1 #agfa1 ,loch ,ness rose suddenly for the period of three-quarters of an hour4#adi ,as another example of the disturbance of water at the time of a great earthquake in districts where the earthquake was not felt1 may be mentioned the swelling of the waters of the ,maraon1 in #agdf1 on the night when ,callao was overwhelmed4 ,sudden variations in the level of the water have been many times observed in the ,north ,american lakes4 ,the changes in level which sometimes take place in the ,genfer and ,boden lakes are supposed to have some relation to the condition of the atmosphere4 ,a rising and falling of especial note took place on ,april #ah1 #ahee4 ,in ,switzerland these sudden changes are known as #8seiches' or #8rhussen4' ,from the observations and calculations of ,prof4 ,forel it would seem that the period of the #8seiches' depends upon the dimensions of the lakes2 the calculated periods dependent on the depths of the lakes being approximately equal to the observed periods4#aej ,w4 ,t4 ,bingham1 writing on the volcanoes of the ,hawaiian ,islands1 remarks that it is not unusual for the sea to be agitated by great and unusual tides1 and that such sea waves have not been attended with volcanic eruptions or seismic disturbances4 ,thus in ,may #ahai the tide rose and fell thirteen times4 ,on ,november #g1 #ahcg1 there was an ebb and flow of eight feet every twenty-eight minutes4 ,again1 on ,may #ag1 #ahda1 like phenomena1 unaccompanied by any other unusual occurrences1 were recorded4#aea ,phenomena which may possibly hold a relationship to earth pulsations are the periodical swellings of the ocean on the coast of ,peru4 ,dr4 ,c4 ,f4 ,winslow1 who made a long period observation upon the coast of ,peru1 found #8the highest tides to prevail at ,callao and ,paita in ,december and ,january1' and #8also a series of enormous waves or sea-swells to be thrown from time to time upon the coast1 varying from twenty-four to twenty-seven hours in continuance1 accompanied by unusual height of the tide during the same period4' ,during ,june and ,july the ocean was unusually tranquil4 ,these phenomena do not appear to be connected with great atmospheric storms1 nor do they hold any relation to the prevailing wind4 ,they increase with and accompany the swelling of the tides1 and occur generally1 but not always1 about full moon4 ,sometimes they break suddenly upon the coast4 #8,they are annual and constant in their periodicity4' ,the periodical swellings are most noticeable between ,tumbez #c ,s4,l4 and the ,chincha ,islands #ad ,s4,l4 ,these oceanic phenomena synchronise with the periodic intensity of earthquake phenomena in that part of the globe1 and these with tidal movements4#aeb ,other phenomena possibly attributable to earth pulsations4--,if we assume that earth pulsations have an existence1 these many phenomena which are otherwise difficult to understand meet with an explanation4 ,the curious effects which were produced in the springs at ,toplitz at the time of the ,lisbon earthquake may have been due to a pulse-like wave4 ,the flow of the principal spring was greatly increased4 ,before the increase it became turbid and at one time stopped4 ,subsequently it became clear and flowed as usual1 but the water was hotter and more strongly mineralised4 ,sudden changes in the flow of underground waters which from time to time are observed may be attributed to like causes4 ,secondary earthquakes such as occurred after the ,lisbon earthquake1 as for instance in ,derbyshire1 may have been produced by pulsations disturbing the equilibrium of ground in a critical state4 ,the falling in of subterranean excavations is also possibly connected with these phenomena4 ,possible causes of earth pulsations4--,mr4 ,george ,darwin1 in a report to the ,british ,association 7#ahhb71 has shown that movements of considerable magnitude may occur in the earth's crust in consequence of fluctuations in barometrical pressure4 7,a rise of the barometer over an area is equivalent to loading that area with a weight1 in consequence of which it is depressed4 ,when the barometer falls1 the load is removed from the area1 which1 in virtue of its elasticity1 rises to its original position4 ,this fall and rise of the ground completes a single pulsation47 ,on the assumption that the earth has a rigidity like steel1 ,mr4 ,darwin calculates that if the barometer rises an inch over an area like ,australia1 the load is sufficient to sink that continent two or three inches4 ,the tides which twice a day load our shores cause the land to rise and fall in a similar manner4 ,on the shores of the ,atlantic1 ,mr4 ,darwin has calculated that this rise and fall of the land may be as much as #e inches4 ,by these risings and fallings of the land the inclination of the surface is so altered that the stile of a plummet suspended from a rigid support ought not always to hang over the same spot4 ,there would be a deflection of the vertical4 ,in short1 calculations respecting the effects of loads of various descriptions1 which we know are by natural operations continually being placed upon and removed from the surface of various areas of the earth's surface1 indicate that slow pulsatory movements of the earth's surface must be taking place1 causing variations in inclination of one portion of the earth's crust relatively to another4 ,although it is possible that phenomena like the surging of levels may be attributable to causes like these1 we can hardly attribute the other phenomena to such agencies4 ,rather than seek an explanation from agencies exogenous to our earth1 we might perhaps with advantage appeal to the endogenous phenomena of our planet4 ,when the barometer falls1 which we have shown corresponds to an upward motion of the earth's crust1 we know1 from the results of experiments1 that microseismic motions are particularly noticeable4 ,as a pictorial illustration of what this really means1 we may imagine ourselves to be residing on the loosely fitting lid of a large cauldron1 the relief of the external pressure over which increases the activity of its internal ebullition--the jars attendant on which are gradually propagated from their endogenous source to the exterior of our planet4 ,this travelling outwards would take place much in the same way that the vibrations consequent to the rattle and jar of a large factory slowly spread themselves farther and farther from the point where they were produced4 ,admitting an action of this description to take place1 it would then follow that this extra liberation of gaseous material beneath the earth's crust would result in an increased upward pressure from within1 and a tendency on the part of the earth's crust to elevation4 ,if we accept this as an explanation of the increased activity of a tremor indicator1 then such an instrument may be regarded as a barometer1 measuring by its motions the variations in the internal pressure of our planet4 ,the relief of external pressure and the increase of internal pressure1 it will be observed1 both tend in the same direction--namely1 to an elevation of the earth's crust4 ,this explanation of the increased activity of earth tremors1 which has also been suggested by ,m4 ,s4 di ,rossi1 is here only advanced as a speculation1 more probable perhaps than many others4 ,we know how a mass of sulphur which has been fused in the presence of water in a closed boiler gives up in the form of steam the occluded moisture upon the relief of pressure4 ,in a similar manner we see steam escaping from volcanic vents and cooling streams of lava4 ,we also know how gas escapes from the pores and cavities in a seam of coal on the fall of the barometrical column4 ,we also know that certain wells increase the height of their column under like conditions4 ,the latter of these phenomena1 resulting in an increase in the rate of drainage of an area by its tendency to render such an area of less weight1 facilitates its rise4 ,if we follow the views of ,mr4 ,mallet in considering that the pressures exerted on the crust of our earth may in volcanic regions be roughly estimated by the height of a column of lava in the volcanoes of such districts1 we see that in the neighbourhood of a volcano like ,cotopaxi the upward pressures must be enormously great4 ,further1 the phenomena of earthquakes and volcanoes indicate that these pressures are variable4 ,before a volcano bursts forth we should expect that there would be in its vicinity an upward bulging of the crust1 and after its formation a fall4 ,further1 it is not difficult to conjecture other possible means by which such pressures may obtain relief4 ,should these pressures then find relief without rupturing the surface1 it is not difficult to imagine them as the originators of vast pulsations which may be recorded on the surface of the earth as wave-like motions of slow period4 ,as an explanation of the strange movements observed on seas and lakes1 ,kluge brings forward the following strange and remarkable theory4 ,the oxygen of the air is magnetic1 whilst water is diamagnetic and the earth magnetic3 we have1 therefore1 in our seas and lakes a diamagnetic body lying between and being1 consequently1 repelled from two magnetic bodies4 ,by variation in temperature1 the balance of repulsions exerted by the air and the earth is destroyed4 ,thus1 by an elevation of temperature the air expands and flows away from the heated area1 where1 in consequence1 there is less oxygen4 ,the result of this is1 that the repulsion of the air upon the waters is less than that of the earth upon the waters1 and the waters are in consequence raised up4 ,by a falling of temperature the waters may be depressed1 and by either of these actions waves may be produced without the intervention of earthquakes or earth pulsations4 ,the more definite kinds of information which we have to bring forward1 tending to prove the existence of earth pulsations1 too slow in period to be experienced by ordinary observers1 are those which appear to be resultant phenomena of great earthquakes4 ,the phenomena that we are certain of in connection with earth vibrations1 whether these vibrations are produced artificially by explosions of dynamite in bore-holes1 or whether they are produced naturally by earthquakes1 are1 first1 that a disturbance as it dies out at a given point often shows in the diagrams obtained by seismographs a decrease in period2 and1 secondly1 a similar decrease in the period of the disturbance takes place as the disturbance spreads4 ,as examples of these actions ,i will quote the following4 ,the diagram of the disturbance of ,march #a1 #ahhb1 taken at ,yokohama1 shows that the vibrations at the commencement of the disturbance had a period of about three per second1 near the middle of the disturbance the period is about #aa1 whilst near the end the period has decreased to #df4 ,that is to say1 the backward and forward motion of the ground at the commencement of the earthquake was six times as great as it was near the end1 when to make one complete oscillation it took between two and three seconds4 ,probably the period became still less1 but was not recorded owing to the insensibility of the instruments to such slow motions4#aec ,we have not yet the means of comparing together diagrams of two or more earthquakes1 one having been taken near to the origin1 and the other at a distance4 ,the only comparisons which ,i have been enabled to make have been those of diagrams taken of the same earthquake1 one in ,tokio and the other in ,yokohama4 ,as this base is only sixteen miles1 and the earthquake may have originated at a distance of several hundreds of miles1 comparisons like these can be of but little value4 ,other diagrams illustrating the same point are those obtained at three stations in a straight line1 but at different distances from the origin of a disturbance produced by exploding a charge of dynamite in a bore-hole4 ,a simple inspection of these diagrams shows that at the near station the disturbance consisted of backward and forward motions1 which1 as compared with the same disturbance as recorded at a more distant station1 were very rapid4 ,further1 by examining the diagram of the motions1 say1 at the near station1 it is clearly evident that the period of the backward and forward motion rapidly decreased as the motion died out4 ,these illustrations are given as examples out of a large series of other records1 all showing like results4 ,an observation which confirms the records obtained from seismographs respecting the increase in period of an earthquake as it dies out ,i have had opportunities of twice making with my levels4 ,after all perceptible motion of the ground subsequent upon a moderately severe shock had died away1 ,i have distinctly seen the bubble in one of these levels slowly pulsating with an irregular period of from one to five seconds4 ,although we must draw a distinction between earth waves and water waves1 we yet see that in these points they present a striking likeness4 ,let us take1 for example1 any of the large earthquake waves which have originated off the coast of ,south ,america1 and then radiated outwards1 until they spread across the ,pacific1 to be recorded in ,japan and other countries perhaps twenty-five hours afterwards1 at a distance of nearly #i1jjj miles from their origin4 ,near this origin they appeared as walls of water which were seen rapidly advancing towards the coast4 ,these have been from twenty to two hundred feet in height1 and they succeeded each other at rapid intervals1 until finally they died out as a series of gentle waves4 ,by the time these walls of water traversed the ,pacific1 to1 let us say1 ,japan1 they broadened out to a swell so flat that it could not be detected on the smoothest water excepting along shore lines where the water rose and fell like the tide4 ,instead of a wall of water sixty feet in height1 we had long flat undulations perhaps eight feet in height1 but with a distance from crest to crest of from one to two hundred miles4 ,if we turn to the effects of large earthquakes as exhibited on the land1 ,i think that we shall find records of phenomena which are only to be explained on the assumption of an action having taken place analogous to that which takes place so often in the ocean1 or an action similar to that exhibited by small earthquakes1 and artificially produced disturbances1 if greatly exaggerated4 ,the only explanation for the phenomena accompanying the ,lisbon earthquake appears to be that the short quick vibrations which had ruined so many cities in ,portugal had1 by the time that they had radiated to distant countries1 gradually become changed into long flat waves having a period of perhaps several minutes4 ,in countries like ,england these pulse-like movements were too gentle to be perceived1 except in the effects produced by tipping up the beds of lakes and ponds4 ,the phenomenon was not unlike that of a swell produced by a distant storm4 ,it would seem possible that in some cases pulsations producing phenomena like the #8seiches' of ,switzerland might have their origin beneath the ocean1 or deep down beneath the earth's crust4 ,perhaps1 instead of commencing with the #8snap and jar' of an earthquake1 they may commence as a heaving or sinking of a considerable area1 which may be regarded as an uncompleted effort in the establishment of an earthquake or a volcano4 ,from what has now been said it would seem that earth pulsations are phenomena with a real existence1 and that some of these are attributable to earthquakes4 ,on the other hand1 certain earthquakes are attributable to earth pulsations4 ,some of the phenomena which have been brought forward have only a possible connection with these movements1 and they yet require investigation4 ,elastic tides in the earth's crust have for long been realities in the minds of physicists4 ,these1 however1 are due to lunar and solar influences1 and are regular in their action4 ,the tidal-like movements called pulsations are of greater magnitude1 and their goings and comings are irregular4 ,,chapter ,,xxi4 ,,earth ,,oscillations4 ,evidences of oscillation--,examples of oscillation--,temple of ,jupiter ,serapis--,observations of ,darwin--,causes of oscillation4 ,evidences of oscillation4--,by earth oscillations are meant those slow and quiet changes in the relative level of the sea and land which geologists speak of as elevations or subsidences4 ,these movements are especially characteristic of volcanic and earthquake-shaken countries4 ,as evidences of elevations we appeal to phenomena like raised beaches1 sea-worn caves1 raised coral reefs1 and the remains of other dead organisms like barnacles1 and the borings of lithodomous shells in and on the rocks of many coasts high above the level of the highest tides4 ,as a proof that subsidence has taken place1 there is the evidence afforded by submerged forests1 the prolongation of certain valleys beneath the bed of the ocean1 the formation of coral islands1 the peculiar distribution of the plants and animals which we find in many countries1 and the submergence of works of human construction4 ,inasmuch as these phenomena are discussed so fully in many treatises on physical geology1 the references to them here will be made as brief as possible4 ,elevations and depressions which have taken place at the time of large earthquakes in a paroxysmal manner have already been mentioned4 ,the movements referred to in this chapter1 although generally taking place with extreme slowness1 in certain instances1 by an increase in their rapidity1 have approached in character to earth pulsations4 ,in most instances it would appear that the upward movement of the ground1 which may be likened to a process of tumefaction1 goes on so gently that it only becomes appreciable after the lapse of many generations4 ,examples of movements4--,lyell estimated that the average rate of rise in ,scandinavia has been about two and a half feet per century4 ,at the ,north ,cape the rise may have been as much as five or six feet per century4 ,observations made at the temple of ,jupiter ,serapis1 between ,october #ahbb and ,july #ahch1 showed that the ground was sinking at the rate of about one inch in four years4 ,since the ,roman period1 when this temple was built1 the ground has sunk twenty feet below the waves4 ,now the floor of the temple is on the level of the sea4 ,lyell remarks that if we reflect on the dates of the principal oscillations at this place there appears to be connection between the movements of upheaval and a local development of volcanic heat1 whilst periods of depression are concurrent with periods of volcanic quiescence4#aed ,as examples of movements even more rapid than those at the ,temple of ,jupiter ,serapis we refer to an account of the earthquakes in ,vallais 7,november #agee71 when the ground about a mountain at a small distance from ,brigue sank about a thumb's-breadth every twenty-four hours4 ,this took place between ,december #i and ,february #bf4aee ,another remarkable example of earth movement is given in the account of the earthquake at ,scarborough1 on ,december #bi1 #agcg1 when the head of the spa water well was forced up in the air about ten yards high4 ,at this time the sands on the shore are said to have risen so slowly that people came out to watch them4#aef ,two other examples of rapid earth movement are taken from ,professor ,rossi's #8,meteorologia ,endogena4' ,professor ,d4 ,seghetti1 writing to ,professor ,rossi1 says that a few lustres ago 7one lustre twenty years7 ,mount ,s4 ,giovanni hid the towns ,jenne and ,subiaco from each other4 ,from ,subiaco the church at ,jenne is now visible1 which a few years ago was invisible4 ,the people at ,jenne also can see more than formerly4 ,the supposition is that the side of ,mount ,s4 ,giovanni is lowered4 ,this fact corresponds to a fact stated by ,professor ,carina1 who says that forty or fifty years ago from ,granaiola you could not see either the church of ,s4 ,maria ,assunta di ,citrone or the church of ,s4 ,pietro di ,corsena4 ,now you can see both4#aeg ,for a remarkable example illustrating the connection between seismic activity and elevation we are indebted to the patient labours of ,darwin1 who carefully investigated the evidences of elevation which are visible upon the western coasts of ,south ,america4 ,these evidences1 consisting of marks of erosion1 caves1 ancient beaches1 sand dunes1 terraces of gravel1 c41 were traced between latitudes #de #ce to #ab #e1 a distance north and south of #b1jge geographical miles1 and there is but little doubt that they extend much farther4 ,as deduced from observations upon upraised shells alone1 a summary of ,mr4 ,darwin's observations are contained in the following table3-- ,feet ,at ,chiloe the recent elevation has been #cej ,concepcion #fbe to #a1jjj ,valparaiso #a1cjj ,coquimbo #beb ,lima #he ,shells1 similar to those clinging to uplifted rocks1 which are evidences of these elevations1 still exist in the neighbouring seas1 and in the same proportionate numbers as they are found in the upraised beds4 ,in addition to this1 ,mr4 ,darwin shows us that at ,lima1 during the ,indo-human period1 the elevation has been at least eighty-five feet4 ,at ,valparaiso1 during the last #bbj years1 the rise was about nineteen feet1 and in the seventeen years subsequent to #ahag the rise has been ten or eleven feet1 a portion only of which can be attributed to earthquakes4 ,in #ahcd the rise there was apparently still in progress4 ,at ,chiloe there has been a gradual elevation of about four feet in four years4 ,these1 together with numerous other examples1 testify to the gradual but1 as compared with other parts of the globe1 exceedingly rapid rise of the ground upon the western shores of ,south ,america4#aeh ,the most important point to be noticed is that this district of rapid elevation is one of the most earthquake-shaken regions of the world4 ,and further1 judging from ,darwin's remarks1 in those portions of it where the movements have been the most extensive1 and at the same time probably the most rapid1 the seismic disturbances appear to have been the most noticeable4 ,similar remarks may be applied to ,japan1 it being in those districts where evidences of recent elevation are abundant that earthquakes are numerous4 ,thus1 in the bay of ,yedo1 where we have borings of lithodomi in the tufaceous cliffs ten feet above high-water mark1 which1 inasmuch as the rock in which they are found is soft and easily weathered1 indicate an exceedingly rapid elevation1 earthquakes are of common occurrence4 ,from the evidences of elevation which we have upon the ,south ,american coast1 ,japan1 and in other countries1 it appears that these movements are intermittent1 there being periods of rest1 when sea cliffs are denuded1 and perhaps even periods of subsidence4 ,there is also evidence to show that1 although these movements have been gradual from time to time1 they have been aided by starts occasioned by earthquakes4 ,as to whether earthquakes are more numerous during periods of elevation1 or of subsidence1 or during the intermediate periods of rest1 we have no evidence4 ,sudden displacements which occasionally accompany earthquakes might1 it was said1 sometimes be regarded as the cause of an earthquake1 and sometimes as the effect4 ,the slow elevations here referred to may be looked upon as being one of the more important factors in the production of earthquakes4 ,by various causes the rocky coast is bent until1 having reached the limit of its elasticity1 it snaps1 and1 in flying back like a broken spring1 causes the jars and tremors of an earthquake4 ,if this is the case1 then the number of earthquakes felt in a district which is being elevated may possibly be a function of the rate of elevation4 ,,appendix4 ,,list ,,of ,,the ,,principal ,,books1 ,,papers1 ,,periodicals1 ,,which ,,are ,,referred ,,to ,,in ,,the ,,preceding ,,pages4 ,for a more complete bibliography of earthquakes refer to ,mallet's catalogue of works given in his report to the ,british ,association in #aheh4 ,a ,true and ,particular ,relation of the ,dreadful ,earthquake which happened at ,lima1 c4 7#agdf74 #agfh4 ,abbot1 ,gen4 ,h4 ,l4 ,on the ,velocity of ,transmission of ,earth ,waves4 ,am4 ,jour4 ,sci4 ,,xv41 ,march #ahgh4 -- ,shock of the ,explosion at ,hallet's ,point1 ,nov4 #ad1 #ahgf4 ,battalion ,press4 ,alexander1 ,prof4 ,t4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,american ,journal of ,science4 ,annali del reale osservatorio meteorologico ,vesuviano4 ,annual ,register1 ,the4 ,anonymous1 ,a ,chronological and ,historical ,account of the most ,memorable ,earthquakes in the ,world1 c4 #agej4 -- ,a ,vindication of the ,bishop of ,london's ,letter occasioned by the ,late ,earthquake4 #agej4 -- ,phenomena of the ,great ,earthquake of ,nov4 #a1 #agee4 -- ,serious ,thoughts occasioned by the ,late ,earthquake at ,lisbon4 #agee4 ,asiatic ,society of ,japan1 ,transactions of4 ,ayrton1 ,prof4 ,w4 ,e4 ,see ,perry1 ,j4 ,brceno1 ,m4 ,estudio del ,terremoto 7,may #ag1 #ahgi7 ,mexico4 #ahgi4 ,beke1 ,dr4 ,c4 ,t4 ,mount ,sinai a ,volcano4 ,bissett1 ,rev4 ,j4 ,a ,sermon 7on account of the ,earthquake at ,lisbon1 ,nov4 #a1 #agee74 #ageg4 ,bittner1 ,a4 ,beitrge zur ,kenntniss des ,erdbebens von ,belluno vom #bi4 ,juni #ahgc4 -- ,sitzungsb4 der ,k4 ,akad4 d4 ,wissensch41 lxix4 ,,ii4 ,abth41 #ahgd4 ,bollettino del ,vulcanismo ,italiano4 ,bou1 ,dr4 ,a4 ,ueber das ,erdbeben welches ,mittel-,albanien im ,october d4 ,j4 so schrecklich getroffen hat4 ,die ,k4 ,akad4 d4 ,wissenschaften1 ,nov4 #ahea4 -- ,parallele der ,erdbeben1 des ,nordlichtes und des ,erdmagnetismus4 -- ,ueber die ,nothwendigkeit die ,erdbeben und vulkanischen ,erscheinungen genauer als bis jetzt beobachten zu lassen4 ,die ,k4 ,akad4 d4 ,wissenschaften1 #ahea and #aheg4 ,bouguer1 ,m4 ,of the ,volcanoes and ,earthquakes in ,peru4 ,british ,association1 ,reports of4 ,brunton1 ,r4 ,h4 ,constructive ,art in ,japan4 ,trans4 ,asiatic ,soc4 of ,japan1 ,,ii4 and ,,iii41 ,pt4 #b4 ,bryce1 ,j4 ,report to ,british ,association1 #ahda4 ,buffour1 ,m4 ,the ,natural ,history of ,earthquakes and ,volcanoes4 ,c4 ,h4 ,a ,physical ,discussion of ,earthquakes1 c4 #afic4 ,canterbury1 ,thomas1 ,lord ,archbishop of1 ,the ,theory and ,history of ,earthquakes4 ,casariego1 ,e4 ,a4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,cawley1 ,g4 ,some ,remarks on ,construction in ,brick and ,wood1 c4 ,trans4 ,asiatic ,soc4 of ,japan1 ,,vi4 ,plate ii4 ,chaplin1 ,prof4 ,w4 ,s4 ,an ,examination of the ,earthquakes recorded at the ,meteorological ,observatory1 ,tokio4 ,trans4 ,asiatic ,soc4 of ,japan1 ,,vi4 ,part ii4 ,comptes ,rendus4 ,credner1 ,h4 ,das ,dippoldiswalder ,erdbeben vom ,oktober #ahgg4 -- ,zeitschr4 f4 d4 ,naturwiss4 f4 ,sachsen u4 ,thringen4 -- ,das ,vogtlndisch-erzgebirgische ,erdbeben1 #bc4 ,nov4 #ahge4 -- ,zeitschr4 f4 d4 gesammt4 ,naturwissenschaften1 xlviii41 ,oktober4 ,dan1 ,t4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,darwin1 ,charles4 ,researches on ,geology and ,natural ,history4 -- ,geological observations4 ,darwin1 ,g4 ,h4 ,reports on ,lunar ,disturbance of ,gravity to ,british ,association1 #ahha4 #ahhb4 ,diffenbach1 ,f4 ,plutonismus und ,vulkanismus in der ,periode von #ahfh-ahgb1 und ihre ,beziehungen zu den ,erdbeben im ,rheingebiet4 ,doelter1 ,c4 von4 ,ueber die ,eruptivgebilde von ,fleims1 nebst einigen ,bemerkungen ber den ,bau lterer ,vulcane4 -- lxxiv4 ,band d4 ,sitzungsb4 d4 ,k4 ,akad4 d4 ,wissensch41 ,i4 ,abth41 ,dec4 ,heft1 ,jahrg4 #ahgf4 ,doolittle1 ,rev4 ,t4 ,earthquakes ,explained and ,practically ,improved1 c4 #afic4 ,doyle1 ,p4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,emerson1 ,prof41 ,b4,a4 ,review of ,von ,seebachs' ,earthquake of ,march #f1 #ahgb4 ,am4 ,jour4 ,sci41 ,series ,,iii4 ,ewing1 ,prof4 ,j4 ,a4 ,earthquake ,measurement4 ,a memoir published by the ,tokio ,university4 #ahhc4 -- ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,falb1 ,r4 ,gedanken und ,studien ber den ,vulkanismus1 c4 #ahge4 -- ,grundzge zu einer ,theorie der ,erdbeben und ,vulkanausbrche4 -- ,das ,erdbeben von ,belluno4 #8,sirius1' ,bd4 ,,vi41 ,heft ii4 ,flamstead1 ,j4 ,a ,letter concerning ,earthquakes4 #afic4 ,forel1 ,f4 ,a4 ,les ,tremblements de ,terre 7,suisse74 ,arch4 des ,sciences ,physiques et ,naturelles1 ,,vi4 p4 #dfa4 -- ,tremblement de ,terre du #cj ,dcembre #ahgi4 ,fuchs1 ,karl4 ,vulkane und ,erdbeben4 -- ,die ,vulkanischen ,erscheinungen der ,erde4 ,garcia1 ,j4 ,c4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,geinitz1 ,dr4 ,e4 ,das ,erdbeben von ,iquique am #i4 ,mai #ahgg1 c4 ,die ,k4 ,leop4-,carol4-,deutschen ,akademie der ,naturforscher1 ,band xl41 ,nr4 #i4 ,gentleman's ,magazine1 ,the4 ,geographical ,society1 ,proceedings of4 ,geological ,society1 ,proceedings of4 ,girard1 ,dr4 ,h4 ,ueber ,erdbeben und ,vulkane4 #ahde4 ,gray1 ,t4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 -- ,on ,instruments for ,measuring and ,recording ,earthquake ,motions4 ,phil4 ,mag4 ,sept4 #ahha4 -- ,on ,recent ,earthquake ,investigation4 ,the ,chrysanthemum1 #ahha4 ,guiscardi1 ,prof4 ,g4 ,notizie del ,vesuvio4 #aheg4 -- ,il terremoto di ,casamicciola del #d ,marzo4 #ahha4 ,hales1 ,s41 ,d4,d41 ,f4,r4,s4 ,some ,considerations on the ,causes of ,earthquakes4 #agej4 ,hamilton1 ,sir ,w4 ,observations on ,mount ,vesuvius1 ,mount ,etna1 c4 #aggd4 ,hattori1 ,i4 ,destructive ,earthquakes in ,japan4 ,trans4 ,asiatic ,soc4 of ,japan1 ,v4 ,plate i4 ,heim1 ,prof4 ,a4 ,les ,tremblements de ,terre et leur ,etude ,scientifique4 #ahhj4 -- ,prof4 ,a4 ,die ,schweizerischen ,erdbeben in #ahha-ahhb4 ,hoeffer1 ,prof4 ,h4 ,die ,erdbeben ,krntens und deren ,stosslinien4 ,die ,kais4 ,akademie d4 ,wissenschaften1 ,band xlii4 ,hfer1 ,prof4 ,h4 ,das ,erdbeben von ,belluno1 am #bi4 ,juni #ahgc4 ,sitzungsb4 der ,k4 ,akad4 d4 ,wissensch41 ,i4 ,abth41 ,band lxxiv4 ,hoff1 ,k4 ,e4 ,a4 von4 ,geschichte der durch ,ueberlieferung nachgewiesenen natrlichen ,vernderungen der ,erdoberflche4 #ahbb4 ,hooke1 ,r41 ,m4,d41 ,f4,r4,s4 ,discourses concerning ,earthquakes4 ,hopkins1 ,william4 ,report to the ,british ,association on the ,geological ,theories of ,elevation and ,earthquakes4 #ahdg4 ,horton1 ,rev4 ,mr4 ,an ,account of the ,earthquake which happened at ,leghorn in ,italy 7,jan4 #agdb74 #agej4 ,humboldt1 ,alexander von4 ,cosmos4 -- ,travels4 ,jeitteles1 ,l4 ,a4 ,bericht ber das ,erdbeben am #ae4 ,januar #aheh4 -- ,sitzungsberichte der mathem4-naturw4 ,classe d4 ,k4 ,akad4 d4 ,wissensch41 xxxv4 ,s4 #eaa4 ,judd1 ,j4 ,w41 ,prof4 ,volcanoes1 ,what they ,are and ,what they ,teach4 ,knipping1 ,e4 ,verzeichniss von ,erdbeben wahrgenommen in ,tokio1 c4 ,mitt4 d4 ,deutsch4 ,gesellsch4 fr ,natur- und ,vlkerkunde ,ostasiens1 ,heft #ad4 -- ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,lasaulx1 ,a4 von4 ,das ,erdbeben von ,herzogenrath am #bb4 ,october #ahgc4 ,lemery1 ,m4 ,a ,physico-,chemical ,explanation of ,subterranean ,fires1 ,earthquakes1 c4 ,lescasse1 ,m4 ,j4 ,etude sur les ,constructions ,japonaises1 c4 ,mmoires de la ,socit des ,ingnieurs ,civils4 ,lister1 ,m41 ,m4,d41 ,f4,r4,s4 ,of the ,nature of ,earthquakes4 ,little1 ,rev4 ,j4 ,conjectures on the ,physical ,causes of ,earthquakes and ,volcanoes4 #ahbj4 ,mallet1 ,r4 ,the ,neapolitan ,earthquake1 ,vol4 ,,ii4 ,reports to the ,british ,association1 #ahej1 #ahea1 #aheb1 #ahed1 #aheh1 #ahfa4 -- ,secondary ,effects of the ,earthquake of ,cachar4 ,proc4 ,geolog4 ,soc41 #ahgb4 -- ,dynamics of ,earthquakes4 ,trans4 ,royal ,irish ,acad4 #ahdf4 ,milne1 ,david4 ,reports to ,british ,association1 #ahda1 #ahdc1 #ahdd4 ,milne1 ,john4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 -- ,on ,seismic ,experiments 7with ,t4 ,gray1 ,b4,sc41 ,f4,r4,s4,e47 ,trans4 ,royal ,soc4 #ahhb4 -- ,on ,seismic ,experiments 7with ,t4 ,gray1 ,b4,sc41 ,f4,r4,s4,e47 ,proc4 ,royal ,soc4 ,no4 #bag1 #ahha4 -- ,earthquake ,observations and ,experiments in ,japan 7with ,t4 ,gray1 ,b4,sc41 ,f4,r4,s4,e47 ,phil4 ,mag41 ,nov4 #ahha4 -- ,on the ,elasticity and ,strength ,constants of certain ,rocks 7with ,t4 ,gray1 ,b4,sc41 ,f4,r4,s4,e47 ,jour4 ,geolog4 ,soc41 #ahhb4 -- ,a ,visit to the ,volcano of ,oshima4 ,geolog4 ,mag41 ,dec4 #b1 ,vol4 ,,iv41 pp4 #aic-aig1 #bee4 -- ,on the ,form of ,volcanoes4 ,geolog4 ,mag41 ,dec4 #b1 ,vol4 ,v41 and ,dec4 #b1 ,vol4 ,,vi4 -- ,note upon the ,cooling of the ,earth1 c4 ,geolog4 ,mag41 ,dec4 #b41 ,vol4 ,,vii41 p4 #ii4 -- ,investigation of the ,earthquake ,phenomena of ,japan4 ,rep4 ,brit4 ,assoc41 #ahha and #ahhb4 -- ,a ,large ,crater4 ,popular ,science ,review4 -- ,the ,volcanoes of ,japan 7a series of ,articles74 ,japan ,gazette4 -- ,earthquake ,literature of ,japan 7a series of ,articles74 ,japan ,gazette4 -- ,the ,earthquake of ,dec4 #bc1 #ahhj4 ,the ,chrysanthemum1 #ahha4 -- ,earthquake ,motion4 ,the ,chrysanthemum1 #ahhb4 -- ,seismology in ,japan4 ,nature1 ,oct4 #ahhb4 -- ,earth ,movements4 ,the ,times1 ,oct4 #ab1 #ahhb4 ,mitchell1 ,rev4 ,j4 ,conjectures ,concerning the ,cause and ,observations upon the ,phenomena of ,earthquakes4 #agfj4 ,mohr1 ,dr4 ,f4 ,geschichte der ,erde4 #ahge4 ,naturkundig ,tijdschrift voor ,nederlandsch ,indie4 #ahge-ahhj4 ,naumann1 ,dr4 ,e4 ,ueber ,erdbeben und ,vulkanausbrche in ,japan4 ,mitt4 d4 ,deutsch4 ,gesellsch4 fr ,natur- und ,vlkerkunde ,ostasiens4 ,heft #ae4 ,noggerath1 ,dr4 ,j4 ,die ,erdbeben vom #bi4 ,juli #ahdf im ,rheingebiet1 c4 -- ,die ,erdbeben im ,vispthale 7#ahee74 -- ,die ,erdbeben im ,rheingebiet in den ,jahren #ahfh1 #ahfi1 #ahgj4 -- ,jahrgnge d4 ,verbandlungen d4 ,natur4 ,vereins fr #ahgj4 ,rheinland u4 ,westphalen1 xxvii4 ,oldham1 ,dr4 ,secondary ,effects of the ,earthquake of ,cachas4 ,proc4 ,geolog4 ,soc4 #ahgb4 -- ,thermal ,springs of ,india4 ,memoirs of ,geolog4 ,survey of ,india1 ,,xix4 ,plate #b4 -- ,a ,catalogue of ,indian ,earthquakes4 ,memoirs of ,geolog4 ,survey of ,india1 ,,xix4 ,plate #c4 -- ,the ,cachas ,earthquake4 ,memoirs of ,geolog4 ,survey of ,india1 ,,xix4 ,plate #a4 ,palmer1 ,col4 ,h4 ,s4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,palmieri1 ,prof4 ,l41 e ,scacchi1 ,a4 ,della ,regione ,volcanica del ,monte ,vulture1 e del ,tremuoto ivi avvenuto nel d #ad ,agosto #ahea1 #aheb4 -- ,annali del reale ,osservatorio ,meteorologico ,vesuviano4 -- ,il ,vesuvio1 il ,terremoto d' ,isernia e l'eruzione sottomarina di ,santorino4 ,r4 ,accad4 d4 ,sci4 ,fis4 e ,mat4 di ,napoli1 iv4 #ahff4 -- ,sul recente ,terremoto di ,corleone4 ,r4 ,accad4 d4 ,sci4 ,fis4 e ,mat41 v4 #ahgf4 -- ,il ,terremoto di ,scio del d #d ,aprile4 ,r4 ,accad4 d4 ,sci4 ,fis4 e ,mat4 di ,napoli1 v4 #ahha4 -- ,sul ,terremoto di ,casamicciola del #d ,marzo #ahha4 ,r4 ,accad4 d4 ,sci4 ,fis4 e4 ,mat4 di ,napoli4 #ahha4 ,paul1 ,prof4 ,h4 ,m4 ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,perrey1 ,prof4 ,a4 ,earthquake ,catalogue and ,memoirs4 7,for list see ,mallet's ,report to ,british ,association4 #aheh47 -- ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,perry1 ,j41 and ,w4 ,e4 ,ayrton4 ,on a ,neglected ,principle that may be ,employed in ,earthquake ,measurement4 -- ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,philosophical ,magazine4 ,pickering1 ,rev4 ,r4 ,an ,address to those who have either retired or intend to leave ,town under the ,imaginary ,apprehension of the ,approaching ,shock of another ,earthquake4 #agej4 ,ray1 ,j41 ,f4,r4,s4 ,a ,summary of the ,causes of the ,alterations which have happened to the ,face of the ,earth4 ,rockstroh1 ,e4 ,informe de la ,comision ,cientfica del ,instituto ,nacional de ,guatemala1 nombrada por el ,sr4 ,ministro de ,instruccion ,pblica para el ,estudio de los ,fenmenos ,volcnicos en el ,lago de ,ilopango4 #ahhj4 ,rockwood1 ,prof4 ,c4 ,g4 ,notes on ,earthquakes4 ,annually in the ,am4 ,jour4 ,sci4 -- ,japanese ,seismology4 ,am4 ,jour4 ,sci41 ,,xxii4 ,dec4 #ahha4 ,romaine1 ,w4 ,a ,discourse occasioned by the ,late ,earthquake4 #agee4 ,rossi1 ,prof4 ,m4 ,s4 di4 ,intorno all' odierna fase dei ,terremoti in ,italia1 e segnatamente sul ,terremoto in ,casamicciola del #d ,marzo #ahha4 ,societ ,geografica ,italiana4 #ahha4 -- ,la ,meteorologia ,endogena1 #b vols4 ,royal ,society1 ,transactions of4 ,scacchi1 ,a4 ,see ,palmieri4 ,schmidt1 ,dr4 ,j4 ,f4 ,untersuchungen ber das ,erdbeben am #ae4 ,januar #aheh4 -- ,studien ber ,erdbeben4 #ahgi4 -- ,die ,eruption des ,vesuv 7#ahee74 #ahef4 ,scrope1 ,g4 ,p4 ,volcanoes4 ,seebach4 ,das mittle ,deutsche ,erdbeben 7#ahgb74 ,mitt4 der ,k4,k4 geograph4 ,gesellsch41 ,,ii4 ,jahrg41 #b4 ,heft1 #ahgc4 ,serpieri1 ,prof4 ,a4 ,c4 ,s4 ,nuove ,osservazioni sul ,terremoto avvenuto in ,italia il #ab ,marzo #ahgc4 ,istituto ,lombardo4 #ahgc4 -- ,il ,terremoto di ,rimini della notte #ag-ah ,marzo #ahge4 -- ,documenti nuove e ,riflessioni sul ,terremoto della notte #ag-ah ,marzo #ahge4 ,meteorologia ,italiana1 iv4 #ahge4 -- ,determinazione delle fasi e delle leggi del grande ,terremoto avvenuto in ,italia nella notte #ag-ah ,marzo #ahge4 ,istituto ,lombardo4 #ahge4 -- ,dell' influenza del ,lume ,solare sui ,terremoti4 ,istituto ,lombardo4 #ahhb4 ,sherlock1 ,t41 ,d4,d4 7,lord ,bishop of ,london74 ,a ,letter on the occasion of the late ,earthquakes4 #agej4 ,shower1 ,rev4 ,j41 ,d4,d4 ,practical ,reflections on the ,earthquakes that have happened in ,europe and ,america1 c4 #agej4 ,stbel1 ,a4 7see ,reiss1 ,w47 ,stukeley1 ,rev4 ,w41 ,m4,d41 ,f4,r4,s4 ,the ,philosophy of ,earthquakes1 ,natural and ,religious1 c4 ,plates #a1 #b1 and #c4 #agef4 ,sturmius1 ,j4 ,c4 ,a ,methodical ,account of ,earthquakes4 ,suess1 ,e4 ,die ,erdbeben ,niedersterreiches4 ,die ,kais4 ,akademie der ,wissenschaften1 ,bd4 xxxiii4 -- ,die ,erdbeben des sdlichen ,italiens4 ,die ,kais4 ,akademie der ,wissenschaften1 ,bd4 xxxiv4 ,volger1 ,dr4 ,g4 ,h4 ,untersuchungen ber das ,phnomen der ,erdbeben4 #aheg4 ,wagener1 ,dr4 ,g4 ,bemerkungen ber ,erdbebenmesser und ,vorschlge zu einem neuen ,instrumente dieser ,art4 ,mitt4 d4 ,deutsch4 ,gesellsch4 fr ,natur- und ,vlkerkunde ,ostasiens1 ,heft #ae4 -- ,see ,trans4 ,seis4 ,soc4 of ,japan4 ,winchilsea1 ,the ,earl of4 ,a ,true and ,exact ,relation of the late ,prodigious ,earthquake and ,eruption of ,mount ,etna4 #affi4 ,woodward1 ,j41 ,m4,d41 ,f4,r4,s4 ,earthquake caused by some ,accidental ,obstruction of a ,continual ,subterranean ,heat4 ,,seismological ,,society ,,of ,,japan4 ,the following are a list of the papers published by this ,society3-- ,,vol4 ,i4 ,milne1 ,j4 ,seismic ,science in ,japan4 #ce pages4 ,ewing1 ,j4 ,a4 ,new ,form of ,pendulum ,seismograph4 #f pages1 #c plates4 ,gray1 ,t4 ,seismometer and ,torsion ,pendulum ,seismograph4 #h pages1 #b plates4 ,mendenhall1 ,t4 ,c4 ,acceleration of ,gravity at ,tokio 7abstract74 #b pages4 ,wagener1 ,g41 and ,e4 ,knipping4 ,new ,seismometer and ,observations with same4 #ah pages1 #a plate4 ,milne1 ,j4 ,earthquake in ,japan of ,feb4 #bb1 #ahhj4 #aaf pages1 #e plates1 #h woodcuts4 ,,vol4 ,,ii4 ,milne1 ,j4 ,recent ,earthquakes of ,yeddo1 ,effects on ,buildings1 c4 #ch pages1 #b plates1 and many tables4 ,mendenhall1 ,t4 ,c4 ,gravity on ,summit of ,fujiyama 7abstract74 #b pages4 ,paul1 ,h4 ,m4 ,earth ,vibrations from ,railroad ,trains 7abstract74 #d pages4 ,ewing1 ,j4 ,a4 ,astatic ,horizontal ,lever ,seismograph 7abstract74 #e pages1 #a plate4 ,milne1 ,j4 ,peruvian ,earthquake of ,may1 #i1 #ahgg4 #dg pages1 #b plates1 tables4 ,constitution1 ,rules1 ,officers and ,members of the ,society1 ,dec41 #ahha4 ,,vol4 ,,iii4 ,gray1 ,t4 ,steady ,points for ,earthquake ,measurements4 #aa pages1 #c plates4 ,milne1 ,j4 ,experiments in ,observational ,seismology4 #ec pages1 #a plate1 tables4 -- ,the ,great ,earthquakes of ,japan4 #ch pages1 #a plate1 many tables4 ,perry1 ,j4 ,theory of a ,rocking ,column4 #d pages4 ,knipping1 ,e4 ,earthquake of ,july #be1 #ahhj1 with ,dr4 ,wagener's ,seismometer4 #d pages4 ,ewing1 ,j4 ,a4 ,earthquake ,observation at three or more ,stations1 c4 #d pages4 -- ,records of three recent ,earthquakes4 #f pages1 #c plates4 -- ,earthquake of ,march #h1 #ahha4 #h pages1 #a plate4 ,milne1 ,j4 ,horizontal and ,vertical ,motion in ,earthquake of ,march #h1 #ahha4 #h pages1 #c plates4 ,gray1 ,t4 ,seismograph for ,registering ,vertical ,motion4 #c pages1 #a plate4 ,ewing1 ,j4 ,a4 ,seismometer for ,vertical ,motion4 #c pages1 #a plate4 ,gray1 ,t4 ,seismograph for ,large ,motions4 #b pages4 -- ,compensating a ,pendulum to make it ,astatic4 #c pages4 ,palmer1 ,h4 ,s4 ,note on ,earth ,vibrations4 #c pages4 ,kuwabara1 ,m4 ,the ,hot ,springs of ,atami4 #b pages4 ,,vol4 ,,iv4 ,milne1 ,j4 ,distribution of ,seismic ,activity in ,japan4 #cj pages1 #a plate4 ,wada1 ,t4 ,notes on ,fujiyama4 #g pages4 ,casariego1 ,e4 ,abella y4 ,earthquakes of ,nueva ,vizcaya in #ahha4 #bc pages1 #b maps4 ,milne1 ,j4 ,utilisation of ,earth's ,internal ,heat4 #ab pages4 ,ewing1 ,j4 ,a4 ,earthquake of ,march #aa1 #ahhb4 #e pages4 ,doyle1 ,p4 ,note on an ,indian ,earthquake4 #f pages4 ,milne1 ,j4 ,systematic ,observation of ,earthquakes4 #ca pages1 #e plates4 ,,vol4 ,v4 ,naumann1 ,dr4 ,e4 ,notes on ,secular ,changes of ,magnetic ,declination in ,japan1 p4 #a-ah4 ,casariego1 ,don ,e4 ,abella y4 ,monografa ,geolgica del ,volcan de ,albay ,el ,myon4 p4 #ai-dc4 ,garcia1 ,don ,j4 ,centeno y4 ,abstract of a ,memoir on the ,earthquakes on the ,island of ,luzon in #ahhj4 p4 #dc-hi4 ,ewing1 ,prof4 ,j4 ,a4 ,seismological ,notes4 -- ,a ,duplex ,pendulum ,seismometer4 -- ,the ,suspension of a ,horizontal ,pendulum4 -- ,a ,speed ,governor for ,seismograph ,clocks1 p4 #hi-ie4 ,dan1 ,t41 ,s4,b4 ,notes on the ,earthquake at ,atami1 in the ,province of ,idzu1 on ,september #bi1 #ahhb4 p4 #ie-aje4 ,,vol4 ,,vi4 ,alexander1 ,prof4 ,t4 ,the ,development of the ,record given by a ,bracket ,machine4 ,milne1 ,j4 ,earth ,pulsations4 ,ewing1 ,j4 ,a4 ,note on a ,duplex ,pendulum with a ,single ,bob4 ,gergens1 ,f4 ,note on an ,iron ,casting1 ,supposed to have been ,disturbed whilst ,cooling by an ,earthquake4 ,west1 ,c4 ,d4 ,on a ,parallel ,motion ,seismograph4 ,ewing1 ,j4 ,a4 ,certain ,methods of ,astatic ,suspension4 ,alexander1 ,t4 ,ball and ,cup ,seismometer4 ,knipping1 ,messrs4 ,paul and4 ,report on a ,system for ,earthquake ,observation4 ,catalogues of ,earthquakes4 ,,index4 ,abbadie1 ,m4 d'1 on earth tremors1 #cji ,abbot1 ,general ,h4 ,l41 on the transmission of vibrations1 #fb ,abella1 ,m41 on the earthquake in the ,philippines in #ahha1 #gg ,activity1 on seismic1 #f ,aristotle1 on the classification of earthquakes1 #da ,artificial earthquakes1 experiments on1 #eg -- -- intensity of1 #fa ,aurora1 on the occurrence of1 with earthquakes1 #bfd ,ayrton and ,perry1 on the effect of soft foundations1 #acj -- -- on the period of vibration of buildings1 #aae -- -- on the principle of1 #ca ,barometer1 effect of changes of1 on earthquakes1 #bff ,bertelli1 on aurora and earthquakes1 #bfe -- on earth tremors1 #caf1 #cbj -- on the normal tromometer of1 #cag ,bittner1 ,a41 on the buildings of ,belluno1 #ajj ,bridges1 on earthquake1 #adj ,brunton1 ,r4 ,h41 on buildings in earthquake countries1 #abc ,buckle1 on the history of civilisation1 #a ,builders1 interest of the study of earthquakes to1 #c ,buildings1 on cracks in1 #ih1 #ajh -- the effect of earthquakes on1 #if -- on the irregular destruction of1 #if -- -- effect on the end house in a row1 #aab -- -- church of ,st4 ,augustin at ,manilla1 #aac -- -- relation of destruction of1 to earthquake motion1 #ajc -- -- protection of1 #adc -- -- pitch of the roof of1 #aaj -- -- position of openings in the walls of1 #aaa -- -- swing of1 #aae -- -- period of vibration of1 #aae -- -- principle of relative periods in1 #aaf -- -- types of1 for earthquake countries1 #aba -- -- effect of underlying rocks on1 #acj -- general conclusions regarding1 #add ,cacciatore1 definition of the1 #ah ,caldcleugh1 ,a41 on earthquake frequency1 #bde -- on barometric height and earthquakes1 #bff ,carruthers1 ,j41 on earthquakes and tides1 #bia ,centrum1 definition of1 #i -- on the depth of1 #bac -- on the maximum depth of1 #bah ,centrum1 determination of position of1 see origins ,chaplin1 ,w4 ,s41 on the bracket seismometer of1 #bg -- on earthquakes and the position of the moon1 #beb ,coast line1 on the movement of1 #afj ,cocks1 ,r41 on earthquakes and tides1 #bij ,coseismic lines1 definition of1 #aj ,curves1 on microseismic1 #cba ,darwin1 ,charles1 on the movement of coast lines1 #afj -- ,george ,h41 on earth tides1 #bhe -- on tidal loads1 #bia -- on earth pulsation1 #ccj -- on the effect of fluctuations of barometric pressure1 #ccf -- experiments at ,cambridge1 #caj ,delauney1 ,m4 ,j41 on the influence of the planets on earthquakes1 #bfa ,diagonic1 definition of1 #aa ,diastrophic1 definition of1 #aa ,direction of motion1 from instrumental records1 #aih ,distribution1 on earthquake1 #bbf -- examples of1 #bca ,disturbance1 on the propagation of1 #ej ,douglas1 ,j41 on ,south ,american houses1 #abf ,earth particle1 on the velocity and acceleration of1 #gi ,earthquake motion1 nature of1 as deduced from the feelings1 #fg -- direction of1 derived from instrumental records1 #fi -- duration of1 #ga -- period of vibration in1 #gd -- examples of extent of1 #ge-gg -- absolute intensity of force in1 #hc -- radiation of1 #he -- velocity of propagation of1 #hg ,earthquake at ,lisbon1 velocity of propagation of1 #hh ,earthquakes1 general examples of effects of1 #adb -- geological changes produced by1 #afa -- hunting1 #ahg -- distribution of1 #bbf -- maps1 #ahi -- secondary1 #bdh -- table of1 for nineteenth century1 #bei -- on the course of1 #bgg-bha -- and tides1 #bij -- prediction of1 #big-cjd ,elastic waves1 nature of1 #dd ,emergence1 angle of1 #i ,energy1 dissipation of1 in earthquakes1 #eb -- seismic1 in relation to geological time1 #bcd -- -- table of1 #bdj ,epicentrum1 definition of1 #i ,euthutropic1 definition of1 #aa ,ewing1 ,j4 ,a41 pendulum seismograph of1 #be -- astatic pendulum of1 #bf -- bracket seismograph of1 #bf ,falb1 ,r41 on the influence of the sun and moon on earthquakes1 #bhf ,fissures1 on the material discharged from1 #adh -- on the explanation of1 #aea ,focal cavity1 definition of1 #i -- on the form of1 #bba ,forbes1 ,d41 on an earthquake in ,mendoza1 #aea ,frequency of earthquakes1 #bdc ,frere1 ,sir ,h4 ,bartle1 on geological changes produced by earthquakes1 #afa ,fuchs1 on sea waves1 #agf -- on the movement of the seismic centre1 #bcc -- on earthquakes and volcanic outbursts1 #bga -- on hot springs1 #aeg ,fumaroles1 the effect of earthquakes on1 #aef ,geinitz1 ,dr41 on sea waves1 #ahb ,geologists1 on the interest of seismology to1 #b ,gray1 ,t41 astatic pendulum of1 #bf -- bracket seismometer of1 #bg -- conical pendulum of1 #bi -- dead heat pendulum of1 #bb -- on the rotation of bodies1 #aif -- rolling spheres and cylinders of1 #bi -- torsion pendulum seismometer of1 #be -- vertical motion seismometers of1 #cb1 #cc -- and ,milne1 seismograph of1 #ch ,hattori1 ,i41 on the large earthquakes of ,japan1 #bdd ,haughton1 ,prof41 list of active volcanoes of1 #bbg -- method of finding earthquake origins of1 #bji ,hills1 on the want of support on the face of1 #acf ,hfer1 on an earthquake at ,belluno1 #bbe ,hoffmann1 ,f41 on the barometer and earthquakes1 #bfg ,hooke1 on earthquake motion1 #db ,hopkins1 on the thickness of the earth's crust1 #bhd ,humboldt1 on meteors and earthquakes1 #bfa -- on the barometer and earthquakes1 #bfg -- on volcanoes and earthquakes1 #bgi ,imagination1 effect of earthquakes on the1 #b ,instruments1 direction of motion derived from1 #aih ,intensity1 on earthquake1 #ea1 #ga -- seismic curve of1 for ,kioto1 #bdb ,isoseismic circles1 definition of1 #aj -- areas1 definition of1 #aj ,kluge1 on sea waves1 #age -- on earthquake frequency1 #bdf -- on simultaneous earthquakes1 #bdh -- on earthquakes and sun spots1 #bfc -- on earth pulsations1 #cci ,kreil1 pendulum seismometer of1 #be ,lakes1 on disturbances in1 #aed ,land1 effect of earthquakes on1 #adf-afb -- on the reason of movements of1 #afb -- on cracks and fissures formed in1 #adf ,level1 on the use of for earth pulsations1 #cbh ,literature1 on seismic1 #f -- on ,japanese earthquake1 #g ,mallet1 ,r41 on area of disturbance as a test of seismic energy1 #gh -- on clock stopping1 #cf -- list of works on earthquakes of1 #e -- curve of seismic energy of1 #bch -- definition of earthquake of1 #dc -- on earthquake frequency1 #bdc -- on the influence of the heavenly bodies on earthquakes1 #bec -- on maximum depth of origin1 #bah -- on pendulum seismometers1 #bj -- projection seismometer of1 #ag -- on the ,neapolitan earthquake1 #fi1 #gg1 #hc1 #ig1 #ajc1 #acb1 #adb1 #bah1 #bhj -- on sea waves1 #agj -- on the swing of mountains1 #ace -- on propagation from a fissure1 #bag ,mallet on the temperature of focal cavity1 #hd ,malvasia1 ,m4 le ,conte1 on earth tremors1 #caf ,martin1 ,d4 ,s41 on the ,new ,england earthquake of #ahgd1 #adb ,meizoseismic area1 definition of1 #aj ,melzi1 on curves of microseismic motion1 #cbb ,meteors1 on earthquakes and1 #bfj ,microseismic movements1 on cause of1 #cbd ,milne1 ,d41 on the ,lisbon earthquake1 #hg -- on earthquake synchronism1 #bdg ,mitchell1 on earthquake motion1 #db ,moon1 effect of1 on earthquakes1 #bea1 #bhe ,mountains1 on the swing of1 #ace ,naumann1 ,e41 on meteors and earthquakes1 #bfa -- on sun spots and earthquakes1 #bfc ,ocean1 on disturbances in1 #afc-ahf ,origin1 definition of1 #i -- on the determination of1 #ahg -- position of1 deduced from direction of motion1 #aib -- -- from destruction of buildings1 #aid -- -- from rotation of bodies1 #aie -- -- from time of occurrence1 #aii -- -- examples of methods of calculating1 #bjj-bab ,oscillations1 on earth1 #cdd ,overturning moment1 on the area of greatest1 #ec ,palmer1 ,col4 ,h4 ,s41 on earth tremors1 #cjg ,palmieri1 on clock stopping1 #cf1 #fb ,paul1 ,h4 ,m41 on earth tremors1 #cjh ,perrey1 ,a41 on the influence of the moon on earthquakes1 #bea ,perrey on the periodicity of earthquakes1 #h ,perry1 ,j41 on position of openings in walls1 #aaa ,physicists1 on the interest of earthquakes to1 #b ,planets1 influence of1 on earthquakes1 #bfj ,plantamour1 ,m41 on earth pulsations1 #cbh ,pleistoseists1 definition of1 #aj ,poly1 ,m4 ,a41 on earthquakes and sun spots1 #bfc -- on earthquakes and revolving storms1 #bid ,prost1 ,m4 le ,baron1 on earth tremors1 #caf ,pulsation1 on earth1 #d1 #cbf-cdc ,records1 on receivers of1 #cc ,rivers1 on disturbances in1 #aed ,rockwood1 ,prof41 on ,american earthquakes1 #f ,ronaldson1 ,t41 on ,san ,francisco houses1 #abi ,rossi1 ,m4 ,s4 di1 on an eruption of gas in the ,tiber1 #aec -- aurora and earthquakes1 #bfd -- earth tremors1 #cag1 #cbj -- earth oscillations1 #cdf -- earth pulsations1 #cbg -- microseismograph of1 #cah -- microphonic observations of1 #cai1 #cbc -- normal tromometer of1 #cag ,schmidt1 on the influence of barometric pressure on earthquakes1 #bfg ,sea waves1 on nature of1 #afe -- on cause of1 #aga -- seldom produced by earthquakes which originate inland1 #age -- on velocity of propagation of1 #agg -- examples of1 #agi ,seasons1 frequency of earthquakes at different1 #bed ,seebach1 on the determination of origins1 #baa -- on the focal cavity1 #bbd ,seismic vertical1 definition of1 #i ,seismic and volcanic phenomena1 relation of1 #bgj -- -- conclusions regarding1 #bge1 #bie ,seismology1 definition of1 #i ,seismometers1 on various forms of1 #ag-dj ,seismoscopes1 on various forms of1 #ac-bj ,serpieri1 ,p4 ,a41 on distribution of seismic movement1 #bca ,shadows1 on earthquake1 #acg ,spring1 on frequency of earthquakes during1 #aef ,stukeley1 on earthquake motion1 #db -- earthquakes and aurora1 #bfe ,succussatore1 definition of1 #aj ,sun1 on the effect of1 on earthquakes1 #bec1 #bhe ,temperature1 effect of changes of1 on earthquakes1 #bfh1 #bid ,terremoto1 definition of1 #aj ,thomson1 ,sir ,w41 on the rigidity of the earth1 #bhe ,time1 on recording apparatus for1 #ce ,travagini1 ,f41 on earthquake motion1 #db ,trembelores1 definition of1 #aj ,tremors1 on earth1 #c1 #cjf-cbe ,understanding1 effects of earthquakes on1 #b ,verbeck1 on the ball and plate seismometer of1 #ca ,vibration1 on the nature of earthquake1 #ab ,vorticose motion1 on1 #gj -- definition of1 #aj ,wagener1 on the pendulum seismometer of1 #be -- vertical motion seismometer of1 #cc -- list of earthquakes1 #gf ,wave paths1 definition of1 #i ,waves1 on the nature of earthquake1 #ee -- on the interference of1 #ach ,wells1 on the effect of earthquakes on1 #aef ,wenthrop1 on the ,new ,zealand earthquake of #ahee1 #gi ,west1 on the parallel motion seismometer of1 #bh ,winslow1 on pulsations of the ocean1 #ccd ,wolf1 ,r41 on earthquakes and sun spots1 #bfc ,woodward1 on earthquake motion1 #db ,young1 ,dr4 ,t41 on earthquake motion1 #dc ,zantedeschi1 ,m4 ,f41 on the influence of the sun and moon on earthquakes1 #bhe ,zllner1 on the bracket seismometer of1 #bg -- on earth tremors1 #cji ---------------------------------------- ---------------------------- ,,footnotes3 #a ,mmoires de l',acadmie ,imp4 de ,dijon1 vols4 xiv4 and xv41 #bnd ,series1 #ahee-ef4 #b ,trans4 ,seis4 ,soc4 of ,japan1 vol4 iii4 p4 #fe4 #c ,gentleman's ,magazine1 #agec4 #d #a ,kings xix4 #aa1 #ab4 #e #8,notes on the ,great ,earthquake of ,japan4' ,j4 ,milne1 ,trans4 ,seis4 ,soc4 of ,japan1 vol4 iii4 #f ,see ,mallet's ,list of ,works on ,earthquakes1 ,report of the ,british ,association1 #aheh1 p4 #ajg4 #g ,quarterly ,review1 vol4 lxiii4 p4 #fa4 #h ,de ,mundo1 c4 iv4 #i ,see ,phil4 ,trans4 ,r4 ,s41 ,part ,,iii4 #ahhb4 #aj ,report of the ,british ,association1 #ahea4 #aa #8,on the ,velocity of ,transmission of ,earth ,waves1' by ,general ,h4 ,l1 ,abbot1 ,american1 ,journal of ,science and ,arts1 vol4 xv4 ,march #ahgh2 #8,shock of the ,explosion at ,hallet's ,point1' by ,bvt4 ,brig4-,gen4 ,henry ,l4 ,abbot1 read before the ,essayons ,club of the ,corps of ,engineers1 ,nov4 #ahgf4 #ab ,west4 ,rev41 ,july #ahdi4 #ac ,phil4 ,trans41 ,l41 #agee4 #ad ,the solution is taken from ,mallet's ,account of the ,neapolitan ,earthquake1 vol4 i4 p4 #aee4 #ae ,neapolitan ,earthquake1 ii4 p4 #cjj4 #af ,see ,edinburgh ,phil4 ,trans41 vol4 xxxi4 #ag ,see ,report of ,british ,association1 #aheh1 p4 #aj4 #ah ,meteorologia ,endogena1 i4 p4 #cjf4 #ai ,see remarks on the ,earthquake #8,push1' p4 #afb4 #bj ,see ,researches in ,geology and ,natural ,history1 p4 #cgd4 #ba #8,the ,city of ,earthquakes1' ,h4 ,d4 ,warner1 ,atlantic ,monthly1 ,march1 #ahhc4 #bb ,mallet1 ,dynamics of ,earthquakes4 #bc ,stud ,mill at ,haywards4 #bd ,see #8,constructive ,art in ,japan1' by ,r4 ,h4 ,brunton1 ,c4,e41 ,f4,r4,g4,s41 ,f4,g4,s41 ,transactions of ,asiatic ,society of ,japan1 ,december #bb1 #ahgc1 and ,january #ac1 #ahge4 #be ,journal of the ,american ,geographical ,society1 vol4 x4 #bf ,phil4 ,trans41 li4 #agfj4 #bg ,ibid41 xviii4 #bh #8,the ,city of ,earthquakes1' ,h4 ,d4 ,warner1 ,atlantic ,monthly1 ,march #ahhc4 #bi ,t4 ,ronaldson1 ,a ,treatise on ,earthquake ,dangers c4 #cj ,principles of ,geology1 ,lyell1 vol4 ii4 p4 #ajf4 #ca ,the ,neapolitan ,earthquake of #aheg1 ,r4 ,mallet1 vol4 ii4 p4 #cei4 #cb ,am4 ,j4 ,sci4 x4 #aia4 #cc ,reports of ,british ,association1 #aheh1 p4 #ajf4 #cd ,see chapter #8,causes of ,earthquakes' for details of this myth4 #ce ,am4 ,jour4 ,sci4 vol4 x4 p4 #aia4 #cf ,the ,earth1 p4 #eii4 #cg ,lyell1 ,principles of ,geology1 vol4 ii4 chap4 xxix4 #ch ,gent4 ,mag4 vol4 xx4 p4 #bab4 #ci ,trans4 ,seis4 ,soc4 vol4 v4 p4 #fg-fh4 #dj ,am4 ,jour4 ,sci4 vol4 iv4 #da ,phil4 ,trans4 vol4 xviii4 #db ,oldham and ,mallet1 #8,cachar ,earthquake1' ,proc4 ,geolog4 ,soc4 #ahgb4 #dc ,phil4 ,trans4 vols4 li4 and xviii42 ,gent4 ,mag4 vol4 xx4 #bab4 #dd ,trans4 ,royal ,geog4 ,soc4 vol4 vi4 #de ,phil4 ,trans4 vols4 xxxvi4 and xxxix4 #df ,am4 ,jour4 of ,sci4 #ahfe1 vol4 xl4 p4 #cfe4 #dg ,proc4 ,geolog4 ,soc4 ,ap4 #ahge1 p4 #bgj4 #dh ,gent4 ,mag4 vol4 xxi4 p4 #efi4 #di ,jahrb4 f4 ,min4 #ahdj1 p4 #agc4 #ej ,oldham and ,mallet1 #8,cachar ,earthquake1' ,trans4 ,geolog4 ,soc4 ,ap4 #ahgb4 #ea ,o4 ,volger1 ,unters b4 d4 ,phn4 d4 ,erdb4 vol4 iii4 p4 #dad4 #eb ,meteorologia ,endogena1 vol4 i4 p4 #aff4 #ec ,gent4 ,mag4 vol4 xxvi4 p4 #ia4 #ed ,compte ,rendu1 #ahgc1 p4 #ff4 #ee ,an ,historical ,account of ,earthquakes1 p4 #df4 #ef ,phil4 ,trans4 vol4 xlix4 p4 #dcf4 #eg ,am4 ,jour4 ,sci4 vol4 xlv4 p4 #abi4 #eh ,phil4 ,trans4 vol4 xlix4 p4 #edg4 #ei ,ibid4 vols4 xlii4 and xxxix4 #fj ,phil4 ,trans4 vol4 xlix1 part i4 #fa ,compte ,rendu1 #ahgc1 part ii4 p4 #ff4 #fb ,die ,vulcan4 ,ers4 d4 ,erde1 ,c4 ,w4 ,c4 ,fuchs4 #fc ,comte ,rendu1 #ahge1 p4 #fic4 #fd ,gent4 ,mag4 vol4 xix4 p4 #aij4 #fe ,phil4 ,trans4 vol4 xlix4 p4 #aae4 #ff ,gent4 ,mag4 vol4 xxi4 #agea4 #fg ,jour4 ,royal ,geo4 ,soc4 vol4 vi4 p4 #cai4 #fh ,darwin1 ,geolog4 ,observations1 p4 #bcb4 #fi ,ibid4 p4 #bde4 #gj ,lyell1 ,principles of ,geology1 vol4 ii4 pp4 #ajg-h4 #ga ,gent4 ,mag4 #agcc1 vol4 iii4 p4 #bag4 #gb #8,earthquakes of ,cutch1' ,jour4 ,royal ,geo4 ,soc4 vol4 xl4 #gc ,m4 ,daussy1 #8,sur l'existence probable d'un volcan sousmarin situ ar environ #j #bj de lat4 ,s41 et #bb #j de long1 ouest1' ,comptes ,rendus1 vol4 vi4 p4 #eab4 #gd ,am4 ,jour4 ,sci4 vol4 xlv4 p4 #acc4 #ge ,am4 ,jour4 ,sci4 vol4 xiv4 p4 #bji4 #gf ,d4 ,c4 ,f4 ,winslow1 #8,tides at ,tahiti1' ,am4 ,jour4 ,sci4 #ahfe1 p4 #de2 also ,mallet's ,catalogue of ,earthquakes4 #gg ,am4 ,jour4 ,sci4 vol4 i4 p4 #dfi4 #gh ,darwin1 ,researches in ,geology1 c41 p4 #cgh4 #gi ,kluge1 ,jahrb4 f4 ,min4 #ahfa1 p4 #igg4 #hj ,darwin1 ,voyage of a ,naturalist1 p4 #cji4 #ha ,prof4 ,a4 ,d4 ,bache1 ,united ,states ,coast ,survey ,report1 #ahee1 p4 #cdb4 #hb ,united ,states ,coast ,surrey ,report1 or ,am4 ,jour4 ,sci4 vi4 p4 #gg4 #hc ,petermann's ,mittheilungen1 #ahgg1 ,heft xii4 ,s4 #ded1 and ,nova ,acta der ,ksl4 ,leop4 ,carol4 ,deutschen ,acad4 d ,naturforscher1 ,band xl4 ,no4 #i4 #hd ,j4 ,milne3 #8,peruvian ,earthquake of ,may #i1 #ahgg4' ,see ,trans4 ,seis4 ,soc4 of ,japan1 vol4 ii4 #he ,report of ,british ,association1 #ahdg1 p4 #hd4 #hf ,das ,erdbeben von ,herzogenrath1 c41 p4 #acd4 #hg ,phil4 ,trans4 vol4 li4 #hh ,see ,am4 ,jour4 ,sci4 #ahgb4 #hi ,david ,milne says that #8out of #aaj shocks recorded in ,england1 thirty-one originated in ,wales1 thirty-one along the south coast of ,england1 fourteen on the borders of ,yorkshire and ,derbyshire1 and five or six in ,cumberland4' #ij ,e4 ,suess1 ,die ,erdbeben ,niedersterreiches4 #ia ,h4 ,hoeffer1 ,die ,erdbeben ,krntens4 #ib ,six ,lectures on ,physical ,geography1 by ,rev4 ,s4 ,haughton1 ,f4,r4,s41 chap4 i4 #ic ,ramsay1 #8,geological ,history of ,mountain ,chains1' ,mining ,journal4 #id ,a notable example of a rapid diminution in the number of earthquakes felt at a place is that of ,comrie in ,scotland4 ,in #ahci-dj1 no less than sixty shocks were felt in eleven months4 ,in #ahdb-dc1 about thirty shocks were felt1 and in the following year thirty-seven4 ,since this time the number of shocks has decreased until they are almost of as rare occurrence at ,comrie as in other portions of the ,british ,isles4 #ie ,phil4 ,trans4 vol4 i4 #ahcf4 #if ,am4 ,jour4 of ,sci4 vol4 xxxvii4 p4 #a4 #ig ,milne1 #8,british ,earthquakes1' ,edin4 ,phil4 ,jour4 vol4 xxxi4 #ih ,phil4 ,trans4 vol4 xlix4 pt4 i4 #ii ,compte ,rendus1 #ahge1 p4 #fij4 #ajj ,am4 ,jour4 ,sci4 vol4 xi4 p4 #bcc4 #aja ,transactions of the ,asiatic ,society of ,japan1 vol4 vi4 pt4 i4 p4 #cec4 #ajb ,kluge1 ,ueber die ,ursachen1 c41 p4 #gd4 #ajc ,am4 ,jour4 ,sci4 vol4 xix4 p4 #afb4 #ajd ,mitt4 d4 ,deutsch4 ,ges41 ,aug4 #ahgh4 #aje ,report to ,british ,association1 #ahej1 p4 #gd4 #ajf ,fuchs1 ,die ,vulkanischen ,erscheinungen der ,erde1 p4 #dbd4 #ajg ,bern4 ,naturf4 ,gesellschaft1 #aheb4 #ajh ,comptes ,rendus1 #ahgd1 ,jan4 to ,june1 p4 #ea4 #aji ,bou1 ,parallele der ,erdbeben1 ,nordlichter und ,erdmagnetismus1 in ,sitz4 der ,k4 ,a4 d4 ,wissensch4 #ahef1 vol4 iv4 p4 #cie4 #aaj ,meteorologia ,endogena1 vol4 i4 p4 #ajg1 c4 #aaa ,phil4 ,trans4 vol4 lxviii4 p4 #bba4 #aab ,gent4 ,mag4 vol4 xxvii4 p4 #ejh4 #aac ,die ,vulkanischen ,erscheinungen der ,erde1 p4 #dai4 #aad ,petermann's ,geogr4 ,mitth4 #aheh1 sec4 #bdf4 #aae ,notes on volcanoes of the ,hawaiian ,islands1 ,w4 ,t4 ,brigham1 ,mem4 ,boston ,soc4 of ,nat4 ,hist41 #ahfh4 #aaf ,gent4 ,mag4 vol4 xxiii41 #agec4 #aag ,jour4 ,royal ,geog4 ,soc4 vol4 vi4 #aah ,ibid4 vol4 vi4 #aai ,phil4 ,trans4 vol4 xlii4 #abj ,am4 ,jour4 ,sci4 vol4 x4 p4 #aia4 #aba #8,earthquakes of ,san ,salvador1 ,december #ba-cj1 #ahgi4' ,am4 ,jour4 ,sci4 vol4 xix4 p4 #dae4 #abb ,gent4 ,mag4 #ageg1 p4 #cbc4 #abc ,phil4 ,trans4 vol4 li41 #agfj4 #abd ,mallet1 ,report to ,brit4 ,ass41 #aheh1 p4 #fg4 #abe ,von ,lasaulx1 ,earthquakes of ,herzogenrath4 #abf ,lyell1 ,principles1 vol4 ii4 p4 #ea4 #abg ,lyell1 ,principles1 vol4 i4 p4 #djb4 #abh ,fuchs1 p4 #dfd4 #abi ,comptes ,rendus1 ,august #ahed4 #acj ,nature1 ,april #bf1 #ahhc4 #aca ,phil4 ,soc41 ,wellington1 ,new ,zealand1 #ahge4 #acb ,phil4 ,trans41 vol4 xlii4 #acc ,m4 ,s4 di ,rossi1 ,earthquakes of ,casamicciola4 #acd ,phil4 ,trans41 vol4 xviii4 #afhc-e4 #ace ,ibid4 vol4 xlix4 #acf ,h4 ,d4 ,warner1 #8,the ,city of ,earthquakes1' ,atlantic ,monthly1 ,march #ahcc4 #acg ,palmer1 ,trans4 ,seis4 ,soc4 of ,japan1 vol4 iii4 p4 #adh4 #ach ,palmer1 ,trans4 ,seis4 ,soc4 of ,japan1 vol4 iii4 p4 #adh4 #aci ,paul1 ,trans4 ,seis4 ,soc4 of ,japan1 vol4 ii4 p4 #da4 #adj ,g4 ,h4 and ,h4 ,darwin1 ,reports of ,british ,association1 #ahha4 #ada ,reports of ,british ,association1 #ahha4 #adb ,comptes ,rendus1 #ahge1 ,january to ,june1 p4 #fhe4 #adc ,tel4 ,jour41 ,november #ae1 #ahha4 #add ,minutes and proceedings of the ,institute of ,civil ,engineers1 vol4 lx4 p4 #dab1 and vol4 lxiv4 p4 #cdc4 #ade ,see #8,earth ,tremors1' p4 #cji1 experiments of ,m4 d',abbadie1 c4 #adf ,meteorologia ,endogena4 #adg ,ibid4 #adh ,phil4 ,trans4 vol4 xlix4 p4 #edd4 #adi ,annual ,register1 vol4 iv4 #agfa1 p4 #ib4 #aej ,phil4 ,mag41 ,may #ahgf1 p4 #ddg4 #aea ,boston ,soc4 ,nat4 ,hist41 #ahfh4 #aeb #8,notes on ,tides at ,tahiti1' c41 ,am4 ,jour4 ,sci4 #ahff1 vol4 xlii4 p4 #de4 #aec ,trans4 ,seis4 ,soc4 of ,japan1 vol4 iv4 ,milne1 ,systematic ,observation of ,earthquakes4 #aed ,principles of ,geology1 vol4 ii4 #agg4 #aee ,gent4 ,mag41 vol4 xxvii4 p4 #ddh4 #aef ,phil4 ,trans41 vol4 xli4 p4 #hje4 #aeg ,meteorologia ,endogena1 vol4 i4 pp4 #ahf1 #ahg4 #aeh ,darwin1 ,geological ,observations1 p4 #bge et seq4 ---------------------------------------- ---------------------------- ,,the ,,international ,,scientific ,,series4 ,,each ,,book ,,complete ,,in ,,one ,,volume1 #ab,,mo1 ,,and ,,bound ,,in ,,cloth4 #a4 ,,forms ,,of ,,water3 ,a ,familiar ,exposition of the ,origin and ,phenomena of ,glaciers4 ,by ,j4 ,,tyndall1 ,,ll4 ,d41 ,f4 ,r4 ,s4 ,with #be ,illustrations4 #a4ej4 #b4 ,,physics ,,and ,,politics2 ,or1 ,thoughts on the ,application of the ,principles of 8,natural ,selection0 and 8,inheritance0 to ,political ,society4 ,by ,,walter ,,bagehot4 #a4ej4 #c4 ,,foods4 ,by ,,edward ,,smith1 ,m4 ,d41 ,,ll4 ,b41 ,f4 ,r4 ,s4 ,with numerous ,illustrations4 #a4ge4 #d4 ,,mind ,,and ,,body3 ,the ,theories of their ,relation4 ,by ,,alexander ,,bain1 ,,ll4 ,d4 ,with #d ,illustrations4 #a4ej4 #e4 ,,the ,,study ,,of ,,sociology4 ,by ,,herbert ,,spencer4 #a4ej4 #f4 ,,the ,,new ,,chemistry4 ,by ,professor ,j4 ,p4 ,,cooke1 of ,harvard ,university4 ,with #ca ,illustrations4 #b4jj4 #g4 ,,on ,,the ,,conservation ,,of ,,energy4 ,by ,,balfour ,,stewart1 ,m4 ,a41 ,,ll4 ,d41 ,f4 ,r4 ,s4 ,with #ad ,illustrations4 #a4ej4 #h4 ,,animal ,,locomotion2 or1 ,walking1 ,swimming1 and ,flying4 ,by ,j4 ,b4 ,,pettigrew1 ,m4 ,d41 ,f4 ,r4 ,s41 etc4 ,with #acj ,illustrations4 #a4ge4 #i4 ,,responsibility ,,in ,,mental ,,disease4 ,by ,,henry ,,maudsley1 ,m4 ,d4 #a4ej4 #aj4 ,,the ,,science ,,of ,,law4 ,by ,professor ,,sheldon ,,amos4 #a4ge4 #aa4 ,,animal ,,mechanism3 ,a ,treatise on ,terrestrial and ,arial ,locomotion4 ,by ,professor ,e4 ,j4 ,,marey4 ,with #aag ,illustrations4 #a4ge4 #ab4 ,,the ,,history ,,of ,,the ,,conflict ,,between ,,religion ,,and ,,science4 ,by ,j4 ,w4 ,,draper1 ,m4 ,d41 ,,ll4 ,d4 #a4ge4 #ac4 ,,the ,,doctrine ,,of ,,descent ,,and ,,darwinism4 ,by ,professor ,,oscar ,,schmidt 7,strasburg ,university74 ,with #bf ,illustrations4 #a4ej4 #ad4 ,,the ,,chemical ,,effects ,,of ,,light ,,and ,,photography4 ,by ,dr4 ,,hermann ,,vogel 7,polytechnic ,academy of ,berlin74 ,translation thoroughly revised4 ,with #ajj ,illustrations4 #b4jj4 #ae4 ,,fungi3 ,their ,nature1 ,influences1 ,uses1 etc4 ,by ,m4 ,c4 ,,cooke1 ,m4 ,a41 ,,ll4 ,d4 ,edited by the ,rev4 ,m4 ,j4 ,berkeley1 ,m4 ,a41 ,f4 ,l4 ,s4 ,with #aji ,illustrations4 #a4ej4 #af4 ,,the ,,life ,,and ,,growth ,,of ,,language4 ,by ,professor ,,william ,,dwight ,,whitney1 of ,yale ,college4 #a4ej4 #ag4 ,,money ,,and ,,the ,,mechanism ,,of ,,exchange4 ,by ,w4 ,,stanley ,,jevons1 ,m4 ,a41 ,f4 ,r4 ,s4 #a4ge4 #ah4 ,,the ,,nature ,,of ,,light1 with a ,general ,account of ,physical ,optics4 ,by ,dr4 ,,eugene ,,lommel4 ,with #ahh ,illustrations and a ,table of ,spectra in ,chromo-lithography4 #b4jj4 #ai4 ,,animal ,,parasites ,,and ,,messmates4 ,by ,monsieur ,,van ,,beneden4 ,with #hc ,illustrations4 #a4ej4 #bj4 ,,fermentation4 ,by ,professor ,,sch,,tzenberger4 ,with #bh ,illustrations4 #a4ej4 #ba4 ,,the ,,five ,,senses ,,of ,,man4 ,by ,professor ,,bernstein4 ,with #ia ,illustrations4 #a4ge4 #bb4 ,,the ,,theory ,,of ,,sound ,,in ,,its ,,relation ,,to ,,music4 ,by ,professor ,,pietro ,,blaserna4 ,with numerous ,illustrations4 #a4ej4 #bc4 ,,studies ,,in ,,spectrum ,,analysis4 ,by ,j4 ,,norman ,,lockyer1 ,f4 ,r4 ,s4 ,with #f ,photographic ,illustrations of ,spectra1 and numerous ,engravings on ,wood4 #b4ej4 #bd4 ,a ,,history ,,of ,,the ,,growth ,,of ,,the ,,steam-,,engine4 ,by ,professor ,r4 ,h4 ,,thurston4 ,with #afc ,illustrations4 #b4ej4 #be4 ,,education ,,as ,a ,,science4 ,by ,,alexander ,,bain1 ,,ll4 ,d4 #a4ge4 #bf4 ,,students' ,,text-,,book ,,of ,,color2 ,or1 ,modern ,chromatics4 ,with ,applications to ,art and ,industry4 ,by ,professor ,,ogden ,n4 ,,rood1 ,columbia ,college4 ,new edition4 ,with #acj ,illustrations4 #b4jj4 #bg4 ,,the ,,human ,,species4 ,by ,professor ,a4 ,,de ,,quatrefages1 ,membre de l',institut4 #b4jj4 #bh4 ,,the ,,crayfish3 ,an ,introduction to the ,study of ,zology4 ,by ,t4 ,h4 ,,huxley1 ,f4 ,r4 ,s4 ,with #hb ,illustrations4 #a4ge4 #bi4 ,,the ,,atomic ,,theory4 ,by ,professor ,a4 ,,wurtz4 ,translated by ,e4 ,cleminshaw1 ,f4 ,c4 ,s4 #a4ej4 #cj4 ,,animal ,,life ,,as ,,affected ,,by ,,the ,,natural ,,conditions ,,of ,,existence4 ,by ,,karl ,,semper4 ,with #b ,maps and #ajf ,woodcuts4 #b4jj4 #ca4 ,,sight3 ,an ,exposition of the ,principles of ,monocular and ,binocular ,vision4 ,by ,,joseph ,,le ,,conte1 ,,ll4 ,d4 ,with #acb ,illustrations4 #a4ej4 #cb4 ,,general ,,physiology ,,of ,,muscles ,,and ,,nerves4 ,by ,professor ,j4 ,,rosenthal4 ,with #ge ,illustrations4 #a4ej4 #cc4 ,,illusions3 ,a ,psychological ,study4 ,by ,,james ,,sully4 #a4ej4 #cd4 ,,the ,,sun4 ,by ,c4 ,a4 ,,young1 ,professor of ,astronomy in the ,college of ,new ,jersey4 ,with numerous ,illustrations4 #b4jj4 #ce4 ,,volcanoes3 ,what they ,are and what they ,teach4 ,by ,,john ,w4 ,,judd1 ,f4 ,r4 ,s41 ,professor of ,geology in the ,royal ,school of ,mines4 ,with #if ,illustrations4 #b4jj4 #cf4 ,,suicide3 ,an ,essay in ,comparative ,moral ,statistics4 ,by ,,henry ,,morselli1 ,m4 ,d41 ,professor of ,psychological ,medicine1 ,royal ,university1 ,turin4 #a4ge4 #cg4 ,,the ,,formation ,,of ,,vegetable ,,mould1 ,,through ,,the ,,action ,,of ,,worms4 ,with ,observations on their ,habits4 ,by ,,charles ,,darwin1 ,,ll4 ,d41 ,f4 ,r4 ,s4 ,with ,illustrations4 #a4ej4 #ch4 ,,the ,,concepts ,,and ,,theories ,,of ,,modern ,,physics4 ,by ,j4 ,b4 ,,stallo4 #a4ge4 #ci4 ,,the ,,brain ,,and ,,its ,,functions4 ,by ,j4 ,,luys4 #a4ej4 #dj4 ,,myth ,,and ,,science4 ,by ,,tito ,,vignoli4 #a4ej4 #da4 ,,diseases ,,of ,,memory3 ,an ,essay in the ,positive ,psychology4 ,by ,,th4 ,,ribot1 author of 8,heredity40 #a4ej4 #db4 ,,ants1 ,,bees1 ,,and ,,wasps4 ,a ,record of ,observations of the ,habits of the ,social ,hymenoptera4 ,by ,sir ,,john ,,lubbock1 ,bart41 ,f4 ,r4 ,s41 ,d4 ,c4 ,l41 ,,ll4 ,d41 etc4 #b4jj4 #dc4 ,,science ,,of ,,politics4 ,by ,,sheldon ,,amos4 #a4ge4 #dd4 ,,animal ,,intelligence4 ,by ,,george ,j4 ,,romanes4 #a4ge4 #de4 ,,man ,,before ,,metals4 ,by ,n4 ,,joly1 ,correspondent of the ,institute4 ,with #adh ,illustrations4 #a4ge4 #df4 ,,the ,,organs ,,of ,,speech ,,and ,,their ,,application ,,in ,,the ,,formation ,,of ,,articulate ,,sounds4 ,by ,g4 ,h4 ,,von ,,meyer1 ,professor in ,ordinary of ,anatomy at the ,university of ,zrich4 ,with #dg ,woodcuts4 #a4ge4 #dg4 ,,fallacies3 ,a ,view of ,logic from the ,practical ,side4 ,by ,,alfred ,,sidgwick1 ,b4 ,a41 ,oxon4 #a4ge4 #dh4 ,,origin ,,of ,,cultivated ,,plants4 ,by ,,alphonse ,,de ,,candolle4 #b4jj4 #di4 ,,jelly-,,fish1 ,,star-,,fish1 ,,and ,,sea-,,urchins4 ,being a ,research on ,primitive ,nervous ,systems4 ,by ,,george ,j4 ,,romanes4 #a4ge4 #ej4 ,,the ,,common ,,sense ,,of ,,the ,,exact ,,sciences4 ,by the late ,,william ,,kingdon ,,clifford4 #a4ej4 #ea4 ,,physical ,,expression3 ,its ,modes and ,principles4 ,by ,,francis ,,warner1 ,m4 ,d41 ,assistant ,physician1 and ,lecturer on ,botany to the ,london ,hospital1 etc4 ,with #ea ,illustrations4 #a4ge4 #eb4 ,,anthropoid ,,apes4 ,by ,,robert ,,hartmann1 ,professor in the ,university of ,berlin4 ,with #fc ,illustrations4 #a4ge4 #ec4 ,,the ,,mammalia ,,in ,,their ,,relation ,,to ,,primeval ,,times4 ,by ,,oscar ,,schmidt4 #a4ej4 #ed4 ,,comparative ,,literature4 ,by ,,hutcheson ,,macaulay ,,posnett1 ,m4 ,a41 ,,ll4 ,d41 ,f4 ,l4 ,s41 ,barrister-at-,law2 ,professor of ,classics and ,english ,literature1 ,university ,college1 ,auckland1 ,new ,zealand1 author of 8,the ,historical ,method10 etc4 #a4ge4 #ee4 ,,earthquakes ,,and ,,other ,,earth ,,movements4 ,by ,,john ,,milne1 ,professor of ,mining and ,geology in the ,imperial ,college of ,engineering1 ,tokio1 ,japan4 ,with #ch ,figures4 ,new ,york3 ,d4 ,,appleton ,,co41 #a1 #c1 #e ,bond ,street4 ,,volcanoes3 ,,what ,,they ,,are ,,and ,,what ,,they ,,teach4 ,by ,j4 ,w4 ,,judd1 ,professor of ,geology in the ,royal ,school of ,mines 7,london74 ,with ,ninety-six ,illustrations4 #abmo4 ,cloth1 #b4jj4 8,the volume before us is one of the pleasantest science manuals we have read for some time40--,athenum4 8,mr4 ,judd's summary is so full and so concise1 that it is almost impossible to give a fair idea in a short review40--,pall ,mall ,gazette4 8,professor ,judd discusses the nature of volcanic action1 the internal structure of volcanic mountains1 the distribution of volcanoes upon the surface of the globe1 their activity in different periods of the earth's existence1 the use of volcanoes in the economy of nature1 the various theories that have been made to explain volcanic action4 ,he has abbreviated in this volume a vast amount of information1 which has a fascinating interest for many minds by reason of its relation to the past history and future destiny of this little bubble of earth upon which we sail through the infinite spaces of ether40--,new ,york ,home ,journal4 8,the book gives an exhaustive statement of the phenomena of volcanoes1 and of the facts in the formation of mountain-chains1 and relates a mass of interesting observations and facts1 the results of patient and extensive personal investigation and study1 mostly in different places in ,southern ,europe1 but not neglecting the world's larger volcanoes in other regions40--,hartford ,times4 8,a fascinating example of patient observation1 sound judgment1 and acute reasoning4 ,under ,professor ,judd's skillful treatment the volcano is forced not only to tell its own history1 but also to solve a number of earth problems seemingly disconnected with it2 and the story is told in strong1 nervous language1 and with an earnestness and subdued enthusiasm that are delightfully stimulating40--,boston ,gazette4 8,professor ,judd first points out the errors in the old definition of a volcano4 ,the volcanic hole is very often not on the summit1 but on the side1 sometimes at the base of the mountain or hill1 and it sends forth steam rather than smoke1 and the supposed raging flames are nothing more than the glowing light of a mass of molten material reflected from those vapor-clouds4 ,so our old ignorance vanishes1 and in this admirable work the internal structure of volcanic mountains1 the nature and products of volcanic action1 and the distribution of the materials rejected from volcanic vents1 the succession of operations taking place at volcanic centers1 are all very ably and clearly discussed40--,philadelphia ,times4 8,a succinct and excellent treatise on a very interesting subject40--,philadelphia ,north ,american4 ,for sale by all booksellers2 or sent by mail1 post paid1 on receipt of price4 ,new ,york3 ,d4 ,,appleton ,,co41 #a1 #c1 #e ,bond ,street4 ,,the ,,concepts ,,and ,,theories ,,of ,,modern ,,physics4 ,by ,j4 ,b4 ,,stallo4 #abmo1 cloth #a4ge4 8,judge ,stallo's work is an inquiry into the validity of those mechanical conceptions of the universe which are now held as fundamental in physical science4 ,he takes up the leading modern doctrines which are based upon this mechanical conception1 such as the atomic constitution of matter1 the kinetic theory of gases1 the conservation of energy1 the nebular hypothesis1 and other views1 to find how much stands upon solid empirical ground1 and how much rests upon metaphysical speculation4 ,since the appearance of ,dr4 ,draper's #8,religion and ,science1' no book has been published in the country calculated to make so deep an impression on thoughtful and educated readers as this volume4444 ,the range and minuteness of the author's learning1 the acuteness of his reasoning1 and the singular precision and clearness of his style1 are qualities which very seldom have been jointly exhibited in a scientific treatise40--,new ,york ,sun4 8,judge ,j4 ,b4 ,stallo1 of ,cincinnati1 is a ,german by birth1 and came to this country at about the age of seventeen4 ,he was early familiar with science1 and he lectured for some years in an ,eastern college2 but at length he adopted the profession of law4 ,he is also remembered by many as an author1 having a number of years ago written a metaphysical treatise of marked ability for one of his youthful years4 ,his present book must be read deliberately1 must be studied to be appreciated2 but the students of science1 as well as those of metaphysics1 are certain to be deeply interested in its logical developments4 ,it is a timely and telling contribution to the philosophy of science1 imperatively called for by the present exigencies in the progress of knowledge4 ,it is to be commended equally for the solid value of its contents and the scholarly finish of its execution40--,the ,popular ,science ,monthly4 8,the book is of vital interest to a much larger class than specialists--to all1 in fact1 who value clear thinking or are interested in the accuracy more than the progress of scientific thought4 ,it deals with the results and theories of physical science1 and in no sense with the processes of the laboratory4 ,it is written with a clearness that is uncommon in philosophic works and with a desire to find truth1 conscious of the fact that a prime prerequisite of finding it is to clear the way of accumulated and fast-settling untruths4 ,it is a scientific rebuke1 as severe as it is lucid1 of the scientists who leave their apparatus and go star-gazing3 here is the pit into which they have fallen40--,new ,york ,world4 8,the volume is an important contribution to scientific discussion1 and is marked by closeness of reasoning1 and clearness and cogency of statement40--,boston ,journal4 ,for sale by all booksellers2 or sent by mail1 post paid1 on receipt of price4 ,new ,york3 ,d4 ,,appleton ,,co41 #a1 #c1 #e ,bond ,st4 ,transcriber's ,notes3 - ,text enclosed by underscores is in italics 7italics74 - ,text enclosed by equals is in bold 7bold74 - ,blank pages have been removed4 - ,silently corrected typographical errors4 - ,spelling and hyphenation variations made consistent4 - ,front publication list moved to the back4 - ,tables pages #gg1 #hi3 removed unneeded right braces4 - ,tables pages #bdj1 #beg3 changed to use cell borders instead of right braces4 - ,table page #bei3 ,northern ,hemisphere average #aej corrected to #aej4