,illustration3 ,a tornado near ,elmwood1 ,nebraska4 ,a painting made from what is probably one of the most remarkable photographs ever taken of a tornado4 ,the original photograph was made in two parts1 as the photographer was too close to get the whole funnel cloud into the field of his camera4 7,photograph by ,g4 ,b4 ,pickwell7 ,,popular ,,science ,,library ,,editor-,,in-,,chief ,,garrett ,p4 ,,serviss ,,authors ,,william ,j4 ,,miller ,,hippolyte ,,gruener ,a4 ,,russell ,,bond ,d4 ,w4 ,,hering ,,loomis ,,havemeyer ,,ernest ,g4 ,,martin ,,arthur ,,selwyn-,,brown ,,robert ,,chenault ,,givler ,,ernest ,,ingersoll ,,wilfred ,,mason ,,barton ,,william ,b4 ,,scott ,,ernest ,j4 ,,streubel ,,norman ,,taylor ,,david ,,todd ,,charles ,,fitzhugh ,,talman ,,robin ,,beach ,,arranged ,,in ,,sixteen ,,volumes ,,with ,a ,,history ,,of ,,science1 ,,glossaries ,,and ,a ,,general ,,index ,,illustrated ,illustration ,,volume ,,one ,p4 ,f4 ,,collier ,,son ,,company ,,new ,,york ,copyright #aibb ,,by ,p4 ,f4 ,,collier ,,son ,,company ,,manufactured ,,in ,u4 ,s4 ,a4 ,,meteorology ,,the ,,science ,,of ,,the ,,atmosphere ,,by ,,charles ,,fitzhugh ,,talman ,,chairman1 ,,committee ,,of ,,public ,,information1 ,,american ,,meteorological ,,society ,illustration ,p4 ,f4 ,,collier ,,son ,,company ,,new ,,york ,,preface ,meteorology is the science of the atmosphere and its phenomena1 including weather4 ,nowadays1 when we speak of a 8meteor10 we generally mean a shooting star2 but formerly this term was applied 7and it still often is in technical literature7 to a great variety of phenomena and appearances in the atmosphere1 including clouds1 rain1 snow1 rainbows1 and so forth4 ,that is how the science of the atmosphere came to have its present name4 ,meteorology is not a branch of astronomy4 ,these two sciences are as different from each other as zology is from botany4 ,they are both founded on physics1 and they 8overlap0 each other to some extent1 just as every science does certain others2 but if you want information about the atmosphere1 weather and climate1 an astronomical observatory is not the place to seek it2 while if you wish to make inquiries about comets1 sun spots1 eclipses1 standard time1 or the date on which ,easter fell in the year #afff1 do not apply to the ,weather ,bureau4 ,in the city of ,washington the ,government maintains an astronomical and timekeeping institution known as the ,naval ,observatory1 and it maintains in the same city the central office of the ,united ,states ,weather ,bureau4 ,the two establishments are a mile apart in space and nearly a whole library apart in the subjects with which they are concerned4 ,the fact that their functions are persistently confounded by the public indicates the necessity of writing this preface to a popular book on meteorology4 ,,contents ,,chapter ,,page ,i4 ,,the ,,anatomy ,,of ,,the ,,atmosphere #i ,,ii4 ,,the ,,resources ,,of ,,the ,,atmosphere #bd ,,iii4 ,,the ,,atmosphere ,,as ,a ,,highway #ci ,,iv4 ,,dust ,,and ,,smoke ,,in ,,the ,,atmosphere #eb ,v4 ,,weather ,,and ,,weather ,,instruments #ff ,,vi4 ,,cloudland #ij ,,vii4 ,,precipitation #ajf ,,viii4 ,,winds ,,and ,,storms #abc ,,ix4 ,,atmospheric ,,electricity #ada ,x4 ,,atmospheric ,,optics #afd ,,xi4 ,,atmospheric ,,acoustics #ahf ,,xii4 ,,climate ,,and ,,climates #aig ,,xiii4 ,,organized ,,meteorology #bab ,,xiv4 ,,weather ,,maps ,,and ,,forecasts #bbd ,,xv4 ,,agricultural ,,meteorology #bde ,,xvi4 ,,commercial ,,meteorology #bfa ,,xvii4 ,,marine ,,meteorology #bga ,,xviii4 ,,aeronautical ,,meteorology #bhd ,,xix4 ,,military ,,meteorology #cjf ,,xx4 ,,medical ,,and ,,physiological ,,meteorology #caf ,,xxi4 ,,weather-,,making #ccb ,,xxii4 ,,atmospheric ,,byways #cdf ,,glossary #cfe ,,list ,,of ,,illustrations ,,funnel-,,shaped ,,cloud ,,of ,a ,,tornado ,frontispiece ,painted from an unusual ,photograph ,,facing ,,page ,,exploring ,,the ,,upper ,,air--,,beginning ,,of ,a ,,pilot ,,balloon ,,flight #cb ,,exploring ,,the ,,upper ,,air--,,sending ,,up ,a ,,sounding ,,balloon #cb ,,meteorograph ,,for ,,use ,,with ,a ,,sounding ,,balloon #cc ,,kite ,,meteorograph ,,to ,,be ,,sent ,,aloft ,,attached ,,to ,a ,,kite #cc ,,alto-,,cumulus--,,fleecy ,,masses ,,showing ,,blue ,,sky ,,between #if ,,cumulus1 ,,or ,,wool-,,pack ,,cloud #if ,,mammato-,,cumulus1 ,,or 8,,rain ,,balls0 #ig ,,cumulo-,,nimbus--,,the ,,thundercloud #ig ,,cloud ,,banner ,,over ,,mount ,,assiniboine1 ,,canadian ,,rockies #ajj ,,cirrus1 ,,with ,,lower ,,clouds ,,in ,,the ,,foreground #ajj ,,lenticular ,,cloud ,,over ,,mount ,,rainier #aja ,,ice ,,storm ,,at ,,philadelphia--,,trees ,,covered ,,with ,,glaze #aaf ,,nieve ,,penitente ,,in ,,the ,,argentine ,,andes #aag ,,clouds ,,or ,,fog ,,cascading ,,through ,,last ,,fork ,,ca,,on ,,into ,,santa ,,anita ,,ca,,on #acf ,,cloudburst ,,in ,,southern ,,utah #acg ,,photographic ,,analysis ,,of ,,lightning--,,single ,,and ,,double ,,discharges #afj ,,photograph ,,of ,,lightning1 ,,showing 8,,black0 ,,flashes #afa ,,atmospheric ,,electricity ,,instruments #afa ,,glass ,,weather ,,map ,,in ,,the ,,united ,,states ,,weather ,,bureau #bbd ,,the ,,sun ,,drawing ,,water #bbe ,,orchard ,,heaters ,,in ,,operation ,,as ,,protection ,,against ,,expected ,,frost #bef ,,snow ,,surveyor ,,at ,,work1 ,,using ,a ,,cylindrical ,,snow ,,sampler #beg ,,snow ,,rollers1 ,,or ,,wind-,,blown ,,snowballs #beg ,,bed ,,of ,,the ,,potomac ,,river ,,photographed ,,from ,,the ,,air #bhh ,,drilling ,,with ,,compressed ,,air ,,in ,a ,,copper ,,mine #bhi ,,launching ,a ,,weather ,,bureau ,,kite ,,to ,,explore ,,the ,,air ,,over ,,the ,,ocean #bhi ,,weather ,,bureau ,,kiosk1 ,,union ,,square1 ,,san ,,francisco #cbj ,,united ,,states ,,weather ,,bureau ,,station ,,at ,,peoria1 ,,illinois #cbj ,,central ,,office ,,of ,,the ,,united ,,states ,,weather ,,bureau ,,at ,,washington #cba ,,chapter ,i ,,the ,,anatomy ,,of ,,the ,,atmosphere ,two quite different conceptions of the substance called 8air0 are current in the world4 ,one has prevailed from time immemorial4 ,the other is wholly modern4 ,one is the popular view1 the other the scientific4 ,ancient philosophers regarded air as one of the four 8elements0 of which all things were supposed to be made4 ,average humanity1 though it did not concern itself with philosophy1 must have begun1 almost as soon as it realized the existence of air at all1 to think of it as something that1 however it changed its state from hot to cold1 dry to moist1 pure to impure1 was fundamentally uniform--a single entity4 ,certainly this idea is in full vigor today4 ,the air that we breathe1 supply to our fires1 stir with fans1 pump into bicycle tires1 fly in--the air that asserts its independence of our will in the wind and the weather--gives us the impression of individuality4 ,we instinctively rank it with water among the simple1 definite things in the repertory of nature4 ,even the man of science often finds it convenient to discuss and deal with air as if it were a single substance1 but he is well aware that it is nothing of the kind4 ,he knows that it is1 in fact1 a jumble of gases having very different properties4 ,some are heavy1 others light4 ,some are chemically very active1 others extremely inactive4 ,some are abundant1 others very rare4 ,these gases constitute the earth's atmosphere4 ,other planets have atmospheres that are quite different in composition from ours4 ,the sun itself has a very complex atmosphere4 ,the earth's atmosphere is1 then1 a collection of gases1 which are mixed but not chemically combined4 ,some of them are themselves chemical compounds4 ,each of these gases behaves very much the same as if the others were not present1 and each of them has its separate business to perform in the economy of nature4 ,for example1 a tree draws upon the store of carbon dioxide gas in the atmosphere to build up its tissues4 ,presently the tree is cut down and its wood is burned for fuel4 ,in this process a different atmospheric gas is brought into play4 ,we often say that the 8air0 supports combustion--that we supply 8air0 with a bellows to make a fire burn more brightly--but it is not the air as a whole that enables things to burn4 ,four-fifths of the atmospheric substance takes no part in the process4 ,we burn with oxygen alone4 ,so it is with breathing4 ,oxygen and not air constitutes the breath of life4 ,near the surface of the earth the proportions of the more abundant gases mixed together in the air are remarkably constant4 ,ignoring a variable admixture of water vapor1 oxygen is always about #ba per cent1 by volume1 and nitrogen about #gh per cent4 ,the remaining #a per cent is mainly argon4 ,at great altitudes1 however1 these percentages no longer obtain4 ,the atmospheric gases differ greatly among themselves in weight1 and in the high atmosphere1 where they are not mixed by the winds1 as they are below1 the heavier tend to settle to the bottom and the lighter to float on top1 as oil floats on water4 ,it is calculated that at a height of thirty miles above sea level the percentage of nitrogen is about #hf and of oxygen only #aj1 while at the same altitude the gas hydrogen1 which at low levels constitutes less than one-hundredth of #a per cent of the atmosphere amounts to more than #b per cent4 ,going higher1 the percentage of hydrogen is supposed to increase rapidly1 until1 at an altitude of forty-eight miles1 the atmosphere is more than half hydrogen1 and at eighty miles above the earth this gas forms #ii per cent of the whole4 ,these figures are not necessarily final2 for some authorities believe that the atmosphere contains an unknown gas lighter than hydrogen1 while others think that the hydrogen found in the lower air enters into chemical combinations before it can reach the higher levels2 but it is beyond doubt that the composition of the upper atmosphere is quite different from that of the lower4 ,of course almost any gas may be found locally and occasionally in the atmosphere1 but there are several that are always found wherever a refined analysis of the air is made1 and others that are generally present4 ,the following is a fairly complete list3 ,nitrogen1 oxygen1 water vapor1 argon1 carbon dioxide1 hydrogen1 helium1 neon1 krypton1 xenon1 niton 7radium emanation71 ozone1 hydrogen dioxide1 ammonia and other compounds of nitrogen4 ,a number of these substances have only become known to science within the last quarter of a century4 ,argon1 though it constitutes nearly #a per cent of the atmosphere1 escaped detection until the year #ahid4 ,the investigation of argon led to the discovery of some of the others4 ,in #ahie it was found that the air1 as well as certain minerals1 contains helium4 ,this substance was not new to science1 but it had never before been found on earth4 ,it was discovered in the atmosphere of the sun1 by means of the spectroscope1 as early as #ahfh4 ,terrestrial helium1 neon1 krypton1 and xenon were all discovered by ,sir ,william ,ramsay1 who also shared with ,lord ,rayleigh the distinction of discovering argon4 ,ramsay has published the following figures for the proportions in which some of the rare gases exist in the atmosphere3 ,helium #a part in #bde1cbj by volume ,neon #a 8 #hj1hjj 8 8 ,krypton #a 8 #b1jjj1jjj 8 8 ,xenon #a 8 #ag1jjj1jjj 8 8 ,niton1 or radium emanation1 is one of the products of the disintegration of radium4 ,niton itself disintegrates very rapidly1 one-half of any given quantity disappearing in about four days1 and one of its products is helium4 ,the amount of niton in the atmosphere is never more than an infinitesimal trace4 ,thus we are told that the total quantity of this substance present in the atmosphere of the whole earth up to an altitude of one kilometer 7#j4f mile7 weighs less than nine ounces1 and that each cubic centimeter of air contains among its thirty million million million molecules only between one and two molecules of niton1 on an average4 ,turning1 now1 to the more abundant constituents of the atmosphere1 we find that oxygen and nitrogen differ strikingly from each other in the fact that1 while the former has a strong chemical affinity for nearly all other elements1 the latter is chemically inert1 having little tendency to unite directly with other elements1 though by indirect processes1 and chiefly through the agency of plants and animals1 a large number of nitrogen compounds are produced4 ,oxides of nitrogen are formed directly from the atmospheric gases by lightning discharges1 and these unite with the moisture of the air to form nitric and nitrous acids4 ,a certain amount of ammonia 7a compound of nitrogen and hydrogen7 may also be formed by lightning from nitrogen and atmospheric water1 but most of the ammonia in the air is derived from the decomposition of plant and animal matters4 ,the compounds of nitrogen that occur in the air are washed down by rain in considerable quantities4 ,analyses of rain water made in different parts of the world show from one to nine pounds of such substances per acre per annum4 ,carbon dioxide 7more familiarly known as carbonic acid gas7 occurs in the atmosphere in the almost constant proportion of three parts in #aj1jjj by volume4 ,it is a little more abundant in the air of towns than in the open country or over the ocean1 and it undergoes slight periodic variations1 but the fact that it is not much more variable is rather surprising1 considering that it is continually being added to and abstracted from the air by numerous agencies that have no dependence upon one another4 ,it is supplied to the air by volcanoes1 mineral springs1 the combustion of fuel1 the respiration of animals and plants1 and the decay of organic matter4 ,the amount supplied annually by the burning of coal alone is estimated to be equivalent to more than one-thousandth of the total volume of the gas present in the atmosphere at any one time4 ,on the other hand1 all green plants1 in the presence of sunlight1 withdraw carbon dioxide from the air1 abstract the carbon from it for the use of the plant1 and return the oxygen to the atmosphere4 ,thus it is estimated that an acre of beech forest takes a ton of carbon out of the air annually4 ,a vast amount of atmospheric carbon dioxide enters into chemical combination with certain rocks at the earth's surface4 ,lastly1 a large quota of this atmospheric gas is absorbed by sea water1 and certain authorities have seen in this process a regulator of the total amount in the atmosphere1 the hypothesis being that the ocean gives back some of the carbon dioxide whenever this substance becomes deficient in the air4 ,water vapor--i4 e41 water in an invisible gaseous form--is always present in the atmosphere1 but its amount is subject to wide fluctuations4 ,an important fact in this connection is that1 at any given temperature1 the air can hold only a definite amount of this vapor4 ,this maximum amount increases rapidly with temperature4 ,when the air is fully charged with water vapor it is said to be 8saturated40 ,properly speaking1 the temperature limits the amount of the vapor that can occur in a given space1 regardless of the presence of the other constituents of air1 and in scientific language it is the vapor itself that is said to be saturated1 and not the air2 but in a popular book about the atmosphere1 where much has to be said about atmospheric water vapor1 adherence to scientific usage in this matter invariably leads to awkward complications4 ,speaking1 then1 in familiar terms--when the air is saturated with water vapor1 a fall in temperature causes some of the vapor to condense in visible form1 as cloud1 fog1 rain1 dew1 snow1 hail1 etc4 ,as the sole source of these various forms of moisture1 and on account of the important part it plays in many atmospheric processes1 water vapor is1 from a meteorological point of view1 the most interesting constituent of the atmosphere4 ,one more atmospheric gas requires notice here1 both on account of the great popular interest attaching to it1 and because of recent scientific discoveries concerning it--viz41 ozone4 ,this substance may be described1 in nontechnical language1 as a concentrated form of oxygen4 ,it is one of the most powerful oxidizing agencies known1 and has found useful applications in medicine and various industries4 ,its popular renown1 however1 is due to the fact that for many years it was regarded as a great natural purifier of the atmosphere4 8,life-giving ozone0 was reputed to be abundant in the air of forests1 mountains1 and the seashore4 ,systematic observations were made of the prevalence of ozone at different places throughout the world1 generally by noting the change of color of test-papers exposed to the air4 ,these 8ozonometric0 observations are now a closed chapter in the history of meteorology1 for it has been found that the reactions of so-called ozone papers are due chiefly or entirely to atmospheric substances other than ozone4 ,moreover1 direct examination of the air by more accurate methods--including samples collected with the aid of kites and balloons up to a height of several thousand feet above the earth--shows that the amount of ozone in the whole of the lower atmosphere is exceedingly small--much too small to be of hygienic significance4 ,whatever ozone is produced from oxygen at such levels by lightning discharges or other possible agencies probably enters promptly into chemical union with oxidizable substances and therefore has only a brief existence4 ,on the other hand1 the spectroscope has brought us evidence that far aloft in the atmosphere1 many miles above the earth1 ozone is quite abundant4 ,here it is supposed to be generated by two agencies--the electrical discharges of the aurora and ultra-violet radiations from the sun4 ,the ultra-violet rays that help to produce it are prevented from reaching the earth1 and astronomers are thus deprived of much interesting information they might otherwise obtain concerning the spectra of the sun and stars4 ,however1 as the present ,lord ,rayleigh has pointed out1 we can console ourselves for this fact by reflecting that if the ozone did not shut off much of the ultra-violet light from the sun1 this light would probably ruin our eyesight2 or1 rather1 we should be put to the inconvenience of constantly wearing some sort of protective spectacles in the daytime4 ,the high-level ozone is further interesting because of exercising a certain control over the temperature of the lower air4 ,it is more transparent for incoming solar radiation than for outgoing earth radiation4 ,hence1 when it is unusually abundant1 it should raise the general temperature of the earth4 ,this presumably happens when the condition of the sun is such that an unusual amount of ultra-violet radiation reaches the upper atmosphere1 a fact that must be taken into consideration in any attempt to establish a relation between climatic fluctuations and the sun-spot period4 ,the lowest part of our atmosphere is the densest because it is compressed by the weight of the air above it4 ,thus it happens that1 although the atmosphere is at least several hundred miles in height1 one-half of its mass--i4 e41 one-half of the quantity of matter in it1 as expressed in terms of weight--lies below an altitude of about #c miles above sea level1 while about seven-eighths lies below the ten-mile level4 ,above about five miles the atmosphere is too rare to support life4 ,the highest clouds seldom occur higher than ten miles4 ,storms hardly ever reach that height4 ,in short1 the phenomena of life and the phenomena of weather are confined to a layer of air so shallow1 in proportion to the dimensions of our globe1 that on the surface of an orange it would be represented by a sheet of thin paper4 ,the actual height of the atmosphere is not even approximately known4 ,there are theoretical reasons for believing that even at a height of thousands of miles above the earth there are molecules of atmospheric gases still under the control of the earth's gravity1 while at such levels yet other atmospheric molecules are constantly escaping into outer space4 ,at an altitude of fifty miles the atmosphere is less than #a_/ge1jjj as dense as at sea level--i4 e41 more than seventy-five times as attenuated as the best 8vacuum0 obtainable with an ordinary mechanical air pump4 ,at #cjj miles it is computed to be about one two-millionth as dense as at sea level4 ,the loftiest atmospheric phenomenon that we can observe directly is the aurora1 which has been photographed up to heights of more than #cjj miles4 ,the altitude of the aurora is determined by simultaneous observations made at two or more points1 and the same is true of shooting stars and their trails1 which seem to be especially numerous between the levels of sixty and ninety miles4 ,the so-called 8noctilucent clouds10 which shone by reflected sunlight throughout the night for some years after the great eruption of ,krakatoa and were supposed to consist of fine dust from that volcano1 were probably about fifty miles above the earth4 ,from the duration of twilight we infer that above about forty-five miles the air is so tenuous that it cannot reflect sunlight to the earth4 ,clouds furnish information concerning the movements of the air at various levels up to ten miles or more4 ,observations on mountains contribute further to our knowledge of the atmosphere above the ordinary levels of habitation4 ,of all methods of exploring the atmosphere in a vertical direction1 the most fruitful is the use of kites and balloons4 ,in recent years investigations of this character have become so extensive and so highly specialized that they are regarded as forming a separate department of meteorology1 known as ,aerology4 ,it is by virtue of developments in this field that meteorology has become 8a science of three dimensions40 ,formerly meteorologists could do but little more than study the bottom of the weather1 so to speak2 but now they observe it and chart it at all levels4 ,the weather forecaster has daily reports of conditions aloft to aid his predictions both for dwellers on terra firma and for the aeronaut2 while the accumulated data of upper-air observations are throwing new light on many difficult atmospheric problems4 ,scientific balloon ascents are no novelty4 ,some were made in the eighteenth century1 and many famous ones in the nineteenth1 including those of ,biot1 ,gay-,lussac1 ,glaisher1 ,tissandier1 and other daring savants4 ,the 8record0 height for such personal ascents was attained in #aija1 when ,berson and ,sring rose to #ce1djj feet above ,berlin4 ,kites were sent up for meteorological purposes even before ,benjamin ,franklin's immortal experiment in #ageb4 ,modern aerological methods have1 however1 little in common with these pioneer undertakings4 ,existing types of box kites1 pilot balloons1 sounding balloons1 and self-registering meteorological apparatus for upper-air research were developed in the latter part of the nineteenth century1 but their use did not begin to bulk large in meteorology until about the beginning of the present century4 ,the epoch-making event in these undertakings was the discovery of the isothermal layer4 ,it is a matter of common knowledge that the air is found to be colder the higher one ascends in the atmosphere4 ,thus1 even in equatorial regions1 the tops of high mountains are mantled in perpetual snow4 ,the rate of this temperature decrease averages about #a degree ,fahrenheit per #cjj feet4 ,previous to the year #aijb meteorologists supposed that the atmosphere continued to grow steadily colder in an upward direction indefinitely2 but in that year a ,frenchman1 ,m4 ,teisserenc de ,bort1 who had sent aloft hundreds of small unmanned balloons carrying self-recording thermometers1 announced that above a height of about six and one-half miles the temperature ceased to fall4 ,in fact1 he found that at about that level there was often a slight increase of temperature with increasing altitude for a certain distance upward1 and then a nearly uniform temperature as high as the balloons ascended4 ,this announcement was at first received with considerable skepticism1 but very soon similar observations were reported from other parts of the world4 ,a new 8shell0 of the atmosphere had been revealed--which1 as subsequent investigations proved1 differs from the lower air in other respects besides temperature--and it was at first named by its discoverer the isothermal layer4 ,he afterward substituted the name stratosphere1 now generally employed4 ,in distinction from the stratosphere1 the part of the atmosphere lying below it is called the troposphere4 ,the stratosphere has been explored in widely scattered parts of the earth1 and information concerning it is daily accumulating4 ,although it extends over the whole world1 the altitude at which it begins is by no means uniform4 ,the altitude is greater in summer than in winter2 it varies with the barometric pressure at the earth's surface2 and it is decidedly greater over the equator than over the poles4 ,the last fact leads to an interesting paradox4 ,since over the equatorial regions the temperature keeps on falling with ascent to a greater height than in other latitudes1 it is here that the lowest temperatures in the atmosphere are found4 ,a sounding balloon sent up from ,batavia1 ,java1 in ,november1 #aiac1 recorded #aac below zero ,fahr41 the lowest air temperature ever observed4 ,in middle latitudes the temperature of the stratosphere averages something like #fh below zero ,fahr4 ,the temperature of this interesting upper atmosphere varies a good deal1 both vertically and horizontally1 but never shows the steady vertical variation that characterizes the lower air4 ,the stratosphere contains no clouds 7except occasional dust clouds71 and has a circulation quite distinct from that of the troposphere1 the exact nature of which1 however1 has not yet been determined4 ,the sounding balloon1 already mentioned1 is one of the four principal types of aerial vehicle used in the study of the atmosphere1 the others being the pilot balloon1 the captive balloon1 and the kite4 ,the sounding balloon1 or ballon-sonde1 is a small free balloon that carries no human aeronaut1 but instead a set of superhuman meteorological instruments1 which register the temperature1 the barometric pressure1 and sometimes the humidity continuously and automatically through the whole course of their journey4 ,the record is traced on a revolving drum or disk1 usually coated with lampblack4 ,in its commonest form the balloon is made of india-rubber1 and when launched is inflated to less than its full capacity with hydrogen4 ,as it rises to regions of diminished air pressure it gradually expands1 and it finally bursts at an elevation determined approximately in advance4 ,a sort of parachute1 or sometimes an auxiliary balloon1 insures a gentle fall to the ground4 ,attached to the apparatus there is generally a ticket offering the finder a reward for its return1 and giving instructions as to packing and shipping4 ,sooner or later it generally comes back4 ,in fact1 the large percentage of records recovered1 even in sparsely settled countries1 is not the least remarkable feature of this novel method of research4 ,thus1 of seventy-two balloons sent up by a ,franco-,swedish expedition in ,lapland1 forty-one were eventually recovered with their instruments4 ,one of these fell into a lake and was found after three years4 ,no instruments are carried by the pilot balloon1 which merely serves to show1 by its observed drift1 the speed and direction of the air currents at different levels4 ,the pilot balloon is sighted1 while in flight1 through a special form of theodolite1 or1 preferably1 two theodolites some distance apart4 ,several ingenious methods have been devised for computing and plotting its actual course through the air4 ,such balloons1 apart from their use in scientific research1 have become one of the principal adjuncts of aeronautical undertakings all over the world1 and are also used by artillerists to enable them to make proper allowance for the deflective effect of the wind on the flight of projectiles4 ,hundreds of thousands of pilot balloons were sent aloft for military purposes during the world war4 ,meteorological instruments are sent up attached to kites or captive balloons whenever--as in connection with weather forecasting--the observations must be obtained more promptly than would be possible with the aid of sounding balloons1 but such devices can attain only moderate altitudes4 ,kites have been raised to about four and one-half miles above sea level1 as compared with nearly twenty-two miles reached by a sounding balloon and twenty-four miles by a pilot balloon4 ,the average height of sounding-balloon ascents is about ten miles4 ,as already stated1 balloonists have risen to #f4g miles4 ,this is a little higher than the best aeroplane record4 ,the use of the aeroplane for making meteorological observations is still quite limited1 but will inevitably increase4 ,one other device gives promise of yielding valuable aerological information1 on account of its ability to rise to extraordinary altitudes4 ,this is a special form of rocket1 recently invented by ,prof4 ,r4 ,h4 ,goddard1 which is propelled by several successive discharges of an explosive in the course of its upward flight1 and with which the inventor thinks it will be possible to explore the whole vertical extent of the atmosphere4 ,meteorological apparatus for use with the ,goddard rocket has been planned by ,mr4 ,s4 ,p4 ,fergusson of the ,weather ,bureau4 ,the atmosphere presses down upon the earth with a weight that1 at sea level1 amounts to about #ad4g pounds to the square inch1 on an average4 ,this pressure is1 at any point1 exerted equally in all directions2 it acts1 for example1 on the whole surface of the human body1 and this means that a man of average size lives under a burden of some seventeen tons of air4 ,he is not incommoded because the pressure from without is balanced by that of the air that permeates his body4 ,the pressure of the atmosphere decreases upward at nearly the same rate as its density4 ,thus on mountains and plateaus it is considerably less than in lowlands4 ,at no place is the pressure invariable1 nor is there a constant relation between pressure and altitude1 but1 knowing approximately the average atmospheric pressure over the earth's surface1 and knowing also the area of the latter1 we can compute in round numbers the total weight of the atmosphere--about #e1jjj1jjj1jjj1jjj1jjj tons4 ,this is about #a_/a1bjj1jjj of the entire weight of the earth4 ,,chapter ,,ii ,,the ,,resources ,,of ,,the ,,atmosphere ,in the economic stress of our times much is heard about 8natural resources40 ,this phrase suggests to most people's minds the store of minerals1 fuels1 and oil locked up in the ground2 the waters available for drinking1 washing1 irrigation1 power production1 and navigation2 the forests and other natural growths of useful vegetation2 and the soil in which we raise our crops4 ,a moment's reflection1 however1 will show that this is a one-sided enumeration4 ,the resources of the atmosphere are as essential to humanity as those of the land and the waters1 if not more so4 ,the coal that is dug out of the earth consists mainly of carbon1 which1 in bygone ages1 was extracted by plants from the air4 ,moreover1 it would be of no use to us if we did not have the oxygen of the air in which to burn it4 ,neither could we smelt metallic ores without oxygen4 ,all our forests and all our crops draw far more of their solid substance from the air than from the soil4 ,fuel and water are valuable sources of power1 but so is the moving air that drives sailing ships and windmills1 and the atmospheric pressure that helps to operate suction pumps4 ,it is the moisture of the air that feeds our streams and1 directly or indirectly1 waters all plants that grow upon the land4 ,lastly1 it is the atmospheric oxygen that we breathe that keeps us from very speedily becoming incapable of using any of the other resources of ,nature4 ,air and water together contain1 in their oxygen1 nitrogen1 hydrogen1 and carbon1 all the major constituents of our foods in unlimited abundance4 ,it is tantalizing to think of the slow and roundabout way in which these things are wrought into edible shape--and the prices we have to pay for them4 ,no less tantalizing1 when coal is scarce and costly1 is the thought that every vagrant breeze is laden with the carbon dioxide from which the chemistry of living plants so readily extracts the chief element of fuels4 ,the total carbon dioxide of the atmosphere amounts to something like #b1bjj1jjj1jjj1jjj tons1 equivalent to #fjj1jjj1jjj1jjj tons of carbon4 ,we have spoken of the utility of the air as a source of power4 ,it is1 perhaps1 even more useful as providing an easy means of storing and transmitting power4 ,the engineer stores up energy in a mass of air by compressing it4 ,when the air subsequently expands it gives up its energy1 and1 in so doing1 may be made to perform a variety of useful tasks4 ,by a somewhat analogous process energy is applied to creating a vacuum1 in order that the ordinary pressure of the atmosphere may be made available for doing a particular piece of work4 ,the suction pump1 the siphon1 and the vacuum cleaner furnish examples of this process2 and so do such familiar operations as sucking beverages through a straw and filling a medicine dropper4 ,from crude types of bellows1 with which1 from remote antiquity1 air was compressed for the purpose of blowing fires1 have been developed a host of wonder-working appliances of the present day1 such as the air brake1 the pneumatic tube1 the compressed-air locomotive1 diving apparatus1 the caisson1 certain kinds of refrigerating machinery1 and a long list of pneumatic tools4 ,to cap the climax of ingenuity in this field1 methods involving both the compression and the expansion of air have been discovered whereby this invisible1 elusive substance may be changed to a visible liquid and a visible solid2 a process having extremely valuable applications1 as we shall presently see4 ,compressed air1 as a means of transmitting power1 rivals such mechanical devices as gearing1 belting1 and rope drives1 when it is applied near the compressor2 or it may be conducted for many miles in pipes1 thus competing with the electric current2 or1 finally1 it may be transported in tanks to the place where it is to be used1 a process analogous to the use of the electric storage battery4 ,compressed air has1 moreover1 certain advantages over other methods of transmitting power for a number of special purposes4 ,thus for use in coal mines it is safer than electricity because it is free from the danger of sparks4 ,there are a great many cases in which the air itself is used in the process to which the power is applied1 as in different kinds of air blast1 from the simple bellows to the blowers of blast furnaces2 also in aerating apparatus1 oil and fuel burners1 spraying1 cleansing1 etc4 ,a familiar form of air compressor is the hand pump used for inflating bicycle tires4 ,this simple device illustrates two important facts2 first1 that a considerable amount of energy must be used to overcome the expansive force of the air1 and1 second1 that part of the energy applied to the pump produces heat4 ,that the heat thus produced and dissipated in the surrounding air represents a loss of energy is apparent2 but energy is wasted in another way that is1 perhaps1 not so evident4 ,when a gas is heated its expansive force is increased4 ,hence1 on account of the heating of the air in the tire1 the pump has to do more work to accomplish a given amount of compression than it would need to do if the air remained cool4 ,in order to avoid this loss1 the air compressors used for industrial purposes are provided with some sort of device for keeping the air cool during compression4 ,this is accomplished by a spray of water inside the compressor cylinder1 or1 more commonly1 by inclosing the cylinder in a water jacket4 ,in producing high pressures1 the air is compressed by degrees in two or more cylinders1 and cooled between the successive stages4 ,lastly1 before compressed air is applied to driving tools or machinery1 it is often reheated to increase its pressure4 ,for most industrial purposes the pressure of compressed air does not exceed #ge pounds to the square inch 7#e 8atmospheres074 ,for charging the tanks of compressed-air locomotives1 for liquefying gases1 and a few other purposes1 much higher pressures are used4 ,in laboratory experiments air has been compressed to the enormous pressure of #fj1jjj pounds to the square inch1 or #d1jjj atmospheres4 ,at a pressure of #ad1jjj pounds to the square inch compressed air has been successfully used for blasting in mines in place of ordinary explosives4 ,the use of pneumatic tools began in the sixties of the last century1 when pneumatic drills were employed with conspicuous success in the construction of the ,mont ,cenis and ,hoosac tunnels4 ,such tools are now indispensable adjuncts not only of tunneling and mining1 but also of nearly every department of metal-working and wood-working1 and have contributed incalculably to the welfare of mankind4 ,imagine a workman with an ordinary hammer driving such a tool as a chisel1 punch1 or calking iron1 and estimate the amount of work accomplished in the course of a day spent in this wearisome labor4 ,then consider how such operations are performed with the help of that versatile substance1 air4 ,the pneumatic hammer consists of a piston working in a cylinder1 to which compressed air is conveyed from a compressor by means of a flexible hose4 ,the hammer is so designed that the air causes the piston to work back and forth with great rapidity4 ,a chisel1 rammer1 or other percussion tool is loosely fitted in the nose of the hammer1 so that the piston will strike it a blow at each forward motion4 ,the workman has nothing to do but hold the tools in place4 ,with a common hammer or mallet a workman will strike from twenty to a hundred blows a minute1 according to the nature of the work4 ,the speed of the pneumatic hammer ranges from #a1jjj to #bj1jjj blows per minute1 so that its sound is a continuous buzz4 ,such hammers are used for calking1 chipping1 riveting1 and a great number of other purposes4 ,in another large class of pneumatic tools work is done by rotation instead of percussion4 ,the piston is replaced by a motor1 which turns an auger1 drill1 or other tool for such operations as boring1 screwing1 reaming1 etc4 ,the use of pneumatic tubes for transporting letters1 parcels1 and the like1 although suggested as early as #affg1 has been in practical operation only since #ahed1 when a tube #bbj yards long was built in ,london to convey telegraphic dispatches4 ,the articles to be transported are placed in a carrier fitting closely inside the tube and propelled either by introducing air under pressure behind it or by exhausting the air in front of it4 ,scores of miles of such tubes laid underground are now in operation in ,london1 ,paris1 ,berlin1 ,new ,york1 and other large cities for carrying mail matter4 ,in the ,united ,states the pneumatic cash carrier1 used in stores1 is the commonest application of 8pneumatic dispatch10 as this system of transportation is called4 ,the use of compressed air instead of a brush for applying paint1 varnish1 and whitewash is a further illustration of the versatile possibilities of air as a means of transmitting power4 ,when an inclosed body of air or other gas is subjected to pressure1 its volume is diminished and its density is increased4 ,it is natural to inquire what will happen if the external pressure be increased indefinitely4 ,will the inclosed substance eventually cease to be gaseous and become a solid or a liquid8 ,the answer to this question1 furnished about half a century ago through the researches of ,thomas ,andrews1 is that no amount of pressure will liquefy a gas unless its temperature is below a certain point4 ,this point1 known as the critical temperature1 is widely different for different substances4 ,for most of the atmospheric gases it is exceedingly low4 ,thus oxygen must be cooled to #aah below zero ,centigrade 7#ahj below zero ,fahrenheit7 before it will liquefy under any pressure1 and the critical temperature of nitrogen is still lower4 ,efforts to liquefy the gases of the atmosphere were unsuccessful for a long time on account of the difficulty of attaining such low temperatures4 ,nowadays the problem is so completely solved that the manufacture of liquid air is a commonplace commercial enterprise1 and millions of gallons are produced every year4 ,liquid air is the principal commercial source of pure oxygen1 nitrogen1 and other gases found in the atmosphere4 ,it is also used as a refrigerating substance in various industrial and scientific processes1 and new uses are being found for it from year to year4 ,like many other latter-day miracles1 compared with which the alleged feats of necromancy seem tame and puerile1 the liquefaction of air is founded on quite simple principles4 ,the earliest commercial process was invented1 in its main features1 by ,linde in #ahie1 and the newer processes are merely modifications of this one4 ,experiments of the ,english physicists ,joule and ,thomson showed that when a gas under pressure is forced through a small orifice1 beyond which it expands1 it undergoes a certain amount of cooling4 ,this fall in temperature1 known as the 8,joule-,thomson effect10 is generally quite small1 but ,linde devised a means of multiplying it in his 8regenerative cooling process40 ,the air to be liquefied is first compressed to1 say1 #ajj atmospheres1 cooled as much as possible by water1 and passed through a long spiral tube4 ,at the end of the spiral it escapes through a small nozzle1 and is thus somewhat further cooled by the effect above mentioned4 ,this cooled air then passes back around the spiral tube1 and causes still more cooling of the air in the latter4 ,the escaping air is again compressed and goes through the same process as before4 ,thus its temperature grows constantly lower1 until finally the stream issuing from the nozzle is a liquid instead of a gas4 ,the liquid collects in a reservoir1 from which it can be drawn off when desired4 ,the liquid air thus obtained has a temperature of about #cae below zero ,fahrenheit4 ,it is generally drawn into a vessel called1 from the name of the inventor1 the ,dewar flask1 which is open at the top1 but otherwise insulated from the temperature of the surrounding air by having a double wall1 with a vacuum between the walls4 ,the familiar thermos bottle is constructed on the same principle4 ,in such a vessel liquid air can be kept for hours and even days1 and it is thus available for use in many interesting laboratory experiments4 ,liquid air looks much like water1 except for its slight bluish color4 ,it boils--i4 e41 changes back to ordinary air--at a temperature only slightly above that at which it is produced1 and this boiling1 of course1 goes on rapidly at the surface of the liquid1 owing to absorption of heat from the air above4 ,liquid air is lighter than water1 upon which it consequently will float4 ,a cubic foot of liquid air is the equivalent of about #hjj cubic feet of ordinary air at #fj ,fahrenheit and atmospheric pressure4 ,the curious effects of liquid air1 only a few of which can be mentioned here1 are not irrelevant to the subject of atmospheric resources1 since they aid in various ways in carrying out important scientific researches4 ,almost all liquids are solidified and almost all solids are hardened and stiffened by immersion in liquid air4 ,alcohol is promptly frozen in it1 and at the same time gives out so much heat that the liquid air boils violently and the congealing alcohol overflows the vessel in a little avalanche of snow4 ,india rubber becomes as brittle as glass4 ,meats become so hard that when struck by a hammer they ring like steel4 ,chemical action is enormously reduced by exposure to the low temperature of liquid air1 and so is the electric resistance of metals4 ,one might suppose that such a temperature would be fatal to all forms of life1 but this is not the case4 ,a goldfish1 frozen solid in liquid air1 revives and swims vigorously a few seconds after being replaced in water4 ,bacteria survive hours of exposure to the temperature of liquid air1 while the seeds of higher plants1 even after several days of similar treatment1 sprout the same as other seeds4 ,most of the atmospheric gases have not only been liquefied1 but also frozen solid4 ,an important exception is helium1 which has been liquefied only at a temperature of #deb below zero ,fahrenheit4 ,the remarkable feat of liquefying helium was accomplished in #aijh by the ,dutch physicist ,kamerlingh ,onnes1 who subsequently1 in his attempts to solidify this substance1 attained the unprecedented temperature of less than #b 7,centigrade7 degrees above 8absolute zero10 or #def below zero ,fahrenheit1 by the rapid evaporation of the liquid under greatly reduced pressure4 ,illustration ,illustration3 ,,exploring ,,the ,,upper ,,air4 ,left3 ,beginning of a pilot-balloon flight4 ,right3 ,sending up a sounding-balloon4 ,note the parachute1 which wafts the basket of instruments gently to the ground after the balloon bursts4 7,photographs from ,u4 ,s4 ,weather ,bureau47 ,although1 when air is liquefied1 the oxygen and nitrogen are condensed simultaneously1 the latter has a lower boiling point than the former and therefore passes off more rapidly when the liquid is allowed to evaporate4 ,this fact makes it possible to separate the two substances1 by the process known as 8fractional distillation10 and hence liquid air plants have been established for the special purpose of manufacturing oxygen and nitrogen1 for both of which there is a large and growing commercial demand4 ,scores of millions of cubic feet of oxygen are used every year in the wonderfully efficient process of welding metals with the oxyacetylene blowpipe1 the flame of which has a temperature of about #f1jjj ,fahrenheit4 ,most of the supply now comes from liquid air4 ,an equally large amount is used in a recently introduced method of cutting metal4 ,the object to be cut is first heated to incandescence1 after which a jet of oxygen is played upon it4 ,the metal actually burns away in the stream1 and a clean cut is made like that of a saw4 ,it is interesting to reflect1 when we fill our lungs with oxygen in order to keep our bodily machinery in operation1 that the same atmospheric gas is applied to the building of motor cars1 bicycles1 safes1 boilers1 and battleships4 ,cartridges made of lampblack1 dipped for a few moments in liquid oxygen and then primed with a fulminate cap1 constitute an explosive as powerful as dynamite and much cheaper to produce4 ,a small percentage of oxygen added to the air supplied to blast furnaces has been found to effect a great saving of fuel used in the furnace4 ,illustration3 ,,meteorograph ,,for ,,use ,,with ,,sounding ,,balloon4 7,fergusson pattern4 ,u4 ,s4 ,weather ,bureau1 #aiai47 ,the aluminum case1 surrounded by hoops of rattan to protect the apparatus when it falls to the ground at the end of the flight1 contains a set of very light self-registering meteorological instruments4 7,photograph from ,u4 ,s4 ,weather ,bureau47 ,illustration3 ,,kite ,,meteorograph4 7,u4 ,s4 ,weather ,bureau ,pattern47 ,the four pens record the barometric pressure1 temperature1 humidity1 and wind-force on a sheet of paper wound around the large cylinder1 which is turned by clockwork4 ,note the fan wheel inside the tube1 for measuring the force of the wind4 ,the apparatus is made chiefly of aluminum and is inclosed in an outer case of aluminum when sent aloft attached to the kite4 7,photograph from ,u4 ,s4 ,weather ,bureau47 ,the most important industrial demand for nitrogen is for use in 8fixation0 processes--i4 e41 for making nitrogen compounds to be used as fertilizers1 explosives1 etc4 ,before describing these processes1 it may be of interest to mention that some of the 8rare0 gases of the atmosphere are now obtained on a commercial scale as by-products of the manufacture of oxygen and nitrogen from liquid air4 ,thus neon1 on account of its exceedingly small resistance to the passage of electric discharges1 is a promising substance for filling glow lamps2 especially as means have been found of correcting the glaring red color of the light which characterized the original neon lamps4 ,argon is likewise used for filling electric lamps4 ,the idea of using the unlimited store of atmospheric nitrogen for the benefit of agriculture and the manufacturing industries has been very prominently before the public in recent years1 and gained special notoriety during the late war1 when great efforts were being made to increase the supply of nitrogenous materials suitable for use in explosives4 ,nitrogenous matters in the soil are indispensable to the growth of plants1 and as long ago as #ahih ,sir ,william ,crookes1 in an address before the ,british ,association for the ,advancement of ,science1 alarmed the world by pointing out the possibility of a general famine owing to the prospective exhaustion of ,chilean nitrates and other sources of nitrogenous fertilizers4 ,nitrogen also enters on an immense scale into the composition of many industrial products besides explosives4 ,no wonder popular writers have dwelt upon the fact that the atmosphere contains far more nitrogen than mankind needs for every possible purpose--actually something like #bj1jjj1jjj tons over every square mile of the earth's surface4 ,a widespread misunderstanding1 however1 prevails as to the problem involved in utilizing this supply of nitrogen4 ,free 7i4 e41 uncombined7 nitrogen is of no use as a fertilizer1 and it cannot be readily used in the arts4 ,the process of extracting it from the atmosphere is an easy one1 thanks to the liquid air industry4 ,the real difficulty is to make this inert gas enter into chemical combination with other substances1 forming useful compounds such as ammonia and nitrates2 in other words1 to 8fix0 it4 ,as we have stated on another page1 lightning discharges cause nitrogen and oxygen to combine in the atmosphere1 and perhaps also combine nitrogen and hydrogen to form ammonia4 ,there is one other natural process by which atmospheric nitrogen is fixed4 ,certain species of bacteria are able to extract this gas from the atmosphere and combine it with other materials4 ,some of these bacteria are independent organisms1 while others form colonies of parasites growing on the roots of higher plants1 chiefly members of the pea family4 ,in the latter case the bacteria use the nitrogen of the air and carbohydrates drawn from the roots on which they grow to form nitrogenous compounds1 which are1 in part1 transmitted to the host plant4 ,unfortunately these natural processes do not suffice to maintain agricultural soils in a high state of fertility4 ,mineral deposits of combined nitrogen are practically limited to the nitrate fields of ,chile1 from which more than two million tons of nitrate of soda are exported annually2 but this supply cannot last more than a few decades4 ,combined nitrogen in the form of ammonia is supplied on a large and rapidly growing scale from by-product coke ovens1 and another perennial source of nitrogenous matter is found in animal and vegetable refuse of all kinds1 including fish scrap and slaughter-house refuse1 garbage1 sewage1 manure1 etc4 ,since1 however1 the demands of agriculture and the manufacturing industries greatly exceed the total amount of combined nitrogen obtainable from all these sources1 the ingenuity of inventors has been spurred to the task of fixing atmospheric nitrogen by artificial methods1 and several such methods have now been put in operation commercially4 ,their combined product at present constitutes nearly one-third of the total nitrogen supply of the world4 ,it is not proposed here to describe these methods in detail1 but it may be mentioned that one of them1 known as the 8arc process10 imitates the action of lightning in combining the nitrogen and oxygen that occur naturally in the air1 while the others utilize nitrogen that has been previously separated from the air by the liquid air process4 ,the arc process requires1 for commercial success1 a large supply of cheap electrical power1 and it is at present almost confined to ,norway and ,sweden1 where electricity is obtained from waterfalls4 ,in this process air is blown through a huge electric flame1 spread out by a powerful electromagnet4 ,the air yields nitric oxide1 which is combined with water to form nitric and nitrous acids1 and these substances are combined with others to form marketable products4 ,the most widely used fixation process1 and the one which the ,united ,states ,government proposed to employ in the large plants that were in course of construction in this country at the close of the war1 is known as the 8cyanamide process40 ,this process requires1 as a part of its raw materials1 large supplies of limestone and coke1 from which calcium carbide is made in an electrical furnace4 ,the calcium carbide1 at red heat1 absorbs nitrogen1 forming an intermediate product from which1 by further processes1 are made ammonia and nitric acid4 ,a third method of fixing atmospheric nitrogen1 which has been applied on a vast scale in ,germany and is now coming into use in other countries1 is commonly called the 8,haber process40 ,in this process nitrogen is combined with hydrogen1 obtained from water1 to form ammonia1 the combination being facilitated by the presence of what chemists call a 8catalyzer10 i4 e41 a substance that enables other substances to combine without itself undergoing any change4 ,several different catalyzers have been used in the ,haber process4 ,two or three other methods of nitrogen fixation are beginning to assume commercial importance4 ,while the power of the wind holds an important place among the resources of the atmosphere1 it cannot be said that the utilization of this resource has undergone developments in modern times at all comparable with the striking inventions and discoveries we have just been recording1 if we except the use of the wind in aeronautics4 ,atmospheric resources used by aeronauts will be discussed in subsequent chapters4 ,the chief use made of the wind to-day1 as in ages past1 is to propel sailing ships1 and its use for this purpose is1 of course1 of less importance1 in a relative sense1 than it was before the introduction of steam4 ,the importance of windmills has also greatly declined4 ,this fact was strikingly brought out some years ago when the ,united ,states ,bureau of ,statistics collected1 through ,american consuls abroad1 detailed information concerning the use of the windmills in foreign countries4 ,in most parts of ,europe windmills are rapidly disappearing4 ,in ,holland1 for example1 the traditional home of the windmill1 the perpetual task of draining the polders is now performed by steam pumps1 and the total number of windmills is estimated to be only about one-tenth what it was centuries ago4 ,our own country is probably the only one in which the use of windmills is increasing4 ,the modern ,american windmill1 with its disklike assemblage of numerous light sails1 and ingenious contrivances for veering1 reefing1 etc41 is a much more efficient contrivance than the old-fashioned windmill2 but its utility1 like that of other windmills1 is limited by the irregular force of the winds4 ,for years the hope has been entertained that the windmill would eventually become a common means of generating electricity1 but this hope has not yet been realized1 though isolated installations of this character are in successful use4 ,,chapter ,,iii ,,the ,,atmosphere ,,as ,a ,,highway ,within the last few years the atmosphere has assumed a new and tremendous importance in human affairs as a medium that affords facilities for travel and transportation far superior1 in many respects1 to those offered by the land or the water4 ,the aerial highways are now open for business and pleasure4 ,this is a fact that the majority of people find it difficult to realize4 ,the navigation of the air on a general scale has so long been looked upon as a dream of the future that we cannot readily adjust our minds to the reality4 ,the story of the slow steps by which this momentous fact has been brought to pass is far too long to be told here4 ,what we purpose to do in the present chapter is to sketch the multifarious uses to which man is now applying the aeronautical knowledge and skill that he has acquired4 ,at the same time we shall anticipate1 to some extent1 the developments of the near future2 for the lines of progress are so clearly marked out that it is possible to do this without giving too much rein to the imagination4 ,in a subsequent chapter1 dealing with ,aeronautical ,meteorology1 we shall touch briefly upon the mechanical principles that underlie aerial navigation1 by way of preface to a more detailed description of the conditions of wind and weather encountered by aircraft1 and of the services that the meteorologist is rendering to the aeronaut4 ,the history of aeronautics may be divided into two periods1 with the year #aiad as the dividing line between them4 ,before the great war the many brilliant minds that were trying to solve the problems of aerial navigation received comparatively little help or encouragement from humanity at large4 ,the airship and the aeroplane were both accomplished facts1 but most people looked upon them as ticklish contrivances of very little practical value4 ,from the year #aiji onward aviation occupied an immense share of public attention2 liberal prizes for aerial feats were offered2 new records for speed1 altitude1 and endurance were made from day to day2 but to the public1 and perhaps to most of the aviators themselves1 all this meant merely that a new and thrilling sport had been created1 rather than a new art of boundless utility4 ,very few business men felt inclined to invest money in the development of aircraft1 and the governments of the leading nations1 with a single exception1 were incredibly blind to the importance of building air fleets for use in war4 ,the exception was ,germany1 which not only gave strong support to ,count ,zeppelin in the building of his dirigibles1 but developed military aviation to such an extent that she entered the war with about #hjj aeroplanes and a thousand trained pilots4 ,with the outbreak of the war the budding art burst into vigorous bloom4 ,unlimited funds were now available for experimenting and building4 ,thousands of flyers invaded the air1 and the battle zone was a testing ground on a vast scale1 where one improvement was hardly introduced before it was replaced by another4 ,some of the best engineering talent of the world was diverted from many and various fields to the one task of supplying the demands of the military aeronauts for more speed1 more power1 more reliable motors1 better materials and appliances4 ,thus the war not only perfected aeronautics--especially aviation--as an art1 but practically created it as an industry4 ,at the close of hostilities the world found itself in possession of a vast fleet of aircraft1 a multitude of aircraft factories1 and a great army of trained aeronauts4 ,for a time people asked--and perhaps some still ask--8,what shall we do with them80 ,there are many answers to this question1 and new ones are coming to light every day4 ,in the aggregate they mean that a new era has dawned in human affairs--the era in which the sky has been annexed to the world in which man lives4 ,henceforth we shall have more elbow room4 ,we shall no longer be imprisoned in ,flatland1 but set free in ,spaceland4 ,it is impossible to foresee all the implications of this fact1 but those that are already apparent suffice to fill us with enthusiasm4 ,some of the most vexed problems of the present day will soon be solved by aerial navigation4 ,take that of our overcrowded cities4 ,everybody knows how first the trolley car and then the automobile helped to relieve the congestion of towns by making it feasible for people to live many miles from the scenes of their daily work1 but at the same time seriously swelled the traffic of the streets in business quarters4 ,aircraft will bring far greater improvements in this respect1 without corresponding disadvantages4 ,in a few years it will probably be no inconvenience to live fifty or a hundred miles from one's place of business4 ,aeroplanes1 built for carrying several passengers in perfect comfort1 already fly at speeds of from #abj to #aej miles an hour1 and are almost independent of weather4 ,much greater speeds will doubtless be common in the future4 ,automobiles1 all running on the same level1 have almost reached the limit of space available in our busiest streets1 and1 under such conditions1 they have nearly lost the advantage of speed they once possessed over the obsolete horse-drawn vehicle4 ,there can never be such crowding in the air4 ,when a great volume of aerial traffic is concentrated toward the centers of towns1 people will fly their vehicles at various prescribed levels1 and probably 8park0 them on many-storied landing stages4 ,new methods of landing will undoubtedly be invented4 ,the device known as the 8helicopter10 which has made progress toward the practical stage during the past year1 points out the possibilities in this direction4 ,in the helicopter the propeller blades revolve around a vertical shaft1 thus permitting the vehicle to rise or descend vertically4 ,a prize of #ajj1jjj has recently been offered by ,m4 ,michelin1 the well-known ,french patron of aviation1 for the perfection of this device1 which may soon revolutionize the design of flying machines4 ,mr4 ,holt ,thomas1 the ,englishman whose foresight and enthusiasm have done so much to hasten the arrival of practical commercial aeronautics1 believes that in the near future the main airways of the world will be served by airships rather than by aeroplanes4 ,for long journeys the airship has the advantage that it can carry an ample supply of fuel without encroaching too much upon the space available for passengers and cargo4 ,it is1 therefore1 especially suitable for transoceanic journeys4 ,hitherto airships1 when not in flight1 have been housed in enormous hangars1 involving heavy cost of installation and their landing has required the services of hundreds of men--an operation that will probably seem laughable in its crudity to the next generation4 ,the airship of the future will probably never go into a hangar at all except for occasional overhauling1 as an ordinary ship goes into drydock4 ,hence only a few of these costly structures will be needed4 ,while in service the airship will1 on reaching an air port1 moor herself at the bow to a great steel tower1 and swing with the wind as a marine vessel swings at her anchor4 ,at the top of the tower there will be a landing stage for passengers and freight1 connected by lifts with the ground below4 ,from the main air ports1 thus equipped1 will radiate minor air routes1 served by aeroplanes1 and1 in some cases1 by flying boats4 ,such landing places for airships were predicted by ,kipling in his 8,with the ,night ,mail0--but the author's vista was of the year #bjjj6 ,we are not traveling so slowly as that4 ,consider what it means that the world heard with bated breath of ,blriot's flight over the ,english ,channel in #aiji2 and just ten years later men had flown over the ,atlantic ,ocean4 ,we have been writing of the future2 but we need not look ahead for illustrations of the practical value of aerial navigation4 ,useful feats already accomplished are so astonishing in their variety that they make one cautious about assigning a limit to the possible applications of the new art4 ,it has happened1 for example1 that a man who had booked passage on a trans-,pacific steamer missed his boat at ,seattle2 whereupon he hired an aeroplane1 at a cost of #ge1 and overtook the steamer on her way down ,puget ,sound1 thus saving some weeks of delay in waiting for the next one4 ,another man1 who produces honey on a large scale1 found that spray-poisoned orchards were playing havoc with his bees4 ,he traveled in an aeroplane over the surrounding country1 selecting stands for his hives at safe distances from such orchards1 and he estimates that this precaution saved him #aj1jjj in a single year4 ,in ,august1 #aiai1 a flying boat deposited a bag of mail on the ,white ,star liner ,adriatic two hours after the ship had left ,new ,york4 ,several aerial mail routes are now in operation on both sides of the ,atlantic4 ,the first regular service of this character in ,america was begun ,may #ae1 #aiah1 between ,new ,york and ,washington1 and during the first year carried #g1gbj1hdj letters1 with few accidents and no fatalities4 ,the first year of service cost the ,government #acg1ijj1 and the sale of aeroplane mail stamps during the same period yielded a revenue of #aei1gjj4 ,out of #a1bfa possible trips on this route1 #a1bjf were undertaken1 and only fifty-five were abandoned on account of unfavorable weather4 ,during #aiai the ,post ,office ,department not only established other aerial routes1 but relegated the aerial mail service to the ranks of the commonplace by reducing the postage on letters carried by aeroplane to the ordinary first-class rate of two cents an ounce4 ,in ,europe lines of fast aeroplanes carrying mails1 passengers1 and freight daily over regular routes are becoming part of the established order of things4 ,the operators of a line between ,london and ,paris1 which was inaugurated in ,november1 #aiai1 are now planning to establish an hourly service4 ,some of these lines have been equipped with wireless telephony1 so that the pilots can keep in constant communication with numerous stations of the company along the route1 and also with one another4 ,they are thus able to obtain1 among other things1 current information about the prevalence of fog or other atmospheric conditions at points ahead of them4 ,presumably the passengers who patronize the aeroplane express will also1 eventually1 enjoy the use of the wireless telephone en route4 ,in connection with the new air routes suitable landing grounds1 for regular or emergency use1 are being laid out at short intervals2 the ideal aimed at1 for the present1 being the so-called 8ten-mile chain02 i4 e41 a series of emergency landing grounds about ten miles apart4 ,from ordinary flying levels a pilot on such a route can always glide to one of these grounds in case his motor fails4 ,the landing grounds will be utilized1 under certain restrictions1 for grazing cattle and for agricultural purposes1 to help cover the cost of rental and maintenance4 ,during #aiai the ,british ,government established a chain of landing grounds in ,africa1 all the way from ,cairo to the ,cape4 ,one of the developments of the war was the use of aeroplanes for photographic mapping4 ,the aeroplane flies over a long tract of ground1 and the camera1 exposed vertically1 takes pictures automatically at fixed intervals4 ,the pictures thus taken are carefully joined together in a single strip4 ,a second tract1 parallel with the first1 is photographed in the same manner1 and so on1 until the whole area has been covered4 ,eventually all the pictures are assembled to form a so-called 8mosaic40 ,this process is highly successful for mapping a flat country1 but presents difficulties when there are hills and mountains4 ,some sort of stereoscopic process will probably be perfected for depicting accurately differences in level and producing a 8contoured0 map4 ,although aeronautical mapping does not yet replace old-fashioned methods1 it already has several obvious uses4 ,it is especially suitable for the revision of existing maps4 ,thus the plan of a city can be quickly brought up to date by this process4 ,in the ,united ,states the ,geological ,survey has been engaged for many years in producing large-scale topographic maps of all parts of the country4 ,this work proceeds slowly1 and some of the maps are ten or fifteen years old4 ,the contours and other natural features on such a map are still correct1 but changes in the region due to the work of man are often extensive4 ,revision of these features can easily be made by the method above described4 ,for the preliminary mapping of a new country1 by photography or by hand1 the aeroplane offers the means of saving an immense amount of time and effort4 ,the surveyor no longer needs to cut tracks through the jungle or scale mountains4 ,no region is very difficult of access to the aviator4 ,the summit of ,mount ,everest1 the highest mountain in the world1 is actually a mile lower than the greatest altitude attained by an aeroplane4 ,aviation has become an important feature of exploring expeditions4 ,captain ,amundsen1 the polar explorer1 qualified as an air pilot before he embarked on his drift across the ,north ,polar basin1 and took aeroplanes with him on that journey4 ,in ,india the ,survey ,department has organized a regular aerial photographic and reconnoissance service1 and has lately photographed the high waters of the ,river ,sutlej in order to obtain data for a big electrification project4 ,photographs of the ,nile country have also been made for hydrological purposes4 ,british aviators in ,mesopotamia have mapped the flood boundaries of the ,tigris and provided data for estimating crop areas4 ,in the ,philippines an engineer recently made a long aeroplane flight to determine which of three general routes was most suitable for a new railway4 ,many months of time and thousands of dollars were thus saved1 as it was only necessary to send out one party of locating engineers instead of three after the selection had been made4 ,recently the aerial surveyor has become the rival of the hydrographer in mapping shoals1 channels1 submerged rocks1 and other features beneath the water4 ,if the water is clear and suitable atmospheric conditions prevail1 objects submerged to a considerable depth may be distinctly seen from an aeroplane flying far above the surface4 ,it was on account of this fact that ,allied aviators were able to spot submerged ,german submarines during the ,world ,war4 ,the camera1 equipped with proper plates and ray filters1 can pierce the water even better than the eye4 ,thus objects have been photographed at a depth of more than #ej feet4 ,british aviators charted the harbor of ,rahbeg1 on the coast of ,arabia1 by the process in #aiag4 ,in this country the leading exponent of underwater photography is ,dr4 ,willis ,t4 ,lee1 of the ,united ,states ,geological ,survey1 who has taken scores of photographs showing submerged features of the waters adjacent to ,chesapeake ,bay4 ,it is likely that rivers like the ,mississippi1 with ever shifting sand bars1 will soon be made safe by monthly or weekly mapping from the air4 ,in earthquake regions1 such as southern ,italy and ,japan1 the changing coast lines1 shallows and harbors can easily be photographed after each new quake1 thus keeping navigation open and protecting the lives of mariners4 ,another application of this process of sighting submerged objects from the air is the aerial fish patrol4 ,the plan of using aircraft to locate schools of fish appears to have been first suggested by ,professor ,joubin1 of the ,oceanographic ,institute of ,monaco1 and it has been carried out with much success in both ,europe and ,america4 ,its promoters hope that it will eventually revolutionize the fishing industry and add greatly to the world's food supply4 ,in the year #aiai seaplanes from the ,north ,island ,air ,station at ,san ,diego1 ,california1 made regular flights at an altitude of about #ejj feet over the adjacent waters as an adjunct to the important fisheries in that vicinity4 ,when a school of fish was detected1 the aviator dropped low enough to ascertain the species1 and if it proved to be of a commercial kind1 such as the sardine1 the news was flashed by wireless to the fishing fleet4 ,the ocean in the neighborhood of ,san ,diego was divided into numbered squares1 shown on charts1 and locations were reported by number4 ,in #aibj a daily patrol was maintained by ,navy seaplanes over the waters of ,chesapeake ,bay in behalf of the menhaden fishery4 ,according to an official report1 8the experiments fully demonstrated the commercial value of planes in this fishery40 ,it is believed that aircraft might be used with equal success in connection with the whaling industry4 ,the ,united ,states ,forest ,service has made considerable use of ,army aeroplanes and aviators in patrolling the great forests of the ,west1 where a constant lookout for fires must be kept throughout the summer4 ,there are about #bh1jjj forest fires in this country every year1 and the average area burned over amounts to more than #h1jjj1jjj acres1 entailing an average annual loss of #aj1jjj1jjj worth of timber4 ,observations are maintained on mountain peaks and towers1 but the aerial watchman commands a much greater range of vision and can readily detect fires in places such as deep canyons where they are1 in many cases1 hidden from the existing lookout points4 ,when a big fire is in progress1 the aviator can quickly ascertain its extent and report the information by wireless to the fire-fighting forces4 ,in case the fire is difficult of access on account of the absence of roads1 the fire fighters can be transported to the spot in aeroplanes4 ,it has even been proposed to fight forest fires by dropping bombs filled with fire-extinguishing chemicals4 ,at one time it was thought that aeroplanes might largely replace fixed lookout stations1 but experience shows that both systems of observation are desirable4 ,many foresters favor the use of small dirigible airships in place of aeroplanes1 owing to their ability to fly very low1 when desired1 land in any small clearing1 discharge passengers by rope-ladder while hovering over a selected spot1 and transport relatively large loads of men and supplies4 ,such are a few of the valuable peace-time uses that have already been found for the aerial vehicles that owed their production chiefly to the late war and for the host of pilots trained during the same conflict4 ,undoubtedly the immediate future holds far more interesting developments in store4 ,one important practical aspect of aeronautics remains to be mentioned1 and that is the question of safety4 ,in their early days the steamboat and the steam railway were both risky contrivances4 ,it is recorded that at one time steamboats were barred from the ,thames on account of their dangers4 ,undoubtedly the tradition of frequent boiler explosions lingered in people's minds long after it had ceased to be a substantial fact4 ,aerial navigation--and particularly aviation--has now passed beyond the pioneer stage1 but it still bears the dubious reputation that it acquired when it was in its infancy4 ,aerial travel1 under standardized conditions1 is no longer unsafe4 ,there are good reasons for regarding it already as safer than automobiling4 ,according to a report of the ,british ,department of ,civil ,aviation1 there were #ba1jjj commercial flights in ,great ,britain during the six months from ,may #a to ,october #ca1 #aiai1 and #eb1jjj passengers were carried4 ,the total mileage covered was #cjc1jjj4 ,not a single passenger was killed during this period1 and only ten were injured4 ,there were two fatalities among pilots and six pilots were injured4 ,commander ,read1 who made the first transatlantic flight1 writes on this subject3 8,there are some pilots with whom ,i would refuse to risk my life4 ,but1 given a modern machine with the proper attention paid it1 and a skillful but conservative flyer1 it is as safe a means of rapid transit as an automobile traveling at less than half the speed4 ,nowadays there is scarcely ever an accident in an aeroplane of standard type due to the fault of material2 they are all due to the inexperience or to the dare-devil stunting proclivities of the pilot--the pilot who #8takes chances4'0 ,aeronautics is now more than an art4 ,it is a rapidly expanding branch of applied science4 ,aeronautical engineering has become one of the recognized professions4 ,some of the leading government laboratories of the world1 including the ,national ,physical ,laboratory in ,great ,britain and the ,united ,states ,bureau of ,standards1 are devoting their attention to aeronautical research4 ,there are also many unofficial 8aerodynamical0 laboratories for studying1 with the aid of wind tunnels and other apparatus1 the many problems pertaining to the physics of flight and the principles of aeroplane designing4 ,aeronautical questions have begun to figure conspicuously in jurisprudence4 ,legislators1 as somebody has said1 are busy making vertical laws to supplement the old-fashioned horizontal ones4 ,in international law1 especially1 aerial navigation has given rise to thorny problems and it is already the subject of elaborate international agreements4 ,the physiological effects of flight and altitude have added a new chapter to the science of medicine4 ,seasickness has been the crux of the ship's doctor2 will 8air sickness0 prove equally baffling8 ,what are the therapeutic possibilities of flying8 ,will physicians advise their patients to seek a 8change of air0 vertically instead of horizontally8 ,the atmosphere1 once monopolized by the birds1 has become the abode of man4 ,that is one excellent reason why everybody should acquire a knowledge of meteorology--the science of the air4 ,,chapter ,,iv ,,dust ,,and ,,smoke ,,in ,,the ,,atmosphere ,when the moralist reminds us that we are children of the dust and predestined to a dusty end1 there is a grain of comfort in the discovery that modern science regards dust as one of the most important things in the whole economy of nature4 ,no longer does dust seem an appropriate symbol of insignificance and humility when one surveys the bulk of serious literature that has been written about it1 considers the caliber of the men who have devoted the better part of their lives to the study of it1 or inspects the great array of ingenious apparatus that has been devised for its investigation4 ,the dust of which we have to speak in the present chapter embraces all small particles of solid matter found anywhere1 or at any time1 in the earth's atmosphere4 ,particular kinds of dust have1 of course1 their special names4 ,soot1 the visible part of smoke1 is a form of dust that has played a very conspicuous part in human affairs2 hence the separate mention of smoke in the heading of this chapter4 ,while there are many agencies that help to charge the atmosphere with dust1 the most important of them all is the wind4 ,let us see what happens when the wind blows over the surface of a dusty road1 for example4 ,if the air flowed in a smooth horizontal stream over such a surface1 its friction would drag the dust along on the ground1 but would not lift it4 ,such surface drifting1 due to the horizontal component of the wind's motion1 does1 of course1 occur1 and its effects are strikingly visible in the shifting dunes that often form over a broad surface of sand or snow4 ,all winds near the earth's surface are1 however1 full of waves and eddies1 and in many cases1 as over a stretch of strongly heated soil1 there are strong updrafts1 sometimes extending to a great height in the atmosphere4 ,all kinds of dust are heavier than air1 and1 contrary to popular belief1 never truly 8float0 in the atmosphere4 ,dust may enter the atmosphere at high levels1 through the disintegration of meteors1 or it may be spouted up by volcanoes1 but dust blown up from the earth's surface rises only because the air is rising with it2 and1 in still air1 all dust sinks more or less rapidly toward the ground4 ,the rate of its fall depends upon its specific gravity1 and upon the size and shape of the dust particles4 ,other things being equal1 the finest particles fall most slowly4 ,exceedingly fine dust1 even without upward air movements to support it1 requires months or even years to fall to the ground from the higher levels of the atmosphere4 ,upward movements in the air suffice to carry millions of tons of dust aloft every year1 and horizontal air currents carry the same dust far and wide over the earth4 ,the transportation of soil by the wind leads to some results of remarkable interest1 practical as well as scientific4 ,in the first place1 far-reaching changes in topography are brought about by this process4 ,thus in ,china vast areas are covered to a depth of hundreds or even thousands of feet with a fine yellowish earth1 called 8loess10 which is believed to have been blown thither by the winds from the deserts of ,central ,asia4 ,less extensive deposits of this wind-borne material are found in many other parts of the world1 including the ,mississippi ,valley4 ,another effect of wind transportation is the mixing of soils4 ,there is a constant interchange of soil material between different regions1 so that the composition of the soil on a particular farm1 for instance1 is not the same now that it was a few years ago or that it will be a few years hence4 ,lastly1 the presence of dust in the atmosphere1 whether derived from the soil or otherwise1 has various interesting and important effects upon the heat and light we receive from the sun and modifies1 in numerous ways1 the conditions of human life upon our planet4 ,several cases in which enormous quantities of solid matter have been carried to great distances by the wind have formed the subject of elaborate investigations on the part of meteorologists4 ,thus1 during the three days1 ,march #h-aj1 #aija1 heavy dust storms occurred in the deserts of southern ,algeria1 and the sequel of these storms was carefully studied by ,hellmann and ,meinardus4 ,a widespread cyclonic storm1 central over ,tunis at the time1 sucked up the dust1 which was carried northward by the winds at high altitudes4 ,deposits from this dust cloud occurred over an area extending as far as #b1ejj miles from the place of origin4 ,reports collected from hundreds of observers indicated that #a1hjj1jjj tons of dust fell over the continent of ,europe1 and one-third of this fell north of the ,alps4 ,as much more is believed to have fallen over the ,mediterranean1 while on the ,african coast itself the deposit is supposed to have amounted to #aej1jjj1jjj tons4 ,in ,march1 #aiah1 a shower of dust discolored falling snow at various places in the ,united ,states over an area of at least #ajj1jjj square miles1 extending in an east-west direction from ,dubuque1 ,iowa1 to ,chelsea1 ,vt4 ,reports of this shower were collected by ,messrs4 ,e4 ,r4 ,miller and ,a4 ,n4 ,winchell1 who estimate that the amount of dust could not have been less than a million tons1 and may have been several hundred million4 ,the dust is believed to have been blown up from the arid regions of the far southwestern ,united ,states and to have been transported a thousand miles or more4 ,off the west coast of ,africa1 between the ,canaries and the ,cape ,verde ,islands1 haze due to dust blown up from the ,sahara ,desert is frequently encountered by vessels1 especially during the first four months of the year4 ,this haze probably gave rise to the ancient legend of a ,sea of ,darkness--the ,mare ,tenebrosum--one of the mysterious terrors of the ocean reported by the navigators who first sailed toward the ,new ,world4 ,extensive deposits of atmospheric dust have attracted attention from the earliest times4 ,ehrenberg1 in #ahdi1 collected records of #cdi such cases1 and published a map showing their distribution1 which embraces the greater part of the world4 ,atmospheric dust is always brought down in greater or less quantities by rain4 ,when it consists of fine powdery sand1 the rain sometimes acquires a brownish or reddish tinge1 staining objects on which it falls and constituting the 8showers of blood0 that have been regarded as prodigies from remote antiquity4 ,homer describes such a shower1 and many similar occurrences are recorded by the ,roman historians4 ,italy1 owing to its proximity to the ,african coast1 is often visited by these showers1 which still strike superstitious terror into the hearts of the peasantry4 ,the millions of meteors that enter the earth's atmosphere every day contribute their quota of dust1 though the total amount is small compared with that of the material lifted from the earth4 ,fine ferruginous particles are often seen on the snowy summits of high mountains and the polar ice fields1 and both their appearance and their composition indicate that they are derived from meteors4 ,forest fires1 burning peat beds1 and other conflagrations on a large scale discharge quantities of dust into the atmosphere4 ,cinders from the great ,chicago fire spread over a large part of the globe4 ,they are said to have reached the ,azores some forty days after the beginning of the catastrophe4 ,in ,europe1 the once common practice of burning the moors to prepare them for cultivation gave rise to huge volumes of smoke1 which was carried by the wind hundreds and even thousands of miles4 ,the stronghold of this old custom--which still survives to some extent--was ,east ,friesland1 in northwestern ,germany1 and the characteristic haze to which it gave rise1 known as 8moor smoke0 7,german1 ,moorrauch71 was sometimes observed as far away as ,spain1 ,italy1 and ,greece4 ,the famous 8dark days0 that figure in both ancient and modern history1 though in a few cases probably due to eclipses of the sun1 have generally been the result of an abnormal accumulation of smoke or dust in the air2 sometimes arising from volcanic eruptions1 but more often from burning forests1 moors1 or prairies4 ,forest fires are the principal cause of dark days in the ,united ,states4 ,probably the most celebrated of such days was ,may #ai1 #aghj1 when1 in consequence of great forest fires along ,lake ,champlain and down to the vicinity of ,ticonderoga1 darkness like that of night prevailed in ,new ,england4 ,all but the most necessary business was suspended1 the schools were dismissed1 and the greater part of the population flocked to church to prepare for the end of the world1 which was believed to be at hand4 ,the great ,idaho fire of ,august1 #aiaj1 was responsible for dark days over a larger area than in any other case on record in this country4 ,artificial light was required in the daytime over a broad belt1 extending from ,idaho to northern ,vermont1 but smoke was observed far beyond this area4 ,the ,british ship ,dunfermline reported that on the ,pacific ,ocean1 #ejj miles west of ,san ,francisco1 the smell of smoke was noticed and haze prevailed for ten days4 ,when smoke in the air forms a rather thin layer1 through which the sunlight penetrates feebly1 we sometimes get an effect similar to the golden glow of sunset1 a yellow or coppery tinge being cast over the landscape4 ,such was the cause of the 8yellow day0 still remembered in ,new ,england--,september #f1 #ahha--;attributed to the burning of the immense peat bogs of the ,labrador barrens4 ,another occasional cause of atmospheric dustiness is the eruption of volcanoes1 especially those of an explosive character1 which carry fine dust to heights at which it cannot be washed out of the atmosphere by rain4 ,the remarkable dry fog of #aghc--the most famous in history--which covered the greater part of ,europe and ,north ,america for three or four months--was undoubtedly due to the violent eruptions of that year in ,iceland and ,japan4 ,its connection with the ,iceland eruption was suggested even by contemporary writers4 ,the outbreak of ,krakatoa1 in the ,east ,indies1 in #ahhc1 spread a veil of dust over the greater part of the globe4 ,for two or three years its presence in the air was the cause of striking optical phenomena1 including gorgeous sunset glows4 ,the story is told of an ,american fire brigade which1 deceived by one of these brilliant sunsets1 set out to extinguish what was mistaken for a great fire in a neighboring village4 ,a large species of corona around the sun1 known as 8,bishop's ring10 because it was first observed by the ,rev4 ,sereno ,bishop of ,honolulu1 appeared shortly after the eruption and reached its maximum intensity the following year4 ,this was due to the diffraction of light by the exceedingly fine dust from the volcano1 and the same phenomenon has been seen after other great explosive eruptions2 e4 g41 that of ,mont ,pele1 in #aijb4 ,some authorities believe that the finest particles of dust from the ,krakatoa eruption were carried to an altitude of over fifty miles above the earth1 and remained suspended at very high levels for several years1 constituting the strange 8noctilucent clouds10 seen on summer nights from #ahhe onward4 ,these clouds glowed with a silvery luster1 attributed to reflected sunlight4 ,a persistent veil of volcanic dust in the upper air is thought to exercise marked effects upon terrestrial temperatures1 and prolonged periods of intense vulcanism have been regarded as the cause1 or one of the causes1 of the recurrent ice ages of which geology furnishes the record4 ,this explanation of ice ages was advanced by ,p4 and ,f4 ,sarasin1 in #aija1 and was first put upon a scientific basis by ,dr4 ,w4 ,j4 ,humphreys in #aiac2 but the idea that volcanic dust might be the cause of cold seasons was suggested by ,benjamin ,franklin as early as #aghd4 ,franklin's speculations on this subject were prompted by the cold winter of #aghc-aghd1 which followed the extraordinary fog of #aghc1 already mentioned4 ,humphreys has published a list of all the great volcanic outbreaks recorded since #agej1 and has shown that each of them registered itself in the temperatures of the earth and also1 since accurate measurements began to be made of solar radiation1 in these instrumental records4 ,thus1 the intensely cold winters of #aghc-aghe followed the tremendous eruptions of ,asama1 ,japan1 and ,skaptar ,jkull1 ,iceland1 in #aghc2 the famous 8year without a summer0 7#ahaf7 was the sequel of the gigantic outbreak of ,tomboro1 in the ,sunda ,islands1 in #ahae1 which is said to have hurled thirty-six cubic miles of solid matter into the atmosphere2 and definite periods of low temperatures and reduced sunshine were observed after the eruptions of ,mont ,pele1 in #aijb1 and ,mount ,katmai1 ,alaska1 in #aiab4 ,the effect of a volcanic dust veil in lowering temperatures on earth is attributed chiefly to the fact that1 while the fine grains of dust are able to reflect back into space the short waves of radiation coming from the sun1 they do not bar the passage of the long heat waves radiated outward from the earth4 ,according to ,humphreys's calculations1 such a veil is about thirtyfold more effective in shutting solar radiation out than in keeping terrestrial radiation in4 ,this process is just the reverse of the familiar effect of the greenhouse2 where the glass lets in the short waves of solar radiation but does not readily let out the long waves of earth radiation4 ,a small contingent of atmospheric dust consists of common salt 7sodium chloride7 due to the evaporation of spray from the ocean4 ,this substance is frequently found in rain1 as well as in samples of air1 not only near the seashore1 but even in the interior of continents and on high mountains4 ,according to ,du ,bois the amount of sodium chloride annually deposited on the dunes of ,holland is at least #f1jjj1jjj kilograms 7more than #f1fjj tons74 ,one of the striking phenomena of arid regions is the dust whirlwind2 exemplified in the 8devils0 of ,india and ,south ,africa1 the 8twisters0 of ,texas1 etc4 ,e4 ,e4 ,free1 in his treatise on 8,the ,movement of ,soil ,material by the ,wind0 7,u4 ,s4 ,bureau of ,soils1 ,bulletin #fh71 says of these whirls3 8,they may be seen nearly every hot day1 sometimes running rapidly over the surface2 sometimes remaining nearly1 if not quite1 stationary1 but never losing their rapid rotation4 ,they usually last only a few minutes1 but occasionally persist much longer4 ,one observed by ,pictet lasted for over five hours4 ,they are largest and last longest on the flat1 bare plains of the desert1 and are usually seen in a calm or when only a light breeze is blowing1 although their occurrence in windy weather is not unknown4 ,these whirls have been noticed by many travelers in desert and steppe regions and have been carefully observed by ,baddeley in ,india1 and by ,pictet in ,egypt4 ,they are frequent in ,china and on the pampas of ,south ,america1 and occasionally occur during the dry season even in the humid regions4 ,one of the most interesting phenomena in connection with the dust whirls is the occurrence of systems of several whirls1 each revolving rapidly about its own center and also moving about a common center in a more or less perfect circle a few rods in diameter40 ,the little whirls often seen on dusty roads are a miniature variety of the same phenomenon4 ,one very important class of dust particles in the atmosphere consists of organic matter1 living or dead1 including the pollen of plants and the countless myriads of microorganisms1 as well as a variety of other products of the animal and vegetable kingdoms4 ,an abundance of pollen in the air accounts for the occasional fall of yellow rain1 described as 8sulphur rain10 8golden showers10 etc4 ,the promptness with which a piece of stale bread becomes moldy in a damp atmosphere is one of many proofs of the omnipresence in the atmosphere of the microscopic spores of fungi1 ready to propagate their species with amazing rapidity as soon as they light upon a suitable nutrient medium4 ,last1 but not least1 bacteria1 the most minute of all known organisms--so small that thousands or millions of them clustered together would make a mass not larger than the head of a pin--swarm in the air1 as they do in water1 the soil1 and the bodies of animals4 ,fortunately1 while certain species of bacteria carry disease and death with them1 the great majority are harmless to mankind4 ,illustration3 ,,aitken',s ,,dust ,,counter ,a great many different methods are in use for determining the total amount of solid matter present in a given volume of air1 counting the number of particles1 or gathering samples for microscopic examination4 ,thus a known volume of air may be drawn through a filter of cotton wool or bubbled through distilled water1 and the dust detained by the cotton or deposited in the water may be weighed4 ,in certain types of apparatus the air is drawn or forced against a plate or tube coated with glycerin1 oil1 varnish1 gelatin1 or other adhesive surface1 to which the dust remains attached4 ,several devices depend for their operation upon the fact that when a volume of confined air is cooled by expansion a point is eventually reached at which the water vapor present condenses to form a fog1 each droplet of which is supposed to have a single particle of dust as its 8nucleus40 ,this is the principle involved in the well-known ,aitken dust counter1 which has been so extensively used in different parts of the world1 and has furnished most of the impressive statistics of air dustiness found in textbooks and reference books4 ,thus1 from indications supplied by this instrument1 it is stated that a cubic inch of town air contains #ej1jjj1jjj particles of dust2 that a room1 near the ceiling1 was found to contain #hh1jjj1jjj particles per cubic inch2 and that a cigarette smoker sends #d1jjj1jjj1jjj particles into the air at every puff4 ,recent authorities are inclined to look upon these figures as misleading1 for the reason that the nuclei counted with ,aitken's instrument are probably so infinitesimal in size that they hardly deserve to be called dust2 indeed there is good reason to believe that an indefinitely large proportion of them may actually be molecules of gases4 ,the effects of dust1 both inorganic and organic1 upon the health of humanity will be considered in another chapter4 ,certain kinds of dust are of economic importance on account of their inflammable and explosive character when mixed with the right proportions of air4 ,thus the cereal dusts made in the handling and working up of grain into food products occasionally give rise to serious accidents4 ,these occur in cereal1 flour1 and feed mills1 grain elevators1 starch and glucose factories1 and on farms in connection with the use of threshing machines4 ,during a period of ten years1 #aijf-aiaf1 cereal dust explosions resulted in the loss of eighty lives and the destruction of property to a value of #b1jjj1jjj in the ,united ,states4 ,a study of this subject has been made by the ,united ,states ,department of ,agriculture1 and various recommendations have been published with a view to preventing the occurrence of sparks in the neighborhood of these dangerous dusts4 ,coal dust in mines likewise causes numerous explosions4 ,preventive measures include wetting the dust1 moistening the air1 and powdering the walls1 roof and floor of the mine with a nonexplosive rock dust1 which has the effect of stifling an incipient fire or explosion4 ,the last species of dust that we have to consider in this chapter is one that constitutes a literal blot on civilization1 since the noblest cities and monuments of mankind are defaced with it4 ,neither are the evils of this kind of dust wholly sthetic1 for it is extremely injurious to health and enormously expensive4 ,after enduring coal smoke as a necessary evil for generations1 civilised humanity has now embarked upon a vigorous campaign for its elimination1 and very encouraging results have already been achieved in many parts of the world4 ,the war against smoke is carried on by numerous societies in ,europe and ,america2 a multitude of laws and ordinances 7not all of them effective7 have been enacted on the subject2 it has been the occasion of international conferences and expositions2 and its literature has grown so copious that a partial bibliography of the subject1 published a few years ago by the ,mellon ,institute1 of ,pittsburgh1 fills #afd pages4 ,the smoking of chimneys is costly1 in the first place1 because it is due to imperfect combustion and the waste of part of the heating value of the fuel1 and1 in the second place1 on account of the damage wrought by the deposit of the soot4 ,thus a smoky atmosphere entails big laundry and dry-cleaning bills1 frequent repainting of houses1 injury to metal work1 damage to goods in shops1 and excessive artificial lighting in the daytime4 ,throughout the ,united ,states it is said that smoke causes an annual waste and damage amounting to five hundred million dollars4 ,in ,pittsburgh alone--before the reform produced by vigorous legislative and scientific measures1 following an exhaustive investigation by the ,mellon ,institute of ,industrial ,research--the cost of the smoke nuisance was estimated at nearly ten million dollars a year4 ,means of mitigating this evil include the introduction of improved appliances for burning soft coal1 and the use of other kinds of fuel4 ,the electrification of the railway lines entering cities is an important measure of relief4 ,it is estimated that more than one-third of the smoke found in certain ,american cities comes from locomotives4 ,systematic measurements of the amount of solid matter contributed to the atmosphere by smoke have been made at various places in this country and abroad1 and yield startling figures4 ,measures of the 8sootfall0 in ,pittsburgh1 before the evil there was mitigated1 showed an annual average deposit amounting to #a1jca tons per square mile4 ,london's average is #bdh tons per square mile for the whole city and #dbf tons in the central districts4 ,in the heart of ,glasgow the annual sootfall is #hbj tons per square mile4 ,in ,great ,britain measurements and analyses of soot and the study of its effects have been carried out on a large scale for a number of years by the ,advisory ,committee on ,atmospheric ,pollution1 attached to the ,meteorological ,office4 ,the ,committee has installed 8pollution gauges10 of uniform type1 at about twenty-five places in ,england and ,scotland4 ,the soot that falls into these gauges is collected once a month1 weighed and analyzed4 ,this organization also makes direct measurements of the purity of the air1 and has acquired a unique body of observations that can be used to test the success of efforts made to abate the smoke nuisance1 besides providing interesting comparisons between the incidence of respiratory diseases and the amount of solid matter in the air4 ,,chapter ,v ,,weather ,,and ,,weather ,,instruments ,the fact that a vast proportion of the conversations in which human beings engage begin with remarks about the weather has often been noted1 but perhaps never fully explained4 ,meteorologists sometimes adduce this fact as evidence that weather is a subject of overshadowing importance4 ,this bit of reasoning will not1 however1 bear critical analysis4 ,it carries with it the implication that people talk about weather because weather is uppermost in their thoughts4 ,how often is such the case8 ,brown1 meeting ,jones1 remarks that it is a fine day4 ,are we to infer that ,brown was meditating upon the agreeable state of the atmosphere before he vouchsafed this not altogether novel observation8 ,hardly4 ,there is about one chance in a thousand that weather was in his mind at all4 ,it is a plausible thesis that people talk so much about weather because1 at an earlier period in the history of mankind1 this subject was of supreme importance4 ,perhaps it is a custom handed down from our remote ancestors1 whose occupations were nearly all carried on out-of-doors and who enjoyed but a precarious shelter from the elements in their rude habitations4 ,in ,india1 as the period of the monsoon rains approaches1 anxiety about the timely arrival and the abundance of these showers eclipses all other thoughts in the mind of the peasant1 because a severe drought at this season means a famine4 ,when our forefathers lived by hunting1 fishing1 and crude systems of grazing and agriculture1 they were1 no doubt1 equally solicitous about atmospheric conditions that directly affected their food supply4 ,in those days comments on the weather were by no means empty formulas4 ,men rejoiced together that the day was fine1 because it was a circumstance upon which their dinner depended2 and the prehistoric equivalent of 8,what beastly weather60 was probably accompanied by a significant tightening of the belt4 ,certain it is that in very early times people gave a great deal of attention to the weather and acquired a fund of wisdom on the subject which1 along with a certain amount of superstitious unwisdom1 has come down to us in the shape of weather proverbs4 ,many of these proverbs undoubtedly originated before the dawn of history1 for they are found in substantially the same form among widely scattered races of mankind4 ,various popular weather prognostics familiar at the present day are mentioned in such ancient documents as the ,vedas1 the ,bible1 and the cuneiform tablets from the library of ,assurbanipal4 ,speculations about the weather occupy much space in the writings of the ,greek philosophers1 and a formal treatise on meteorology1 written by ,aristotle 7fourth century ,b4 ,c471 remained the standard work on this subject for two thousand years4 ,more or less systematic weather records were kept by the ,greeks long before the ,christian era1 and they produced a number of almanacs1 in the shape of marble tablets1 showing the average winds and weather for particular dates throughout the year4 ,a copious collection of the weather indications found in both ,greek and ,roman almanacs1 dating back to the fifth century ,b4 ,c41 has been made by ,dr4 ,gustav ,hellmann4 ,some of the meteorological instruments used today have a very respectable antiquity4 ,ancient statistics of the rainfall of ,india1 recently brought to light1 show that some sort of rain gauge must have been in use in that country in the fourth century before our era4 ,measurements of rainfall were made in ,palestine in the first century ,a4 ,d4 ,the only other meteorological instrument dating back to classical antiquity1 so far as known1 is the weather vane4 ,the ,tower of the ,winds1 at ,athens1 built about a century before the ,christian era1 originally bore at its summit a vane in the shape of a bronze ,triton1 holding in his hand a wand1 which was designed to point at one or another of the eight symbolical figures of the principal winds surrounding the octagonal tower1 thus showing which way the wind was blowing at the time4 ,the ,roman writer ,varro has left us a description of a vane that could be read indoors by means of a dial on the ceiling4 ,instrumental weather observations did not become the rule1 however1 until the end of the seventeenth century1 when the use of thermometers1 hygrometers1 barometers1 and rain gauges began in ,italy and spread rapidly to other countries4 ,the origin of each of these instruments is commonly ascribed to a particular inventor--the thermometer to ,galileo1 the barometer to ,torricelli1 etc4--but the truth is that the idea of the instrument was1 in each case1 a slow growth1 to which many minds contributed4 ,thus a form of thermoscope--a device for showing but not for measuring the expansion and contraction of air with changes of temperature--was described by ,philo of ,byzantium in the third century ,b4 ,c4 ,galileo supplied such an instrument with a scale1 but without fixed points1 thus converting it into a crude thermometer1 but it was not until half a century later that the ,grand ,duke ,ferdinand ,,ii of ,tuscany introduced the idea of filling the thermometer with alcohol1 in place of air1 and sealing it so that it was not affected by changes in barometric pressure4 ,the thermometric scale now used in ,english-speaking countries1 which bears the name of ,fahrenheit1 appears to have been devised by the ,danish astronomer ,ole ,rmer1 from whom ,fahrenheit borrowed it4 ,in short1 any brief account of the invention of the principal meteorological instruments necessarily ignores the just claims of many inventors2 to say nothing of the fact that what is written on the subject to-day is likely to be refuted to-morrow by the discovery of some forgotten book or manuscript4 ,we are on safer ground in saying that the plan of measuring the weather1 instead of merely observing it1 became general early in the eighteenth century2 and that about the middle of the nineteenth century the further improvement was introduced of making meteorological instruments trace their own records1 so that the human observer was1 to a great extent1 dispensed with4 ,self-registering instruments are now the rule at important meteorological observatories and stations1 though they do not1 even yet1 record all the elements of weather1 and at a host of minor stations none of them have yet replaced the eye of the observer4 ,now let us see what things go to make up the weather1 and how these things are observed by the modern meteorologist4 ,the pressure of the atmosphere1 if not exactly a part of the weather1 is so intimately associated with it that we cannot exclude it from our list of weather phenomena4 ,atmospheric pressure is measured with the barometer1 and the importance of this instrument as a key to weather changes is fully recognized--and indeed overrated--by the layman1 who sometimes calls it the 8weather glass40 ,illustration3 ,,mercurial ,,barometer 7,fortin type7 ,until recently all ,british and ,american barometers were read in inches and all others in millimeters4 ,since atmospheric pressure is a force1 the practice of measuring it in units of length is rather like measuring time in bushels or potatoes in hours4 ,the inconsistency is serious from a scientific point of view1 because it divorces barometric measurements from other physical measurements1 in which pressures are measured in units that have nothing to do with length2 viz41 dynes per square centimeter4 ,accordingly1 some of the leading meteorological services of the world have lately adopted a new unit of barometric pressure1 known as the bar1 which is equivalent to #a1jjj1jjj dynes per square centimeter4 ,it is subdivided according to the ordinary metric notation1 and its most commonly used subdivision is the millibar1 equivalent to #j4jc inch on the old-fashioned barometer scale1 under standard conditions4 ,illustration3 ,,aneroid ,,barometer1 ,,graduated ,,in ,,millibars ,,and ,,inches ,for the benefit of sailors a curve is shown indicating the mean annual pressure in different latitudes along the meridian of #cj ,w4 7,courtesy of the ,british ,meteorological ,office47 ,the mercurial barometer is so delicate and cumbersome that for many practical purposes it is replaced by the more convenient though less accurate aneroid barometer4 ,a self-recording barometer 7usually an aneroid7 is called a barograph4 ,in its ordinary form1 this instrument carries a pen1 which traces a continuous record of the barometric pressure on a strip of paper wound around a cylinder turned by clockwork4 ,generally the instrument runs for a week before the paper has to be changed4 ,the barograph is a very instructive instrument1 because it shows1 not only the pressure1 but also the changes of pressure--i4 e41 just how fast the barometer is rising or falling1 or1 as meteorologists say1 the 8barometric tendency40 ,the way in which barometric changes are related to weather will appear in a later part of this book4 ,the mercurial barometer consists of a glass tube1 sealed at its upper end and having at its lower end a 8cistern10 which is open to the air4 ,the tube is filled with mercury at its open end1 and then inverted over the cistern1 and the mercury descends until the weight of the portion standing above the level of the mercury in the cistern just balances the pressure of the air on an area equal to the cross section of the tube4 ,the height of the mercurial column is read from a graduated scale attached to the tube4 ,certain corrections are applied to the reading1 in order to eliminate variations due to temperature1 etc41 and1 if to be entered on a weather map1 the reading is reduced to sea-level value4 ,in the aneroid barometer1 a thin-walled metal box1 exhausted of air1 undergoes changes of shape in response to changes in atmospheric pressure4 ,the movements of the box are communicated by levers to a pointer moving around a dial 7or to the recording pen1 in the barograph74 ,since the pressure of the atmosphere diminishes with increasing altitude at a fairly definite rate1 the barometer is used for measuring heights4 ,sometimes it is graduated directly1 for this purpose1 in feet or meters1 and it is then called an altimeter4 ,among the meteorological elements that unmistakably pertain to weather the most important is the temperature of the air4 ,the thermometer1 with which temperature is measured1 is1 in its common form and in its essential features1 too familiar to require description here2 but we may remark that1 as in the case of the barometer1 several methods of graduating this instrument have been used4 ,besides numerous obsolete systems1 there are three different thermometric scales--the ,fahrenheit1 the ,centigrade1 and the ,absolute4 ,the first is still the prevailing one in ,english-speaking countries1 and the second prevails in all other countries4 ,the ,absolute scale1 long familiar to physicists1 has recently come into somewhat limited use in meteorology4 ,it starts at the 8absolute zero0--the temperature of a body totally devoid of heat4 ,this temperature has been nearly attained in laboratory experiments with liquid helium4 ,one advantage that the ,absolute scale possesses over the others is that it has no below-zero readings4 ,such readings are a source of occasional errors when temperature is recorded on the ,fahrenheit or the ,centigrade scale4 ,the freezing point of water is #cb ,fahrenheit #j ,centigrade #bgc ,absolute4 ,the boiling point of water1 at sea level1 is #bab ,fahrenheit #ajj ,centigrade #cgc ,absolute4 ,while the layman is well acquainted with the thermometer1 he sometimes fails to understand certain differences between the scientific and unscientific methods of using this instrument for weather-measuring purposes4 ,on a hot summer day he is1 perhaps1 inclined to feel aggrieved because the official record of temperature does not adequately express the state of his feelings1 to say nothing of being at odds with the impressive instrument displayed at the corner drug store4 ,hence the following explanation is in order3 ,it is the function of the official thermometer to indicate the true temperature of the air4 ,a thermometer exposed to direct sunshine records its own temperature--i4 e41 the temperature of the glass and mercury--and nothing else4 ,a thermometer 8in the shade0--under a tree1 for example--comes nearer to showing the true air temperature2 but it is exposed to radiation from surrounding objects and its readings will vary with the nature and location of these objects4 ,the meteorological thermometer is nearly always installed in a kind of latticed screen1 or shelter4 ,it is thus largely protected from radiation1 while the air circulates freely around it4 ,only when thermometers are exposed under such standard conditions is it possible to obtain comparable readings of the temperature at different places1 so that1 for instance1 maps may be drawn showing the distribution of this element over a country4 ,the best location for the thermometer screen is a few feet above sod4 ,many thermometers of the ,united ,states ,weather ,bureau are installed on the roofs of tall buildings2 not because this is an ideal location1 but because no better is available in the heart of a large city1 where1 for practical reasons1 the office has to be placed4 ,in many small towns the site of the station is such that the thermometer screen 7or 8instrument shelter10 as it is called in the ,weather ,bureau7 can be placed close to the ground1 and at the same time get ample ventilation and be free from the radiation of buildings4 ,in certain large cities the ,bureau maintains a branch station in a park or in the suburbs1 where a satisfactory exposure for all instruments can be secured4 ,the artificial temperature of a city street is too local and indefinite a thing to be inscribed on weather maps1 utilized by the forecaster1 or embodied in climatic statistics4 ,as a concession1 however1 to the demand of the 8man in the street0 for a record of conditions prevailing in his own sphere1 the ,weather ,bureau has installed in several cities little pavilions in which working meteorological instruments are displayed for the benefit of the public4 ,the thermometers in these so-called 8kiosks0--which are modeled1 with improvements1 after the weather pavilions found at ,european health resorts--always read several degrees higher in hot weather than the thermometer at the regular ,weather ,bureau station in the same vicinity4 ,such records are erratic1 at best1 and present indications are that the kiosks will eventually be abolished4 ,illustration3 ,,maximum ,,and ,,minimum ,,thermometers ,besides the ordinary thermometer1 there are instruments that answer the questions 8,how hot was it to-day80 and 8,how cold was it last night80 ,these are known1 respectively1 as the maximum and the minimum thermometer4 ,they hang almost horizontally in the screen4 ,the former has a constriction just above the bulb1 which prevents the mercury from retreating after it has reached the highest reading for the day4 ,it can be reset by whirling it on a pivot4 ,the minimum thermometer is filled with spirit instead of mercury4 ,a little index inside the column is carried toward the bulb by the surface of the alcohol as the temperature falls4 ,when the temperature rises the index remains behind1 marking the lowest point reached4 ,the highest and lowest temperature of the day1 as well as the temperature at any moment of the day1 can be read from the thermograph1 or self-registering thermometer4 ,in the commonest type of thermograph changes of temperature alter the curvature of a flexible metal tube filled with spirit1 and the movements of the free end of the tube are communicated by levers to a recording pen4 ,on an average day1 in our climates1 the air is coldest about sunrise4 ,the appearance of the sun checks the atmospheric cooling due to the loss of heat from the earth that has been going on through the night1 and the air begins to warm up4 ,as long as the amount of incoming heat from the sun is greater than the amount of outgoing heat from the earth1 the temperature will continue to rise4 ,after noon1 when the sun is highest1 the supply of solar heat diminishes1 but it is still greater1 for a time1 than the heat loss from the earth1 and for this reason the temperature1 as a rule1 keeps on rising until some time toward the middle of the afternoon1 when the maximum temperature of the day occurs4 ,humidity is an element of weather that is more often talked about than understood4 ,atmospheric humidity is the state of the atmosphere with respect to the amount of moisture it contains in a gaseous form1 not in the form of a liquid4 ,this gaseous moisture is called water vapor1 and it is not directly perceptible to the senses1 as liquid water is4 ,as we have explained elsewhere1 the capacity of the air for water vapor increases with the temperature4 ,the actual amount present at any time1 per unit volume1 is called the absolute humidity1 and the ratio of this amount to the maximum amount the air can hold at the same temperature is called the relative humidity4 ,the latter is generally expressed in percentage4 ,when the air is charged to its full capacity with aqueous vapor its relative humidity is #ajj per cent4 ,the relative humidity usually varies greatly through the day1 being generally lowest when the temperature is highest1 and vice versa4 ,it is an element of much practical interest1 because it is one of the main factors in determining the drying power of the air1 the other important one being wind4 ,the air feels dry when evaporation proceeds rapidly from our skin1 either on account of low relative humidity1 brisk air movement1 or both4 ,people are hardly conscious of high relative humidity except when1 in hot weather1 it retards the evaporation of perspiration1 and the latter collects in liquid form on the skin4 ,illustration3 ,,thermograph ,relative humidity does not owe its importance in human affairs solely to its physiological effects1 for it plays a prominent part in numerous industries--textile1 metallurgical1 chemical1 leather1 food1 and all those employing drying processes4 ,in the spinning of cotton and wool1 for example1 the humidity of the workroom greatly affects the weight of the material1 the size of the yarn1 and the length and flexibility of the fibers4 ,humidity must likewise be taken into account in such diverse industries as manufacturing candy1 bread1 high explosives and photographic films1 drying macaroni and tobacco1 and operating blast furnaces4 ,there are engineers who specialize in the business of installing 8humidifying0 and 8dehumidifying0 systems in workshops1 and also1 for hygienic purposes1 in schoolhouses and other public buildings4 ,the absolute humidity1 the relative humidity and the dew point 7the temperature to which the air must be brought to start condensation of its moisture7 are all determined by means of instruments called hygrometers4 ,the hair hygrometer depends for its action upon the fact that a hair1 freed from oil1 not only absorbs moisture from the atmosphere1 but elongates when damp and contracts when dry4 ,the instrument1 which includes a single human hair or a bundle of such hairs1 is so designed that these changes move an index over a graduated scale4 ,this and other types of hygrometer can be arranged to record their own readings continuously1 constituting a hygrograph4 ,the form of hygrometer most commonly met with at meteorological stations is called a psychrometer4 ,this usually consists of a pair of mercurial thermometers1 one of which1 known as the 8wet-bulb thermometer10 has its bulb wrapped in thin muslin4 ,the other1 called the 8dry-bulb10 is an ordinary thermometer4 ,the muslin is moistened1 either just before making a reading1 or continuously with a wick4 ,in the former case the thermometer is generally whirled several times before the reading is taken4 ,unless the air is saturated1 the wet bulb is cooled by evaporation1 and the difference between the readings of the two instruments enables the observer1 with the aid of suitable tables1 to obtain the absolute and relative humidity and the dew point4 ,the most accurate results are obtained from the aspiration psychrometer1 of ,assmann1 in which air is drawn past the bulb of the thermometer by a small fan1 driven by clockwork4 ,deposits of liquid and frozen water from the atmosphere1 in their various forms1 are known collectively as 8precipitation10 and in the aggregate they constitute a feature of the weather hardly less important than temperature4 ,indeed an average rainstorm or snowstorm is a more obtrusive event than any other equally common manifestation of the weather2 while an excess of precipitation or a prolonged lack of it1 constituting a drought1 may be as serious in its consequences as a 8hot wave0 or a 8freeze40 ,precipitation--familiarly called 8rainfall0--is much more extensively measured than any other meteorological element1 for there are1 throughout the world1 a vast number of places at which this is the only feature of the weather that is regularly observed4 ,in ,europe alone there are about #ai1jjj 8rainfall stations40 ,rainfall is measured in depth2 viz41 in inches or millimeters4 ,a moderate shower of several hours' duration will yield an inch or two of rain1 while in extreme cases several inches may fall in an hour4 ,snow is sometimes measured as such--i4 e41 the actual depth that falls1 or1 more commonly1 the amount lying on the ground from day to day--but in order that records of snowfall may be combined with those of rainfall for the purpose of determining the total precipitation1 the snowfall must be reduced to its 8water equivalent10 either by melting the snow before measurement or by estimating this equivalent or by weighing the snow caught in a receiver of known area and computing the corresponding depth of water4 ,there are many kinds of rain gauge4 ,as a rule the gauge has a funnel-shaped receiver with a small opening through which the water flows into the lower part of the gauge2 loss of the accumulated water by evaporation is thus checked4 ,there is usually some device for magnifying the depth of rainfall in order to facilitate measurement4 ,in ,american gauges the rain flows into an inner tube having one-tenth the horizontal area of the receiver1 and its depth is thus magnified ten times4 ,a measurement is made by thrusting a graduated wooden stick to the bottom of the tube and noting the height to which the stick is wetted4 ,illustration3 ,,tipping-,,bucket ,,rain ,,gauge ,of devices for obtaining an automatic record of rainfall1 the tipping bucket 7or1 as the ,british call it1 the 8tilting bucket07 is probably the most serviceable1 and it is the one most widely used in this country4 ,this instrument is as simple as it is ingenious4 ,the 8bucket0 is a little metal trough1 pivoted in the middle1 so that it can tilt back and forth1 seesaw-fashion4 ,it is divided into two compartments by a central partition4 ,rain falling into the funnel-shaped receiver at the top of the gauge flows into whichever compartment of the bucket is uppermost1 until the weight of the water causes the bucket to tip1 thus emptying one compartment and presenting the other to the incoming stream4 ,when the second compartment is filled1 the bucket tips in the opposite direction4 ,the parts of the gauge are of such dimensions that each tip of the bucket corresponds to #j4ja inch of rainfall4 ,the gauge is connected electrically with registering apparatus indoors1 so that every tip of the bucket is recorded4 ,the registration sheet shows the time of occurrence as well as the amount of rainfall4 ,the two most important things about the wind that are observed and recorded by meteorologists are its direction and its force4 ,it is the universal custom to regard as 8the direction of the wind0 the direction from which1 rather than toward which1 it blows4 ,moreover1 it is only the horizontal direction of the wind that is ordinarily observed1 though many winds have a considerable upward or downward slant1 and1 locally1 a wind may even blow straight up or straight down4 ,the direction of the wind may be observed in several makeshift ways1 such as by watching the drift of smoke from chimneys1 or1 as sailors do1 holding up a wet finger to the breeze4 ,instrumentally and scientifically it is observed with a special type of vane1 much more accurate in its indications than the weather vanes and weather cocks of ornamental and symbolical architecture4 ,the nonscientific vane1 once set in motion1 is likely to be carried too far by its own momentum1 and may even spin completely around under a sudden impulse4 ,in the scientific vane this tendency is restrained by means of a spread tail2 the pressure of the wind on the diverging blades serving to hold the vane in the correct position4 ,the vane1 like most other meteorological instruments1 is self-recording at all important meteorological stations4 ,the type used by the ,weather ,bureau registers the direction of the wind every minute4 ,the force of the wind is obtained from an anemometer4 ,most anemometers do not1 however1 show this directly1 but are designed to measure the speed or so-called 8velocity0 of the wind1 from which its force may be computed4 ,the speed is observed in miles per hour or meters per second4 ,in considering some of the possible effects of wind it is well to bear in mind that its force increases as the square of the velocity4 ,this means1 for example1 that a wind of #bj miles an hour is four times as strong1 and one of #cj miles an hour nine times as strong as a wind of #aj miles an hour4 ,one of the external features of a weather station that invariably attracts the attention of the passer-by is an instrument consisting of four hemispherical cups revolving horizontally in the wind4 ,this scientific whirligig is the ,robinson cup anemometer1 which1 in spite of its shortcomings1 is the most widely used instrument of its class throughout the world4 ,as generally constructed1 the cups are supposed to turn #ejj times for a mile of wind movement4 ,actually the relation between the speed of the cups and the speed of the wind is somewhat variable1 and at high velocities the indications of the instrument are seriously erroneous4 ,the ,robinson anemometer has a dial from which direct readings can be made1 but at large stations it is connected electrically with a registering device in the observer's office1 which makes a mark for each mile of wind and shows how the speed of the wind varies through the day4 ,there are many other types of anemometer1 and some of them tell a much more detailed story of the wind's variations than does the ,robinson instrument4 ,on the other hand1 thousands of weather observers dispense with anemometers altogether and merely estimate the strength of the wind from its effects4 ,this applies to nearly all observers at sea1 and1 in ,europe1 to the vast majority of observers on land4 ,such estimates are recorded on a scale ranging from zero1 for a calm1 generally up to ten or twelve for the strongest winds ever experienced4 ,several different scales are in use4 ,the best known is the ,beaufort ,scale1 devised by ,admiral ,sir ,f4 ,beaufort1 in #ahje4 ,the following table of the ,beaufort ,scale1 as adapted for use on land1 is from the 8,observer's ,handbook0 of the ,british ,meteorological ,office3 ---------------------------------------- --------------------------- ,beaufort ,explanatory ,specification of ,beaufort ,scale ,equivalent number titles for use on land based on speed in observations made at land miles per stations hour at #cc feet ---------------------------------------- --------------------------- #j ,calm ,calm2 smoke rises vertically #j #a ,light air ,direction of wind shown by smoke drift1 but not by wind vanes #b #b ,slight breeze ,wind felt on face2 leaves rustle2 ordinary vane moved by wind #e #c ,gentle breeze ,leaves and small twigs in constant motion wind extends light flag #aj #d ,moderate ,raises dust and loose paper2 breeze small branches are moved #ae #e ,fresh breeze ,small trees in leaf begin to sway2 crested wavelets form on inland waters #ba #f ,strong breeze ,large branches in motion2 whistling heard in telegraph wires2 umbrellas used with difficulty #bg #g ,high wind ,whole trees in motion2 inconvenience felt when walking against wind #ce #h ,gale ,breaks twigs off trees2 generally impedes progress #db #i ,strong gale ,slight structural damage occurs 7chimney pots and slates removed7 #ej #aj ,whole gale ,seldom experienced inland2 trees uprooted2 considerable structural damage occurs #ei #aa ,storm ,very rarely experienced2 accompanied by widespread damage #fh #ab ,hurricane ,above #ge ---------------------------------------- --------------------------- ,the clouds receive more attention at some weather stations than at others4 ,a routine observation consists of noting the kinds of clouds visible1 the direction or directions from which they are moving1 and the degree of cloudiness--i4 e41 the extent to which the sky is clouded1 stated in tenths1 from ,o cloudless1 to #aj completely overcast4 ,at many of the more important stations the movements of clouds are observed with a nephoscope4 ,the reflecting nephoscope1 used in this country1 consists of a black mirror in which the image of the moving cloud is watched1 the direction of its motion being read off from the graduated circular frame of the mirror4 ,there is also a device for measuring the apparent speed of the cloud4 ,from this the actual speed can be calculated if the height of the cloud is known4 ,there are other nephoscopes1 such as ,besson's in which the cloud's movements are watched directly1 and not by reflection4 ,illustration3 ,,besson',s ,,comb ,,nephoscope ,the importance of sunshine among the elements of weather and climate is evidenced by the fact that at least two ,states of the ,union1 ,south ,dakota and ,california1 contend for the title of 8the ,sunshine ,state0--which does not properly belong to either of them4 ,arizona is the sunniest ,state of all1 and the whole ,southwest is sunnier than ,south ,dakota4 ,devices for registering the duration of sunshine are called sunshine recorders4 ,one type 7the ,campbell-,stokes7 works on the burning-glass principle2 in others the sun's rays trace a record on photographic paper4 ,the instrument used by the ,weather ,bureau consists of an air thermometer having a bulb at each end1 one bulb being coated with lampblack4 ,there is a small column of mercury between the two inclosed masses of air4 ,the thermometer is inclosed in a sheath of glass1 from which the air is exhausted4 ,when the sun shines on this instrument1 the air in the black bulb warms and expands1 and the mercury is forced toward the other bulb until it comes in contact with a pair of electrodes1 thus closing an electrical circuit4 ,while the circuit is closed1 the registering apparatus connected with the instrument makes a step-shaped mark once every minute4 ,when the sun stops shining1 the mercury drops back1 the circuit is broken1 and the recording pen merely traces a straight line4 ,illustration3 ,,electrical ,,sunshine ,,recorder ,at the larger stations of the ,united ,states ,weather ,bureau the direction and speed of the wind1 the rainfall and the duration of sunshine are all recorded on a single sheet of paper1 wound around a large cylinder1 which is turned by clockwork4 ,the paper is ruled with lines to denote the hours and minutes of the day1 and a fresh sheet is put on the cylinder every day at noon4 ,this complex registering device1 sometimes called in book language a meteorograph1 but colloquially referred to by weather men as the 8triple register10 is entitled to high rank among labor-saving machines2 for1 with hardly any attention1 except for a few minutes at noon1 it does the work of a staff of trained meteorologists on duty day and night4 ,illustration3 ,,british ,,type ,,of ,,sunshine ,,recorder 7,campbell-,stokes ,pattern7 ,we have now enumerated the elements of weather most commonly observed at meteorological stations1 and the principal types of meteorological instruments1 with special reference to those used in the ,united ,states4 ,in nearly every civilized country there are certain stations at which regular observations are maintained of a number of phenomena not mentioned in the foregoing paragraphs1 such as the intensity of solar radiation 7measured with the pyrheliometer71 evaporation 7measured with atmometers or evaporimeters71 and the temperature of the soil2 and the number of stations is rapidly growing at which the winds and weather far aloft in the atmosphere are observed by means of kites and balloons4 ,meteorologists of the ,old ,world use a great many types of apparatus that are rarely seen in this country1 and some of our instruments are but little known abroad4 ,,chapter ,,vi ,,cloudland ,one of the things a tea kettle is good for is to provide1 by means of the little cloud seen at its nozzle and erroneously called 8steam10 an example of what happens when the invisible gas that is truly steam1 or water vapor1 is cooled below its dew point in the free air4 ,this cloud has1 however1 been the starting point of a vast number of halfway explanations4 ,a generation or so ago physicists were content to say that aqueous vapor turns to drops of water in the air merely on account of being cooled4 ,the question of how the drops get their start1 or why the moisture forms drops at all1 does not seem to have troubled them4 ,one way in which air or any other gas is cooled is by expanding against pressure4 ,some of the energy in the gas1 originally manifesting itself as heat1 is applied to the work of expansion1 and thus ceases to be heat4 ,hence the temperature of the gas falls4 ,conversely1 if a mass of gas is compressed1 the mere process of compression raises its temperature4 ,the heat produced in pumping up a bicycle tire is the classic example of the latter fact4 ,heating by compression and cooling by expansion are called1 respectively1 8dynamic heating0 and 8dynamic cooling40 ,the processes thus described are of the utmost importance in meteorology4 ,if air of average humidity is admitted to the receiver of an air pump in the usual way and suddenly expanded by partial exhaustion1 a cloud of moisture is seen to form in the receiver4 ,this moisture is condensed and made visible by the dynamic cooling of the air4 ,if1 however1 after the receiver is exhausted air of the same humidity as before is admitted through a filter of cotton wool1 and is then similarly cooled by expansion1 no cloud will form4 ,evidently the filter has removed from the air something that is essential to the process of condensation4 ,perhaps it will occur to the reader that1 in some obscure way1 the filter has prevented water vapor itself from entering the receiver4 ,there are several methods by which we can ascertain whether such is the case4 ,one of the simplest is to admit a little smoke to the receiver before expanding the filtered air4 ,in this case the cloud does form1 showing that moisture is present1 and also showing that smoke1 though a perfectly dry substance1 aids the formation of the water drops4 ,such experiments have led to the conclusion1 now universally admitted1 that when water drops form in the atmosphere they always form around 8nuclei0 of something that is not water4 ,these nuclei are often referred to as 8dust particles10 but it is recognized that a vast proportion of them are very much more minute than the dust that worries housewives4 ,they are largely beyond the power of the microscope1 and some of them1 indeed1 appear to be of molecular size1 consisting of molecules of hygroscopic gases1 such as the oxides of sulphur and of nitrogen4 ,another important fact about water drops in the atmosphere has come to light within the last half century4 ,since water is much heavier than air1 meteorologists of an earlier generation were puzzled by the fact that the drops in clouds apparently float1 instead of falling to the ground4 ,in the attempt to account for this supposed floating1 bygone authorities assumed that the drops were hollow 8vesicles10 like little bubbles4 ,this assumption was eventually disproved by the optical phenomena exhibited by the drops1 as well as on other physical grounds4 ,moreover1 it is now known that a cloud never really floats1 though the rate at which its constituent particles fall with respect to the air is generally very small1 on account of the resistance they encounter4 ,thus a very slight upward current usually suffices to maintain the altitude of a cloud1 or even to increase it4 ,the speed with which a drop falls increases with its size4 ,hence large drops may fall rapidly from great heights all the way to the ground1 constituting rain2 but in a great many cases such drops evaporate on falling into warmer air below the cloud level1 and thus the lower surface of the visible cloud remains at about a constant height4 ,the drops in clouds and fog have often been measured1 either by noting their optical effects or by microscopic examination4 ,many are found to be from #j4jjjf to #j4jjjh inch in diameter4 ,the speed with which such drops fall through still air can be calculated4 ,a drop #j4jjjh inch in diameter falls at the rate of about half an inch a second1 or #aej feet an hour4 ,even if a cloud consisting of such drops preserved its integrity for an hour or more while sinking1 its descent at this slow rate would hardly be perceptible from the ground4 ,some clouds consist of ice needles or tiny snowflakes4 ,apparently these icy particles are produced directly in solid form1 without passing through the liquid stage4 ,it is supposed that1 like drops1 they require nuclei on which to condense1 but this matter has not been fully investigated4 ,another point that awaits elucidation is the fact that the clouds that form in air much below the freezing point sometimes consist of water and sometimes of ice4 ,the common fleecy clouds of our winter skies are composed of water drops1 and such clouds also occur in the polar regions4 ,dr4 ,g4 ,c4 ,simpson1 when serving as meteorologist of ,scott's antarctic expedition1 observed fog consisting of liquid water at a temperature of #bi below zero1 ,fahrenheit4 ,why such greatly 8undercooled0 drops should sometimes occur in the atmosphere when at other times1 with higher temperatures1 atmospheric moisture takes the form of ice is not at all clear4 ,there are several ways in which the free air may be cooled to the point at which condensation occurs4 ,the commonest is dynamic cooling1 due to the rise of a mass of moist air and its expansion under the reduced pressure that prevails at the higher levels4 ,this process is beautifully illustrated in the formation of the roundish masses of fleecy cloud known as cumulus1 on a warm summer day4 ,each of these clouds marks the summit of a column of air that is rising after having been heated at the surface of the earth4 ,when the process goes on very actively1 the cloud may tower up to enormous heights1 forming a thundercloud4 ,some clouds are formed by the mixing of air of different temperatures4 ,fog1 which is merely cloud at the surface of the earth1 is often formed by the cooling of the air in contact with cold land or water4 ,the persistent fogs of the ,newfoundland ,banks are due to the passage of warm moist air from the ,gulf ,stream region over the cold ,labrador ,current4 ,on the other hand1 a cold wind blowing over warm water will also often produce a fog by lowering the temperature of the moist air overlying the water4 ,a common cause of land fog is the cooling of the air adjacent to the ground in consequence of nocturnal radiation4 ,the moister the air1 the more readily fog forms1 and hence the frequent formation of fog by night along rivers and over marshes and damp valleys4 ,town fogs1 such as the famous 8,london particular0 and the fogs of ,lyons1 usually consist partly of smoke4 ,dense fogs of this sort occur when the conditions of the atmosphere are such as to cause the smoke to hang low over the city1 instead of being dispersed4 ,these fogs constitute a serious economic problem4 ,thus it is estimated that they cost the people of ,london upwards of half a million dollars a year1 due to extra lighting1 damage to vehicles1 loss of business1 etc4 ,since marine fog is also a source of enormous loss1 through causing delays and accidents1 and since fog along air routes is the greatest of all obstacles to successful aerial navigation1 it is no wonder that much ingenuity has been devoted to the attempt to disperse fog artificially4 ,electric discharges have been successfully used for this purpose on a small scale4 ,the depth of a fog may be anything from inches to miles4 ,measurements made by the ,united ,states ,coast ,guard during the international ice patrol of the ,north ,atlantic show that the fogs on the ,newfoundland ,banks are very commonly so shallow that the mastheads of vessels rise above them1 though in some cases they were found1 from observations with kites1 to be from #b1ejj to #c1jjj feet thick4 ,observations on the mountains of the ,california coast show that the upper level of fog in that region rarely exceeds #d1jjj feet4 ,on the other hand1 aviators flying between ,london and ,paris have encountered fog more than #aj1jjj feet deep4 ,the ,united ,states ,weather ,bureau classifies a fog as 8dense0 if it hides objects at a distance of #a1jjj feet2 otherwise it is described as 8light40 ,british meteorologists record fogs on a scale of five degrees4 ,during the ice patrol of the ,seneca in #aiae samples of foggy air were examined for the purpose of calculating the amount of water and the number of drops they contained per unit volume1 as well as the size of the drops4 ,a block of dense fog #c feet wide1 #f feet high1 and #ajj feet long was found to contain less than one-seventh of a glassful of water1 distributed in #fj1jjj1jjj1jjj drops4 ,during the densest fog of the voyage the diameter of the fog particles averaged #j4jjjd inch2 just about the limit of visibility with the naked eye4 ,in spite of the extremely attenuated state of the water in fogs1 as indicated by these figures1 the moisture they deposit on terrestrial objects is great enough to be of considerable agricultural importance in some parts of the world4 ,thus along the coast of ,peru1 where the rainfall is negligible 7though not1 as often stated1 nonexistent71 a wet fog known as the 8gara0 suffices to maintain a luxuriant vegetation during several months of each year4 ,there are frozen fogs as well as frozen clouds4 ,the 8frost smoke0 that rises over the ,norwegian fjords and over ice-free spots in the polar seas is generally composed of icy particles or snowflakes4 ,an ice fog that sometimes forms in mountain valleys in the western ,united ,states is known as the 8pogonip0--a name derived from the ,shoshonean language4 ,this fog often appears very suddenly1 even in the brightest weather4 ,the minute needles of ice of which it consists are said to be extremely injurious to the lungs4 ,there are tales of a whole tribe of ,indians perishing from its effects4 ,whatever truth there may be in such stories1 it is greatly dreaded by both the ,indians and the whites4 ,the mountains of ,nevada appear to be the favorite home of the pogonip4 ,what meteorologists call 8dry fog0 is a haze of dust or smoke1 sometimes very dense4 ,we have already described the prevalence of this turbid state of the atmosphere following volcanic eruptions1 the burning of forests and moors1 and desert dust storms4 ,under the head of dry fog many writers include a sort of heat haze1 which does not necessarily involve the suspension of either solid or liquid matter in the air1 but is due to the mixing of local air currents of different densities1 especially when evaporation is proceeding rapidly from moist ground under strong sunshine4 ,the callina of ,spain and the qobar of the upper ,nile region are probably due partly to this cause1 and partly to dust4 ,illustration3 ,,alto-,,cumulus ,,clouds4 ,these clouds always occur in roundish fleecy masses or in elongated fleecy rolls1 with blue sky between4 ,a score of different types have been distinguished and named by certain cloud specialists4 7,photographed by ,a4 ,j4 ,weed47 ,illustration3 ,,cumulus4 ,cloud photography has become a special branch of photographic art1 entailing not only the use of appropriate lenses and plates1 but also of ray filters1 or other special devices for sharpening the contrast between the cloud and the blue sky4 ,mr4 ,ellerman's pictures1 made on ,mt4 ,wilson and elsewhere in ,california1 stand in the front rank4 7,photographed by ,f4 ,ellerman47 ,one more species of fog requires mention here1 viz41 the dirty1 foul-smelling 8painter0 of the ,peruvian coast1 which deposits on vessels lying in the harbor of ,callao and elsewhere a slimy brown substance known as 8,peruvian paint40 ,this substance comes from the ocean and is probably due to the decomposition of marine organisms4 ,the 8painter0 prevails during the months ,december to ,april4 ,according to a plausible hypothesis a change in the temperature of the water at that season1 resulting from a periodical shift of ocean currents1 kills vast quantities of plankton1 the decay of which would give rise to the phenomena observed4 ,illustration3 ,,mammato-,,cumulus4 ,a rather rare cloud form1 associated with thunderstorms and tornadoes4 ,it is known in ,scotland as the 8pocky0 7i4 e4 baggy7 cloud and in parts of ,england as 8rain balls40 7,photographed by ,l4 ,c4 ,twyford47 ,illustration3 ,,cumulo-,,nimbus4 ,this is the thundercloud4 7,courtesy of the ,naval ,air ,service47 ,clouds1 though they are nothing more than masses of fog situated at some distance from the earth1 are susceptible of a classification1 according to shape and texture1 that is not applicable to fog4 ,among the billions of human beings who1 in all ages1 have amused themselves by discovering pictures in the clouds it would be remarkable if a good many had not1 from time to time1 conceived the idea of reducing these pictures to a few general types4 ,according to a note published a few years ago in the 8,quarterly ,journal0 of the ,royal ,meteorological ,society1 there is some reason to believe that an elaborate classification of the clouds was in use among the ancient ,hindus4 ,a passage quoted from an ,indian work of the fourth century ,b4 ,c4 says3 8,three are the clouds that continuously rain for seven days2 eighty are they that pour minute drops2 and sixty are they that appear with the sunshine40 ,in the occidental world1 however1 we have no record of any attempt to classify the clouds prior to the year #ahja1 when the following classification was proposed by the ,french naturalist ,lamarck3 ,nuages en balayures 7cloud sweepings71 ,nuages en barres 7clouds in bars71 ,nuages pommels 7dappled clouds71 ,nuages groups 7grouped or piled clouds71 ,nuages en voile 7veil clouds71 ,nuages attroups ou moutonns 7clouds in flocks74 ,in #ahjc the ,english meteorologist ,luke ,howard published the system of classification that1 with some additions and modifications1 is now in general use4 ,this system is based upon three fundamental forms2 viz41 fibrous or feathery clouds 7cirrus71 clouds with rounded tops 7cumulus71 and clouds arranged in horizontal sheets or layers 7stratus74 ,intermediate forms are described by compounding the names of the primary types2 e4 g41 cirro-cumulus1 cirro-stratus1 etc4 ,the rain cloud is called nimbus4 ,howard's classification was quickly adopted in all countries4 ,his definitions were translated into ,german by no less a personage than ,goethe1 who1 in his enthusiasm over ,howard's achievement1 wrote a poem about it1 and also a separate poem about each of the principal types of cloud6 ,the ,latin names that ,howard gave to the clouds made his system immediately available for international use2 and in nearly all of the many systems of cloud nomenclature that have since been proposed the excellent plan of using ,latin names has been preserved4 ,very soon1 however1 after ,howard's classification appeared1 a list of proposed ,english equivalents of his names was published in the 8,encyclopdia ,britannica0--which1 nevertheless1 did not change its name to 8,british ,encyclopdia0--for the benefit of the unlettered majority1 supposed to be incapable of using a few ,latin terms that were1 in fact1 shorter and no more difficult to pronounce than their suggested ,english substitutes6 ,a piquant sequel to this episode is that these superfluous ,english cloud names1 8curl cloud10 8stackencloud10 8fall cloud10 8sondercloud10 8wane cloud10 and 8twain cloud10 still survive in the dictionaries--and nowhere else4 ,they are practically unknown to meteorologists1 and were never adopted generally by the laity4 ,of course some ,english names1 which have been evolved and not deliberately invented1 are applied to certain types of cloud in ,english-speaking countries2 but the ,latin names1 comprised in the ,international ,cloud ,classification1 should be learned by everybody4 ,this classification1 which has been adopted by the ,international ,meteorological ,committee and is used by all official weather services1 is a little more detailed than ,howard's1 upon which it is based2 and there is a tendency to add new terms to it from time to time4 ,there are ten principal types of cloud in the ,international ,classification1 and the name of each type has an official abbreviation 7a great convenience for those who record the clouds from day to day74 ,the following definitions1 translated from the ,french text of the 8,international ,cloud ,atlas10 have been published by the ,british ,meteorological ,office3 #a4 ,,cirrus 7,,ci47--,detached clouds of delicate appearance1 fibrous 7threadlike7 structure and featherlike form1 generally white in color4 ,cirrus clouds take the most varied shapes1 such as isolated tufts of hair--i4 e41 thin filaments on a blue sky--branched filaments in feathery form1 straight or curved filaments ending in tufts 7called cirrus uncinus71 and others4 ,occasionally cirrus clouds are arranged in bands1 which traverse part of the sky as arcs of great circles1 and as an effect of perspective appear to converge at a point on the horizon1 and at the opposite point also1 if they are sufficiently extended4 ,cirro-stratus and cirro-cumulus also are sometimes similarly arranged in long bands4 ,certain forms of cirrus are called 8mares' tails40 ,the long bands crossing the sky1 as just described1 are known as 8polar bands0 or 8,noah's ark40 #b4 ,,cirro-,,stratus 7,,ci4-,,st47--,a thin sheet of whitish cloud2 sometimes covering the sky completely and merely giving it a milky appearance2 it is then called cirro-nebula1 or cirrus haze2 at other times presenting more or less distinctly a fibrous structure1 like a tangled web4 ,this sheet often produces halos around the sun or moon4 #c4 ,,cirro-,,cumulus 7,,ci-,,cu47 7,mackerel sky7--,small rounded masses or white flakes without shadows1 or showing very slight shadow2 arranged in groups and often in lines4 #d4 ,,alto-,,stratus 7,a4-,,st47--,a dense sheet of a gray or bluish color1 sometimes forming a compact mass of dull gray color and fibrous structure4 ,at other times the sheet is thin1 like the denser forms of cirro-stratus1 and through it the sun and moon may be seen dimly gleaming as through ground glass4 ,this form exhibits all stages of transition between alto-stratus and cirro-stratus1 but1 according to measurements1 its normal altitude is about one-half that of cirro-stratus4 #e4 ,,alto-,,cumulus 7,a4-,,cu47--,larger rounded masses1 white or grayish1 partially shaded1 arranged in groups or lines1 and often so crowded together in the middle region that the cloudlets join4 ,illustration3 ,a ,,cloud ,,banner ,,over ,,mt4 ,,assiniboine1 ,,canadian ,,rockies4 7,photographed by ,dr4 ,c4 ,d4 ,walcott47 ,illustration3 ,,cirrus 7with a few patches of lower clouds in the foreground74 ,this is cirrus1 but not of the 8mare's tail0 variety4 ,there are many distinct types of cirrus1 which have sometimes been given separate names4 7,photographed at the ,observatory of ,trappes1 ,france47 ,the separate masses are generally larger and more compact 7resembling strato-cumulus7 in the middle region of the group1 but the denseness of the layer varies and sometimes is so attenuated that the individual masses assume the appearance of sheets or thin flakes of considerable extent with hardly any shading4 ,at the margin of the group they form smaller cloudlets resembling those of cirro-cumulus4 ,the cloudlets often group themselves in parallel lines1 arranged in one or more directions4 #f4 ,,strato-,,cumulus 7,,st4-,,cu47--,large lumpy masses or rolls of dull gray cloud1 frequently covering the whole sky1 especially in winter4 ,generally strato-cumulus presents the appearance of a gray layer broken up into irregular masses and having on the margin smaller masses grouped in flocks1 like alto-cumulus4 ,sometimes this cloud form has the characteristic appearance of great rolls of cloud arranged in parallel lines close together 78roll cumulus074 ,the rolls themselves are dense and dark1 but in the intervening spaces the cloud is much lighter and blue sky may sometimes be seen through them4 ,strato-cumulus may be distinguished from nimbus by its lumpy or rolling appearance1 and by the fact that it does not tend to bring rain4 ,illustration3 ,copyright ,o4 ,p4 ,anderson ,a ,,lenticular ,,cloud ,,over ,,mt4 ,,rainier #g4 ,,nimbus 7,,nb47--,a dense layer of dark1 shapeless cloud with ragged edges from which steady rain or snow usually falls4 ,if there are openings in the cloud an upper layer of cirro-stratus may almost invariably be seen through them4 ,if a layer of nimbus separates in strong wind into ragged cloud1 or if small detached clouds are seen drifting underneath a large nimbus 7the 8scud0 of sailors71 either may be specified as fracto-nimbus 7,,fr4-,,nb474 #h4 ,,cumulus 7,,cu47 7,wool-pack cloud7--,thick cloud of which the upper surface is dome-shaped and exhibits protuberances1 while the base is generally horizontal4 ,these clouds appear to be formed by ascensional movement of air in the daytime1 which is almost always observable4 ,when the cloud and the sun are on opposite sides of the observer1 the surfaces facing the observer are more brilliant than the margins of the protuberances4 ,when1 on the contrary1 it is on the same side of the observer as the sun1 it appears dark with bright edges4 ,when the light falls sideways1 as is usually the case1 cumulus clouds show deep shadows4 ,true cumulus has well-defined upper and lower margins2 but one may sometimes see ragged clouds1 like cumulus torn by strong wind1 of which the detached portions are continually changing2 to this form of cloud the name fracto-cumulus may be given4 #i4 ,,cumulo-,,nimbus 7,,cu4-,,nb477,the thundercloud7--,great masses of cloud rising in the form of mountains or towers or anvils1 generally having a veil or screen of fibrous texture 78false cirrus07 at the top1 and at its base a cloud mass similar to nimbus4 ,from the base local showers of rain or snow1 occasionally of hail or graupel1 usually fall4 ,sometimes the upper margins have the compact shape of cumulus1 or form massive heaps round which floats delicate 8false cirrus40 ,at other times the margins themselves are fringed with filaments similar to cirrus clouds4 ,this last form is particularly common with spring showers4 ,the front of a thunderstorm of wide extent is frequently in the form of a large low arch above a region of uniformly lighter sky4 #aj4 ,,stratus 7,,st47--,a uniform layer of cloud1 like fog1 but not lying on the ground4 ,the cloud layer of stratus is always very low4 ,if it is divided into ragged masses in a wind or by mountain tops1 it may be called fracto-stratus4 ,the complete absence of detail of structure differentiates stratus from other aggregated forms of cloud4 ,we have given the foregoing official definitions and descriptions in full in order to aid the reader as much as possible1 so far as verbal information goes1 in learning to call the common clouds by their names4 ,good pictures are1 of course1 an essential part of this process1 and apart from those that illustrate the present text1 many collections of such pictures are easy of access4 ,some may be obtained free or at nominal cost from the ,weather ,bureau in ,washington and from the ,meteorological ,office in ,london4 ,the 8,international ,cloud ,atlas0 7second edition1 ,paris1 #aiaj7 is now out of print1 but may be consulted in libraries4 ,of the clouds above enumerated1 cirrus1 cirro-cumulus1 and cirro-stratus are the highest1 and are always ice clouds4 ,they consist in some cases of separate1 minute crystals--a fine dust of ice--producing1 according to the forms of the crystals1 one or another of the various forms of halo around the sun and moon2 while in other cases the crystals are aggregated in small snowflakes1 so that the cloud is a real snowstorm in midair4 ,the altitude of these clouds generally ranges from #d to #h miles4 ,in the equatorial region their height is often #aj miles or more4 ,the other main types of cloud are composed wholly or chiefly of water4 ,alto-cumulus and alto-stratus are clouds of medium altitude2 strato-cumulus and nimbus are low clouds 7generally not more than a mile high72 while stratus1 the lowest cloud of all1 grades into fog1 which commonly rests on the earth4 ,since cumulus and cumulo-nimbus are produced by the condensation of moisture from rising air currents1 the height of their bases varies widely with the temperature and humidity of the lower air2 the average height is rather less than a mile4 ,their vertical extent1 however1 is much greater than that of the other cloud types4 ,cumulo-nimbus sometimes towers to a height of #d or #e miles above its base1 and it is then commonly crowned with ice clouds1 including a filmy 8scarf cloud0 draping the summit1 and spreading wisps of so-called 8false cirrus10 drawn out horizontally by the upper winds4 ,besides the ten main classes of clouds1 a few distinct minor varieties are recognized by all meteorologists4 ,among these is the 8lenticular cloud02 an isolated small cloud1 which frequently shows iridescence1 and the shape of which has been compared to that of a lens or an almond4 ,this cloud may remain stationary1 or nearly so1 but it really marks the position of a billow in a stream of air1 the moisture condensing at one edge of the cloud and dissolving at the other4 ,another distinctive and rather rare form of cloud1 seen chiefly in connection with thunderstorms1 is mammato-cumulus1 likewise known as 8pocky cloud10 8festoon cloud10 8rain balls10 etc4 ,it consists of numerous sacklike or udderlike protuberances1 convex downward4 ,when a stream of moist air is forced to ascend in passing over a mountain its moisture is often condensed by the process of dynamic cooling1 already explained1 and a 8cloud cap0 is seen over the summit4 ,in local weather lore such caps are generally regarded as a sign of rain4 ,these clouds attached to mountains were called 8parasitic clouds10 by writers of a century ago1 who proposed some nave explanations of them4 ,occasionally a 8cloud banner0 streams far to the leeward of the mountain4 ,one of the most famous and striking of cloud caps is the 8tablecloth0 that spreads over ,table ,mountain1 near ,cape ,town1 when a moist wind blows in from the sea4 ,sometimes the local topography causes the wind that has swept up over a mountain to form a second 8standing0 wave to the leeward of the summit1 and this may also be marked by a cloud1 which1 like the cloud cap1 presents a delusive appearance of permanence1 while it is1 in reality1 in constant process of formation on the windward side and dissipation on the leeward4 ,the two clouds thus formed1 one over the summit and the other to the leeward1 are often seen at ,table ,mountain1 and are further exemplified in the celebrated 8helm and bar0 of ,crossfell1 in the ,english ,lake ,district4 ,in the case of a wind blowing athwart a ridge or mountain range1 a bank of cloud may extend along the whole crest1 as in the 8foehn wall0 that appears along ,alpine heights when the foehn wind is blowing4 ,some day meteorology will be taught in art schools1 for the same reason that anatomy now is4 ,when that blissful day arrives painters will probably show us skies less at odds with nature than those that deface the work of artists of all degrees of celebrity1 including the 8old masters40 ,,chapter ,,vii ,,precipitation ,meteorologists have been in much perplexity over the naming and classification of the various deposits of atmospheric moisture known collectively as 8precipitation40 ,the subject is one to which a good deal of attention has been paid in recent years1 but it must be admitted that1 even at the present time1 the terminology of this group of atmospheric phenomena is not yet satisfactorily settled1 either in ,english or in any other language4 ,when1 for example1 a record of weather occurrences states that hail has fallen1 this statement1 unequivocal as it may seem to the layman1 often raises a question in the mind of the meteorologist4 ,for centuries people talked and wrote about hail before it occurred to men of science to inquire whether one and the same thing was always described under this name4 ,the pursuit of this inquiry led to disconcerting results1 one of them being the discovery that we do not now know1 in many cases1 what bygone weather observers meant when they made the entry 8hail0 in their records4 ,there are at least three different kinds of icy lumps and pellets that fall from the sky1 and they have all been called hail4 ,what science now regards as true hail occurs only in connection with thunderstorms1 and therefore chiefly in warm weather4 ,it consists of balls or irregular lumps1 each of which1 on examination1 is found to have an opaque snowlike center1 surrounded by ice1 which is often in alternately clear and opaque layers4 ,the second class of icy particles takes the form of miniature snowballs1 about the size of large shot or small peas4 ,it falls in cold weather1 often in conjunction with ordinary snow4 ,because it readily crumbles1 ,english-speaking meteorologists have called it 8soft hail02 but this name is inappropriate for the two cogent reasons that1 though friable1 it is not soft1 and that it is not hail2 hence this term is now giving way to the ,german name 8graupel0 7in which au ow in 8growl074 ,lastly1 little pellets or angular particles of clear ice sometimes fall in cold weather4 ,these frozen drops1 though fairly common1 have1 until recently1 enjoyed the distinction of being anonymous1 so far as the scientific world was concerned1 while the general public called them various things1 including 8hail40 ,a few ,british authorities have tentatively styled this form of precipitation 8ice rain10 a name which has1 however1 been otherwise applied4 ,finally1 in the year #aiaf1 the ,united ,states ,weather ,bureau took the bull by the horns and decreed that such ice particles should be called 8sleet40 ,although this decision of the ,weather ,bureau was arrived at only after an exhaustive overhauling of literature and much correspondence with philologists1 scientific men1 engineers1 and others1 it remains to be seen whether it will eventually prevail throughout the ,english-speaking world4 ,in ,england 8sleet0 nearly always means a mixture of snow and rain4 ,on the other hand1 a great many ,americans have been in the habit of applying this term to the coating of smooth ice1 due to rain in cold weather1 which often breaks down the branches of trees1 lays low miles of wires1 and incidentally produces one of the most beautiful spectacles of ,american winters4 ,this leads us to another difficulty4 ,the icy coating just mentioned has1 for some years1 been called 8glazed frost0 by the ,british ,meteorological ,office1 and the ,united ,states ,weather ,bureau now calls it 8glaze40 ,it has likewise been called1 even in scientific books1 8silver thaw02 and an instance of its occurrence on a large scale is termed1 both popularly and scientifically1 an 8ice storm40 ,to pursue this lamentable record of cross-purposes just a little further1 it may be added that the expression 8silver thaw10 besides being one of the aliases of glaze1 or glazed frost1 has been applied in various official ,british publications1 until recently1 to a very different rough or feathery deposit of ice from fog1 now called by both the ,meteorological ,office and the ,weather ,bureau 8rime40 ,needless to say1 when the scientific authorities are unable to agree about these terms1 our dictionaries are sadly at sea in regard to them2 so1 altogether1 the task of writing a chapter on precipitation is beset with verbal difficulties that would not be encountered in writing on many far more recondite subjects4 ,fortunately the name of the most important kind of precipitation--rain--is reasonably free from ambiguity4 ,to be sure1 opinions may differ as to whether a 8,scotch mist0 is a rain or a wet fog--and if one happened to have insured a lawn fte against rain at ,lloyds' the uncertainty on this point might lead to litigation--but1 generally speaking1 8it rains or it does not rain10 as we are told in the books on logic4 8,rain10 says ,dr4 ,hellmann1 8is the most widespread1 most frequent1 and most copious form in which the aqueous vapor of the atmosphere condenses4 ,the area of its distribution embraces the whole surface of the earth1 with the exception of the interior of ,antarctica and probably of northern ,greenland4 ,the ,english and the ,norwegian expeditions found no rain even at the edge of ,antarctica4 ,as the land rises inland to an altitude of about #b1hjj meters about the ,south ,pole1 it may safely be assumed that only snow and no rain falls in the heart of ,antarctica4 ,at the ,north ,pole1 which lies in the midst of the sea1 it probably rains at times2 while on the high plateau of northern ,greenland probably snow alone falls4 ,as to its frequency1 there are arid regions in which the average annual number of days with rain is less than one1 while this number probably rises to #bhj in some tropical districts4 ,with the exceptions of the polar regions already mentioned1 there are probably no regions where it never rains40 ,in its intensity rain varies all the way from the finest drizzle or the sprinkle of occasional drops up to the torrential downpours often known as 8cloud-bursts40 ,before citing instances of heavy rains1 it may be well to remind the reader that an inch of rainfall is equivalent to #aja tons of water per acre1 or #fd1fdj tons per square mile4 ,in the county of ,norfolk1 ,england1 in ,august1 #aiab1 a single day's rainfall brought down #fgj1gbj1jjj tons of water--more than twice the volume of water contained in ,england's largest lake1 ,windermere4 ,doubtless this record1 for showers of similar extent and duration1 has often been surpassed in other countries1 including our own1 and a fortiori within the tropics4 ,the most remarkable example of a heavy brief shower was recorded at ,porto ,bello1 on the ,isthmus of ,panama1 ,may #a1 #aijh1 when a fall of #b4dg inches in three minutes was registered by a self-recording rain gauge4 ,an average heavy rainstorm in the eastern ,united ,states yields about this amount in twenty-four hours4 ,at ,baguio1 in the ,philippines1 forty-six inches of rain fell from noon of ,july #ad1 #aiaa1 to noon of the following day--probably a 8world record0 for twenty-four-hour rainfall4 ,the corresponding record for the ,united ,states is #bb4bb inches at ,altapass1 ,n4 ,c41 ,july #ae-af1 #aiaf4 ,statistics of what the meteorologist calls 8excessive rainfall0--i4 e41 abnormally heavy rain during brief periods--have been collected over the greater part of the world for much more weighty reasons than to satisfy curiosity as to which showers were 8record breakers40 ,such data are indispensable to engineers in connection with the building of sewers1 reservoirs1 and dams1 and in flood-protection work4 ,sewers must be made large enough to carry off the 8storm water0 from the heaviest showers that ever occur in the locality2 while1 on the other hand1 in the absence of rainfall statistics1 much money might be wasted in making them larger than necessary4 ,a great flood raises questions as to the intensity of the rainfall that caused it1 and the frequency with which similar rains may be expected to occur in the drainage area concerned4 ,the unprecedented floods in the ,ohio ,valley and adjacent regions in ,march1 #aiac1 which caused losses amounting to #bjj1jjj1jjj1 led to an exhaustive study of the records of storm rainfall in the eastern ,united ,states1 carried out by the engineers of the ,miami ,conservancy ,district4 ,their report on this subject 7published at ,dayton1 ,ohio1 in #aiag7 is probably the most elaborate discussion of the kind hitherto prepared for any part of the world4 ,of the #b1fda storms investigated1 seventy-eight1 which covered areas of #ejj square miles or more1 were found to have had a rainfall amounting to at least #bj per cent of the normal rainfall for a year4 ,the distribution of rainfall over the earth 7using the word 8rainfall0 in the broad sense to include snow reduced to its water equivalent7 is most conveniently described in terms of mean annual values4 ,this element is very unevenly divided between different parts of the globe and between the different regions of every large country4 ,the raininess or dryness of a climate is determined especially by the prevailing movement of moisture-bearing winds and the relief of the land1 while a second important control is the location of a region with respect to storm tracks4 ,the rainiest regions are found on the windward slopes of mountain ranges not far from the ocean1 where the moist winds1 forced by the mountains to ascend rapidly1 cool dynamically and shed their moisture4 ,thus the southern slopes of the eastern ,himalaya receive an enormous rainfall from the southwest monsoon1 blowing from the ,indian ,ocean1 and an abundant rainfall also prevails on the south slopes of the high mountains of eastern ,tibet1 while northern ,tibet1 in the lee of the mountains1 is a desert4 ,for more than half a century the little hill station of ,cherrapunji1 in ,assam1 at an altitude of #d1ajj feet1 has been credited with having the heaviest rainfall in the world4 ,according to the latest official record1 its average annual precipitation is #dbf inches4 ,recently it has come to light that ,cherrapunji has a serious rival in the ,hawaiian ,islands4 ,a fragmentary record totaling #ij months1 between #aiaa and #aiba1 kept on ,mount ,waialeale 7altitude #e1jge feet71 in the island of ,kauai1 showed an average of #dee inches per annum1 and there is reason to believe that a longer record will give an even higher average for this place4 ,the spot in question1 which has been described as 8,uncle ,sam's dampest corner10 is so difficult of access that it can be reached only after a three-day trip on foot over mountain trails4 ,hence the ,united ,states ,geological ,survey has installed here a huge rain gauge--said to be the largest in the world--capable of holding an entire year's rainfall1 so that measurements need be made only once a year4 ,the heaviest average annual rainfall in the ,united ,states 7not including ,alaska7 is about #acj inches in ,tillamook ,county1 ,ore4 ,over most of our ,atlantic seaboard ,states the rainfall ranges from forty to fifty inches4 ,extensive tracts in southern ,california and western ,nevada have a rainfall of five inches or less4 ,any region with an annual rainfall of less than ten inches is normally a desert1 though irrigation or 8dry farming0 methods may enable its inhabitants to practice agriculture4 ,the process of rain formation is not well understood4 ,as we have seen1 the existence of nuclei in the air serves to explain why1 when the conditions of temperature and humidity are right1 moisture condenses in the tiny droplets that constitute clouds4 ,the difficulty is to explain how1 at certain times1 quantities of drops are formed of a size large enough to carry them rapidly to the earth4 ,the number of nuclei is so great that1 as ,humphreys has pointed out1 even if all the water vapor in a volume of humid air was condensed upon them1 the size of each drop would remain very small4 ,he has suggested that1 in a column of rising air1 the small drops formed at the base of a cloud filter out most of the nuclei1 so that at greater heights there are relatively few of the latter1 which can1 therefore1 gather sufficient water about them to form drops of 8falling0 size4 ,the speed with which drops fall through the air1 which is only a fraction of an inch per second for the average cloud droplet1 increases rapidly with the size of the drop up to a certain point1 but for the drops that reach the earth as rain the speed of fall tends to become approximately uniform4 ,several investigators have measured the size of raindrops4 ,one method of doing this is to allow the drops to fall into a shallow layer of fine1 uncompacted flour4 ,each drop forms a little pellet of dough1 which is found1 by experiments with previously measured drops 7produced for the purpose and dropped from various heights71 to correspond very closely with the size of the drop4 ,these pellets dry and harden1 and can then be carefully measured1 photographed1 etc4 ,hundreds of samples of raindrops were thus measured by ,mr4 ,w4 ,a4 ,bentley of ,jericho1 ,vt41 and the measurements were tabulated with reference to the kinds of clouds from which they fell1 the distribution of large and small drops in the different parts of a storm1 and other circumstances attending their fall4 ,drops of very different dimensions are found to fall at one time4 ,the commonest sizes recorded by ,bentley were from one-thirtieth to one-eighth of an inch in diameter2 but many drops too minute to form casts were estimated to be less than a hundredth of an inch in diameter1 while the largest drops observed had a diameter of a quarter and even a third of an inch4 ,this range of size corresponds to a range in the rate of fall from about five feet a second for the smallest drops up to about twenty-five feet a second for the largest4 ,the maximum size of raindrops is limited by the fact that very large drops are broken up in their fall through the air4 ,theoretically1 the limiting size is somewhat less than the largest sizes found by ,bentley4 ,illustration3 ,,casts ,,of ,,raindrops ,,from ,a ,,thundershower ,collected and ,photographed by ,w4 ,a4 ,bentley ,while rain is often the final product of snow that melts before it reaches the ground1 snow is probably never formed from raindrops1 but always condensed directly from water vapor4 ,the finest snow consists of separate ice crystals1 while snowflakes of larger sizes are always made up of several crystals partly melted together4 ,the flakes on rare occasions attain a diameter of three or four inches1 and larger sizes have been reported4 ,for ages mankind has admired the diversity of beautiful forms exhibited by snow crystals4 ,drawings of such crystals1 and also of the frost tracery on window-panes1 were made as early as the sixteenth century1 by the learned ,swedish historian ,olaus ,magnus1 and many collections of similar drawings have been published since his time2 but nowadays the combination of the camera and the microscope gives us a far greater wealth of information concerning these interesting objects4 ,bentley1 whose study of raindrops we have just mentioned1 has made and published photomicrographs of hundreds of different forms of snow and ice crystals1 and several collections have been published in ,europe4 ,one of the facts revealed by the camera is that the perfectly regular forms of these crystals seen in drawings are comparatively uncommon in snow as it reaches the ground4 ,a snow crystal is so fragile that it is easily mutilated by the wind and by contact with other crystals4 ,in very calm weather and at the beginning of a snowstorm many single and perfect crystals are wafted gently to the ground1 and their beauty is revealed when they fall on dark objects1 especially if they are examined with a magnifying glass4 ,in spite of their immense variety in detail1 all perfect snow crystals and other ice crystals have six sides or principal rays4 ,when secondary rays form they are parallel with the adjacent primary rays4 ,there are two principal forms of ice crystal--the tabular and the columnar4 ,sometimes the two forms are combined2 a column or rod of hexagonal section will have at one or both ends a hexagonal plate4 ,both the size and the shape of snow crystals depend to some extent upon the temperature of the air4 ,the smallest crystals form in the coldest weather4 ,star-shaped crystals are most abundant when the temperature is not far below freezing1 while at lower temperatures there is a preponderance of hexagonal plates4 ,the cohesive character of moist snow1 which is utilized by the younger generation in the making of snowballs and snow men1 enables this substance to assume naturally a variety of striking forms4 ,thus a strip of snow lying along a window ledge or the branch of a tree1 will sometimes slip down in the middle and hang in festoon-shape1 supported only at the ends1 constituting a 8snow garland40 ,over a level or gently sloping surface of snow the wind occasionally rolls muff-shaped snowballs1 which are known as 8snow rollers40 ,thousands of them are sometimes formed at once1 and the largest may grow to the size of barrels4 ,huge overhanging caps of snow formed on tree stumps1 posts1 and the like have been aptly named 8snow mushrooms0 by ,mr4 ,vaughan ,cornish1 who has described those that occur in great numbers in the ,selkirk ,mountains of western ,canada4 ,illustration3 ,,an ,,ice ,,storm ,,at ,,philadelphia1 ,,december1 #aiad4 ,the branches are broken by heavy deposits of glaze4 ,the photograph in the upper left corner1 by ,dr4 ,david ,fairchild1 shows a glaze-incased twig4 7,photographs from ,u4 ,s4 ,weather ,bureau47 ,perhaps the strangest of all the shapes assumed by snow is seen in the greatest perfection in the high ,andes of tropical ,argentina and ,chile4 ,here are found innumerable pinnacles of snow or glacier ice1 averaging from four to seven feet in height1 though sometimes much higher4 ,viewed from a distance1 they bear an uncanny resemblance to throngs of white-robed human beings1 and they have thus acquired the ,spanish name of nieve de los penitentes 78snow of the penitents074 ,in the abridged form nieve penitente this name is now applied to more or less similar formations in other mountainous regions4 ,fine examples are found in the ,himalaya1 and one of the ,himalayan peaks has been named ,mount ,nieves ,penitentes4 ,the origin of these pinnacles has been the subject of much discussion4 ,sunshine and wind both appear to take part in their formation4 ,some remarkable 8snow honeycombs10 approaching the form of nieve penitente1 are produced in hot1 dry summer weather among the glacier fields of ,mount ,rainier4 ,illustration3 ,,the ,,nieve ,,penitente ,,in ,,the ,,argentine ,,andes 7,photograph by ,dr4 ,juan ,keidel47 ,snow has its economic aspects1 comparable in importance to those of rain4 ,the problem of snow-removal crops up every winter in our ,american cities1 and is not always solved with brilliant success4 ,in the larger cities of ,europe snow is removed by spreading salt on the streets to reduce the snow to slush1 which is then washed into the sewers with water1 but this method does not seem to be generally applicable to the heavier snowfall of this country4 ,the snow-removal conference held by a number of municipal engineers in ,philadelphia in #aiad brought this difficult phase of street cleaning prominently before the engineering world1 and it has been actively discussed in recent years in the technical journals4 ,snow presents a formidable problem in the operation of many railway lines1 the solution of which takes the form of snow sleds1 fences1 plows of various types1 flangers1 gasoline torches for melting snow in switches1 etc4 ,economically1 snow is perhaps most important in its effects on water supply1 and this is true especially of mountain snowfields1 the melting of which feeds adjacent streams4 ,there are great areas in our ,western ,states where the water required for irrigation is obtained almost entirely from melting snow4 ,the mountain slopes constitute natural reservoirs1 from which the moisture that falls in the winter as snow is gradually fed through the spring and summer to the surrounding country4 ,in these regions extensive 8snow surveys0 are sometimes made in the early spring1 in order to ascertain the total amount of water available4 ,professor ,j4 ,e4 ,church1 of the ,university of ,nevada1 was one of the pioneers of this idea1 and both he and the experts of the ,weather ,bureau have developed ingenious apparatus and methods for making rapid estimates of the snowfall and its equivalent volume of water lying over a given area4 ,the snow surveyor travels over the watershed1 often on skis or snowshoes1 cutting sections of snow with a cylindrical 8snow sampler0 and weighing them with a small spring balance4 ,the ,weather ,bureau also maintains in the ,western mountains a number of special stations at which daily measurements of snowfall are made for the benefit of irrigation projects4 ,the use of 8snow bins0 and other forms of gauge for holding an entire winter's snowfall--thus obviating the necessity of frequent measurement--has not proved very satisfactory in this country4 ,an analogous device1 known in ,french as a totalisateur1 is1 however1 very extensively used in the ,swiss and ,italian ,alps4 ,the heaviest snowfall in the ,united ,states occurs in the high ,sierra ,nevada of ,california and in the ,cascade ,range of ,washington and ,oregon4 ,at places in both of these regions more than sixty-five feet of snow has fallen in a single winter4 ,the snow sometimes lies twenty-five feet deep on the ground1 burying one-story houses to the eaves4 ,a fall of snow under a cloudless sky is fairly common in the polar regions and is sometimes observed in calm and very cold weather in the temperate zones4 ,rain from a cloudless sky is a more doubtful phenomenon1 of which only a few observations are recorded1 most of them of early date4 ,if such rain occurs1 it may come from clouds that have passed beyond the horizon before the raindrops reach the earth4 ,probably the older reports of this phenomenon really relate to dew1 which was once believed to fall from the sky4 ,of the three haillike forms of precipitation that we have mentioned above1 true hail is much the most important1 on account of the large size sometimes attained by hailstones and the damage that they are consequently able to cause4 ,the maximum possible size of a hailstone cannot be positively stated1 but stones larger than a man's fist and weighing over a pound have several times been reported on good authority4 ,during a hailstorm in ,natal1 on ,april #ag1 #ahgd1 stones fell that weighed a pound and a half and passed through a corrugated iron roof as if it had been made of paper4 ,hailstones fourteen inches in circumference fell in ,new ,south ,wales in ,february1 #ahdg4 ,at ,cazorla1 ,spain1 on ,june #ae1 #ahbi1 houses were crushed under blocks of ice1 some of which are said to have weighed four and one-half pounds4 ,in ,october1 #ahdd1 a hailstorm at ,cette1 ,france1 wrecked houses and sank vessels4 ,in the state of ,bihar1 ,india1 ,october #e1 #ahic1 hail covered the ground to a depth of four to six feet2 six persons were buried beneath it and perished1 and hundreds of cattle were killed4 ,in the ,moradabad district of ,india1 ,may #a1 #ahhh1 about #bej people were killed by hail4 ,the velocity attainable by falling hailstones is perhaps most strikingly shown by the fact that1 even when falling obliquely1 they have been known to pierce a pane of glass with a clear round hole1 like a bullet hole1 leaving the rest of the pane intact4 ,hail appears to be formed in the violent updraft of air at the front of a thunderstorm4 ,in this turbulent region the hailstone1 first frozen at a high level1 probably makes several journeys alternately up and down1 as it encounters stronger or weaker rising currents2 at one time gathering a coating of snow aloft1 and at another a coat of ice from the rain below1 until finally1 on account of its large size or on account of a weakening of the upward blast1 it falls to the ground4 ,a record of these ups and downs in the life of a hailstone is seen in the concentric layers of clear and snowlike ice of which it is composed4 ,although1 from immemorial usage1 we still speak conventionally of the 8falling of the dew10 it has now been known for more than a century--especially since the publication of ,wells's 8,essay of ,dew0 in #ahad--that dew does not fall4 ,the cooling of air below the dew point of its water vapor by contact with any cold object results in a deposit of visible moisture1 which is liquid or frozen1 according to whether the temperature is above or below the freezing point1 respectively4 ,this process is not exclusively nocturnal4 ,it is observed by day in the familiar 8sweating0 of ice pitchers and also in the appearance of moisture on pavements1 stone walls1 and the like1 in places shaded from the sun4 ,at night the rapid cooling of the earth by radiation1 especially 7but not1 as often stated1 exclusively7 under a clear sky and in still weather1 favors this condensation of moisture1 in the liquid form1 as dew1 or in the frozen form1 as hoarfrost4 ,the deposit occurs most copiously on objects that lose heat rapidly by radiation and gain it but slowly by conduction4 ,water vapor exhaled from the tissues of plants and from the soil undoubtedly contributes its quota to the moisture available for condensation1 but this hardly seems to be a reason for asserting1 as some writers have done1 that dew comes mainly from the earth rather than the air4 ,hoarfrost is often described as 8frozen dew40 ,this expression is misleading1 for1 although dew-drops are sometimes frozen into little globules of ice1 hoarfrost is more often condensed directly from atmospheric water vapor in the shape of ice crystals4 8,glaze0 and 8rime0--to use the latest official designations of the two kinds of ice coating formed from water in the atmosphere--differ greatly in appearance1 as a rule1 though transition forms are sometimes found4 ,glaze is produced by the falling of rain on surfaces whose temperature is below freezing1 and is typically smooth and transparent4 ,rime is a rough deposit formed from fog1 the drops of which are 8undercooled0--i4 e41 are below the freezing point--and turn to ice on coming in contact with solid objects4 ,the most remarkable examples of rime are seen on mountains and in the polar regions4 ,it occurs on the branches and leaves of trees1 and on the corners and edges of upright objects1 rather than on horizontal surfaces4 ,in drifting fog it grows most rapidly if not entirely on the windward side of objects--i4 e41 it builds up against the wind4 ,on ,ben ,nevis it has been observed to grow at a rate of more than an inch an hour4 ,trees1 posts1 telegraph poles1 and the like are thus eventually changed to shapeless masses of rough or feathery ice4 ,,chapter ,,viii ,,winds ,,and ,,storms ,the study of the movements of the atmosphere constitutes a rather formidable branch of science known as dynamic meteorology4 ,this subject has engaged the attention of a number of able physicists--though far too few--and has begun to assume the character of an exact science1 but is still fruitful of unverified hypotheses4 ,we shall have only a little to say here about the theories and hypotheses relating to atmospheric circulation4 ,they are at present1 to a notable degree1 in process of revision4 ,important modifications in them have resulted from the revelations of upper-air research1 as well as from progress in other fields of inquiry4 ,there are1 however1 a few fundamental matters that we must not ignore4 ,we shall start with the solar heat that keeps the atmospheric machinery in motion4 ,of the heat that comes to us from the sun1 it is estimated that more than one-third is reflected by clouds and the earth1 or scattered by dust and air molecules1 and thus passes back into space without having had any effect in heating the atmosphere4 ,part of the remainder heats the atmosphere directly1 and the rest indirectly1 after first heating the underlying land and water4 ,in both cases1 certain atmospheric gases--notably water vapor--absorb a great deal more heat than others4 ,the first step in the production of a wind is a difference in temperature between two parts of the earth's surface1 and hence of the overlying air4 ,such contrasts of temperature always exist1 both locally and on a large scale4 ,the high sun of the equatorial regions heats the earth much more strongly than the low sun of high latitudes2 a water surface has a more equable temperature than an adjacent land surface2 a stretch of bare earth is warmer by day and colder by night than a neighboring tract covered with vegetation2 and so on4 ,differences in atmospheric temperature produce differences in pressure1 which gravity tends to adjust by setting up a circulation4 ,the exact manner in which this circulation is begun and maintained is not yet perfectly clear1 and current ideas on the subject are difficult to put into brief language4 ,meteorological writers now lay less stress than formerly upon the lateral spreading1 at high levels1 of air that has been heated and expanded at the earth's surface1 and the inward flowing of the lower air toward the heated area4 ,there is1 we know1 an initial impulse that tends to drive air from a region of high pressure toward a region of low pressure2 but the actual movement of the air is another matter4 ,the 8life history0 of an air current is found to be a very devious affair4 ,the important fact1 for practical purposes1 is that air does not flow in a straight line from the place where the pressure is high to that where it is low4 ,as soon as it begins to flow it curves from the straight path1 in accordance with ,ferrel's ,law1 which is thus stated3 8,in whatever direction a body moves on the surface of the earth1 there is a force arising from the earth's rotation that deflects it to the right in the northern hemisphere1 and to the left in the southern hemisphere40 ,this law applies to all bodies moving freely over the earth1 and not merely to the winds4 ,at the earth's surface1 if the atmospheric pressure is measured simultaneously at various places by means of barometers1 we can get a clear picture of the horizontal distribution of pressure by drawing on a map lines1 called isobars1 through places at which the pressure is identical4 ,the isobars reveal the presence of extensive areas over which the pressure is above the average and of others over which it is below the average4 ,if1 at the same time1 we chart the flow of air by indicating the direction of the winds at various points1 we shall notice that the air shows a strong tendency to travel around these areas2 and if we could observe its course a thousand feet or so above the earth we should find the tendency even more pronounced at that level4 ,another important law1 springing in part from ,ferrel's ,law and describing the movements of the air around areas of high and low pressure1 is called ,buys ,ballot's ,law4 ,one way of stating this law is as follows3 8,if you stand with your back to the wind1 in the northern hemisphere1 the barometer will be lower on your left than on your right4 ,the reverse is true in the southern hemisphere40 ,the reader1 whether he lives in the ,united ,states or any other civilized country1 will have no difficulty in securing documentary evidence of the correctness of ,buys ,ballot's ,law in the shape of the daily weather maps issued by the various meteorological services4 ,on a weather map showing conditions anywhere in the northern hemisphere it will be found that the winds 7which are indicated by little arrows71 though subject to a good many local variations1 have a general tendency to blow in the direction followed by the hands of a clock 78clockwise07 around an area of high pressure1 and in the opposite direction 78counterclockwise07 around an area of low pressure4 ,it will likewise be noticed that1 in general1 the winds1 instead of blowing along the isobars1 are strongly inclined inward in the case of a low-pressure area and outward in the case of a high-pressure area4 ,lastly1 if the map indicates the force of the winds at different places1 it will be seen that winds are strongest where the isobars are close together and weakest where they are far apart4 ,it is a matter of much interest to aeronauts that the force of the wind generally increases with altitude1 and that1 in the lower flying levels1 the winds are little1 if any1 inclined to the isobars4 ,the spacing of the isobars is called the barometric gradient4 ,one of the conventional ways of expressing a gradient numerically is to state the horizontal difference of pressure1 in hundredths of an inch1 for an interval of fifteen nautical miles2 but meteorologists as a rule merely describe gradients as 8steep10 8gentle10 8moderate10 etc41 without indicating their numerical values4 ,if the great difference in temperature between the equatorial and polar regions were the only factor in the control of atmospheric circulation1 there would be a strong barometric gradient between these regions and there would result a simple circulation of winds1 blowing poleward from the equator aloft and equatorward from the poles at the earth's surface4 ,the former tendency of writers on meteorology and physical geography was to regard such a circulation as a substantial fact1 though modified by the effects of the earth's rotation and various local causes4 ,thus the idea has prevailed of a wholesale1 direct exchange of air between the poles and the equator4 ,nowadays we can hardly maintain this idea1 because we see that1 on account of the great deflections they undergo1 the main drifts of air are approximately along parallels of latitude and not along meridians of longitude4 ,within the tropics the general drift of the lower air is from the east 7and near the equator this drift prevails up to a great height72 in middle latitudes it is from the west2 and in the circumpolar regions it is again from the east4 ,air from the equator presumably does find its way to high latitudes1 and vice versa1 but neither rapidly nor directly4 ,perhaps the dominant feature of the whole circulation is the banking up of the air in so-called high-pressure belts at about latitude #cj ,north and ,south4 ,from these 8belts0--which are really broken up into separate areas of high pressure1 and which shift north and south to a certain extent with the seasons--blow the northeast and southeast trade winds1 in the full development of which1 found only over the ,atlantic and the eastern ,pacific1 we have the most remarkable 8permanent winds0 of the globe4 ,between the trade wind belts lies the equatorial region of low pressure1 known as the 8doldrums40 ,this is1 in general1 a region of light and variable winds1 heavy rains1 and thunderstorms4 ,in the temperate zones of both hemispheres1 on the poleward side of the high-pressure belts above mentioned1 the general drift of the atmosphere near the earth's surface is from west to east4 ,in the south temperate zone there is a very strong preponderance of west winds1 especially over the vast oceanic tract of the 8roaring forties10 where blow the boisterous 8brave west winds10 well known to sailors4 ,the corresponding belt of the northern hemisphere1 which includes all but the southernmost part of the ,united ,states1 is described as a region of 8prevailing westerly winds10 but it is also a region of storm tracks1 and hence1 as local episodes in the general movement of the atmosphere from west to east1 there are constant shifts of the wind to all points of the compass1 for reasons that will presently be explained4 ,on the poleward borders of the two belts of 8prevailing westerlies10 a little outside the ,arctic and ,antarctic ,circles1 there are zones of low pressure4 ,that of the southern hemisphere is a continuous girdle around the earth1 and has the lowest pressures found anywhere in the world4 ,the corresponding subarctic zone1 while fairly continuous in summer1 is broken up in winter by the formation of high-pressure areas over ,siberia and northern ,canada4 ,the permanent ice sheets of ,greenland and ,antarctica are regions of high pressure1 with calm air in the interior and strong outblowing winds at the borders4 ,furious blizzards prevail at the margin of ,antarctica4 ,the table on the opposite page will serve as a recapitulation of the facts above stated4 ---------------------------------------- --------------------------- ,,north ,,pole ,calms and high pressure over the interior of ,greenland4 ,out-blowing winds at the border4 ,more or less broken subarctic belt of low pressure4 ,prevailing westerlies 7much interrupted by moving cyclones and anticyclones74 ,belt of high pressure at about lat4 #cj ,n4 8,horse latitudes10 or 8calms of ,cancer40 ,northeast trade winds4 ,equatorial belt of low pressure1 calms1 and variable winds4 ,the 8doldrums40 ,southeast trade winds4 ,belt of high pressure at about lat4 #cj ,s4 8,calms of ,capricorn40 ,prevailing westerlies1 more constant than in the northern hemisphere4 8,brave west winds40 ,subantarctic belt of very low pressure4 ,calms and high pressure over the interior of ,antarctica4 ,violent outblowing winds at its border4 ,,south ,,pole ---------------------------------------- --------------------------- ,,wind ,,and ,,pressure ,,belts ,,of ,,the ,,globe4 ,the great wind and pressure belts of the globe are much more constant and sharply defined over the oceans than over the land1 and it was upon the high seas that mankind first distinguished them and gave them their names4 ,the northeast trade winds of the ,atlantic wafted ,columbus to the ,new ,world and aroused the misgivings of his sailors1 who wondered how they should ever sail homeward against them4 ,the high-pressure belt north of these trade winds is a region of calms1 which ,maury called the 8calms of ,cancer40 ,this region1 or a part of it1 is likewise known as the 8horse latitudes10 the story being that1 in the old sailing days1 vessels laden with horses were often becalmed here so long that the cargoes had to be thrown overboard4 ,as a matter of course1 the prosaic modern etymologist declines to accept this origin of the name and has proposed others less picturesque4 ,the so-called equatorial calms1 which lie mostly a little north of the equator1 are often nicknamed the 8doldrums10 or sometimes the 8equatorial doldrums10 to distinguish them from other regions of dolorous1 baffling calms4 ,the doldrums vary a great deal in width and the masters of sailing ships try to cross them where they are narrowest4 ,the name of the trade winds implies that1 according to the old nautical phrase1 they 8blow trade10 or constantly in one direction4 ,strictly speaking1 they vary considerably in direction1 at any one spot1 though they are nearly always from an easterly quadrant1 and they are even more variable in force4 ,the average speed of the ,atlantic trades is about eleven miles an hour4 ,in view of the prospective requirements of aeronauts1 it is a fact of much interest that the trades are rather shallow winds4 ,their vertical thickness has been found1 by observations with pilot balloons and otherwise1 to range from less than a mile to two or three miles4 ,some distance above the trades there are winds blowing more or less in the opposite direction1 known as the counter-trades4 ,aircraft will probably use the trade winds in flying from southern ,europe to the ,caribbean1 and the countertrades on the return voyage to ,europe4 ,in contrast to the permanent or quasi-permanent winds just described1 there are certain important winds of the 8periodic0 type1 which reverse their directions in the course of the year or from day to night4 ,some of these1 also1 first became generally known through the reports of mariners4 ,the ancient ,greek navigators utilized the monsoons in trading with ,india2 while we owe to the voyages of ,william ,dampier1 in the seventeenth century1 one of the earliest and best descriptions of land and sea breezes4 ,a monsoon is a wind that blows from a continent toward the sea in winter1 when the land is colder than the water1 and in the opposite direction in summer1 when the reverse conditions of temperature prevail4 ,the pressure gradient is reversed with the seasons1 and the wind varies accordingly4 ,the most striking example of monsoon winds is found in southern ,asia--where these winds are of special economic importance because they control the rainfall of ,india--but well-developed monsoons also occur in ,australia and ,west ,africa1 over the ,caspian ,sea1 on the coast of ,texas1 and elsewhere4 ,an analogous reversal of gradients1 due to the change of temperature over the land from day to night1 is of common occurrence on the shores of large bodies of water1 resulting in land and sea breezes 7or land and lake breezes74 ,the breeze blows from the land to the water by night and in the opposite direction by day4 ,these breezes are generally best developed and most regular within the tropics1 and particularly on shores adjacent to mountains4 ,east ,indian fishermen put out to sea with the land breeze in the early morning and come home with the sea breeze in the afternoon4 ,the refreshing and health-giving character of the sea breeze of tropical climates has earned it the sobriquet of 8the doctor40 ,mountain and valley breezes furnish another example of diurnally reversed winds4 ,relatively cold and heavy air drains down from the upper slopes by night1 constituting the mountain breeze4 ,by day the air in the valley is warmed and expanded1 and as it is confined laterally by the sides of the valley it flows up the slopes1 constituting the valley breeze4 ,long before meteorologists undertook to classify the winds of the globe1 these mountain air currents attracted attention and acquired local names4 ,among the ,alps1 alone1 we find scores of such names4 ,in many cases1 too1 the breezes have acquired a legendry of their own4 ,thus the pontias1 a cold1 nocturnal wind that blows out of a narrow valley opening upon the plains of the ,rhne near the town of ,nyons1 is said to have been brought thither in a glove by ,st4 ,csarius1 ,archbishop of ,aries1 for the purpose of improving the fertility of the valley6 ,there is a quaint little book about the pontias1 published by ,gabriel ,boule in #afdg1 in which the author sets forth at length the arguments for and against the miraculous origin of this wind4 ,the ,italian lakes are especially rich in locally named mountain and valley breezes4 ,parenthetically it may be remarked that wind nomenclature in general is a vast subject1 owing to the habit that prevailed in prescientific times1 and still prevails to some extent among nonscientific people1 of giving individual names to the winds characteristic of different localities4 ,as a matter of curious interest1 we set down here some of these names 7a small fraction of the total number73 ,khamsin1 leveche1 leste1 levanter1 pampero1 zonda1 papagayo1 buran1 purga1 brickfielder1 southerly burster1 williwaw1 willy-willy1 pontias1 vsine1 solore1 joran1 morget1 rebat1 vaudaire1 breva1 tivano1 ora1 ,wisperwind1 ,erlerwind1 ,rotenturmwind1 vent du ,mont ,blanc1 vent d'aloup1 autan1 tramontana1 gregale1 imbat1 kite and junk winds1 bad-i-sad-o-bist roz 7the furious 8wind of #abj days0 of ,persia and ,afghanistan74 ,the present writer has collected several hundred local wind names--and is constantly adding to the list4 ,there are several other types of wind peculiar to mountains besides the alternating mountain and valley breezes4 ,most of these are descending winds1 or 8fall winds10 which may blow by day as well as by night4 ,thus a strong daytime wind sometimes blows down from lofty snowfields and glaciers4 ,a foehn 7pronounced like 8fern10 but without the r7 is a wind that has been robbed of most of its moisture through precipitation on the windward slope of mountains and which is further dried1 and also strongly heated by compression1 in descending the leeward slope4 ,winds of this type are common in the ,alps1 where they were first described and named1 and their heat and aridity led to the belief that they came by way of the upper atmosphere from the distant deserts of ,africa4 ,now that their origin is better understood1 we find that foehns prevail in many other mountainous countries throughout the world1 including the western ,united ,states1 where they are called chinooks4 ,when the foehn blows in winter1 it causes snow to disappear with amazing rapidity--not only melting it1 but speedily drying the ground--whence it has earned the name of 8snow eater0 in ,america1 and 8,schneefresser10 which means the same thing and a little more1 in ,switzerland4 ,the bora of the ,adriatic and the mistral of southern ,france are winds that blow from a cold1 mountainous interior down to a warm coastal region1 where they arrive as relatively cold winds1 in spite of the dynamic heating they have undergone in their descent4 ,the bora is sometimes moderate 7borina7 and at other times a tremendous gale 7boraccia71 while the mistral has been known to blow a railway train from the track in the valley of the ,rhne4 ,the blizzard is a wind of which ,americans once thought they had almost a monopoly until ,sir ,douglas ,mawson located the 8home of the blizzard0 on the shores of the ,antarctic continent4 ,the true blizzard1 whether ,american or ,antarctic1 is a violent1 intensely cold wind1 heavily charged with snow4 ,such winds are a characteristic feature of the winter climate of our ,middle ,western ,states4 ,although the name of this wind first became current as recently as the seventies of the last century1 nobody knows its origin4 ,nowadays the name is often loosely applied to big snowstorms that are not really blizzardlike4 ,the dry 8hot winds0 that sometimes wither the crops of our western plains are the ,american antithesis of the blizzard4 ,these winds belong to the great sirocco family--the name 8sirocco0 having become1 in recent scientific usage1 a generic designation for extensive hot winds1 whether dry or moist1 as distinguished from local hot winds1 such as the foehn4 ,the harmattan of ,west ,africa is a dry1 dusty wind from the ,sahara1 and one that feels relatively cool2 perhaps on account of causing rapid evaporation from the skin4 ,the simoom 7with a final m71 especially the variety blowing in southern ,asia1 is perhaps the hottest and most parching of all winds--judging from its effects on animal life4 ,the great majority of the winds above enumerated are merely minor features of what are called cyclonic and anticyclonic wind systems4 ,reverting to what has been said about weather maps and ,buys ,ballot's ,law--if the reader will examine a series of maps for successive days1 he will notice that the areas of high pressure and low pressure are not stationary1 but show a more or less rapid displacement1 the general direction of which1 in our latitudes1 is from west to east4 ,the fact that there are great traveling vortices or swirls in the atmosphere1 which1 in whatever regions they occur1 partake of the general drift of the air around the globe1 has been known for about a century1 and constitutes the corner stone of practical meteorology4 ,in the temperate zone1 where these swirls are sometimes of moderate force and sometimes very stormy1 they are the chief factor in controlling changes of weather from day to day1 and their observation is the basis of weather forecasting4 ,within the tropics1 where they are much less frequent and are confined to a few restricted regions1 they are always violent storms4 ,an area of high pressure1 with its attendant system of winds1 is called an anticyclone or high4 ,an area of low pressure1 with its winds1 is called a cyclone--sometimes4 ,the word 8cyclone0 was invented by ,henry ,piddington in the year #ahdh4 ,nearly all the early studies of cyclones were made chiefly for the benefit of mariners1 and related to the severe revolving storms encountered at sea4 ,hence the word 8cyclone0 passed into the general vocabulary with a connotation of violence1 which1 in everyday speech1 it still retains4 ,perhaps the early 8cyclonologists0 themselves hardly realized that a 8gentle cyclone0 was not a contradiction in terms4 ,meteorologists are still so much under the influence of the popular idea of a 8cyclone0 that they hesitate to apply this term to a disturbance of moderate force1 except in a few special phrases 7such as 8extra-tropical cyclone071 though the adjective 8cyclonic0 is used freely without reference to the force of the wind4 ,british meteorologists speak mostly of 8depressions10 while ,american meteorologists speak of 8lows40 ,the status of the latter term1 as well as that of the term 8high10 is1 however1 paradoxical4 ,though both words have been used for years1 they are nearly always printed with quotation marks around them1 as if they had not yet been assimilated in the vocabulary4 ,the ,weather ,bureau has lately taken to printing these words in capital letters4 ,neither of these practices will be followed in the present book4 ,illustration3 ,,photo ,,by ,,prof4 ,,ellerman ,,showing ,,clouds ,,or ,,fog ,,cascading ,,through ,,last ,,fork ,,ca,,on ,,and ,,into ,,the ,,santa ,,anita ,,ca,,on4 7,letter from ,f4 ,a4 ,carpenter1 ,may #bi1 #aiai47 ,tropical cyclones are called 8hurricanes0 in the ,west ,indies and the ,south ,pacific1 8typhoons0 off the east coast of ,asia1 8baguios0 in the ,philippines1 and 8cyclones0 in the ,indian seas4 ,they form in the doldrums1 and generally take a long1 sweeping course1 curving westward and poleward1 and sometimes passing into the temperate zones1 where they either die out or increase in size1 diminish in violence1 and become similar to the storms originating in the higher latitudes4 ,one of the curious features they often exhibit within the tropics is the calm center at the 8eye of the storm10 to which ,tennyson alludes when he writes of the blast 7unknown to meteorologists7 that drove a ship ,across the whirlwind's heart of peace1 ,and to and thro' the counter-gale4 ,these cyclones are the worst of all storms found at sea1 and also exercise their destructive effects over islands and along continental coasts4 ,the greatest disasters attending them have been due to the inundation of low-lying shores by the huge waves they generate1 as in the ,galveston hurricanes of #aijj and #aiae and in the far worse catastrophes that have occasionally visited the coast of ,india4 ,hurricanes of the ,west ,indies occur chiefly from ,august to ,october1 inclusive4 ,the number varies from none to a dozen a year 7with four as an average74 ,illustration3 ,copyright1 ,ewing ,galloway ,a ,,cloudburst ,,near ,,cedar ,,brakes1 ,,utah ,a snapshot taken from the edge of the caon4 ,over the large land areas of the north temperate zone highs and lows show a tendency to travel over typical tracks1 the locations of which vary a good deal with the season4 ,one of the most remarkable facts about the lows of ,north ,america is that1 wherever they come from1 whether from the ,canadian northwest1 the western ,united ,states1 or the ,west ,indies1 they nearly always leave the continent by way of the ,gulf of ,st4 ,lawrence or the northeastern corner of this country4 ,our ,north ,american lows travel at an average speed of #fjj miles a day4 ,highs travel somewhat more slowly2 about #edj miles a day is the average in this country4 ,a tornado is a small vortex in the atmosphere1 occurring generally in the southeastern part of a cyclonic area1 where1 in some cases1 several separate tornadoes develop at the same time4 ,the tornado1 for some reason that is not altogether clear1 is far more common in the interior of ,north ,america1 east of the ,rocky ,mountains1 than anywhere else in the world1 though true tornadoes do occur in other countries4 ,the ,west ,african storms bearing this name are merely thundersqualls1 quite different from the ,american tornado4 ,the chief visible feature of a tornado is the so-called funnel-shaped cloud 7sometimes balloon-shaped or1 again1 like a great coiling serpent71 which is always in contact with the ground when destruction is in progress4 ,the passage of the storm is attended by a loud roaring or rumbling4 ,the path of a tornado varies in width from a few rods to half a mile or 7rarely7 more4 ,within its borders buildings are blown to pieces1 trees are uprooted and human beings only find safety underground2 while even at a distance of a few yards outside the path no damage is done4 ,the tornado travels at an average speed of about twenty-five miles an hour4 ,its speed of rotation has been estimated1 from the effects produced1 to amount to #ejj miles an hour in some cases2 a wind force far exceeding that of any other type of storm4 ,waterspouts1 which occur on the ocean and other large bodies of water1 are similar in character to tornadoes1 though much less violent4 ,they range in height from #ajj to #a1jjj yards1 or more4 ,one measured recently from the ,british steamer ,war ,hermit1 near ,cape ,comorin1 was #d1fjj feet high to the base of the overlying cloud4 ,the column tapered from #ejj feet wide at the junction with the cloud to #aej feet wide at the sea4 ,spray was thrown up to a height of more than #hjj feet over a region #bej feet in diameter4 ,thunderstorms occur chiefly in warm climates and during the warm season in temperate climates1 but they are by no means unknown in the polar regions4 ,they are characterized by rapidly rising air currents1 which may be either incidental to the circulation of a low1 or due to local overheating of the lower atmosphere4 ,in the former case they are called 8cyclonic thunderstorms10 and in the latter 8heat thunderstorms40 ,this is only a rough classification1 however4 ,some thunderstorms partake of the features of both these types1 and1 on the other hand1 additional classes are distinguished by many authorities4 ,it is a common occurrence for thunderstorm conditions1 starting in some small area1 to travel across country at a speed of perhaps thirty or forty miles an hour1 at the same time spreading out fanwise until the front of the storm is hundreds of miles in length4 ,this front constitutes a 8line squall0 7so called from the long line or apparent arch of dark cloud that marks its location71 and is attended by more or less thunder and lightning1 but is not necessarily a continuous thunderstorm4 ,the characteristic wind of a thunderstorm is the squall that rushes out in front of the storm when close at hand4 ,this blast of wind1 lightning1 hail and torrential rain are all agencies of destruction in severe thunderstorms4 ,illustration3 ,,ideal ,,cross ,,section ,,of ,a ,,typical ,,thunderstorm ,a1 ascending air2 ,d1 descending air2 ,c1 storm collar2 ,d'1 wind gust2 ,h1 hail2 ,t1 thunderheads2 ,r1 primary rain2 ,r'1 secondary rain4 7,w4 ,j4 ,humphreys47 ,concerning the winds of the globe in general and the remarkable atmospheric interchanges that they involve1 ,sir ,napier ,shaw writes3 8,of the millions of tons of air which form the atmosphere nearly the whole is moving4 ,the regions of calm at the surface at any one time1 taken all together1 do not form a large part of the earth's surface1 and above the surface calm regions are still rarer4 ,let us remember that the motion of the air is always #8circulation'2 air cannot move forward or backward or upward or downward without displacing other air in front of it and being replaced by other air behind it1 though the circulation may be quite local and limited in extent1 as is frequently the case when warm air rises or cold air sinks4 ,in the course of investigations into the life history of surface air currents in the ,meteorological ,office we have traced air over long stretches of the surface of the ,atlantic4 ,we have found1 on one occasion1 the shores of ,greenland to be fed with air that left the middle of the ,atlantic four days previously1 while in the course of six days air traveled from ,spitsbergen to join the northeast trade wind off the west coast of ,africa4 ,on another occasion the air that formed the wind off the south of ,ireland was traced back to the north of ,africa1 but that which blew at the opening of the ,channel two days later came from ,hudson ,bay1 via the ,azores40 ,such are the ever-shifting currents of the ocean of air4 ,,chapter ,,ix ,,atmospheric ,,electricity ,every schoolboy has read how ,benjamin ,franklin1 by means of his famous kite experiment1 demonstrated the electrical nature of lightning1 and how the same versatile genius invented the lightning rod4 ,it is not proposed to repeat familiar history here4 ,neither shall we discuss the dubious statements frequently put forth that lightning rods were known before ,franklin's time1 nor consider how much credit is due the many philosophers who1 at earlier periods1 suspected lightning to be a manifestation of electricity4 ,the facts and ideas concerning atmospheric electricity that we have to present in this chapter were1 for the most part1 quite unknown to ,franklin and to many generations of savants after him1 and some of them are just now finding their way into the textbooks4 ,science still recognizes the existence of two kinds of electricity--positive and negative--which1 by combining1 neutralize each other's effects4 ,according to current ideas1 however1 the more active agent in electrical phenomena is negative electricity1 which is believed to consist of 7or to provide electrical charges for7 exceedingly minute particles called electrons4 ,only a few years ago the smallest thing that science had to deal with was the atom1 and the lightest of atoms is that of hydrogen4 ,the discovery of electrons marks a new step toward the infinitely little4 ,the mass of the electron--or1 in more popular and less exact terms1 its weight--is about #a_/ahjj that of a hydrogen atom4 ,as to its size3 ,imagine a billiard ball magnified to the size of the earth4 ,its constituent atoms would be the actual size of billiard balls1 but the electrons of which each atom is composed would still be too small to be seen with the naked eye4 ,now imagine each of these billiard-ball atoms further magnified to the size of a large church4 ,the electrons would then be about as big as one of the periods on this page4 ,when we say that a body has an electrical charge we mean that it has an excess of positive or negative electricity4 ,an ordinary molecule of an atmospheric gas contains 7or perhaps actually consists of7 equal amounts of the two kinds of electricity1 and is therefore not charged4 ,there are1 however1 various ways in which an electron may be detached from such a molecule1 leaving it positively charged2 and again it may receive an extra electron1 and thus acquire a negative charge4 ,under the former circumstances it becomes a positive ion1 and under the latter a negative ion4 ,ions play a very important role as carriers of electricity1 because they are impelled to move toward oppositely charged bodies or particles and combine with them4 ,a gas containing ions is said to be ionized2 and it is the ionization of the atmosphere that makes it a conductor of electricity4 ,the number of ions in a given volume of air has been the subject of a great many measurements1 both at observatories on land and in the course of scientific expeditions at sea4 ,there are ingenious instruments called 8ion counters10 in which air is drawn at a measured rate through the apparatus and its electrical effects are noted4 ,the number of positive ions found in a cubic centimeter of the lower atmosphere varies from a few hundred to a thousand or more1 while the number of negative ions in the same space is generally one or two hundred smaller4 ,the ionization is about the same over the ocean as over the land4 ,there are several ways in which the air may become ionized4 ,the different rays given off by radioactive substances 7,alpha1 ,beta1 and ,gamma rays7 all have the power of driving off electrons from the molecules of gases2 i4 e41 ionizing them4 ,air is undoubtedly ionized by radioactive matters in the soil 7radium and thorium7 and especially by the gaseous 8emanations0 of these substances in the atmosphere1 which are also radioactive4 ,it has1 however1 been a problem to account for ionization over the ocean2 because the amount of radioactive matter in sea water is immeasurably small1 while the amount of radioactive emanation in sea air is1 according to the latest observations1 only about #b4e per cent of that occurring over the land4 ,the clue to this mystery seems to be found in a special kind of ,gamma rays coming from some region far above the surface of the earth4 ,these rays are called the 8penetrating radiation10 because they not only are able1 like the ,gamma rays due to radioactive substances on earth1 to pass through the walls of hermetically sealed metal vessels and ionize the air inside1 but they also have the power of passing through a great extent of atmosphere without being absorbed4 ,they are estimated to be about ten times as 8penetrating0 as the ,gamma rays coming from known terrestrial substances4 ,the best proof that a radiation of this sort comes from above is that when closed metal vessels are carried up in balloons1 there is1 above an altitude of about half a mile1 a rapid increase in the rate at which ions are produced within them4 ,as to the source of this radiation1 one suggestion has been that it comes from strongly radioactive cosmic dust in the upper atmosphere4 ,a hypothesis that seems more plausible at present attributes it to the bombardment of the atmosphere by electrons shot off from the sun4 ,the knowledge of ions in the atmosphere is one of the recent acquisitions of science4 ,on the other hand1 it has been known for some generations that the earth has normally a negative charge as compared with the air1 or the air a positive charge as compared with the earth4 ,thus between the earth and any point in the air 7except1 as we now know1 at great altitudes7 there is a difference of what is called 8potential10 of such a character that negative electricity will follow any conductor provided for it away from the earth4 ,variations of potential with altitude have long been measured by means of instruments called 8collectors10 which gather1 so to speak1 a sample of the electrical charge of the air at any point and enable it to be compared with that of the earth4 ,the difference of potential is measured in volts per meter of vertical distance4 ,thus we get the 8potential gradient10 which averages about #aej volts per meter in the lowest part of the atmosphere4 ,it is subject to great irregular variations--especially during thunderstorms--and also to somewhat regular rises and falls during each day1 and to an annual fluctuation1 being much greater in winter than in summer4 ,it has also been known for a good many years that the air is a conductor of electricity--though a poor one--and1 therefore1 does not insulate the earth4 ,dr4 ,w4 ,f4 ,g4 ,swann has expressed the extremely small conductive capacity of the air for electricity in the statement that a column of it one inch long offers as much resistance to the passage of an electrical current as a copper cable1 of the same cross section1 thirty thousand million million miles long6 ,a fact more recently learned1 from observations in balloons1 is that the potential gradient falls off rapidly at high levels1 and becomes practically zero at an altitude of about six miles4 ,from this fact it is concluded that the lower six miles of the atmosphere contains a charge of positive electricity just equal to the negative charge at the earth's surface4 ,in other words1 the lower atmosphere is not only positive with respect to the earth1 but in an absolute sense it contains an excess of positive electricity4 ,thus we have a negatively charged earth surrounded by a layer of positively charged air4 ,since air is a conductor1 it is not easy to see why the opposite charges of the earth and the atmosphere do not combine and neutralize each other4 ,an interchange is1 in fact1 always going on between them2 negative ions flow upward from the earth and positive ions flow in the opposite direction4 ,this 8earth-air current0 is1 however1 exceedingly small4 ,moreover1 the opposite charges of the earth and air remain from year to year in spite of it4 ,how does the earth retain its negative charge and the air its positive charge8 ,no other question relating to atmospheric electricity has1 in recent years1 been so much debated as this4 ,discussion centers1 as a rule1 upon the negative charge of the earth2 for there are certain reasons for assuming that1 when once this is explained1 the positive charge of the atmosphere will require no special explanation4 ,one hypothesis is that the earth is bombarded by positive and negative corpuscles from the sun1 and that the negative corpuscles have such penetrating power that they are able to reach the earth1 while the positive corpuscles are caught by the atmosphere4 ,another hypothesis 7,swann's7 is that the same 8penetrating radiation0 that1 as we have seen1 helps to ionize the lower atmosphere has the effect of driving downward a stream of electrons detached from the air molecules1 thus maintaining a constant supply of negative electricity to the earth4 ,the question is not yet settled4 ,it is now time to turn from these somewhat abstruse matters to a subject of universal interest2 viz41 lightning4 ,as recently as a few decades ago1 though there was already a copious literature on the subject of lightning1 very little was really known about it4 ,even its superficial features were strikingly misunderstood until the advent of photographic methods of investigation4 ,thus until the middle of the nineteenth century sharply zigzag lightning flashes were represented in scientific books as they still are in conventional art4 ,that so-called zigzag lightning is really sinuous was first asserted by ,james ,nasmyth1 in #ahef1 and his contention was soon afterward confirmed by photography4 ,the camera has revealed a large number of other interesting things about lightning4 ,everybody has noticed an appearance of flickering in lightning flashes that are of sensible duration4 ,several early investigators1 such as ,arago1 ,dove1 and ,o4 ,n4 ,rood1 had reached the conclusion that such flashes are multiple1 consisting of several successive discharges along an identical path4 ,rough measurements of the intervals of time between these discharges were made with various forms of rotating disk4 ,far more accurate information is now obtained on this subject by the use of a camera mounted on a vertical axis and swung in a wide arc1 at a fixed rate1 by clockwork4 ,the perfection of this device is due1 in part1 to ,a4 ,larsen1 in ,america1 but especially to ,dr4 ,b4 ,walter1 of ,hamburg1 whose achievements in the photography of lightning far surpass those of any other investigator4 ,it is obvious that if a discharge of lightning is not instantaneous1 but has a sensible duration1 the rotary movement of the camera1 arranged as just mentioned1 will spread out the image of the flash1 on the photographic plate1 into a more or less broad band or ribbon4 ,most photographs of ribbonlike streaks of lightning made with ordinary cameras are1 in fact1 due to accidental movements of the apparatus during exposure--such as an involuntary start of the operator1 in case the camera is held in the hands--though a certain amount of spreading of the image is sometimes caused by what photographers call 8halation40 ,pictures taken with the revolving camera show that some flashes are practically instantaneous while others may last as long as half a second or more4 ,those of the latter class nearly always show several parallel streams of light1 more or less distinctly separated by darker spaces4 ,each of these bright streams represents a separate discharge along the common path4 ,as the speed with which the camera turns is known1 it is possible to determine the intervals of time between the discharges of a multiple flash4 ,these intervals may vary from a few thousandths to one or two-tenths of a second1 while the duration of each of the consecutive discharges is probably not more than two or three hundred-thousandths of a second in most cases4 ,sometimes the path of the lightning flash is shifted by the wind while the picture is being taken4 ,in one case this shift was estimated at #cf feet4 ,photography is also applied to determining the distance of a lightning flash and hence the dimensions of any of its features4 ,for this purpose a stereoscopic method is used1 two cameras being mounted side by side and exposed at the same time4 ,sometimes one of the cameras is made to revolve1 while the other remains stationary4 ,the stationary camera will then show the relative positions of the flashes occurring during exposure1 while the moving camera will indicate the times at which they occurred4 ,streaks of 8black lightning0 and black borders of the white flashes1 both often seen in photographs1 are a trick of the camera and are due to what is called the 8,clayden effect40 ,some kinds of plates are much more susceptible to this effect than others4 ,when a flash of lightning has registered its impression on such a plate1 and1 before the shutter is closed1 another flash occurs1 the general illumination of the field by light reflected from clouds1 etc41 often 8reverses0 the original image1 and consequently it prints black4 8,sheet lightning0 presents the appearance of a diffuse glow over the sky4 ,when lightning of this character is seen playing about the horizon on summer evenings1 in the absence of an audible thunderstorm1 it is often called 8heat lightning40 ,most sheet lightning is probably a mere reflection of ordinary streak lightning below the horizon or hidden by clouds4 ,some authorities believe1 however1 that diffuse1 silent discharges actually occur in the clouds4 ,balloonists claim to have encountered such discharges near at hand4 ,an analogous phenomenon is the glowing of so-called 8incandescent0 or self-luminous clouds1 to which several observers have called attention4 ,a remarkable phenomenon of somewhat similar character has been reported by ,dr4 ,knoche1 late director of the ,chilean meteorological service1 who states that it occurs on a vast scale along the crest of the ,andes during the warm season4 ,the mountains seem to act as gigantic lightning rods1 giving rise to more or less continuous diffuse discharges between themselves and the clouds1 with occasional outbursts simulating the beams of a great searchlight4 ,these displays are visible hundreds of miles out at sea4 ,something akin to this so-called 8,andes lightning0 has occasionally been reported from other mountainous regions1 including the mountains of ,virginia and ,north ,carolina4 8,beaded0 lightning and 8rocket0 lightning are as rare as they are interesting4 ,the former resembles a string of glowing beads1 while the latter is a form of streak lightning that shoots up into the air at about the apparent speed of a skyrocket4 8,ball lightning0 takes the form of a fiery mass 7not always globular71 which generally moves quite deliberately through the air or along the ground1 and in many cases disappears with a violent detonation4 ,it occurs inside of buildings1 as well as out of doors4 ,in order that a discharge of electricity may break through the resistance of the air along paths as long as those commonly observed1 enormous differences of potential must exist in the atmosphere during thunderstorms4 ,how such conditions arise has been the subject of an immense amount of speculation4 ,the explanation now generally accepted was proposed in the year #aiji by the ,english physicist and meteorologist1 ,dr4 ,george ,simpson4 ,this hypothesis is based upon the fact1 well attested by laboratory experiments1 that the breaking up of drops of water involves a separation of positive from negative electricity2 in other words1 the production of both positive and negative ions4 ,in this process the drops become positively charged2 i4 e41 they retain a greater number of positive than of negative ions1 the latter being set free in the air4 ,about three times as many negative as positive ions are thus released4 ,now a thunderstorm is accompanied by strong upward movements of the air2 so strong that small drops cannot fall to the ground1 while large drops1 which would be heavy enough to fall through such rising currents if they could retain their integrity1 are broken up by the blast of air and carried aloft1 where they tend to accumulate1 recombine1 and fall again4 ,this process may be repeated many times1 so that the positive charge of the drops is continually increasing1 and at the same time negative ions are being set free and carried by the ascending air to the upper part of the clouds4 ,here they unite with the cloud particles and give them a strong negative charge4 ,thus eventually there is formed a heavily charged positive layer of cloud between a heavily charged negative layer above and the negatively charged earth beneath4 ,when the differences of potential thus brought about become great enough1 disruptive discharges of electricity will occur1 and these may be either between the upper and lower layers of cloud or between the clouds and the earth1 or1 sometimes1 between two different clouds4 ,probably much the most frequent lightning flashes are those that occur within a single thundercloud and do not reach the earth4 ,however1 it will often happen that the negatively charged upper layer of cloud is either carried very high or drifted away by the wind1 and then the discharges that occur will be chiefly between cloud and earth4 ,such conditions are likely to prevail in the case of cyclonic thunderstorms1 in which there is often great difference in the direction and force of the winds at different levels4 ,on the other hand1 heat thunderstorms usually occur when the general winds are light at all levels1 and it is probable that such storms are relatively free from cloud-to-earth discharges4 ,we seem to have here an explanation of the paradox that tropical thunderstorms1 which are nearly always of the noncyclonic type1 though notoriously violent1 are generally harmless4 ,it must not be inferred from what has been said above that the mystery of the lightning flash is now fully resolved4 ,this is far from being the case4 ,it is not at all clear how an electrical discharge can break down the resistance of the air along a path a mile or more in length1 as commonly happens in the thunderstorm4 ,it was formerly stated1 on good authority1 that the difference of potential required to produce such a flash would amount to upward of #e1jjj1jjj1jjj volts4 ,certain facts have lately been adduced to show that such great differences of potential need not be assumed4 ,moving-camera photographs of the sparks produced by electric machines show that such sparks begin with small brush discharges which gradually ionize the air and thus build up a conductive path for the complete discharge4 ,something of this kind may occur in the atmosphere4 ,streaks of air already strongly ionized and more or less continuous sheets of rain would also help to provide conductors for a discharge4 ,if lightning does build up its path somewhat gradually1 the process might1 in certain cases1 be so slow as to account for the deliberate movement of rocket lightning1 and also1 perhaps1 furnish a clue to the hitherto unsolved mystery of ball lightning4 ,humphreys has tentatively suggested that all genuine cases of ball lightning are 8stalled thunderbolts02 i4 e41 lightning discharges that have come to a halt1 or nearly so1 in their progress through the air4 ,as to the visibility of lightning ,humphreys says1 in his 8,physics of the ,air03 8,just how a lightning discharge renders the atmosphere through which it passes luminous is not definitely known4 ,it must and does make the air path very hot1 but no one has yet succeeded1 by any amount of ordinary heating1 in rendering either oxygen or nitrogen luminous4 ,hence it seems well-nigh certain that the light of lightning flashes owes its origin to something other than high temperature1 probably to internal atomic disturbances induced by the swiftly moving electrons of the discharge1 and to ionic recombination40 ,a few attempts have been made to measure the strength of current in a lightning discharge4 ,many substances become magnetized when an electric discharge occurs in their vicinity1 and it has been pointed out by ,f4 ,pockels that when basalt rock is magnetized in this way the amount of magnetism is an indication of the greatest strength of current to which it has been exposed4 ,pockels examined specimens of basalt from the top of ,mount ,cimone1 in the ,apennines1 where lightning strokes are common1 and found many of them more or less magnetized4 ,he also exposed blocks of basalt close to a branch of a lightning rod in the same region4 ,he thus obtained values for the strength of current in lightning discharges ranging from #aa1jjj to #bj1jjj amperes4 ,humphreys1 from the crushing effect of a lightning stroke upon a hollow lightning rod1 has computed the strength of current in the case examined to be about #ij1jjj amperes4 ,the effects of lightning are so various that it would take a book to describe them all4 ,its audible effects are discussed in our chapter on atmospheric acoustics4 ,its chemical effects consist chiefly in the production of oxides of nitrogen1 ozone1 and probably ammonia from the constituents of the atmosphere along the path of the discharge1 and these substances1 either directly or after further combinations in the atmosphere1 contribute to the fertility of the soil4 ,lightning sometimes bores holes several feet deep in sandy ground and fuses the material along its path1 forming the glassy tubes known as fulgurites4 ,similar holes are bored in solid rock4 ,the destructive effects of lightning are due chiefly to the heat generated by the passage of an electric current through a poor conductor4 ,when moisture is present in the object struck1 its sudden conversion into steam produces the explosive effects seen in the shattering of trees1 the ripping of clothes from the human body1 etc4 ,there is almost no end to the curious pranks played by lightning--some disastrous1 some comical1 and some benevolent1 as when persons crippled with rheumatism1 after having been knocked down and temporarily stunned by a stroke of lightning1 have found themselves completely cured of their malady6 ,a well-known book by ,camille ,flammarion1 translated into ,english under the title 8,thunder and ,lightning10 is almost wholly devoted to these eccentricities of the lightning stroke4 ,illustration3 ,a ,,lightning ,,print ,,on ,,the ,,arm ,,of ,a ,,boy ,,struck ,,by ,,lightning ,,near ,,duns1 ,,scotland1 ,,in #ahhc ,drawn from a photograph taken a few hours after the accident4 ,from the ,lancet4 ,there is a very common belief that lightning sometimes impresses a photographic image of trees or other objects of the landscape upon the human body4 ,the ramifying pink marks1 known as 8lightning prints10 often found on the skin of persons who have been struck by lightning1 are1 however1 in no sense photographic1 but are merely the lesions due to the passage through the tissues of a branching electric discharge4 ,a few practical suggestions in regard to danger from lightning are offered by ,humphreys1 as follows3 8,generally it is safer to be indoors than out during a thunderstorm1 and greatly so if the house has a well-grounded metallic roof or properly installed system of lightning rods4 ,if outdoors it is far better to be in a valley than on the ridge of a hill1 and it is always dangerous to take shelter under an isolated tree--the taller the tree1 other things being equal1 the greater the danger4 ,an exceptionally tall tree is dangerous even in a forest4 ,some varieties of trees appear to be more frequently struck1 in proportion to their numbers and exposure1 than others1 but no tree is immune4 ,in general1 however1 the trees most likely to be struck are those that have either an extensive root system1 like the locust1 or deep tap roots1 like the pine1 for the very obvious reason that they are the best grounded and therefore offer1 on the whole1 the least electrical resistance4 8,if one has to be outdoors and exposed to a violent thunderstorm1 it is advisable1 so far as danger from lightning is concerned1 to get soaking wet1 because wet clothes are much better conductors1 and dry ones poorer1 than the human body4 ,in extreme cases it might even be advisable to lie flat on the wet ground4 ,in case of severe shock1 resuscitation should be attempted through persistent artificial respiration and prevention from chill4 8,the contour of the land is an important factor in determining the relative danger from lightning because the chance of a discharge between cloud and earth1 the only kind that is dangerous1 varies somewhat inversely as the distance between them4 ,hence thunderstorms are more dangerous in mountainous regions1 at least in the higher portions1 than over a level country4 ,clearly1 too1 for any given region the lower the cloud the greater the danger4 ,hence a high degree of humidity is favorable to a dangerous storm1 partly because the clouds will form at a lower level and partly because the precipitation1 and probably therefore the electricity generated1 will be abundant4 ,hence1 too1 a winter thunderstorm1 because of its generally lower clouds1 is likely to be more dangerous than an equally heavy summer one40 ,it is estimated that the total property loss due to lightning in the ,united ,states is about #h1jjj1jjj a year1 and the number of persons struck about #a1ejj1 of whom one-third are killed4 ,nine-tenths of these accidents occur in rural localities4 ,lightning rods neither prevent lightning stroke nor do they1 as is sometimes alleged1 attract lightning to buildings4 ,they merely provide good conductors along which a stroke of lightning may reach the earth without doing damage1 and1 within very moderate limits1 determine the path of discharge4 ,while there are many unsettled points regarding the theory of lightning rods and details of construction1 their general utility is strikingly indicated by statistics showing the comparative amount of damage done by lightning to rodded and unrodded buildings4 ,according to the ,united ,states ,bureau of ,standards1 information gathered in this country shows that 8taking rods as they come in the general run of installations1 they reduce the fire hazard from lightning by #hj to #ij per cent in the case of houses1 and by as much as #ii per cent in the case of barns40 ,the same bureau1 in its valuable publication1 8,protection of ,life and ,property ,against ,lightning0 7,washington1 #aiae71 supplies the answers to a multitude of questions that are constantly asked about lightning rods4 ,buildings with metal roofs and frames connected with the ground are generally well protected from lightning 7except as to nonmetallic chimneys7 without rods4 ,during actual thunderstorms1 and also at other times when there are high potential gradients in the atmosphere1 luminous electric discharges of a more or less continuous character are sometimes observed to occur in the shape of small jets and flames1 chiefly from pointed objects1 including lightning rods1 the masts and spars of vessels1 the angles of roofs1 etc4 ,these are identical in character with the 8brush0 discharges1 or incomplete sparks1 produced by electric machines4 ,they are accompanied by a hissing or crackling sound4 ,their luminosity is comparatively feeble1 and for this reason they are much more often observed by night than by day4 ,they are especially common during snowstorms4 ,this phenomenon is known as ,st4 ,elmo's fire or corposants 7not to mention a score of other names1 ancient and modern74 ,as seen at sea1 corposants sometimes take the form of one or two starlike objects at the trucks of the masts or the ends of yard arms1 but occasionally the spars1 rigging and other parts of the ship are lighted up with a great number of stationary or moving flames1 producing a weird spectacle4 ,the finest examples of corposants are1 however1 observed on high mountains1 and the phenomenon has been carefully studied at certain mountain observatories1 such as those on ,ben ,nevis and the ,sonnblick4 ,of its occurrence on ,ben ,nevis1 ,angus ,rankin writes3 8,the most frequent manner in which it makes its appearance is as caps of light on the tips of the lightning rod1 but occasionally it appears as jets of flame projecting from all objects on the top of the tower and from the cowl of the kitchen chimney1 which rises from the roof at some distance from the tower4 ,these jets are at times from #d to #f inches in length1 and make a peculiar hissing sound4 ,during a very brilliant display1 the observer's hair1 hat1 pencil1 etc41 are aglow with the #8fire1' but1 except for a slight tingling sensation in the head and hands1 he suffers no inconvenience from it4 ,on such occasions1 if a stick be raised above the head1 jets of electric light will be seen at its upper end4 ,the only drawback to observing it with advantage is the unpleasant character of the weather in which it appears1 namely blinding showers of snow and hail1 and squally winds1 causing a good deal of snowdrift40 ,rankin records that it was sometimes heard in the daytime1 when its light was invisible4 ,on the ,sonnblick a display of ,st4 ,elmo's fire has been observed to last as long as eight hours4 ,no luminous electrical phenomenon is more beautiful or1 at first sight1 more mysterious than the aurora1 popularly known1 in the northern hemisphere1 as the 8northern lights40 ,this phenomenon is due to the passage of electrical discharges through the rarefied gases of the upper atmosphere1 and it now appears to be settled beyond controversy that the discharges are caused by corpuscles or radiations of some kind emitted from the sun4 ,most accounts of the aurora describe the typical appearances that it assumes as seen from a single place on the surface of the earth1 but say little1 if anything1 about the form of the phenomenon as a whole or about its position in space4 ,we shall follow a different plan here1 and ask the reader1 first of all1 to imagine himself viewing the aurora from a point some thousands of miles away from our planet4 ,the solar emission above mentioned1 when sufficiently intense1 produces in the upper atmosphere a glow like that seen in a vacuum tube when an electrical discharge passes through it4 ,from our vantage point in outer space we shall notice that this glow is not spread over the whole globe1 but forms two rings1 which encircle the polar regions of both hemispheres1 though neither the geographic nor the magnetic poles lie at their centers4 ,the rings do not extend down into the lower atmosphere1 but hang about #fj miles above the earth's surface4 ,the reason for this segregation of the aurora in high latitudes is that the earth is a great magnet1 and magnets have the power of deflecting an electrical discharge in their vicinity4 ,an appearance much resembling the two auroral zones of the earth was produced1 on a small scale1 by the late ,professor ,kr4 ,birkeland of ,christiania1 who magnetized a metal globe and allowed an electrical discharge to play upon it in a vacuum4 ,the surface of the globe was coated with a phosphorescent substance1 which glowed under the discharge in two rings1 corresponding roughly to those of the aurora4 ,in both cases the discharge follows what are called the magnetic 8lines of force40 ,our earth1 like other magnets1 is enveloped and penetrated by such lines4 ,at any point on the earth the direction of the neighboring lines of force is shown by the dipping needle1 which assumes a position parallel to them4 ,at a magnetic pole the needle points straight up and down1 and everywhere in high latitudes it has a position not very much inclined to the vertical1 while in low latitudes it is more or less horizontal4 ,if1 now1 for the sake of simplicity we confine our attention to the northern hemisphere1 and imagine ourselves maintaining our watch for months and years together1 we shall discover that much of the time there is no ring to be seen2 at other times there may be a small or partial ring2 and occasionally there is a very broad1 conspicuous ring1 spreading so far south that it overlies the northern part of the ,united ,states and most of ,europe4 ,evidently the emission from the sun that causes the auroral discharge varies greatly in strength1 and this is in accordance with what we know about solar activities in general4 ,next let us take a closer look at the ring1 whether from outer space or from the earth's surface4 ,we shall find that it is made up1 at least in part1 of a multitude of luminous beams directed out into space and undergoing rapid changes in position and form4 ,these beams1 which really mark out the streams of the discharge in the upper air1 follow the lines of force4 ,in high latitudes they are nearly vertical with respect to the underlying surface of the earth4 ,even in the ,united ,states 7when the aurora extends so far south7 they are much more nearly vertical than horizontal4 ,a dipping needle will show1 at any place1 just how they should stand4 ,illustration3 ,,photographic ,,analysis ,,of ,,lightning4 ,this double photograph was made by ,dr4 ,b4 ,walter of ,hamburg1 the leading expert in the field of lightning photography4 ,the picture at the left was taken with a stationary camera4 ,the photograph at the right1 taken at the same time with a revolving camera1 shows that one of the main flashes 7the one to the right7 was a single discharge1 and the other a multiple discharge4 ,from any distant point on the earth's surface either north or south of it1 the visible portion of the auroral ring presents the appearance of an arch across the horizon4 ,arctic explorers1 far within the ,arctic ,circle1 see this arch to the south of them4 ,in our latitudes it spans the northern horizon4 ,separate beams or streamers may be distinguishable or not1 according to the brightness of the discharge or its distance from the point of observation4 ,combinations of beams constitute so-called 8draperies40 ,illustration3 ,,photograph ,,of ,,lightning1 ,,showing 8,,black0 ,,flashes4 7graph by ,f4 ,ellerman47 ,illustration3 ,,atmospheric ,,electricity ,,instruments ,,on ,,board ,,the 8,,carnegie40 ,left3 ,penetrating radiation apparatus4 ,right3 active-content apparatus4 ,below3 ,arrangement for supplying potentials to electroscopes and ionization chambers1 7,carnegie ,institution47 ,occasionally1 at times of great solar activity1 part of the ring actually overlies our ,northern ,states1 and the aurora then becomes a magnificent spectacle in this part of the world4 ,the whole sky may be filled with the shifting streamers1 along which travel rapid pulsations of light1 so that the phenomenon then suggests strongly what it really is--a vast electrical discharge passing down through the atmosphere from outer space4 ,when the observer is thus surrounded by the beams1 they seem1 on account of perspective1 to converge toward a point south of the zenith1 where they form a beautiful corona or crown4 ,the position of this crown depends upon the slant of the beams1 which1 as already explained1 follow the lines of force4 ,a brilliant aurora is always accompanied by disturbances of the magnetic needle1 which moves about erratically1 so that compasses can no longer be depended upon4 ,at the same time there are strong 8earth currents10 which interfere with the operation of telegraph lines4 ,observations with the spectroscope seem to show that the light of the aurora is chiefly due to glowing nitrogen1 though the most prominent line in the auroral spectrum has sometimes been referred to an unknown atmospheric gas4 ,the various colors seen in bright auroras1 including reds1 greens1 and yellows1 are believed by some authorities to depend upon the varying speed of the electrical discharge4 ,experiments with vacuum tubes show that nitrogen1 especially1 gives great changes of color with changes in the velocity of the discharge4 ,another interesting revelation of the spectroscope is that there is apparently1 a faint auroral illumination in the sky at all times and in all parts of the world1 the so-called 8permanent aurora40 ,photography has been used with great success in studying the aurora1 especially by the ,norwegian physicists ,strmer1 ,vegard1 and ,krogness4 ,simultaneous photographs of a single detail are taken from two points several miles apart against a background of stars4 ,the apparent position of the auroral detail among the stars will differ in the two pictures1 and a comparison of them makes it possible to determine the actual position of the aurora in space4 ,a slow-moving cinematograph has also been used to obtain series of pictures4 ,the measurements of these observers show that the base of the aurora is1 generally between #fj and #gj miles above the earth with a strong tendency to assume a definite location at an altitude of about #fa or #fg miles4 ,its upper limits are not well defined1 but it has been photographed up to an altitude of more than #cjj miles4 ,earlier observers reported seeing the aurora at altitudes of only a few miles1 and even down to the earth's surface1 but recent authorities are inclined to discredit these observations4 ,one more phenomenon of atmospheric electricity requires brief mention1 viz41 the electric waves that produce the erratic disturbances known to wireless telegraph operators as 8strays0 or 8static40 ,as heard in the receiver of a wireless outfit the noise of strays has been described as 8like hailstones beating against a sheet of tin10 or 8short hisses from a steam pipe10 or 8periodic discharges of coal down a chute40 ,another characteristic sound is a sharp 8click40 ,the study of strays has been carried out on a world-wide scale by a committee of the ,british ,association for the ,advancement of ,science1 but their nature is not yet fully understood4 ,some strays are undoubtedly due to near or distant discharges of lightning1 and special forms of wireless apparatus1 known as 8thunderstorm recorders0 or 8ceraunographs10 have been used to give notice of the approach of thunderstorms4 ,on the other hand1 strays seem frequently to have no connection with thunderstorms1 and their principal origin is now sought in electrical disturbances in the upper atmosphere1 perhaps similar to those which cause the aurora1 and1 as in the case of the aurora1 having their ultimate source in the sun4 ,,chapter ,x ,,atmospheric ,,optics ,when we look up into the sky on a cloudless day we behold a continuous canopy1 the prevailing color of which is blue4 ,this canopy is a veil that hides the starry hosts beyond1 and its presence seems1 at first sight1 incompatible with the fact that the air is a transparent medium4 ,we see the stars by night through the same intervening atmosphere4 ,why are they cut off from our sight by day8 ,the answer to this question can1 perhaps1 best be made plain by a simple experiment4 ,place a lighted candle behind a sheet hung across a room not otherwise illuminated4 ,the flame of the candle will be distinctly visible through the sheet4 ,next1 let the room be brightly lighted1 say with electric light or daylight4 ,the candle can now no longer be seen through the sheet1 owing to the bright illumination of the latter as compared with the feeble light of the candle4 ,in the atmosphere the counterpart of our sheet is a layer1 several miles in depth1 of minute particles1 which by day are lighted up by the sun4 ,some of the particles are tiny dust motes1 others are fine droplets of water or bits of ice1 and the rest are the molecules of the atmospheric gases themselves4 ,it is the light that comes to us from these particles that makes our eyes insensitive to the fainter light of the stars1 and makes the sky itself a visible luminous vault4 ,next1 why is the clear sky generally blue1 rather than some other color8 ,to answer this question1 we must recall the fact that sunlight is made up of ether waves of many different sizes4 ,in combination1 these waves produce upon our eyes the sensation of white light4 ,when they are separated1 as by passing through a prism1 the smallest waves--or1 in more technical language1 the vibrations of shortest wave length--register the sensation of violet1 and the largest or longest waves that of red4 ,the whole sequence of colors runs in the order violet1 indigo1 blue1 green1 yellow1 orange and red 7easily fixed in the memory by means of the word ,,vibgyor1 formed from the initial letters of these words74 ,now the passage of sunlight through the atmosphere is obstructed to a certain extent1 not only by suspended dust particles1 but also by the molecules of the air4 ,let us consider1 first1 the effect of air molecules and of the finest dust particles1 not much above molecular size4 ,these tiny objects have different effects on light waves of different lengths4 ,the longest waves are little disturbed by them1 just as ordinary waves in water are little affected by a floating cork1 for instance4 ,the shortest waves are so small in proportion to the size of the obstacles that they are diffused or scattered by them1 as a tiny ripple in water might be broken up by a floating cork4 ,it is this diffuse light1 of short wave length1 that gives the sky its color4 ,a large part of the violet and indigo light is lost by further scattering before it reaches the earth1 leaving a preponderance of blue in the sky as we see it4 ,when the air contains a considerable amount of suspended particles larger than those above considered--whether in the form of solid dust or crystals of ice or tiny droplets of water--light of all wave lengths is reflected by them1 and the sky looks white or grayish4 ,on account of the action of atmospheric particles in filtering out the shorter light waves1 as just described1 sunlight becomes relatively rich in red and orange in passing through the air4 ,when the sun is high1 the path of the sunbeams to the earth is short1 and the color of their light is but little affected4 ,near the time of sunrise and sunset1 however1 sunlight comes to us through a much greater extent of air1 and the filtering process is much more effective4 ,hence the sunshine is both enfeebled and reddened when the sun is near the horizon4 ,the diffuse light of the sky around the sun is filtered in the same manner1 and therefore is commonly red when the sun is low4 ,a gray sunset sky after a clear day is due to the presence of water drops in the air1 and indicates conditions favorable for rain1 since1 unless the air were saturated to a considerable altitude1 the comparatively warm sunshine of the afternoon would favor evaporation rather than condensation of moisture4 ,a gray sunrise sky has1 as a general rule1 just the opposite meaning4 ,it often indicates the presence in the air of water drops formed on dust particles during the night1 after the manner of dew1 because the upper air has been dry enough to permit rapid radiation from the dust4 ,these drops will be speedily evaporated by the rising sun1 and the general dryness of the atmosphere will not favor further condensation4 ,several familiar weather proverbs are thus justified1 e4 g43 ,evening red and morning gray ,help the traveler on his way2 ,evening gray and morning red ,bring down rain upon his head4 ,there are many other interesting optical phenomena connected with sunrise and sunset1 including1 first of all1 the morning and evening twilight4 ,when the sun1 or any other heavenly body1 is only a little below a clear horizon1 it is still visible1 on account of the bending of its rays by the atmosphere4 ,this lifting effect1 known as astronomical refraction1 amounts to about half a degree 7at the horizon71 which is about equivalent to the apparent diameter of the sun or moon4 ,as the sun sinks farther below the horizon1 in the evening1 the only daylight that comes to us is that reflected from the upper levels of the atmosphere1 which are still illuminated4 ,this is called twilight1 and it lasts until the sun is about #ah degrees below the horizon1 when total darkness sets in4 ,the period as a whole is sometimes called astronomical twilight1 in distinction from the briefer period known as civil twilight1 during which there is light enough for outdoor occupations2 the latter lasts from sunset until the sun is about #f degrees below the horizon4 ,morning twilight is more commonly called 8dawn40 ,an interesting succession of light and color effects is observed before and after sunset and1 in inverse position and order1 about sunrise4 ,considering sunset only3 ,after the sun has sunk out of sight1 a broad band of golden light1 called the bright segment1 is seen along the western horizon4 ,above this1 in the western sky1 appears a more or less circular expanse of rosy glow1 known as the purple light4 ,in the eastern heavens1 after sunset1 there rises steadily from the horizon the so-called dark segment1 which is the blue or ashy shadow of the earth on the sky4 ,this is bordered above by the pink or purplish antitwilight arch4 ,as time goes on1 the purple light in the west1 after increasing in brightness for a while1 finally sinks behind the bright segment2 while in the east the rising dark segment encroaches upon and finally obliterates the antitwilight arch4 ,sometimes1 in clear weather1 there is a fainter repetition of these lights and colors 7second purple light1 etc474 ,among the ,alps and other snow-capped mountains1 these sunset and sunrise phenomena assume a particularly beautiful form1 known as the ,alpenglow4 ,in fine weather1 just before sunset1 the peaks to the eastward begin to show a reddish or golden hue4 ,this fades gradually1 but in a few minutes1 when the sun is a little below the horizon of the observer1 but the peaks themselves are still bathed in direct sunlight1 an intense red glow1 beginning down the slopes1 moves upward to the summits4 ,this is identical with the antitwilight arch described above4 ,presently this glow is succeeded by an ashy tint1 as the peaks are immersed in the rising shadow of the earth 7the dark segment74 ,their rocks and snows assume a livid appearance1 aptly described by the inhabitants of ,chamonix1 whence the phenomena in question are well seen on the summit of ,mont ,blanc1 as the teinte cadavreuse4 ,in ordinary weather darkness succeeds without any further notable phenomena1 but occasionally there occurs a remarkable renewal of rosy light upon the peaks1 known as the recoloration or afterglow4 ,at ,chamonix this is termed the 8resurrection of ,mont ,blanc40 ,the afterglow has been variously explained1 but it is probably due1 mainly at least1 to the reflection of the purple light in the western sky4 ,sometimes it lasts until an hour after sunset1 and it passes away from below upward4 ,on very rare occasions there is a second afterglow1 presumably the reflection of the second purple light mentioned above4 ,similar phenomena are often seen in reverse order at sunrise4 ,a pretty phenomenon observed chiefly in the late afternoon and early morning consists of beams of light radiating from the sun1 known technically as crepuscular rays4 ,the beams are made visible by the presence of abundant dust or water droplets in the atmosphere1 and the intervening dark spaces are the shadows of clouds4 ,when the sun is above the horizon and the beams are directed downward1 the phenomenon is popularly described as 8the sun drawing water0 and is regarded as a sign of rain4 ,sailors call these beams the 8backstays of the sun10 and they have several other names based upon the legendry associated with them in different parts of the world4 ,after sunset or before sunrise a fanlike sheaf of the beams often extends upward from the western or eastern horizon1 respectively4 ,the ,homeric expression 8rosy-fingered dawn0 probably refers to this phenomenon4 ,in all cases the apparent divergence of these beams is an effect of perspective1 as they are really parallel4 ,a rarer phenomenon is that of anticrepuscular rays1 which appear to converge to a point opposite the sun4 ,in this case the beams and shadows are projected entirely across the sky1 but their paths can very seldom be traced in the upper part of the heavens because in this direction the observer's line of sight passes through a comparatively shallow extent of dusty atmosphere4 ,an analogous phenomenon is seen in the shadows which near-by isolated mountain peaks frequently cast upon the sky opposite the sun at sunrise and sunset4 ,travelers have described such shadows cast by ,adam's ,peak in ,ceylon1 ,pike's ,peak in the ,rocky ,mountains1 and ,fujiyama in ,japan4 ,the phenomenon is said to be especially striking in the polar regions1 where the air is often heavily charged with particles of ice4 ,one more optical phenomenon of sunrise and sunset that requires mention here seems to be comparatively little known to the nonscientific public1 notwithstanding the fact that it has supplied the subject and title of a diverting novel by ,jules ,verne4 ,the conditions required for its appearance are a clear and steady atmosphere and a sharply defined horizon1 such as that of the ocean4 ,at the instant the sun is appearing or disappearing1 and when only a very small segment of its disk is visible above the horizon1 this portion appears to be colored a bright emerald green1 sometimes blending into blue4 ,this transient phenomenon is known as the green flash4 ,it is best explained as due to the different degrees of refraction undergone by rays of different wave lengths coming to us from the sun4 ,the effect of refraction in elevating the solar image as a whole when near the horizon has already been mentioned4 ,this effect is a little greater for the green and blue rays than for the orange and red4 ,it is still more pronounced for the violet and indigo rays1 but these are mostly sifted out of the solar beams in their long passage through the atmosphere when the sun is low4 ,hence at the upper edge of the solar image there is a narrow green or blue fringe1 which is not1 however1 perceptible except when a screen is interposed between the eye and the bright image of the sun4 ,a sharp horizon furnishes such a screen4 ,through a telescope it is possible1 in suitable weather1 to see the green flash--and also a corresponding 8red flash0 at the lower edge of the sun--by placing an opaque diaphragm in the focal plane of the object glass4 ,another explanation of the green flash--which could1 however1 account only for its appearance at sunset and not at sunrise--is that it is a physiological effect2 the eye1 fatigued by the reds and yellows that predominate in the light of the setting sun1 sees an 8after image0 of complementary hue the instant after the real image has disappeared4 ,we now turn to a group of phenomena1 also due to atmospheric refraction1 which includes some of the most bizarre of optical illusions4 ,the simplest of these phenomena consists of a slight apparent elevation of all objects in the surrounding landscape through terrestrial refraction1 which is identical in principle with astronomical refraction and depends upon the difference in density1 and hence of refractive power1 of the air at different levels above the earth4 ,normally the air decreases in density at a nearly regular rate with increasing altitude4 ,sometimes1 however1 this change in density is greatly modified by local effects of temperature4 ,over a cold surface of land or water the adjacent air may be abnormally dense1 resulting in an unusually rapid decrease of density with altitude4 ,over a hot surface1 as in the case of a desert under strong sunshine1 the adjacent air may become so much rarefied that1 for a certain distance upward1 there is actually an increase of density with ascent1 instead of the reverse4 ,the rays of light coming to us from distant objects are bent in different directions and to various degrees by virtue of these abnormalities in the density of the atmosphere4 ,the apparent positions of such objects depend upon the angle at which the light rays1 coming from them1 strike the eye of the observer4 ,sometimes the objects appear to be lifted far above their true positions 7a phenomenon known as looming7 and sometimes depressed far below them2 and occasionally local irregularities in air density produce curiously distorted images of these objects4 ,most of these strange effects are known collectively as mirage4 ,there are many varieties4 ,there is the 8desert mirage10 first made famous through the experience of ,napoleon's soldiers in ,egypt4 ,there are mirages that suspend the images of remote objects in the sky2 sometimes inverted1 sometimes right side up4 ,there is the lateral mirage1 occasionally seen when one looks along the face of a heated wall or cliff4 ,lastly1 there are the complex displacements and distortions of objects known as the ,fata ,morgana--a name originally applied to a phenomenon of this kind visible1 on rare occasions1 at the ,straits of ,messina1 but now used generically for similar appearances in other parts of the world4 ,some of the finest examples of ,fata ,morgana are witnessed in the polar regions4 ,in the desert mirage an image of the lower part of the sky is brought down to earth and simulates the appearance of water1 while the images of terrestrial objects1 also depressed and inverted by the mirage1 look like the reflections of the same objects upon the liquid surface4 ,humphreys says3 8,this type of mirage is very common on the west coast of ,great ,salt ,lake4 ,indeed1 on approaching this lake from the west one can often see the railway over which he has just passed apparently disappearing beneath a shimmering surface4 ,it is also common over smooth-paved streets1 provided one's eyes are just above the street level40 ,the confusing and obscuring effects of the desert mirage were illustrated during the fighting between the ,british and ,turks in ,mesopotamia1 in ,april1 #aiag1 when1 according to the report of ,general ,maude1 a battle had to be suspended on account of one of these optical disturbances4 ,illustration3 ,,fata ,,morgana ,,on ,,the ,,coast ,,of ,,greenland 7,from drawing by ,scoresby7 ,the strong vertical contrasts in air temperature that occur in the polar regions produce many remarkable examples of mirage4 ,the pictures and descriptions of those observed a century ago along the coast of ,greenland by ,captain ,william ,scoresby1 ,jr41 have become classical4 ,a recent episode connected with mirage was the expedition sent north in #aiac to explore 8,crocker ,land10 which ,peary believed he had sighted from an elevated point in ,grant ,land in #aijf1 and which for a time figured on all maps of the ,arctic4 ,the later explorers found no land at the place indicated1 but they observed the same mirage that ,peary had mistaken for distant hills and mountains4 ,currents of air of different densities produce1 through their varying effects on atmospheric refraction1 the twinkling or scintillation of the stars1 as well as of distant terrestrial lights4 ,twinkling is much more violent near the horizon than near the zenith1 and more pronounced on some nights than others4 ,the shimmering of the air over heated surfaces faces and the 8boiling0 of celestial objects as seen in the telescope are analogous phenomena4 ,illustration3 ,,inferior ,,mirage 7,from ,american ,museum ,journal4 ,drawing by ,chester ,a4 ,reeds47 ,out-of-doors when a layer of warm rarefied air arises from contact with heated ground or warm water1 occupying a position below the colder1 more dense normal air1 two images of a distant object may be seen--one inverted beneath the other4 ,this is 8inferior mirage0 and is explanatory of the appearance of trees and their reflections1 which haunts the desert traveler with the hope of water4 ,illustration3 ,,superior ,,mirage 7,from ,american ,museum ,journal4 ,drawing by ,chester ,a4 ,reeds47 ,when a zone of warm rarefied air is sandwiched between normal air above and colder air below1 a 8superior mirage0 of distant objects may be seen4 ,three images are produced1 one above the other1 the middle one inverted4 ,in the refraction phenomena that we have thus far considered the air is the medium in which the light rays are bent and distorted4 ,in the production of the rainbow1 light undergoes refraction1 dispersion 7separation of the spectral colors7 and reflection by passing through drops of water in the atmosphere2 especially falling raindrops4 ,the rainbow1 perhaps because it is such a common sight1 is seldom observed with careful attention4 ,hence few people realize that there are many varieties of this beautiful meteor1 and various erroneous ideas about it are prevalent4 ,the rainbow is always seen in the part of the sky opposite the sun--or the moon1 in the case of the lunar rainbow--and is high in the heavens when the luminary is low1 and low when the luminary is high4 ,generally less than a semicircle of the bow is visible1 and never more1 except from an eminence4 7,aeronauts occasionally see a complete circle47 ,the outer border of the bow is red and the inner blue or violet4 ,contrary to popular belief and to statements sometimes found in reference books1 it is almost never possible to distinguish all seven of the spectral colors in a rainbow2 four or five is the usual limit4 ,the ordinary or primary rainbow has a radius of about #db degrees at its outer edge4 ,very commonly a secondary rainbow is seen1 concentric with the primary bow1 and having a radius of about #ej degrees4 ,the secondary is fainter than the primary1 and its colors are in opposite order--red inside and violet outside4 ,additional bands of color1 chiefly red and green1 may often be detected adjacent to the inner edge of the primary bow and1 less frequently1 along the outer edge of the secondary bow4 ,these are known as supernumerary bows4 ,the space between the primary and secondary bows is somewhat darker than the rest of the sky4 ,the common rainbows differ much among themselves in the number and purity of their colors1 the width of the bows1 etc41 these differences depending especially on the size of the raindrops4 ,the minute drops of a fog sometimes give rise to a bow that is almost devoid of color--the 8white rainbow10 or 8fog bow40 ,the rainbows produced by the moon commonly show little color1 on account of the relative faintness of the light1 but the brighter lunar rainbows are often very distinctly colored4 ,illustration3 ,,intersecting ,,rainbows 7,after a sketch by ,t4 ,hodge4 ,courtesy of ,scientific ,american47 ,reflected rainbows are sometimes seen upon a sheet of water2 and again the image of the sun1 as reflected by such a surface1 may give rise to both primary and secondary rainbows in the sky1 which appear to intersect those produced by the sun directly4 ,a horizontal layer of water drops below the level of the observer's eye occasionally produces the so-called horizontal rainbow4 ,this may be formed over a bedewed field or other surface 7the 8dew bow072 or the drops may be those of a low-lying sheet of fog1 or of water deposited on a floating film of oil1 or1 finally1 actual raindrops1 seen from an elevation1 such as the summit of a mountain4 ,horizontal rainbows formed by rain have been seen from the ,eiffel ,tower4 ,the common saying1 ,a rainbow in the morning ,is the shepherd's warning2 ,a rainbow at night ,is the shepherd's delight1 is1 on the whole1 well justified for the following reasons3 ,we see the rainbow where rain is falling1 while the sun is shining in the opposite part of the sky4 ,our rainstorms usually come from the west and pass away to the east4 ,a morning rainbow can only be seen in the west1 and indicates that rain is approaching us4 ,an evening rainbow 7ignoring lunar bows7 is seen only in the east1 and shows that the rain area is receding from us1 giving place to clear skies4 ,illustration3 ,,the ,,circumzenithal ,,arc 7,from a drawing by ,l4 ,besson in ,la ,nature47 ,parts of the halos of #bb and #df1 upper tangent arc of the #bb halo1 and two parhelia are also shown4 ,the circumzenithal arc is always brightly colored4 ,ice crystals in the atmosphere1 such as those composing the higher clouds1 produce a great variety of optical phenomena1 known as halos4 ,some phenomena of this class are common1 others exceedingly rare4 ,moreover1 there are several theoretically possible forms of halo of which observations have never yet been reported1 so that halo observing can be recommended to the amateur meteorologist as offering opportunities for making interesting discoveries4 ,halos take the form of narrow rings of definite angular size around the sun or moon 7not to be confused with the coronas1 of variable dimensions1 described below71 rings passing through the luminary1 arcs in various other positions1 and roundish spots of colored or white light4 ,they may be seen separately or in combination4 ,in rare cases1 a dozen or more different forms of halo are visible at the same time1 producing a most spectacular display4 ,one of the most remarkable displays of this kind in the history of science was seen1 in different degrees of development1 over the eastern ,united ,states on ,november #a and #b1 #aiac2 an event which greatly stimulated interest in the study of halos in this country4 ,complex halos are quite common in the polar regions2 where they are seen not only in the sky1 but also in the air1 charged with ice particles1 close to the earth4 ,whenever a thin veil of cirrus or cirro-stratus clouds overspreads the sky there is a likelihood that halos will be visible4 ,those formed near the sun1 however1 frequently pass unnoticed1 on account of the dazzling brightness of that luminary4 ,smoked or tinted glasses greatly facilitate their observation4 ,illustration3 ,,diagrams ,,of ,,the ,,principal ,,forms ,,of ,,halo 7,after ,besson1 ,monthly ,weather ,review1 ,july1 #aiad47 #a4 7,upper74 ,perspective view of the sky1 showing the sun 7,s72 ordinary halo of #bb 7a72 great halo of #df 7b72 upper tangent arc of the halo of #bb 7c72 lower tangent arc of the halo of #bb 7d72 ordinary parhelia of #bb 7e1 e'72 ,lowitz arcs 7f1 f72 parhelia of #df 7g1 g72 circumzenithal arc 7h72 infralateral tangent arcs of the halo of #df 7i72 the parhelic circle 7m72 a paranthelion of #ij 7q72 light pillar1 7u1 u72 the observer 7,o74 #b4 7,lower74 ,perspective view of the sky1 showing the observer 7,o72 the parhelic circle 7m73 ordinary paranthelia of #abj 7p72 the paranthelion of #ij 7q'72 the oblique arcs of the anthelion 7r1 r72 and the anthelion 7n74 ,the commonest halo is a circle of #bb degrees radius 7the #bb-;degree halo7 about the sun or moon4 ,when formed by the sun it generally shows a distinct reddish inner border and traces of other spectral colors4 ,the lunar #bb-;degree halo usually appears colorless4 ,this halo is visible1 in whole or in part1 to the attentive observer about once in three days1 on an average4 ,less common1 but by no means rare1 are the parhelia or 8sun dogs0 of #bb degrees 7called paraselen or 8moon dogs0 when formed by the moon71 the beautiful circumzenithal arc1 and a few other members of the halo family4 ,most forms of halo are so uncommon that their appearance is an event of some scientific importance4 ,the accompanying diagrams1 by ,dr4 ,louis ,besson of the ,observatoire de ,montsouris1 show the positions1 with respect to the sun 7or moon71 of the majority of known halo phenomena4 ,the upper diagram shows the halos that occur on the same side of the sky as the sun 7or moon71 and the lower those that appear on the opposite side4 ,most of these halos1 when bright1 show the spectral colors4 ,the circumzenithal arc1 h 7commonly described1 by the uninitiated1 as a 8rainbow071 and the parhelia of #bb degrees1 e1 e1 are especially brilliant in their coloration4 ,the parhelic circle1 m1 which sometimes extends entirely around the sky1 is white1 and so are a few of the rarer forms of halo4 ,the upper and lower tangent arcs of the halo of #bb degrees1 c and d1 undergo striking alterations1 with changes in the altitude of the sun4 ,when the luminary is more than about #dj degrees above the horizon1 these two arcs become joined at their tips to form the circumscribed halo1 and at still greater solar altitudes this halo contracts from an elliptical to a circular form1 thus blending into the #bb-;degree halo as shown on the next page1 where the solar altitudes corresponding to the different forms of the halo are indicated4 ,the positions of the parhelia of #bb degrees1 e1 e1 also depend upon solar altitude4 ,when the sun is on the horizon these 8sun dogs0 are #bb degrees from the luminary1 and therefore lie in the #bb-;degree halo2 at greater solar altitudes they lie outside this halo4 ,the reader who wishes to acquaint himself further with the different forms of halo and the methods of observing them will find a comprehensive article on the subject 7devoid of mathematical discussions7 in the 8,monthly ,weather ,review0 7,washington1 ,d4 ,c47 for ,july1 #aiad4 ,illustration3 ,,successive ,,stages ,,of ,,the ,,upper ,,and ,,lower ,,tangent ,,arcs ,,of ,,the #bb ,,halo ,when the sun is high they unite to form the 8circumscribed halo40 7,altitude of sun shown in the center of each figure47 ,the ice crystals that produce halos consist of hexagonal plates or columns1 occasionally including complications of structure1 such as pyramidal bases1 combinations of plates and columns1 etc4 ,these have the well-known effect of prisms in refracting and dispersing light that passes through them4 ,it is evident that there are many possible paths for the light rays through the sides and bases of such crystals1 resulting in different deflections and corresponding differences in the forms and positions of the halos produced4 ,the attitudes assumed by the crystals as they slowly sink through the air1 and the oscillations they undergo1 are further points to be considered in working out the theory of each form of halo by the application of the laws of optics4 ,nearly all the known forms have been fully explained4 ,a few species of halo--notably the parhelic circle 7called paraselenic circle when formed by the moon7--are due to simple reflection from the faces of the ice crystals1 and not to refraction4 ,the last group of optical phenomena that we shall consider consists of those due to the process called diffraction1 which occurs when light is bent around objects in its path1 instead of passing through them1 as in refraction4 ,the process involves separation of the prismatic colors4 ,the diffraction phenomena of the atmosphere are produced by the water drops of clouds and fog1 or sometimes by fine dust4 ,everybody is familiar with the nocturnal spectacle which ,tennyson describes as 444 the tender amber round ,which the moon about her spreadeth1 ,moving thro' a fleecy night4 ,this diffuse reddish or rainbow-tinted circle is called a corona4 ,it occurs about the sun as well as the moon 7though not easy to see on account of the glaring brightness of the luminary71 and also about street lamps and other terrestrial lights when viewed through a misty atmosphere4 ,unlike the halos1 it has no definite angular size4 ,it is usually only a few degrees in radius4 ,small coronas are produced by large water drops and large coronas by small drops1 while the largest of all coronas1 known as ,bishop's ring1 is due to exceedingly fine dust in the atmosphere1 and has been seen after great volcanic eruptions4 ,in its commonest form the corona consists of a brownish-red ring1 which1 together with the bluish-white inner field between the ring and the luminary1 forms the so-called aureole4 ,if other colors are distinguishable1 they follow the brownish red of the aureole 7in the direction away from the luminary7 in the order from violet to red2 the reverse of the order seen in halos4 ,sometimes the sequence of colors is repeated three or four times4 ,patches and fringes of iridescence are sometimes seen in the clouds at a greater distance from the luminary than that of the ordinary corona4 ,probably they are fragments of coronas of unusual size produced by exceedingly fine cloud particles4 ,similar in appearance to the corona is the glory2 a series of concentric colored rings seen around the shadow of the observer1 or of his head only1 cast upon a cloud or fog bank4 ,such a shadow1 with or without the glory1 constitutes the specter of the ,brocken1 often seen from mountain tops and from aircraft4 ,the colored circles are sometimes called ,ulloa's rings1 from the name of a ,spanish savant who observed the phenomenon among the mountains of ,south ,america in the eighteenth century and has left us a vivid description of it4 ,the ,brocken specter1 though it owes its name to legends associated with the famous ,german mountain where witches were once believed to assemble on ,walpurgis ,night1 is actually less frequently witnessed there than in many other parts of the world4 ,whenever the sun is low on one side of a mountain and a wall of mist arises from a near-by valley on the other1 the mountaineer is likely to see his shadow upon the mist4 ,if the latter consists of fine droplets of approximately uniform size1 the colored rings will probably appear1 and occasionally there is also a white fogbow outside of the glory4 ,as all shadows cast by the sun taper rapidly 7on account of the angular breadth of the solar disk71 a well-defined ,brocken specter can never be more than a few yards away from the observer4 ,its distance is1 however1 commonly overestimated--some observers have supposed it to be miles away6--and hence the erroneous idea prevails that the specters are of enormous size4 ,rarely from a favorable point of vantage on a mountain1 and very frequently from aircraft1 the specter1 instead of being seen on a vertical wall of mist when the sun is low1 appears on a horizontal sheet of cloud below the observer when the sun is high4 ,the aeronaut may thus observe the complete outline of his balloon or aeroplane1 encircled with the rainbow tints of the glory4 ,during the ,world ,war the appearance of the luminous rings was likened to the emblem painted on the wings of the ,allied aeroplanes and was regarded by superstitious aviators as an omen favorable to their cause4 ,the glory is due to the light that is reflected back to the observer after penetrating the cloud or fog a little way and is diffracted by the superficial layer of drops in emerging4 ,the ,brocken specter and the glory have occasionally been photographed4 ,,chapter ,,xi ,,atmospheric ,,acoustics ,though air is but one of an unlimited number of elastic substances that transmit sound1 it is the one through which sounds ordinarily reach our ears4 ,hence the acoustic properties of the atmosphere are of great interest to mankind4 ,science deals with several kinds of 8waves10 and those of the atmosphere that produce the sensation of sound are quite different from the waves of the sea4 ,in quiet unconfined air sound travels in concentric spherical waves1 consisting of successive condensations and rarefactions of the medium4 ,sound is not transmitted through a vacuum4 ,a familiar laboratory experiment is to install an electric bell inside the receiver of an air pump and notice the dying away of the sound as the air is exhausted4 ,the colossal eruptions that astronomers witness on the surface of the sun would probably be audible on earth if interplanetary space were filled with air4 ,in the rarefied air of high mountains the intensity of sounds is much reduced4 ,thus we are told that on the top of ,mont ,blanc the report of a pistol sounds no louder than that of a firecracker at sea level4 ,the speed with which sound travels through air depends upon the temperature4 ,at #cb ,f4 7the freezing point7 it is #a1jhg feet per second1 and at #fh ,f4 it is #a1abf feet per second4 ,the increase of speed with increase of air temperature is very close to #b feet per degree ,centigrade1 or a little more than #a foot per degree ,fahrenheit4 ,the sounds of violent explosions travel considerably faster than ordinary sounds near the place of explosion1 but slow down to the normal speed at greater distances4 ,this is true of heavy claps of thunder4 ,the effect is not important enough1 however1 to invalidate the well-known rule that1 if you count seconds between the flash and the detonation and divide the result by #e1 you get approximately the distance of the source of sound in miles4 ,since the speed of sound varies with the temperature of the air1 differences in the latter cause deviations of the paths of sound waves similar to the deviations which rays of light undergo on account of differences in the density of the air4 ,sound is also reflected by obstacles1 in the same manner as light4 ,moreover1 whereas light travels too swiftly to be affected by the wind1 this is not true of sound4 ,the latter travels faster with the wind than against it1 and sound waves are more or less broken up by the gusts and irregularities that are a feature of most winds near the earth's surface4 ,for all these reasons the acoustic qualities of the air are subject to marked variations1 as everybody has observed4 ,unusual audibility of distant sounds is a popular prognostic of rain4 ,the fact underlying this belief is that when the air is full of moisture it is likely to be of uniform temperature1 and therefore favorable for transmitting sound4 ,it is impossible to assign any limit to the distance at which loud sounds may occasionally be heard4 ,no fact of nature has yet1 so far as we know1 matched ,emerson's metaphor of the 8shot heard round the world10 but it is literally true that the sounds of eruption of ,krakatoa1 in ,august1 #ahhc1 were heard1 like the roar of distant heavy guns1 in the island of ,rodriguez1 in the ,indian ,ocean1 #c1jjj miles from the volcano4 ,moreover1 the atmospheric waves set up by this outburst actually made the circuit of the globe1 not only once1 but at least three times1 and the successive journeys were registered by barometers1 if not detected by human ears4 ,during the ,world ,war gun firing in ,flanders was very commonly heard at places in ,england #adj to #aej miles distant4 ,several observers also reported that pheasants appeared1 from their disturbed behavior1 to hear cannonading over the ,north ,sea that was beyond the range of the human ear4 ,writers have often commented on the fact that thunder cannot be heard so far as the sounds of artillery4 ,it has been affirmed that #aj miles or thereabouts is its maximum range of audibility4 ,as a matter of fact1 however1 thunder has occasionally been heard at much greater distances1 up to #bj or #cj miles2 but it remains true that the distance is always much less than that at which loud terrestrial sounds are audible4 ,the reasons why this should be so are not far to seek4 ,in the first place1 the intensity of a sound depends upon the density of the air in which it is generated1 and not upon that of the air in which it is heard4 ,the air1 as we know1 diminishes in density upward4 ,balloonists thousands of feet above the earth hear with remarkable clearness sounds from the ground below1 but people on the ground cannot hear similar sounds from the balloon4 ,as thunder is mainly produced at the level of the clouds1 it is subject to this peculiarity4 ,again1 cannonading is heard at great distances only when the air is comparatively calm1 and perhaps only when it is arranged in well-defined horizontal layers of such a character as to keep the sound from spreading far aloft4 ,very different conditions prevail during a thunderstorm2 in fact the conditions are then just such as would scatter and dissipate the sound waves4 ,lastly1 the noise of a cannon or the like comes from a single place and the energy of the disturbance is concentrated to produce a single system of sound waves2 while the disturbance due to lightning is spread over the long path of the discharge4 ,the audibility of sounds at abnormally great distances is not usually a matter of practical importance1 but the converse phenomenon--the failure of sounds to carry to normal distances--has been responsible for a great number of marine disasters on such fog-ridden coasts as those of the ,british ,isles1 eastern ,canada and ,california4 ,hence some of the ablest physicists of both the ,old ,world and the ,new have tried to ascertain the conditions under which this phenomenon occurs4 ,the scientific study of fog signals1 dating especially from ,tyndall's well-known investigations at the ,south ,foreland1 in ,england1 in #ahgc1 and those of ,general ,duane and ,professor ,joseph ,henry in ,america1 begun somewhat earlier but continued contemporaneously with ,tyndall's1 has probably raised more questions than it has answered4 ,the caprices of these signals take the shape of variations in the range of audibility--a signal may at one time carry #aj miles and at another only #b--;and the formation of 8zones of silence10 comparatively near the signal1 within which the sound is not heard though audible at much greater distances4 ,the silent zones are sometimes more or less permanent and are then generally due to peculiarities of topography2 but in many cases they are transient and opinions differ as to their cause or causes4 ,since it is only when fog prevails that fog signals are sounded 7except for experimental purposes71 and that vessels meet with accidents on account of the failure to hear such signals1 the idea has become rooted in the public mind that these acoustic eccentricities are entirely due to fog4 ,when1 however1 experiments are made in clear weather1 similar phenomena are observed4 ,in foggy weather audibility is often better than the average1 because fog prevails chiefly when the air is still and of uniform temperature1 and such conditions favor the transmission of sound4 ,tyndall strongly denied that either fog or falling rain1 snow1 and hail have1 as has been commonly believed1 a muffling effect on sound1 and he attributed the peculiar behavior of fog signals to the presence in the atmosphere of invisible 8acoustic clouds10 consisting of patches of air containing irregularities of temperature and humidity4 ,to the same cause he ascribed the occurrence of mysterious 8aerial echoes10 not due to any visible object4 ,several recent investigators have disputed these conclusions4 ,thus it is asserted that when the fog signal is in fog and the observer in a clear atmosphere1 or vice versa1 or when the signal and the observer are in different fog banks1 the fog reflects the sound very strongly4 ,apart from the possible effects of fog itself1 the very extensive investigations made by ,prof4 ,l4 ,v4 ,king1 of ,mc,gill ,university1 at ,father ,point1 ,quebec1 led him to conclude that the effects are chiefly due to eddies in the atmosphere4 ,prof4 ,king used in his observations the latest devices for obtaining exact measurements of sound and such up-to-date meteorological apparatus as pilot balloons for measuring the wind at various levels4 ,he discovered1 among other things1 that existing types of fog-signal machinery are very wasteful of energy1 and he has pointed out how their 8acoustic efficiency0 may be much improved4 ,before we dismiss this subject it should be noted that submarine bells and the radio compass have made mariners much less dependent than they formerly were upon the types of signals that are affected by meteorological conditions4 8,zones of silence0 on a much more extensive scale than those that disturb the operation of fog signals have been frequently observed1 in recent years1 in connection with great explosions1 cannonading1 and volcanic eruptions4 ,the first case of this kind to attract scientific notice was that of a dynamite explosion at ,frde1 ,westphalia1 on ,december #ad1 #aijc1 the acoustic phenomena of which were investigated by ,dr4 ,g4 von dem ,borne2 and among the many cases that have since been studied was that of the bombardment of ,antwerp in ,october1 #aiad4 ,without describing these various cases separately1 we may state that when reports were collected from the surrounding country to determine the places at which the sounds were audible and these reports were entered on a map1 it was found that there was a large and usually very irregular area of audibility surrounding the source of sound1 beyond which lay a broad1 more or less circular zone of inaudibility1 and finally1 beginning about #ajj miles from the source1 there was a second large region of audibility1 extending perhaps #aej miles from the source4 ,in some cases a single sound at the source gave multiple reports 7double1 triple1 or quadruple71 chiefly in the outer zone of audibility4 ,in his attempt to explain these curious silent zones1 ,von dem ,borne pointed out that the atmosphere at very high levels is supposed to consist mainly of hydrogen1 in which sound travels nearly four times as fast as in the common gases of the lower air1 and that sound waves ascending to such heights along a slanting course would be bent strongly toward the earth4 ,another student of this phenomenon1 ,dr4 ,a4 ,wegener1 who is the champion of the idea that the atmosphere contains an unknown gas lighter than hydrogen 7called 8geocoronium0 or 8zodiacon071 sees in the prevalence of this gas at high levels the cause of a similar quasi-reflection of sound waves4 ,probably the majority of investigators1 however1 believe that the effect is due chiefly or entirely to the refraction of sound by wind4 ,of acoustic phenomena that belong especially to the domain of meteorology1 probably thunder is the one that excites most general interest4 ,the sudden expansion of the air along the path of a lightning discharge1 due partly but probably not entirely to the heat generated1 appears to be an adequate explanation of the explosive sound of thunder1 though somewhat different explanations have been suggested4 ,if the discharge is near at hand1 we generally hear a single loud crash4 ,more distant lightning is usually attended by rumbling4 ,the common and obvious explanation of rumbling is that it is due to the arrival of the sound progressively from different points along the path of discharge1 which may be a mile or more in length4 ,a crooked path would account for reenforcements and diminutions of the sound4 ,another cause of irregularities in the sound is probably 8interference0 7combinations of waves that tend either to strengthen or to neutralize each other71 especially in the case of multiple lightning discharges1 such as we have described elsewhere4 ,lastly1 thunder is further complicated by echoes from the ground and probably also from the air 7not exclusively from clouds71 though much uncertainty prevails concerning these aerial echoes4 ,the sounds of thunder have been the subject of some interesting investigations on the part of an ,austrian meteorologist1 ,dr4 ,wilhelm ,schmidt1 who has devised apparatus for making an automatic registration of the sound waves that constitute a thunderclap4 ,he finds that there is a great preponderance of waves of very long period1 including many of too low a pitch to be audible1 though perceptible through the rattling of windowpanes1 etc4 ,in fact1 the greater part of the energy involved is represented by these long1 inaudible waves1 so that one really hears only a small part of a clap of thunder4 ,the statement has often been made1 on the authority of ,humboldt1 that thunder is never heard at sea1 at any point far from land4 ,this matter was investigated by the magnetic survey yacht ,carnegie during a long cruise in the ,pacific in #aiae4 ,of twenty-two displays of lightning1 six were accompanied by thunder4 ,the late war gave prominence to certain acoustic phenomena which1 though hardly mysterious1 were novel to the world at large4 ,one of those was the double report 7triple in the case of an exploding shell7 heard near the line of fire of large guns4 ,this effect is due to the fact that modern projectiles travel much faster than sound4 ,the moving projectile sets up its own waves in the air1 like those at the bow of a steamer1 which may reach the ear of the observer and produce the sensation of a sharp sound before he hears the sound coming from the mouth of the gun4 ,another phenomenon frequently observed when heavy firing was in progress was the appearance in the sky of rapidly moving parallel arcs of light and shade4 ,these were generally seen against clouds1 but sometimes they swept across blue sky4 ,they probably occurred only in calm weather4 ,these arcs were the result of the successive condensations and rarefactions of the air constituting waves of sound--visible sound waves4 ,their visibility was due to contrasts in the refraction of light passing through air of different densities2 the same sort of refraction contrasts that cause the tremulous appearance of the air over a hot stove1 for example4 ,the same 8flashing arcs0 of light have been described by ,prof4 ,f4 ,a4 ,perret as attending explosive volcanic outbursts at the craters of ,vesuvius and tna4 ,the humming of telegraph wires has been the subject of a certain amount of discussion in meteorological circles1 but without altogether satisfactory results4 ,this sound is not1 of course1 caused or affected by the electric currents passing along the wire1 and it is almost certainly due solely to the wind1 though the suggestion has been made that it might be caused by the microseisms1 or small and rapid earthquake tremors1 that are so commonly registered by seismographs while imperceptible to the human senses4 ,the humming is best heard when one's ear is placed against a telegraph pole4 ,several persons have made systematic observations of these sounds from day to day1 and it has often been alleged that they vary with the temperature1 the movements of storms1 etc41 and even constitute a safe basis for weather predictions4 ,they are sometimes heard when the air appears to be perfectly calm1 but in such cases there might be some movement of the air at the level of the wires1 though there was none at the lower level of the observer4 ,from what is known about 8olian tones0 7such as those of the olian harp71 it would seem that the humming requires a wind more or less at right angles to the wire1 and that the pitch of the sound depends upon the force of the wind and the diameter 7but not the length or tension7 of the wire4 ,for a given wire1 the stronger the wind the higher the pitch of its sound4 ,of all the sounds that haunt the air1 probably the most mysterious are those which are best called by the generic name 8brontides0 7coined1 in the ,italian form brontidi1 by ,prof4 ,tito ,alippi from two ,greek words meaning 8like thunder071 though they rejoice in scores of other names in various parts of the world4 ,brontides take the form of muffled detonations1 resembling the sound of distant cannon or peals of thunder1 and are heard chiefly in warm1 clear weather4 ,the first systematic investigations of these phenomena were made in ,india4 ,the fact that they were frequently reported from the neighborhood of ,barisal1 a town in the ,ganges delta1 led to their being called 8,barisal guns10 under which name they were first made known to ,european science in #ahij4 ,a few years later they were discussed in an extensive memoir by ,e4 van den ,broeck1 who had collected numerous reports of their occurrence in ,belgium1 especially on the seacoast1 where they are known as 8mistpoeffers0 7i4 e41 8fog belchings0 or 8fog hiccups074 ,the majority of descriptions1 however1 have come from ,italy1 where the sounds appear to be extremely common1 though peculiar to certain localities1 and where they bear a great variety of names4 ,in ,australia the noises are called 8desert sounds10 in ,haiti1 8gouffre10 etc4 ,they have been reported from parts of the ,united ,states1 including ,california and1 above all1 from the vicinity of ,moodus1 ,conn41 which owes its original ,indian name1 ,morehemoodus 78place of noises071 to the brontides which appear to have formerly been much more common there than they are to-day4 ,there is a reference in one of ,lord ,bacon's works to 8an extraordinary noise in the sky when there is no thunder02 apparently a description of brontides4 ,the source of these sounds is undoubtedly subterranean in a great many cases1 though perhaps not in all4 ,prof4 ,w4 ,h4 ,hobbs1 who has made a painstaking study of the seismic geology of ,italy1 concludes that the brontides of that country are due to the slow settling of the blocks of the earth's crust2 a process which1 in its more abrupt and violent phases1 causes definite earthquakes4 ,alippi believes that in order that the sounds may be heard they must be reenforced by a peculiar configuration of the ground1 above or below the surface1 and he attaches special importance to the effects of caverns1 which he suggests act as resonance boxes in the production of audible brontides4 ,occasionally an apparent brontide may be due to the explosion of an unseen meteor4 ,lastly1 a certain proportion of these thunderlike sounds1 if not merely distant thunder1 may be such noises as cannonading1 blasting1 or the like1 made audible at unusual distances by the refraction of sound waves4 ,,chapter ,,xii ,,climate ,,and ,,climates ,some day the meteorologists of the world will join forces to produce a great encyclopdia of climate4 ,no work of science is more sorely needed1 but the magnitude that it would1 ideally1 assume is simply staggering4 ,few people realize the multiplicity and complexity of climates4 ,it is a common occurrence for a prospective traveler or a business man to write to a meteorological establishment requesting1 for example1 a description of the climate of ,south ,america4 ,of course1 no such thing exists4 ,a continent does not have a climate1 but a multitude of climates4 ,even to set forth1 in general terms1 the more important types of climate that prevail between ,cape ,horn and ,panama is no small undertaking4 ,moreover1 general descriptions often fail to supply the needs of those who make inquiries about climate4 ,suppose1 instead of the wholesale order above mentioned1 the meteorologist receives the relatively modest request to describe the climate of ,buenos ,aires or ,rio de ,janeiro4 ,is it easy to comply with such a request8 ,that depends4 ,if the information is sought by a tourist who wishes chiefly to know whether he will need light or heavy clothing at a specified season1 or whether his excursions are likely to be hampered by frequent rains1 we can enlighten him in a few brief paragraphs4 ,if the inquiry comes from a manufacturer who aspires to invade the ,south ,american markets1 we must know1 before replying1 what kind of goods he purposes to export1 and just how they are affected by climatic conditions4 ,are they liable to injury by high or low temperatures1 dryness or humidity8 ,does the demand for them depend1 as in the case of rubber coats1 upon the prevalence of rain1 or1 as in the case of electric fans1 upon the occurrence of hot weather during at least a part of the year8 ,for each branch of the export trade certain elements of climate are important1 and the more detailed and explicit the information that can be obtained about them the better4 ,suppose1 again1 climatic data are desired by a horticulturist who has to solve the problem of introducing a ,south ,american plant into the ,united ,states4 ,in order to find the best environment for it in this country1 he should know something about the climate of its original home4 ,the data he requires are1 however1 different from those sought by the tourist or the manufacturer4 ,is the plant's habitat a region where frosts occur8 ,how long is the growing season8 ,is the rainfall rather evenly distributed over the year1 or are there definite dry and rainy seasons8 ,such are some of the questions he will ask4 ,for the purposes of medical climatology a different set of data will be sought4 ,the astronomer1 selecting a site for a new observatory1 will ask about freedom from clouds1 and also about the pureness and steadiness of the air that insure good 8seeing40 ,the aviator will want information about winds and fog4 ,and so on4 ,thus it appears that climate means very different things to different people4 ,climate has been variously defined as the sum total of weather1 average weather1 typical weather1 etc41 but the conception is still somewhat indefinite4 ,we know that1 while the weather of any place is subject to incessant changes1 its climate persists2 but we need not assume that it persists indefinitely4 ,the geological record proves1 on the contrary1 that vast changes of climate have occurred in the course of long ages4 ,in ,antarctica and in ,spitzbergen are found deposits of coal1 constituting the dbris of ancient forests such as could not exist in the climates now prevailing in those regions4 ,there are plenty of other proofs that great climatic changes have taken place from one geological period to another2 but what of changes in shorter intervals of time8 ,an immense amount of zeal and energy has been devoted to the study of supposed changes of climate4 ,evidence of such changes is sought1 on the one hand1 in a painstaking examination of weather records 7a process often involving the tabulation of hundreds of thousands of figures71 and1 on the other1 in the collection of geographical and historical data bearing on the question4 ,there have been numerous reports of the gradual drying up of ,african and ,asiatic lakes1 of the discovery of ancient ruins indicating that prosperous agricultural communities once flourished in regions that are now deserts1 and of various other tokens that marked vicissitudes of climate have occurred within historic times4 ,a recent ingenious method of studying climatic variations is to measure the successive annual rings seen in cross sections of old trees4 ,thick rings are supposed to have been formed during periods of abundant rainfall1 and thin rings when the rainfall was deficient4 ,this method has been applied to the giant ,sequoias of ,california1 some of which are more than #c1jjj years old4 ,the net result of a wide range of investigations appears to be that1 on the whole1 climate has everywhere been remarkably constant since the dawn of human history4 ,there is much evidence that1 in certain regions1 there have been alternate increases and decreases--recurrent oscillations--of temperature1 rainfall1 etc41 but there is little evidence of progressive changes in one direction4 ,in contrast to the uncertainty that still prevails in the scientific world on the subject of climatic changes is the confidence with which the average layman may be heard to assert that such changes have taken place within his own recollection4 ,the popular idea that climate has changed perceptibly within a single human lifetime is a world-wide delusion1 and one that has1 apparently1 always flourished4 ,in the ,united ,states we hear of the 8old-fashioned winter10 with its unlimited sleighing1 and also of a marked increase or falling off in the rainfall in certain districts4 ,it is an interesting fact that a century and more ago ,americans were indulging in the same sort of retrospections4 ,in the year #aggj1 when ,benjamin ,franklin was president of the ,american ,philosophical ,society of ,philadelphia1 a paper was read before that society entitled3 8,an ,attempt to account for the ,change of ,climate which has been ,observed in the ,middle ,colonies of ,north ,america40 ,it is published in the first volume of the society's ,transactions4 ,barring the long s's and the use of the word 8colonies10 the greater part of it might have been addressed to the owners of automobiles and ,liberty bonds4 ,we are told of a 8very observable change of climate10 remarked by everybody who has resided long in ,pennsylvania and the neighboring colonies4 8,our winters10 says the author1 8are not so intensely cold1 nor are our summers so disagreeably warm as they have been40 ,these changes he ascribes to the clearing and cultivation of the country4 ,another firm believer in old-fashioned winters and old-fashioned summers was ,thomas ,jefferson4 ,in his 8,notes on ,virginia10 written in #agha1 he says3 8,a change in our climate is taking place very sensibly4 ,both heats and colds are become much more moderate1 within the memory even of the middle-aged4 ,snows are less frequent and less deep4 ,they do not often lie1 below the mountains1 more than one1 two or three days1 and very rarely a week4 ,they are remembered to have been formerly frequent1 deep1 and of long continuance4 ,the elderly inform me1 the earth used to be covered with snow about three months in every winter40 ,samuel ,williams1 who published a 8,history of ,vermont0 in #agid1 uses almost identical language in reference to the climate of that ,state4 8,snows10 he says1 8are neither so frequent1 deep1 or of so long continuance as they were formerly2 and they are yet declining very fast in their number1 quantity1 and duration40 ,that these changes1 he adds1 8are much connected with and greatly accelerated by the cultivation of the country cannot be doubted40 ,what are the facts8 ,when the statements above quoted were written few regular records of the weather had been maintained for any length of time in this country4 ,the earliest instrumental record was begun at ,charleston1 ,s4 ,c41 in #agcj4 ,much information was1 however1 available concerning the dates of harvest1 of the formation and breaking up of ice in rivers and harbors1 and other events dependent upon the weather1 which1 if anybody had taken the trouble to collect and analyze it1 would have dispelled the universal belief that marked changes of climate had recently taken place4 ,nowadays it is much easier to refute the common assertion that the climate has changed within the memory of living men4 ,the meteorological history of our country for more than three-quarters of a century has been recorded from day to day by a host of careful observers in every ,state of the ,union4 ,the records show that1 while the weather of one year has often differed strikingly from that of the next1 there has been no real change in climate4 8,old-fashioned0 winters1 for example1 were neither more nor less common half a century ago than they are to-day4 ,our memories of past weather mislead us1 chiefly because we remember the exceptional weather and forget that which commonly prevailed4 ,other circumstances may contribute to the illusion4 ,thus many people who now live in cities1 where modern appliances make them more or less independent of the weather1 passed their childhood under the more primitive conditions of the country4 ,if climates were not fairly constant for long periods of years1 it would be a waste of time to compile the climatic statistics that1 as we have seen1 are wanted by so many different kinds of people for so many different purposes4 ,such statistics are based upon past events1 but their practical value depends upon the fact that1 within certain limits1 they are a safe guide to the future4 ,the climatic data for any place are a sort of digest of the meteorological observations that have been made there1 special emphasis being given to those features of the meteorological record that bear important relations to the life and activities of mankind4 ,temperature and rainfall are the leading elements of climate2 others are wind1 humidity1 evaporation1 cloudiness1 etc4 ,we have not space to enumerate here all the kinds of data found in elaborate climatic tables2 but in order to illustrate how the records of a meteorological station are utilized in compiling climatic statistics and to show what complications may arise in this process1 we shall consider the question of temperature alone4 ,the instruments used in measuring temperature have been described in another chapter4 ,from these instruments are obtained the current temperature of the air1 the wet bulb temperature 7used to compute the humidity71 and the maximum and minimum temperatures of the day4 ,readings are made at fixed hours1 known as 8term hours40 ,at regular stations of the ,united ,states ,weather ,bureau the term hours for the observation of all the meteorological elements are #h a4 m4 and #h p4 m41 ,eastern ,time1 and an observation of temperature1 humidity1 and clouds is made at noon4 ,in most other countries tri-daily readings have been the rule1 though in ,europe four or more observations a day are now taken at many stations in order to supply the frequent weather bulletins required by aeronauts4 ,important stations are generally equipped with thermographs1 which make a continuous record of temperature4 ,theoretically1 the mean temperature of any day is the average of #bd hourly observations1 from midnight to midnight4 ,in practice1 the mean is generally computed from the observations at the term hours1 or from the maximum and minimum4 ,having obtained the mean daily temperature for each day of a month1 the average of these values gives us the mean monthly temperature4 ,the average of the mean temperatures for the twelve months of the year is the mean annual temperature4 ,these data for each day and month1 and for the year--sometimes also for other intervals1 such as five-day periods1 or 8pentads10--are computed year after year1 and eventually the values for all the years of the record are averaged to form what are called 8normals40 ,we thus obtain1 for example1 for a given station1 the normal temperature for ,january #ba1 the normal temperature for the month of ,march1 the normal annual temperature1 etc4 ,all this is a mere beginning toward the complete discussion of a body of temperature observations for the purposes of climatology4 ,we have still to obtain from the readings of the maximum and minimum thermometers the normal maximum and minimum temperatures and range of temperature for each day1 each month1 and the year2 also the 8absolute0 maxima1 minima1 and ranges 7i4 e41 the extreme values that have occurred during the entire record7 for corresponding intervals of time4 ,these data furnish answers to such questions as3 ,what was the lowest temperature ever recorded on ,january #ba8 ,what is the lowest on an average ,january #ba8 ,what is the average range of temperature in ,march8 ,what was the highest temperature ever recorded1 on any day1 at the station8 ,having thus disposed of the extremes and ranges1 we may compute what is called the 8variability0 of temperature1 i4 e41 the average difference between the means of two successive days in a given month1 and the corresponding average for the entire year4 ,these data are of considerable importance in medical climatology4 ,we may also compute the frequency of occurrence of various values among the temperature data above enumerated4 ,the most frequent value is often quite different from the average value4 ,many climatologists compute the number of days1 in an average year1 on which the temperature rises to #gg degrees 7,fahr47 or above 78summer-days071 and the number of days on which the temperature does not rise above the freezing point 78winter-days074 ,especially valuable in agricultural regions are data of the average and extreme dates of the last frost in spring and of the first frost in autumn4 ,these define the length of the 8growing season40 ,statistics of the temperature of the ground at the surface and at various depths below the surface are also of agricultural interest4 ,from the foregoing outline it will be seen that a bewildering variety of climatic statistics may be computed merely from observations of temperature1 and the same is true of the other elements4 ,moreover1 the list set forth above is by no means exhaustive even for temperature4 ,in fact1 there is almost no limit to the number of ways in which the raw material of climatic data--i4 e41 the original records of observation--may be grouped1 averaged1 or otherwise treated in order to bring out certain features of the climate that may conceivably serve some useful purpose4 ,the reader will now be able to understand why a treatise on the climate of a single locality often fills a substantial volume4 ,the numerical data contained in such a work are generally supplemented by text descriptions and by various graphic devices1 such as curves showing the normal fluctuation or 8march0 of a weather element during a day1 year1 or other interval4 ,works which deal with the climates of larger areas1 such as whole countries1 are usually accompanied by climatic charts4 ,these charts furnish a quick and easy way of getting a general idea of the climate of a region4 ,among the more important climatic charts are the following3 #a4 ,temperature 7isothermal7 charts4 ,these include charts showing the distribution of normal temperatures for months1 seasons1 and the year2 normal range of temperature for similar periods2 highest and lowest temperatures ever recorded at the different stations2 etc4 ,lines known as isotherms are so drawn as to pass through places having identical values of the element in question 7mean temperature1 highest temperature1 etc474 #b4 ,rainfall 7isohyetal7 charts4 ,these show the distribution of rainfall 7including snowfall1 expressed in equivalent depth of water72 especially for each month and for the year4 ,other charts may show the average number of rainy days2 average snowfall 7actual depth1 not water equivalent72 seasonal distribution of rainfall2 etc4 #c4 ,wind charts4 ,these are drawn in various forms1 to show the prevailing wind directions1 the frequency of winds from different directions1 the average force of the winds1 etc4 ,charts of the winds at different levels above the earth's surface will eventually be drawn for the use of aeronauts1 but such charts are still in a tentative stage4 ,illustration3 ,a ,,modern ,,isothermal ,,chart ,,of ,,the ,,globe4 7,hann1 #aija7 ,the isotherms show the mean annual temperature in centigrade degrees4 ,as in the case of tabulated climatic data1 the number of charts that might be drawn to bring out different features of climate is practically unlimited4 ,sunshine1 cloudiness1 humidity1 barometric pressure1 and the frequency of various special phenomena1 such as thunderstorms1 hail1 tornadoes1 droughts1 etc41 are all charted in some of the more extensive works on climate4 ,large atlases have been published to portray the climates of certain countries4 ,the study of the actual distribution of climates over the earth1 as distinguished from that of climate in general1 is sometimes called climatography4 ,climates are variously classified1 usually on the basis of one or more of the climatic elements1 but sometimes with reference to their effects4 ,the most familiar classifications refer to temperature4 ,we speak of tropical1 temperate1 and polar climates2 but in using these terms it should not be forgotten that other things besides latitude control the distribution of temperature4 ,location with respect to the ocean or other large bodies of water is almost equally important4 ,a land surface grows warm by day and in summer1 and grows cold by night and in winter1 much more rapidly than a water surface1 and the adjacent air varies in temperature accordingly4 ,hence we have a classification of climates as marine and continental4 ,the former1 under the influence of oceanic winds1 have a moderate range of temperature1 while the latter are subject to extremes of heat and cold4 ,with increase of altitude temperature is diminished1 but rainfall is generally increased4 ,the distribution of rainfall is also determined to a great extent by the paths of cyclonic storms4 ,such are a few of the many things that control the complex distribution of climates4 ,people who never travel far from their own homes usually cherish quite erroneous ideas regarding the climates of distant lands4 ,it is hard for most ,americans to realize1 for example1 that the ,isthmus of ,panama1 in the heart of the tropics1 never experiences temperatures nearly so high as those which occur every summer in the ,united ,states4 ,a citizen of ,south ,dakota1 where the mercury1 in the shade1 frequently rises above #ajj ,fahr41 and has been known to reach #aae1 will be inclined to revise his definition of the term 8tropical0 when he learns that at ,colon1 the ,atlantic terminus of the ,canal1 a temperature as high as #ij is decidedly exceptional1 and that the maximum reading during a period of six years was only #ib4 ,in thirteen years ,canal ,zone vital statistics showed only two deaths from sunstroke and twenty-one non-fatal cases of heat prostration among a population of #abj1jjj4 ,it will also surprise most ,americans to learn that the highest natural air temperatures that have been recorded anywhere on earth were not observed near the equator1 but in a ,california desert4 ,at a place on the edge of ,death ,valley1 rejoicing in the ironical name of ,greenland ,ranch1 a temperature of #acd ,fahr4 was registered in ,july1 #aiac4 ,the thermometer which furnished this remarkable reading was a tested instrument1 installed in a standard screen over an alfalfa sod1 and not exposed to the reflected heat of the desert4 ,at the same place the temperature reached #ajj or more on #edh days in four years4 ,outside of the ,united ,states the highest temperature ever recorded at a meteorological station was #abg ,fahr4 at ,wargla 7,ouargla71 ,algeria4 ,the lowest temperatures encountered by polar explorers are considerably higher than those experienced each winter by the inhabitants of northern ,siberia4 ,the 8record10 so far as instrumental observations go1 is held by the town of ,verkhoyansk1 at which the temperature fell to #ij below zero 7,fahrenheit7 in ,february1 #ahib4 ,strange to say1 this 8winter cold pole0 of the earth has warm summers4 ,at ,verkhoyansk the temperature sometimes rises to #hj above zero1 or higher4 ,at ,yakutsk1 ,siberia1 the thermometer has been known to fall to #hd below zero in winter and to rise #ajb above zero in summer2 a range of temperature exceeding the interval between the freezing point and the boiling point of water6 ,another climatic paradox is that experienced by mountaineers who1 in scaling peaks mantled in eternal snow1 often suffer with the heat1 on account of the intensity of solar radiation in the pure1 dry air of high altitudes4 ,at the health resort of ,davos1 in the high ,alps 7altitude #e1bej feet71 invalids sit out-of-doors without wraps in midwinter1 and1 indeed1 are sometimes driven into the shade to escape the too ardent rays of the sun4 ,at the same time the temperature of the air itself may be far below freezing1 and the ground covered with snow4 ,certain parts of the world are often loosely described as 8rainless10 but1 as we have stated elsewhere1 there is actually no spot on earth at which rain 7or snow1 in the polar regions7 has never been known to fall4 ,in the driest part of the ,sahara--the ,libyan ,desert1 between ,dakhel and ,kufra--the explorer ,rohlfs experienced a drenching rainstorm of three days' duration in #ahgd4 ,neither is the ,sahara1 in spite of its proverbial heat1 exempt from touches of real winter4 ,snow is a common occurrence in many parts of this desert1 even at moderate altitudes4 ,on the higher ,saharan peaks snow lies on the ground all winter1 and is sometimes found1 in sheltered spots1 in summer4 ,occasional falls of snow occur in all parts of ,algeria1 and several falls have been recorded in ,lower ,egypt4 ,when all is said and done1 the whole fabric of what now constitutes the science of climatology leaves much to be desired4 ,climate is of practical interest1 first of all1 on account of its effects on human life and health1 and secondly because of its influence upon the crops that are the mainstay of man's material prosperity4 ,under both these heads climatic data1 as now commonly presented1 ignore certain atmospheric activities of the utmost importance4 ,for biological purposes no description of a climate can be regarded as even approximately complete that does not furnish1 for the region under discussion1 a detailed account of the different kinds of radiation received from the sun1 their intensities and fluctuations2 and there are few places in the world at which even a beginning has been made in the collection of such data4 ,again1 the phenomena of atmospheric electricity1 including radioactivity1 are probably of real climatic significance1 but we are still in the stage of speculation with regard to this subject4 ,possibly there are still other elements of climate1 now wholly neglected1 that will figure prominently in the climatology of the future4 ,,chapter ,,xiii ,,organized ,,meteorology ,no other branch of science is so dependent upon the constant systematic cooperation of a multitude of workers as meteorology4 ,there are1 to be sure1 some kinds of atmospheric phenomena that can be studied advantageously by the individual meteorologist1 with no further aid from his scientific confrres than the same sort of interchange of ideas that prevails in all departments of knowledge2 but the widespread processes that constitute weather and climate require for their observation--whether the purpose in view be weather forecasting1 or the collection of climatic statistics1 or the assembling of data from which to deduce the laws of atmospheric movements--a veritable army of colaborers1 equipped with standardized instruments and keeping their records according to a uniform plan4 ,probably few people1 in looking at the charts portraying the climates of the world that are found in reference books1 realize how many observers have contributed to the preparation of such charts or the number of separate instrumental observations upon which they are based4 ,in the ,united ,states alone there are something like #f1jjj meteorological stations1 at which upward of two and a quarter million observations are made every year--and a climatic chart is1 of course1 the fruit of many years of observations4 ,at the beginning of the present century it was estimated that there were #ca1jjj meteorological stations in operation throughout the world4 ,the present number is doubtless much greater4 ,at some of these stations observations have been made regularly1 once1 twice or three times a day1 for #ajj or #aej years4 ,in round numbers one may say that1 during the last few decades1 meteorological observations have been made1 the world over1 at the rate of ten million a year1 and the total number1 since the keeping of regular weather records began1 runs far up in the hundred millions4 ,organized meteorological observations were not unknown to antiquity--we have mentioned elsewhere the early rainfall measurements in ,india and ,palestine--but the present era of such undertakings dates back only to the middle of the seventeenth century4 ,in the year #afed the ,grand ,duke ,ferdinand ,,ii of ,tuscany1 through his chaplain and secretary1 ,luigi ,antinori1 secured the cooperation of several observers in ,italy and the adjacent countries1 to whom were distributed instruments and forms for maintaining daily records of the principal meteorological elements4 ,antinori and most of the observers belonged to the ,jesuits1 an order which has displayed extraordinary zeal in the furtherance of meteorology down to the present day4 ,the observations thus inaugurated appear to have been kept up until about #affg1 but unfortunately few of the records have been preserved4 ,several undertakings of similar character were launched during the next hundred years in ,france1 ,england1 and ,germany4 ,the most notable of such enterprises1 however1 antedating the foundation of the present official weather services1 was the international system of observations maintained by the ,meteorological ,society of the ,palatinate1 founded at ,mannheim in #aghj under the auspices of the ,elector ,karl ,theodor4 ,the chief credit for the epoch-making work of this society is due to its secretary1 ,j4 ,j4 ,hemmer4 ,the society distributed standard instruments to its observers1 who were widely scattered over the world2 viz41 fourteen in ,germany1 two in ,austria-,hungary1 two in ,switzerland1 four in ,italy1 three in ,france1 four in ,belgium and ,holland1 three in ,russia1 four in ,scandinavia1 one in ,greenland1 and two in ,north ,america 7at ,bradford and ,cambridge1 ,mass474 ,the very detailed observations of this network of stations down to the year #agib were published in twelve large volumes4 ,although the activities of the ,mannheim society came to an end in the troublous days of the ,french ,revolution1 the records that it had collected served as the groundwork for fruitful studies during the next generation4 ,there are two distinct uses that can be made of statistics of this sort4 ,first1 they can be digested in such a way as to bring out the characteristic features of the climate at each of the localities included in the collection1 and likewise to illustrate the distribution of climates over the globe4 ,second1 the data for individual days from the various stations can be charted separately1 so as to illustrate the instantaneous distribution of barometric pressure1 wind and weather1 and1 by a comparison of the charts for successive days1 to provide a sort of moving picture of the atmospheric machinery in operation4 ,charts based on approximately simultaneous observations showing the state of the atmosphere at a particular moment of time over an extensive area of the earth are called synchronous charts1 or sometimes synoptic charts1 though the latter term is also applicable to charts showing average values for a particular month1 year1 etc4 ,synchronous charts1 as used nowadays for the purpose of making forecasts1 are prepared from data collected by telegraph2 but the same kind of charts can be prepared in a more leisurely manner from the statistics gathered at any previous time1 and such charts were frequently made for the purpose of study before the days of telegraphy4 ,the pioneer in such undertakings was the ,german physicist1 ,h4 ,w4 ,brandes1 who1 about #ahbj1 utilized the observations collected by the ,meteorological ,society of the ,palatinate1 together with some others1 in compiling a series of daily synchronous charts of ,europe for the year #aghc4 ,very similar studies were carried out in ,america1 a few years later1 by ,j4 ,p4 ,espy1 ,w4 ,c4 ,redfield and ,elias ,loomis4 ,early in the nineteenth century a copious fund of meteorological observations had already accumulated in this country4 ,the first undertaking in the nature of a meteorological organization1 foreshadowing the present ,weather ,bureau1 was due to ,josiah ,meigs1 ,commissioner of the ,general ,land ,office1 who in #ahag established a system of tri-daily observations at the various land offices4 ,at an almost equally early period the ,surgeon ,general of the ,army inaugurated regular weather observations at the military posts throughout the country4 ,local systems of observations were established by the authorities of ,new ,york ,state in #ahbe and ,pennsylvania in #ahcg1 and systems of broader scope by the ,patent ,office in #ahda and the ,smithsonian ,institution in #ahdg4 ,experiments in collecting weather reports by telegraph for the purpose of forecasting storms were undertaken by the ,smithsonian ,institution as early as #ahdi4 ,at about the same period ,lieut4 ,m4 ,f4 ,maury1 of the navy1 was gathering meteorological reports from mariners and laying the foundations of marine meteorology4 ,finally1 in #ahgj1 ,congress was induced to establish a full-fledged telegraphic weather service1 similar to those that were already in successful operation in ,europe4 ,one of the great promoters of this enterprise was ,dr4 ,i4 ,a4 ,lapham of ,wisconsin2 it had been repeatedly advocated by ,maury2 and a convincing object lesson in its behalf was furnished by the local service of reports and forecasts conducted by ,prof4 ,cleveland ,abbe1 at the ,cincinnati ,observatory1 with the aid of the ,western ,union ,telegraph ,company1 in #ahfi and #ahgj4 ,during the first twenty years of its existence1 from #ahgj to #ahij1 the ,federal weather service was under the ,signal ,corps of the army4 ,since #ahij it has been a branch of the ,department of ,agriculture1 as the ,united ,states ,weather ,bureau1 though the name 8,signal ,service0 stuck to it1 in popular speech1 long after it ceased to belong to the army4 ,in this country weather forecasts are--or once were--said to emanate from 8,old ,probabilities10 or 8,old ,probs40 ,our first 8,old ,probs0 appears to have been ,professor ,abbe1 who has explained the origin of this name in an account of his pioneer forecasting experiments at ,cincinnati4 ,he says of the initial ,cincinnati ,weather ,bulletin1 issued ,september #a1 #ahfi3 8,it contained only a few observations telegraphed from distant observers and announced #8probabilities' for the next day4 ,this bulletin1 in my own hand-writing1 was posted prominently in the hall of the ,chamber of ,commerce1 but unfortunately ,i had misspelled #8,tuesday1' and ,i soon found below my ,probabilities the following humorous line by ,mr4 ,davis1 the well-known packer3 #8,a bad spell of weather for 8,old ,probs40' ,this established my future very popular name of #8,old ,probs4'0 ,the name has1 however1 been more particularly associated with ,gen4 ,albert ,j4 ,myer1 who1 as ,chief ,signal ,officer1 was the first head of the ,federal meteorological service4 ,desultory experiments in the collection of current weather reports and their use in constructing weather maps were first carried out in ,europe at about the same time as the early undertakings of this character in ,america4 ,such reports were gathered and published by ,james ,glaisher1 with the cooperation of the ,british railways1 in #ahdi4 ,the existing national weather services of the ,old ,world owe their origin to an episode of the ,crimean ,war4 ,in ,november1 #ahed1 a violent storm wrought havoc among the ,french and ,british warships in the ,black ,sea and sank many vessels containing invaluable stores intended for the ,allied armies in the ,crimea4 ,the ,french astronomer ,le ,verrier1 director of the ,observatory of ,paris1 collected information showing the progress of this storm across ,europe1 and the results of this inquiry were so significant that he submitted to the ,emperor ,napoleon ,,iii the plan of organizing an international system of telegraphic reports1 by means of which timely warning could be obtained of similar atmospheric disturbances4 ,the ,french ,government1 with the aid of other ,european countries1 established such a system in #ahee4 ,within the next two decades most of these countries organized their own services1 and at the same time maintained an international exchange of observations by telegraph4 ,before the close of the nineteenth century nearly all the civilized countries of the world1 including many colonial possessions1 such as ,canada1 ,australia1 ,algeria and the ,philippines1 had established meteorological services1 entailing more or less extensive arrangements for collecting daily reports by telegraph and issuing storm warnings and weather forecasts4 ,the chief exceptions were several of the ,latin-,american republics and the ,ottoman ,empire1 in which such organizations are still lacking4 ,meteorology is essentially an international science4 ,the atmosphere knows no political boundaries1 and the more it is studied the more strongly meteorologists are impressed with the fact that intimate relations exist between the atmospheric events of widely separated regions of the world4 ,thus1 the great anticyclone that is built up every year over the cold interior of ,siberia exercises an influence upon the weather of the ,united ,states2 the behavior of the ,indian monsoons has been found to have some connection with barometric conditions in ,south ,america2 and fluctuations in the force of the trade winds are apparently of world-wide significance--whence these winds have been described as the 8pulse0 of the general atmospheric circulation4 ,the ,french meteorologist ,l4 ,teisserenc de ,bort called attention many years ago to the existence of what he called 8centers of action02 viz41 large permanent or semi-permanent areas of high and low barometric pressure1 the variations of which correspond strikingly with the vicissitudes of wind and weather in countries thousands of miles distant4 ,last but not least1 persistent attempts have been made to interpret all the weather happenings on our globe in terms of a fluctuating supply of radiant energy received from the sun4 ,fortunately meteorology has possessed an international organization for a great many years4 ,the ,international ,meteorological ,organization was founded at a conference held at ,leipzig in #ahgb1 and was perfected at a formal congress of meteorologists convoked at ,vienna in the following year4 ,the ,international ,meteorological ,committee1 which is the permanent working body of the organization1 was established at the ,vienna ,congress4 ,finally1 the organization was reconstituted at a conference held at ,paris1 by invitation of the ,french ,government1 in #aiai4 ,the ,international ,committee consists of not more than twenty members1 all of whom are directors of official meteorological services4 ,it is supposed to meet at least once in three years4 ,at less frequent intervals are held 8conferences10 to which are invited representatives of all the meteorological services and the principal independent meteorological observatories of the world4 ,attached to the organization are several international 8commissions10 which supervise and coordinate the work of meteorologists in various special fields4 ,at the close of the year #aiba there were commissions on the following subjects3 ,agricultural ,meteorology1 ,weather ,telegraphy1 ,marine ,meteorology1 ,solar ,radiation1 ,application of ,meteorology to ,aerial ,navigation1 ,rseau ,mondial1 and ,polar ,meteorology1 ,investigation of the ,upper ,air1 ,terrestrial ,magnetism and ,atmospheric ,electricity1 ,study of ,clouds4 ,each commission includes in its membership at least one member of the ,international ,committee1 besides a number of experts1 from different countries1 in the particular subject with which the commission is concerned4 ,the resolutions adopted at the various international meetings of meteorologists have been collected in the 8,international ,meteorological ,codex10 the chief object of which is to secure uniformity in methods of observation1 forms of publication1 etc4 ,one of the most notable international undertakings in the history of meteorology was the plan of simultaneous observations1 at ,greenwich noon1 both at land stations and on board ships1 adopted by the ,vienna ,congress at the suggestion of ,general ,myer1 and carried out under the auspices and mainly at the expense of the ,united ,states ,signal ,service4 ,the results of these daily observations1 from #ahge to #ahhg1 were published in detail1 with charts1 by the ,signal ,service4 ,the many bulky volumes of this series1 illustrating the meteorology of the globe 7or mainly the northern hemisphere7 day by day for a period of more than a decade1 are the modern analogue of the 8,ephemerides0 issued a century earlier by the ,meteorological ,society of the ,palatinate--which cover very nearly the same length of time4 ,in recent years the efforts of meteorologists have been bent toward establishing a so-called 8rseau mondial10 or world-wide network of stations1 which will not only provide telegraphic reports for the use of forecasters1 but will also send their detailed records to an international commission to be compiled and published4 ,the telegraphic feature of this project now bids fair to be realized in a manner that was not contemplated when the plan was originally proposed2 viz41 by the broadcasting of weather reports from high-powered radio stations all over the world4 ,an effective 8world weather bureau10 with permanent headquarters and staff1 is at present the most urgent desideratum of practical meteorology4 ,such a bureau would not only tie together the national weather services of the world and greatly facilitate their operations1 but would also digest the great mass of existing climatic statistics and provide for extending the climatological survey of the globe to regions where meteorological stations are scarce or lacking4 ,a typical national meteorological service comprises a central station or institute1 usually1 but not always1 situated at the national capital1 and a network or 8rseau0 of subordinate stations1 which are sometimes classified1 according to the extent of their observations1 as stations of the first1 second1 and third order4 ,they may also be classified1 from another point of view1 as telegraphic and nontelegraphic stations4 ,the former provide telegraphic reports of their observations1 which serve as the foundation for forecasts1 while the latter are maintained chiefly for the purposes of climatology4 ,in some countries--notably in the ,united ,states--there are additional classes of stations engaged in particular lines of work2 these include storm-warning stations1 river stations 7which report river stages and rainfall in the river basins71 stations for agricultural meteorology1 etc4 ,several of the great maritime nations collect reports from vessels on the high seas1 including a small percentage of wireless reports4 ,a number of the national meteorological services carry on work in other branches of geophysics1 such as seismology and terrestrial magnetism4 ,the ,united ,states ,weather ,bureau is an exception to the rule that1 apart from the central offices and a few special stations and large observatories1 meteorological stations are not generally manned by professional meteorologists1 nor are the observers paid specifically for their meteorological work1 though in a great many cases they are public functionaries who are expected to take meteorological observations in addition to their other duties4 ,in this country there are about #bjj stations at which the observers1 of whom there are from one to a dozen or more at each station1 devote all their time to the work of the stations and are salaried employees of the ,weather ,bureau1 and there are several hundred minor stations manned by part-time paid employees4 ,but even in the ,united ,states the great majority of the meteorological stations are operated by unpaid observers4 ,there are about #d1ejj of these so-called 8cooperative stations10 which provide the bulk of the climatic statistics of the country4 ,some of the leading meteorological services of the world1 and the places at which their central offices are located1 are as follows3 ,united ,states ,weather ,bureau 7,washington71 ,meteorological ,service of ,canada 7,toronto71 ,meteorological ,office 7,london71 ,office ,national ,mtorologique 7,paris71 ,reale ,ufficio ,centrale di ,meteorologia e ,geodinamica 7,rome71 ,zentralanstalt fr ,meteorologie und ,geodynamik 7,vienna71 ,indian ,meteorological ,department 7,simla71 ,central ,meteorological ,observatory 7,tokyo71 ,commonwealth ,bureau of ,meteorology 7,melbourne71 ,oficina ,meteorolgica ,argentina 7,buenos ,aires74 ,in ,germany there are several mutually independent meteorological establishments1 of which the ,prussian ,meteorological ,institute1 with headquarters in ,berlin1 is the most important with respect to climatology and research1 while the ,deutsche ,seewarte1 at ,hamburg1 is the chief center for telegraphic weather reports and issues the principal weather map4 ,russia1 before her debacle1 had one of the most splendidly organized meteorological services in the world1 with headquarters at the ,central ,physical ,observatory in ,petrograd1 and a separate service for agricultural meteorology1 which was the model institution of its kind4 ,the ,philippine ,islands have a ,weather ,bureau which is entirely distinct from that of the ,united ,states4 ,this ,bureau1 with headquarters at the ,manila ,observatory1 was founded by the ,jesuits1 who also maintain a quasi-official meteorological service in ,china1 with headquarters at the ,zikawei ,observatory1 near ,shanghai4 ,many meteorological societies have done much for the progress of the science1 and in some cases have shared the duties of the official meteorological services1 especially in maintaining stations for climatology4 ,these include the ,royal ,meteorological ,society and the former ,scottish ,meteorological ,society1 in ,great ,britain1 the ,french1 ,italian1 ,german1 ,austrian1 and ,japanese meteorological societies1 and the ,american ,meteorological ,society1 which was founded in ,december1 #aiai4 ,,chapter ,,xiv ,,weather ,,maps ,,and ,,forecasts 8,forecast0--with the stress on the first syllable when it is a noun1 but often on the second when it is a verb--is a word that meteorology has made peculiarly its own4 ,this fact is not the result of accident1 but of design4 ,the founder of scientific weather prediction in ,great ,britain was ,admiral ,robert ,fitz,roy--the same talented officer who explored the coasts of ,south ,america in the ,beagle and had ,darwin for a fellow-voyager--and his first predictions were issued in #ahfa from the ,meteorological ,department of the ,board of ,trade1 which was under his charge4 ,the boldness of this pioneer undertaking is not easily realized by the present generation1 which is accustomed to see the official weather forecast at the head of every daily newspaper4 ,weather prognostication had previously been the undisputed province of charlatans and quacks4 ,for a civilized government to embark upon such an enterprise must have seemed1 to the educated public1 very much like charging the ,astronomer ,royal with the duty of casting horoscopes4 ,illustration3 ,a ,,glass ,,weather ,,map ,,of ,,the ,,united ,,states ,,weather ,,bureau 7,courtesy of ,u4 ,s4 ,weather ,bureau47 ,there is much virtue in a name4 ,a few years ago the ,united ,states ,bureau of ,fisheries persuaded the ,american public to eat dogfish by changing its name to 8grayfish40 ,similarly1 ,fitz,roy induced the ,british public to take his weather predictions seriously by calling them 8forecasts40 ,the name has stuck2 and nowadays1 throughout the ,english-speaking world1 the expression 8weather forecast0--except as applied comprehensively to predictions of the 8long-range0 variety--means something decidedly less chimerical than the average weather prophecy4 ,illustration3 ,,the ,,sun ,,drawing ,,water 7,photograph by ,p4 ,k4 ,budlong47 ,it is still necessary1 however1 to emphasize the distinction4 ,there are probably many people among us1 well above the illiterate level1 who have no clear idea as to what constitutes a scientific weather forecast4 ,the distinguishing feature of such a prediction1 apart from the fact that it is made by a trained meteorologist1 is that it is1 in all cases1 based upon a weather map4 ,the forecasting machine is a big one1 with its human gear spread over a wide territory4 ,eventually it will be spread over the entire globe1 and then we shall have better forecasts4 ,a little manual entitled 8,the ,weather ,map10 published by the ,british ,meteorological ,office1 says3 8,the making of a single forecast in any one of the meteorological offices of ,europe1 ,america1 ,australia1 or the ,far ,east requires the organized cooperation of some hundreds of persons2 about a hundred observers who note the necessary observations simultaneously at as many separate places and hand in their reports to the telegraphists who transmit them to one center1 where the meteorological expert charts them on a map and draws therefrom the conclusions on which the forecasts are based4 ,the preparation of the map is an essential part of the process4 ,no meteorologist in the modern sense attempts to forecast the weather without reference to a map prepared either by himself or by some one with whom he is in direct communication1 from observations transmitted by telegraph for the purpose4 ,no amount of weather wisdom or weather lore or experience is a substitute for the map4 ,the more expert and accomplished the meteorologist1 the more certain he is that all he can do without the materials for constructing a map1 though he may have a barometer and other instruments at hand1 is to make a guess at what the map is like and think out from that what the weather changes are likely to be4 ,it is a common experience of professional meteorologists away from their base to find themselves appealed to for an opinion about the weather1 judging from the signs of the sky alone1 because they are learned in such things4 ,that is exactly what they are not4 ,accustomed to refer everything to a map1 without one they feel themselves to be rather worse off than those who are unaccustomed to its use4 ,a modern meteorologist thinks in maps2 his language and modes of expression are formed thereby40 ,while the weather map is prepared1 first of all1 for the use of the forecaster1 who makes his predictions from the map before it has passed beyond the manuscript stage1 it has other important uses1 which justify its publication and widespread distribution4 ,the weather map is a weather newspaper4 ,like other newspapers1 it is founded on a system of telegraphic dispatches and is designed to keep us in touch with what is going on in the world4 ,weather news is of general interest because weather plays a part in most of the doings of humanity4 ,sometimes the news we read on the face of the map merely satisfies our curiosity2 at other times it renders us more substantial service4 ,by way of illustrating the manifold purposes served by weather maps1 let us set down two cases that are1 perhaps1 at opposite ends of the scale of utility4 ,our first case is that of the traveler who scans the map to see whether the atmospheric conditions at his distant home are propitious1 that day1 for some outdoor pleasure event on the family program4 ,this we may describe as a sentimental use of the map4 ,the second case is that of an aviator embarking on a flight some time in the fore part of the day1 soon after the morning map has made its appearance4 ,here is a case in which the map is of vital utility1 purely as a record of current conditions4 ,the aviator is not concerned with the forecast of the morrow's weather1 unless he is making an unusually long flight1 but he is immensely concerned with the winds and weather prevailing along his route at the time he flies1 and these will not1 as a rule1 differ radically from the conditions shown on the map of the same morning4 ,since weather affects business in a variety of ways1 people who have business interests away from their places of residence frequently have occasion to consult the weather map4 ,the influence of the weather on crops explains why the map is watched with keen interest by dealers in agricultural products4 ,owners of vessels navigating the ocean or the ,great ,lakes take a practical interest in the present as well as the future location of storms4 ,and so on4 ,it is not necessary to prolong this list of those who use the weather map1 because the popular demand for it speaks for itself4 ,it is worth while to record the fact that the demand far exceeds the supply4 ,in this country the ,weather ,bureau has been constantly harassed with urgent requests for the publication of maps at places where1 in consequence of limited appropriations1 it has not been possible to issue them4 ,the weather maps published in various parts of the world exhibit much diversity in detail1 though they have1 of course1 many features in common4 ,as a rule a weather map covers a wider area than that of the country in which it is published4 ,the aim has always been to make these publications international1 as far as practicable4 ,the longest continuous file of printed daily weather maps in existence1 viz41 that established in ,france by ,le ,verrier in #ahfc and still published1 has been called from its beginning the 8,bulletin ,international40 ,it embraces nearly the whole of ,europe1 a little of ,africa1 ,iceland1 and the ,azores4 ,the other ,european maps now cover the same area or a considerable part of it4 ,before the war the ,russian meteorological service was issuing a map that included1 in addition to ,europe1 a wide zone of ,asia extending all the way to the ,pacific ,ocean4 ,the ,united ,states map1 as published in its most extensive form at ,washington1 comprises the whole of this country and southern ,canada1 besides presenting tabulated statistics for more distant parts of the world4 ,manuscript maps prepared daily at ,washington have a still broader outlook2 they are drawn on a base map that covers the northern hemisphere1 and the printing of a map of this sort1 including a chain of stations extending around the globe1 was undertaken in #aiad1 but was interrupted by the war4 ,the map published by the ,argentine ,meteorological ,office1 at ,buenos ,aires1 covers more than half of ,south ,america4 ,most national meteorological services issue weather maps1 but there are a few that do not4 ,no such maps are published in ,south ,africa or any of the ,south ,american countries except ,argentina4 ,illustration3 ,,land ,,areas ,,embraced ,,in ,,daily ,,weather ,,maps ,,as ,,published ,,in #aiba ,thus there is still much room for the horizontal extension of the weather map1 and there is even more room for its vertical extension4 ,daily weather maps for aeronauts 7chiefly wind maps7 are now more or less on the programme of all the leading meteorological services1 and in a few cases their publication has already begun4 ,probably the first maps of this character1 showing the winds at various levels over a whole country1 were those that began to appear in ,italy in #aiac4 ,the ,british ,meteorological ,office now publishes such maps1 showing winds and clouds at different levels over the ,british ,isles at three hours of the day4 ,in the ,united ,states maps of the 8wind aloft0 are prepared daily1 at ,washington1 from the reports of kite and balloon stations1 but they are not yet published4 ,the ,weather ,bureau has1 moreover1 invented an ingenious method of depicting the winds at several levels on a single map2 in other words1 constructing a map in three dimensions4 ,this consists of attaching arrows to little metal posts erected on an ordinary weather map at points corresponding to the location of the upper-air stations4 ,each post bears a series of arrows--one arrow for each level charted--and the arrows are set in positions showing the direction of the wind at each level4 ,numbers on the arrowheads indicate the force of the wind4 ,when the map is finished it is photographed from two different angles so as to make a pair of pictures suitable for viewing through a stereoscope4 ,these stereoscopic pictures were formerly made every day and a file of them is available for reference and study4 ,illustration3 ,,stereoscopic ,,map ,,of ,,the 8,,winds ,,aloft0 ,there are a few conspicuous points of difference between the weather maps issued in foreign countries and those issued in this country4 ,thus a majority of the foreign weather services publish two or more charts on the same sheet2 either for the sake of showing different meteorological elements separately or1 in most cases1 to represent the conditions prevailing not only at the hour of the current morning observation1 but also at certain hours of the previous day4 ,one of the three editions of the ,british map includes four charts1 corresponding to observations at four different hours4 ,by means of such series of charts one can observe the recent changes of weather as well as the current conditions4 ,weather maps published in the ,united ,states show primarily the conditions at #h a4 m41 ,eastern ,standard ,time1 of the morning of issue2 though certain features of past weather are also indicated1 including changes of temperatures1 movements of storm centers1 etc4 ,evening maps are drawn at ,washington and at many other places1 but are not published4 ,in this country the publication of weather maps has been carried out on a much more liberal scale than elsewhere4 ,instead of issuing maps at only one or a few places1 as is the custom in other parts of the world1 it has been the policy of the ,american service to publish them at populous centers all over the country4 ,in some cases they are printed or manifolded at the local ,weather ,bureau station1 and distributed by mail and messenger2 in other cases they are published in the newspapers4 ,the daily circulation of the maps has thus1 at times1 run up into the millions4 ,this comprehensive duplication of the chart is made possible by special arrangements with the telegraph companies4 ,the reports of observations are1 to a large extent1 sent over circuits1 along which the telegraph offices1 besides forwarding the local report1 copy the reports from other stations as they pass over the wires4 ,certain stations1 forming connecting links between the circuits1 effect the transfer of collected reports from one circuit to another2 so that1 in a very short time1 upward of #aej stations receive the reports from a large number of other stations4 ,the maps issued at stations or published in newspapers are generally rather crude1 though they answer their purpose2 but the large lithographed map issued every day at the ,central ,office1 in ,washington1 is much the most artistic production of its kind published anywhere in the world4 ,illustration3 ,,enlarged ,,section ,,of ,,the ,,stereoscopic ,,wind ,,map ,large weather maps1 drawn with colored chalk on a ground-glass base1 may be seen at certain produce exchanges and railway stations1 on the 8boardwalk0 at ,atlantic ,city1 and in the ,capitol at ,washington4 ,motion-picture weather maps1 made from series of maps showing conditions at successive intervals of time1 have been prepared experimentally in this country and abroad4 ,the reports used in the construction of weather maps are telegraphed from the stations in cipher1 in order to save expense4 ,in ,europe groups of figures are used for this purpose1 but the ,united ,states ,weather ,bureau makes use of a word code1 which offers the advantage over a figure code that1 as a rule1 mistakes in the telegrams can easily be detected by anybody familiar with the code4 ,the ,american weather code is something of a literary curiosity4 ,in each of the many thousand words it contains there are certain significant letters1 and these must fall in certain sequences in order to convey the information required4 ,the ,english language has been ransacked--and somewhat stretched--to secure the necessary words4 ,observers consult the code book in enciphering their reports1 but translating is easily done without the book by those who have mastered the relatively simple principles on which the code is constructed4 ,illustration3 ,,simplified ,,weather ,,map ,,for ,,jan4 #be1 #aije1 #h ,a4 ,m41 ,,eastern ,,standard ,,time ,the language of lines1 shadings and symbols used in weather maps can be learned in a few minutes1 and it is1 as a rule1 fully explained on the face of the map4 ,this is true of foreign maps as well as ,american4 ,a full-fledged weather map is hardly susceptible of reproduction in a book of ordinary dimensions4 ,the simplified map that we show here1 taken from a ,weather ,bureau bulletin1 will1 however1 serve to illustrate some of the features of such publications4 ,the reader should first fix in his mind the explanations printed at the lower left-hand corner of the map and then study the map in the light of what has been said in ,chapter ,,viii about the circulation and movements of highs and lows4 ,on this map we have an exceptionally well-developed high over the middle of the country and a pronounced low on the ,atlantic coast4 ,the former1 with clear skies and very cold weather1 constitutes a cold wave4 ,the latter is attended by a widespread snow storm and1 as may be inferred from the crowded isobars1 by stormy winds4 ,now bear in mind the fact that charts identical with this one1 except that they contained much more detailed information1 were issued in all the more important cities and towns of the ,united ,states on the morning of ,january #be1 #aije1 about a couple hours after the taking of the morning observations1 at #h a4 m41 ,eastern time4 ,the same morning1 weather forecasts1 cold-wave warnings and storm warnings1 deduced from this map1 were issued to some hundreds of thousands of addresses by telegraph1 telephone1 mail1 and messenger4 ,the map itself conveys information comparable in interest to the news of public events published on the first page of the newspapers the same day4 ,the forecasts and especially the warnings are1 in such a case1 worth millions of dollars to the people of the ,united ,states4 ,the following account of the cold wave appears in the ,annual ,report of the ,chief of the ,weather ,bureau for #aije3 8,a severe cold wave appeared over the ,dakotas1 ,minnesota1 ,nebraska1 and ,iowa on ,january #bd1 #aije1 and on the #beth covered the central and upper ,mississippi valleys and extended over the northern portions of the east ,gulf ,states1 the line of zero temperature reaching into northern ,tennessee4 ,on the #bfth the cold wave covered ,florida1 and temperatures below freezing were reported as far south as ,tampa and ,jupiter4 ,at the latter place1 the minimum temperature1 #bd degrees1 equaled the lowest ever recorded since the establishment of the ,weather ,bureau station at that point4 ,considerable damage was done to orange trees where groves could not be fired or protected4 ,ample warnings had been given of the expected low temperatures40 ,the subject of making forecasts from a weather map is one concerning which some big books have been written1 and it cannot be dealt with very satisfactorily in the brief space at our disposal4 ,there are two cardinal rules--viz41 7#a7 the weather has a characteristic distribution in relation to the distribution of barometric pressure1 and 7#b7 pressure systems1 with their attendant winds and weather1 move1 in a general way1 from west to east--but these rules require various qualifications and are subject to various exceptions4 ,thus highs and lows generally take rather circuitous routes in getting1 eventually1 to the eastward1 and sometimes they break up or fade out4 ,the high shown on the annexed map actually moved much more south than east during the following twenty-four hours1 while the low moved up the coast2 i4 e41 more north than east4 ,these were1 however1 the movements expected by the experienced forecaster4 ,well-developed highs are nearly always regions of clear weather and1 in winter1 of cold weather4 ,lows are attended by clouds and precipitation2 rising temperature usually precedes them and falling temperature follows them4 ,the professional forecaster recognizes several types of pressure distribution other than ordinary highs and lows1 and they1 also1 have their characteristic winds and weather4 ,the seven typical forms of isobars1 as classified many years ago by ,r4 ,abercromby1 are3 ,cyclone2 anticyclone2 secondary2 ,v-shaped depression1 or trough2 wedge of high pressure2 col1 or saddle1 between two anticyclones2 and straight isobars4 ,these may be combined in a variety of ways on the weather map4 ,the forecaster learns to classify these combinations consciously or subconsciously1 and grows familiar with their habits and mannerisms4 ,forecasters spend a good deal of time in studying the files of weather maps for past years2 but the results of such studies are not easy to reduce to definite statements4 ,scientific forecasting is1 in its present stage1 almost wholly empirical4 ,the dependence of weather changes upon the phenomena of atmospheric circulation is generally easy to make out1 but the vagaries of winds and pressure are still in the main mysterious2 notwithstanding such interesting developments as 7#a7 the much-discussed rules of ,m4 ,gabriel ,guilbert for predicting the movements of barometric depressions from abnormalities in the force and direction of the winds2 7#b7 the systematic charting of 8isallobars10 or lines of equal pressure change1 associated especially with the name of ,dr4 ,nils ,ekholm2 and finally 7#c7 the hypothesis of a sharp line of demarcation between masses of equatorial and polar air along the so-called 8polar front10 forming the basis of a system of forecasting that originated at the ,geophysical ,institute of ,bergen1 ,norway1 and has had a marked influence upon the methods of forecasters in other parts of the world4 ,as to the practical results of this empirical art1 one point of the utmost importance is commonly overlooked by the public when it complains about the mistakes of the forecaster4 ,he is required to make forecasts of weather day after day1 regardless of the kind of map that is laid before him4 ,sometimes the map is so featureless 7or1 as the forecasters say1 8flat07 that there is little in it on which to build a forecast4 ,at other times there is an abundance of features1 but they are in process of rapid and disconcerting change4 ,in either case the ordinary day-to-day weather forecast is likely to go astray4 ,the brighter side of this picture is that the atmospheric phenomena that count heavily in terms of dollars and imperiled human lives are not found on 8flat0 maps1 and1 when they appear on the map1 generally behave in a simple1 straightforward way4 ,in other words1 such events as great storms and cold waves are far easier to forecast than everyday weather1 and it is the successful prediction of these events that furnishes the principal raison d'tre of an expensive telegraphic forecasting service4 ,since weather predictions serve a variety of purposes1 many different kinds of forecasts and warnings have been developed by meteorological services4 ,in this country there are1 first of all1 district forecasts and local forecasts2 the former1 covering whole ,states and groups of ,states1 being issued at a few main forecasting centers1 while the latter1 applying to a single town and its vicinity1 are issued at a large number of the ordinary ,weather ,bureau stations4 ,there is a long list of forecasts and warnings intended for special classes of the community2 indeed the specialization of forecasts is carried so far that an individual citizen or a single business firm can generally obtain1 by asking for it1 a forecast of any specified predictable feature of the weather for a particular place4 ,the established types of special prediction issued regularly1 or when conditions warrant1 include wind and weather forecasts and storm warnings for mariners2 shippers' forecasts1 relating to temperatures injurious to perishable goods2 aviation forecasts2 8fire-weather0 warnings1 issued when the weather is conducive to fires in the western forests2 avalanche warnings2 and several different kinds of advices for the benefit of agriculture and horticulture4 ,the ,united ,states ,weather ,bureau1 although it is not the only branch of the ,government that carries on work in hydrology1 is the one charged with the duty of issuing river-stage predictions and flood warnings4 ,an elaborate organization is maintained for this purpose1 and the results are extremely successful4 ,the period of time covered by an official weather forecast is generally from one to two days4 ,in this country the morning forecast is ordinarily for #cf hours from #h a4 m41 and the evening forecast for #dh hours from #h p4 m41 but occasionally the period is extended for an additional day4 ,for some years the ,weather ,bureau has issued every ,saturday a forecast in quite general terms relating to the whole of the following week4 ,these long-range forecasts are made for extensive areas of the country1 such as the ,north and ,middle ,atlantic ,states1 the ,ohio ,valley and ,tennessee1 and the ,great ,lakes region4 8,from the weekly forecast10 says an official publication1 8a farmer may know whether it is safe to cut his hay at the beginning of the week or whether it would be better to wait till the last of the week2 and a produce dealer may know whether it is safe1 at a particular time in the early spring1 to start a carload of strawberries to a northern market40 ,the ,british ,meteorological ,office follows a more cautious plan4 ,its regular forecasts are for twenty-four hours1 but occasionally1 when conditions are fairly settled1 announcements are made of what is termed the 8further outlook40 ,the same office sends notices to the agricultural districts when a spell of fine weather1 favorable for haying or the like1 appears to be on the programme4 ,there are a few official meteorological establishments that have embarked on much more ambitious undertakings in long-range forecasting4 ,the classic example is furnished by the ,indian ,meteorological ,department1 which has issued seasonal forecasts of rainfall ever since #ahhb4 ,these were originally based upon reports of the snowfall in the ,himalaya1 abnormalities of which1 as noted in the spring1 appear to be related to the intensity of the subsequent monsoon rainfall4 ,eventually the ,indian meteorologists began to seek in more remote regions for clues to the character of the ,indian seasons1 and they believe they have found them2 the barometric pressure in ,south ,america and at ,mauritius1 the rainfall at ,zanzibar and ,seychelles1 the ,nile flood1 and summer rains in ,australia all seems to bear some relation to meteorological conditions in ,india4 ,the study of world-wide interrelations of weather1 although it has not generally1 as in the case just mentioned1 furnished the basis of official forecasts1 has engaged the attention of a great many able meteorologists4 ,we have spoken on another page of the 8centers of action0 that seem to be such important indexes to changes in the circulation of the atmosphere1 with concomitant fluctuations in weather4 ,telegraphic reports from some of these centers1 including the ,iceland and ,aleutian lows and the ,siberian and ,azores highs1 have helped to guide the ,weather ,bureau in making its weekly forecasts4 ,many attempts have been made to predict the weather months in advance from variations in the temperatures of the water in different parts of the ocean or from the distribution of sea ice in high latitudes4 ,another line of attack upon the problem of long-range forecasting is through observations of solar activities1 as indicated by fluctuations in solar radiation1 the prevalence of sun spots1 etc4 ,lastly1 an immense amount of energy has been expended in efforts to detect definite cycles or periodicities in the weather itself1 without regard to their causes4 ,the thirty-five year period of rainfall and temperature variations1 announced in #ahij by ,prof4 ,e4 ,brckner1 has found a place in all the current textbooks on meteorology1 and several other alleged weather periods have been the subject of serious discussion4 ,from all of which it appears that the professional meteorologist is not at all inclined to discountenance attempts at long-range weather prediction1 provided they are made both honestly and intelligently4 ,unfortunately the vast majority of people who1 in all ages1 have indulged in this sort of vaticination--and their name is legion--have been either dishonest or ignorant1 or both4 ,the world is still well supplied with them1 and they are1 undeniably1 a thorn in the flesh of the scientific forecaster1 who sometimes sees his predictions confounded with theirs by the public1 and who commonly incurs the charge of jealousy and narrow-mindedness because he declines to acknowledge brotherhood with the cranks and impostors who hang about the outskirts of his profession4 ,quack weather predictions are nearly always made for long periods in advance1 and their popularity depends upon the fact that they give the public something--however fallacious it may be--that science does not attempt to give4 ,the making of such predictions appears to be a particularly easy way of acquiring both fame and fortune4 ,in this country there has hardly ever been a time when some exponent of this industry did not enjoy a nation-wide reputation4 ,it is a satisfaction to record1 however1 that foreign countries produce the same sort of celebrities4 ,dr4 ,gustav ,hellmann1 writing in ,germany1 has recently published an extremely interesting account of the famous 8weather prophets0 of the #aith and #bjth centuries4 ,their geographical distribution is given as follows3 ,belgium1 #b2 ,germany1 #cf2 ,england1 #be2 ,france1 #ad2 ,italy1 #b2 ,austria-,hungary1 #h2 ,russia1 #a2 ,sweden1 #a2 ,switzerland1 #e2 ,spain1 #b2 ,north ,america1 #i4 ,the list for the ,united ,states is1 to be sure1 conspicuously incomplete1 but we need not grieve over the fact that the fame of the ,american prophets omitted from the list has not spread to the ,old ,world4 ,the almanac is1 as it has always been1 the chief stronghold of long-range weather predicting4 ,nobody knows to what extent the almanac prognostications are taken seriously by the public1 or are meant to be by the publishers4 ,it is to be feared that the percentage of the population that 8swears by them0 is not inconsiderable4 ,almanac publishers would undoubtedly perform a public service1 and perhaps save themselves some pangs of conscience1 if they would append to their weather predictions the statement that1 like the portrait of the gentleman who displays his anatomy to the signs of the zodiac at the front of the book1 they are published merely for the sake of keeping up an old custom1 and if they would conclude every almanac with the following candid avowal1 which we find in ,gabriel ,frende's 8,almanack and ,prognostication0 for #aehi3 ,thou hast my guess at daily weather ,here present in thy view4 ,my credit shall not lie thereon ,that every word is true3 ,yet some to please ,i thought it best ,to shew my mynde among the reste4 ,,chapter ,,xv ,,agricultural ,,meteorology ,two farmers are grumbling about the weather4 ,the scene is ,ohio1 the time ,july1 and the prevalent crop corn 7i4 e41 maize74 ,farmers have grumbled about the weather from time immemorial4 ,the point of interest in this particular case is that the two grumblers do not agree about what is wrong4 ,farmer ,a thinks the corn needs rain4 ,farmer ,b declares that at this stage rain would do more harm than good4 ,plenty of warm sunshine is1 he thinks1 the right prescription to insure a 8bumper0 crop4 ,of course ,providence will do as it pleases1 and whatever weather comes1 since it cannot be cured1 must be endured2 but it is a matter of practical as well as academic interest to get some inkling betimes as to how your crop is going to turn out1 and the weather is likely to be the decisive factor4 ,moreover1 it is a very significant fact that our two farmers are not of the same mind about which atmospheric blessing is in default4 ,it is painful to reflect that an enormous amount of grumbling about the weather on the part of the rustic community must1 at one time or another1 have been misapplied4 ,it is a plausible assumption that farmers have sometimes worried themselves to death over meteorological events that were either harmless or actually beneficial to their crops4 ,how can we arrive at the facts8 ,admitting1 as everybody does1 that the weather has a preeminent influence upon plant life1 is this influence susceptible of analysis8 ,is there anything definite about it8 ,are not the effects of various atmospheric conditions so entangled with one another1 and with the effects of soil and methods of cultivation--to say nothing of insects and plant diseases--as to baffle all attempts to gauge them separately8 ,there is a new branch of applied science that teaches farmers how to grumble right about the weather4 ,it is called ,agricultural ,meteorology4 ,as a coherent branch of knowledge1 this subject is so new that the first formal textbook about it in the ,english language was published in the year #aibj4 ,it happens that the author of this book1 ,professor ,j4 ,warren ,smith1 of the ,united ,states ,weather ,bureau1 began his investigations in the new field by making a careful study of the relation of weather to the yield of corn in ,ohio4 ,let us see what light his studies shed upon the question at issue between our friends ,a and ,b4 ,day after day1 and year after year1 the principal atmospheric conditions are observed and measured at a great number of points scattered over the ,state of ,ohio1 as they are elsewhere throughout the ,union1 and the records thus obtained are carefully compiled1 summed up1 averaged and otherwise discussed by officials of the ,weather ,bureau4 ,thus a great fund of detailed statistical information about the weather is available for comparison with the statistics gathered by other agencies concerning the yield of crops and their condition at different stages of growth4 ,professor ,smith's analysis of the ,ohio records revealed a fact of so much practical importance that this discovery alone suffices to place agricultural meteorology among the most fruitful branches of knowledge cultivated by mankind4 ,he discovered that the success of the ,ohio corn crop depends chiefly upon the amount of rain that falls during the month of ,july4 ,the normal rainfall of that month for the ,state is #d inches1 while the average yield of corn during the past sixty years has been #cd4e bushels per acre4 ,comparing the values for individual years1 it is found that the yield is strikingly sensitive to variations from the normal ,july rainfall1 and especially so when the rainfall is a little more or less than #c inches4 ,near this critical rainfall point1 a variation of one-fourth inch of rain in ,july means a variation in the value of the corn crop of ,ohio of nearly #c1jjj1jjj1 and a variation of one-half inch makes an average variation in the value of the crop of more than #g1ejj1jjj4 ,when the rainfall for ,july averages over #e inches the probable yield of corn will be more than #bg1jjj1jjj bushels greater than it will be if the rainfall averages less than #c inches4 ,in other words1 this difference of #b inches in the rainfall for the month of ,july adds #ac1fej1jjj to the income derived by ,ohio farmers from corn alone4 ,variations of the temperature in ,july1 in ,ohio1 have been compared with variations in the yield of corn1 with the result that the temperature of the month appears to have little effect upon the crop4 ,thus we find ,farmer ,a to have been right and ,farmer ,b wrong2 but both were merely expressing personal opinions based upon an insignificant sum-total of experience4 ,science rests upon a surer foundation4 ,although the case of the ,ohio corn crop is probably simpler than most of those that agricultural meteorology has to deal with1 for the reason that a single meteorological element is1 in this case1 of decisive importance1 it illustrates a rule of quite general application that has recently come to light2 viz41 that in the growth of any particular crop there is usually a rather brief 8critical period10 when it is most sensitive to the influence of weather4 ,for corn1 in a considerable area of the northern ,united ,states1 this period is ,july1 or more specifically1 in ,ohio1 the interval from ,july #aa to ,august #aj4 ,the rainfall and temperature of other months have1 however1 definite though minor influences1 which can be evaluated for the same regions4 ,with respect to the ,american 8corn belt0 in general1 it is not certain how far the rules deduced for ,ohio are applicable4 ,professor ,smith has been inclined to look upon ,july rainfall as the dominating factor for the whole of that region2 so that1 for example1 a difference of #a inch in the rainfall 7viz41 a total for ,july of #d4d inches or more1 as compared with #c4d inches or less7 has been held responsible for an increase of #ejj1jjj1jjj bushels of corn in the eight principal corn-growing ,states4 ,it has also been stated that in the four ,states of ,indiana1 ,illinois1 ,iowa and ,missouri an increase of half an inch of rain in ,july meant an increase of #aej1jjj1jjj in the value of the crop4 ,these figures have1 however1 been challenged1 and the subject is still under discussion4 ,the study of the critical periods of different crops1 and the determination of the amounts of heat and moisture most favorable to the success of the crop at such periods1 may be regarded as the leading task of the agricultural meteorologist4 ,the most elaborate researches of this character have been made in ,russia by ,professor ,p4 ,brounov1 who founded in #ahif a meteorological bureau1 attached to the ,ministry of ,agriculture1 with an extensive network of stations scattered over the ,russian ,empire4 ,this bureau was quite distinct from the ordinary meteorological service1 under the direction of the ,central ,physical ,observatory in ,st4 ,petersburg4 ,just before the war ,professor ,brounov had #aej stations in operation2 most of them for observing the effects of weather on the leading cereal crops1 though some studied the corresponding relations of horticulture or the animal industries4 ,each agricultural station comprised a small plot of land1 on which a certain sequence of crops was grown year after year under conditions of cultivation as nearly uniform as possible1 the only variable factor being the weather4 ,meteorological instruments were installed in the immediate proximity of the plants under investigation4 ,prior to #aiad ,brounov had determined the critical periods of most of the crops grown in ,russia1 and had published a great deal of information on this subject that could be turned to practical account by ,russian farmers4 ,it will perhaps not be immediately apparent to the reader just how such information can be utilized4 ,its practical applications vary1 in fact1 according to circumstances4 ,first of all1 a knowledge of critical periods and of the weather requirements of crops at these periods enables the farmer to select his crops and time his farming operations on the basis of climatic statistics4 ,brounov published a series of charts showing the probability of dry weather1 as deduced from many years of observations1 for each ten-day period throughout the agricultural year for every part of ,european ,russia4 ,with such charts at our disposal1 and knowing how long after planting each crop arrives at its critical period with respect to moisture1 we can readily estimate the probable success of a given crop planted at a given time and place2 at least1 so far as this is determined by rainfall4 ,if temperature or other meteorological conditions are of special importance at the critical periods1 we shall need additional climatic charts4 ,of course1 the weather in any particular year may differ widely from the climatic averages2 but in the long run crops will prosper in proportion as their critical periods coincide with the occurrence of favorable weather as shown by the climatic record4 ,it will be seen that this is quite a different idea from the traditional one that a certain crop needs a 8moist climate10 another a 8hot climate10 etc4 ,the agriculturist now asks the man of science to tell him when1 between planting and harvesting1 heat or moisture is of vital importance to the crop1 and how much of each will produce the biggest yield4 ,in regions where irrigation is practiced it is obviously advantageous to the farmer to know at what stage of its growth a crop becomes sensitive to the amount of moisture received4 ,during the greater part of its life the plant may be quite indifferent to moisture1 and at such times irrigation would be wasteful4 ,the farmer needs to know not only when the critical period has arrived1 but also what the water requirements are at that period4 ,too much water may be as bad as too little4 ,even when agricultural practice ignores the rules laid down by the agricultural meteorologist1 a knowledge of these rules may be applied with great advantage to the prediction of crop yields4 ,it is hardly necessary to tell any farmer or business man that accurate crop forecasts are an economic desideratum of the utmost importance4 ,the ,united ,states ,government maintains an army of more than #bjj1jjj volunteer crop reporters1 supervised by a staff of experts1 for the purpose of determining month by month the condition of every agricultural crop and its prospective yield4 ,with regard to the monthly announcements of the ,bureau of ,crop ,estimates1 ,professor ,h4 ,l4 ,moore1 of ,columbia ,university1 says3 8,the commodity markets are in a state of nervous expectancy as the time approaches for the official forecasts1 because great values are at stake4 ,it has been estimated that in the case of the cotton crop alone an error in the forecasts which should lead to a depression of one cent a pound in the price of cotton-lint would--assuming a crop equal to that of #aiad--;entail a loss of eighty million dollars to the farmers4 ,the vast values at stake and the dangers when no official estimate is available of the manipulation of the markets in the interest of speculators are held to justify the large recurrent annual cost of the employment of the numerous correspondents1 clerks1 and experts40 ,professor ,moore is one of those who have pointed out that the forecasts based upon the actual condition of the growing crops can be vastly improved by a mathematical analysis of the weather reports from the various regions in which the crops are grown4 ,in fact1 he goes so far as to assert that much better forecasts can be made from the weather reports alone than from reports on the condition of the crops4 ,whether or not this view is unduly optimistic1 it goes without saying that the precise data which agricultural meteorology is now acquiring cannot fail to enhance greatly the accuracy of crop forecasts4 ,of course1 the weather has always been watched with keen interest by everybody concerned with the purchase or sale of agricultural products and has been one of the chief factors determining the rise and fall of prices4 ,at produce exchanges throughout the ,united ,states daily weather bulletins are received from the agricultural districts1 and at many of them a large weather map is drawn every morning by an employee of the ,weather ,bureau detailed for this purpose4 ,the ,bureau has made various other arrangements for supplying the information that is so eagerly desired concerning the weather as it affects crops1 as well as the animal industries4 ,during the 8growing season0 in the cotton1 corn1 wheat1 sugar1 rice1 broom-corn and cattle-producing areas1 designated centers receive telegraphic reports of rainfall and the daily extremes of temperature from substations in the regions concerned1 and these are distributed in bulletin form4 ,each local center1 besides publishing detailed reports from its own area1 issues condensed reports from all the others4 ,the ,bureau also issues every week during the agricultural season a 8,national ,weather and ,crop ,bulletin10 with text and charts setting forth the current conditions of moisture1 temperature1 etc41 and the state of the crops in all parts of the country4 ,the use which dealers and farmers make of these weather reports is1 however1 very far from having been reduced to science4 ,some of these persons1 it is true1 are frequently able1 by a purely instinctive process of deduction1 to make successful forecasts of crop yields from a close study of the weather1 and others have worked out crude rules of their own for the same purpose2 but the agricultural meteorologist approaches the problem in a different way4 ,immense progress has been made in the past decade in applying the mathematical theory of correlation to this problem4 ,this branch of mathematics1 originally developed chiefly for statistical studies in biology by ,galton1 ,pearson1 and others1 is now extensively used by meteorologists not only for studying the effects of weather on crops1 but also for finding out what correspondences or relationships exist between variations of weather in different parts of the world1 as well as between weather and sun spots1 weather and vital statistics1 etc4 ,sometimes1 when the farmers do not disagree on the subject of favorable and unfavorable weather for the crops1 they hold opinions in common that agricultural meteorology is unable to substantiate4 ,an illustration is found in the idea that a good covering of snow during the winter is favorable to the yield of winter wheat4 ,apparently this is one of the host of popular ideas that are based merely on the delusive foundation of 8everybody says so40 ,smith has investigated the statistics of wheat for ,ohio and ,c4 ,j4 ,root those for ,illinois4 ,in both cases their results negative the prevailing opinion4 ,professor ,smith finds 8some evidence to indicate that wheat has a better prospect if it is not covered by snow during the month of ,january10 while ,mr4 ,root states that1 in general1 8the winters of light snowfall are followed by good wheat yields and the winters of heavy snowfall by light yields40 ,the study of the relations between weather and crops is really a branch of a science of broader scope1 known as phenology4 ,this science is devoted to the investigation of all periodic phenomena of plant and animal life that are controlled by the weather4 ,there are1 in some parts of the world1 large corps of phenological observers1 who maintain records year after year of the leafing1 flowering1 and fruiting of both wild and cultivated plants1 the migrations and first songs of birds1 and various other events of a biological character that recur with the seasons4 ,in the course of time it becomes possible to compute from such records the normal dates of these events2 and then1 in any particular year1 a comparison between the actual dates and the normal shows whether the season is early or late1 and by how many days4 ,phenological observations on plants also make it possible to draw charts showing the normal march of the seasons over a country1 expressed in terms of plant life1 and such charts are often more valuable to the agriculturist or horticulturist as a guide in selecting varieties for cultivation and in timing his operations1 than any charts that can be compiled from ordinary climatic data4 ,some admirable charts of this kind have been drawn for parts of ,europe4 ,there are many practical applications of phenology to agriculture1 and there would be more if phenological observations had been made more extensively throughout the world4 ,good phenological charts of different regions would1 for example1 greatly facilitate the work of foreign plant introduction carried on by the ,united ,states ,bureau of ,plant ,industry4 ,in the ,united ,states phenological observations were made systematically between #ahej and #ahfc1 but only desultory work has been done in this line subsequently4 ,the most comprehensive individual record is that maintained by ,thomas ,mikesell from #ahgc to #aiab1 at ,wauseon1 ,ohio1 and published in full by the ,weather ,bureau in #aiae4 ,the old rule of ,american farmers1 inherited from the ,indians1 that the time to plant corn is when the leaf of the white oak is 8the size of a mouse's ear10 illustrates the use that can be made of so-called 8index plants0 of the native flora as guides for farming operations4 ,professor ,a4 ,d4 ,hopkins writes on this subject3 8,if such guide plants do not occur on the farm1 they can be found among the ornamental trees and shrubs and hardy flowering plants of other localities or countries and transplanted4 ,the periodical event of the falling of the flower catkins of the ,carolina poplar has been found to be one of the best guides to the general early or late character of one season as compared with the average1 while the opening of the leaf buds and unfolding of the leaves serve as reliable guides to the progress of spring4 ,the various magnolias in their succession of flowering events serve as excellent guides to the rate of progress of spring and the time to do various kinds of work4 ,the ornamental ,spiras1 ,deutzias1 ,diervillas1 climbing roses1 and ,clematis among the ornamentals1 and the dogwood1 service tree1 redbud1 and oaks among the native trees of the middle and eastern regions of the ,united ,states are more or less constant in their response to prevailing local influences which are indicative of the time to plant certain field and garden crops4 ,the opening of the leaf and flower buds and the flowering of the common fruit trees and shrubs of almost every farm serve as more or less reliable guides to the time to spray for certain insect and plant diseases40 ,dr4 ,hopkins has worked out an interesting rule known as the 8bioclimatic law10 according to which the periodical events of plant and animal life advance over the ,united ,states at the rate of #a degree of latitude1 #e degrees of longitude1 and #djj feet of altitude every four days--northward1 eastward1 and upward in spring1 and southward1 westward1 and downward in autumn4 ,thus1 when the date of any phenological occurrence is known for one locality1 it may be approximately determined for any other4 ,this law has enabled the ,department of ,agriculture to publish rules of general application concerning the best time to plant winter wheat in order to escape the ravages of the ,hessian fly1 thus saving many millions of dollars to ,american farmers4 ,the same law is susceptible of various other profitable uses4 ,illustration3 ,,orchard ,,heaters ,,in ,,operation4 ,the economical use of this method of frost protection depends upon accurate forecasts of the right time to 8fire0 the orchard4 7,courtesy of ,hamilton ,orchard ,heater ,co47 ,the ,united ,states ,weather ,bureau has been a branch of the ,department of ,agriculture since #ahij1 and a very large share of its routine work is devoted to the agricultural interests of the country4 ,the climatological statistics that it has assembled are indispensable in many departments of agricultural research1 besides furnishing varied information of practical value to farmers4 ,the ,bureau has developed a number of special types of forecasts for the rural industries2 such as predictions1 three or four days in advance1 of favorable weather for cutting alfalfa2 forecasts of weather unfavorable for sheep-shearing2 notices to fruit growers of dry-weather periods in which fruit trees should be sprayed2 and warnings of the occasional summer showers that would do so much damage to the great raisin-drying industry of ,california but for the vigilance of the forecasters and the efficient arrangements made by the industry itself for disseminating and acting upon the warnings4 ,of course1 the ordinary daily weather forecasts1 storm warnings1 and cold-wave warnings are valuable in many ways to agriculturists1 and the ,bureau has made great efforts to give such information prompt and general distribution in the rural districts4 ,the forecasts are generally displayed in post offices1 and in many cases the rural telephone exchanges are pressed into service to distribute weather information regularly to all their subscribers4 ,some exchanges sound a signal every morning when the forecast is ready for distribution4 ,lastly1 the wireless telegraph and the wireless telephone1 which1 in the immediate future1 will form part of the equipment of every up-to-date farm1 afford ideal channels for the dissemination of weather news and are already extensively used for this purpose4 ,illustration3 ,a ,,snow ,,surveyor ,,at ,,work4 ,note the cylindrical snow sampler1 with its serrated cutting edge1 and spring balance for weighing the sample of snow 7,photographed by ,j4 ,c4 ,aller47 ,illustration3 ,,snow ,,rollers1 ,,or ,,wind-,,blown ,,snowballs ,,on ,a ,,lawn ,,at ,,potsdam1 ,n4 ,y4 7,photographed by ,t4 ,j4 ,moon47 ,there remain to be mentioned the various steps the ,weather ,bureau has taken to protect the rural industries from the night frosts of spring and autumn1 in the shape of special forecasting arrangements1 the publication of frost charts1 and a wide range of scientific investigations4 ,the ,bureau's undertakings in this line are merely a part1 though a leading one1 of a great campaign of frost protection that is being carried on by scientific and official agencies in this country on a larger scale than anywhere else in the world4 ,frosts1 classified according to their severity as 8light10 8heavy10 and 8killing10 are most likely to occur in spring and autumn1 when an extensive area of high barometric pressure brings its usual accompaniment of clear skies and calm nights4 ,they are predicted on a general scale from the weather map1 and locally from indications of temperature and humidity and a knowledge of important topographic influences1 such as those due to hills and valleys and neighboring bodies of water4 ,in agricultural usage the term 8frost0 is applied to the occurrence of a temperature low enough to kill or injure tender vegetation1 such as growing vegetables or the buds1 blossoms1 and fruit of fruit trees4 ,the occurrence of a frost1 in this sense1 is not necessarily identical with the deposit of ice crystals known as 8hoarfrost40 ,different species and varieties of plants are1 of course1 susceptible in very different degrees to the effects of low temperature2 i4 e41 they differ greatly in 8hardiness40 ,in the case of fruits and vegetables the danger point generally lies a little below the freezing point of water 7#cb degrees ,f474 ,the occurrence of frost is favored by the rapid cooling1 by radiation1 of the earth and its plant covering1 which goes on at night under a clear sky and in still air4 ,under these conditions a layer of stagnant1 cold air forms close to the ground1 with warmer air lying above it4 ,the difference in temperature at different levels is often so pronounced that fruit on the lower branches of a tree is killed while that growing on the higher branches remains uninjured4 ,similarly1 frost will occur in the bottom of an inclosed valley but not on the surrounding slopes4 ,in the case of a valley the layer of cold air that forms at the bottom is commonly deepened by additional cold air draining down from the hills4 ,many large orchards have their 8warm spots0 and their 8cold islands0 or 8north poles10 well known to the orchardist2 due in some cases to the nature of the soil rather than to topography4 ,certain mountain regions in ,north ,carolina are famous for their 8thermal belts0 or 8verdant zones02 i4 e41 areas part way up the slopes that escape the frosts occurring both above and below them4 ,these frostless belts1 which have been the subject of numerous investigations for three-quarters of a century1 seem to mark the upper level of the pool of cold air that collects in the valley by drainage from the mountainsides4 ,a detailed temperature survey of the thermal belt region of ,north ,carolina was made during the years #aiab-aiaf by the ,united ,states ,weather ,bureau and the ,north ,carolina ,state ,board of ,agriculture4 ,in some places the minimum temperature at night was found to be #ae or #bj degrees higher in the thermal belt than at the bottom of the valley1 a few hundred feet below4 ,clouds1 by checking radiation from the earth1 and wind1 by mixing the colder and warmer layers of air together1 both prevent frosts that would otherwise occur4 ,artificial methods of protection include covering plants with screens of wood1 paper1 or cloth1 building smudge fires to provide a blanket of smoke 7a method of doubtful value71 and1 above all1 heating by means of wood fires or various types of 8orchard heater10 burning either oil or coal4 ,an elaborate technique of orchard heating has been developed1 having in view especially the most economical use of fuel and labor consistent with the object to be attained4 ,in many cases orchards are provided with alarm thermometers1 which ring a bell when the temperature approaches the danger point in the orchard4 ,the local prediction of frost from the readings of meteorological instruments is a problem that has not been fully solved4 ,the idea formerly prevailed that the temperature of the dew point1 as determined from readings of the dry-bulb and wet-bulb thermometers in the early evening1 was a safe guide to the fall of temperature to be expected during the night1 but this belief has not stood the test of accurate observations4 ,at the present writing certain formulas involving data of both temperature and humidity are being used experimentally by ,weather ,bureau specialists for predicting the lowest temperature of the night when the general conditions indicate that frost is possible4 ,a comprehensive discussion of this subject has been published by the ,bureau as ,supplement ,no4 #af of the 8,monthly ,weather ,review40 7,washington1 #aibj47 ,,chapter ,,xvi ,,commercial ,,meteorology ,it is a significant fact that the ,american ,meteorological ,society1 which was organized in #aiai1 has a ,committee on ,commercial ,meteorology4 ,the appointment of this committee was one of the earliest tokens of the fact that the applications of meteorology to business1 always recognized to be important and far-reaching1 had at last been segregated as a distinct field of inquiry4 ,the time is near at hand when this field will have its corps of specialists and its textbooks4 ,courses in commercial meteorology will be given in business colleges1 and meteorologists will be attached to the staffs of large business enterprises4 ,the chamber of commerce of a wide-awake western city already maintains a ,department of ,meteorology1 with a former ,weather ,bureau official at its head1 and 8consulting meteorologists10 now practicing their novel profession in other parts of the country1 find their principal clientele among business concerns4 ,weather not only influences most kinds of business1 but is the foundation of many of them4 ,plenty of illustrations of the latter fact will be found in every large department store4 ,umbrellas1 rubbers1 and mackintoshes are made and sold because of rain2 their best market is in countries with rainy climates1 and their sale from day to day fluctuates with the state of the sky4 ,electric and palm-leaf fans are a drug on the market or the reverse1 according to the readings of the thermometer4 ,sleds and ice skates are sold where and when the weather is cold4 ,this list may be prolonged ad lib4 ,if we leave the department store and walk along any business thoroughfare1 we shall discover other striking examples of commercial undertakings that owe their existence chiefly or entirely to the weather4 ,abolish cold weather and you abolish the dealer in furnaces and heating stoves1 besides reducing the rank of the coal-dealer considerably below the 8baronial0 level4 ,eliminate hot weather from the meteorological program and the ice dealer will likewise tumble from his high estate4 ,all this is so obvious that it seems hardly worth while setting down2 and yet the paradox must somehow be explained that business men have not1 in general1 paid much attention to meteorology1 and that they have made only fragmentary use of the official meteorological establishments that were created1 in part1 for their benefit4 ,probably this paradoxical situation is merely a case of mental inertia4 ,during the long ages of traffic before there were any weather maps1 scientific weather forecasts1 or climatic statistics1 the weather was necessarily an unknown quantity in the mathematics of buying and selling4 ,that it is not so to-day is a fact to which the business mind has been very slow in adjusting itself4 ,we have mentioned some of the obvious relations of weather to commerce1 but there are others that are not so obvious4 ,many of these are indirect4 ,thus the effects of the weather on agriculture are nearly always reflected in the commercial world4 ,it is not the farmer alone who suffers from a prolonged drought1 for example4 ,it has been asserted that every severe financial panic in our history has been closely associated with a protracted period of deficient rainfall1 and that there has been no period of protracted drought without a severe financial panic except one that occurred during the ,civil ,war4 ,mr4 ,h4 ,h4 ,clayton1 who published this assertion in #aija1 has cited the case of the wheat crop as illustrating the magnitude of the effect that rainfall exercises on economic conditions in general through its effects on agriculture4 8,if10 he says1 8the amount of wheat raised in the ,united ,states were reduced one-half or even one-third by a year of deficient rainfall1 it is easy to imagine an enormous strain on the business of the country1 and with a succession of such years the effect might mean disaster4 ,such a deficiency in the wheat supply1 with wheat at #hj cents a bushel1 would mean for a single year a direct loss in wealth of more than #ajj1jjj1jjj2 it would mean that nearly all the wheat which is usually shipped abroad would be needed at home2 it would mean that thousands of railroad cars and ships which ordinarily transport this grain would lie idle1 that thousands of men who usually handle this grain in transport would be out of employment1 that farmers in large numbers would be unable to meet their obligations1 and consequently that banks and business of all kinds would suffer40 ,recent prices of wheat give added force to these statements4 ,in contrast to such broad relations of the weather to business1 it may be interesting to point out certain relations which are of so special a character that1 although familiar to hosts of business men1 they have generally escaped the attention of writers on economics4 ,on this subject ,mr4 ,john ,allen ,murphy says3 8,retail sales are influenced tremendously by the weather4 ,this is one factor that makes it impossible for a retailer to equalize the peaks and valleys in his sales chart4 ,favorable weather will bring him a rush of business4 ,a bad day will keep patrons from his store4 ,there is nothing he can do to prevent it4 ,many merchants have tried the plan of offering #8stormy day specials1' but at best such a scheme is only a makeshift that seldom works4 ,the weather also affects the buying moods of people4 ,a dark1 dreary day in summer seems to influence humans to take on the same cast as the atmosphere4 ,they are grouchy and hard to please4 ,on the other hand1 a cold day in winter has the opposite effect4 ,the warmth and cheer of the store is such a pleasant contrast to the out-of-doors that shoppers like to linger over the wares and indulge themselves more readily in the luxury of buying4 8,a stormy day or a series of them always helps the mail-order business4 ,in such weather people are inclined to stay at home4 ,in passing the time1 they are likely to thumb the pages of such catalogues as they have and thus see in them articles that they want4 ,on the farm1 especially in the bleak days of winter1 it is often the custom to order garden seeds1 incubators1 tools1 and many other things that will be needed as soon as spring opens up4 ,on a bad day traveling salesmen find it easier to get the ear of a merchant4 ,not being busy with customers1 he is prone to be more lenient toward the #8boys with the grips4'0 ,another writer on this subject1 ,mr4 ,f4 ,c4 ,kelly1 says3 8,in a large city1 the business of a department store is seriously hurt by rain in the forenoon1 but rain in the early afternoon is usually a big help4 ,most customers of a big-city department store are women1 and nearly all of them live some distance from the store--at the edge of the city or in the suburbs4 ,if it rains along about eight or nine o'clock in the morning1 the woman who had planned to go shopping that day is quite likely to change her mind1 even though she did not intend to go until afternoon4 ,the rain not only suggests discomfort in getting about1 but diminishes her desire or immediate need for certain articles1 and drives the shopping idea out of her head4 ,on the other hand1 if it is bright and clear in the morning1 but clouds up about noon for a heavy downpour which lasts most of the afternoon1 it is the best thing that could happen for the department store1 because shoppers get in and cannot comfortably get out4 ,they shop all over the store1 buy luncheon there1 and shop some more4 ,while the rain is thus helping the department stores1 it may hurt the smaller shops1 because many customers who would otherwise look around are obliged to do their buying all under one roof40 ,no aspect of business more faithfully reflects the weather1 or1 in a somewhat less degree1 the weather forecasts1 than advertising4 ,so important is it1 in many lines of business1 to make advertising fit the weather that one might expect merchants to be1 as a class1 as weather-wise as sailors and farmers4 ,a page of advertising in a great metropolitan newspaper is a costly investment4 ,if1 for example1 it invites the public to pay a ,sunday visit of inspection to some haven for homeseekers in the suburbs and ,sunday turns out to be the kind of day that converts building-lots into bogs1 the advertiser will perhaps be led to inquire whether there is not some means of avoiding another such fiasco2 and he may thus make the surprising discovery that meteorology is not entirely a theoretical science4 ,the conjunction of a conspicuously advertised sale of rubbers and a soppy week-day morning may be either a lucky accident or the result of studying the weather map4 ,in the former case1 supposing the business to be conducted in the northeastern ,united ,states1 where dry weather is about twice as common as wet1 the odds would be two to one against the occurrence even of light showers on the day the advertisement appeared1 and three or four to one against the occurrence of such weather as would make the advertisement decidedly propos4 ,these remarks about newspaper advertising are1 to a great extent1 applicable also to the dressing of windows and the display of goods inside the shop4 ,in both cases a moderate amount of foresight in the matter of weather will result in placing before the customer the right goods at the right time4 ,one of the minor ways in which the merchant can turn the science of meteorology to advantage consists of using meteorological instruments and the official weather forecasts and bulletins for the purpose of attracting attention to his windows or to his stock-in-trade4 ,the drug-store thermometer is the illustration of this process that comes first to one's mind4 ,there is no reason why1 with the progress of civilization1 this celebrated instrument should not be made a trustworthy index of temperature as well as an effective advertisement4 ,in continental ,europe weather instruments are displayed along with miscellaneous advertising matter in many of the street 8weather columns0 7,wettersulen71 which furnished the idea of the meteorological kiosks installed by the ,weather ,bureau in ,american cities4 ,one of the most important branches of commercial meteorology relates to the effects of weather upon transportation4 ,this is a many-sided subject4 ,in the first place1 the railway and steamship companies1 and other concerns engaged in the transport of goods and passengers have their manifold weather problems1 among which one may mention1 at random1 that of dealing with the snow blockades of railways1 precautions against the skidding of taxicabs in wet weather1 the avoidance of iceberg-infested routes at sea1 and the selection of climatically favorable sites for aerodromes4 ,the shipper has a somewhat different1 but overlapping set of weather problems4 8,in the building of railroads10 says ,mr4 ,e4 ,l4 ,wells1 8many phases of climate are to be considered1 including the probability of floods1 deep snows1 high winds1 sand storms1 etc4 ,it is not long since a considerable length of railroad line in one of the ,western ,states was found to be practically worthless because of having been built too near the bed of a stream and therefore being too much subject to damage from floods1 so it was replaced by a line built higher up4 ,the writer remembers two railroads entering the same town in one of the northern plains ,states1 one of which is seldom blockaded1 while the other is sometimes closed by snow for months at a time4 ,in the former case the cuts are parallel to the wind1 while in the latter the wind blows directly across the cuts4 ,in operating railroads a knowledge of the climate is essential4 ,this is particularly true in the shipment of perishable products1 which may require icing or ventilation as a protection against high temperature1 or insulation against cold4 ,not only is a knowledge of climatic conditions essential in taking precaution against loss in transportation1 but weather records are playing an increasingly large part in the settlement of claims for products and property damaged in transit4 ,the claim agents of the leading transportation companies and the traffic managers of the commission houses and producers' associations keep complete files of climatological data1 and a large percentage of claims for damaged goods1 whether they be for a trainload of chilled bananas or for a traveling man's samples ruined by rain1 are now settled out of court on the basis of the weather records4 ,claims for car demurrage are often settled on the basis of the weather reports40 ,detailed information concerning the effects of temperature on all sorts of food products1 both in transportation and in storage1 was collected by the ,weather ,bureau some years ago and published as the ,bureau's ,bulletin ,no4 #ac4 ,while the domestic shipper can easily obtain from the ,weather ,bureau detailed climatic statistics for all parts of the ,united ,states1 as well as the current weather reports for this country1 and can profit greatly by regulating his operations in accordance therewith1 it is not quite so easy for the shipper to foreign markets to obtain the corresponding data of foreign countries4 ,with the expansion of our foreign trade1 the demand for such data has grown to large proportions4 ,the ,weather ,bureau1 which has an unrivaled meteorological and climatological library in ,washington1 is naturally the place where such data are most frequently sought1 but the labor entailed in extracting and digesting the information in response to individual requests is often too great to be undertaken by a ,government office1 where the time of the employees is absorbed in routine duties4 ,there is1 therefore1 a promising field here for the private commercial meteorologist4 ,unofficial work in this line is already carried on to some extent4 ,thus a great steel company in ,new ,york has a salaried 8consulting geographer0 on its staff1 who advises on meteorological questions4 ,one of the problems he has been called upon to solve was to determine the proper dates for shipping steel from ,atlantic and ,pacific ports of the ,united ,states to various places in ,india1 so that it would never arrive during the monsoon rains4 ,records of current and very recent weather in distant countries are1 in a great majority of cases1 unobtainable anywhere in the ,united ,states4 ,the interchange of detailed weather reports between the different meteorological services of the world involves in the first place1 with few exceptions1 a painfully slow process of publication1 and then distribution by mail2 so that1 for example1 records of observations at some places in ,south ,africa or ,australia1 or even many parts of ,europe1 do not reach the ,weather ,bureau ,library1 in ,washington1 until two or three years after the observations are made4 ,undoubtedly the time will come--and probably in the near future--when there will be a world-wide exchange of weather news by wireless telegraphy4 ,one kind of business wholly dependent upon the weather1 which we have not yet mentioned1 is weather insurance4 ,there are several kinds1 but hail insurance and tornado insurance are those extensively practiced2 the former much more widely and systematically in the ,old ,world than in the ,new1 while the latter is confined to ,america4 ,insurance against frost is said to have been practiced in ,germany1 and there appears to be an excellent field for it in the ,united ,states4 ,the insurance of outdoor events1 such as games1 shows1 and al fresco parties1 against rain has been carried on for a good many years by speculative underwriters at ,lloyd's1 in ,england1 and has more recently been undertaken in this country4 ,of course the weather element enters to a considerable degree into other kinds of insurance4 ,ordinary marine insurance is1 to a large extent1 insurance against storms2 fire insurance is partly insurance against lightning2 window and plate glass insurance involves the risk of breakage by wind and hail2 and even life insurance is greatly concerned with the effects of weather and climate4 ,,chapter ,,xvii ,,marine ,,meteorology ,that it behooves a sailor to be weather-wise has always been admitted1 but there was a time1 almost within the memory of men now living1 when neither seamen nor landsmen had the remotest conception of the benefits that a systematic study of the meteorology of the sea was capable of conferring upon the maritime world4 ,the man who first grasped the importance of such a study and translated his ideas into facts was the ,american naval officer1 ,lieutenant ,matthew ,fontaine ,maury4 ,during his brief career at sea ,maury became impressed with the meagerness of the information then available concerning the winds and currents that aid or hinder the voyages of sailing ships4 ,when1 in consequence of an accident that incapacitated him for shipboard duties1 he was assigned to service in ,washington1 he began to explore the old logs of naval vessels1 filed in the ,navy ,department1 for notes on meteorological conditions1 and eventually developed a plan of securing regular observations from both the ,navy and the merchant marine4 ,the result of this undertaking was the publication of the famous ,wind and ,current ,charts1 which revolutionized navigation throughout the world4 ,the practical value of these charts1 of which #bjj1jjj copies were distributed to the masters of merchant vessels of all nationalities1 was promptly recognized4 ,by taking advantage of the favorable winds and currents shown on the charts1 and avoiding those that were unfavorable1 mariners were able to reduce the average time of a sailing voyage between the ,atlantic and ,pacific ports of the ,united ,states by forty days4 ,the money value of the charts to vessels sailing from the ,united ,states to ,south ,america and the ,far ,east was estimated at #b1bej1jjj per annum4 ,british shipping on all seas is said to have benefited to the extent of #aj1jjj1jjj per annum4 ,neither was the utility of the charts limited to the saving of money4 ,the following episode is cited in ,maury's biography3 8,when the ,san ,francisco1 with hundreds of ,united ,states troops on board1 foundered in an ,atlantic hurricane1 and the rumor reached port that she was in need of help1 everyone looked to ,maury as the only man in the country who could tell where to find the drifting wreck4 ,to him the ,secretary of the ,navy sent for information4 ,he at once set to work and showed how the wind and currents acting upon a helpless wreck would combine to drift her #8just here'1 pointing to a spot on the chart1 and making a cross mark with the blue pencil he had in his hand4 ,just there the relief was sent1 and just there the survivors of the wreck were picked up4 ,this was an incidental result of his study of winds and currents40 ,a further outcome of ,maury's enterprise was the holding1 at his suggestion1 and by invitation of the ,united ,states ,government1 of an ,international ,maritime ,conference1 which met in ,brussels in #ahec1 and worked out a world-wide plan for meteorological observations at sea4 ,the work thus begun has since been carried on by the leading maritime nations of the world4 ,in the ,united ,states the duty of gathering weather reports on a uniform plan from vessel masters has been intrusted1 at different times1 to the ,hydrographic ,office1 the ,signal ,service1 and the ,weather ,bureau4 ,it is now performed by the last-named institution1 through its ,marine ,division1 but the ,pilot ,charts and books of sailing directions 78,pilots07 in which the compiled information is published1 are issued by the ,hydrographic ,office of the ,navy4 ,the modern successors of ,maury's ,wind and ,current ,charts are1 especially1 the ,pilot ,charts for the different oceans issued monthly in ,washington1 and the monthly charts of similar character published by the ,british and ,german governments4 ,apart from these periodical publications1 valuable collections of meteorological charts for oceans or smaller marine areas have been published by the ,british1 ,german1 ,dutch1 ,indian1 ,japanese and other authorities4 ,the value of such publications has not been lessened by the gradual substitution of steam for sails on ocean-going vessels4 ,while wind is no longer all-important1 it is a factor in determining the speed1 and hence the earning capacity1 of all classes of ocean shipping1 and the same is true of marine currents4 ,fog and drifting ice are1 in general1 more serious obstacles to steamers than to sailing ships4 ,a glance at one of the ,hydrographic ,office ,pilot ,charts will suffice to show that these publications are indispensable to the mariner4 ,on these charts we find1 first of all1 in the center of each five-degree square of latitude and longitude a 8wind rose0 showing the frequency of the winds that have been observed in that region from each of the cardinal points1 and their average force from each direction4 ,on the charts will also be found the routes recommended for full-power and low-power steamers and sailing vessels1 lines of magnetic variation1 tracks of storms in past years for the month in question1 location and force of currents1 average limits and prevalence of fog for the month1 recent information about drifting ice and derelicts1 descriptions of storm signals1 and an abundance of other information of vital importance to the seaman4 ,illustration3 ,,ocean ,,weather ,,map ,,prepared ,,from ,,vessel ,,reports ,,jan4 #aa1 #aiac1 ,,greenwich ,,mean ,,noon ,u4 ,s4 ,weather ,bureau ,solid black lines are isobars4 ,arrows fly with the wind1 the center of the arrowhead marking the position of the vessel1 and the number of feathers denoting the force of the wind on the ,beaufort scale4 ,shading of the head shows degree of cloudiness4 ,most of the material used in the preparation of the charts above described is obtained from a great corps of volunteer marine observers1 who enter their observations at stated hours in forms provided for the purpose and send these records to the establishment in charge of the work at the end of each voyage4 ,the forms furnished by the ,united ,states ,weather ,bureau prescribe only one regular observation a day1 to be taken at ,greenwich mean noon4 ,each observation shows the position of the ship1 the direction of the wind1 the force of the wind on the ,beaufort scale1 the height of the barometer1 the readings of the dry-bulb and wet-bulb thermometers1 the temperature of the water at the surface1 the state of the weather1 and the kind1 amount1 and movement of clouds4 ,in order to check the accuracy of the barometric readings1 the observer is instructed to read his barometer at prescribed hours on three successive days when in port and send the readings to the ,weather ,bureau4 ,on receipt of these readings the ,bureau compares them with those of the nearest meteorological station1 and then mails the observer a 8barometer tag10 showing the results of the comparison and the error of his instrument4 ,besides keeping up these routine observations1 the observer keeps a record of fog encountered at any hour of the day and makes detailed reports on storms4 ,many marine observers also report observations at stated hours by wireless telegraphy4 ,the enormous fund of information thus collected over the ocean is applied to several purposes besides the construction of ,pilot ,charts4 ,our ,weather ,bureau and certain foreign meteorological institutions prepare daily charts1 showing approximately the instantaneous conditions over great oceanic areas1 especially the ,north ,atlantic4 ,these maps are analogous to the daily weather maps published for land areas1 but the drawing of each map is1 necessarily1 delayed for several months after the date to which it refers1 in order to allow time for the receipt of as many reports as possible from ships at sea4 ,as a rule such charts are prepared in manuscript only1 but1 though they cannot be distributed after the manner of ordinary weather maps1 they are valuable for studies in the institution itself on the movements of storms and other atmospheric processes4 ,they also enable the meteorological officials to answer inquiries concerning the winds and weather that have prevailed over a particular part of the ocean on any specified date4 ,such inquiries come from vessel owners1 underwriters1 and others1 and the replies are frequently used as evidence in admiralty suits4 ,in the case of one series of such maps--viz41 the daily synoptic charts of the ,north ,atlantic1 begun by ,niels ,hoffmeyer1 of ,copenhagen1 and now prepared jointly by the ,danish ,meteorological ,institute and the ,deutsche ,seewarte1 in ,hamburg--the charts have actually been published and sold1 though they are so costly that the number of sets in libraries throughout the world is probably small4 ,these remarkable charts present daily pictures of the winds and barometric pressure over the ,north ,atlantic ,ocean and the adjacent continents from #ahgc to #ahgf1 and from #ahhj down to a recent date4 ,from what we have already said it will be seen that the marine observers cooperating with the ,united ,states ,weather ,bureau and kindred institutions abroad are all contributing toward the great task of recording the history of the weather over the oceans from day to day and assembling data that can be digested in the form of marine climatic statistics and used as the basis for many scientific investigations4 ,this concerted undertaking does not1 however1 constitute the whole scope of marine meteorology4 ,every intelligent mariner finds it necessary to acquaint himself with the laws of the winds1 indications of coming storms1 means of determining the proximity of icebergs1 the systems of storm signals used in different countries1 the method of constructing weather maps from wireless bulletins1 etc4 ,he ought1 in short1 to become an accomplished meteorologist4 ,one of the classic problems of the navigator is that of handling his ship in a violent cyclonic storm1 especially a tropical hurricane4 ,the reader will recall that a cyclone1 besides traveling as a whole at a rate of several hundred miles a day1 consists of a system of winds rotating around the center4 ,the result of this double motion is that the winds on one side of the center are not only more violent than those on the other1 but they are also so directed as to drive a vessel running before the wind1 across the storm track ahead of the advancing center1 while those on the other side tend to drive a vessel to the rear of the storm4 ,the two halves of the storm area are accordingly known as the 8dangerous0 and 8navigable0 semicircles1 respectively4 ,while this simple statement sets forth the fundamental facts involved1 the actual problem is complicated by many features1 such as the fact that the winds do not blow in circles1 but more or less spirally1 that the area of the storm cannot be readily determined1 that two storms may occur in close proximity to each other1 etc4 ,the accompanying diagram1 published by the ,united ,states ,hydrographic ,office1 represents a cyclonic storm in the northern hemisphere1 the circles being isobars1 or lines passing through places at which the same barometric pressure prevails 7indicated in inches71 and the arrows indicating the direction of the winds4 ,the diagram is thus explained3 8,for simplicity the area of low barometer is made perfectly circular and the center is assumed to be ten points to the right of the direction of the wind at all points within the disturbed area4 ,let us assume that the center is advancing about north-northeast1 in the direction of the long arrow1 shown in the heavy full line4 ,the ship a has the wind at east-northeast2 she is to the left of the storm track1 or technically in the navigable semicircle4 ,the ship b has the wind at east-southeast and is in the dangerous semicircle4999999,a vessel hove to at the position marked b1 and being passed by the storm center1 will occupy successive positions in regard to the center from b to b#d1 and will experience shifts of the wind1 as shown by the arrows1 from east through south to southwest4 ,on the other hand1 if the storm center be stationary or moving slowly and a vessel be overtaking it along the line from b#d to b1 the wind will back from southwest to east1 and is likely to convey an entirely wrong impression as to the location and movement of the center4 ,hence it is recommended that a vessel suspecting the approach of proximity of a cyclonic storm should stop for a while until the path of the center is located by observing the shifts of the wind and the behavior of the barometer40 ,the movement of the winds around the storm center shown in this diagram is that of cyclones of the northern hemisphere2 i4 e41 contrary to the direction of the clock hands4 ,in the southern hemisphere they blow in the opposite direction around the center4 ,illustration3 ,,navigation ,,of ,a ,,ship ,,in ,a ,,cyclonic ,,storm 7,u4 ,s4 ,hydrographic ,office47 ,by observing the rise or fall of the barometer1 the shift of the winds1 and the state of the sea and sky1 the experienced navigator is generally able to lay down on a chart the approximate position of the storm center and steer his vessel so as to avoid danger4 ,various devices1 known as 8storm cards10 8cyclonoscopes10 etc41 have been used to aid in the process of locating a storm from shipboard observations4 ,in the ,far ,east mariners use for locating typhoons an ingenious combination of the storm card and the aneroid barometer1 called the 8barocyclonometer10 an invention of the ,rev4 ,j4 ,algu1 director of the ,philippine ,weather ,bureau4 ,the most important development in marine meteorology in recent years has been the rapidly increasing use of radiotelegraphy1 both by marine observers in transmitting reports of observations to shore and to other ships1 and by meteorological institutions in issuing weather bulletins and storm warnings to vessels at sea4 ,the first regular undertaking in this line was carried out under the auspices of the ,london ,daily ,telegraph in the year #aijd4 ,this newspaper arranged with some of the leading transatlantic steamship lines to furnish weather reports by wireless from their vessels1 and these reports were published in its columns for several months4 ,the following year the ,united ,states ,weather ,bureau began1 in a tentative way1 the collection of wireless weather reports from off-shore vessels1 and similar undertakings were soon afterward launched in other parts of the world1 but for some years such reports were of little practical value1 owing to the limited range of wireless communication4 ,illustration3 ,a ,,shipboard ,,weather ,,map ,vessels off the ,american coast can make their own weather maps every night1 using data supplied at fixed hours by high-power radio stations 7shown by stars on the map71 together with radio reports from other vessels4 ,letters near stations are the code letters used in wireless bulletins to describe the stations4 ,vessel reports are indicated by names4 ,arrows show direction of wind and the force on the ,beaufort scale 7shown by the number of feathers74 ,besides data for constructing maps1 the radio stations issue forecasts and storm reports for each of the numbered zones shown off the ,atlantic coast and over the ,gulf4 ,at the present time wireless reports from ships on the ,atlantic enable the forecasters on both sides of that ocean to extend the areas of the weather maps on which their predictions are based1 and reports from ships are also received to a limited extent by forecasters on our ,pacific coast as well as in the ,far ,east1 ,india1 and elsewhere4 ,in this country such reports have been especially valuable in indicating the movements of ,west ,india hurricanes1 and thus have helped to solve the problem of protecting the vast tonnage that has been attracted to ,caribbean waters by the opening of the ,panama ,canal4 ,the reciprocal process of transmitting weather intelligence to vessels by wireless bulletins1 broadcasted at certain hours every day by high-powered radio stations1 has made much more progress4 ,such bulletins include information concerning the current and prospective weather1 winds and storms over specified ocean areas1 as well as reports of observations made at a number of land stations1 from which it is possible for vessels at sea to construct their own weather maps4 ,they are thus enabled to take advantage of favorable winds and to avoid unfavorable winds and storms4 ,wireless weather reports from other vessels help to piece out these shipboard maps4 ,the meteorological services of all civilized countries adjacent to the sea display signals along their coasts to announce the coming of storms dangerous to navigation4 ,one of the earliest devices used for this purpose was the 8aeroclinoscope10 a form of semaphore formerly employed by the meteorological service of ,holland4 ,the position of the arm of the semaphore indicated the region in which the barometer was low2 i4 e41 the storm center4 ,in the ,british ,isles1 in the middle of the last century1 ,admiral ,fitz,roy introduced the use of canvas cones and 8drums0 7i4 e41 cylinders71 which1 seen from any direction1 have the appearance of solid triangles and squares against the background of the sky4 ,the ,british later abandoned the drum and used the cone only1 pointing up or down for northerly or southerly gales1 respectively4 ,the ,american storm flag--red with a square1 black center--was adopted by the ,united ,states ,signal ,service 7the predecessor of the ,weather ,bureau7 in #ahga4 ,this signal was subsequently amplified by the addition of red and white pennants to show the expected direction of the wind at the beginning of the approaching storm4 ,most countries use lanterns for night storm signals4 ,in the year #aiji a uniform system of signals1 consisting of cones by day and lanterns by night1 was recommended for use in all countries by an international commission which met in ,london4 ,in spite of this recommendation some thirty or forty different systems of daytime storm signals are now in use in different parts of the world4 ,on the ,china coast an elaborate system of signals1 consisting of cones1 balls1 diamonds1 and squares displayed on a mast and yardarms1 indicates the existence of a typhoon anywhere in the neighboring seas1 together with its location and movement4 ,,chapter ,,xviii ,,aeronautical ,,meteorology ,during the great war the ,british ,government decided1 in its wisdom1 to establish a flying field in ,scotland1 at which aviators were to be trained in dropping bombs4 ,the commission having this matter in hand chose a site on the shores of ,loch ,doon4 ,in laying out the field a bog had to be drained2 then a railway was constructed1 hangars were erected1 and other operations were carried out1 entailing altogether an expenditure of half a million pounds4 ,at a certain late stage in the proceedings the disconcerting discovery was made that the field could never be successfully used for the purpose intended1 on account of the gusts and eddies produced by the surrounding hills4 ,the undertaking was therefore abandoned4 ,the authorities had presumably enlisted the skill of engineers from the outset of the work--but they had failed to consult a meteorologist6 ,a few such object lessons seem to be necessary to demonstrate the fact--which ought to be obvious--that meteorology is an indispensable and vital adjunct of aeronautics4 ,this fact is now pretty well understood4 ,nearly all the activities of mankind are more or less influenced by weather1 but few1 if any1 to such an extent as aeronautical enterprises4 ,hence a definite branch of applied science--,aeronautical ,meteorology--is rapidly taking shape4 ,already it enters into the curriculum of aeronauts2 it has profoundly modified the methods of the ordinary meteorological services of the world2 and it is raising a crop of specialists1 some of whom are now employed by the business firms that manufacture or operate aircraft4 ,the statement has constantly been made since the war that aeronauts are becoming 8independent0 of the weather4 ,this statement has a grain of truth in it1 but no more4 ,it is a fact that1 under war conditions1 aviators flew in every sort of weather1 and often with impunity4 ,even since the war commercial aircraft have negotiated adverse atmospheric conditions with remarkable success4 ,a spectacular feat of this sort was achieved on ,august #bh1 #aiai1 when a passenger-carrying aeroplane on the ,paris-,london route1 piloted by ,lieutenant ,shaw1 flew over this route through a hurricane blowing in gusts of from #dj to over #ajj miles an hour1 accompanied by a torrential rainstorm and such poor visibility that the pilot was frequently obliged to fly very low in order to pick up his landmarks and make sure that he was on his course4 ,the flight was accomplished in #a hour and #ej minutes--about half an hour less than schedule time4 ,it is said that 8the two passengers in the cabin of the machine emerged without any appearance at all of strain0--such as they certainly would have experienced if they had made the crossing by the ,channel steamer on that boisterous day4 ,in fact the land and sea route was seriously disorganized by the storm1 and the ,continental trains were arriving in ,london hours late4 ,lest hasty conclusions should be drawn from this episode it should be stated at once that the company operating the air route in question1 far from considering itself independent of weather1 is not content with the detailed bulletins furnished to aeronauts by the ,british ,meteorological ,office 7which specializes in aeronautical meteorology more extensively than any other official weather service in the world71 but maintains an elaborate weather service of its own1 with an able meteorologist at the head of it4 ,an accurate statement of the situation would be that wind and weather are no longer the grave dangers that they once were to the aeronaut2 but they are still1 and will probably always be1 factors of the utmost importance in the successful and profitable operation of aircraft4 ,in order to make this matter plain it will be necessary for us1 first of all1 to devote a few words to some of the fundamental principles involved in aerial navigation4 ,the layman who sees nothing mysterious in the ascent of a balloon is1 in general1 somewhat puzzled by the phenomenon of a heavier-than-air machine rising from the ground4 ,yet1 in both cases1 the ascent of the vehicle depends upon the fact that air is not just empty space1 but a material substance1 possessing density1 weight1 and other properties many of which pertain also to solids4 ,a balloon rises not because it is light1 but because the air about it is heavy4 ,in other words1 gravity pushes the air under the balloon more forcibly than it pulls the balloon downward4 ,the ability of an aeroplane to leave the ground depends upon the fact that air offers resistance to bodies moving through it4 ,illustration3 ,a ,b _/ _/ _/ ------------- -------_/------ _/ _/ _/ ,,the ,,effect ,,of ,,air ,,resistance ,,on ,,an ,,aeroplane ,suppose a vertical plane 7,a7--such1 for example1 as the wind shield of an automobile--is moving horizontally through still air4 ,the resistance of the air impedes its motion1 and a part of the motive power is employed in overcoming this resistance4 ,now1 suppose the plane 7,b7 is nearly1 but not quite1 horizontal1 and is propelled by a force tending to make it move in the direction indicated by the arrow4 ,this is approximately the case of an aeroplane driven by a motor2 the plane representing the wings of the machine4 ,only a part of the air's resistance is now effective in impeding the forward motion of the plane4 ,the rest of it pushes the plane upward4 ,if you hold your hand at such an angle and move it through water you will feel an analogous upward push4 ,moreover1 you will notice that the faster you move your hand the greater is the push4 ,not only does this upward pressure of a fluid upon an inclined plane moving through it vary with the speed of the latter 7to be exact1 as the square of the speed71 but it also varies with the angle which the plane presents to the fluid in its path4 ,if the wing of an aeroplane1 for example1 cuts the air nearly edgewise1 the upward pressure will be slight4 ,as it departs from an edgewise position1 7with the front edge higher than the rear71 the upward pressure increases1 but not indefinitely2 beyond a certain rather small angle it begins to diminish4 ,in an aeroplane the upward pressure1 or 8lift10 is increased by giving the wings a slightly arched shape1 or 8camber40 ,the air flows over the arched wings in such a way as to produce a suction above them which helps the push from below4 ,the actual amount of lift for a given speed has been determined by experiments for wings of various shapes and sizes and set at various angles to the line of motion4 ,if1 when the machine is in the air1 the lift is just sufficient to counterbalance the weight of the aeroplane1 the latter flies horizontally4 ,an increase in lift causes the machine to rise2 a decrease in lift permits gravity to pull it down4 ,now suppose the aviator is flying horizontally and wishes to climb4 ,at the rear of the machine and forming part of its tail is a hinged horizontal flap called the 8elevator10 under the control of the pilot4 ,by giving this flap an upward tilt he causes the air to exert a downward pressure on the tail of the machine1 and hence the nose of the machine is carried upward4 ,while the inertia of the aeroplane tends to carry it along the original path1 its wings now present a greater angle to the air1 the lift is increased1 and the machine rises4 ,the reverse of this operation will cause the machine to descend4 ,illustration3 ,,the ,,bed ,,of ,,potomac ,,river1 ,,at ,,washington4 ,from an altitude of a few hundred or a few thousand feet1 submarine features are clearly revealed to great depths4 ,objects have thus been photographed #de feet under water4 ,the shoals are submerged to a depth of from #b to #e feet4 ,in favorable weather1 aerial photographs are valuable in making hydrographic surveys4 7,photographed from the air by ,dr4 ,w4 ,t4 ,lee1 ,u4 ,s4 ,geological ,survey47 ,a vertically hinged flap in the tail1 acting on exactly the same principle as the rudder of a ship1 enables the pilot to turn horizontally4 ,two or more small horizontal flaps1 known as 8ailerons10 attached to the wings1 are used to preserve the lateral balance of the machine1 and to give it the proper 8bank10 or inclination1 when making a turn4 ,illustration3 ,,drilling ,,with ,,compressed ,,air ,,in ,a ,,copper ,,mine4 ,the drill also forces a stream of water into the hole to lay the dangerous sulphur-bearing dust4 7,courtesy ,sullivan ,machinery ,co47 ,illustration3 ,,launching ,a ,,weather ,,bureau ,,kite ,,from ,,the 8,,seneca0 ,,during ,,the ,,international ,,ice ,,patrol1 ,,to ,,explore ,,the ,,air ,,over ,,the ,,ocean4 7,photograph1 ,u4 ,s4 ,weather ,bureau47 ,with these few details in mind1 we shall be prepared to consider1 in a general way1 how the behavior of an aeroplane is affected by the wind and other atmospheric phenomena4 ,with respect to wind there is an important difference between aircraft and marine craft4 ,mere strength of wind is not dangerous to an aeroplane1 except when starting or landing4 ,an aviator flying above the clouds1 with no landmarks in sight by which to gauge his movements1 is no more conscious of the actual wind at that level1 provided it is steady1 than he is of the rotation of the earth on its axis4 ,he feels the wind produced by the motion of his machine through the air--the so-called 8relative wind0--but no other4 ,the true wind may be a mere zephyr1 or a hurricane blowing #aej miles an hour2 the effect is the same on his machine1 so far as he is able to observe4 ,on the other hand1 a strong wind has a very different effect from a light one upon the course of the aeroplane's flight with respect to the ground beneath4 ,if a pilot1 with no landmarks to guide him1 steers by compass for a certain point1 and if there is a strong cross-wind of which he is unaware1 he will be carried far out of his course2 a wind dead ahead or astern will merely affect the speed of his flight1 so that he will arrive later or sooner at his destination than he expected4 ,one of the important problems of aeronautics1 especially from the commercial point of view1 is to prevent aircraft from being driven off their course by the wind when flying with no visible landmarks2 i4 e41 over clouds1 fog1 the ocean1 or an unmapped country4 ,when this problem is solved1 pilots will fly above the clouds much more commonly than they do now4 ,the winds at high levels are generally both steadier and stronger than at low4 ,the stronger wind is an advantage or a disadvantage1 according to whether it is blowing in the direction of flight or the reverse2 but as the winds at different levels generally blow in different directions1 a pilot who is independent of landmarks can choose whatever level affords the winds most favorable for his intended journey4 ,over established air routes quite elaborate measures are now adopted to keep pilots informed of the direction and speed of the wind at different levels1 so that they can make due allowance for this factor in shaping their course4 ,in clear weather this information is easily obtained by sighting the drift of a pilot balloon with a theodolite1 or by observing in a specially designed graduated mirror or pair of mirrors the drift of the smoke cloud from a shell fired by an anti-aircraft gun and timed to burst at any desired altitude4 ,in cloudy weather the smoke trails can often be successfully observed through small breaks in the clouds4 ,when the sky is completely overcast1 a succession of shells is fired at definite short intervals of time and the distances apart of the puffs of smoke and the direction of the line in which they lie are determined from an aeroplane flying above the spot4 ,another method1 which was devised by the ,french military meteorological service during the war1 is to send up small balloons loaded with bombs which burst after a certain time1 the position of each burst being determined by sound-ranging from the ground4 ,these methods of providing information concerning the winds at flying levels have1 however1 their serious limitations1 and aeronauts now look hopefully to the perfection of the existing systems of 8directional wireless10 whereby the pilot will receive whenever desired1 or at regular intervals1 a wireless signal from the terminus of his route or some other known point1 the direction from which the signal comes being indicated by suitable apparatus on the aeroplane4 ,thus aided1 he should never deviate far from his course1 unless he chooses to4 ,for long journeys1 such as the crossing of the ,atlantic1 the air pilot will naturally make use of all available information concerning the great permanent or semipermanent wind systems of the earth1 such as the trade winds of the lower atmosphere1 the antitrades above them1 and the fairly constant eastward drift of the atmosphere at high levels in middle latitudes4 ,the dividend-earning capacity of commercial aircraft necessarily depends upon taking advantage of favorable winds1 while adverse winds may mean not only a loss of money but the danger of prolonging a journey until the fuel supply is exhausted--a serious predicament over the ocean and also over lands remote from civilization4 ,it is1 however1 a common error on the part of current writers to overrate the constancy and reliability of the winds in various parts of the world1 and to lay too much stress on the value of permanent wind charts4 ,what the aeronaut needs especially to know is the typical behavior of the winds with respect to the distribution of barometric pressure1 as shown by a weather map1 including their variations with altitude4 ,the time will come when the information necessary for plotting the winds at various levels will be flashed at frequent intervals by high-powered radio stations to aerial navigators in all parts of the world--a system that is already in its initial stages1 especially in ,europe4 ,a pilot making a long journey will thus be able to lay his course so as to utilize the winds that will speed him on his way4 ,even violent storms1 such as the mariner seeks to avoid1 will be turned to advantage by the airman4 ,we have now to consider another aspect of wind that is of much more interest to the airman than to the seaman1 and that is the question of 8wind structure40 ,the layman usually thinks of a wind as a nearly steady horizontal flow of air4 ,such winds exist1 but they are exceptional1 especially in the lower levels of the atmosphere4 ,a wind is generally full of gusts and eddies1 upcurrents and downcurrents1 and it is these eccentricities that gradually develop in the aviator a sort of sixth sense--a 8feel0 for atmospheric fluctuations1 that enables him to adjust his machine instinctively to the forces tending to disturb its equilibrium4 ,he also learns by experience the conditions under which irregularities of a pronounced character may be expected4 ,he becomes well acquainted with the great mound of air that drives his machine upward when passing over a hill or mountain2 with the eddy that lurks in the lee of such an obstacle2 with the downward tendency of the air over lakes1 rivers1 swamps and forests4 8,the air is so sensitive10 writes the late well-known ,british flyer1 ,gustav ,hamel1 8that it is affected even by the color of large patches of vegetation4 ,whether this be entirely due to the different heat-radiating power of different colors it is impossible to say1 but invariably an aeroplane on passing from grass land to a field covered with yellow flowers experiences a certain amount of air disturbances only less noticeable than the inevitable bump experienced in passing from green fields to ploughed land1 or from ploughed land to meadow40 ,when the wind is blowing1 the air for at least a few hundred feet above the ground is nearly always in a state of turmoil4 ,this is partly due to the friction of the moving fluid against the irregular surface of the earth1 and partly to the ascending and descending currents caused by differences in temperature4 ,the latter effect is illustrated in the rapid rise of air over a bare sunlit plain and its fall over an adjacent forest or body of water4 ,ascending currents are often made visible by the formation of detached cumulus clouds1 each of which marks the summit of a rising column of moist air1 while in the spaces between the clouds the air is generally sinking4 ,measurements with balloons have shown that vertical currents often attain speeds of #fjj feet a minute or more1 while the process of hail formation appears to indicate that in thunderstorm clouds there are violent uprushes amounting to #b1jjj or #b1ejj feet a minute1 and possibly much more4 ,the descending air current between clouds is sometimes so strong that an aeroplane cannot force its way up through it4 ,illustration3 ,,the ,,flow ,,of ,,air ,,over ,,two ,,ridges 7,after ,dr4 ,franz ,linke47 ,notice the eddy in the valley to the leeward of the first ridge ,illustration3 ,a ,,sheltered ,,landing ,,place ,,may ,,be ,,dangerous 7,after ,dr4 ,franz ,linke47 ,a landing place surrounded by trees is dangerous in windy weather on account of the air waves formed between the moving air above and the calm air below4 ,illustration3 ,,air ,,waves ,,near ,,the ,,earth',s ,,surface ,the waves are made visible by smoke ,the turbulence of the lower air--a phenomenon that adds so much to the difficulties of starting and landing--extends to various heights1 depending especially upon the strength of the wind4 ,a rough rule1 evolved by the ,zeppelin pilots before the war1 was to expect turbulent conditions up to an altitude equal to from ten to twenty times the force of the wind in meters per second4 ,thus1 for a wind of #aj meters per second1 the turbulent layer would be from #ajj to #bjj meters thick4 ,a good picture of the atmospheric ups and downs encountered by the airman when flying low is furnished by the behavior of the smoke from a factory chimney with a moderate wind blowing1 forming smoke waves4 ,illustration3 ,,the ,,wind',s ,,autograph ,,on ,a ,,gusty ,,day1 ,,recorded ,,with ,a ,,pressure-,,tube ,,anemometer ,the vertical lines are hour lines and the horizontal lines show the force of the wind in miles an hour and also in pounds a square foot4 ,these disturbances give rise to the very marked fluctuations in the force of the wind known as gusts4 ,there are certain forms of anemometer especially designed to record the gustiness of the wind4 ,a record of the wind's force is traced by a pen on a moving strip of paper1 and the 8anemogram0 thus obtained shows a continuous series of irregularities1 the extent of which increases with the strength of the wind4 ,the puffs and lulls often alternate at intervals of a few seconds or less1 and the actual force of the wind at a given instant may be many times greater than its average force for1 say1 five minutes4 ,an ordinary anemometer does not indicate these rapid fluctuations1 but merely shows the time required for a mile of wind to flow past the instrument4 ,thus when such an instrument tells us that the wind is blowing at the rate of #dj miles an hour1 it may actually be varying between #bj and #fj miles an hour1 or between even wider limits4 ,since the matter became of practical importance on account of the needs of aviation1 many interesting studies have been made of the effects of different kinds of topography upon the overlying air currents4 ,a striking example of the eccentric winds that sometimes prevail in mountain valleys has been described by ,mr4 ,b4 ,m4 ,varney1 of the ,university of ,california1 in the 8,monthly ,weather ,review40 ,from the summit of a steep cliff about #a1ajj feet above the floor of ,yosemite ,valley the writer launched broad sheets of tissue paper1 and1 with the aid of powerful binoculars1 followed their flight as they were carried in huge spirals1 thousands of feet in diameter1 finally disappearing beyond the mountains on the opposite side of the valley4 ,the accompanying sketch shows the path of one of these papers4 ,from its starting point at ,a until it passed behind the summit of ,liberty ,cap 7,b71 more than a mile distant1 the paper was watched for #g minutes4 ,the top of ,liberty ,cap is some #a1fjj feet above the point at which the flight began4 ,this sketch visualizes one of the ticklish problems that will some day confront the pilot of a sight-seeing or mail-carrying aeroplane in the ,yosemite ,national ,park4 ,illustration3 ,,air ,,currents ,,in ,,yosemite ,,valley 7,sketched by ,b4 ,m4 ,varney47 ,the flight of a sheet of paper across the valley4 ,although1 on an average1 the air is much steadier at high levels than near the ground1 very unsteady currents are sometimes found at all altitudes attainable by aircraft4 ,thunderclouds1 thousands of feet above the earth1 are always the seat of violent turmoil1 but such clouds can1 as a rule1 be avoided by the airman4 ,when a stratum of air glides over another differing sharply from it in density--and distinct strata of this sort are not uncommon in the atmosphere--friction between the strata sets up waves like those produced in water by wind blowing over it4 ,if the two streams are moving in the same direction1 but at different speeds1 the waves are long and regular2 when they are more or less crossed1 the waves are short and choppy4 ,the moisture at the crests of these waves may be cooled to such an extent as to condense into visible clouds1 arranged in long continuous rolls or rows of detached patches2 forms frequently assumed by cirro-cumulus and alto-cumulus4 ,more often1 however1 the waves of air remain invisible1 because the conditions of moisture and temperature are not right for the production of cloud4 ,recalling1 now1 what has been said above about the way in which the lift of an aeroplane varies with the angle at which the wings meet the air and also with the speed of the machine relative to the air1 it will be easy to understand some of the difficulties experienced in maintaining one's equilibrium when flying in a turbulent atmosphere4 ,waves1 eddies1 vertical currents and other features of wind structure cause abrupt changes in the attitude and the speed of the machine with respect to the air stream4 ,the sudden increases and decreases of lift thus produced have much the same effect upon the machine as if it were running over a solid obstacle on the one hand or plunging into a vacuous space in the atmosphere on the other1 and hence are aptly described by aviators as 8bumps0 and 8holes in the air10 respectively4 ,the latter term1 which seems to have become firmly rooted in all languages 7,french1 trou d'air2 ,german1 ,luftloch2 etc471 has had the unfortunate effect of keeping alive in the public mind the idea that the aviator occasionally runs into a vacuum or semivacuum1 such as could not exist in the atmosphere4 7,the nearest approach to such a thing is the rarefaction in the core of a tornado or waterspout1 due to the enormous centrifugal force of the vortex2 something that no aviator has yet encountered47 ,to make matters worse1 different parts of the sustaining surface of the machine may receive different impulses4 ,one wing1 for example1 may graze a violent uprush of air not encountered by the other1 giving the aeroplane a tilt to one side1 or the tail of the machine may be driven in one direction and the nose in the other4 ,again1 the whole machine may suddenly enter an air current of quite different speed and direction from the one in which it has been flying4 ,to take an extreme case1 it may run into a stream of air flowing just as fast1 and in the same direction1 as the machine itself1 with the result that the relative wind becomes zero1 and the machine1 deprived of all lift1 drops like a stone until it acquires a velocity with respect to its new environment4 ,when such conditions prevail1 the pilot is kept busy with his 8controls02 now moving his elevator to adjust his fore-and-aft balance1 and now his ailerons to set him on an even keel laterally1 and occasionally turning his rudder to offset the effects of horizontal gusts4 ,the elevator and the ailerons are worked with a single lever1 colloquially called the 8joy-stick10 and the rudder with a bar which the pilot operates with his feet4 ,ordinary adjustments of this kind are performed automatically by the trained aviator1 but violent disturbances call for the exercise of skill and judgment4 ,generally speaking1 no amount of atmospheric turbulence causes any serious trouble to the trained pilot1 except when he is flying close to the ground1 as in starting and landing4 ,before we leave the subject of wind it will be well to emphasize once more the fact1 which the average layman has difficulty in grasping1 that the only movements of the air that affect the safety and comfort of flight are the movements relative to the machine1 and not those relative to the ground4 ,to the aviator1 when he is once clear of the ground1 a steady wind of any speed is merely a mass of calm air4 ,hence an aviator will sometimes have perfectly smooth flying when the wind1 as measured on the earth1 is blowing #dj or #ej miles an hour2 and again he will describe the air as rough and bumpy when flags are hanging limp from their staffs and dwellers on terra firma declare that not a breath of air is stirring4 ,in the early days of flying aviators themselves were afraid of a strong wind4 ,thus ,wilbur ,wright1 during his pioneer exhibition flights in ,france1 would never go up unless the smoke from his cigarette rose in a straight line1 and until about the end of #aiji no aviator attempted to fly in a wind of #bj miles an hour4 ,at the present time the only atmospheric condition that seriously hampers flying is fog or low cloud4 ,an aviator flying in a fog or cloud is not only liable to wander far from his course1 on account of the unknown leeway of his machine1 but he is often in great doubt as to his proximity to the ground4 ,one of the curious effects of such a situation is that the airman loses his sense of the vertical4 ,on land our sense of up and down is determined by the force of gravity1 pulling us toward the earth4 ,when riding in a terrestrial vehicle1 we are conscious of other pushes and pulls2 such1 for example1 as the jolt that pitches us forward when a train stops suddenly1 or the outward thrust that we feel when swinging around a curve4 ,again1 in descending in a lift we seem to lose weight1 as if gravity had suddenly grown weaker4 ,on earth all such impressions are corrected by the sight of objects around us2 but the aviator enveloped in mist has no such guides1 and he often becomes quite confused about the direction of the ground4 ,a turn1 which involves banking1 increases his confusion4 ,eventually he may be flying almost upside down without being aware of the fact4 ,professor ,melville ,jones1 who has been through such experiences1 says of the pilot's confusion3 8,his first indication that something is wrong is1 as a rule1 either an increase or a decrease of speed that is not counteracted by the accustomed movements of the controls4 ,a period of wild suspense and utter bewilderment now follows1 during which the pilot makes violent efforts to recover control1 but without success4 ,the next thing that he realizes1 if he realizes anything at all1 is that he is either on his back or spinning1 and the next thing he knows is that he is out of the clouds with the earth standing up at a ridiculous angle and spinning round like a drunken dinner plate4 ,happy is he that has plenty of air room under these circumstances40 ,spirit-levels and similar instruments are affected by the same disturbances that mislead the pilot in his estimation of the vertical2 but fortunately there are certain other devices1 due to the exigencies of the war1 during which cloud flying was a part of the tactics of the military aviator1 which have virtually solved this problem1 though their use has not yet become general4 ,the outstanding difficulty of a fog is the problem of landing4 ,in the case of a forced landing1 at a distance from a regular landing-ground1 the pilot must simply trust to luck4 ,he may descend in the water or the treetops1 or on rough ground that will wreck his machine1 but he has no choice4 ,the only solution of this difficulty is the installation of a reserve engine1 or some other expedient that will obviate the necessity of forced landings4 ,the task of finding a landing ground in a fog and descending to it in safety will1 in the near future1 be comparatively simple4 ,most fogs1 though by no means all1 are so shallow that it is possible to tether a kite-balloon so that it will float above the fog and indicate the position of the aerial harbor4 ,several such balloons1 flying tandem1 would afford sufficient lift to support a series of electric lanterns along the cable1 for use at night4 ,searchlights and 8star shells0 have been employed for the same purpose4 ,directional wireless and the wireless telephone seem likely1 however1 to be the chief dependence of the future aeronaut seeking port in a fog4 ,these devices will also be the means of averting collisions in a fog or cloud along crowded airways1 and especially in the congestion that will prevail in the vicinity of important air ports4 ,last but not least1 the artificial dispersion of fog by means of electrical discharges1 although still in the experimental stage1 holds out possibilities of being the ultimate solution of the fog problem1 not only for the aeronaut1 but also for the mariner1 the railway manager1 and everybody else who is incommoded by a misty atmosphere4 ,even when he is not flying in clouds or fog the aviator by no means always enjoys a clear view of distant objects4 ,a slight haze impairs visibility1 while a heavy rainstorm or snowstorm may obstruct the aeronaut's view as badly as a fog4 ,of the meteorological elements that affect aeronautics1 other than those we have mentioned1 the most important is the density of the atmosphere--generally expressed in terms of barometric pressure4 ,the air diminishes in density upward1 and the rarefied atmosphere of high levels has several effects on aircraft4 ,its decreased buoyancy imposes a limit upon the ascent of balloons2 its decreased resistance makes it necessary for an aeroplane to fly at greater speed in order to get the same lift2 it diminishes the power of gasoline engines1 on account of the reduced supply of air2 and it has various unpleasant and even dangerous effects on the aeronaut1 similar to 8mountain sickness40 ,the level that a given aeroplane cannot exceed owing to the combined effect of reduced lift and reduced engine power is known as its 8ceiling40 ,different types of aeroplane have very different ceilings4 ,at great altitudes the air is always very cold1 summer and winter4 ,the low temperature may interfere with the efficient working of the engine1 and it is1 of course1 a source of discomfort to the pilot4 ,the formation of ice and heavy deposits of snow lead to inconveniences in both aeroplanes and airships4 ,the pelting of hail is sometimes a painful experience for aeronauts4 ,lastly1 lightning has hitherto left aviators unscathed1 but has caused numerous disasters among balloonists4 ,the recent rapid development of aeronautics has laid a heavy burden of additional labor upon the meteorological services of the world1 and is producing something like a revolution in their methods4 ,the history of these changes is interesting4 ,from the beginning of the twentieth century until a few years before the ,world ,war meteorologists were engaged in a great campaign of upper-air research1 utilizing kites1 captive balloons1 pilot balloons1 and sounding balloons to measure the winds1 temperature1 humidity and pressure at various levels in the atmosphere4 ,in other words1 aeronautical methods were employed in the service of meteorology1 but the investigators hardly entertained the idea of reversing the relation and making meteorology the handmaiden of aeronautics4 ,the point of view prevailing in those days is well indicated by the fact that the organization that had charge of the upper-air explorations throughout the world was known as the 8,international ,commission for ,scientific ,aeronautics10 a name that it bore until the year #aiai4 ,the plan for providing regular weather reports for the benefit of aeronauts began with some small-scale enterprises in ,germany about #aiji4 ,in the summer of that year ,dr4 ,franz ,linke organized a storm-warning service in connection with the ,international ,aeronautical ,exposition at ,frankfort1 and at the beginning of the year #aiaa an aeronautical weather bureau for the whole of ,germany was established1 with headquarters at the ,observatory of ,lindenberg4 ,shortly before the war a similar undertaking was launched in ,italy1 under ,dr4 ,matteucci1 whose service was the first one in the world to publish daily charts1 based on telegraphic reports1 of the winds at various levels over an entire country4 ,during the war the regular meteorological services of the belligerent countries and the meteorological units attached to the armies and navies maintained an almost continuous service of weather information for the great fleets of fighting aircraft4 ,bulletins1 distributed chiefly by wireless telegraphy1 supplied particulars of the current and prospective winds at the flying levels1 the prevalence of fog1 the degree of visibility1 etc4 ,new telegraphic weather codes1 far more elaborate than those in use before the war1 were devised for transmitting such information1 and the whole business of observing and reporting weather became immensely more arduous than it had been in the days when the only interests served by practical meteorology were those of the land and the water4 ,since the close of hostilities great efforts have been made to maintain these new operations of the meteorological establishments at something like the level attained during the war4 ,the task is1 however1 beset with difficulties1 on account of the great expense involved4 ,it is being accomplished with different degrees of success in different countries4 ,,chapter ,,xix ,,military ,,meteorology ,one of the most astonishing paradoxes connected with the misapplication of human brains and energy glorified with the name of the 8art of war0 is this--that1 while weather has always played an important part1 and often a decisive one1 in military operations1 no attempt was ever made until a few years ago to include meteorology in the purview of military science or to utilize the services of meteorologists at the battle front4 ,the most casual survey of the history of warfare reveals the fact that atmospheric conditions rank high among the 8controls0 of fighting4 ,from a military point of view1 weather and climate bear a certain analogy to topography4 ,they are a part of the physical environment with which a commander has to reckon4 ,weather1 however1 differs from topography in the fact that it is subject to rapid changes1 and is therefore doubly worthy of attention on the part of an army1 which must not only take account of the weather as observed and in progress1 but must also1 as far as possible1 anticipate that which is to follow4 ,everybody will recall the ruin that overtook the ,french army in ,russia in #ahab on account of untoward weather conditions1 but it is less well known that ,napoleon1 with his usual sagacity1 obtained from his scientific advisers a report on the ,russian climate before he planned his campaign2 that the winter set in much earlier than usual in that fatal year2 and1 most interesting of all1 that it was actually a brief period of thawing weather1 rather than the intense cold that preceded and followed it1 which1 by turning the roads into bogs and breaking up the ice in the ,beresina1 brought about the culminating disaster4 ,another fateful spell of weather ushered in the battle of ,waterloo4 ,it is described in a well-known passage of 8,les ,misrables10 which contains enough truth mingled with hyperbole to be worth quoting3 8,s'il n'avait pas plu dans la nuit du #ag au #ah janvier1 #ahae1 l'avenir de l',europe tait chang4 ,quelques gouttes de plus ou de moins out fait pencher ,napolon4 ,pour que ,waterloo ft la fin d',austerlitz1 la ,providence n'a eu besoin que d'un peu de pluie1 et un nuage traversant le ciel contre-sens de la saison a suffi pour l'croulement d'un monde40 ,the rains and floods that led to the annihilation of the ,roman legions under ,varus in ,a4 ,d4 #i and the great tempests that helped ,english seamen defeat the ,spanish ,armada furnish additional well-known examples of the immense importance of weather as a factor in warfare4 ,we need not1 however1 look farther back than to the recent world conflict to find similar examples in profusion4 ,leaving out of consideration the indirect effects of the weather upon the progress of the war as exercised through its control of crops1 transportation1 and other features in the economic life of the belligerent and neutral nations1 we need only examine war-time newspapers to see how the armies themselves were helped or harassed by meteorological conditions at every turn4 ,the war was a great popular teacher of climatography1 just as it was of geography4 ,the drenching misery of ,flemish winters1 as formidable to the soldiers in the trenches as the bullets of the enemy1 became as familiar to the present generation of ,americans as did somewhat similar conditions in ,virginia to ,americans of the ,civil ,war period4 ,the ,british campaigns in ,mesopotamia were as much a conflict with climate as with human foes4 ,marches were made when the temperature stood at #aaj degrees ,fahrenheit and over4 ,the temperature in the hospital tents is said to have reached #acj degrees4 ,the disaster at ,kut-el-,amara was due to the rains and floods that prevented reenforcements from reaching the beleaguered garrison4 ,the failure of the ,dardanelles expedition was partly due to the fact that the extreme dryness of the country was not realized--as it would have been if the ,war ,office had called climatologists into council--and totally inadequate provision was made for the water supply4 ,the new engines of war brought forth by the recent struggle were peculiarly susceptible to the effects of weather4 ,the larger guns and heavy motor trucks were difficult to move over muddy roads4 ,the aircraft1 though they managed to fly in all kinds of weather1 suffered innumerable disasters for which atmospheric conditions--chiefly storms and fog--were responsible1 and their operations were conspicuously affected by favorable and unfavorable winds4 ,shells were fired to unprecedented heights1 and their trajectories were modified by unknown conditions in the upper air4 ,last but not least1 the use of poisonous gases1 especially in the period before gas clouds were largely replaced by gas shells1 was dependent upon the occurrence of appropriate winds2 and a slight miscalculation in this respect sometimes brought disaster to the troops using the gas4 ,it is not surprising that professional meteorologists played a part in the ,world ,war1 but it is difficult to understand why meteorological units were not attached to all armies1 at least when on active service1 several decades before the year #aiad4 ,meteorologists did1 indeed1 take a hand in one earlier conflict1 but not as enrolled soldiers4 ,during the ,spanish-,american ,war a special service was organized by the ,united ,states ,weather ,bureau to protect the ,american fleet in southern waters from unpleasant surprises in the shape of ,west ,india hurricanes4 ,in the summer of #ahih a chain of observation stations was established by the ,bureau around the ,caribbean ,sea4 ,the service then inaugurated in consequence of the exigencies of war proved so valuable to shipping in time of peace that it has continued to operate1 with some intermissions1 down to the present day4 ,when the ,world ,war broke out1 the only country that immediately put meteorologists1 as such1 into the field was ,germany4 ,the ,germans were fortunate in having a far greater number of trained meteorologists at their disposal than had their enemies4 ,there were chairs of meteorology in several ,german universities and high schools1 and the numerous meteorological observatories and institutes of the ,empire had provided occupation for a large amount of professional talent in this line4 ,one of the first acts of the army that invaded ,belgium was to establish an aerological service in that country4 ,the ,entente countries were slow in adding meteorological units to their armies1 but their civilian meteorological services were utilized to the utmost for military purposes from the beginning of the war4 ,they at first worked under difficulties arising from the cessation of the customary weather reports from central ,europe1 but1 to offset this disadvantage1 the weather map was expanded in other directions1 the number of daily hours of observation was increased1 and eventually the forecasters in ,london and ,paris acquired much better facilities for making their predictions than they had enjoyed in time of peace4 ,the supply of weather information to the public was suspended1 and great precautions were taken to prevent the reports of the ,allied services from being utilized by the enemy4 ,the ,german meteorologists were seriously hampered by the lack of reports from the westward4 ,it has been asserted that such reports were sometimes obtained by radio from submarines stationed off the coast of ,ireland1 but such a service1 if it existed1 must have been fragmentary and unsatisfactory4 ,that the ,germans made many mistakes in their attempts to infer the atmospheric conditions over the ,british ,isles from the limited weather map at their disposal is proved by the fact that their airships frequently crossed the ,channel when1 with an ampler knowledge of impending weather1 they would certainly have remained at home4 ,several ,zeppelins came to grief in the course of these ill-timed raids4 ,one of the interesting routine duties of the ,british ,meteorological ,office during the war was to draw the weather map for a given moment as the ,germans would probably draw it1 with their curtailed set of telegraphic reports1 and then predict the ,german prediction6 ,in the spring of #aiae a small meteorological section was organised in the ,british ,army1 and attached to the ,royal ,engineers4 ,this force was afterward enlarged1 and provided units for service on several battle fronts4 ,the ,british also developed a naval meteorological service1 which had existed in embryo before the war1 and1 eventually1 a special meteorological service for the ,royal ,air ,force4 ,analogous services were organized by the ,french and the ,italians4 ,the ,united ,states ,army and the ,united ,states ,navy both established meteorological services not long after this country entered the war4 ,the former was attached to the ,signal ,corps1 and was partly officered and recruited from the ,weather ,bureau4 ,a training school for army meteorologists was opened at ,college ,station1 ,texas4 ,upward of #cjj men were given instruction in this school1 and most of them were sent overseas4 ,the naval meteorological service was headed by the director of ,blue ,hill ,observatory1 and the junior officers received special training at that institution4 ,the varied activities carried on by these war-time units were so different from the traditional duties of meteorologists that they may be said to mark the advent of a new branch of applied science--,military ,meteorology4 ,they were1 moreover1 as we shall see1 extremely fruitful of effects upon the science of meteorology in general4 ,in the principal battle zones the military weather men maintained a dense network of observation stations1 the reports from which1 combined with those received from the regular peace-time weather stations of the ,allied and neutral countries1 enabled the forecasters at headquarters to keep closely in touch with atmospheric changes4 ,observations of both surface and upper-air conditions were made at frequent intervals1 and radiotelegraphy was largely used to insure prompt transmission of the reports4 ,in general1 weather maps were drawn four times a day4 ,information was distributed locally to the fighting units by telephone and otherwise4 ,the vast fleet of aircraft called into being by the war would1 of itself1 have imposed upon the military meteorologists the necessity of paying a great amount of attention to the upper air4 ,pilot balloons were sent up so frequently and at so many points that the aviators generally knew just what winds they would encounter aloft4 ,special arrangements were made to follow the progress across the country of the thundersqualls which constituted a serious danger to the 8sausages10 or observation balloons1 as well as to aeroplanes on the ground1 and to hangars4 ,there was1 however1 another urgent reason for keeping a close watch of the winds and other atmospheric conditions at various levels above the earth's surface4 ,experience acquired early in the war proved that old-fashioned methods of correcting the aim of artillery for meteorological disturbances were extremely inadequate for modern guns1 the projectiles of which rise to altitudes of from #aj1jjj to #bj1jjj feet and encounter conditions quite different from those prevailing at the surface4 ,the flight of a projectile is affected by the force and direction of the wind1 and the density of the air through which it passes4 ,some modern projectiles remain in the air as long as #gj seconds1 and a moderate wind blowing across the path of such a projectile may easily cause it to fall half a mile away from the point at which it would strike if fired in still air4 ,one of the routine duties of the army weather service was to observe the winds and compute the air-densities at different heights wherever such information was required by the artillery4 ,in order to facilitate the application of such data by the gunners ingenious methods were developed for computing what is known as the 8ballistic wind40 ,this is a fictitious wind which1 if affecting the projectile throughout its flight1 would produce the same total deflective effect and effect on range as the various winds that the projectile actually encounters4 ,meteorological observations were also of great importance in connection with the new process of locating distant guns known as 8sound-ranging40 ,this process consists1 briefly1 in determining the exact instant of arrival at several points of the sound waves propagated through the air from the gun that is being located4 ,if sound traveled at a uniform speed1 these observations would show the exact distance of each of the observing points from the gun1 and a simple geometrical construction would indicate the position of the latter4 ,the speed of sound waves in the air is1 however1 affected by both wind and temperature4 ,accordingly1 allowance had to be made for these varying factors1 and the necessary data were supplied by the meteorological units4 ,the observation and prediction of winds favoring the use of poisonous gases by friend or foe was one of the most delicate tasks allotted to the army meteorologists4 ,the flow of such gases is determined by the winds close to the surface of the earth1 and these are greatly affected by topography4 ,local air currents controlled by the slope of the ground were especially utilized for gas attacks4 ,strong winds were unfavorable1 because they quickly dissipated the gas cloud4 ,the meteorologists not only advised their own troops when to use gas1 but also gave warning when the atmospheric conditions were such that gas was likely to be used by the enemy4 ,the use of gas shells was less dependent for its success upon the wind than the liberation of gas clouds1 but even when shells were used the wind and weather at the objective point were factors of importance4 ,the exigencies of warfare developed several new features of meteorological practice1 the utility of which did not cease with the war4 ,thus it became customary to measure the degree of 8visibility0 of distant objects1 for the benefit of aviators and gunners1 and this element was included in the routine weather reports4 ,scales of visibility1 ranging from 8very bad0 to 8excellent10 etc41 were adopted1 and eventually certain forms of apparatus 78visibility meters07 were devised for getting fairly precise measurements of this weather factor4 ,another novel practice that deserves to be perpetuated was the plan adopted by the military forecasters of adding to their predictions a statement as to their probable accuracy2 this was expressed on a numerical scale of 8odds10 instead of by use of the vague terms 8probably0 and 8possibly10 which have generally served the purpose of the dubious forecaster4 ,the war brought about many improvements in the instruments and methods used in sounding the upper air2 and the intensive campaign of pilot-balloon observations carried out at the military stations provided a body of data for study quite unparalleled in the history of meteorology4 ,lastly1 the war revolutionized weather telegraphy in ,europe4 ,before the war the ,european forecasters were hampered by exasperating delays in the collection of reports over the telegraph lines1 especially in the international exchange of observations4 ,wireless telegraphy had been extensively used for gathering reports from vessels and supplying vessels with forecasts1 but not for the interchange of meteorological information on land4 ,the war changed all this4 ,radiotelegraphic weather messages became the rule1 and the advantages of the new system were so obvious that the tendency has been to retain it as far as possible since the war4 ,,chapter ,,xx ,,medical ,,and ,,physiological ,,meteorology ,the starting point in any study of the physiological effects of weather and climate upon humanity is the remarkable fact that1 on the hottest days of summer and the coldest of winter1 in tropical deserts and amid polar snows1 the temperature within the body of a healthy man remains constant to a fraction of a degree4 ,there are slight temperature differences between different parts of the body2 there is a periodic daily variation of about half a degree2 and there are other slight changes1 due to eating and exercise2 but an internal temperature of about #ih4f degrees ,f4 is maintained with little or no regard to fluctuations in the temperature of the air4 ,the body has often been compared to a building in which the temperature is regulated by a thermostat1 but the comparison is not exact4 ,the thermostat controls the temperature merely by regulating the combustion of fuel2 and with the advent of mild weather we let the fires go out altogether4 ,in the body the fires are always burning1 the briskness with which they burn--or1 to drop the metaphor1 the rate at which bodily heat is generated--depending1 above all1 upon muscular activity1 but also upon other causes4 ,it is true that we possess a nervous mechanism1 analogous to the thermostat1 which tends to adjust the production of animal heat in such a manner as to offset the cooling effect of our environment2 but this mechanism appears to be less important in maintaining our constant temperature than another1 which regulates the loss of heat from the body4 ,according to ,m4 ,j4 ,rosenau3 8,heat is lost from the body chiefly in two ways2 7#a7 by heat transfer1 or loss by radiation1 conduction1 and convection2 7#b7 by evaporation1 chiefly by the evaporation of the water of perspiration4 ,pettenkofer and ,voit estimated the loss of water by the lungs at #bhf grams1 and from the skin at from #ejj to #a1gjj grams daily4 ,this will give some idea of the effects here concerned4 ,the loss by heat transfer diminishes as the temperature of the surrounding air rises4 ,the temperature of the body would rise when the atmospheric temperature goes above #gj degrees ,f4 were not perspiration then secreted4 ,so long as the perspiration can evaporate freely the heat production and heat loss are balanced4 ,with a high humidity evaporation is lessened and the balance is maintained by rushing blood to the skin1 which causes an elevation of the temperature of the surface1 and thus the loss of heat by radiation1 conduction1 and convection is facilitated40 ,human sensations of temperature are paradoxical4 ,we talk of being 8hot0 and 8cold10 as if we belonged to the class of cold-blooded animals--the fishes and the reptiles--that actually undergo great variations of temperature1 with variations in the temperature of their environment4 ,we hear people say1 for example1 that they are most comfortable at a temperature of #fe2 yet we know that their temperature is always #ih1 except just at the surface of the body4 ,the human body is1 in fact1 a poor thermometer4 ,our sensations do not register the temperature of the air1 but they do1 in a way1 register the cooling power of the air1 which depends upon temperature1 humidity1 and air movement1 and they register1 especially1 changes in this cooling power1 for within certain limits the body soon adapts itself to a constant rate of cooling1 so as to lose any impression of heat or cold4 ,when a steady outflow of heat from the body has been set up and the external cooling power is suddenly increased1 we become conscious of a difference between the temperature at the surface of the body and the 8blood temperature0 beneath4 ,the action of the nerves at the surface and the nerves underneath1 under these circumstances1 has been compared to that of a thermo-junction1 in which an electric current is produced by differences of temperature4 ,the rate of evaporation from the skin1 also1 has a marked effect upon our sensations of comfort and discomfort4 ,the common thermometer was long ago discredited as a means of measuring atmospheric comfort4 ,then1 for a time1 the wet-bulb thermometer had its day1 and its indications were once published on a large scale in this country as representing the 8sensible temperature10 or temperature that we actually feel4 ,the wet-bulb thermometer is cooled by evaporation below the air temperature1 except when the air is saturated with moisture1 and may therefore give a rough indication of the temperature acquired by the skin when moistened with perspiration4 ,the temperature of the skin is not1 however1 an accurate indication of our feelings of heat or cold1 nor is it a satisfactory guide to the physiological effects of atmospheric conditions4 ,several instruments have been devised for the purpose of measuring the cooling power of the air1 to which the bodily mechanism must respond in order to maintain a uniform temperature within4 ,one of these was invented nearly half a century ago by ,j4 ,w4 ,osborne4 ,a porous cylinder was filled with warm water1 and an agitator1 driven by clockwork1 kept the water in the cylinder at uniform temperature at any given moment4 ,the rate at which heat was lost from the wet surface of the cylinder was determined by a thermometer1 having its bulb immersed in the water1 and a stop watch4 ,a different plan was adopted by ,a4 ,piche1 in an instrument which he called the deperditometer1 and which was supposed to imitate more closely the behavior of the body4 ,a porous vessel is filled with water1 the temperature of which is kept constantly at 8blood heat0 7#ih4f degrees ,f47 by a gas jet provided with an automatic regulator4 ,the amount of gas burned in a given time is then supposed to measure the cooling power of the atmosphere as it affects humanity4 ,j4 ,r4 ,milne's psuchrainometer is constructed on the same principle1 but heat is supplied and measured electrically4 ,among many other instruments of this class1 one that now enjoys special favor is the katathermometer1 devised by ,prof4 ,leonard ,hill1 in ,england4 ,this consists of a pair of large-bulbed spirit thermometers1 one of which has its bulb covered with fine cotton mesh4 ,to use the instrument1 the bulbs are immersed in water at about #aej degrees ,f4 until the spirit rises to the top of the thermometer tubes4 ,the excess of water is then jerked off the wet bulb1 and the other bulb is dried4 ,the instruments are finally suspended in the air1 and the rate of cooling from #aaj to #ajj degrees1 or from #ajj to #ij degrees1 is taken with a stop watch4 ,the dry-bulb measurements are supposed to show how fast the human body loses heat at its surface by radiation and convection1 while the wet-bulb measurements also take account of evaporation4 ,in order to connect the readings of this device with human sensations1 ,hill and his collaborators have used the instrument under a great variety of atmospheric conditions1 both indoors and out1 and compared the readings with independent estimates of comfort and discomfort4 ,on an ideal summer day the 8wet kata0 fell from #aaj to #ajj in #be seconds1 and the 8dry kata0 in #he seconds4 ,indoors at the seaside in summer1 under comfortable conditions1 the readings were #ej seconds and #adj seconds1 respectively4 ,a large number of other readings1 taken under different conditions in various parts of the word1 have been published4 ,the katathermometer is now used in both ,great ,britain and the ,united ,states in the study of ventilation problems1 and has acquired a rather extensive literature4 ,according to its inventor1 8the heating and ventilation of rooms should be arranged so that the wet-bulb falls from #ajj to #ij degrees in about one minute1 and the dry-bulb in about three minutes40 ,illustration3 ,a ,,weather ,,bureau ,,kiosk1 ,,in ,,union ,,square1 ,,san ,,francisco4 7,photograph1 ,u4 ,s4 ,weather ,bureau47 ,illustration3 ,,the ,,united ,,states ,,weather ,,bureau ,,station1 ,,observatory ,,type1 ,,at ,,peoria1 ,,illinois4 7,photograph1 ,u4 ,s4 ,weather ,bureau47 ,regardless of the merits of these particular instruments1 it is certain that the cooling power of the air--which is quite a different thing from the temperature of the air--is a very important factor in determining our comfort and our health4 ,within certain limits the body can easily adjust itself to changes in the cooling power of the air2 within wider limits the adjustment is effected with difficulty1 and we experience discomfort and possibly suffer in health2 and finally there are extreme conditions1 in either direction1 to which adjustment is not possible2 the internal temperature is then either lowered or raised1 as the case may be1 and a comparatively small change of this sort is fatal2 i4 e41 death results by chilling or by heat stroke4 ,illustration3 ,photo ,u4 ,s4 ,weather ,bureau ,,the ,,central ,,office ,,of ,,the ,,united ,,states ,,weather ,,bureau ,,in ,,washington ,one interesting result of recent inquiries on this subject is the discovery that the bad effects of crowded1 8stuffy0 rooms are not generally due to impurities in the air1 but to heat1 humidity1 and especially lack of air movement4 ,it seems to be now demonstrated that there is no such thing as 8crowd-poisoning10 and that the bad smells of confined places are no indication that the air is deleterious4 ,professor ,hill1 who has done more than anybody else to upset traditional ideas with regard to ventilation1 tells us that 8the deaths in the ,black ,hole of ,calcutta1 the depression1 headache1 etc41 experienced in close rooms are alike due to heat stagnation2 the victims of the ,black ,hole died of heat stroke40 ,most recent writers on physiology also discredit the time-honored methods of testing the purity of the air by measuring the percentage of carbon dioxide it contains4 ,the amount of this gas normally present in the free air is about three-hundredths of one per cent1 but experiments have shown that thirty times this amount--a percentage higher than is found in the worst ventilated rooms--may be breathed for hours together without detrimental effects4 ,a further departure from old-fashioned views is seen in the assertion of recent authorities that a deficiency of oxygen1 unless far more pronounced than ever actually occurs in buildings1 mines1 etc41 where the supply of this gas has been the subject of so much solicitude1 has no physiological significance whatever4 ,in support of this assertion it is pointed out that at mountain health resorts the concentration of oxygen out-of-doors is much less than that found in the worst ventilated rooms at sea-level4 ,in mines an ample supply of oxygen may be positively dangerous1 as favoring the occurrence of explosions4 ,these were rare before the enactment of laws requiring a high percentage of oxygen in mine air4 ,illustration3 ,,hill',s ,,katathermometer ,excessive dryness of the skin1 which is a common cause of discomfort1 is not very closely related to the humidity of the air4 8,in winter10 says ,hill1 8if there be a wind the rate of evaporation is so accelerated that the skin feels dry1 because in order to check the loss of body heat the sweat glands are inactive and the blood vessels of the chilled skin are constricted40 ,there has been a great deal of discussion about the dry air of ,american buildings in winter1 and startling figures have been adduced to show that the air of such buildings is dryer than that of deserts4 ,so far as measurements of relative humidity go1 this is perfectly true2 but1 as ,dr4 ,g4 ,t4 ,palmer1 of the ,new ,york ,state ,commission on ,ventilation1 has pointed out1 there is an important difference between dryness and 8dryingness40 ,the latter depends upon the movement of the air1 as well as the relative humidity4 ,the circulation of the air in a desert is generally much more active than that of the air in a building with the windows shut1 and therefore much more conducive to rapid evaporation4 ,there are systems of ventilation in which the air is kept in steady and rapid motion1 and it is probably only in such cases that the air of our heated houses can be compared to that of a desert4 ,from the ,european point of view ,american buildings are notoriously overheated1 but this is probably due to the fact that our hot summers--much hotter than those of ,europe--have adapted us to a tropical climate4 ,it is natural to inquire whether the atmospheric conditions that affect the comfort of man do not also exercise a marked influence upon his muscular efficiency and his mental powers4 ,this question has been answered in the affirmative by a number of ingenious writers1 who have sought to establish definite quantitative relations between certain states of the atmosphere and the output of work in factories1 the grades attained by school children1 etc4 ,thus1 ,dr4 ,ellsworth ,huntington1 a well-known worker in this field1 declares that the most favorable daily mean temperature for mental activity 7the temperature being measured out-of-doors7 is about #dj degrees ,f41 and for physical activity about #fj degrees ,f4 ,contrary to the common opinion1 he holds that our general efficiency is at low ebb in midwinter and fairly high in summer4 ,variability in temperature1 within certain limits1 he finds to be stimulating2 equable temperature the reverse4 ,he has drawn charts showing the distribution of what he calls 8climatic energy0--i4 e41 the combination of certain weather factors supposed to control human efficiency--throughout the world1 and other charts showing a more or less similar distribution of 8civilization40 ,he has also made an ambitious attempt to interpret the history of mankind in terms of weather and climate4 ,another fruitful worker along similar lines is ,dr4 ,griffith ,taylor1 of ,australia1 who has made interesting studies of the control of settlement in his own country and elsewhere by temperature and humidity1 and has introduced some novel graphic methods 78climographs07 for comparing climates with respect to their effects on humanity4 ,there has1 in short1 arisen a new school of climatologists whose aim is to develop exact mathematical formul whereby we shall be able to adjust the economic arrangements of mankind on an intelligent basis as regards climate4 ,the success of their efforts is a question for the future to decide1 but there is no doubt that their work is profoundly suggestive4 ,these undertakings1 it may be noted1 bear a striking analogy to those of the present generation of agricultural meteorologists1 who are applying climatic statistics to the problem of selecting crops and to the improvement of agricultural methods4 ,a certain number of specialists are engaged in studying the physiological effects of sunlight and other special kinds of solar radiation1 the distribution of which varies greatly from place to place and from time to time1 especially on account of differences in the selective absorption of such rays by the atmosphere4 ,the chemical action of sunshine that causes sunburn--even at very low temperatures1 as1 for example1 on high mountains--may have far-reaching effects on the human organism 7as it certainly has on plants71 and there is great need of collecting more data of 8photochemical climate0 than we now possess1 in order that this subject may be thoroughly investigated4 ,one of the few institutions in the world at which a large amount of work has been done in this line is the private observatory of ,dr4 ,c4 ,dorno1 at ,davos1 the well-known health resort in the ,alps4 ,dorno's studies throw a good deal of light upon the therapeutic effects of sunshine in a mountain climate4 ,many forms of dust in the atmosphere are capable of producing pronounced physiological and pathological effects4 ,there is a long list of 8dusty trades0 in which the production of excessive dust has notoriously evil effects upon the health of workmen1 leading especially to pulmonary diseases2 sometimes to various kinds of poisoning4 ,these harmful dusts are by no means confined to factories1 mines1 quarries1 and the like4 ,the air of the average city street abounds in them4 ,dr4 ,j4 ,g4 ,ogden states that #fa per cent of the dust found in the air of the ,new ,york subways consists of jagged splinters of steel1 resulting from the wearing away of brake shoes1 wheels1 and rails4 ,the amount of danger to human health incurred through the presence of disease germs in the atmosphere has been the subject of much controversy4 ,the present tendency is to regard this danger as very slight1 under ordinary conditions4 ,thus1 ,dr4 ,f4 ,s4 ,lee writes3 8,evidence that disease germs pass through the air from room to room of a house or from a hospital to its immediate surroundings always breaks down when examined critically4 ,it is indeed not rare now to treat cases of different infectious diseases in the same hospital ward4 ,the one place of possible danger is in the immediate vicinity of a person suffering from a disease affecting the air passages1 the mouth1 throat1 or lungs1 such as a #8cold' or tuberculosis4 ,such a person may give out the characteristic microbe for a distance of a few feet from his body1 not in quiet expiration1 for simple expired air is sterile1 but attached to droplets that may be expelled in coughing1 sneezing1 or forcible speaking4 ,in this manner infection may1 and probably does1 occur1 the evidence being perhaps strongest in the case of tuberculosis4 ,but apart from this source there appears to be little danger of contracting an infectious disease from germs that float in the air40 ,in regard to sewer gas1 which still inspires so much dread in the popular mind1 ,dr4 ,lee says3 8,workmen in sewers are notoriously strong1 vigorous1 healthy men1 with a low death rate among them4 ,the specter of an invisible monster entering our homes surreptitiously from our plumbing pipes and sapping our lives and the lives of our children must be laid aside2 we need no longer leave saucers of so-called #8chlorides' standing about our floors to neutralize in an impossible manner mysterious effluvia that do not exist2 and when we return to our town houses in the autumn we may enter them with no fears that we are risking our lives by coming into a toxic1 germ-infected1 sewer gas-laden1 deadly atmosphere40 ,present-day knowledge on the subject of infectious diseases discredits many ideas that once prevailed with regard to the effects of tropical climates on health4 ,the remarkable results accomplished by vigorous sanitary measures in such places as ,havana1 the ,isthmus of ,panama and ,guayaquil have aroused hopes--perhaps too sanguine--that eventually all parts of the tropics will be made healthful for the white race4 ,in the ,canal ,zone the death rate of the large population of ,american men1 women1 and children is not higher than prevails in many cities of the ,united ,states2 whereas1 a generation ago1 when the ,french were at work on the canal1 the 8climate0 of this region was regarded as one of the most unhealthful in the world4 ,some authorities go so far as to assert that the deterioration in the general health and efficiency of white people in the tropics1 so far as it actually occurs1 is due entirely to preventable diseases4 ,it would seem more rational1 however1 to assume that there are climates both in and out of the tropics which1 on account of their heat1 humidity1 and other purely physical factors1 are not so suitable for habitation for any race of humanity as others4 ,how far acclimatization can go toward offsetting the effects of these atmospheric conditions is problematical4 ,the changes in the barometer that occur from day to day in regions where these changes are most pronounced are1 on an average1 not greater than those encountered in going from the bottom to the top of a good-sized hill1 and are probably not directly of physiological importance4 ,certain ,european investigators1 however1 ascribe pathological effects to the minute and rapid barometric fluctuations--too small to be detected with an ordinary barometer--that occur1 for example1 when the foehn wind is blowing4 ,whether this is the cause1 or a contributory cause1 of 8foehn-sickness10 of which one hears in ,switzerland1 is still uncertain4 ,the physiological effects of a rarefied atmosphere1 as experienced in mountain climbing1 ballooning1 and aviation1 are not yet well understood1 despite the large amount of study that has been devoted to this subject4 ,recent views are thus summarized by ,rosenau3 8,the symptoms produced by a marked diminution in atmospheric pressure vary with circumstances4 ,the effects are increased by cold1 active muscular exertion1 or improper clothing4 ,the noticeable symptoms are increased rapidity of respiration and acceleration of the circulation1 noises in the head and dizziness1 impairment of the senses of sight1 hearing1 and touch1 dullness of the intellectual faculties1 and a strong desire to sleep4 ,sudden changes to a rarefied atmosphere cause syncope1 weakness1 dyspna1 dizziness1 and nausea4 ,these threatening symptoms go by the name of #8mountain sickness1' ,bert and ,journet believe this condition is due to lack of oxygen1 and the symptoms may1 in fact1 be relieved by adding oxygen to the air inspired4 ,kronecker concludes that mountain sickness is caused by a congestion of the lungs1 impeding the flow of blood through them4 ,mosso and his followers attribute the physical disturbances of a reduced atmospheric pressure to the fact that the blood loses carbon dioxide more quickly than it loses oxygen1 and they ascribe mountain sickness to this decrease of carbon dioxide in the blood4 ,cohnheim believes there is a concentration of the blood at high altitudes2 in fact1 insignificant increases have been found by competent observers40 ,divers and workers in caissons are subjected to high barometric pressure1 amounting1 at the maximum1 to about #d atmospheres4 ,according to ,rosenau3 8,the physiological effects of an increased atmospheric pressure are mainly due to an increase in the amount of atmospheric gases 7especially nitrogen7 which are taken up by the blood1 and also to an increase in the chemical absorption of oxygen by the blood4 ,the serious consequences usually result from too rapid decompression4 ,as the pressure is released gas bubbles form4 ,gradual decompression gives a chance for the gas to escape from the lungs and be expelled without the production of bubbles40 ,the health and comfort of many people seem to be affected1 in a rather striking way1 by the passage of the barometric depressions and areas of high pressure that alternate at intervals of a few days in the temperate zones4 ,these effects should not be ascribed to changes of pressure1 but rather to the accompanying changes in the other meteorological conditions4 ,the late ,dr4 ,weir ,mitchell1 who was a pioneer student of such phenomena1 wrote of 8a neuralgic belt1 within which1 as it sweeps along in advance of the storm1 prevail in the hurt and maimed limbs of men1 in the tender nerves and rheumatic joints1 renewed torments called into existence by the stir and perturbation of the elements40 ,victims of neuralgia and rheumatism are probably quite justified in regarding themselves as human barometers1 capable of predicting with considerable accuracy the advent of stormy and rainy weather4 ,the fluctuations of temperature1 humidity1 and wind that attend the passage of barometric highs and lows would seem1 in virtue of their effects on the heat-regulating mechanism of the body and consequent reactions upon the nervous system in general1 to supply an ample explanation of the unpleasant symptoms above noted in the case of sensitive people2 conditions to which the collective name of 8cyclonopathy0 has been given by ,european investigators1 and which are extensively discussed in the works of ,hellpach1 ,frankenhuser1 and ,berliner4 ,some authorities have1 however1 invoked in this connection the possible effects of atmospheric electricity1 and pointed to the extreme sensitiveness of many persons to the approach of thunderstorms2 a condition which ,dr4 ,g4 ,m4 ,beard named 8astraphobia40 ,it is stated that the passage of a low-pressure area favors the emission of radioactive emanations from the ground1 that the ionization of the atmosphere1 and hence its electrical conductivity1 is thus increased1 and that the electric charge of the body is carried away more rapidly than usual4 ,here we enter upon a debatable subject1 but one that thoroughly merits investigation4 ,the human organism is the seat of various electrical phenomena1 and these certainly cannot be independent of changes in the electrical state of the atmosphere4 ,apart from possible direct effects of atmospheric electricity upon the human system1 it has been suggested that electrical changes in the atmosphere affect the rate of reproduction of bacteria1 and may therefore have some influence on the spread of infectious diseases4 ,the weather has many subtle influences upon the human mind1 producing moods of cheerfulness and depression1 and manifesting themselves in the records of the behavior of school children1 in statistics of crime1 insanity1 suicide1 drunkenness1 etc4 ,an interesting account of these manifestations is given by ,dr4 ,e4 ,g4 ,dexter in his book 8,weather ,influences0 7,new ,york1 #aijd74 ,finally1 the aspect of meteorology that has thus far acquired the most definite shape in medical circles and given rise to the most coherent body of literature is ,medical ,climatology1 which is designed to be applied in the climatic treatment of disease 7climatotherapy74 ,thus many compilations have been made of the climatic statistics of health resorts1 and these resorts have been classified with respect to their supposed climatic effects upon various diseases4 ,from the point of view of the physical climatologist1 the statistics found in such books seem1 in general1 both meager and ill adapted to bring out important features of the climates discussed2 to say nothing of the fact that the whole subject of climatotherapy is fraught with controversy--whereof the history of the treatment of tuberculosis furnishes a shining example6 ,,chapter ,,xxi ,,weather-,,making ,meteorologists1 in their candid moments1 have been heard to express disappointment over the amount of progress made in the art of weather forecasting during the past half-century4 8,shall we ever10 they ask1 8be able to predict the weather with mathematical certainty1 as the astronomer predicts an eclipse of the sun or moon80 ,perhaps even within the meteorological fold there are unorthodox optimists who would answer such a question thus3 8,yes1 because some day we shall control the weather4 ,it is inconceivable that man1 who is every day achieving new miracles in the conquest of nature1 should not eventually find a way of regulating the rainfall and sunshine that are of such vital importance to his crops1 the winds that must be reckoned with in his voyages by sea and air1 and the various other elements of weather that have so much to do with his happiness and welfare4 ,the attainment of this object is so tremendously desirable that it cannot forever baffle human ingenuity40 ,in support of such a bold assertion it might be pointed out that we already control the weather to a certain limited extent4 ,when the horticulturist burns orchard heaters to protect his fruit from frost he certainly alters the weather for a few hours over a small area of the earth4 ,if there were any practical justification of the process1 the temperature of the air over an entire ,state1 for example1 could be raised throughout the winter1 with appreciable effects on agriculture4 ,the difference between heating a single orchard for a night and heating a ,state for a season is one of degree1 and not of principle4 ,the climate of a city is1 through causes dependent upon man1 materially different from the natural climate of the surrounding country4 ,every dwelling provided with heating arrangements enjoys an artificial summer amid the blasts of winter4 ,local control of the winds is exemplified in the planting of thousands of miles of trees as windbreaks in the prairie regions of our ,middle ,west4 ,by moderating the winds this process has a marked effect on temperature and evaporation and is so beneficial to crops that in the aggregate it furnishes a striking example of successful 8weather-making0 by mankind4 ,analogous methods1 perfectly feasible with means already at our disposal1 would change the whole climatic aspect of large areas of the earth's surface4 ,the question 8,can we make it rain80 may be answered in the affirmative by those who are neither impostors nor victims of self-delusion4 ,the deposit of spray from the spout of a teakettle might1 without much stretching of terms1 be described as a miniature artificial rainstorm2 but much bigger showers1 in nowise different from those occurring in nature1 can also be produced artificially4 ,huge clouds have often been observed to form over forest fires and other great conflagrations4 ,these clouds1 composed of water drops1 tower far above the smoke cloud1 and are identical in character and mode of origin with the cumulus and cumulo-nimbus clouds formed by currents of moist air rising from the heated ground on a summer day4 ,there are several well-authenticated cases in which rain has been seen to fall from such clouds1 and these showers have sometimes been so heavy as to extinguish the fires that generated them4 ,hence1 given favorable conditions of humidity1 temperature and wind1 mankind can certainly produce a rainstorm 7and perhaps a thunderstorm into the bargain7 by the relatively simple process of building a big fire4 ,unfortunately the vast majority of methods whereby man has attempted to regulate the weather have no such rational foundation as those we have just mentioned4 ,some are wholly superstitious1 others are purely empirical1 and yet others are based upon ideas that their promoters suppose or pretend to be scientific1 but that are actually fallacious4 ,in the history of superstitious practices weather-making plays a prominent part4 ,sir ,j4 ,g4 ,frazer1 in that great storehouse of myth and folklore1 8,the ,golden ,bough10 says3 8,of the things which the public magician sets himself to do for the good of the tribe1 one of the chief is to control the weather and especially to insure an adequate fall of rain4 ,in savage communities the rain-maker is a very important personage2 and often a special class of magicians exists for the purpose of regulating the heavenly water supply40 ,frazer devotes ninety pages of his work to a rapid survey of the superstitious methods of controlling the weather that have found credence among the various races of mankind4 ,these range all the way from the most complicated ceremonies to the summary expedient of throwing a passing stranger into a river to bring rain4 ,the sailor who whistles or scratches the mast to raise a wind is merely keeping up a quaint custom1 in the efficacy of which he may or may not put some lingering faith1 but which the world at large long since ceased to take seriously4 ,when1 however1 a vessel master attempts to disperse a waterspout by firing a cannon at it1 he is doing what nine educated persons out of ten would probably do under the circumstances4 ,yet one process is no more futile than the other1 and both are based on superstition4 ,ages ago sailors sought to frighten waterspouts away by pointing knives at them1 or by shouts and the clashing of swords1 and the use of cannon originally embodied the same idea of terrifying the watery monster4 ,it is our purpose in the present chapter to describe especially several processes of weather-making which1 while not obviously chimerical from the point of view of the layman1 have been more or less positively discredited through the scrutiny of men of science4 ,the efforts of modern weather-makers have been directed especially to two objects2 viz41 the production of rain and the prevention of hailstorms4 ,in the ,united ,states a certain amount of ingenuity has also been devoted to the task of dispelling tornadoes4 ,some years ago a device for the latter purpose was patented1 consisting of a box1 containing explosives1 mounted on a pole and erected a mile or so to the southwestward of the village to be protected from these unwelcome visitors4 ,the force of the wind was expected to detonate the explosives by driving a movable board against percussion caps4 ,the inventor believed that a violent explosion would disperse the passing tornado funnel4 ,apart from the fact that a single installation of this character1 or even several of them1 would seldom happen to be at exactly the right spot to explode close to the relatively small vortex of a tornado1 the effect of the explosion1 even in the very heart of the storm1 would certainly be negligible4 ,the energy that keeps the tornado in action is supplied continuously from a level far above the earth1 while the disturbance due to the explosion would be only momentary4 ,above all1 the energy developed in any discharge of explosives that the community could afford to pay for would be quite insignificant compared with that which prodigal nature supplies to the tornado4 ,the same disproportion between the giant forces at work in the atmosphere and the pygmy forces at the disposal of mankind is a point that is overlooked in most attempts at weather-making4 ,the widespread belief that rain can be produced by explosions rises so far above the level of ordinary popular delusions that it has sometimes led to large expenditures of money on the part of drought-ridden communities and even of national governments4 ,perhaps the most remarkable example of official confidence in the efficacy of this process was that furnished some years ago by the ,volksraad1 or legislative assembly1 of the ,transvaal1 which passed a law forbidding the bombardment of the clouds to produce rain1 on the ground that the rain-makers were thwarting the will of the ,almighty6 ,one manifestation of the belief in question is found in the common assertion that rain is the usual sequel of battles4 ,this idea originated1 however1 long before the invention of gunpowder4 ,it is mentioned by ,plutarch and other writers of antiquity4 ,whatever superstition or crude process of reasoning may have first given support to this notion in the popular mind1 the explanation now commonly advanced is that the condensation of moisture is promoted by the concussion due to cannonading1 or that the drops already condensed and constituting the clouds are jostled together by the same disturbance1 with the result that they coalesce and fall as rain4 ,there is no ground for such assumptions4 ,as was once pointed out by the late ,professor ,simon ,newcomb1 the effect of a violent explosion upon a body of moist air a quarter of a mile distant is about the same as that which the clapping of one's hands would produce upon the moist air of the room in which the experiment is performed4 ,again1 if we stand in the steam escaping from a teakettle and clap our hands we shall not produce a shower1 though we jostle the water drops much more than the explosion does at a distance of a quarter of a mile4 ,in recent years another explanation has been offered for the alleged production of rain by explosions2 viz41 that the smoke and gases arising from an explosion increase condensation by increasing the number of 8nuclei0 in the atmosphere4 ,as we have seen1 however1 in considering the natural formation of rain1 the number of condensation nuclei normally present in the atmosphere is so great that it must be diminished1 rather than increased1 before drops as large as raindrops can be formed4 ,moreover1 the nuclei required for the condensation of water vapor1 including molecules of highly hygroscopic gases1 are given forth in abundance by great manufacturing centers1 yet these places do not have a heavier rainfall than the surrounding country4 ,pittsburgh1 for example1 is actually one of the driest places in ,pennsylvania4 ,one obvious reason why rain often follows a battle is that battles are frequently fought in regions where rain normally occurs every two or three days1 on an average1 whether in peace or war4 ,in northern ,france1 for example1 where the battles of the ,world ,war were plenteously interspersed with showers1 meteorological records show that the average number of rainy days per annum is upward of #aej4 ,the drenching rains that made 8,virginia mud0 a byword during the ,american ,civil ,war gave great currency to the belief in 8rain after battles10 ,here1 again1 we have accurate weather records to help us dispel a fallacy4 ,thus at ,richmond rain falls on #abb days in an average year1 at ,lynchburg on #abd days1 and at ,petersburg on #aje days4 ,there is1 however1 a particular reason why rain is rather more likely to occur soon after a battle than shortly before one2 viz41 the fact that intervals of fair weather1 with consequent dry roads1 are used by commanders in carrying out the movement of troops that precede an engagement4 ,by the time such arrangements1 often occupying several days1 are completed1 the 8spell0 of fine weather is likely to be over1 and a rainstorm is due in accordance with the normal program of nature4 ,the most famous undertaking in the history of rain-making--and one which has had an incalculable effect in fostering the credulity of the public with respect to similar enterprises--was that carried out by ,general ,robert ,dyrenforth on behalf of the ,united ,states ,government in #ahia4 ,congress voted appropriations amounting to #i1jjj for these experiments1 and ,dyrenforth was appointed a 8special agent0 of the ,department of ,agriculture to direct them4 ,after some preliminary trials in the suburbs of ,washington1 the experimenters proceeded to a ranch near ,midland1 ,texas4 ,here a few balloons filled with a mixture of oxygen and hydrogen1 as well as several sticks of dynamite carried up by kites1 were exploded in the air1 but the only explosions of considerable magnitude were set off on the ground4 ,the experiments continued over a period of three weeks and in some cases showers fell within a few hours after an explosion1 but1 in spite of the somewhat favorable tone of the official report1 the consensus of scientific opinion was that the undertaking was a failure1 while the views of the public at large were divided4 ,the attitude of the ,government is sufficiently indicated by the fact that it has never since undertaken experiments in this line4 ,the one tangible outcome of this affair was that a crop of private rain-makers sprang up all over the country1 and to this day the example set by the official experimenters is cited in support of every sort of harebrained scheme for juggling with the weather4 ,in #aiaa and #aiab the late ,c4 ,w4 ,post1 of breakfast-food fame1 expended many thousand pounds of dynamite in efforts to produce rain in ,texas and ,michigan4 ,showers undoubtedly occurred in conjunction with ,post's experiments1 but conditions favoring their occurrence were plainly indicated on the current daily weather maps1 and they had been duly forecast by the ,weather ,bureau4 ,the professional rain-maker does not generally resort to the expensive process of bombarding the clouds4 ,his methods most frequently involve the use of chemicals1 and the details are shrouded in mystery4 ,for example1 about a quarter of a century ago one ,frank ,melbourne1 known as 8the ,australian rain-maker10 enjoyed great celebrity and coined money by his exploits in this field4 ,his plan was to shut himself up in a barn1 freight car1 or other structure1 and manipulate his chemicals and electric batteries for hours or days4 ,naturally rain sometimes came after these operations1 but as often it did not4 ,several of the methods that have been suggested from time to time for producing rain are sufficiently discredited by the fact that the expense of putting them into execution would more than offset any benefits derived from the rain1 if the experiments proved successful4 ,thus one genius1 observing the deposit of water on the outside of an ice pitcher in a warm room1 proposed to set up a barrier packed with ice in the path of moisture-bearing winds4 ,another plan occasionally suggested is to sprinkle the atmosphere aloft with liquid air or liquid carbon dioxide1 in order to lower the temperature1 by the rapid evaporation of these substances1 below the point of condensation4 ,a third proposal is to create a local updraft of air by means of powerful fans or blowers1 thus imitating the convectional process by which clouds and rain are formed in nature4 ,lastly1 various plans have been suggested for altering the electrical condition of the upper atmosphere--for example1 by electrical discharges from balloons--on the assumption that rainfall might thus be promoted4 ,this assumption1 however1 is not consistent with known facts as to the relation between atmospheric electricity and the condensation of atmospheric water vapor4 ,while in ,america a vast amount of money has been wasted on futile experiments in rain-making1 far more has been spent in ,europe on schemes for averting hailstorms4 ,methods of accomplishing this purpose have varied from age to age4 ,in antiquity it was the custom to shoot arrows or hurl javelins toward the gathering clouds in the hope of frightening them away4 ,in the ,middle ,ages ecclesiastical or occult agencies were invoked2 8hail crosses0 7such as are still seen in the ,tyrol7 were erected2 and the ringing of church bells was considered efficacious against both hail and lightning1 as is shown by the inscriptions found on many old bells4 ,the custom of firing cannon at the clouds to avert hail began centuries ago in ,styria and northern ,italy1 and it was well established in ,france before the ,revolution4 ,toward the end of the eighteenth century1 however1 another method of hail protection was introduced in ,france1 whence it spread over the rest of ,europe4 ,this consisted in setting up tall1 metal-tipped poles1 imitated from lightning rods4 ,it was supposed that these poles1 which were known as paragrles1 would draw the electric charge from the clouds and thereby 7though nobody could say why7 would prevent the formation of hailstones4 ,this device1 though reported on unfavorably by the ,french ,academy of ,sciences1 gained great popularity4 ,one of its advocates1 writing in #ahbg1 states that more than a million paragrles were at that time in use in ,france1 ,switzerland1 ,italy1 ,austria1 ,bavaria1 and the ,rhine country4 ,the vogue enjoyed by these contrivances is said to have come to a sudden end when a tremendous hailstorm not only devastated the fields and vineyards they were supposed to protect1 but also knocked down a great number of the rods themselves4 ,in recent times both the hail cannon and the paragrle have been revived4 ,the new era of 8hail-shooting10 as the process of cannonading the hail clouds is called1 dates from the year #ahif1 when a number of cannon of a new type were installed in the vine-growing district of ,windisch-,feistritz1 in ,styria4 ,the success claimed for them in this region led to their introduction on a vast scale over the greater part of southern and central ,europe4 ,the cannon employed were small mortars1 to the muzzles of which were attached sheet-iron funnels4 ,no projectile was used1 but the explosion of the charge sent aloft a curious whirling ring of smoke and gas1 powerful enough to splinter sticks and kill small birds several hundred feet from the cannon4 ,by the year #aijj at least #aj1jjj hail cannon were in use in ,italy alone4 ,several modifications of the device were introduced1 such as the use of acetylene in place of gunpowder2 and eventually certain forms of rocket and bomb were adopted1 for concentrating the effects of the explosion at as high a level as possible4 ,about the year #ahii a new form of hail rod was introduced in ,france1 and this has become the favorite means of protection against hail in that country4 ,it is essentially a very large lightning rod of pure copper1 grounded by means of a broad copper conductor4 ,such rods have been installed1 in some cases1 on church steeples and other tall edifices1 including the ,eiffel ,tower1 in ,paris1 and in other cases on tall steel towers erected for this purpose4 ,this device is called fantastically an 8electric ,niagara10 because1 according to the claims of its promoters1 it draws down 8torrents0 of electricity from the clouds4 ,hundreds of these 8,niagaras0 have been constructed in ,france4 ,some of them are set up in rows1 or so-called barrages1 across the habitual paths of hailstorms4 ,the ,french ,government was induced to appoint a 8,comit de ,dfense contre la ,grle0 7,hail-protection ,committee71 which before the war had made elaborate plans for 8protecting0 not only the whole of ,france1 but also ,algeria and ,tunis1 with these devices4 ,similar rods have been erected in ,argentina1 and plans for introducing them in ,south ,africa were near consummation at the time the ,world ,war broke out4 ,in order to understand the extraordinary hold that the various hail-protecting devices have taken upon the minds of ,european cultivators it should be remembered that the intensive cultivation of the soil is the rule over the greater part of ,europe1 so that a hailstorm of relatively small extent often does enormous damage4 ,vineyards are especially subject to injury from this cause1 and many of the richest vine-growing districts of the ,old ,world are notoriously afflicted with hailstorms4 ,scientific commissions appointed by the ,austrian and ,italian governments conducted long series of tests of the methods of bombarding the clouds with mortars1 bombs1 and rockets1 and declared them to be of no value4 ,the erection of hail rods1 though it has received a certain amount of official encouragement in ,france1 is also strongly discountenanced by the majority of scientific men1 as well as by a large proportion of intelligent agriculturists4 ,reports on the actual operation of the rods support conflicting opinions--as might be expected from the fact that the hailstorm is a decidedly erratic phenomenon4 ,thus1 some observers claim that the storm clouds change conspicuously in appearance as they approach a 8,niagara10 and if they shed hail upon the spot it is in a soft and harmless form4 ,others deny the accuracy of these observations1 and point to the stubborn fact that ordinary hail has fallen on several of the rods themselves1 including the one on the ,eiffel ,tower4 ,in the suburbs of ,clermont-,ferrand a 8,niagara0 is installed on an iron tower1 #ajj feet high4 ,this rod was pelted with hail twice in #aiab and four times in #aiac1 and in one case the hailstones attained the size of hen's eggs6 ,nobody has ever offered any plausible scientific hypothesis to explain why these rods should have an effect upon hail1 even if they are able1 as seems unlikely1 to reduce the electrical charge of the clouds2 since the formation of hail is due to movements of the air1 which1 in turn1 are the cause and not the result of the charge in question4 ,fortunately for the farmer and the horticulturist--especially in ,europe--a method of averting the losses due to hailstorms is available in the shape of insurance1 and its cost is decidedly less than that entailed in systematic hail-shooting or in the general erection of hail rods4 ,hailstorm insurance has been extensively practiced in the ,old ,world since the end of the eighteenth century4 ,in some countries it has been conducted or subsidized by the government4 ,generally each country is divided into a number of zones1 according to the recorded frequency of hailstorms1 and the premiums vary proportionately4 ,premiums also vary for different crops1 since some are better able to withstand the effects of hail than others4 ,the amount of insurance of this kind carried in ,germany1 alone1 shortly before the ,world ,war1 was more than #hjj1jjj1jjj4 ,hailstorm insurance is fairly common in the ,united ,states1 especially in the ,middle ,west1 but still lacks an adequate statistical basis in the shape of detailed records of hail frequency4 ,in #aiai growing crops in this country were insured against hail to the extent of #eei1acd1jjj4 ,much information on this subject will be found in ,v4 ,n4 ,valgren's 8,hail ,insurance on ,farm ,crops in the ,united ,states0 7,u4 ,s4 ,dept4 of ,agriculture1 ,bulletin #iab71 published in #aibj4 ,besides the weather-making schemes already noted1 mention should be made of certain more ambitious projects of this character that have been bruited from time to time1 and that have found plenty of credulous supporters4 ,in the year #ahde an ,american meteorologist of undoubted ability1 but much inclined to the riding of hobbies--viz41 ,james ,p4 ,espy--proposed the building of great fires in the western part of the ,united ,states in order to regulate the winds and rainfall to the eastward4 ,the fires were to extend in a line of six or seven hundred miles from north to south1 and were to be set off once a week throughout the summer4 ,another genius1 of less celebrity1 proposed to destroy blizzards by means of a line of coal stoves along the northern boundary of the country4 ,a favorite idea of those who aspire to produce wholesale changes of climate is to alter the course of ocean currents for this purpose4 ,one early plan contemplated the damming of the ,strait of ,belle ,isle in order to improve the climate of ,new ,england and the ,canadian provinces2 while1 a few years since1 a proposal to build an immense jetty eastward from ,newfoundland for the purpose of 8protecting the warm north-flowing ,gulf ,stream from the onslaughts of the ice-cold1 south-flowing ,labrador ,current0 actually received1 serious attention from the ,congress of the ,united ,states4 ,,chapter ,,xxii ,,atmospheric ,,byways #a4 ,,ignis ,,fatuus1 ,,or ,,will-,o'-,,the-,,wisp ,will-o'-the-wisp is proverbially elusive4 ,it has thus far escaped the fate of the rainbow1 deplored by ,keats4 ,we do not know its woof and texture1 and it is not given in the dull catalogue of common things4 ,a strong argument in favor of the reality of this phenomenon is found in the great number of names that have been applied to it4 ,there are forty or fifty in the ,british dialects alone4 ,a myth generally carries its nomenclature with it1 as it spreads from one community to another1 while a fact of nature may give rise to a variety of local names4 ,it is certain1 however1 that a great many different phenomena have been described as will-o'-the-wisp4 ,some of these are3 7#a7 ,the phosphorescence of decaying wood 78fox fire07 and other vegetable matter4 ,this is due to luminous fungi4 ,according to ,h4 ,molisch there are some forty-five species of fungi1 including twenty species of bacteria1 that have the property of luminosity4 ,sometimes the ground under a forest is illuminated on all sides with a soft1 white light from decaying leaves4 7#b7 ,fireflies1 including glowworms 7the wingless females of the firefly and the larv74 7#c7 ,luminous birds and animals4 ,their luminosity is supposed to be due to parasitic fungi4 ,certain species of skunk have been described as giving off in the darkness a continuous flame1 the head being fiery red1 which blends into a bright blue at the tail4 7#d7 ,ball lightning4 7#e7 ,st4 ,elmo's fire4 7#f7 ,moving lanterns1 distant lights of houses1 and other lights due to human agency4 7#g7 ,burning gas ascending from marshes1 stagnant pools1 and the like4 ,marsh gas and other inflammable gases commonly rise from such places1 and are often ignited by man1 or by lightning1 etc4 ,such fires are sometimes seen by day as well as by night4 7#h7 ,burning naphtha springs4 ,excluding the numerous reported cases of will-o'-the-wisp in which the phenomenon may be plausibly identified with one of those mentioned above1 there remain several cases1 some of them reported by very careful observers1 which appear to belong to a different category4 ,the reports in question differ somewhat in details1 but yield the following composite description3 ,small luminous bodies1 8about as large as your fist10 or 8the size of a candle flame10 are seen hovering a few feet above the ground2 not only over marshes and pools1 but also over dry land4 ,sometimes they are stationary2 at other times they appear to drift with the wind1 or even to move independently4 ,they appear and disappear1 after the manner of fireflies4 ,they do not set fire to objects with which they come in contact1 and are believed to be without sensible heat4 ,their color is most often described as bluish1 but may be yellow1 purple1 green1 etc42 rarely pure white4 ,they are without odor and without smoke4 ,traditionally they are associated with graveyards1 but in very few of the cases heretofore recorded were they actually seen in such places4 ,the popular idea that they flee from the traveler who tries to approach them and follow him when he seeks to avoid them is also unsupported by the evidence thus far adduced4 ,one of the most circumstantial accounts of these objects is that published in the ,belgian journal 8,ciel et ,terre0 for ,july-,august1 #aibj1 by a retired army surgeon1 ,jules ,rossignol1 who observed them repeatedly in the autumn of #aijh in and about some marshy woods near ,grupont4 ,they were generally seen to rise from the ground1 at first in the shape of little white clouds1 which changed to luminous globes on attaining an altitude of a dozen yards1 and returned by a circular path toward the ground4 ,they lasted from one to several minutes before disappearing in the air4 ,it is astonishing that the phenomenon of ignis fatuus1 though reported from so many parts of the world1 has not yet been made the subject of direct scientific examination4 ,nobody has ever studied its light with the spectroscope1 for example4 ,chemists have1 indeed1 attempted to reproduce the phenomenon1 yet the chemical explanations of it that have appeared in reference books down to a recent date are quite untenable4 ,it has sometimes been attributed to marsh gas 7methane1 ,,ch#d71 and sometimes to phosphureted hydrogen 7phosphine1 ,,ph#c74 ,but marsh gas1 besides not being spontaneously combustible1 diffuses too rapidly in the air to produce the effects described1 while phosphureted hydrogen1 though it takes fire spontaneously in the air1 produces thick wreaths of smoke when burning and has a powerful odor--features never reported in connection with will-o'-the-wisp4 ,at least two more plausible explanations of ignis fatuus have been offered in the last few years4 ,mr4 ,f4 ,sanford 78,scientific ,monthly10 ,oct41 #aiai7 believes that it is due to 8swarms of luminous bacteria which are carried up from the bottom of the marsh by rising bubbles of gas40 ,a ,belgian chemist1 ,m4 ,lon ,dumas 78,la ,nature10 ,dec4 #aa1 #aiji71 claims to have produced little luminous clouds1 corresponding to the traditional descriptions of will-o'-the-wisp1 by combining the two gases sulphureted hydrogen and phosphine4 ,both these substances are produced in the decay of animal matter1 especially of the brain and spinal cord4 ,the body of an animal1 buried in some wet place1 would accumulate the two gases under pressure in the skull and spinal canal1 and their escape1 simultaneously1 would fulfill the conditions of ,m4 ,dumas' experiments4 7,at the request of the present writer1 these experiments were repeated at the ,bureau of ,standards1 in ,washington1 with only partial success4 ,further trials with these and other gases due to putrefaction are desirable47 #b4 ,,the ,,rain ,,tree ,from time to time the newspapers publish accounts of a wonderful tree1 said to grow wild in ,peru or elsewhere1 from the leaves of which falls a continuous shower of rain1 even in the driest weather4 ,the writers generally urge the introduction of this tree in regions where the rainfall is deficient1 and a so-called 8rain tree0 has actually been sold for this purpose by nurserymen4 ,the story of this tree is very old4 ,early voyagers reported finding it in the ,east ,indies1 ,guinea1 ,brazil1 and especially the island of ,ferro1 in the ,canaries4 ,nowadays the name 8rain tree0 is applied especially to a magnificent tree of tropical ,america generally known to botanists as ,pithecolobium 7or ,enterolobium7 saman4 ,one of its common names is 8guango40 ,illustration3 ,,the ,,rain ,,tree ,from 8,voyageurs anciens et modernes0 7,by ,e4 ,t4 ,charton7 ,a legendary scene in the island of ,ferro ,that many plants spontaneously exude moisture under suitable conditions is well known4 ,the phenomenon is called 8guttation40 ,the moisture drawn up from the roots is usually transpired from the leaves in the form of invisible water vapor2 i4 e41 it is evaporated on passing into the air4 ,if1 however1 the humidity of the surrounding air is sufficiently high1 or its temperature sufficiently low1 to check evaporation1 the water will collect on the surface of the plant in liquid form1 and may ultimately trickle to the ground in considerable quantities4 ,guttation occurs chiefly at night1 or in cloudy or foggy weather4 ,in a very dry climate it does not occur at all2 and for this reason1 even if the so-called rain tree could be successfully introduced in such a climate1 it would not help solve the problem of irrigation4 ,the dripping of moisture deposited on plants by drifting fog is another common process that may have contributed to the legend of the rain tree4 ,a classic example of this process--technically called 8fog drip0--is that described by ,dr4 ,r4 ,marloth1 who has made actual measurements of the abundant moisture captured by the vegetation of ,table ,mountain1 ,south ,africa1 from the driving clouds of the southeast trade winds during the nearly rainless summer months4 ,mr4 ,madison ,grant1 writing of a similar phenomenon witnessed in the redwood forests of ,california1 tells us that 8these forests are sometimes so wet that the dripping from the high crowns is like a thin rain1 and in summer it is oftentimes hard to tell whether it is raining or not1 so saturated with moisture are the foliage and the trunks when the fog darkens the forest40 ,a copious production of 8honeydew0 by plant lice1 scale insects1 etc41 may be at the bottom of some of the rain-tree stories4 ,f4 ,e4 ,lutz1 in his 8,field ,book of ,insects10 writes of 8weeping trees10 which drip fluid of insect origin1 and he says of the honeydew secreted by the pear psylla 7,psylla pyricola73 8,when the psyllas are numerous the leaves and fruit become coated with this sticky substance and it even drops from them like rain and runs down the trunk40 ,the following account of the ,peruvian rain tree1 quoted from the traveler ,spruce1 was published in 8,nature0 of ,feb4 #bh1 #ahgh1 by ,prof4 ,thiselton ,dyer3 8,the ,tamia-caspi1 or rain tree of the eastern ,peruvian ,andes1 is not a myth1 but a fact1 although not exactly in the way popular rumor has presented it4 ,i first witnessed the phenomenon in ,september1 #ahee1 when residing at ,tarapoto4 ,i had gone one morning at daybreak1 with two assistants1 into the adjacent wooded hills to botanize4 ,a little after seven o'clock we came under a lowish spreading tree1 from which with a perfectly clear sky over-head a smart rain was falling4 ,a glance upward showed a multitude of cicadas1 sucking the juices of the tender young branches and leaves and squirting forth slender streams of limpid fluid40 #c4 ,,dew ,,ponds ,the ,down country of southern ,england is one of the few places in the world where the people go to the hilltops to seek water in dry weather4 ,on the summits of the ,downs are found many artificial shallow ponds1 most of them very old4 ,some1 indeed1 date back to prehistoric times4 ,the bottom of these ponds consists of a layer of puddled chalk or clay and is impervious to water1 so that there is no loss by seepage4 ,as the ponds are not fed by springs or surface drainage1 and as lack of rain does not cause them to dry up1 it is popularly believed that their maintenance depends upon dew4 ,hence they are called 8dew ponds40 ,kipling mentions them in his poetical description of ,sussex3 ,we have no waters to delight ,our broad and brookless vales-- ,only the dew pond on the height ,unfed1 that never fails4 ,the leading authority on dew ponds is ,mr4 ,edward ,a4 ,martin1 who has written a book about them4 ,mr4 ,martin's experiments have demonstrated that dew can make no important contribution to the water supply of these ponds4 ,the rainfall on the hilltops is somewhat higher than in the valleys1 and the greater part of the water in the ponds is undoubtedly derived from this source4 ,the real key to the mystery1 however1 is found in the wet fogs that drift in from the sea4 ,the process of 8fog drip10 which we have mentioned in connection with the rain tree1 supplies the deficiencies of the rainfall1 and the name 8mist ponds10 occasionally applied to these bodies of water1 is more appropriate than 8dew ponds40 ,it remains1 however1 an interesting paradox that1 in time of drought1 the farmers of the ,downs drive their cattle to the hilltops to be watered and send their carts uphill to procure water for household use in the valleys below4 ,was it1 perhaps1 in this topsy-turvy region--where uplands are called 8downs0--that ,jack and ,jill went 8up the hill0 on their ill-starred water quest8 #d4 ,,blowing ,,wells ,wells that predict weather changes are local curiosities in many parts of the world4 ,such wells are not uncommon in the ,united ,states4 ,if the well is open at the top1 its manifestations consist of occasional disturbance of the water and the discharge of numerous bubbles4 ,if it is covered1 a strong current of air is1 at times1 emitted from any small orifice in the cover4 ,this may be strong enough to lift and blow away light objects placed over the aperture4 ,its emission is frequently accompanied by a loud whistling or roaring sound4 ,such occurrences are supposed to betoken an approaching storm4 ,these wells are called 8blowing wells02 sometimes 8weather wells0 or 8barometer wells40 ,in certain cases an indraft of air is sometimes observed2 i4 e41 the well alternately 8sucks0 and 8blows40 ,as a rule these phenomena correspond to fluctuations in barometric pressure1 and therefore are1 in a rough way1 indicative of changes in weather4 ,it is obvious that a body of air inclosed in the earth and communicating by one or a few small openings with the air above will set up outdrafts and indrafts in adjusting its tension to that of the latter4 ,the amount of air contained in the well itself would not suffice to produce the violent effects observed and it is therefore assumed that the typical blowing well taps a subterranean reservoir of air1 probably filling the interstices of sand and gravel beds4 ,when the pressure of the external air is diminished1 some of the imprisoned air escapes4 ,for a given body of inclosed air1 the smaller the channel or channels by which it emerges1 the stronger the outdraft4 ,when the barometric pressure outside increases1 the current of air flows in the reverse direction4 ,in winter the indraft of cold air in such a well sometimes causes the water to freeze1 even at a depth of #ajj feet or more below the surface of the ground1 and is therefore a source of inconvenience to the owner4 ,various other circumstances may give rise to the bubbling and blowing of wells4 ,carbon dioxide and other gases dissolved in the well water account for the bubbling of many wells1 and this process is more active at times of low barometric pressure1 because at a given temperature1 the amount of gas that the water can hold in solution varies with the pressure4 ,another cause of the blowing of a well is1 in some cases1 a sudden rise in the water level 78water table07 in the surrounding ground1 as after a heavy rainstorm4 ,if the ground is overlain by an impervious stratum1 the air imprisoned between this stratum and the surface of the ground water over an extensive area will escape with violence through any available channel1 such as that supplied by the well4 ,lastly1 cases have been described in which subterranean air currents arise from the friction of rapidly flowing underground streams1 setting up permanent indrafts or outdrafts through wells communicating with such streams4 #e4 ,,curious ,,showers4 ,showers of blood1 sulphur1 manna1 frogs1 fishes1 and what not figure in all the old chronicles1 and are still frequently reported4 ,many occurrences of this kind are recorded in ,camille ,flammarion's book 8,the ,atmosphere10 ,dr4 ,e4 ,e4 ,free's 8,movement of ,soil ,material by the ,wind0 7,u4 ,s4 ,bureau of ,soils1 ,bulletin #fh71 and ,mr4 ,w4 ,l4 ,mc,atee's article 8,showers of ,organic ,matter0 in the 8,monthly ,weather ,review0 for ,may1 #aiag4 ,the power of the wind to whirl objects aloft is a matter of familiar observation4 ,mc,atee tells of seeing a silk hat lifted from its owner's head and blown over a ten-story building in the city of ,washington4 ,the vortex of a tornado or a waterspout furnishes the most favorable skyward route for things that belong on terra firma4 ,objects weighing scores or even hundreds of pounds are lifted by these whirls4 ,within a mile or so of a tornado a shower of cart wheels or cook stoves would not necessarily constitute a 8prodigy40 ,a chicken coop weighing #ge pounds has been carried four miles and a church spire seventeen miles4 ,oersted tells of a waterspout at ,christians1 on the ,baltic1 that emptied the harbor to such an extent that the greater part of the bottom was uncovered1 while ,mc,atee says that 8waterspouts have been observed to accomplish the comparatively insignificant feat of emptying fish ponds and scattering their occupants40 ,there is1 in fact1 no mystery about the way in which terrestrial objects of many sorts get into the air2 nor1 considering the force of the winds and their occasional strong vertical components1 is it strange that such objects sometimes travel a long way from home before they return to earth4 ,there are1 however1 a great many cases of reported showers in which the objects did not really fall1 as supposed4 ,mc,atee gives the following account of these spurious showers in the 8,monthly ,weather ,review03 8,insect larv4--,the rains of insect larv that have been investigated have proved to be merely the appearance in large numbers on the surface of the ground or upon snow of the larv of soldier beetles 7,telephorus71 or sometimes caterpillars1 which have been driven from their hibernating quarters by the saturation of the soil by heavy rains or melting snow4 8,ants4--,accounts of showers of ants have usually been founded on incursions of large numbers of winged ants1 which of course needs no assistance from the elements to follow out their habit of swarming forth periodically in immense numbers4 8,honey2 sugar4--,showers of honey and of sugar are popular names for what scientists know are exudations of certain plants1 or of plant lice which feed on a great variety of plants and whose product is often known also as honeydew4 8,grains4--,showers of grain1 usually considered miraculous1 have in most cases been determined to be merely the accumulation by washing during heavy rains of either the seeds or root tubercles of plants of the immediate neighborhood4 8,manna4--,an account of manna #8rains' certainly pertains to the discussion of showers of vegetable matter1 for the substance manna consists of lichens of the genus ,lecanora but in none of the numerous recorded instances of manna #8rains' is there any direct evidence that the substance really fell from the sky4 ,these lichens form small1 round bodies that are easily blown over the surface of the ground and accumulate in depressions2 they are very buoyant also and hence easily drifted into masses during the run-off of rain water4 ,manna #8rains' have not occurred except in countries where these lichens are common1 and as for statements of their falling down upon roofs or upon people1 or for any other proofs that they really rained down1 ,i have seen none4 8,blood rains4--,the most frequently reported showers that are spurious1 at least in name1 are the so-called blood rains4 ,in all times the phenomena going under this name have frightened the people and have been taken as portents of terrific calamities4 ,one of the famous plagues of ,egypt was a bloody rain which prevailed throughout the whole land1 continuing three days and three nights4 ,homer and ,virgil both allude to blood rains1 and1 in fact1 the general subject of preternatural rains was a favorite with the older writers4 8,but scientific investigation has done away with the element of mystery in these phenomena and has explained1 with the others1 the rains of blood4 ,some blood rains have been found to be the meconial fluid ejected by large numbers of certain lepidoptera simultaneously emerging from their chrysalides2 other red rains are due to the rapid multiplication in rain pools of alg and of rotifers containing red coloring matter2 8red snow0 results from the presence of similar organisms4 ,but in no case have they rained down1 except in the sense that their spores or eggs have at some time been transported1 probably by the wind4 ,the precipitation of moisture furnishes favorable conditions for their rapid development and multiplication40 ,most of the reported showers of blood1 however1 have probably been rainstorms in which the rain was colored with reddish dust4 ,the occurrence of such dust in the atmosphere is very common in some parts of the world1 as we have stated in a previous chapter4 ,it has been asserted that rain which fell at ,oppido ,mamertina1 ,italy1 ,may #ae1 #ahij1 actually contained blood1 believed to be from birds4 ,showers of supposed 8sulphur0 are due to pollen1 chiefly from pine trees4 ,the air in the vicinity of pine forests is sometimes filled with clouds of this material and the wind carries it for many miles4 ,it is reported that a pollen shower at ,pictou1 ,nova ,scotia1 in ,june1 #ahda1 was so heavy that bucketfuls were swept up on a ship4 ,in the case of alleged showers of 8paper0 the material has been found to be the crusts of dried alg1 which form on the surface of the ground exposed by the evaporation of the water of shallow ponds4 #f4 ,,the ,,year ,,without ,a ,,summer ,the ,weather ,bureau is a bureau of information1 and one of the ways in which it strives to give a good account of itself is by answering endless questions about 8the year without a summer40 ,this title has been given to the year #ahaf4 ,blodget1 in his 8,climatology of the ,united ,states10 tells us that all the summers from #ahaa to #ahag were cold in this country1 and that in every month of the summers of both #ahab and #ahaf snows and frosts occurred in the ,northern ,states4 ,it is the latter summer1 however1 that has lived in popular tradition4 ,the year #ahaf is known further as 8poverty year10 or 8eighteen hundred and froze to death40 ,it acquired the name of 8mackerel year0 in ,new ,hampshire1 where people ate mackerel as a substitute for pork1 little of which was fattened on account of the extreme scarcity of corn4 ,western ,europe1 also1 had a cold summer in #ahaf1 and the year as a whole seems to have been a cold one over a great part of the world4 ,sources of information about the cold summer in this country1 besides ,blodget's book above mentioned1 include ,perley's 8,historic ,storms of ,new ,england10 which devotes a whole chapter to the subject1 and ,charles ,peirce's 8,weather in ,philadelphia40 ,peirce tells us that at ,philadelphia 8there was ice during every month of the year1 not excepting ,june1 ,july1 and ,august1 ,there was scarcely a vegetable came to perfection north and east of the ,potomac40 ,according to the 8,monthly ,weather ,review10 citing the recollections of ,james ,winchester1 of ,vermont3 8,it is said that in ,june of that year snow fell to the depth of three inches in ,new ,york1 ,pennsylvania1 and ,new ,jersey on the #agth2 five inches in all the ,new ,england ,states1 except three inches in ,vermont4 ,there was snow and ice in every month of this year4 ,the storm of ,june #ag was as severe as any that ever occurred in the depth of winter2 it began about noon1 increasing in fury until night1 by which time the roads were impassable by reason of snowdrifts2 many were bewildered in the blinding storm and frozen to death4444 ,there was a heavy snowstorm ,august #cjth4444 ,the year #ahaf had neither spring1 summer1 nor autumn4 ,the only crop of corn raised in that part of ,vermont that summer was saved by keeping bonfires burning around the cornfield night and day40 ,at the time of its occurrence the frigid weather of the summer of #ahaf was popularly attributed to sun spots1 which were big enough to be seen with the naked eye in ,may and ,june4 ,a present-day hypothesis on the subject has been mentioned in our chapter on atmospheric dust4 ,the dust cloud from the eruption of ,tomboro1 in #ahae1 was so vast that for three days there was darkness at a distance of #cjj miles from the volcano4 ,a proximate cause of the cold summer is perhaps to be sought in an unusual intensity and extent of the area of low barometric pressure which is more or less permanently located in the vicinity of ,iceland and1 as one of the principal atmospheric 8centers of action10 has a great deal to say about the weather of the countries adjacent to the ,north ,atlantic4 ,dr4 ,c4 ,f4 ,brooks has called attention to the fact that the ,arctic navigator1 ,scoresby1 found unusually mild and open weather that summer in the seas east of ,greenland4 ,this would be explained by strong southerly winds1 forming part of the 8counter-clockwise0 circulation around the ,iceland low2 and if the same pressure system extended its influence to our shores1 persistent cold northwest winds might be expected to result over the northeastern ,united ,states4 #g4 ,,indian ,,summer ,,and ,,the ,,ice ,,saints ,indian summer weather is an undeniable fact4 ,every inhabitant of the northern ,united ,states and southern ,canada is familiar with the mild1 calm1 hazy state of the atmosphere that frequently occurs in the autumn1 sometimes following a brief period of unseasonable cold known as 8squaw winter40 ,it is1 however1 one thing to recognize the existence of a certain type of weather as characteristic of our autumns1 and quite another to admit that one definite spell of such weather occurs more or less regularly from year to year4 ,one true summer1 and only one1 comes to pass each year1 and occupies an approximately fixed place in the calendar4 ,even the so-called 8year without a summer10 which we have just described1 was merely a year in which the regular annual rise of the temperature curve was less marked than usual4 ,indian summer1 on the contrary1 has never been tied down to a particular part of a particular month4 ,in his notes on the meteorological conditions at ,concord1 ,massachusetts1 during the ten years1 #ahea-ahfj1 ,thoreau records the occurrence of ,indian summer weather on dates all the way from ,september #bg to ,december #ac2 a range of #gg days4 ,the belief in the definite occurrence1 year after year1 of what has sometimes been called the 8after-summer0 is not peculiar to ,america4 ,it prevails also in ,europe1 where this supposed period of renewed warmth has been assigned to certain dates1 owing in part to its association with the names of particular saints in the calendar4 ,these dates vary widely1 however1 from one region to another1 ranging from ,august #ae 7,julian calendar71 the beginning of the 8young women's summer0 of ,russia1 to ,november #ae1 ,st4 ,martin's day1 a date popularly associated with after-summer in ,germany1 ,holland1 ,france1 ,italy1 and sometimes ,england4 ,the supposed tendency of particular types of weather to occur at about the same period every year1 independently of and often in sharp contrast to the regular march of the seasons1 has been described by ,r4 ,abercromby under the name of 8recurrence10 and there is a large literature on the subject2 especially in connection with periods of unseasonable temperature4 ,while ,indian summer is the most discussed example of recurrence in the ,american weather calendar1 in the ,old ,world more attention1 both popular and scientific1 has been devoted to a frosty period supposed to recur in ,may4 ,with the elaboration of the ecclesiastical calendar1 the frosts in question became definitely associated with the days dedicated to ,saints ,mamertus1 ,pancras1 and ,servatius 7,may #aa1 #ab1 #ac71 or1 in south-central ,europe1 ,saints ,pancras1 ,servatius1 and ,boniface 7,may #ab1 #ac1 #ad71 hence known as the ,ice ,saints4 ,these saints and their days are called in ,french saints de glace1 and in ,german ,eisheiligen1 ,eismnner1 or gestrenge ,herren4 ,yet other examples of the elusive phenomenon of recurrence are the 8,january thaw0 of ,new ,england1 the ,april 8blackthorn winter0 of ,england1 and the ,june 8sheep-cold0 7,schafklte7 of ,germany1 dangerous to newly shorn sheep4 ,in the middle of the last century the cold weather of the ,ice ,saints was variously ascribed to the melting of the ice and snow of high latitudes1 the passage of periodic meteor showers between the earth and the sun1 and other far-reaching terrestrial or cosmical causes4 ,fitz,roy believed that the liberation of latent heat in autumn during the formation of ice in the circumpolar regions was accountable for ,indian summer4 ,a review of the whole body of literature concerning supposed recurrent irregularities in the annual march of temperature will be found in the 8,monthly ,weather ,review0 7,washington7 for ,august1 #aiai4 ,whether recurrence1 in ,abercromby's sense of the term1 is a real phenomenon is still an unsettled question4 ,many periods of unseasonable weather occur in the course of each year1 and it is easy for the uncritical observer to identify one of them with the ,ice ,saints1 another with ,indian summer1 and so on4 ,about the best that meteorologists can do at present is to explain each particular instance of such weather by reference to barometric and other conditions shown on the daily weather map4 ,,glossary ,the vast vocabulary of meteorology is very inadequately represented in ordinary dictionaries1 and has never been made the subject of a comprehensive special glossary4 ,the writer of this book has been gathering material toward such a glossary for some years1 and from the material now in hand it appears that an approximately complete ,english meteorological dictionary1 embracing both scientific and nonscientific terms relating to the atmosphere and its phenomena1 would contain upward of fifteen thousand definitions4 ,from this statement it will be evident that the brief glossary herewith appended is of the most fragmentary character4 ,it includes only a selection of the meteorological terms found in the present book4 ,it does not1 in general1 include terms pertaining primarily to physics1 chemistry1 astronomy1 physiology1 etc41 even though they figure to some extent in meteorology1 as all such terms used in the book are more or less satisfactorily defined in the latest editions of the large ,american dictionaries4 ,absolute ,extremes4--,the highest and lowest values of a meteorological element 7especially temperature7 that have ever been recorded at a station2 known1 respectively1 as the absolute maximum and the absolute minimum4 7,the term is sometimes improperly applied to the highest and lowest values for a specified year47 ,aeroclinoscope4--,a semaphore formerly used in ,holland for displaying weather signals4 ,aerology4--,the branch of meteorology dealing with the 8free0 atmosphere2 i4 e41 all parts of the atmosphere not near the earth's surface4 ,aerological investigations are made with kites and balloons1 and also include observations of clouds1 meteor trails1 the aurora1 etc4 ,afterglow4--#a4 ,the glow in the western sky after sunset4 #b4 ,a renewal of rosy light on mountain peaks after the first sunset illumination has faded2 also called recoloration4 ,this is one stage of the ,alpenglow4 ,after-summer4--,a renewal of mild weather in the autumn2 called ,indian summer in ,america1 ,st4 ,martin's summer1 etc41 in ,europe4 ,alpenglow4--,successive appearances and disappearances of rosy light sometimes seen on mountain peaks in clear weather after sunset or before sunrise4 ,altimeter4--,a barometer used for measuring altitude4 ,alto-cumulus2 ,alto-stratus4--,forms of cloud4 7,see ,chapter ,,vi47 ,anemogram4--,the record traced by a self-registering anemometer4 ,anemometer4--,an instrument for measuring the force or speed of the wind4 ,aneroid ,barometer4--,a barometer consisting of a thin-walled metal vacuum-box1 which changes its shape with changes of atmospheric pressure4 ,the movements of the box are communicated1 by levers1 to an index or 7in the barograph7 to a recording pen4 ,anthelion4--,a rare species of halo1 consisting of a brilliant1 usually white image of the sun opposite the latter in azimuth4 7,this term has also been applied to the glory1 q4 v47 ,anticrepuscular ,rays4--,the continuation of the crepuscular rays converging toward a point in the sky opposite to the sun4 ,anticyclone4--,an area of high barometric pressure and its attendant system of winds4 7,cf4 cyclone47 ,antitrades4--,term formerly applied to the prevailing westerly winds of middle latitudes1 but now more frequently applied to the westerly return-currents lying over the trade winds4 ,some writers prefer to call the former the antitrades and the latter the countertrades4 ,antitwilight ,arch4--,the pink or purplish zone of illumination bordering the shadow of the earth 7dark segment7 in the part of the sky opposite the sun after sunset and before sunrise4 ,arcs of ,lowitz4--,a pair of rare halo phenomena4 ,these arcs are directed obliquely downward from the parhelia of #bb degrees on either side of the sun toward the halo of #bb degrees4 ,astraphobia4--,a pathological condition experienced by certain persons before and during thunderstorms4 ,atmometer4--,an instrument for measuring evaporation2 also called atmidometer1 evaporimeter1 etc4 ,aureole4--7,see corona4 #a74 ,aurora4--,a luminous phenomenon due to electrical discharges in the atmosphere2 probably confined to the tenuous air of high altitudes4 ,it is most commonly seen in sub-,arctic and sub-,antarctic latitudes4 ,called aurora borealis or aurora australis1 according to the hemisphere in which it occurs4 ,observations with the spectroscope seem to indicate that a faint 8permanent aurora0 is a normal feature of the sky in all parts of the world4 8,backstays of the ,sun40--,a sailor's name for crepuscular rays extending downward from the sun4 ,baguio4--,the name current in the ,philippines for a tropical cyclone4 ,ballistic ,wind4--,a military term applied to a fictitious wind which1 if affecting a projectile throughout its flight1 would produce the same total effect in deflecting it from its course and altering its range as do the various winds that it actually encounters4 ,ballon-sonde4--,a sounding-balloon4 ,bar4--,a unit of pressure equal to #a1jjj1jjj dynes per square centimeter4 ,a bar #ajj centibars #a1jjj millibars4 ,a barometric pressure of one bar is sometimes called a 8,c4 ,g4 ,s4 atmosphere10 and is equivalent to a pressure of #bi4eca inches of mercury at #cb degree ,f4 and in latitude #de degrees4 ,barisal ,gun4--,same as brontide4 ,barocyclonometer4--,one of several instruments that have been devised for locating tropical hurricanes without the aid of a weather map4 ,barograph4--,a self-registering barometer4 ,barometer4--,an instrument for measuring the pressure of the atmosphere4 ,the two principal types are the mercurial and the aneroid4 ,the microbarometer is used to show minute changes of pressure4 ,certain forms of hygroscope are popularly miscalled 8barometers40 ,barometer ,well4--,same as blowing well4 ,barometric ,tendency4--,the change of barometric pressure within a specified time 7usually three hours7 before one of the regular observations4 ,beaufort ,scale4--,a scale of wind force1 originally devised for use at sea1 but now used also on land4 ,the scale runs from #j calm to hurricane4 ,many other scales are similarly employed in the noninstrumental observation of wind force4 ,bioclimatic ,law4--,a phenological law1 announced by ,dr4 ,a4 ,d4 ,hopkins1 according to which periodical events of plant and animal life advance over the ,united ,states at the rate of #a degree of latitude1 #e degrees of longitude1 and #djj feet of altitude every four days--northward1 eastward1 and up-ward in spring1 and southward1 westward1 and downward in autumn4 ,bishop's ,ring4--,a large corona due to fine dust in the atmosphere4 ,it has been seen after certain great volcanic eruptions1 especially that of ,krakatoa1 in #ahhc4 ,blizzard4--,a violent1 intensely cold wind1 laden with snow4 ,blowing ,well4--,a well which emits a strong current of air from any small opening in its cover during a fall of barometric pressure4 ,during a rise of barometric pressure such wells are sometimes observed to 8suck40 ,wells that are thus responsive to barometric changes are sometimes called 8barometer wells0 or 8weather wells40 ,bora4--,a cold wind of the northern ,adriatic1 blowing down from the high plateaus to the northward4 ,also1 a similar wind on the northeastern coast of the ,black ,sea4 ,brave ,west ,winds4--,the boisterous westerly winds blowing over the ocean between latitudes #dj and #ej degrees ,s4 ,this region is known as the 8roaring forties40 ,bright ,segment4--,the broad band of golden light that1 in clear weather1 borders the western horizon just after sunset and the eastern just before sunrise4 ,brontide4--,a sound resembling a distant muffled detonation1 usually indefinite as to direction4 ,brontides are rather common in certain parts of the world4 ,they are called mistpoeffers on the ,belgian coast1 ,barisal guns in the ,ganges delta1 bulldag1 desert sounds1 or ,hanley's guns in parts of ,australia1 gouffre in ,haiti1 ,moodus noises at ,moodus1 ,connecticut1 ,nebelzerteiler1 ,seedonner1 ,seeschiessen1 etc41 in ,germany1 baturlio1 boniti1 bombiti1 etc41 in ,italy4 ,these sounds are probably of subterranean origin in most cases4 ,bump4--,an upward jolt experienced by an aviator1 as if running over an obstruction4 ,a bump may be caused by any condition that suddenly increases the lift of the machine1 but is perhaps most frequently due to rising air currents4 ,air in which bumps are experienced is said to be 8bumpy40 7,cf4 hole in the air47 ,callina4--,a ,spanish name for dry fog4 ,calms of ,cancer2 ,calms of ,capricorn4--,the belts of high pressure lying north of the northeast trade winds and south of the southeast trade winds1 respectively4 ,center of ,action4--,any one of several large areas of high and low barometric pressure1 changing little in location1 and persisting through a season or through the whole year2 e4 g41 the ,iceland low1 the ,siberian winter high1 etc4 ,changes in the intensity and positions of these pressure systems are associated with widespread weather changes4 ,ceraunograph4--,a self-registering thunderstorm recorder4 ,chinook1 or ,chinook ,wind4--,a foehn blowing down the eastern slopes of the ,rocky ,mountains over the adjacent plains1 in the ,united ,states and ,canada4 ,in winter1 this warm1 dry wind causes snow to disappear with remarkable rapidity1 and hence it has been nicknamed the 8snow-eater40 7,cf4 foehn47 ,the 8wet chinook0 is a wind of a different character1 blowing from the ,pacific ,ocean over the northwestern ,united ,states4 ,circumscribed ,halo4--,a halo formed by the junction of the upper and lower tangent arcs of the halo of #bb degrees1 when the luminary is about #dj degrees or more above the horizon4 ,as the altitude of the luminary increases1 the circumscribed halo gradually assumes an elliptical form and finally merges into the halo of #bb degrees4 ,circumzenithal ,arc4--,a rainbow-tinted halo1 often very bright1 convex to the luminary and #df degrees or a little more above it4 ,it is sometimes called the upper quasi-tangent arc of the halo of #df degrees1 but the circumzenithal arc and the halo of #df degrees are rarely seen at the same time4 ,cirro-cumulus2 ,cirro-stratus2 ,cirrus4--,forms of cloud4 7,see ,chapter ,,vi47 ,cistern4--,the cup1 containing mercury1 at the base of a mercurial barometer4 ,climatography4--#a4 ,descriptive and statistical climatology4 #b4 ,an account of the climate of a particular place or region4 ,climatology4--#a4 ,the science of climate4 #b4 ,a body of knowledge concerning the climate of any place or region2 as1 8the climatology of ,panama40 ,climograph4--,a diagram introduced by ,dr4 ,griffith ,taylor1 of ,australia1 for showing the mean monthly values of wet-bulb temperature and relative humidity at any place1 and for comparing such data as recorded at different places throughout the world2 especially with reference to the effects of climate on mankind4 ,other pairs of elements can be used in constructing climographs3 e4 g41 the dry-bulb temperature and the relative humidity4 ,cloud-banner4--,a bannerlike cloud streaming off from a mountain peak4 ,cloud-burst4--,a sudden and extremely heavy downpour of rain2 especially one in which the water falls in a continuous stream rather than in drops4 ,the term has been most commonly applied to downpours in mountainous regions4 ,cloud-cap4--,a caplike cloud crowning 7#a7 a mountain summit1 or 7#b7 another cloud1 especially a mass of cumulo-nimbus4 ,col4--,the neck of low pressure between two anticyclones2 also called a saddle4 ,cold ,wave4--,a rapid and marked fall of temperature during the cold season of the year4 ,the ,united ,states ,weather ,bureau applies this term to a fall of temperature in #bd hours equaling or exceeding a specified number of degrees and reaching a specified temperature or lower2 the specifications varying for different parts of the country and for different periods of the year4 ,collector4--,a device used in measurements of atmospheric electricity for determining the potential gradient4 ,continental ,climate4--,the type of climate characteristic of the interior of a continent4 ,as compared with a marine climate1 a continental climate has a large annual and daily range of temperature4 ,corona4--#a4 ,a colored luminous circular area formed1 by diffraction2 around the sun1 moon1 or other source of light seen through clouds or dust haze4 ,coronas invariably show a brownish-red inner ring1 which1 together with the bluish-white inner field between the ring and the luminary1 forms the so-called aureole4 ,most frequently the aureole alone is visible4 ,well developed coronas show one or more series of spectral colors outside the aureole4 #b4 ,a luminous circle formed by the apparent convergence of auroral beams about the place in the sky toward which the dipping-needle points4 ,corposant4--7,see ,st4 ,elmo's fire47 ,countertrades4--7,see antitrades47 ,crepuscular ,rays4--,beams of light radiating from the sun1 seen both before and after sunrise and sunset4 ,the beams are made visible by the presence of water-drops or dust in the atmosphere1 and the intervening dark spaces are the shadows of clouds4 ,the beams are actually parallel2 their apparent divergence is the result of perspective4 ,critical ,period4--,a period in the growth of a plant when it is especially susceptible to the effects of atmospheric conditions4 ,cumulo-nimbus2 ,cumulus4--,forms of cloud4 7,see ,chapter ,,vi47 ,cyclone4--,an area of low barometric pressure with its attendant system of winds4 ,the cyclones of the region within the tropics 7tropical cyclones7 are violent storms2 those of higher latitudes 7extra-tropical cyclones7 may be stormy or otherwise4 ,tropical cyclones are also called hurricanes1 typhoons or baguios4 ,extra-tropical cyclones are commonly known as lows or barometric depressions4 ,cyclonopathy4--,the abnormal sensitiveness of certain persons to the weather changes attending the passage of barometric depressions4 ,cyclonoscope4--,a pasteboard dial formerly used in the ,west ,indies for locating cyclones4 ,dark ,segment4--,the shadow of the earth which1 in clear weather1 rises from the eastern horizon at sunset and sinks below the western horizon at sunrise4 ,deperditometer4--,an instrument devised by ,a4 ,piche for measuring the cooling power of the atmosphere1 with reference to its physiological effects4 ,depression4--,a cyclonic area1 or low4 ,desert ,sounds4--7,see brontide47 ,devil4--,the name applied to a dust whirlwind in ,india4 ,the term is also current in ,south ,africa4 ,dew4--,atmospheric moisture condensed1 in liquid form1 upon objects cooler than the air1 especially at night4 ,dew-point4--,the temperature at which1 under ordinary conditions1 condensation of water vapor begins in a cooling mass of air4 ,it varies with the absolute humidity4 ,dew ,pond4--,the name applied in southern ,england to certain artificial ponds on the uplands4 ,they contain water in the driest weather1 and are popularly supposed to be fed by dew4 8,doctor40--,a colloquial name for the sea breeze in tropical climates4 ,the name is sometimes applied to other cool1 invigorating breezes4 ,doldrums4--,the equatorial belt of calms or light1 variable winds1 lying between the two trade-wind belts4 ,drought4--,a protracted period of dry weather4 ,in the ,united ,states a drought has been defined as a period of thirty or more consecutive days during which precipitation to the amount of #j4be inch does not occur in twenty-four hours4 ,other quantitative definitions have been used in other countries4 ,dry ,fog4--,a haze due to the presence of dust or smoke in the air4 ,dust-counter4--,an instrument for determining approximately the number of dust particles or condensation nuclei per unit volume in a sample of air4 ,dynamic ,meteorology4--,the branch of meteorology that treats of the motions of the atmosphere and their relations to other meteorological phenomena4 ,earth-air ,current4--,the electrical current that passes between the earth and the air on account of their difference of potential4 ,eddy4--,a more or less fully developed vortex in the atmosphere1 constituting a local irregularity in a wind4 ,all winds near the earth's surface contain eddies1 which at any given place1 produce 8gusts0 and 8lulls40 ,air containing numerous eddies is said to be 8turbulent40 ,electric ,niagara4--7,see hail rod47 ,evaporimeter4--7,see atmometer47 ,eye of the ,storm4--,a calm region at the center of a tropical cyclone1 or a break in the clouds marking its location4 ,fall ,wind4--,a wind blowing down a mountain-side2 or any wind having a strong downward component4 ,fall ,winds include the foehn1 mistral1 bora1 etc4 ,false ,cirrus4--,cirruslike clouds at the summit of a thundercloud2 probably identical in structure with true cirrus1 or cirro-stratus4 ,sometimes more appropriately called 8thunderstorm cirrus40 ,fata ,morgana4--,a complex form of mirage1 characterized by marked distortion of images4 ,festoon ,cloud4--,mammato-cumulus4 ,flashing ,arcs4--,visible atmospheric sound waves1 or explosion waves4 ,flat4--,featureless2 said of weather maps4 ,foehn4--,a dry fall wind warm for the season1 characteristic of many mountainous regions4 ,the air is cooled dynamically in ascending the mountains1 but this leads to condensation1 which checks the fall in temperature through the liberation of latent heat4 ,the wind deposits its moisture as rain or snow4 ,in descending the opposite slope it is strongly heated dynamically and arrives in the valleys beyond as a warm and very dry wind4 ,some writers apply this term to any wind that is dynamically heated by descent2 e4 g41 the sinking air of an anticyclone4 ,foehn-sickness4--,headache1 lassitude1 depression1 etc41 attributed1 in the ,alpine valleys1 to the blowing of the foehn4 ,foehn-wall 7,german3 ,fhnmauer74--,a wall of cloud that forms along the crest of a mountain ridge over which the foehn is blowing4 ,fog4--,a cloud at or near the earth's surface4 ,a fog and a cloud are identical in structure1 though the former is due to thermal conditions of the earth's surface1 while the latter is most frequently clue to the dynamic cooling of ascending air4 ,in ordinary speech1 the term 8fog0 generally implies an obscurity of the atmosphere sufficiently great to interfere with navigation or locomotion4 7,cf4 dry fog47 ,fogbow4--,a rainbow1 colorless or nearly so1 formed in a fog4 ,fog-drip4--,moisture that is deposited on terrestrial objects by fog1 and drips from them to the ground4 ,fracto-cumulus2 ,fracto-nimbus2 ,fracto-stratus4--,forms of cloud4 7,see ,chapter ,,vi47 ,freeze4--#a4 ,freezing of plants without deposit of hoarfrost4 #b4 ,freezing temperatures prevailing generally over a region2 not exclusively nocturnal and not confined to the air close to the earth's surface4 7,cf4 frost47 ,frost4--#a4 ,the act or state of freezing4 ,in ,america1 a 8frost0 generally means the occurrence1 near the beginning or end of the growing season1 of nocturnal temperatures low enough to be injurious to vegetation2 distinguished from a 8freeze10 which is more general and severe4 ,the ,weather ,bureau classifies frosts1 according to their effects1 as 8light10 8heavy10 and 8killing40 #b4 ,atmospheric moisture condensed upon terrestrial objects in the form of ice2 sometimes frozen dew4 ,also called hoarfrost4 ,frost-smoke4--,frozen fog rising from the water4 ,fulgurite4--,a glassy tube formed in sandy soil or in rock by the passage of lightning4 ,gara4--,a wet fog of the west coast of ,south ,america4 ,geocoronium4--,the name applied by ,dr4 ,a4 ,wegener to a hypothetical atmospheric gas1 supposed to be much lighter than any gas now known to chemists4 ,glaze4--,term applied by the ,u4 ,s4 ,weather ,bureau to a smooth coating of ice on terrestrial objects due to the freezing of rain2 often popularly called 8sleet40 ,in ,great ,britain such a deposit is called glazed frost4 ,a deposit of glaze on an extensive scale constitutes an 8ice storm40 ,glory4--,a series of concentric colored rings seen around the shadow of the observer1 or of his head only1 cast upon a cloud or fog bank4 ,it is due to the diffraction of reflected light4 ,gouffre4--7,see brontide47 ,gradient4--,change of value of a meteorological element per unit of distance4 ,the gradients commonly discussed in meteorology are the horizontal gradient of barometric pressure1 the vertical gradient of temperature1 and the vertical gradient of electric potential4 ,british meteorologists now prefer the term lapse-rate to vertical gradient4 ,graupel4--,a kind of granular snow1 sometimes called soft hail4 ,green ,flash4--,a bright green coloration of the upper edge of the sun's disk1 sometimes seen when the rest of the disk is below the horizon1 at sunrise or sunset4 ,growing ,season4--,in agricultural meteorology1 the interval between the last killing frost in spring and the first killing frost in autumn4 ,gust4--,a sudden brief increase in the force of the wind4 ,most winds near the earth's surface are made up of alternate gusts and lulls1 the majority of which are too brief to be registered by an ordinary anemometer4 ,hail4--,balls or irregular lumps of ice1 often of considerable size1 having a complex structure2 large hailstones generally have a snowlike center1 surrounded by layers of ice1 which may be alternately clear and cloudy4 ,hail falls al-most exclusively in connection with thunderstorms4 ,for so-called 8soft hail0 see graupel4 7,cf4 sleet47 ,hail ,rod4--,a device analogous to a lightning rod1 supposed to have the property of averting the fall of hail4 ,hail rods have been especially popular in ,france1 where they are called paragrles4 ,large hail rods of recent construction are known as 8electric ,niagaras40 ,hail-shooting4--,bombarding the clouds to prevent the fall of hail4 ,halo4--,a generic name for a large group of optical phenomena caused by ice crystals in the atmosphere4 ,the commonest of these phenomena is the halo of #bb degrees 7i4 e41 of #bb degrees radius7 surrounding the sun or moon4 ,the halo of #df degrees and the rare halo of #ij degrees1 or halo of ,hevelius1 also surround the luminary4 ,other forms of halo are the tangent arcs1 parhelia 7or paraselen71 parhelic 7or paraselenic7 circle1 anthelion1 etc4 ,harmattan4--,a dry1 dusty wind of the west coast of ,africa1 blowing from the deserts4 ,haze4--,a lack of transparency in the atmosphere2 sometimes due to irregularities in the density of the air 7optical haze71 sometimes to dust 7dust haze1 which when dense constitutes dry fog71 sometimes to fine particles of water or ice 7grading into true fog74 ,helm and ,bar4--,a pair of clouds seen when the 8helm wind0 is blowing over ,crossfell1 an ,english mountain2 the 8helm0 capping the mountain and the 8bar0 lying to leeward of it4 ,high4--,an area of high barometric pressure2 an anticyclone4 ,hoarfrost4--7,see frost47 ,hole in the ,air4--,a colloquial name for any condition in the atmosphere that suddenly decreases the lift of an aeroplane4 7,cf4 bump47 ,horse ,latitudes4--,the regions of calms and variable winds coinciding with the subtropical high-pressure belts lying on the poleward sides of the trade winds4 7,the term has generally been applied only to the northern of these two regions1 in the ,north ,atlantic ,ocean1 or to the portion of it near ,bermuda47 ,hot ,wave4--,a period of abnormally high temperatures4 ,it has sometimes been defined1 in the ,united ,states1 as a period of three or more consecutive days during each of which the maximum temperature is #ij degrees ,f4 or over4 ,hot ,wind4--,a hot1 parching wind characteristic of certain continental interiors2 especially ,australia1 northern ,india and the prairie region of the ,united ,states4 ,humidity4--,the degree to which the air is charged with water vapor2 viz41 the actual amount of water vapor present 7absolute humidity1 which may be expressed in terms of weight per unit volume or as vapor pressure71 or the ratio which this amount bears to the maximum amount the air can contain at the prevailing temperature 7relative humidity1 expressed in percentage74 ,hurricane4--,a tropical cyclone2 especially one of the ,west ,indies region4 7,a cyclone originating in this region and passing northward into the temperate zone is still called a 8,west ,india hurricane10 even after it has assumed the character of an extratropical cyclone1 and1 if sufficiently severe1 justifies the display of 8hurricane warnings0 at ports of the ,united ,states4 8,hurricane0 is also the designation of the highest wind force on the ,beaufort scale1 and is thus applied to any wind exceeding about seventy-five miles an hour47 ,hygrograph4--,a self-registering hygrometer4 ,hygrometer4--,any instrument for measuring the humidity of the air4 ,hygroscope4--,a device that gives a rough indication of the relative humidity of the air4 ,most hygroscopes are mere toys4 ,ice ,rain4--#a4 ,a rain that causes a deposit of glaze4 #b4 ,falling pellets of clear ice 7called sleet by the ,u4 ,s4 ,weather ,bureau74 ,ice ,saints4--,a period of cold weather popularly reputed in ,europe to occur yearly about ,may #aa-ac 7or1 in south-central ,europe1 ,may #ab-ad72 also1 the saints whose days in the ecclesiastical calendar fall on these dates4 ,ice ,storm4--7,see glaze47 ,ignis ,fatuus4--,will-o'-the-wisp4 7,see ,chapter ,,xxii47 ,indian ,summer4--,a period of mild1 calm1 hazy weather occurring in autumn or early winter1 especially in the ,united ,states and ,canada2 popularly regarded as a definite event in the calendar1 but weather of this type is really of irregular and intermittent occurrence4 7,cf4 ,st4 ,martin's ,summer47 ,instrument-shelter4--,the ,american name of the cage or screen in which thermometers are exposed at meteorological stations4 ,called thermometer-screen in ,great ,britain4 ,inversion4--,more fully temperature inversion2 an increase of air temperature with increase of altitude1 instead of the normal decrease4 ,ion-counter4--,an instrument for determining the number of ions present1 per unit volume1 in a sample of air4 ,isobar4--,a line of equal barometric pressure4 7,isobars are generally drawn on maps to show the horizontal distribution of pressure reduced to sea level1 or the pressure at some specified altitude2 but in a broader sense any line on a chart or diagram drawn through places of equal pressure is an isobar47 ,isohyet4--,a line of equal rainfall4 ,isotherm4--,a line of equal temperature4 ,isothermal ,layer4--7,see stratosphere47 ,january ,thaw4--,a period of mild weather popularly supposed to recur each ,january1 especially in ,new ,england4 ,katathermometer4--,a device consisting of a dry-bulb and a wet-bulb thermometer1 designed for measuring the cooling power of the atmosphere1 with reference to its physiological effects4 ,it was invented by ,leonard ,hill4 ,kiosk4--,the name given by the ,u4 ,s4 ,weather ,bureau to a small street pavilion in which are displayed meteorological instruments1 maps1 tables1 etc4 ,land and ,sea ,breezes4 ,land and ,lake ,breezes4--,the breezes that1 on certain coasts and under certain conditions1 blow from the land by night and from the water by day4 ,lenticular ,cloud4--,a cloud having approximately the form of a double-convex lens1 marking the position of a standing wave in the atmosphere4 7,see ,chapter ,,vi47 ,lightning4--,a disruptive electrical discharge in the atmosphere1 or1 generally1 the luminous phenomena attending such a discharge4 ,the various forms of lightning are named and described in ,chapter ,,ix4 ,lightning ,print4--,a collection of marks1 often treelike in form1 sometimes found on the body of a person or animal that has been struck by lightning4 ,lightning ,rod4--,a metallic rod1 connected with a suitable 8ground10 in earth or water1 set up for the purpose of protecting some structure from lightning4 ,light-pillar4--,a form of halo1 consisting of a column of light1 vertical or nearly so1 extending from or through the sun or moon4 ,called a sun-pillar1 or a moon-pillar1 as the case may be4 ,line-squall4--,a more or less continuous line of squalls and thunderstorms traveling broadside over the country4 ,looming4--,an apparent elevation of distant objects by mirage4 ,low4--,an area of low barometric pressure1 with its attendant system of winds4 ,also called a barometric depression or cyclone4 ,mackerel ,sky4--,an area of sky covered with cirro-cumulus clouds2 especially when the clouds resemble the patterns seen on the backs of mackerel4 ,mammato-cumulus4--,a form of cloud showing pendulous sacklike protuberances4 7,see ,chapter ,,vi47 ,march4--,the variation of a meteorological element in the course of a day1 year1 or other interval of time2 e4 g41 the diurnal march of temperature2 the annual march of barometric pressure4 ,mares'-tails4--,cirrus in long slender streaks4 ,marine ,climate4--,a type of climate characteristic of the ocean and oceanic islands4 ,its most prominent feature is equability of temperature4 ,meteorograph4--,autographic apparatus for recording simultaneously two or more meteorological elements4 ,certain types of meteorograph are connected1 electrically or otherwise1 with some of the instruments at meteorological stations2 others are sent aloft attached to kites and balloons4 ,meteorology4--,the science of the atmosphere4 ,millibar4--7,see bar47 ,mirage4--,an apparent displacement or distortion of distant objects by abnormal atmospheric refraction4 ,sometimes the images of objects are inverted1 multiplied1 etc4 ,mist4--,generally1 a wet fog or a very fine drizzle of rain2 hence the expression1 8it is misting40 ,the 8,scotch mist0 of mountainous or hilly regions is a combination of thick fog and heavy drizzle2 it has been suggested that this occurs when the rain clouds actually rest on the earth4 ,mistpoeffer4--7,see brontide47 ,mistral4--,along the ,mediterranean coast1 from the mouth of the ,ebro to the ,gulf of ,genoa1 a stormy1 cold northerly wind1 blowing down from the mountains of the interior4 7,the name is sometimes applied to northerly winds on the ,adriatic1 in ,greece1 and in ,algeria47 ,monsoon4--,a wind that reverses its direction with the season1 blowing more or less steadily from the interior of a continent toward the sea in winter1 and in the opposite direction in the summer4 ,moon ,dog4--,a paraselene4 ,mountain and ,valley ,breezes4--,the breezes that1 in mountainous regions1 normally blow up the slopes by day 7valley breeze7 and down the slopes by night 7mountain breeze74 ,nephoscope4--,an instrument for measuring the movements of clouds4 ,nieve ,penitente4--,fields of pinnacled snow found on certain high mountains in tropical or subtropical regions4 ,nimbus4--,the rain cloud4 7,see ,chapter ,,vi47 ,noctilucent ,clouds4--,luminous1 cirruslike clouds sometimes visible throughout the short nights of summer2 supposed to be clouds of dust at great altitudes shining with reflected sunlight4 ,such clouds were observed during several summers after the eruption of ,krakatoa 7#ahhc7 and are still occasionally reported4 ,normal4--,the average value which1 in the course of years1 any meteorological element is found to have on a specified date or during a specified month or other portion of the year1 or during the year as a whole4 ,also used as an adjective in such expressions as 8normal temperature10 etc4 ,thus1 for any station at which records have been maintained for many years1 we may compute the normal temperature of ,january #a1 the normal pressure of ,february1 the normal rainfall of the year1 etc4 ,the normal serves as a standard with which values occurring in a particular year may be compared in order to determine the departure from the normal4 ,nucleus4--,a particle upon which condensation of water vapor occurs in the free atmosphere in the form of a water drop or an ice crystal4 ,oblique ,arcs of the ,anthelion4--,a rare form of halo1 consisting of intersecting arcs1 usually white1 passing through the anthelion or the place where the anthelion would occur if visible4 ,ozone4--,an allotropic form of oxygen1 which occurs transiently in small quantities in the lower atmosphere1 and is supposed to be permanently present and relatively abundant at high atmospheric levels4 ,painter4--,a dirty fog frequently experienced on the coast of ,peru4 ,the brownish deposit from it is sometimes called 8,peruvian paint40 ,paragrle4--,a hail rod4 ,paranthelion4--,a halo phenomenon similar to a parhelion1 but occurring at a distance of #ij degrees or more in azimuth from the sun4 ,the solar distance of the ordinary paranthelia is #abj degrees4 7,analogous phenomena produced by the moon as source of light are called parantiselen47 ,paraselene4--7,plu4 paraselen47 7,see parhelion47 ,paraselenic ,circle4--7,see parhelic circle47 ,parasitic ,clouds4--,the name formerly given to clouds capping the summits of mountains4 ,parhelic ,circle4--,a halo consisting of a white circle passing through the sun and parallel to the horizon4 ,a similar phenomenon in connection with the moon is called a paraselenic circle4 ,parhelion4--,a mock sun1 or sun dog2 a form of halo consisting of a more or less distinctly colored image of the sun at the same altitude as the latter above the horizon1 and hence lying on the parhelic circle1 if present4 ,the ordinary parhelia are #bb degrees from the sun in azimuth1 or a little more1 according to the altitude of the luminary4 ,parhelia have occasionally been seen about #df degrees from the sun4 ,analogous phenomena seen in connection with the moon are called paraselen1 mock moons1 or moon dogs4 ,penetrating ,radiation4--,a form of radiation that has the property of passing through a great extent of air without being absorbed and of ionizing the air inside hermetically sealed metal vessels4 ,it is supposed to consist of a special kind of ,gamma rays and to come from the higher levels of the atmosphere4 ,phenology4--,the study of the periodic phenomena of animal and plant life and their relations to weather and climate4 ,photochemical ,climate4--,the chemical activity of sunlight characteristic of any place or region4 ,the variations of this feature of solar radiation are more or less strikingly different from those of solar heat and the brightness of solar light4 ,certain types of 8chemical actinometer0 are used in its measurement4 ,pilot ,balloon4--,a small free balloon the drift of which1 as observed from the ground1 indicates the movements of the air aloft4 ,pocky ,cloud4--,mammato-cumulus4 ,pogonip4--,a fog1 composed of fine needles of ice1 which occurs in mountainous regions of the western ,united ,states and is reputed to be very injurious to the lungs4 ,pollution ,gauge4--,a gauge for measuring soot and other impurities found in the atmosphere4 ,pontias4--,a wind that blows by night from a narrow valley at ,nyons1 ,france4 ,potential ,gradient4--7,see gradient47 ,precipitation4--,the collective name for deposits of atmospheric moisture in liquid and solid form1 including rain1 snow1 hail1 dew1 hoarfrost1 etc4 ,pressure4--,an elliptical expression1 current in meteorological literature1 for atmospheric pressure1 or barometric pressure4 ,prevailing ,westerlies4--,the belts of winds lying on the poleward sides of the subtropical high-pressure belts4 ,psuchrainometer4--,an instrument devised by ,j4 ,r4 ,milne for measuring the cooling power of the atmosphere with reference to physiological effects4 ,psychrometer4--,an instrument for measuring atmospheric humidity1 consisting usually of a dry-bulb thermometer and a wet-bulb thermometer4 ,the former is an ordinary mercurial thermometer4 ,the latter has its bulb covered with muslin or other fabric1 which is either permanently wet or is wetted before use4 ,in some psychrometers there is only one thermometer1 readings being taken both before and after moistening the bulb4 ,purple ,light4--,the purple or rosy glow observed over a large area of the western sky after sunset and the eastern sky before sunrise2 it lies above the bright segment that borders the horizon4 ,pyrheliometer4--,an instrument that measures solar radiation by its heating effects4 ,qobar4--,a dry fog or heat haze of the upper ,nile region4 7,also spelled kobar and gobar and occasionally applied to a hazy condition of the atmosphere in other parts of the world47 ,rain ,balls4--,mammato-cumulus4 ,rainbow4--,a luminous arc formed by the refraction and reflection of light in drops of water4 7,see ,chapter ,x47 ,rainfall4--,a term sometimes synonymous with rain1 but most frequently used in reference to amounts of precipitation 7including snow1 hail1 etc474 ,rain ,gauge4--,an instrument for measuring rainfall4 ,rain ,tree4--,a mythical tree which is alleged to exude copious showers of water even in the driest weather4 78,rain tree0 is also the common name of an ornamental tree variously known to botanists as ,albizzia saman1 ,pithecolobium saman1 ,enterolobium saman1 and ,samanea saman47 ,recoloration4--7,see afterglow47 ,recurrence4--,the alleged tendency of any particular type of weather to occur at about the same period every year1 independently of and generally in contrast to the regular march of the seasons4 ,refraction4--,astronomical refraction4 ,change in the apparent position of a heavenly body1 due to atmospheric refraction4 ,terrestrial refraction4 ,change in the apparent position of distant terrestrial objects1 due to the same cause4 ,relative ,wind4--,in aeronautics1 the motion of the air with reference to an aeroplane or airship moving through it4 ,rseau4--,a collection of meteorological stations operating under a common direction1 or in the same territory4 ,an international rseau is a group of stations in different countries cooperating for any purpose4 ,the ,rseau mondial is a world-wide system of selected stations1 the observations of which may be utilized in studies of the meteorology of the globe4 ,rime4--#a4 ,hoarfrost4 #b4 ,a rough or feathery coating of ice deposited on terrestrial objects by fog4 7,the second meaning is the one now used in technical literature47 ,roaring ,forties4--7,see brave west winds47 ,saddle4--7,see col47 ,saint ,elmo's ,fire4--,a luminous brush discharge of electricity from elevated objects1 such as the masts and yardarms of ships1 lightning rods1 steeples1 etc41 occurring in stormy weather4 ,also called corposant4 ,st4 ,martin's ,summer4--,one of several names given in ,europe to a mild period in autumn1 corresponding approximately to the ,indian summer of ,north ,america4 ,scarf ,cloud4--,a thin cirruslike cloud which often drapes the summits of tall cumulo-nimbus clouds4 ,scotch ,mist4--7,see mist47 ,scud4--,shreds or small detached masses of cloud moving rapidly below a rain cloud or other heavy clouds4 ,sea ,breeze4--7,see land and sea breezes47 ,secondary4--,a small cyclone developed1 or tending to develop1 on the border of a large one4 ,sensible ,temperature4--,the temperature felt at the surface of the human body2 formerly identified1 by some authorities1 with the temperature indicated by the wet-bulb thermometer4 ,silence1 ,areas1 ,zones1 or ,regions of4--,regions within which a sound is not heard1 though heard in regions more distant from the source4 ,silver ,thaw4--,a term variously applied to rime1 glaze1 and a thin coating of ice deposited on cold objects by a damp wind4 ,simoom4--,an intensely hot and dry wind of ,asian and ,african deserts2 often described as a sand storm or dust storm1 but certain authorities state that the typical simoom is free from sand or dust4 ,sirocco4--,a name applied to various types of warm wind in the ,mediterranean region4 ,some of these siroccos are foehns4 ,the term is also used as the generic name for winds blowing from a warm region toward an area of low pressure in a normally colder region4 ,sleet4--#a4 ,frozen or partly frozen rain2 frozen raindrops in the form of particles of clear ice4 #b4 ,snow and rain falling together4 7,other definitions have been proposed and the proper technical application of this term is still a subject of controversy4 ,in popular and engineering use the word is often applied to a coating of glaze on trees1 wires1 rails1 etc47 ,snow ,bin4--,a large receptacle for collecting the snowfall of an entire winter1 or other long period1 for measurement at one time4 ,snow ,garland4--,an elongated mass of snow suspended at the ends and sagging in the middle4 ,snow ,mushroom4--,an overhanging cap of snow resting on a tree stump1 post1 or the like4 ,snow ,roller4--,a mass of snow rolled by the wind2 generally muff-shaped4 ,snow ,sampler4--,a device for collecting a sample of snow1 cut vertically through a snowfield1 for the purpose of determining the depth and density of the snow4 ,snow ,survey4--,a measurement of the total amount of snow lying over a particular area1 especially with a view to determining the total amount of water it will yield1 when melted1 for purposes of irrigation1 etc4 ,soft ,hail4--,graupel4 ,sounding ,balloon4--,a free1 unmanned balloon carrying a set of self-registering meteorological instruments4 ,specter of the ,brocken4--,the shadow of an observer and of objects in his immediate vicinity cast upon a cloud or fog bank2 sometimes attended by a series of colored rings1 called the glory or ,brocken-bow4 ,squall4--#a4 ,a sudden storm of brief duration2 closely akin to a thunderstorm but not necessarily attended by thunder and lightning4 #b4 ,a sudden brief blast of wind1 of longer duration than a gust4 ,squaw ,winter4--,in ,north ,america1 a brief cold spell popularly reputed to precede ,indian summer4 ,static4--7,see stray47 ,storm ,card4--,a device intended for use on shipboard in determining the direction of a storm center from the ship4 ,storm ,water4--,the water resulting from a heavy and rapid fall of rain2 especially the portion that occurs as run-off4 7,the term has been used mainly in connection with the subject of sewers47 ,strato-cumulus4--,a form of cloud4 7,see ,chapter ,,vi47 ,stratosphere4--,the upper region of the atmosphere1 formerly called the isothermal layer1 in which there is no marked or systematic decrease of temperature with altitude4 ,the stratosphere is free from clouds 7except occasional dust clouds7 and from strong vertical air currents1 and its circulation appears to be more or less independent of that of the lower atmosphere4 ,the height of its base1 which varies with latitude and otherwise1 averages between #f and #g miles4 7,cf4 troposphere47 ,stray4--,a natural electromagnetic wave in the ether4 ,the term is used in reference to the effects of such waves in producing erratic signals in radiotelegraphic receivers4 ,strays are known collectively as static4 ,summer ,day4--,a day in which the temperature reaches or exceeds #gg degrees ,f4 ,sun ,dog4--,a mock sun or parhelion4 8,sun ,drawing ,water40--,the sun popularly said to be 8drawing water0 when crepuscular rays extend down from it toward the horizon4 ,sunshine ,recorder4--,an instrument for recording the duration of sunshine2 certain types also record the intensity of sunshine4 ,synchronous ,chart4--,a form of synoptic chart1 such as the ordinary weather map1 which shows the meteorological conditions prevailing over any area at a given moment of time4 ,synoptic ,chart4--,a chart showing the distribution of meteorological conditions over an area at a given moment or the average conditions during a given period of time1 such as a month or a year4 ,table-cloth4--,a sheet of cloud that sometimes spreads over the flat top of ,table ,mountain1 near ,cape ,town4 ,tangent ,arc4--,any halo that occurs as an arc tangent to one of the heliocentric halos4 ,term ,hours4--,prescribed hours for taking meteorological observations4 ,thermal ,belt4--,a well-defined zone1 found on some mountain-sides1 in which vegetation is particularly exempt from frosts in spring and autumn4 ,also called verdant zone4 ,thermograph4--,a self-registering thermometer4 ,thermometer4--,an instrument for measuring temperature2 in meteorology1 generally the temperature of the air4 ,maximum and minimum thermometers indicate1 respectively1 the highest and lowest temperatures occurring between the times of setting the instruments4 ,a wet-bulb thermometer is used in measuring humidity4 7,see psychrometer47 ,thermometer ,screen4--,a cage1 or sometimes merely a roof1 for protecting thermometers from direct sunshine and other radiation that would cause the readings to indicate a temperature different from that of the air4 ,in the ,united ,states generally called an instrument shelter4 ,thunder4--,the sound produced by a lightning discharge4 ,thunderstorm4--,a storm attended by thunder and lightning4 ,thunderstorms are local disturbances1 often occurring as episodes of cyclones1 and1 in common with squalls1 are marked by abrupt variations in pressure1 temperature1 and wind4 ,thunderstorm ,recorder4--,any device that furnishes a record of thunderstorms1 either near or distant4 ,most thunderstorm recorders register1 by radiotelegraphy1 the strays set up by lightning discharges4 ,tornado4--#a4 ,a violent vortex in the atmosphere1 usually attended by a pendulous1 more or less funnel-shaped cloud4 #b4 ,in ,west ,africa3 ,a violent thundersquall4 ,totalizer4--,a form of snow gauge used chiefly in the ,alps1 designed to be read only once a year4 7,french1 totalisateur47 ,trade ,winds4--,two belts of winds1 one on either side of the equatorial doldrums1 in which the winds blow almost constantly from easterly quadrants4 ,troposphere4--,the part of the atmosphere lying below the stratosphere4 ,trough4--#a4 ,a line drawn at right angles to the path of a cyclonic area through all points at which the pressure has reached a minimum and is about to rise4 #b4 ,an elongated area of low barometric pressure4 ,twilight4--,astronomical twilight is the interval between sunrise or sunset and the total darkness of night4 ,civil twilight is the period of time before sunrise and after sunset during which there is enough daylight for ordinary outdoor occupations4 8,twister40--,a tornado2 also1 a small whirling dust storm4 ,typhoon4--,the name applied in the ,far ,east to a tropical cyclone4 ,ulloa's ,ring4--#a4 ,a glory4 #b4 ,a halo 7also called ,bouguer's halo7 surrounding a point in the sky diametrically opposite the sun2 sometimes described as a 8white rainbow40 ,vane4--,a device that shows which way the wind blows2 also called weather vane or wind vane4 ,variability4--,interdiurnal variability is the mean difference between successive daily means of a meteorological element4 ,verdant ,zone4--7,see thermal belt47 ,visibility4--,the transparency and illumination of the atmosphere as affecting the distance at which objects can be seen4 ,it is often expressed on a numerical scale4 7,this term was formerly applied by ,british meteorologists to a state of unusual clearness of the atmosphere1 regarded as a weather prognostic47 ,v-shaped ,depression4--,a trough of low barometric pressure bounded on the weather map by ,v-shaped isobars4 ,waterspout4--,a tornadolike vortex and cloud occurring over a body of water4 ,weather ,well4--7,see blowing well47 ,wedge4--,a wedge-shaped area of high barometric pressure4 ,wet-bulb thermometer4--7,see psychrometer47 ,wind4--,moving air2 especially a mass of air having a common direction of motion4 ,the term is generally limited to air moving horizontally1 or nearly so2 vertical streams of air are usually called 8currents40 ,wind ,aloft4--,the wind blowing at high levels as distinguished from that near the earth's surface4 ,wind ,rose4--#a4 ,a diagram showing the relative frequency and sometimes also the average strength of the winds blowing from different directions in a specified region4 #b4 ,a diagram showing the average relation between winds from different directions and the occurrence of other meteorological phenomena4 ,winter ,day4--,a day on which the temperature does not at any time rise above the freezing point4 ,wool-pack ,cloud4--,cumulus4 ,transcribers' ,notes ,punctuation1 hyphenation1 and spelling were made consistent when a predominant preference was found in this book2 otherwise they were not changed4 ,simple typographical errors were corrected2 occasional unbalanced quotation marks retained4 ,ambiguous hyphens at the ends of lines were retained4 ,in versions of this book that do not support accented letters1 8,canon0 7with a tilde over the middle 8n07 is spelled 8,canyon04 ,page #ajc3 ,for consistency with the preceding enumerated definitions1 the ,transcriber added extra spacing after the last of them1 just before 8,we have given04 ,page #cdh3 ,in some versions of this e,book1 the chemical symbols for methane and phosphine are represented as ,,ch#d and ,,ph#c4 ,page #cfg3 8,the scale runs from #j calm to hurricane0 is missing the value for hurricane1 which is 8#ab04