,,the ,,story ,,of ,,the ,,solar ,,system ,,by ,,george ,f4 ,,chambers1 ,f4,r4,a4,s4 ,,of ,,the ,,inner ,,temple1 ,,barrister-,,at-,,law ,,author ,,of ,,the ,,story ,,of ,,the ,,stars ,illustration3 ,,with ,,twenty-,,eight ,,illustrations ,,new ,,york ,mc,c,l,u,r,e1 ,,phillips ,,co4 ,,mcmiv ,copyright1 #ahie1 ,by ,d4 ,,appleton ,,and ,,company4 ,illustration3 ,fig4 #a4--,the ,planet ,saturn4 ,,preface4 ,having in my 8,story of the ,stars0 told of far distant suns1 many of them probably with planets revolving around them1 ,i have in the present volume1 which is a companion to the former one1 to treat of the ,sun in particular--our ,sun as we may call him--and the body of attendants which own his sway by revolving round him4 ,the attendants are the planets1 commonly so called1 together with a certain number of comets4 ,i shall deal with all these objects rather from a descriptive and practical than from a speculative or essay point of view1 and with special reference to the convenience and opportunities of persons possessing1 or having access to1 what may be called popular telescopes--telescopes say of from two to four inches of aperture1 and costing any sum between #aj and #ej4 ,there is much pleasure and profit to be got out of telescopes of this type1 always presuming that they are used by persons possessed of patience and perseverance4 ,it is a very great mistake1 though an extremely common one1 to suppose that unless a man can command a big telescope he can do no useful work1 and derive no pleasure from his work4 ,to all such croakers ,i always point as a moral the achievements of ,hermann ,goldschmidt1 who from an attic window at ,fontenay-aux-,roses near ,paris1 with a telescope of only #b inches aperture1 discovered no fewer than #ad minor planets4 ,as this volume is intended for general reading1 rather than for educational or technical purposes1 ,i have kept statistical details and numerical expressions within very narrow limits1 mere figures being always more or less unattractive4 ,john ,richard ,green1 in the ,preface to his book on ,the ,making of ,england1 writes as follows3--8,i may add1 in explanation of the reappearance of a few passages 444 which my readers may have seen before1 that where ,i had little or nothing to add or to change1 ,i have preferred to insert a passage from previous work1 with the requisite connections and references1 to the affectation of rewriting such a passage for the mere sake of giving it an air of novelty40 ,i will venture to adopt this thought as my own1 and to apply it to the repetition1 here and there1 of ideas and phrases which are already to be found in my ,handbook of ,astronomy4 ,g4 ,f4 ,c4 ,northfield ,grange1 ,eastbourne1 #ahie4 ,,contents4 ,,chapter ,,page ,i4 ,introductory ,statement #g ,,ii4 ,the ,sun #ah ,,iii4 ,mercury #eg ,,iv4 ,venus #fa ,v4 ,the ,earth #fi ,,vi4 ,the ,moon #hi ,,vii4 ,mars #ajj ,,viii4 ,the ,minor ,planets #aaj ,,ix4 ,jupiter #aae ,x4 ,saturn #abb ,,xi4 ,uranus #ach ,,xii4 ,neptune #adc ,,xiii4 ,comets #aej ,appendix--,tables of the ,solar ,system #ahb ,general ,index #ahe ,,list ,,of ,,illustrations4 ,,figure ,,page #a4 ,the ,planet ,saturn ,frontispiece #b4 ,inclination of ,planetary ,orbits #i #c4 ,comparative ,sizes of ,major ,planets #aa #d4 ,comparative ,size of the ,sun as seen from the ,planets ,named #ag #e4 ,ordinary ,sun-spots1 ,june #bb1 #ahhe #bb #f4 ,change of ,form in ,sun-spots ,owing to the ,sun's ,rotation #bi #g4 ,sun-spots seen as a ,notch #cg #h4 ,the ,sun ,totally ,eclipsed1 ,july #ah1 #ahfj #ef #i4 ,venus1 ,dec4 #bc1 #ahhe #fd #aj4 ,venus ,near ,conjunction as a ,thin ,crescent #fe #aa4 ,mare ,crisium 7,lick ,observatory photographs7 #ij #ab4 ,four ,views of ,mars 7,barnard7 #aja #ac4 ,mars1 ,aug4 #bg1 #ahib 7,guyot7 #ajg #ad4 ,jupiter1 ,nov4 #bg1 #aheg 7,dawes7 #aaf #ae4 ,saturn1 #ahhi #abc #af4 ,general ,view of the ,phases of ,saturn's ,rings #abf #ag4 ,phases of ,saturn's ,rings at ,specified ,dates #abi #ah4 ,saturn with ,titan and its ,shadow #acg #ai4 ,telescopic ,comet with a ,nucleus #aed #bj4 ,comet seen in ,daylight1 ,sept41 #ahhb #aee #ba4 ,quenisset's ,comet1 ,july #i1 #ahic #aef #bb4 ,holmes's ,comet1 the ,head on ,nov4 #i1 #ahib 7,denning7 #aei #bc4 ,holmes's ,comet1 the ,head on ,nov4 #af1 #ahib 7,denning7 #aei #bd4 ,comet ,,iii4 of #ahfb1 on ,aug4 #bb1 showing ,jet of ,luminous ,matter 7,challis7 #afj #be4 ,sawerthal's ,comet1 ,june #d1 #ahhh 7,charlois7 #afe #bf4 ,biela's ,comet1 #ahdf #afi #bg4 ,the ,great ,comet of #ahaa #agg #bh4 ,the ,great ,comet of #ahhb #agi ,,the ,,story ,,of ,,the ,,solar ,,system4 ,,chapter ,i4 ,,introductory ,,statement4 ,by the term 8,solar ,system0 it is to be understood that an ,astronomer1 speaking from the standpoint of an inhabitant of the ,earth1 wishes to refer to that object1 the ,sun1 which is to him the material and visible centre of life and heat and control1 and also to those bodies dependent on the ,sun which circulate round it at various distances1 deriving their light and heat from the ,sun1 and known as planets and comets4 ,the statement just made may be regarded as a general truth1 but as the strictest accuracy on scientific matters is of the utmost importance1 a trivial reservation must perhaps be put upon the foregoing broad assertion4 ,there is some reason for thinking that possibly one of the planets 7,jupiter7 possesses a little inherent light of its own which is not borrowed from the ,sun2 whilst of the comets it must certainly be said that1 as a rule1 they shine with intrinsic1 not borrowed light4 ,respecting these reservations more hereafter4 ,the planets are divided into 8primary0 and 8secondary40 ,by a 8primary0 planet we mean one which directly circulates round the ,sun2 by a 8secondary0 planet we mean one which in the first instance circulates round a primary planet1 and therefore only in a secondary sense circulates round the ,sun4 ,the planets are also 8major0 or 8minor02 this1 however1 is only a distinction of size4 ,the secondary planets are usually termed 8satellites10 or1 very often1 in popular language1 8moons10 because they own allegiance to their respective primaries just as our ,moon--the ,moon--does to the ,earth4 ,but the use of the term 8moon0 is inconvenient1 and it is better to stick to 8satellite40 ,there is yet another method of classifying the planets which has its advantages4 ,they are sometimes divided into 8inferior0 and 8superior40 ,the 8inferior0 planets are those which travel round the ,sun in orbits which are inside the ,earth's orbit2 the 8superior0 planets are those whose orbits are outside the ,earth4 ,the following is an enumeration of the major planets in the order of their distances1 reckoning from the ,sun outwards3-- #a4 ,mercury4 #b4 ,venus4 #c4 ,the ,earth4 #d4 ,mars4 #e4 ,jupiter4 #f4 ,saturn4 #g4 ,uranus4 #h4 ,neptune4 ,all the above are major planets and also primary planets4 ,in between ,nos4 #d and #e circulate the 8,minor0 planets1 an ever-increasing body1 now more than #djj in number1 but all1 except one or perhaps two1 invisible to the naked eye4 ,the 8,inferior0 planets it will be seen from the above table comprise ,mercury and ,venus1 whilst the 8,superior0 planets are ,mars and all those beyond4 ,great differences exist in the inclinations of the orbits of the different planets to the plane of the ecliptic1 a fact which is better shown by a diagram than by a table of mere figures4 ,the orbit of ,uranus is indeed so much inclined that its motion is really retrograde compared with the general run of the planets3 and the same remark applies1 though much more forcibly1 to the case of ,neptune4 ,illustration3 ,fig4 #b4--;,inclination of ,planetary ,orbits4 ,the actual movements of the planets round the ,sun are extremely simple1 for they do nought else but go on1 and on1 and on1 incessantly1 always in the same direction1 and almost1 though not quite1 at a uniform pace1 though in orbits very variously inclined to the plane of the ecliptic4 ,but an element of extreme complication is introduced into their apparent movements by reason of the fact that we are obliged to study the planets from one of their own number1 which is itself always in motion4 ,if the ,earth itself were a fixture1 the study of the movements of the planets would be a comparatively easy matter1 whilst to an observer on the ,sun it would be a supremely easy matter4 ,greatly as the planets differ among themselves in their sizes1 distances from the ,sun1 and physical peculiarities1 they have certain things in common1 and it will be well to make this matter clear before we go into more recondite topics4 ,for instance1 not only do they move incessantly round the ,sun in the same direction at a nearly uniform pace1 but the planes of their orbits are very little inclined to the common plane of reference1 the ecliptic1 or to one another4#a ,the direction of motion of the planets as viewed from the north side of the ecliptic is contrary to the motion of the hands of a watch4 ,their orbits1 unlike the orbits of comets1 are nearly circular1 that is1 they are only very slightly oval4 ,agreeably to the principles of what is known as the ,law of ,universal ,gravitation1 the speed with which they move in their orbits is greatest in those parts which lie nearest the ,sun1 and least in those parts which are most remote from the ,sun2 in other words1 they move quickest in ,perihelion and slowest in ,aphelion4 ,illustration3 ,fig4 #c4--;,comparative ,sizes of the ,major ,planets4 ,the physical peculiarities which the planets have in common include the following points3--they are opaque bodies1 and shine by reflecting light which they receive from the ,sun4 ,probably all of them are endued with an axial rotation1 hence their inhabitants1 if there are any1 have the alternation of day and night1 like the inhabitants of the ,earth1 but the duration of their days1 measured in absolute terrestrial hours1 will in most cases differ materially from the days and nights with which we are familiar4 ,i stated on a previous page that1 owing to the circumstances in which we find ourselves on the ,earth1 the apparent and real movements of the planets are widely different4 ,it would be beyond the scope of this little work to go into these differences in any considerable detail2 suffice it then to indicate only a few general points4 ,in the first place1 an important distinction exists between the visible movements of the inferior and superior planets4 ,the inferior planets1 ,mercury and ,venus1 lying as they do within the orbit of the ,earth1 are much restricted in their movements1 in the sky4 ,we can never see them except when they are more or less near to the rising 7or risen7 or setting 7or set7 ,sun4 ,the extreme angular distance from the ,sun in the sky to which ,mercury can attain is but #bg1 and therefore we can never observe it otherwise than in sunlight or twilight1 for it never rises more than #a hours before sunrise nor sets later than #a hours after sunset4 ,of course between these limits the planet is above the horizon all the time that the ,sun is above the horizon1 but except in very large telescopes is not usually to be detected during the day-time4 ,these remarks regarding ,mercury apply likewise in principle to ,venus2 only the orbit of ,venus being larger than the orbit of ,mercury1 and ,venus itself being larger in size than ,mercury1 the application of these principles leads to somewhat different results4 ,the greatest possible distance of ,venus may be #dg instead of ,mercury's #bg4 ,venus is therefore somewhat more emancipated from the effects of twilight4 ,the body of ,venus being also very much larger and brighter than the body of ,mercury1 it may be more often and more easily detected in broad daylight4 ,it follows from the foregoing statement that the inferior planets can never be seen in those regions of the heavens which are1 as it is technically called1 in 8,opposition0 to the ,sun2 that is1 which are on the meridian at midnight whilst the ,sun is on the meridian in its midday splendour to places on the opposite side of the ,earth4 ,on the other hand1 the two inferior planets on stated1 though rare1 occasions exhibit to a terrestrial spectator certain phenomena of great interest and importance in which no superior planet can ever take part4 ,i am here referring to the 8,transits0 of ,mercury and ,venus across the ,sun4 ,if these planets and the ,earth all revolved round the ,sun exactly in the plane of the ecliptic1 transits of these planets would be perpetually recurring after even intervals of only a few months2 but the fact that the orbit of ,mercury is inclined #g1 and that of ,venus about #c1 to the ecliptic1 involves such complications that transits of ,mercury only occur at unequal intervals of several years1 whilst1 in extreme cases1 more than a century may elapse between two successive transits of ,venus4 ,for a transit of an inferior planet over the ,sun to take place1 the ,earth and the planet and the ,sun must be exactly in the same straight line1 reckoned both vertically and horizontally4 ,twice in every revolution round the ,sun an inferior planet is vertically in the same straight line with the ,earth and the ,sun2 and it is said to be in 8inferior conjunction0 when the planet comes between the ,earth and the ,sun2 and in 8superior conjunction0 when the planet is on the further side of the ,sun1 the ,sun intervening between the ,earth and the planet4 ,but for all three to be horizontally in the same straight line is quite another matter4 ,it is the orbital inclinations of ,mercury and ,venus which enable them1 so to speak1 to dodge an observer who is on the lookout to see them pass exactly in front of the ,sun1 or to disappear behind the ,sun2 and so it comes about that a favourable combination of circumstances which is rare is needed before either of the aforesaid planets can be seen as round black spots passing in front of the ,sun4 ,a passage of either of these planets behind the ,sun could never be seen by human eye1 because of the overpowering brilliancy of the ,sun's rays1 even though an ,astronomer might know by his calculations the exact moment that the planet was going to pass behind the ,sun4 ,when an inferior planet attains its greatest angular distance from the ,sun1 as we see it 7which ,i have already stated to be about #bg in the case of ,mercury and #dg in the case of ,venus71 such planet is said to be at its 8greatest elongation10 8east0 or 8west10 as the case may be4 ,at eastern elongation or indeed whenever the planet is east of the ,sun1 it is1 to use a familiar phrase1 an 8evening star02 on the other hand1 at western elongation1 or whenever it is on the western side of the ,sun1 it is known as a 8morning star40 ,if the movements of an inferior planet are followed sufficiently long by the aid of a star map1 it will be seen that sometimes it appears to be proceeding in a forward direction through the signs of the zodiac2 then for a while it will seem to stand still2 then at another time it will apparently go backwards1 or possess a retrograde motion4 ,all these peculiarities have their originating cause in the motion of the ,earth itself1 for the absolute movement of the planet never varies1 being always in the same direction1 that is1 forwards in the order of the signs4 ,turning now to the superior planets1 we have to face an altogether different succession of circumstances4 ,a superior planet is not1 as it were1 chained to the ,sun so as to be unable to escape beyond the limits of morning or evening twilight2 it may have any angular distance from the ,sun up to #ahj1 reaching which point it approaches the ,sun on the opposite side1 step by step1 until it again comes into conjunction with the ,sun4 ,as applied to a superior planet1 the term 8conjunction0 means the absolute moment when the ,earth and the ,sun and the planet are in the same straight line1 the ,sun being in the middle4 ,in such a case1 to us on the ,earth the planet is lost in the ,sun's rays1 whilst to a spectator on the planet the ,earth would appear similarly lost in the ,sun's rays1 as the ,earth would be at that stage of her orbit which we1 speaking of our inferior planets1 call superior conjunction4 ,for a clear comprehension of all the various matters which we have just been speaking of1 a careful study of diagrams of a geometrical character1 or better still1 of models1 would be necessary4 ,something must now be said about the phases of the planets4 ,mercury and ,venus1 in regard to their orbital motions1 stand very much on the same footing with respect to the inhabitants of the ,earth as the ,moon does1 and accordingly both those planets in their periodical circuits round the ,sun exhibit the same succession of phases as the ,moon does4 ,in the case1 however1 of the superior planets things are otherwise4 ,two only of them1 ,mars and ,jupiter1 are sufficiently near the ,earth to exhibit any phase at all4 ,when they are in quadrature 7i4 e41 #ij from the ,sun on either side7 there is a slight loss of light to be noticed along one limb4 ,in other words1 the disc of each ceases for a short time1 and to a slight extent1 to be truly circular2 it becomes what is known as 8gibbous40 ,this occasional feature of ,mars may be fairly conspicuous1 or1 at least1 noticeable2 but in the case of ,jupiter it will be less obvious unless a telescope of some size is employed4 ,if the major planets are arbitrarily ranged in two groups1 ,mercury1 ,venus1 the ,earth and ,mars being taken as an interior group1 comparatively near the ,sun2 whilst ,jupiter1 ,saturn1 ,uranus and ,neptune are regarded as an exterior group1 being at a great distance from the ,sun1 it will be found that some important physical differences exist between the two groups4 ,illustration3 ,fig4 #d4--;,comparative size of the ,sun as seen from the ,planets named4 ,of the interior planets1 the ,earth and ,mars alone have satellites1 and between them make up a total of only three4 ,the exterior planets1 on the other hand1 all have satellites1 the total number being certainly seventeen1 and possibly eighteen4 ,in detail1 ,jupiter has four1 ,saturn eight1 ,uranus four1 and ,neptune one1 and perhaps two4 ,these facts may be regarded as an instance of the beneficence of the ,creator of the ,universe if we consider that the satellites of these remoter planets are so numerous1 in order that by their numbers they may do something to make up for the small amount of light which1 owing to their distance from the ,sun1 their primaries receive4 ,then again1 the average density of the first group of planets greatly exceeds the average density of the second group in the approximate ratio of #e to #a4 ,finally1 there is reason to believe that a marked difference exists in the axial rotations of the planets forming the two groups4 ,we do not know the precise figures for all the exterior planets1 but the knowledge which we do possess seems to imply that the average length of the day in the case of the interior planets is about twenty-four hours1 but that in the case of the exterior planets it is no more than about ten hours4 ,these figures can1 however1 only be presented as possibly true1 because observations on the rotation periods of ,mercury and ,venus on the one hand1 and of ,uranus and ,neptune on the other1 are attended with so much difficulty that the recorded results are of doubtful trustworthiness4 ,it is1 however1 reasonable to presume that the actual size of the respective planets has more to do with the matter than their distances from the ,sun4 ,i think that the foregoing summary respecting the planets collectively embraces as many points as are likely to be of interest to the generality of readers2 we will therefore pass on to consider somewhat in detail the several constituent members of the solar system1 beginning with the ,sun4 ,,chapter ,,ii4 ,,the ,,sun4 ,there was once a book published1 the title of which was 8,the ,sun1 ,ruler1 ,fire1 ,light and ,life of the ,planetary ,system40 ,the title was by no means a bad one1 for without doubt the ,sun may fairly be said to represent practically all the ideas conveyed by the designations quoted4 ,there is certainly no one body in creation which is so emphatically pre-eminent as the ,sun4 ,whether or no there are stars which are suns--centres of systems serving in their degree the purposes served by our ,sun1 ,i need not now pause to enquire1 though ,i think the idea is a very probable one2 but of those celestial objects with which our ,earth has a direct relationship1 beyond doubt the ,sun is unquestionably entitled to the foremost place4 ,it is1 as it were1 the pivot on which the ,earth and all the various bodies comprising the ,solar ,system revolve in their annual progress4 ,it is our source of light and heat1 and therefore may be called the great agent by which an ,almighty ,providence wills to sustain animal and vegetable life4 ,the consideration of all the complicated questions which arise out of these functions of the ,sun belongs to the domain of ,physics rather than that of ,astronomy2 still these matters are of such momentous interest that an allusion to them must be made1 for they ought not to be lost sight of by the student of ,astronomy4 ,half a century ago the actual state of our knowledge respecting the ,sun might without difficulty be brought within the compass of a single chapter in any book on ,astronomy1 but so enormous has been the development of knowledge respecting the ,sun of late years1 that it is no longer a question of getting the materials properly into one chapter1 but it is a matter of a whole volume being devoted to the ,sun1 or even1 as in the case of ,secchi1 of two large octavo volumes of #ejj pages each being required to cover the whole ground exhaustively4 ,the reader will therefore easily understand that in the space at my disposal in this little work nothing but a passing glimpse can possibly be obtained of this great subject4 ,it is great not only in regard to the vast array of purely astronomical facts which are at a writer's command1 but also on account of the extensive ramifications which the subject has into the domains of chemistry1 photography1 optics and cognate sciences4 ,i shall therefore endeavour to limit myself generally to what an amateur can see for himself with a small telescope1 and can readily understand1 rather than attempt to say a little something about everything1 and fail in the effort4 ,the mean distance of the ,earth from the ,sun may be taken to be about #ic millions of miles1 and this distance is employed by ,astronomers as the unit by which most other long celestial distances are reckoned4 ,the true diameter of the ,sun is about #hff1jjj miles4 ,the surface area exceeds that of the ,earth #aa1idf times1 and the volume is #a1cje1jjj times greater4 ,the mass or weight of the ,sun is #ccb1jjj times that of the ,earth1 or about #gjj times that of all the planets put together4 ,bulk for bulk the ,sun is much lighter than the ,earth3 whilst a cubic foot of the ,earth on an average weighs rather more than #e times as much as a cubic foot of water1 a cubic foot of ,sun is only about #c times the weight of the same bulk of water4 ,this consideration of the comparative lightness of the ,sun 7though in his day the ,sun was thought to be lighter than it is now supposed to be7 led ,sir ,j4 ,herschel to infer that an intense heat prevails in its interior1 independent it may be of its surface heat1 so to speak1 of which alone we are directly cognizant by the evidence of our senses4 ,the ,sun is a sphere1 and is surrounded by an extensive but attenuated envelope1 or rather series of envelopes1 which taken together bear some analogy to the atmosphere surrounding the ,earth4 ,these envelopes1 which we shall have to consider more in detail presently1 throw out rays of light and heat to the confines of the ,solar ,system1 though as to the conditions and circumstances under which that light and heat are generated we are entirely ignorant4 ,of the potency of the ,sun's rays we can form but a feeble conception1 for the amount received by the ,earth is1 it has been calculated1 but one #bcjj-millionth of the whole4 ,our annual share would1 it is supposed1 be sufficient to melt a layer of ice spread uniformly over the ,earth to a depth of #ajj feet1 or to heat an ocean of fresh water #fj feet deep from freezing point to boiling point4 ,the illuminating power of the ,sun has to be expressed in language of similar profundity4 ,thus it has been calculated to equal that which would be afforded by #eefc wax candles concentrated at a distance of one foot from the observer4 ,again1 it has been concluded that no fewer than half a million of full moons shining all at once would be required to make up a mass of light equal to that of the ,sun4 ,i present all these conclusions to the reader as they are furnished by various physicists who have investigated such matters1 but it is rather uncertain as to how much reliance can safely be placed on such calculations in detail4 ,illustration3 ,fig4 #e4--,ordinary ,sun-spot1 ,june #bb1 #ahhe4 ,to an amateur possessed of a small telescope1 the ,sun offers 7when the weather is above the ,english average of recent years7 a very great and constant variety of matters for studious scrutiny in its so-called 8spots40 ,to the naked eye1 or even on a hasty telescopic glance1 the ,sun presents the appearance of a uniform disc of yellowish white colour1 though often a little attention will soon result in the discovery of a few1 or it may be many1 little black1 or blackish patches1 scattered here and there over the disc seemingly without order or method4 ,we shall presently find out1 however1 that this last-named suggestion is wholly inaccurate4 ,though commonly called 8spots10 these dark appearances are not simple spots1 as the word might imply1 for around the rather black patch which constitutes generally the main feature of the spot there is almost invariably a fringe of paler tint2 whilst within the confines of the black patch which first catches the eye there is often a nucleus or inner portion of far more intense depth of shade4 ,the innermost and darkest portion being termed the nucleus1 the ordinary black portion is known as umbra1 whilst the encompassing fringe is the penumbra4 ,it is not always the case that each individual umbra has a penumbra all to itself1 for several spots are occasionally included in one common penumbra4 ,and it may further be remarked that cases of an umbra without a penumbra and the contrary are on record1 though these may be termed exceptional1 often having relation to material organic changes either just commencing or just coming to a conclusion4 ,a marked contrast subsists in all cases between the luminosity of the penumbra and that of the general surface of the ,sun contiguous4 ,towards its exterior edge the penumbra is usually darker than at its inner edge1 where it comes in contact with the umbra4 ,the outline of the penumbra is usually very irregular1 but the umbra1 especially in the larger spots1 is often of regular form 7comparatively speaking of course7 and the nucleus 7or nuclei7 of the umbra still more noticeably partakes of a compactness of outline4 ,spots are for the most part confined to a zone extending #ce or so on each side of the solar equator2 and they are neither permanent in their form nor stationary in their position4 ,in their want of permanence1 they are subject1 apparently1 to no definite laws1 for they frequently appear and disappear with great suddenness4 ,their motions are evidently of a two-fold nature2 the ,sun itself rotates on its axis1 and the spots collectively participate in this movement of rotation2 but over and above this it has been conclusively proved that sometimes a spot has a proper motion of translation of its own independently of the motion which it has in consequence of the ,sun's axial rotation4 ,curiously enough1 spots are very rare immediately under the ,sun's equator4 ,it is in the zone extending from #h to #bj ,north or ,south1 as the case may be1 that they are most abundant2 or1 to be more precise still1 their favourite latitude seems to be #ag or #ah4 ,they are often more numerous and of a greater general size in the northern hemisphere1 to which it may be added that the zone between #aa and #ae ,north is particularly noted for large and enduring spots4 ,a gregarious tendency is often very obvious1 and where the groups are very straggling an imaginary line joining the extreme ends of the group will generally be found more or less parallel to the solar equator2 and not only so1 but extending a long way1 or sometimes almost entirely1 across the whole of the visible disc4 ,with respect to the foregoing matters ,sir ,john ,herschel remarked3--8,these circumstances 444 point evidently to physical peculiarities in certain parts of the ,sun's body more favourable than in others to the production of the spots1 on the one hand2 and on the other1 to a general influence of its rotation on its axis as a determining cause in their distribution and arrangement1 and would appear indicative of a system of movements in the fluids which constitute its luminous surface2 bearing no remote analogy to our trade-winds--from whatever cause arising40 ,more often than not when a main spot has a train of minor spots as followers that train will be found extending eastwards from the east side of the spot1 rather than in any other direction4 ,spots remain visible for very diverse lengths of time1 from the extreme of a few minutes up to a few months2 but a few days up to1 say1 one month1 may1 in a general way1 be suggested as their ordinary limits of endurance4 ,as the ,sun rotates on its axis in #be days1 and as the spots may be said to be1 practically speaking1 fixed or nearly so with respect to the ,sun's body1 no spot can remain continuously visible for more than about #ab days1 being half the duration of the ,sun's axial rotation4 ,with regard to their size1 spots vary as much as they do in their duration4 ,the majority of them are telescopic1 that is1 are only visible with the aid of a telescope2 but instances are not uncommon of spots sufficiently large to be visible to the naked eye4 ,the ancients knew nothing about the physical constitution of the ,sun1 and their few allusions to the subject were mere guesses of the wildest character4 ,they were1 however1 able to notice now and then that when the ,sun was near the horizon certain black spots could sometimes be distinguished with the naked eye1 but they took these for planets in conjunction with the ,sun1 or phenomena of unknown origin4 ,earliest in point of date of those who have left on record accounts of naked eye sun-spots are undoubtedly the ,chinese4 ,in a species of ,cyclopdia ascribed to a certain ,ma-touan-lin 7whose records of comets have been of the greatest possible use to astronomers71 we find an account of #de sun-spots seen during a period of #ijd years1 from #cja ,a4 ,d4 to #abje ,a4 ,d4 ,in order to convey an idea of the relative size of the spots1 the observers compared them to eggs1 dates1 plums1 etc41 as the case might be4 ,the observations often extended over several days2 some indeed to as many as ten consecutive days1 and there seem no grounds for doubting the authenticity of the observations thus handed down to us4 ,a few stray observations of sun-spots were recorded in ,europe before the invention of the telescope4 ,adelmus1 a ,benedictine monk1 makes mention of a black spot on the ,sun on ,march #ag1 #hjg4 ,it is also stated that such a spot was seen by ,averres in #aafa4 ,kepler himself seems to have unconsciously once seen a spot on the ,sun with the naked eye1 though he supposed he was looking at a transit of the planet ,mercury4 ,none of these early observers have told us the way in which they made their observations1 but the smallest of boys who has any claim to scientific knowledge is aware of the fact1 that by the use of so simple an expedient as a piece of glass blackened with smoke1 spots which are of sufficient size can be seen with the naked eye4 ,before telescopes came into use it was customary to receive the solar rays in a dark chamber through a little circular hole cut in a shutter4 ,it was thus that ,j4 ,fabricius succeeded in ,december #afaj in seeing a considerable spot and following its movement sufficiently well to enable him to determine roughly the period of the ,sun's rotation4 ,the spots may often be easily observed with telescopes of small dimensions1 taking care1 however1 to place in front of the eye-piece a piece of strongly-coloured glass4 ,for this purpose glasses of various colours are used1 but none so good as dark green or dark neutral tint4 ,it is not altogether easy to say positively how large a spot must be for it to be visible with the naked eye1 or an opera glass1 but probably it may be taken generally that no spot of lesser diameter than #a of arc can be so seen4 ,this measurement must be deemed to apply to that central portion of a normal spot already mentioned as being what is called the nucleus1 because penumbr may be more than #a in diameter without being visible to the naked eye1 for the reason that their shading is so much less pronounced than the shading of umbr4 ,very large and conspicuous spots are comparatively rare1 though during the years #ahic and #ahid there were an unusual number of such spots4 ,it often happens that a conspicuous group is the result of the merging or joining up of several smaller groups4 ,in such cases a group may extend over an area on the ,sun #c or #d of arc in length by #b or #c in breadth4 ,the largest spot on record seems to have been one seen on ,september #cj1 #aheh1 the length of which in one direction amounted to more than #adj1jjj miles4 ,the observation of spots on the ,sun by projecting them on to a white paper screen with the aid of a telescope is a method so convenient and so exact as to deserve a detailed description1 the more so as it is so little used4 ,let there be made in the shutter of a darkened room a hole so much larger than the diameter of the telescope to be used as will allow a certain amount of play to the telescope tube1 backwards and forwards1 up and down1 and from right to left4 ,direct the telescope to the ,sun and draw out the eye-piece to such a distance from the object-glass as that the image projected on a white screen held behind may be sharply defined at its edges4 ,if there are any spots on the ,sun at the time they will then be seen clearly exhibited on the screen4 ,an image obtained in this way is reversed as compared with the image seen by looking at the ,sun through a telescope directly4 ,if therefore the telescope is armed with the ordinary astronomical eye-piece1 which inverts1 then the projection will be direct1 that is to say1 on the screen the ,n4 ,s4 ,e4 and ,w4 points will correspond with the same terrestrial points4 ,under such circumstances the spots will be seen to enter the ,sun's disc on the ,e4 side and to go off on the ,w4 side4 ,the contrary condition of things would arise if a ,galilean telescope or a terrestrial telescope of any kind were made use of4 ,these instruments erect the image1 and therefore will give by projection a reversed image1 in which we shall see the spots moving apparently in a direction contrary to their true direction4 ,if the reader has grasped the broad general outlines now given respecting the ,sun and its spots he will perhaps be interested to learn a few further details1 but these must be presented in a somewhat disjointed fashion1 because the multitude of facts on record concerning sun-spots are so great as to render a methodical treatment of them extremely difficult within the limits here imposed on me4 ,these matters have been gone into in a very exhaustive way by ,secchi in his great treatise on the ,sun1 and in what follows ,i have made much use of his observations4 ,let us look a little further into the laws regulating the movement of the spots4 ,if it is not a question of seeing a spot spring into view1 but of watching one already in existence1 we shall1 in general1 see such a spot appear on the ,eastern limb of the ,sun just after having turned the corner1 so to speak4 ,the spots traverse the ,sun's disc in lines which are apparently oblique with reference to the diurnal movement and the plane of the ecliptic1 and after about #ac days they will disappear at the ,western limb if they have not done so before by reason of physical changes in their condition4 ,it is not uncommon for a spot after remaining invisible for #ac days on the other side of the ,sun1 so to speak1 to reappear on the ,eastern limb and make a second passage across the ,sun2 sometimes a third1 and indeed sometimes even a fourth1 passage may be observed1 but more generally they change their form and vanish altogether either before passing off the visible disc1 or whilst they are on the opposite side as viewed from the ,earth4 ,illustration3 ,fig4 #f4--;,change of ,form in ,sun-spots owing to the ,sun's rotation4 ,when several spots appear simultaneously1 they describe in the same period of time similar paths which are sensibly parallel to one another although they may be in very different latitudes4 ,the conclusion from this is inevitable1 that spots are not bodies independent of the ,sun1 as satellites would be1 but that they are connected with the ,sun's surface1 and are affected by its movement of rotation4 ,if we make every day for a few days in succession a drawing of the ,sun's disc with any spots that are visible duly marked thereon1 we shall see that their apparent progress is rapid near the centre of the ,sun1 but slow near either limb4 ,these differences1 however1 are apparent and not real1 for their movement appears to us to take place along a plane surface1 whilst in reality it takes place along a circle parallel to the solar equator4 ,the spots in approaching the ,sun's ,w4 limb1 if they happen to seem somewhat circular in form when near the centre1 first become oval1 and then seem to contract almost into mere lines4 ,these changes are simple effects of perspective1 and are to be explained in the same manner as the apparent decrease in the size of many of the spots is often explicable4 ,but this condition of things proves1 however1 that the spots belong to the actual surface of the ,sun1 for1 on a contrary supposition1 we should have to regard them as circular bodies greatly flattened like lozenges1 and this would be contrary to all we know of the forms affected by the heavenly bodies4 ,of course besides the apparent changes of form just alluded to as the effect of perspective1 it is abundantly certain that solar spots often undergo very real changes of form1 not only from day to day1 but in the course of a few hours4 ,several spots will often become amalgamated into one1 and it was ephemeral changes of this character which hindered generally the early observers from determining with precision the duration of the ,sun's rotation4 ,the apparent movements of the spots vary also from month to month during the year according to the season4 ,in ,march their paths are very elongated ellipses with the convexity towards the ,n41 the longer axis of the ellipse being almost parallel to the ecliptic4 ,after that epoch the curvature of the ellipse diminishes gradually1 at the same time that the major axis becomes inclined to the ecliptic1 so that by ,june the flattening of the ellipse has proceeded so far that the path has become a straight line4 ,between ,june and ,september the elliptical form reappears but in a reversed position2 then1 following these reversed phases1 the ellipticity decreases1 and for the second time there is an epoch of straight lines4 ,this happens in ,december1 but the straight lines are inclined in a converse direction to that which was the case in ,june4 ,it must again be impressed on the reader that all these seemingly different forms of path pursued by the spots are merely effects of perspective1 for in reality1 the spots in crossing the ,sun's disc describe lines which are virtually parallel to the solar equator4 ,these projections really depend of course on the position of the observer on the ,earth1 and vary as his position varies during the ,earth's annual circuit round the ,sun4 ,the number of the spots varies through wide limits4 ,sometimes they are so numerous that a single observation will enable us to recognise the position of the zones of maximum frequency4 ,sometimes1 on the other hand1 they are so scarce1 that many weeks may pass away without hardly one being seen4 ,a remarkable regularity is now recognised in the succession of these periods of abundance and scarcity1 as we shall see later on4 ,it is both useful and interesting in studying the spots to record methodically their number and their size1 but it is not easy to teach observers how to do this so systematically that observations by one person can be brought into comparison with those of another4 ,photography and hand-drawing on a screen alone furnish a trustworthy basis of operations4 ,spots in general may naturally be classified into 7#a7 isolated spots or points1 and 7#b7 groups of spots2 but often one observer will describe as a small spot an object which another observer would regard as a mere point2 and one observer will record several groups where another observer will see but one4 ,a very few days' experience with a telescope will bring home to the observer's mind the difficulty of dealing with the spots where it is a question of systematic methodical observation of them4 ,let us now take a brief survey of some of the theories which have been put forth regarding the nature of the spots on the ,sun4 ,in the early days of the telescope1 that is to say1 during the #agth century1 two general ideas were current4 ,some thought the spots to be shapeless satellites revolving round the ,sun2 others that they were clouds1 or aggregations of smoke1 floating about in a solar atmosphere4 ,scheiner1 the author of the first theory1 abandoned it towards the close of his life1 having arrived at the conclusion that the spots were situated below the general level of the ,sun's surface4 ,another idea1 but of later date1 was that the ,sun is a liquid and incandescent mass of matter1 and the spots immense fragments of ,scori1 or clinkers1 floating upon an ocean of fire4 ,somewhat more than a century after the spots had been generally studied with the aid of a telescope a ,scotchman named ,wilson made a memorable discovery4 ,he showed by the clearest evidence that they are cavities1 and he propounded the first intelligible idea of the true physical constitution of the ,sun1 when he compared to a strongly illuminated cloud the luminous layer of solar material which we now term the 8photosphere40 ,on ,november #bb1 #agfi1 he observed on the ,sun's disc a fine round spot encompassed by a penumbra1 also circular1 and concentric with the nucleus4 ,he watched that spot up to the time that it disappeared1 and he soon remarked that the penumbra ceased to be symmetrical3 the part turned towards the centre of the ,sun became smaller and smaller1 and eventually disappeared altogether2 whilst the part on the opposite side preserved its fulness and dimensions almost unchanged4 ,let us suppose we chanced to turn a telescope on to the ,sun on a given day1 and were fortunate enough to discover a spot in the centre of the disc1 with a penumbra concentric with the nucleus4 ,when such a spot arrives about midway towards the limb1 it will exhibit a penumbra narrower on the left side than on the right2 later on the penumbra will disappear almost or quite completely on the left side3 then the nucleus itself will seem to be encroached upon4 ,finally1 very near the limb1 there will remain only a slender thread of penumbra1 and the nucleus will have ceased to be directly visible4 ,such were the phases of transformation observed by ,wilson and often studied since4 ,wilson suspected that he had come upon some great law that was ripe for disclosure1 and in order not to be misled he waited for the return of the same spot1 which indeed reappeared on the ,sun's ,w4 limb after about #ad days4 ,then he found himself face to face with the same phases reproduced1 but in the reverse order3 the penumbra contracted on one side and full on the other1 widening out on the contracted side as the spot came up to the ,sun's centre4 ,henceforth doubt was no longer possible2 the spot had sensibly preserved the same shape during its passage1 and the alterations noticed were only apparent1 and resulted from an effect of perspective which was easy to be understood4 ,the different phases presented by such a spot as that just spoken of will be so much the more sensible according as the depth of the cavity is greater2 but if the depth is inconsiderable the bottom of the cavity will only disappear when a very oblique angle is attained1 and this cannot happen except when the spot is very near to the limb4 ,by observations carefully made under such circumstances it will be possible to determine the depth of the cavity1 and ,wilson found that the depth of a spot often amounted to about one-third of the ,earth's radius4 ,wilson's theory was not accepted without dispute2 it was contested by several astronomers1 and in particular by ,lalande4 ,it was however taken up by ,sir ,w4 ,herschel1 and as modified by him has met with general acceptance down to the present time2 though now and again challenged1 perhaps most recently and most vehemently by ,howlett1 a sun spot observer of great experience4 ,wilson's discovery was the point of departure for the grand labours of ,sir ,w4 ,herschel in the field of ,solar ,physics4 ,man of genius that ,herschel was1 he was above all things an observer who took his own line in what he did4 ,he saw so many phenomena with the powerful instruments constructed by himself1 he described so minutely the marvels which were revealed to him1 that he left comparatively little for his successors to do so far as regards mere telescopic observation4 ,herschel's main idea as to the ,sun was based on ,wilson's discovery4 ,he remarked with reason1 as that astronomer had done1 that if the spots are cavities the luminous matter could neither be properly called liquid nor gaseous2 for then it would precipitate itself with frightful rapidity to fill up the void1 and that would render it impossible that the spots should endure as we often see they do during several revolutions of the ,sun4 ,moreover1 the proper movements of the spots prove that the photosphere is not solid4 ,we can therefore only liken it to fogs or clouds1 and it must be suspended in an atmosphere similar to ours4 ,such is1 according to ,herschel1 the only hypothesis which can explain the rapid changes which we witness4 ,we shall see a little later on that these phenomena do admit of another explanation4 ,in a second memoir ,herschel followed up this inquiry with an acuteness worthy of his genius4 ,unfortunately he allowed himself to be carried away with the idea that the ,sun was inhabited in order to sustain this theory4 ,he needed a solid kernel upon which his imaginary inhabitants could dwell2 and also a means whereby he could protect them from the radiations of the photosphere4 ,with this idea in view he conjectured the existence above the ,sun's solid body of a layer of clouds always contiguous to the photosphere which enveloped it1 and which always being rent when the photosphere was rent1 thus enabled us to see the solid body of the ,sun lying behind4 ,these notions can only be described as very arbitrary1 as unsupported by observation1 and as involving explanations quite out of harmony with the principles of modern physics4 ,however1 the labours of ,herschel resulted in so many positive discoveries of visible facts1 and in so many just conclusions1 that they contributed greatly to the growth of our present knowledge of the true constitution of the ,sun4 ,since ,wilson's time1 as ,secchi pointedly remarks1 astronomers generally have verified his observations with good instruments1 and by an investigation of a great number of spots4 ,de ,la ,rue1 discussing the ,kew observations1 found that of #hi regular spots #gb gave results which conformed to ,wilson's ideas1 whilst the remaining #ag were opposed thereto4 ,there is nothing surprising in the existence of a contrarient minority when we consider the great changes which in reality often occur in the forms of the spots4 ,de ,la ,rue suggested a very simple expedient for showing that the spots are cavities4 ,take two photographs of the ,sun made at an interval of one day3 during that time every point on the ,sun's surface will have been displaced1 so far as the telescope is concerned1 by about #ae4 ,place these photographs in a stereoscope1 and we shall readily see the interior cavity1 the edges of which will appear raised above the photosphere4 ,it is impossible therefore to entertain the least doubt as to the truth of the theory that the spots are excavations in the luminous stratum which envelopes the whole of the solar globe4 ,if it be true that a spot is a cavity1 it follows that when it reaches the margin of the solar disc we ought to detect a hollow place2 and this will be so much the more easy to observe according as the cavity is larger and deeper4 ,as a matter of fact1 numerous observations of this sort have been recorded from the time of ,cassini down to the present time under the designation of 8notches0 on the ,sun's limb4 ,on ,july #h1 #ahgc1 ,secchi observed such a notch #h1 or #cfjj miles deep4 ,faye and some other astronomers are disposed to support a theory according to which the spots are nothing else than arial cyclones1 but this does not seem admissible4 ,if the fundamental principle of a spot is that it arises from a whirling movement1 the rays 7so to speak7 which compose the penumbr must always be crooked1 or the theory falls to the ground4 ,it is quite true that indications of cyclonic action do sometimes appear1 but they are at any rate very rare1 for only a small percentage exhibit in a distinct manner a spiral structure4 ,moreover1 when such a structure is seen it does not endure for the whole lifetime of the spot but only for a day or two3 the spot may last a long time after it has lost its spiral features1 if it ever had any4 ,sometimes even the whirling movement1 after having slackened1 begins again1 but in the contrary direction4 ,under these circumstances1 though this occasional spiral structure is very curious and interesting1 we are not justified in taking it as the basis of a theory which has any pretensions to explain the general nature of sun-spots4 ,illustration3 ,fig4 #g4--,sun-spot seen as a ,notch4 ,when we examine the ,sun with instruments of large aperture and high magnifying power1 we notice that its surface is far from being as smooth and uniform as it appears in a small telescope4 ,on the contrary1 it presents an irregular undulating appearance like a pond or other sheet of water agitated by the wind4 ,careful scrutiny with a powerful eye-piece reveals the fact that the ,sun's surface is marked by a multitude of wrinkles and irregularities which it is well-nigh impossible to describe in words4 ,more or less everywhere there is a general mottling visible2 it is more distinct in some places than others1 and especially so towards the centre of the disc4 ,this peculiar appearance varies very much from time to time1 and its distinctness seems to depend a great deal on the state of the ,earth's atmosphere1 for it becomes invisible when the air is disturbed2 but these variations depend also on real variations of the photosphere--a fact which observations made in very calm weather are thought clearly to indicate4 ,it is often said that the ,sun exhibits a granulated structure4 ,if we wish to realise in the most precise manner what is meant by the word 8granulation0 as applied to the structure of the ,sun1 we must abandon the method of projection and examine the ,sun directly with a powerful eyepiece1 taking advantage of a moment when the atmosphere is perfectly calm1 and before the eyepiece has had time to get hot4 ,it may then be seen that the ,sun's surface is covered with a multitude of little grains1 nearly all of about the same size1 but of different shape1 though for the most part more or less oval4 ,the small interstices which separate these grains form a network which is dark without being positively black4 ,secchi considered it difficult to name any known object which exactly answers in appearance to this structure1 but he thought that we can find something resembling it in examining with a microscope milk which has been a little dried up1 and the globules of which have lost their regular form4 ,exceptionally good atmospheric conditions are under all circumstances indispensable for the study of these details4 ,in point of fact1 there is a mysterious uncertainty about the normal condition of the ,sun's surface1 in a visual sense1 which a few years ago engendered a very vehement controversy1 and led to the use of such expressions as 8willow leaves10 8rice grains10 8sea beach10 and 8straw thatching10 to indicate what was seen4 ,all these words are too precise to be quite suitable to be taken literally1 but perhaps1 on the whole1 8rice grains0 is not altogether a bad expression to recall what certainly seems to be the granular surface of the ,sun as we see it4 ,by making use of moderate magnifying powers1 what we see will often convey the impression of a multitude of white points on a black network4 ,this is very apparent during the first few moments that the telescope is brought to bear on the ,sun1 but its clearness quickly passes away because the eye gets fatigued1 and the lenses becoming warm the air in the telescope tube gets disturbed because also warmed4 ,sometimes the appearance is a little different from that just described1 and along with the white and brilliant points little black holes are intermixed4 ,oftentimes the grains appear as if suspended in a black network and heaped together in knots more or less shaded and more or less broad4 ,sometimes the grains exhibit a very elongated form1 especially in the neighbourhood of the spots4 ,it is these elongated forms to which ,nasmyth applied the term 8willow leaf10 whilst ,huggins thought 8rice grains0 a very suitable expression4 ,this granular or leaf-like structure--call it what we will--cannot be made out except with considerable optical assistance1 for the grains being intrinsically very small1 diffraction in enlarging them and causing them to encroach on one another necessarily produces a general confusion of image4 ,the real dimensions of these grains cannot therefore readily be determined by direct measurement1 but by comparing them with the wires used in micrometer eye-pieces it has been thought that their diameters may usually be regarded as equal to or of a second--say from #abj to #aej miles4 ,the granules seem to be possessed of sensible movement1 but presumably it is not always or even generally a movement of translation from place to place2 only an undulatory movement like that of still water when a stone is cast into it4 ,nevertheless1 probably in certain cases the granules actually are affected by a motion of translation1 for in the vicinity of spots they may sometimes be seen flowing over the edges of the penumbr4 ,in order to explain the existence of the granules the strangest theories have been broached4 ,sir ,william ,herschel having observed the granulations1 applied to them the term 8corrugations0 or 8furrows0--words somewhat inexact1 perhaps1 but by which1 as his descriptions clearly show1 he meant to designate the features which ,i am now treating of4 ,he even noticed the dark network which separates the grains1 and he applied to it the word 8indentations40 ,these granulations are without doubt prominences1 probably of hydrogen gas1 which rise above the general surface1 for this structure is much more sharp and distinct at the centre of the sun's disc than at the limbs2 that is to say1 near the limbs of the ,sun they partially overlap one another1 as indeed ,herschel remarked4 ,the idea of flames would satisfy these appearances3 and as the spectroscope suggests to us that the ,sun is habitually covered over with a multitude of little jets of flame1 the observations which have been made compel the opinion that the grains are the summits of those prominences which exist all over the ,sun's surface4 ,the surface is sometimes so thickly covered over with these granulations--the network is so conspicuous--that we can readily imagine that we see everywhere pores and the beginnings of spots1 but this aspect is not permanent1 and seems to depend to some extent on atmospheric causes combined also with actual changes in the ,sun's surface itself4 ,there seems however no doubt that the joints1 so to speak1 of the dark network already referred to do sometimes burst asunder and develope into spots4 ,the circumstances which accompany the formation of a spot cannot readily be specified with certainty4 ,it is impossible to say that there exists any law as to this matter4 ,whilst some spots develope very slowly by the expansion of certain pores1 others spring into existence quite suddenly4 ,yet it cannot be said that the formation of a spot is ever completely instantaneous however rapid it may be4 ,the phenomenon is often announced some days in advance3 we may perceive in the photosphere a great agitation which often manifests itself by some very brilliant facul 7to be described presently7 giving birth to one or more pores4 ,very often we next notice some groups of little black spots1 as if the luminous stratum was becoming thinner in such a way as to disappear little by little and leave a large black nucleus uncovered4 ,at the commencement of the business there is usually no clearly defined penumbra4 ,this developes itself gradually and acquires a regular outline1 just as the spot itself often takes a somewhat circular form4 ,this tranquil and peaceable formation of a spot only happens at a time when calm seems to reign in the solar atmosphere3 in general the development is more tumultuous and the stages more complicated4 ,as a rule a spot passes through three stages of existence3--7#a7 the ,period of birth2 7#b7 a ,period of calm2 and 7#c7 the ,period of dissolution4 ,when a spot is on the point of closing up1 the flow of the luminous matter which it1 as it were1 attracts1 is not directed uniformly towards the centre2 it seems that the photospheric masses1 no longer meeting with resistance1 are precipitated promiscuously anywhere so as to fill up the hole4 ,it is impossible to describe in detail the phases which irregular spots go through1 but two things may always be remarked3 that their structure is characterized by the existence of luminous filaments1 and that these filaments converge towards one or several centres4 ,secchi thus sums up certain conclusions which he arrived at relating to spots generally3--7#a7 ,it is not on the surface of any solid body that the solar spots are manifested2 they are produced in a fluid mass1 the fluidity of which is represented by a gas1 so that the constitution of this medium may be likened to that of flames or clouds2 7#b7 the known details respecting the constitution of the penumbra and the phenomena exhibited prove that the penumbra is not a mass of obscure matter which floats across luminous matter1 but that it is on the contrary a case of luminous matter invading and floating about over darker materials and so producing a half tint4 ,all the available evidence which we possess may be said to show that the spots are not merely superficial appearances1 but that they have their origin deep in the interior of the ,sun1 and are produced by the operation of causes still unknown to us which affect and disturb the ,sun's mass to an extent which is sometimes very considerable4 ,the spots then are only the results of a great agitation in the materials of which the ,sun is composed1 and this agitation extends far down below the limits of the visible dark nucleus whatever that may consist of4 ,besides the spots1 streaks of light may frequently be remarked upon the surface of the ,sun towards the margin of the disc4 ,these are termed facul 7torches71 and they are often found near the spots1 or where spots have previously existed or have afterwards appeared4 ,when quite near the ,sun's limb these facul are usually more or less parallel to the limb4 ,they are of irregular form and may be likened to certain kinds of coral4 ,they generally appear to be more luminous than the solar surface immediately adjacent to them1 but it is not improbable that this is an optical illusion depending upon the fact that the edges of the ,sun always appear much more luminous than the centre4 ,this last-named fact may be readily recognised by the employment of a high magnifying power1 and moving the telescope rapidly from the limb to the centre of the disc4 ,if the ,sun be projected on a screen1 as already mentioned1 this degradation of the ,sun's light from centre to circumference becomes particularly manifest4 ,after having studied the structure and the movement of the spots1 one is naturally led to ask if their apparitions at different periods are subject to any general law4 ,this question is one which has much engaged the attention of modern astronomers4 ,the older observers noticed that the number of the spots visible differed in different years4 ,there were said to have been periods when months and even years passed away without any spots being observed4 ,even allowing that this statement1 so far as 8years0 are concerned1 might be exaggerated1 and that the absence of spots was due to the want of sufficient care in making the observations1 and especially to the want of efficient instruments1 it is none the less true that the number of the spots is extremely variable1 and that there have been epochs when they were very scarce4 ,sir ,w4 ,herschel was the first who devoted himself to the question of seeking to establish a relation between the variation of the spots and terrestrial meteorology4 ,for the want of any better object1 he compared the annual number of the spots with the price of wheat2 but it is easy to see that nothing could result from such a comparison4 ,without doubt the meteorological phenomena of the globe must depend to some extent on solar changes3 but the term of comparison selected by ,herschel had no direct bearing on the state of the ,sun4 ,in our time this question has been investigated to its very foundation by ,wolf1 ,director for many years at the ,observatory of ,zurich4 ,it is to his zeal that we owe a very interesting assemblage of old observations which were buried in archives and chronicles4 ,it was he who endeavoured to reduce them into a systematic form1 so as to supply as far as possible the numerous gaps which exist in the different series4 ,the two most attentive observers at the period when the spots were discovered were ,marriott at ,oxford and ,scheiner at ,ingoldstadt1 but ,scheiner himself has informed us that he did not note down all the spots which he saw2 he only recorded those which were likely to assist him in his special task of determining the period of the ,sun's rotation4 ,several observers after him made isolated series of observations2 but some of these have been lost and the others show important gaps4 ,j4 ,g4 ,staudacher1 at ,nuremburg1 observed the ,sun with great perseverance during fifty years from #agdi to #agii4 ,before him the ,cassinis1 ,maraldi1 and others were engaged in the same sort of work1 but only in an indirect way3 that is to say1 they contented themselves1 whilst making meridional observations of the ,sun1 with noting anything in the way of spots which they deemed important4 ,zucconi and ,flaugergues also left behind them a good collection of observations which ,wolf utilised1 rendering them comparable one with another by applying suitable corrections4 ,the great difficulty herein arises from the fact that the observers were not provided with instruments of equal power2 one man1 armed with a better telescope than his contemporaries1 naturally observed and recorded spots which would escape the others4 ,the numbers entered in their registers are therefore not comparable inter se4 ,wolf endeavoured to replace these numbers by others which would represent the spots which might have been seen if the observers had all employed telescopes of a given kind and power4 ,the result of his efforts in this direction is an almost continuous series of ,sun-spot records from an epoch sufficiently remote1 up to the time when this branch of science was taken up with the vigour of modern scientific methods4 ,the observer who most assiduously devoted himself to this subject in modern times was ,schwabe of ,dessau4 ,from #ahbf to #ahfh he never failed to make daily observations when the weather permitted him4 ,his series of records is specially valuable1 for ,carrington's fits in with it1 and with that in turn ,sprer's is comparable1 and the chain is complete by the later photographic and other observations4 ,all these ,sun-spot records1 though differing in their details1 may easily be used together when it is a question of working out relative annual fluctuations4 ,at the present time there are many ,astronomers who are engaged in observing the spots with care2 but just as formerly there are few who possess sufficient perseverance4 ,the photographic method is excellent1 but it takes much time and is costly4 ,some have decried1 in a very unreasonable manner1 a drawing made by hand3 such a drawing1 of sufficient size1 and executed by projection by a skilful draughtsman with a telescope driven by clockwork1 may stand comparison with a photograph1 and this method has a better chance of being persevered in4 ,the ,rev4 ,f4 ,howlett's name must be mentioned in this connection as a draughtsman who has accomplished much by hand drawing4 ,though the once famous ,kew observations have been discontinued1 they have been replaced by a new series at ,greenwich with similar appliances2 whilst ,janssen at ,meudon has also been carrying on for a number of years a splendid course of photographic records4 ,schwabe1 when he had collected a considerable number of observations1 recognised clear indications of periodicity4 ,very definite epochs of maxima and minima succeeded one another at intervals of #aj or #aa years4 ,it is true that in following out such a study the observations are certain to be in a sense a little defective4 ,at first it was not possible to observe the ,sun every day1 and the gaps which resulted from bad weather necessarily added to the number of days which had to be set down as being without spots4 ,moreover1 every method of numbering the spots must be a little arbitrary3 there are often groups which1 in consequence of their sub-divisions1 may be counted in different ways3 but in a mass of observations so considerable as those of ,schwabe's1 such uncertainties will compensate for one another and will disappear in the final result4 ,in fact the law is so striking that it suffices to cast one's eye over his table#b to see that4 ,that table is both interesting and instructive at the same time4 ,the numbers exhibited in it speak for themselves1 and it is sufficient to examine them with even a small amount of attention to realise the certainty of the conclusions which have been drawn4 ,it is therefore now to be deemed an ascertained fact that there are periodical maxima and minima in the display of spots1 and that the extent of the period is between #aj and #ab years4 ,in order to determine this value with the utmost exactness1 some astronomers have had recourse to early observations4 ,wolf of ,zurich made this the subject of some very interesting inquiries4 ,he was able to establish the chronology of the phases which the ,sun has passed through from the time of the first discovery of the spots to the present day--more than #b centuries4 ,his calculations led him to a period of #aa-a_/i years4 ,lamont fixed upon #aj4dc years1 but this number does not represent the more recent observations with sufficient precision4 ,in order to exhibit this law in the plainest possible manner the dates of maxima and minima should be laid down on ruled paper in proper mathematical form1 the absciss of the curve representing the years1 and the ordinates the number of spots observed4 ,an examination of a curve thus plotted shows two things3--7#a7 ,that the period is clearly an eleven-year one1 as has been already stated2 7#b7 that it is not however quite as simple in its form as it was at first thought to be2 for in reality there are two periods superposed1 the one rather more than half a century long1 and the other extending over the #aa years already spoken of4 ,we do not possess early observations sufficiently numerous and sufficiently good to enable us to draw any unimpeachable conclusions as to the nature of the long period2 we can only be certain that it exists4 ,the later labours of ,wolf1 however1 fixed that period at #ee years4 ,it is a result of this that1 according to ,loomis1 a period of comparative calm on the ,sun existed between #ahaj and #ahbe4 ,each maximum lies nearer to the minimum which precedes it than to the minimum which follows it1 for the spots increase during #c4g years1 and then diminish during #g4d years4 ,according to ,de ,la ,rue the increase occupies #c4eb years1 and diminution #g4ee years4 ,this concurrence between ,de ,la ,rue and ,wolf is surprising considering the diversity of the methods which led to results almost identical1 the one set being based on the number of the spots1 and the other on the superficial extent of the spots4 ,the different periods in succession are not absolutely identical3 but it has been remarked that if during any one period the decrease is retarded or accelerated1 then the increase next following will be lengthened or contracted to a corresponding extent4 ,in consequence of this we are sometimes able to predict with fair accuracy when the next ensuing maximum or minimum will take place4 ,the most striking feature of such a curve as that just alluded to is the very sensible secondary augmentation which happens very soon after the principal maximum4 ,a very curious circumstance has come to light in connection with the epochs of maxima and minima4 ,in arranging the spots according to their latitude and longitude on a diagram sufficiently contracted1 ,carrington found that their latitude decreases gradually as the period of minimum draws near2 then when their number begins to increase they begin to appear again at a higher latitude4 ,this seems to be a definite law4 ,at any rate ,carrington's conclusion has been found to hold good by the observations of ,sprer and ,secchi4 ,the variations of the spots which we now recognise naturally recall those obscurations of the ,sun which are recorded in history2 but it is necessary to accept many of these with caution4 ,a great number of these phenomena which attracted the attention of people in early times are only eclipses badly observed and still more badly described4 ,in other instances the obscuration has been produced by very protracted dry fogs4 ,it is probably to this last-named cause that we must ascribe the obscuration which1 according to ,kepler and ,gemma ,frisius1 took place in #aedg4 ,it was in some such way as this that1 according to ,virgil 7,georg4 i1 #fcj71 who has echoed a tradition which he found in history1 the ,sun was obscured at the death of ,csar3-- ,ille etiam extincto miseratus ,csare ,romam ,quum caput obscura nitidum ferrugine texit1 ,impiaque ternam timuerunt scula noctem4 ,in the year #eec ,a4,d41 and again in the year #fbf ,a4,d4 the ,sun remained obscured for several months2 but these facts 7if facts they are7 besides being ill-observed1 and clothed1 no doubt1 in extremely exaggerated language1 are brought to our notice as having occurred at epochs which are quite independent of one another1 whilst the variations in the markings on the ,sun1 which we have just been talking about1 present an almost mathematical regularity of sequence4 ,we must now institute some inquiries as to the causes of the periodicity of the spots4 ,a periodicity so well established would naturally invite astronomers to seek the causes which produced it4 ,the presence of spots only in the ,zodiacal regions led ,galileo to suspect the existence of some relation between the spots and the position of the planets2 but there is in this a mere surmise1 which1 when it was made1 had nothing to justify it1 and it is still impossible for us to say anything for certain on the point4 ,the determining cause of the periodicity may exist in the interior of the ,sun1 and may depend on circumstances which will for ever remain unknown to us4 ,or it may be something external3 it may be due after all to the influence of the planets4 ,it remains for us1 therefore1 to search and see if any such influence can be traced4 ,according to ,wolf1 the attraction of the planets1 or of some of them1 is the real cause of the periodicity which we are dealing with2 that attraction producing on the surface of the solar globe true tides1 which give birth to the spots1 these tides themselves experiencing periodic variations owing to the periodic changes of position of the celestial bodies which cause them4 ,it has even been thought safe to assert that the fact of the principal period coinciding with the revolution of ,jupiter is of momentous significance2 but this coincidence seems purely accidental1 and no certain conclusion can be drawn as to this matter4 ,the influence of ,mercury and ,venus would perhaps be much more potent1 for their distance from the ,sun is not very great1 and this should render their influence more sensible4 ,on the other hand1 their masses appear to be too small to be capable of producing any sufficient effect4 ,de ,la ,rue1 ,balfour ,stewart1 and ,lwy most perseveringly studied this point of solar physics4 ,they seem to have arrived at the conclusion that the conjunctions of ,venus and ,jupiter do exercise a certain amount of influence on the number of the spots and on their latitude2 and that this influence is less considerable when ,venus is situated in the plane of the solar equator4 ,at any rate it is a fact1 that a great number of the visible inequalities in a duly plotted curve of the spots do really correspond to special positions of these two planets4 ,in order to determine with more precision these coincidences and the importance which attaches to them1 ,de ,la ,rue extended his inquiries4 ,he separately analysed many different groups of spots1 selecting for his purpose more particularly those of which the observations happened to have been specially continuous and complete1 giving a preference moreover to those which had been observed in the central portions of the ,sun's disc4 ,from an investigation of #gid groups ,de ,la ,rue arrived at the following conclusions3--7#a7 ,if we take a meridian passing through the middle of the disc and represented by a diameter perpendicular to the equator1 we find that the mean size of the spots is not the same with regard to that meridian4 ,it appears certain that the correction required for perspective does not suffice to explain this difference2 and that another element must be introduced in order to secure that the apparent dimensions of the spots may be the same on both sides4 ,we do not yet possess a very clear explanation of this fact2 but the most probable is this3--the spots are surrounded by a projecting bank1 which seems to disappear in part during their transit across the ,sun4 ,this bank is more elevated on the preceding than on the following side2 accordingly1 the spots ought to seem smaller when they are in the eastern half of the disc2 larger when they are in the western half2 for in the first position the observer's eye meets an elevated obstacle1 which hides a portion of the spot itself4 7#b7 ,de ,la ,rue specially studied the spots observed at the times when the planets ,venus and ,mars were at a heliocentric distance from the ,earth equal to #j1 #ij1 #ahj1 and #bgj degrees1 and arrived at this result2 the spots are larger in the part of the ,sun which is away from ,venus and ,mars1 and they are smaller on the side on which these planets happen to be4 ,the same result was obtained1 whether ,carrington's figures or the ,kew photographs were employed4 7#c7 ,meanwhile it does not appear that ,jupiter emits any similar influence4 ,this influence should be easily perceived1 for if we calculate the action of the planets in the way that we calculate the tides1 treating it as directly proportional to the masses and inversely proportional to the cubes of the distances1 the influence of ,jupiter should greatly outweigh that of ,venus4 ,wolf thought that he had noticed traces of some influence being exerted by ,saturn2 but this remains altogether without confirmation4 ,de ,la ,rue noticed that large spots are generally situated at extremities of the same diameter4 ,this law also often applies to the development of large prominences4 ,the coincidence agrees well with the theory that there exists on the ,sun some action resembling that of our tides4 ,whatever may be the amount of probability which attaches to these explanations we ought not to forget that we are still far off from possessing the power of giving a vigorous demonstration of them4 ,if we consider with attention the periodical variations of the spots we shall not be long in coming to the conclusion that it is impossible to connect them directly with any one astronomical function in particular1 for the spots appear in a sudden and irregular manner which contrasts in a striking degree with the continuous and progressive action of the ordinary perturbations which we meet with in the study of ,celestial ,mechanics4 ,there is but one reply possible to this objection4 ,the spots and their changes must be visible manifestations of the periodical activity of the ,sun--an activity which itself depends 7as assumed7 on the action of the planets and on their relative positions4 ,the cause1 thus defined1 of the ,sun's activity may be very regular2 the activity itself may vary in a continuous manner without the resulting phenomena possessing the same continuity and the same regularity4 ,we see this in the periodical succession of the ,seasons on the ,earth4 ,the position of the ,sun1 and consequently its manner of acting upon our globe1 varies with a remarkable uniformity1 but nevertheless the meteorological phenomena which result are irregular and capricious4 ,thus it comes about that physicists are more and more inclined to believe that the spots are only secondary effects produced by causes more important and more fundamental4 ,whatever may be our ignorance as to the causes which produce variations in the ,sun's activity we may at least draw one conclusion from the preceding remarks3 it is1 that the ,sun is a very long way from having arrived at a state of tranquillity and freedom from internal commotion4 ,on the contrary1 it is the seat of great movements4 ,its activity is subject to numberless periodical changes which ought in their turn to influence the intensity of the heat and light given out by the ,sun2 and so re-act on the planets which receive their heat1 light1 and life from the ,sun4 ,no account of the periodicity of the spots on the ,sun can be deemed complete which does not include information respecting certain other periodical phenomena which have been found to exhibit features of alternation closely resembling in their sequence and character the periodical changes which take place in regard to the spots on the ,sun4 ,there is evidently a deep mystery lying hid under the curious fact 7which is clearly established7 that the #aa-year period of the spots coincides in a manner as unexpected as it is certain with the period of the variation of terrestrial magnetism4 ,the magnetic needle is subject to a diurnal variation which reaches its extreme amount every #aa years1 and not only so1 but the epoch of maximum variation corresponds with the epoch of the maximum prevalence of ,sun spots4 ,and similarly years in which the needle is least disturbed are also years in which the ,sun spots are fewest4 ,two other very curious discoveries have also been made which are in evident close connection with the foregoing4 ,the manifestation of the ,aurora ,borealis and of those strange currents of electricity known as magnetic earth currents 7which travel below the ,earth's surface and frequently interfere with telegraphic operations71 likewise exhibit periodical changes which take #aa years to go through all their stages4 ,this fact alone would be sufficiently curious1 but when we come to find that the curve which exhibits the changes these two manifestations of force go through1 also shows that their maxima and minima are contemporaneous with the maxima and minima of the ,sun spots and magnetic needle variations1 we cannot doubt that 7to use ,balfour ,stewart's words7 8a bond of union exists between these four phenomena4 ,the question next arises1 what is the nature of this bond8 ,now1 with respect to that which connects ,sun spots with magnetic disturbances we can as yet form no conjecture40 ,to cut a long story short1 it may be said generally that whilst without doubt electricity is the common basis of the three last-named of the four phenomena just mentioned1 it seems scarcely too great a stretch of the imagination to go one step further and suggest that electricity has in some or other occult manner something to do with all these things and therefore with the spots on the ,sun4 ,illustration3 ,fig4 #h4--,the ,sun totally eclipsed1 ,july #ah1 #ahfj 7,feilitzsch74 ,the reader who has followed me thus far will by this time be in a position to appreciate a remark made in an earlier part of this chapter1 that the multitude of facts known to us in connection with the ,sun and its spots is so great1 as to render it impossible to exhibit in a single chapter anything more than the barest outline of them4 ,the numerous observations of recent eclipses of the ,sun1 especially since that of #ahfj1 and the extensive application of the spectroscope to the ,sun both in connection with these eclipses1 and generally1 may be said to have completely revolutionised our knowledge of solar phenomena during the present generation2 or perhaps it might be more correct to say have enormously increased our knowledge of the facts of the case and have revolutionised in no small degree the conclusions deduced from the facts4 ,,chapter ,,iii4 ,,mercury4 ,so far as we know at present1 ,mercury is the nearest planet to the ,sun4 ,the circumstances under which it presents itself to us and a brief general account of its movements have already been stated4 ,in the present chapter1 therefore 7and this remark applies in substance to each of the succeeding chapters appropriated to particular planets71 ,i shall limit myself to such topics as seem to be of interest to an observer armed with a telescope4 ,mercury1 as already mentioned1 exhibits from time to time phases which may be said to be the same as those of the moon2 but as the only chance of seeing it is when it is at its greatest distance east or west of the ,sun1 practically it can only be studied when in1 or rather near to1 what may be called the half-moon phase2 and even then observations on its physical appearance can only be obtained with difficulty4 ,perhaps its most definite feature is its colour4 ,this1 undoubtedly1 is more or less pink4 ,strange to say1 in spite of the multiplication of telescopes and observers1 comparatively little attention has been paid to this planet1 and we really know very little more about it than ,schrter told us nearly a hundred years ago4 ,he obtained what he conceived to be satisfactory evidence of the existence of at any rate one mountain1 having a height of about #aa ,english miles--a height which it will be noted1 far exceeds1 not only relatively but absolutely1 any mountain on the earth4 ,what ,schrter based this conclusion upon was the fact that when the planet was near inferior conjunction1 the southern horn presented a truncated appearance1 which might be the result of a lofty projection arresting the ,sun's light4 ,schrter also announced that ,mercury rotated on its axis in #bd hours #e minutes4 ,sir ,w4 ,herschel failed to satisfy himself that ,schrter's conclusions were well-founded1 but it must certainly be admitted that some support for them is furnished by certain observations made within the last few years4 ,it is matter for regret1 however1 that most of these were made with instruments of sizes which1 for the most part1 cannot be said to have been equal to the task to which they were applied4 ,the truncature of the southern horn first spoken of by ,schrter1 was thought by ,denning1 in #ahhb1 to be obvious2 and in the same year1 by watching the displacement of certain bright and dusky spaces on the disc1 the same observer concluded that a rotation period of about #be hours was indicated4 ,in #ahhb ,schiaparelli at ,milan commenced a prolonged study of ,mercury4 ,believing that it was essential to observe through a good condition of atmosphere1 and that this was impossible if the planet were only looked at in twilight1 when it was necessarily at a low altitude1 ,schiaparelli made all his observations with the ,sun and planet high up in the heavens4 ,he considered1 in effect1 that the blaze of the ,sun's light was a lesser evil than the tremors inseparable from observations of the planet1 clear it might be in some degree of inconvenient ,sun-light1 but viewed through the vapours and atmospheric disturbances1 which always spoil all observations near the horizon4 ,schiaparelli's observations yielded various results1 most of them novel1 and one of them very startling4 ,he considers ,mercury to be a much spotted globe and to be enveloped in a tolerably dense atmosphere4 ,he thought he noticed brownish stripes and streaks 7which might be regarded as permanent markings71 more clearly visible on some occasions than on others2 and that these systematically disappeared near the limb1 owing to the increased depth there of the atmosphere through which they had to be looked at4 ,the foregoing observations may be regarded as not unreasonable2 they may even be accepted without further question4 ,but what are we to say to ,schiaparelli's conclusions that these markings are so nearly permanent1 taking one day with another1 that ,mercury's rotation cannot be measured in hours at all1 but is a matter of days1--in point of fact1 of #hh days2 and that in reality ,mercury occupies in its rotation on its axis the whole of the #hh days which constitute its sidereal year1 or period of revolution round the ,sun4 ,the counterpart of this for us would be that1 instead of the inhabitants of the earth having a day of #bd hours1 they would have only one day and night every #cfe days4 ,astronomers are not at present satisfied to accept this conclusion in regard to ,mercury4 ,some observers have thought that ,mercury is more easy to observe than ,venus1 and that1 speaking generally1 its surface1 if we could only get to see it constantly under favourable circumstances1 might be considered to resemble in most respects that of ,mars4 ,mercury revolves round the ,sun at a mean distance of #cf millions of miles4 ,owing1 however1 to the fact that the eccentricity of its orbit 7or its departure from the circular form7 is greater than that of any of the other major planets1 it may approach to within #bh millions of miles or recede to more than #dc millions of miles4 ,its apparent diameter varies between #d in superior conjunction to #ac in inferior conjunction4 ,the real diameter may be taken at about #cjjj miles4 ,,chapter ,,iv4 ,,venus4 ,the planet ,venus has two things in common with ,mercury4 ,one is1 that being an inferior planet1 that is to say1 a planet revolving round the ,sun in an orbit within that of the ,earth1 it is never very far distant from the ,sun1 and therefore can never be seen on a distinctly dark sky4 ,the second point alluded to arises out of the first2 ,venus exhibits from time to time a series of phases which are identical in character with those of ,mercury1 and therefore with those of the ,moon4 ,venus differs1 however1 from ,mercury in the very important point of size4 ,inasmuch as its diameter is considerably more than double the diameter of ,mercury it has a surface more than six times as great1 and therefore exhibits a far larger area of illumination than ,mercury does4 ,the result of this 7coupled with another fact which will be stated presently7 is that the planet may often be easily seen in broad daylight1 and sometimes casts a sensible shadow at night4 ,under special circumstances1 which recur every #h years1 this planet shines with very peculiar brilliancy4 ,true1 that only about th of the whole disc is then illuminated1 but that fraction transmits to us more light than phases of greater extent do1 because these latter coincide with epochs when the planet is more remote from the ,earth4 ,spots and shadings have on various occasions been noticed on ,venus1 and though it is not easy to harmonise the various accounts1 there seems no doubt of the reality of the facts1 or that they must be ascribed to the existence of mountains4 ,schrter found very much the same state of things to exist on ,venus that he found on ,mercury1 and putting together what he saw he arrived at the conclusion that ,venus possesses mountains of considerable height1 and that his observations must be taken to imply that the planet revolved on its axis in rather more than #bc hours4 ,this conclusion as regards the planet's axial rotation was not first arrived at by ,schrter1 for the two ,cassinis1 one about #afff1 and the other about #agdj1 both ascribed to ,venus a rotation period of about #bc hours1 an evaluation which was fully confirmed by ,di ,vico at ,rome between #ahci and #ahda1 and by ,flammarion in #ahid4 ,what has been already said with respect to ,mercury is true also of ,venus1 namely that it has been much neglected by modern observers2 and accordingly an announcement made by ,schiaparelli in #ahij1 that the rotation period of ,venus is to be measured not by hours but by months1 came upon the astronomical world as a startling revelation2 but it is a revelation which has been keenly contested1 and certainly awaits legal proof4 ,schiaparelli has not ventured to assert as he has done in the case of ,mercury1 that ,venus's rotation period is identical with the period of #g months in which it revolves round the ,sun2 he only claims this as a strong probability arising out of what he says he is certain of1 namely that its period of rotation cannot be less than six months and may be as much as nine months4 ,his assumption is that previous observers in endeavouring to ascertain ,venus's rotation period have used and relied upon evanescent shadings which probably were of atmospheric origin and scarcely recognisable from day to day1 whereas he fixed his attention upon round defined white spots1 which1 whatever their origin1 are so far permanent that their existence has been spoken of for two centuries4 ,miss ,clarke thus puts the matter3--8,his steady watch over them showed the invariability of their position with regard to the terminator2 and this is as much as to say that the regions of day and night do not shift on the surface of the planet4 ,in other words she keeps the same face always turned towards the ,sun40 ,various recent observations1 some of them made with the express object of throwing light upon ,schiaparelli's conclusions1 are strangely contradictory4 ,perrotin at ,nice in #ahij thought his observations confirmed ,schiaparelli's2 on the other hand ,niesten at ,brussels considered that numerous drawings of ,venus made by himself and ,stuyvaert between #ahha and #ahij harmonised well with ,di ,vico's rotation period of #bc;h4 #bam4 #bbs42 which ,trouvelot in #ahib only wished to increase to about #bd hours4 ,there is a general consensus of opinion that great irregularities exist on the surface of ,venus4 ,these are made specially manifest to us in connection with the terminator or visible edge of the planet seen as an illuminated crescent4 ,if the planet had a smooth surface this line would at all times be a perfect and continuous curve1 instead of which it is frequently to be noticed as a jagged or broken line4 ,observations to this effect go back as far as #afdc1 when ,fontana at ,naples observed this to be the condition of the terminator4 ,la ,hire1 ,schrter1 ,mdler1 ,di ,vico and many others down to the present epoch have noted the same thing4 ,the fact that the southern horn of ,venus is constantly to be seen blunted is so well established as to admit of no doubt1 and this blunting is commonly ascribed to the existence of a lofty mountain1 to which ,schrter ascribed a height of #bg miles4 ,whatever we may think as to the precise accuracy of this figure1 it seems impossible to doubt the main fact on which it depends2 whilst a ,belgian observer1 ,van ,ertborn1 in #ahgf repeatedly saw a point of light in this locality which he regarded as due to ,sun-light impinging on a detached peak1 adjacent valleys remaining in shadow4 ,this effect is common enough in the case of the ,moon1 and is familiar to all who are in the habit of studying the ,moon4 ,illustration3 ,fig4 #i4--,venus1 ,dec4 #bc1 #ahhe4 ,the existence on ,venus of an atmosphere of considerable density and extent is well established4 ,proof of this is to be found in the marked diminution of the planet's brilliancy towards the terminator2 and in the faint curved line of light which occasionally may be seen when the planet is near inferior conjunction4 ,when so situated1 so much of the planet itself as can be seen illuminated shows as a narrow radiant crescent of light1 ending off in two points called indifferently cusps or horns4 ,it sometimes happens1 however1 that from the point of each cusp there runs round to the other cusp a faint continuation of the crescent1 resulting in the general appearance of the planet being that of a nearly uniform ring of light4 ,there is no known way in which the ,sun can illuminate so much more than the half of ,venus so as to permit of a perfect circle being visible except by supposing that an atmosphere exists on the planet and refracts 7or transmits by bending1 as it were1 round the corner7 a sufficient amount of ,sun-light to give rise to the appearance in question4 ,further proof of the existence of an atmosphere on ,venus is obtainable on those very rare occasions when the planet is seen passing across the disc of the ,sun--a phenomenon known as a 8,transit of ,venus40 ,it then nearly always happens that a hazy nebulous ring of feeble light may be detected encompassing the planet's disc indicative of course of the fact that the ,sun's rays are there slightly obstructed in reaching the eye of an observer on the ,earth4 ,some observers scrutinising ,venus when in transit have thought that they were able to obtain1 by means of the spectroscope1 traces of aqueous vapour on the planet1 but the evidence of this does not appear to be altogether clear or conclusive4 ,illustration3 ,fig4 #aj4--,venus near conjunction as a thin crescent1 ,sept4 #ba1 #ahhg 7,flammarion74 ,everybody may be presumed to be acquainted with the spectacle popularly known as 8,the ,old ,moon in the ,new ,moon's ,arms0 whereby when the ,moon is only about two or three days old and exhibits but a narrow crescent of bright light1 yet the whole outline of the disc is traceable on the sky4 ,a phenomenon analogous to this may often be seen in the case of ,venus when near its inferior conjunction4 ,with the ,moon the cause is due to the reflection of ,earth-light 7so to speak7 to the ,moon1 but that explanation seems inadequate in respect of ,venus1 because it is conceived that the amount of ,earth-light available is altogether insufficient for the purpose4 ,many other explanations have been put forward including phosphorescence on the surface of ,venus1 electrical displays in the nature of terrestrial auror1 and what not1 but it must be frankly confessed that astronomers are all at sea on the subject4 ,the existence of snow at the poles of ,venus has been suspected by observers of tried skill and experience such as ,phillips and ,webb1 though the idea was first broached by ,gruithuisen in #ahac4 ,flammarion's observations during #ahib and the two following years are distinctly confirmatory of this idea4 ,he adds that as both polar caps are visible at the same time the planet's axis cannot be much inclined to the plane of its orbit4 ,compared with all the other planets the absolute brightness of ,venus stands very high4 ,of course it must be understood that by this phrase 8absolute brightness0 no more is meant than its reflective power4 ,venus is what it is by virtue of its power of reflecting ,sun-light2 presumably it has no inherent brightness of its own4 ,what its reflective power is was probably never more effectively brought under the notice of a human eye than on ,september #bf1 #ahgh1 when ,nasmyth enjoyed an opportunity of seeing ,venus and ,mercury side by side for several hours in the same field of view4 ,he speaks of ,venus as resembling clean silver and ,mercury as nothing better than lead or zinc4 ,seeing that owing to its greater proximity to the ,sun the light incident on ,mercury must be some #c times as strong as the light incident on ,venus1 it follows that the reflective power of ,venus must be very great4 ,as a matter of fact it has been calculated to be nearly equal to newly fallen snow2 in other words to reflect fully #gj per cent4 of the light which impinges on it4 ,venus has no satellite2 this fact seems certain4 ,yet half a dozen or more observers between #afde and #agfh discovered such a satellite2 observed it2 followed it6 ,this startling mystery1 as it really was1 attracted some years ago the attention of a very careful ,belgian observer1 ,stroobant1 who examined in a most painstaking manner all the recorded observations4 ,his conclusions were that in almost all cases particular stars 7which he identified7 were mistaken for a satellite4 ,where the object seen was not capable of identification1 possibly it was a minor planet2 whilst in one instance it was probable that it was ,uranus which had been seen and regarded as a satellite of ,venus4 ,venus is perhaps the planet which has most impressed the popular mind4 ,for the earliest illustration of this statement we must go as far back as ,homer who makes two references to it in the ,iliad4 ,these1 in ,pope's version1 run as follows3-- 8,as radiant ,hesper shines with keener light1 ,far beaming o'er the silver host of night40 --xxii4 #cii #cah4 8,the morning planet told th' approach of light2 ,and fast behind1 ,aurora's warmer ray ,o'er the broad ocean pour'd the golden day40 --xxiii4 #bha #bbf4 ,the phases of ,venus were first discovered by ,galileo and were made known to the world1 or rather to ,kepler1 in a mystic sentence which has often been quoted3-- 8,hc immatura1 a me jam frustra leguntur--oy40 8,these things not ripe2 at present read in vain by others are read by me40 ,the former sentence transposed becomes-- ,cynthi figuras mulatur mater amorum4 ,the mother of loves ,venus imitates the phases of ,cynthia the ,moon4 ,venus revolves round the ,sun in #bbd days at a mean distance of about #fg millions of miles4 ,its apparent diameter varies between #i in superior conjunction1 and #fb in inferior conjunction4 ,the real diameter is about #gejj miles2 in other words ,venus is nearly as large as the ,earth4 ,,chapter ,v4 ,,the ,,earth4 ,to us1 as its inhabitants1 the ,earth appeals in two characters1 and in writing a book on astronomy it is necessary1 yet difficult1 to keep these two characters separate4 ,the ,earth is an ordinary planet member of the solar system1 amenable to the same laws1 impelled by the same forces1 and going through the same movements as the other members of the ,sun's entourage4 ,yet1 by reason of the fact that we are ourselves on the ,earth and are not spectators of it looking at it from at a distance1 there are many phenomena coming under our notice which require special treatment1 and it is often very difficult to say where the province of the astronomer ends and that of the geographer begins4 ,this volume being specially designed to deal with astronomical matters1 ,i shall pass over many subjects which may be said to be on the border line1 and which some of my readers may therefore be disappointed not to find discussed4 ,besides the geographer1 the geologist and his scientific brother the mineralogist are concerned with the ,earth regarded as a planet moving through space as the other planets do4 ,the geologist studies the actual structure of the ,earth1 its circumstances and history so far as they have been revealed to us1 whilst the mineralogist investigates and names the materials of which it is composed1 and classifies such materials with the assistance of the geologist on the one hand and of the chemist on the other4 ,all these subordinate sciences--subordinate ,i mean from an astronomer's point of view--open up very varied1 instructive1 and interesting fields of study1 but they are of course foreign to the purpose of the present volume4 ,though the ,earth is commonly regarded as a sphere it is not that in reality1 because it is not of identical dimensions from east to west and from north to south4 ,it is somewhat flattened at the poles2 its polar diameter is less than its equatorial diameter1 in the ratio of about #bih to #bii1 or1 expressed in miles1 its polar diameter is about #bf miles less than its equatorial diameter4 ,if a globe #c feet in diameter be taken to represent the ,earth1 then the polar diameter will1 on this scale1 be inch too long4 ,this flattening of the poles of the ,earth finds its counterpart1 so far as we know1 in most1 and probably in all of the planets4 ,it is most considerable and therefore most conspicuous in the case of ,jupiter4 ,it ought here to be added that a suspicion exists that the equatorial section of the ,earth is not a perfect circle1 but that the diameter of the ,earth1 taken through the points on the equator marked by the meridians #ac #eh and #aic #eh east of ,greenwich1 is one mile longer than the diameter at right angles to these two points4 ,the science which inquires into matters of this kind1 including besides the figure of the ,earth1 the length of the degree at different latitudes1 and the distances of places from one another1 alike in angular measure and in time1 is called ,geodesy2 it is1 in point of fact1 land-surveying on a very large scale1 in which instruments and processes of astronomical origin are brought into operation1 and in which astronomers are more or less required to take the lead4 ,although we all of us now perfectly understand that the ,earth is a planet moving round the ,sun as a centre1 it is1 comparatively speaking1 but recently that this fact has become generally recognised and understood4 ,it is true that we can discover here and there in ancient writings some trace of the idea1 yet it is doubtful whether #bjjj years ago more than a few 8advanced0 thinkers thoroughly and clearly accepted it as a distinct truth4 ,it was much more in consonance with popular thought and the actual appearance of things that the ,earth should be the centre round which the ,sun revolved and on which the planets depended2 and accordingly1 sometimes in one shape and sometimes in another1 the notion of the ,earth being the centre of the universe was generally accepted4 ,the contrary opinion had1 however1 a few sympathisers4 ,for instance1 ,aristarchus of ,samos1 who lived in the third century before the ,christian era1 supposed1 if we may trust the testimony of ,archimedes and ,plutarch1 that the ,earth revolved round the ,sun2 this1 however1 was regarded as a 8heresy10 in respect of which he was accused of 8impiety40 ,some few years elapsed and a certain ,cleanthes of ,assos is said by ,plutarch to have suggested that the great phenomena of the universe might be explained by assuming that the ,earth was endued with a motion of translation round the ,sun together with one of rotation on its own axis4 ,the historian states that this idea was so contrary to the received opinions that it was proposed to put ,cleanthes on his trial for impiety4 ,in former times the philosophers who studied the solar system ranged themselves in several 8schools of thought10 to use a modern hackneyed phrase4 ,some upheld the ,ptolemaic system1 which took its name from a great ,egyptian astronomer1 ,claudius ,ptolemy1 though it does not appear that he was actually the first to suggest it4 ,the ,ptolemaic system regarded the ,earth as the centre1 with the following bodies1 all called planets1 revolving round it in the order stated3--the ,moon1 ,mercury1 ,venus1 the ,sun1 ,mars1 ,jupiter1 and ,saturn4 ,it will be observed that there are seven bodies here named1 and as seven was regarded as the 8number of perfection10 it was in later times considered that only these seven bodies 7neither more nor less7 could really be the ,earth's celestial attendants4 ,though ,ptolemy was in one sense an ,egyptian1 there yet prevailed amongst the ,egyptians at large another theory slightly different from ,ptolemy's4 ,according to the 8,egyptian theory10 ,mercury and ,venus were regarded as satellites of the ,sun1 and not as primary planets appurtenant to the ,earth4 ,after ,ptolemy's era many centuries elapsed1 during which the whole subject of the solar system lay practically dormant1 and it continued so until the revival of learning brought new theorists upon the scene4 ,the most important of these was ,copernicus1 who1 in the sixteenth century1 propounded a theory which eventually superseded all others1 and1 with slight modifications1 is the one now accepted4 ,copernicus placed the ,sun in the centre of the system1 and treated it as the point around which all the primary planets revolved4 ,so far1 so good2 but ,copernicus went astray on the question of the orbits of the planets4 ,he failed to realise the true character of the curves which they follow and treated these curves as 8epicycles10 which word may be described as representing a complicated combination of little circles which taken together form a big one4 ,it was left to ,kepler and ,newton to settle all such details on a true and firm basis4 ,but before this stage was reached a man of the highest astronomical attainments and practical experience1 ,tycho ,brahe1 made shipwreck of his reputation as an astronomer by solemnly reviving the idea of the ,earth being the immovable centre of everything4 ,he treated the ,moon as revolving round the ,earth at no great distance and the ,sun as doing the same thing a little farther off2 the five planets revolving round the sun as solar satellites4 ,the 8,tychonic system10 as it is called1 has something in common with the ,ptolemaic system without being by any means as logical as the latter4 ,that such far-fetched ideas as ,tycho's should have been palmed off on the world of science so recently as #cjj years ago is passing strange2 but the explanation appears to be that his action arose out of a misconception of certain passages of ,holy ,scripture1 which seemed irreconcilable with the ,copernican theory4 ,it must not be forgotten that ,copernicus's famous book1 published in #aedc1 in which he had announced his views1 had been condemned by the ,papal 8,congregation of the ,index20 and therefore ,tycho might have had as a further motive a desire to curry favour with the authorities of the ,church of ,rome1 and to gratify his own vanity at the same time4 ,with these explanations it will no longer be misleading if1 for convenience sake1 ,i speak of a certain great circle of the heavens as apparently traversed by the ,sun every year1 owing to the revolution of our ,earth round that body4 ,this circle is called the 8,ecliptic10 and its plane is usually employed by astronomers as a fixed plane of reference4 ,it must be distinguished from that other great circle called the 8celestial equator10 which is the plane of the ,earth's equator extended towards the stars4 ,the plane of the equator is inclined to the ecliptic at an angle of about #bc1 which angle is known as the 8obliquity of the ecliptic40 ,it is this inclination which gives rise to the seasons which follow one another in succession during our annual journey round the ,sun4 ,the two points where the celestial equator and the ecliptic intersect are called the 8equinoxes10 of spring or autumn as the case may be2 the points midway between these being the 8solstices10 of summer or winter as the case may be4 ,these words need but little explanation1 at any rate1 as regards those persons who are able to trace the ,latin origin of the words4 8,equinox0 is simply the place occupied by the ,sun twice every year 7namely about ,march #bj and ,september #bb71 when day and night are theoretically equal throughout the world1 when also the sun rises exactly in the east and sets exactly in the west4 ,the 8solstices0 represent the standing still of the sun at the given times and places1 and are the neutral points where the ,sun attains its greatest northern or southern declination4 ,this usually occurs about ,june #ba and ,december #ba4 ,it must not be forgotten by the way1 that the above application of the words 8summer0 and 8winter0 to the solstices is only correct so far as concerns places in northern terrestrial latitudes--,europe and the ,united ,states1 for instance4 ,in southern terrestrial latitudes--for instance1 when speaking of what happens at the ,cape of ,good ,hope and in ,australia--the words must be reversed4 ,we have seen in a previous chapter that whilst the orbits of the planets are nearly true circles1 none of them are quite such3 and the departure from the truly circular form results in some important consequences4 ,whilst some of these are too technical to be explained in detail here1 one at least must be referred to because of what it involves4 ,not only is the ,earth's orbit eccentric in form1 but its eccentricity varies within narrow limits2 and besides this the orbit itself1 as a whole1 is subject to a periodical shift of place1 from the joint effect of all which changes it comes about that our seasons are now of unequal length1 the spring and summer quarters of the year unitedly extending to #ahf days1 whilst the autumn and winter quarters comprise only #agh days4 ,the sun therefore has the chance of shining for a longer absolute period of time over the northern hemisphere than over the southern hemisphere2 hence the northern is the warmer of the two hemispheres1 because it has a better1 because a longer1 chance of storing up an accumulation of solar radiant heat4 ,probably it is one result of this that the north polar regions of the ,earth are easier of access than the south polar regions4 ,in the northern hemisphere navigators have reached to #ha of latitude1 whereas #ga is the highest limit yet attained in the southern hemisphere4 ,readers who have studied the history of explorations in the ,arctic regions will not need to be reminded of the controversy which has so often arisen respecting the existence or nonexistence of an 8,open ,polar ,sea40 ,it has already been hinted that it is not an easy matter to determine1 when dealing with the ,earth1 where astronomy and its allied sciences1 geography1 geodesy and geology respectively1 begin and end4 ,but as certain topics connected with these sciences1 such as the rotundity of the ,earth and its rotation on its axis1 will come more conveniently under consideration in other volumes of this series1 ,i shall pass them over and only treat of a few things which more directly concern the student of nature observing either with or without the assistance of a telescope4 ,the fact that the ,earth is surrounded by a considerable atmosphere largely composed of aqueous vapour has a material bearing on the success or failure of observations made on the ,earth of bodies situated at a distance4 ,it may be taken as a general rule that the nearer an observer is to the surface of the sea1 or otherwise to the surface of the land at the sea-level1 the greater will be the difficulty which will confront him in carrying on astronomical observations4 ,hence such observations are generally made with unsatisfactory results on the sea coast or on the banks of rivers4 ,an interesting but rather ancient illustration of this last-named fact is to be found in the circumstance that ,copernicus1 who died at the age of #gj1 complained in his last moments that much as he had tried he had never succeeded in detecting the planet ,mercury1 a failure due1 as ,gassendi supposed1 to the vapours prevailing near the horizon at the town of ,thorn on the banks of the ,vistula where the illustrious philosopher lived4 ,the phenomena depending on the presence of aqueous vapour in the atmosphere which especially under the notice of the astronomer are ,refraction1 ,twilight1 and the ,twinkling of the ,stars4 ,refraction is what it professes to be1 a bending1 and what is bent is the ray of light coming from a celestial object to a terrestrial station4 ,olmsted has put the matter in this way3--8,we must consider that any such object always appears in the direction in which the last ray of light comes to the eye4 ,if the light which comes from a star were bent into fifty directions before it reached the eye1 the star would nevertheless appear in a line described by the ray nearest the eye4 ,the operation of this principle is seen when an oar1 or any stick1 is thrust into the water4 ,as the rays of light by which the oar is seen have their direction changed as they pass out of water into air1 the apparent direction in which the body is seen is changed in the same degree1 giving it a bent appearance--the part below the water having apparently a different direction from the part above40 ,the direction of this refraction is determined by the general law of optics that when a ray of light passes out of a rarer into a denser medium 7for instance out of air into water1 or out of space into the ,earth's atmosphere7 it is bent towards a perpendicular to the surface of the medium2 but when it passes out of a denser into a rarer medium it is bent from the perpendicular4 ,the effect of refraction is to make a heavenly body appear to have an apparent altitude greater than its true altitude1 so that1 for example1 an object situated actually in the horizon will appear above it4 ,indeed it sometimes happens that objects which are actually below the horizon and which otherwise would be invisible were it not for refraction are thus brought into sight4 ,it was in consequence of this that on ,april #bj1 #ahcg1 the ,moon rose eclipsed before the ,sun had set4 ,sir ,henry ,holland thus alludes to the phenomenon3--8,i am tempted to notice a spectacle1 having a certain association with this science1 which ,i do not remember to have seen recorded either in prose or poetry1 though well meriting description in either way4 ,this spectacle requires1 however1 a combination of circumstances rarely occurring--a perfectly clear ,eastern and ,western horizon1 and an entirely level intervening surface1 such as that of the sea or the ,african desert--the former rendering the illusion1 if such it may be called1 most complete to the eye4 ,the view ,i seek to describe embraces the orb of the setting ,sun1 and that of the full ,moon rising in the ,east--both above the horizon at the same time4 ,the spectator on the sea between1 if he can discard from mental vision the vessel on which he stands1 and regard only these two great globes of ,heaven and the sea-horizon circling unbroken around him1 gains a conception through this spectacle clearer than any other conjunction can give1 of those wonderful relations which it is the triumph of astronomy to disclose4 ,all objects are excluded save the ,sun1 the ,moon1 and our own ,globe between1 but these objects are such in themselves that their very simplicity and paucity of number enhances the sense of the sublime4 ,only twice or thrice1 however1 have ,i witnessed the sight in its completeness--once on a ,mediterranean voyage between ,minorca and ,sardinia--once in crossing the desert from ,suez to ,cairo1 when the same full ,moon showed me1 a few hours later1 the very different but picturesque sight of one of the annual caravans of ,mecca pilgrims1 with a long train of camels making their night march towards the ,red ,sea40#c ,it is due to the same cause that the ,sun and the ,moon when very near the horizon may often be noticed to exhibit a distorted oval outline4 ,the fact simply is1 that the upper and the lower limbs undergo a different degree of refraction4 ,the lower limb being nearer the horizon is more affected and is consequently raised to a greater extent than the upper limb1 the resulting effect being that the two limbs are seemingly squeezed closer together by the difference of the two refractions4 ,the vertical diameter is compressed and the circular outline becomes thereby an oval outline with the lesser axis vertical and the greater axis horizontal4 ,though the foregoing information merely embraces a few general principles and facts1 the reader will have no difficulty in understanding that refraction exercises a very inconvenient disturbing influence on observations which relate to the exact places of celestial objects4 ,no such observations are available for mutual comparison1 however great the skill of the observer1 or the perfection of his instrument1 unless1 and until certain corrections are applied to the observed positions in order to neutralise the disturbing effects of refraction4 ,in practice this is usually done by means of tables of corrections1 those in most general use being ,bessel's4 ,inasmuch as refraction depends upon the aqueous vapour in the atmosphere1 its amount at any given moment is affected by the height of the barometer and the temperature of the air4 ,accordingly when1 for any purpose1 the utmost precision is required1 it is necessary to take into account the height of the barometer and the position of the mercury in the thermometer at the moment in question4 ,at the zenith there is no refraction whatever1 objects appearing projected on the background of the sky exactly in the position they would occupy were the earth altogether destitute of an atmosphere at all4 ,the amount of the refraction increases gradually1 but in accordance with a very complex law1 from the zenith to the horizon4 ,thus the displacement due to refraction which at the zenith is nothing and at an altitude of #de is only #eg becomes at the horizon more than 4 ,one very curious consequence is involved in the fact that the displacement due to refraction is at the horizon what it is2 the diameter both of the ,sun and ,moon may be said to be 1 more or less1 so that when we see the lower edge of either of these luminaries just touching the horizon in reality the whole disc is completely below it1 and would be altogether hidden by the convexity of the earth were it not for the existence of the earth's atmosphere and the consequent refraction of the rays of light passing through it from the ,sun 7or ,moon7 to the observer4 ,twilight is another phenomenon associated with astronomical principles and effects which depends in some degree on the ,earth's atmosphere and on the laws which regulate the reflection and refraction of light4 ,after the ,sun has set it continues to illuminate the clouds and upper strata of the air just as it may often be seen shining on the tops of hills long after it has disappeared from the view of the inhabitants of the plains below1 and indeed may illuminate the chimneys of a house when it is no longer visible to a person standing in the garden below4 ,the air and clouds thus illuminated reflect some of the ,sun's light to the surface of the earth lying immediately underneath1 and thus produce after sun-set and before sun-rise1 in a degree more or less considerable according as the ,sun is only a little or is much depressed below the horizon1 that luminous glow which we call 8twilight40 ,this word is of ,saxon origin and implies the presence of a twin1 or double1 light4 ,as soon as the ,sun has disappeared below the horizon all the clouds overhead continue for a few minutes so highly illuminated as to reflect scarcely less light than the direct light of the ,sun4 ,as1 however1 the ,sun gradually sinks lower and lower1 less and less of the visible atmosphere receives any portion of its light1 and consequently less and less is reflected minute by minute to the ,earth at the observer's station until at length the time comes when there is no sunlight to be reflected--and it is night4 ,the converse of all this happens before and up to sun-rise2 night ceases1 twilight ensues1 gradually becoming more definite2 the dawn appears1 and finally the full ,sun bursts forth4 ,it may here be stated as a note by the way that the circumstances under which the ,sun first shows itself after it has risen above the horizon has some bearing on the probable character of the weather which is at hand4 ,when the first indications of day-light are seen above a bank of clouds it is thought to be a sign of wind2 but if the first streaks of light are discovered low down1 that is in1 or very near the horizon1 fair weather may be expected4 ,twilight is usually reckoned to last until the ,sun has sunk #ah below the horizon1 but the question of its duration depends on where the observer is stationed1 on the season of the year1 and 7in a slight degree7 on the condition of the atmosphere4 ,the general rule is that the twilight is least in the tropics and increases as the observer moves away from the equator towards either pole4 ,whilst in the tropics a depression of #af or #ag is sufficient to put an end to the phenomenon1 in the latitude of ,england a depression of from #ag to #bj is required4 ,as implied above1 it varies with the latitude2 and as regards the different seasons of the year1 it is least on ,march #a and ,october #ab1 being three weeks before the vernal equinox and three weeks after the autumnal equinox4 ,the duration at the equator may be about #a hour #ab minutes2 it amounts to nearly #b hours at the latitude of ,greenwich1 and so on towards the pole4 ,at each pole in turn the ,sun is below the horizon for #f months1 but as it is less than #ah below the horizon for about #c of those #f months it may be said that there is a continual twilight for those #c months4 ,something of the same sort of thing as this occurs in the latitude of ,greenwich1 for there is no true night at ,greenwich from ,may #bb to ,july #ba1 but constant twilight from sunset to sunrise1 or #b months of twilight in all4 ,though twilight at the equator is commonly set down as lasting about an hour1 this period is there1 as elsewhere1 affected by the elevation of the observer above the sea-level4 ,where the air is very rarified1 as at places situated as ,quito and ,lima are1 the twilight is said to last no more than #bj minutes1 and this would accord with the theory that where there is no air at all 7e4g41 on the ,moon7 there is no twilight at all4 ,the greater purity and clearness of mountain air1 rarified as it is1 is another cause which contributes to vary by reducing the duration of twilight4 ,it is sometimes stated that a secondary twilight may be noticed1 and ,sir ,john ,herschel has spoken of it as 8consequent on a re-reflection of the rays dispersed through the atmosphere in the primary one4 ,the phenomenon seen in the clear atmosphere of the ,nubian ,desert1 described by travellers under the name of the #8afterglow1' would seem to arise from this cause40 ,i am not acquainted with any records which throw light on these remarks of ,sir ,john ,herschel4 ,the phenomenon of twinkling is a subject which has been much neglected1 possibly on account of its apparent1 but only apparent1 simplicity4 ,the familiar verse of our days of childhood-- 8,twinkle1 twinkle little star1 ,how ,i wonder what you are1 ,up above the earth so high1 ,like a diamond in the sky10 contains even in this simple form a good deal of food for reflection2 whilst the new version-- 8,twinkle1 twinkle little star1 ,now we've found out what you are1 ,when unto the midnight sky ,we the spectroscope apply10 does so yet more4 ,as an optical phenomenon the twinkling1 or to use the more scientific phrase1 the scintillation1 of the stars is a matter which has been strangely ignored by physicists4 ,indeed1 the only investigators who seem to have dealt with it in any sort of detail are two ,italians1 ,secchi and ,respighi1 ,dufour1 a ,frenchman1 ,montigny1 a ,belgian1 and the ,rev4 ,e4 ,ledger1 an ,englishman4 ,secchi has truly remarked that the twinkling of the stars is one of the most beautiful of the minor phenomena of the heavens4 ,light1 sometimes bright1 sometimes feeble1 sometimes white1 sometimes red1 darts about in intermittent gleams1 like the sparkling flashes of a well-cut diamond1 and works upon the feelings of even the most stolid spectator4 ,the theory of twinkling is still surrounded by many difficulties4 ,one thing1 however1 is certain--it has nothing to do with recurrent changes in the intrinsic light or physical condition of the star itself1 but arises during the passage of its rays through our atmosphere2 it depends1 therefore1 in some way or other on the varying conditions of the atmosphere4 ,on the summit of high mountains1 according to the observations of all careful observers 7notably ,tacchini1 who studied the subject on ,mount ,etna71 the light of the stars is steady1 like that of the planets2 and it is so likewise during the hours of calm which often precede terrestrial storms4 ,the vibrations are usually more frequent near the horizon1 and diminish with the elevation of the star above the horizon2 in other words1 with the lessening of the thickness of the atmospheric strata which the rays of light have to traverse4 ,nevertheless1 during windy weather1 and specially with northerly wind1 it may be noticed that the stars twinkle high up above the horizon1 and even as far as the zenith4 ,from these and other similar considerations we are justified in drawing the conclusion that twinkling largely depends on the condition and movements of the atmosphere4 ,secchi further points out that it is impossible to study carefully with the naked eye all the features of twinkling1 and that telescopic assistance is imperatively necessary4 ,when1 with the aid of a telescope1 we scrutinise a star during a disturbed evening marked by much twinkling we see an image diffused and undefined and surrounded by rays1 as if several images were superposed1 and were jumping about rapidly4 ,on such occasions we do not see that little defined disc surrounded by motionless diffraction rings1 ordinarily indicative of a tranquil atmosphere4 ,with a telescope armed with a medium power1 the field of view of which is more extensive than that of a high power1 we find that if a light tap is given to the telescope1 the ordinary simple image is changed into a luminous curve1 the perimeter of which is formed entirely of a succession of arcs exhibiting the colours of the rainbow4 ,this coloured curve does not1 in principle1 differ from what one sees on swinging round and round in the air such a thing as a stick1 the end of which is alight1 having been freshly taken from a fire4 ,the glowing tip produces in appearance a continuous arc1 the result of the persistence of the image of the tip on the retina4 ,in such a case the colour is constant1 because the illumination resulting from the blazing wood does not vary2 but in the case of a star the arcs are differently coloured during the very brief space of time in which the vibrating telescope transports the image from one side to another of the visible field4 ,this experiment is from its nature very crude1 but the idea was improved upon and reduced to a systematic shape by ,montigny1 who introduced into his telescope1 at a certain distance from the eyepiece1 a concave lens eccentrically placed with respect to the axis of the instrument1 and endued with a rapid movement of rotation imparted by suitable mechanism4 ,he thus obtained images which revolved with regularity1 and so was able to submit certain features of the phenomenon to a definite system of measurement4 ,to cut a long story short1 ,montigny started with the assumption 7made good by the sequel7 that possibly stars were affected in their twinkling by intrinsic constitutional differences2 and that possibly ,secchi's classification of stars into four types 7a classification which depends on the spectra which they yield7 might put him on the track of some intelligible conclusions with respect to the theory of twinkling4#d ,the results he ultimately arrived at were1 that the yellow and red stars of the ,i,ind and ,i,i,ird types twinkle less rapidly than the white stars of the ,ist type4 ,whilst the average number of scintillations per second of the stars of type ,,iii4 were #ef1 those of type ,,ii4 were #fi1 and those of type ,i4 #hf4 ,these differences may be confidently said to depend upon too many observations of too many different stars to be fortuitous4 ,montigny also arrived at a number of incidental conclusions of considerable interest4 ,the one main thread running through them1 is that there is a connection between the twinkling of a star and its spectrum1 which had never before been thought of4 ,we are justified1 indeed1 in going so far as to say1 that ,montigny's observations point distinctly to a law on this subject1 the law being that the more the spectrum of a star is interrupted by dark lines1 the less frequent are its scintillations4 ,the individual character of the light1 therefore1 emitted by any given star appears to affect its twinkling1 both as regards the frequency thereof and the colours displayed4 ,montigny collected some other interesting facts with reference to twinkling1 which may here be stated in a concise form4 ,there is a greater display of twinkling in showery weather1 than when the atmosphere is in a normal condition2 and in winter than in summer1 whatever may be the weather4 ,in dry weather in ,spring and ,autumn the twinkling is about the same1 but wet has more effect in ,autumn than in ,spring in developing the phenomenon4 ,variations in the barometric pressure and in the humidity of the air also affect the amount of twinkling2 there is more before a rainy period1 likely to last #b or #c days1 than before a single1 or1 so to speak1 casual rainy day4 ,twinkling also varies with the aggregate total rain-fall of any group of days1 being more pronounced as the rain-fall is greater1 but decreasing suddenly and considerably as soon as the rainy condition of the atmosphere has passed away4 ,the number of scintillations found to be observable with the aid of ,montigny's instrument 7which he called a 8scintillomtre071 varied from a minimum of #ej during ,june and ,july1 to #ig in ,january1 and #aja in ,february1 increasing and decreasing in regular sequence from month to month4 ,when an ,aurora ,borealis is visible1 there is a marked increase in the amount of twinkling4 ,it would be interesting to follow up this last named discovery by an endeavour to ascertain whether the fluctuations which are coincident in point of time with an ,auroral display depend upon optical considerations connected with the ,aurora1 or on physical considerations having any relation to the increased development of terrestrial magnetism4 ,i have been thus particular in unfolding somewhat fully the present state of our knowledge concerning the twinkling of the stars1 because it is evident that there are many interesting points connected with it1 which may be studied by any patient and attentive star-gazer1 and which do not need the instrumental appliances and technical refinements which are only to be found in fully-equipped public and private observatories4 ,it should be mentioned in conclusion that the planets twinkle very little1 or1 more often1 not at all4 ,this is mainly due to the fact that they exhibit discs of sensible diameter and therefore that there is1 as ,young puts it1 8a general unchanging average of brightness for the sum total of all the luminous points of which the disc is composed4 ,when1 for instance1 point ,a of the disc becomes dark for a moment1 point ,b1 very near to it1 is just as likely to become bright2 the interference conditions being different for the #b points4 ,the different points of the disc do not keep step1 so to speak1 in their twinkling40 ,the non-twinkling of planets because they possess sensible discs is often available as a means for determining when a planet is looked for1 which1 of several objects looked at1 is the planet wanted and which are merely stars4 ,,chapter ,,vi4 ,,the ,,moon4 ,the ,moon being merely the satellite of a planet1 to wit1 the ,earth1 it should1 according to the plan of this book1 be included in the chapter which deals with its primary2 but for us inhabitants of the ,earth the ,moon has so many special features of interest that it will be better to give it a special chapter to itself4 ,we may regard the ,moon in a twofold aspect1 and consider what it is as a mere object to look at1 and what it does for us2 probably my present readers will prefer that most prominence shall be given to the former aspect4 ,the ,moon as seen with the naked eye exhibits a silvery mass of light1 which at the epoch of what is called 8full ,moon0 has a seemingly even circular outline4 ,full or not full1 its surface appears to be irregularly shaded or mottled4 ,the immediate cause of this shading is the fact that the surface of the ,moon1 not being really smooth1 reflects irregularly the ,sun's light which falls upon it4 ,the causa causans of this is the existence of numerous mountains and valleys on its surface1 and which were first discovered to be such by ,galileo4 ,that there are mountains is proved by the shadows cast by their peaks on the surrounding plains1 when the ,sun illuminates the ,moon obliquely--that is1 when the ,moon is shining either as a crescent or gibbous4 ,such shadows1 however1 disappear at the phase of 8,full-,moon10 because the ,sun's rays then fall perpendicularly on the ,moon's surface4 ,when the ,moon presents either a crescent or a gibbous form 7in point of fact when it presents any form except that of 8,full-,moon071 the boundary line which separates the illuminated from the unilluminated portion 7and which boundary line is generally spoken of as the 8terminator07 has a rough1 jagged appearance2 this is due to the fact that the ,sun's light falls first on the summits of the peaks1 and that the adjacent valleys and declivities are in shade4 ,these remain so till by reason of the ,moon's progress in its orbit a sufficient time has elapsed for the ,sun to penetrate to the bottom of the valleys4 ,with this explanation the reader will have no difficulty in realising why the terminator always exhibits an irregular or jagged edge4 ,illustration3 ,fig4 #aa4--,mare ,crisium4 7,lick ,observatory photographs47 ,various mountains on the ,moon to the number of more than a thousand have been mapped1 and their elevations calculated4 ,of these fully half have received names1 being those of men of various dates and nationalities1 who have figured conspicuously in the annals of science1 including some1 however1 who have not done so4 ,whilst many of these mountains are isolated elevations1 not a few form definite chains of mountains1 and to certain of these chains definite names1 borrowed from the ,earth1 have been given4 ,thus we find on maps of the ,moon the 8,apennines10 the 8,alps10 the 8,altai ,mountains10 the 8,drfel ,mountains10 the 8,caucasus ,mountains10 and so on4 ,besides the mountains there exist on the ,moon a number of plains analogous in some sense to the 8steppes0 of ,asia and the 8prairies0 of ,north ,america4 ,these were termed 8seas0 in the early days of the telescope1 because it was assumed that as they were so large and so smooth they were vast tracts of water4 ,this supposition has long ago been overthrown1 but the names have been retained as a matter of convenience4 ,hence it comes about that in descriptions of the ,moon one meets with such names as ,mare ,imbrium1 the 8,sea of ,showers02 ,mare ,serenitatis1 the 8,sea of ,serenity02 ,mare ,tranquillitatis1 the 8,sea of ,tranquillity02 and so on4 ,it seems probable that the so-called seas represent in nearly its original form what was once the original surface of the ,moon before the mountains were formed4 ,a confirmation of this idea is to be found in the fact that though these plains are fairly level surfaces compared with the masses of mountains which hedge them in on all sides1 yet the plains themselves are dotted over with inequalities 7small elevations and pits71 which seem to suggest that some of them might eventually have developed into mountains if the further formation of mountains had not been arrested by the fiat of the ,creator4 ,though hitherto we have been speaking of the mountains of the ,moon under that generic title1 it is necessary for the reader to understand that the ,moon's surface exhibits everywhere remarkable illustrations of those geological processes which we on the earth associate with the word 8volcano40 ,there cannot be the least doubt that the existing surface of the ,moon1 as we see it1 owes all its striking features to volcanic action1 differing little from the volcanic action to which we are accustomed on the earth4 ,that this theory is well founded may be very easily inferred by comparing the structural details of certain terrestrial volcanoes and their surroundings with a typical lunar mountain1 or indeed1 ,i might say1 with any lunar mountain4 ,this point was very well worked out some #dj years ago by ,professor ,piazzi ,smyth1 who placed on pictorial record his results of an examination and survey of the ,peak of ,teneriffe4 ,any person seeing side by side one of ,smyth's pictures of ,teneriffe and a picture of any average lunar crater would find great difficulty if the pictures were not labelled in determining which was which4 ,the one special feature of the ,moon1 which never fails to attract the attention of everybody who looks at our satellite for the first time through a telescope1 are the crater mountains1 which indeed constitute an immense majority of all the lunar mountains4 ,their outline almost always conforms1 more or less1 to that of the circle1 but when seen near either limb of the ,moon they often appear considerably oval simply because they are then seen considerably foreshortened4 ,in their normal form they exhibit a basin bounded by a ridge1 with a conical elevation in the centre of the basin1 the basin and the cone together being evidently the result of an uprush of gases breaking through the outer crust of the ,moon and carrying with them masses of molten lava4 ,this lava1 with perhaps the materials in fragments1 projected in the first instance up into the air1 fell back on to the ,moon forming first of all the outer edge of the basin1 and subsequently1 as the eruptive force became weakened1 the small central accumulation1 which took1 as it naturally would do1 a conical shape4 ,an experimental imitation of the process thus inferred was carried out some years ago by a ,french physicist1 ,bergeron1 who acted upon a very fusible mixture of metals known as ,wood's alloy by forcing through it a current of hot air4 ,the success of this experiment was complete1 and ,bergeron considered that his experiments1 taken as a whole1 were calculated to throw much light on the past history of the ,moon4 ,several observers at various times have fancied they have seen signs that the lunar mountain ,aristarchus was an active volcano even up to the present century2 but it admits of no doubt that this idea is altogether a misconception1 and that what they saw as a faint illumination of the summit of ,aristarchus was no more than an effect of earth-shine4 ,on the general question of volcanic action on the ,moon1 ,sir ,john ,herschel summed up as follows3--8,decisive marks of volcanic stratification arising from successive deposits of ejected matter1 and evident indications of lava currents1 streaming outwards in all directions1 may be clearly traced with powerful telescopes4 ,in ,lord ,rosse's magnificent ,reflector the flat bottom of the crater called ,albategnius is seen to be strewed with blocks not visible in inferior telescopes1 while the exterior ridge of another 7,aristillus7 is all hatched over with deep gulleys radiating towards its centre40 ,the valleys and clefts or rills visible on the ,moon's surface constitute another remarkable feature in the topography of our satellite4 ,the valleys1 properly so-called1 require no particular comment1 because they are just what their name implies--hollows often many miles long and several miles wide4 ,the clefts or rills1 however1 are more mysterious1 by reason of their great length and remarkable narrowness4 ,one is almost led to infer that they are naught else but cracks in the lunar crust1 the result of sudden cooling1 how caused is of course not known4 ,there is another lunar feature to be mentioned somewhat akin to the foregoing in appearance but apparently1 however1 owing its origin to a different cause4 ,i refer to the systems of bright streaks which1 especially at or near the time of full ,moon1 are seen to radiate from several of the largest craters1 and in particular from ,tycho1 ,copernicus1 ,kepler and ,aristarchus4 ,these bright streaks extend in many cases far beyond what may fairly be considered as the neighbourhood of the craters from which they start1 traversing distant mountains1 valleys and other craters in a way which renders it very difficult to assign an explanation of their origin4 ,there are #ac areas on the ,moon1 which used to be regarded as 8seas10 one of them1 however1 bearing the name of 8,oceanus ,procellarum10 the 8,ocean of ,storms02 but besides these there are several bays1 termed in ,latin ,sinus1 of which the most important is the ,sinus ,iridum or the 8,bay of ,rainbows10 a beautiful spot on the northern border of the ,mare ,imbrium1 and best seen when the ,moon is between #i and #aj days old4 ,the summits of the semi-circular range of rocks which enclose the bay are then strongly illuminated and a greenish shadow marks the valley at its base4 ,by the way1 it is worth mentioning that not a few of the lunar seas1 so-called1 seem to be pervaded by a greenish hue1 though no particular explanation of this fact is forthcoming4 ,much controversy has ranged round the question whether or not the ,moon has an atmosphere4 ,without doubt the preponderance of opinion is on the negative side1 though it must be admitted that some observers of eminence have suggested that there are indeed traces of an atmosphere to be had1 but that it is extremely attenuated and of no great extent1 otherwise it must render its presence discoverable by optical phenomena which it is certain cannot be detected4 ,a brief reference may here be made to a curious phenomenon sometimes seen in connection with occultations of stars by the ,moon4 ,premising that an 8occultation0 is the disappearance of a star behind the solid body of the ,moon by reason of the forward movement of the ,moon in her orbit1 it must be stated that though generally the ,moon extinguishes the star's light instantaneously1 yet this does not invariably happen1 for sometimes the star seems to hang upon the ,moon's limb as if reluctant to disappear4 ,no very clear or satisfactory explanation of this phenomenon has yet been given2 the existence of a lunar atmosphere would be an explanation1 and accordingly this anomalous appearance1 seen on occasions1 has been advanced in support of the theory that a lunar atmosphere does exist2 but1 nevertheless1 astronomers do not accept that idea4 ,any one desirous of carrying out a careful study of the ,moon's surface must be provided with a good map1 and for general purposes none is so convenient or accessible as ,webb's1 reduced from ,beer and ,mdler's ,mappa ,selenographica published in #ahcg1 of which another reproduction is given in ,lardner's ,astronomy4 ,those1 however1 who would desire to study the ,moon with the utmost attention to detail must provide themselves with ,schmidt's map published in #ahgh at the expense of the ,german ,government4 ,when it is stated that this map represents the ,moon on a circle #g feet in diameter1 the size and amount of detail in it will be readily understood4 ,special books on the ,moon furnishing numerous engravings and detailed descriptions have been written by ,carpenter and ,nasmyth 7jointly7 and by ,neison4 ,various attempts have been made to determine the amount of light reflected by the ,moon1 and also the question whether it yields any measurable amount of heat4 ,as regards the light of the full ,moon compared with that of the ,sun1 the estimates range from #a_/cjjjjj to #a_/hjjjjj1 a discrepancy not perhaps greater than might be expected under the circumstances of the case4 ,with respect to the heat possessed by1 or radiated from the ,moon's surface1 the conclusions of those who have attempted to deal with the matter are less consistent4 ,as regards the surface of the ,moon itself ,sir ,john ,herschel was of opinion that it is heated at least to the temperature of boiling water1 but that owing to the radiant heat having to pass through our atmosphere1 which acts as an obstacle1 it is no wonder that it should be difficult for us to become conscious of its existence4 ,in #ahdf ,melloni1 by concentrating the rays of the ,moon with a lens #c feet in diameter1 thought he detected a sensible elevation of temperature2 and in #ahef ,c4 ,p4 ,smyth at ,teneriffe1 but with inferior instrumental appliances1 arrived at the same conclusion4 ,though ,professor ,tyndall in #ahfa obtained a contrary result1 yet the most recent experiments by the younger ,earl of ,rosse1 ,professor ,langley1 and others1 all tend to show that the ,moon does really radiate a certain infinitesimally small amount of heat4 ,perhaps1 however1 it will be best to give ,langley's ideas as to this in his own words3--8,while we have found abundant evidence of heat from the ,moon1 every method we have tried1 or that has been tried by others1 for determining the character of this heat appears to us inconclusive2 and without questioning that the ,moon radiates heat earthward from its soil1 we have not yet found any experimental means of discriminating with such certainty between this and reflected heat that it is not open to misinterpretation40 ,it is obvious from the foregoing that we on the ,earth need not concern ourselves very much about lunar heat2 and ,i will only add that ,f4 ,w4 ,very1 by an ingenious endeavour to localise the ,moon's radiant heat1 has been able1 he thinks1 to establish the fact that on the part of the ,moon to which the ,sun is setting1 what he calls the heat-gradient 7using a phrase suggested by terrestrial meteorology7 appears to be steeper than on that part to which the ,sun is rising4 ,generally1 ,very's observations accord fairly with ,lord ,rosse's4 ,the ,moon revolves round the ,earth in #bg d4 #g h4 #dc m4 #aa s4 at a mean distance of #bcg1cjj miles1 in an orbit which is somewhat1 but not very1 eccentric4 ,its angular diameter at mean distance is #ca #e1 or1 say1 just over 4 ,the real diameter may be called #bafj miles4 ,a few words will probably be expected by the reader on the subject of lunar influences on the weather1 and generally2 this being a matter highly attractive to the popular mind4 ,the truth appears to lie1 as usual1 between two extremes of thought4 ,the ,moon1 of course1 is the main cause of the tides of the ,ocean1 and it is not entirely inconceivable that tidal changes imparted to vast masses of water may be either synchronous with1 or may in some way engender1 analogous movements in the ,earth's atmosphere2 though no distinct proofs of this1 as a determinate fact1 can be brought forward4 ,there is no doubt whatever that at or near the time of full ,moon1 evening clouds tend to disperse as the ,moon comes up to the meridian1 and that by the time the ,moon has reached the meridian a sky previously overcast will have become almost or quite clear4 ,sir ,john ,herschel has alluded to this by speaking of a 8tendency to disappearance of clouds under a full ,moon02 and he considers this 8fully entitled to rank as a meteorological fact40 ,he goes on1 not unnaturally1 to suggest the obvious thought that such dissipation of terrestrial clouds is due to the circumstance that1 assuming heat really comes by radiation from the ,moon 7and we have seen on a previous page the probability of this7 such radiant heat will be more potential if it falls on the ,earth perpendicularly1 as from a ,meridian ,moon1 than if it comes to us at any one locality from a ,moon low down in the observer's horizon1 and therefore has to pass through the denser strata of the ,earth's atmosphere and suffer material enfeeblement accordingly4 ,i am aware that ,mr4 ,ellis1 late of the ,royal ,observatory1 ,greenwich1 has sought to show by a seemingly powerful array of statistics that the idea now under consideration is unfounded1 but ,i consider that we have here only one more illustration of the familiar statement that you can prove anything you like by statistics4 ,i am firmly convinced1 as the result of more than #cj years' observation1 that terrestrial clouds do disperse under the circumstances stated4 ,sir ,j4 ,herschel added that his statement proceeded from his own observation 8made quite independently of any knowledge of such a tendency having been observed by others4 ,humboldt1 however1 in his ,personal ,narrative1 speaks of it as well known to the pilots and seamen of ,spanish ,america40 ,sir ,john ,herschel further remarked3--8,arago has shown from a comparison of rain1 registered as having fallen during a long period1 that a slight preponderance in respect of quantity falls near the #8new' ,moon over that which falls near the #8full4' ,this would be a natural and necessary consequence of a preponderance of a cloudless sky about the #8full1' and forms1 therefore1 part and parcel of the same meteorological fact40 ,bernadin has asserted it to be a fact that many thunderstorms occur about the period of 8new0 or 8full0 ,moon4 ,but what ,i want most to warn the reader against is that popular idea 7wonderfully wide-spread it must be admitted7 that at the epochs of what are called1 most illogically1 the ,moon's 8changes10 changes of weather may certainly be expected4 ,there is absolutely no foundation whatever for this1 and still more void of authority 7if such a phrase is admissible7 is a table of imaginary weather to be expected at changes of the ,moon1 often met with in books published half a century ago1 and still occasionally reprinted in third-rate almanacs1 and designated 8,dr4 ,herschel's ,weather ,table40 ,this precious production is not only devoid of authenticity as regards its name1 but may easily be seen to be fraudulent in its reputed facts any month in the year4 ,it would be beyond both my present available space and the legitimate objects of this work to attempt even an outline of the influences over things terrestrial ascribed to1 or associated1 rightly or wrongly1 with the ,moon1 and of which the word 8lunatic0 perhaps affords the most familiar exponent4 ,,chapter ,,vii4 ,,mars4 ,mars1 though considerably smaller than the ,earth1 is commonly regarded as the planet which1 taken all in all1 bears most resemblance to the ,earth1 though only one-fourth its size4 ,under circumstances which have already been briefly alluded to in ,chapter ,i41 ,mars exhibits from time to time a slight phase1 but nothing approaching in amount the phases presented by the two inferior planets1 ,mercury and ,venus4 ,when in opposition to the ,sun1 that is to say when on the meridian at midnight1 it has a truly circular disc2 but between opposition and its two positions of quadrature it is gibbous4 ,at the minimum phase1 which is at each quadrature1 ,e4 or ,w4 as the case may be1 the planet resembles the ,moon #c days from its 8full40 ,these phases are an indication that ,mars shines by the reflected light of the ,sun4 ,it is a remarkable tribute to ,galileo's powers of observation that with his trumpery telescope1 only a few inches long1 he should have been able to suspect the existence of a ,martial phase4 ,writing to a friend in #afaj he says3--8,i dare not affirm that ,i can observe the phases of ,mars2 however1 if ,i mistake not1 ,i think ,i already perceive that he is not perfectly round40 ,illustration3 ,fig4 #ab4--;,four views of ,mars differing #ij in longitude 7,barnard74 ,the period in which ,mars performs its journey round the ,sun 7called the sidereal period7 is about #fhg days2 but owing to the ,earth's motion we are more concerned with what is called the planet's synodical period of #ghj days than with its sidereal period of #fhg days4 ,the synodical period is the interval between two successive conjunctions or oppositions of the planet as regards the ,earth1 and #ghj days being twice #cfe and #ej days over1 it follows that we have an opportunity of seeing the planet at its best about every #b years2 and this is one of the reasons why ,mars has been so much and so thoroughly studied as regards its physical appearance4 ,of course ,mars is not equally well seen every #b years1 because it may so happen at a given opposition that it may be at its nearest to the ,sun 7perihelion71 and the ,earth at its farthest from the ,sun 7aphelion71 in which case the actual distance between the two bodies will be the greatest possible4 ,what is therefore wanted is for the planet to be nearest to the ,sun and nearest to the ,earth at the same time1 under which circumstances it shines with a brilliancy rivalling ,jupiter4 ,this favourable combination occurs once in #g synodical revolutions1 or about every #ae years4 ,the most favourable oppositions occur at the end of ,august1 and the least favourable at the end of ,february4 ,the next very favourable opposition will not occur until #aiji4 ,mars may approach to within about #ce millions of miles from the ,earth at a favourable opposition1 whilst under extreme circumstances the other way it may be no nearer than #fa millions of miles at opposition4 ,mars in opposition is a very conspicuous object in the ,heavens1 shining with a fiery red light which has always been regarded as a peculiar attribute of the planet1 so much so that its name1 or epithet1 in many languages conveys the idea of 8fiery0 or 8blazing40 ,it is recorded that in ,august #agai its brilliancy was such as to cause a panic amongst the public4 ,telescopically examined1 ,mars is always found to exhibit patches of shade of various sizes and shapes1 and1 on the whole1 fairly permanent from year to year4 ,during the last few years in particular these markings have been subjected to very careful scrutiny and measurement at the hands of numerous observers of skill and experience1 and armed in many cases with very powerful telescopes4 ,the conjoint effect of the observations obtained has been largely to augment our knowledge of the planet's geography1 or 7to use the proper term7 8areography40 ,before describing the minutest details recorded and pencilled by the best observers1 it will be best to speak of the leading general features which are within the grasp of comparatively small telescopes--say1 refractors of #f inches and reflectors of #ab inches in aperture4 ,the first thing which presents itself as very obvious on the disc of ,mars1 is the fact that certain portions are ruddy1 whilst others are greenish in hue4 ,it is generally assumed that the red areas represent land and the green areas water4 ,on this subject ,sir ,john ,herschel's remarks1 penned about half a century ago1 may be said still to stand good4 ,he ascribes the ruddy colour to 8an ochrey tinge in the general soil1 like what the red sandstone districts on the ,earth may possibly offer to the inhabitants of ,mars1 only more decided40 ,the propriety of this thought will be best appreciated by a reader who has travelled through parts of ,north ,gloucestershire1 and seen a succession of ploughed fields in that locality4 ,the deep red colour of the soil is in many places very conspicuous4 ,it has often been remarked that the redness of ,mars is much more noticeable with the naked eye than with a telescope2 and ,arago carried this idea one step further in suggesting that the higher the optical power the less the colour4 ,this1 however1 might naturally be expected4 ,the most prominent surface marking on ,mars is that known as the 8,kaiser ,sea10 sometimes called the 8,v-mark0 from its resemblance to that letter1 though a leg of mutton would be quite as good a simile4 ,east of the ,kaiser ,sea and a little north of the planet's equator is a well-defined dark streak known as 8,herschel ,,ii4 ,strait02 whilst on the west side is another shaded area which has been called 8,flammarion ,sea40 ,these three features are so very conspicuous1 that1 provided the hemisphere in which they are situated is fairly in front of the observer1 his telescope1 if it will show anything on ,mars1 will show these4 ,the white patches seen on certain occasions at ,mars's ,n4 pole and close to its ,s4 pole form another special feature of interest connected with this planet4 ,it admits of no doubt whatever that these are immense masses of snow and ice which undergo at stated intervals changes analogous to the changes which we know happen in the great fields of ice situated in the regions of the ,earth surrounding the ,earth's two poles4 ,not only do these white patches look like snow1 but if attention is paid to the changes they undergo and the epochs at which the changes take place there will be found abundant confirmation of this theory1 for these patches decrease in size when brought under the ,sun's influence on the approach of summer and increase again in size when the summer is over and winter draws near4 ,in the second half of #ahib the ,southern ,pole was in full view1 and during especially ,july and ,august the diminution of the snow area from week to week was very evident4 ,schiaparelli1 who observed it with great attention during that season1 noted at the commencement of the season that the snow reached at the first as far as latitude #gj and formed a polar cap some #abjj miles in diameter4 ,its subsequent decrease1 however1 was so marked that two or three months later the diameter of the snow patch had dwindled to no more than #ahj miles1 and became indeed still smaller at a later period4 ,the summer solstice on ,mars occurred on ,october #ac1 #ahib1 which was therefore the epoch of midsummer for ,mars's southern hemisphere4 ,whilst these changes were taking place in the southern hemisphere1 no doubt changes of the reverse character were going on in the northern hemisphere1 but they were not visible from the ,earth because the ,north ,pole was situated in that hemisphere of ,mars which was turned away from the ,earth4 ,in previous years1 however1 the ,north ,pole being turned towards the ,earth its snow was also seen to undergo the same sort of change2 in other words1 was seen to melt4 ,this happened1 and was seen in #ahhb1 #ahhd1 and #ahhf4 ,these observations of the alternate increase and decrease of the polar snow on ,mars may be viewed with telescopes of moderate power1 but of course it is more interesting and profitable to watch them with a large telescope4 ,the fact 7for it is an undoubted fact7 that the north polar snow is concentric with the planet's axis whilst the southern polar patch is eccentric to the extent of about #ahj miles from the southern pole is one which has not yet received a satisfactory explanation4 ,if both patches were eccentric so as to be exactly opposite to one another an explanation would be much more easy for we might say that the poles of rotation lay in one direction and the poles of cold in another4 ,i have spoken on a previous page of three specially conspicuous shadings of ,mars1 and other similar shadings to the number perhaps of a couple of dozen were generally recognised by astronomers 7having been mapped and named7 down to about the year #ahgg4 ,in that year the astronomical world was startled by the announcement that ,schiaparelli of ,milan1 an able and competent observer1 had discovered that those shaded areas which all previous astronomers had regarded as continents or vast tracts of land1 were in reality islands1 that is to say1 so far1 that the continents in question were cut up by innumerable channels intersecting one another at various angles4 ,when this discovery was announced1 and older observations and drawings came to be examined1 it was found1 or at any-rate thought1 that these so-called canals might be traced in drawings of earlier dates by ,dawes1 ,secchi1 and ,holden4 ,so much for #ahgg4 ,in ,december1 #ahha1 the planet was again in opposition1 but farther off in distance1 and therefore smaller in size than in #ahgg4 ,it was1 however1 higher up in the ,heavens as seen at ,milan and the weather appears to have been more favourable4 ,in these altered circumstances ,schiaparelli again saw his canals1 but this time they were in at least as many as twenty instances seen in duplicate2 that is to say1 a twin canal was seen to run parallel to the original one at a distance of from #bjj to #djj miles1 as the case might be4 ,the existence of not only single canals but of twin canals seems an established fact1 for ,schiaparelli's drawings and descriptions have been confirmed by competent testimony2 but explanation is nowhere2 especially in view of ,schiaparelli's own idea that the duplication of his canals is perhaps not a permanent feature but a periodical phenomenon depending on1 or connected in some way with1 ,mars's seasons4 ,illustration3 ,fig4 #ac4--,mars1 ,august #bg1 #ahib 7,guiot74 ,several points stand out clearly established by the observations of ,mars during the opposition of #ahid1 especially the correctness of ,schiaparelli's discoveries and maps4 ,most of the canals originally seen by him were again seen1 and thus their existence was confirmed1 whilst new ones were also noticed4 ,many of these canals were double4 ,the great extent of the ,s4 ,polar cap and its rapid disappearance as ,mars's summer approached was also a special feature of the observations of #ahid4 ,it dwindled until it became almost invisible1 or at best showed as a tiny speck4 ,it is thought by some observers that as the ,polar cap melts1 the water collects round the ,pole1 and thence flows over the planet's surface1 giving rise to the phenomenon of canals1 and that this is the way the planet's surface is irrigated4 ,it may here be remarked that the word 8canal10 which has been given to these dark streaks crossing and cutting up the large areas of land in ,mars1 is an unfortunate one1 suggesting as it does artificial agency4 ,but these ,martial canals are probably1 especially the largest1 a great many miles in width and hundreds of miles in length1 though some are smaller2 and they are probably nature's method of distributing over the continents and lands of ,mars the water which collects round the ,pole during the rapid melting of the ,polar snows4 ,the idea of the presence of cloud or mist on ,mars also received strong confirmation in #ahid4 ,large portions of the planet's disc were found to be hidden from view4 8,herschel ,i4 ,continent0 and the 8,maraldi ,sea0 7both well-known markings on ,mars1 readily visible with small telescopes7 were at times quite obscured by cloud4 ,indeed1 the ,maraldi ,sea was occasionally quite blotted out3 other well-known markings were also either blotted out or only faintly seen4 ,these facts seem almost to prove conclusively the existence of cloud and vapour in ,mars1 especially as some of these markings subsequently again assumed their ordinary form and colour4 ,bright projections too were seen at times on the terminator of ,mars1 giving rise to the belief that there are high mountains on the planet1 though some observers regarded these projections as high clouds powerfully reflecting the ,sun's light4 ,mars rotates on its axis in #bd;h4 #cgm4 #bbs41 a period so nearly coincident with the period of the ,earth's rotation as greatly to facilitate the mapping of ,mars's features by work continued from day to day by observers who have the necessary instrumental means and artistic skill in handling the pencil4 ,mars has an atmosphere which may be said to be no more than moderately dense2 that is to say much less dense than the ,earth's atmosphere4 ,of course the existence of snow1 which has been taken for granted on a previous page1 carries with it the existence of water and aqueous vapour--a fact capable of independent spectroscopic proof4 ,the inclination of ,mars's axis to the ecliptic has not been ascertained with all desirable certainty1 but if ,sir ,w4 ,herschel's estimate that the obliquity on ,mars is #bh 7the ,earth's obliquity being #bc7 is correct1 it is evident that there must be a very close similarity between the seasons of the ,earth and the seasons of ,mars1 thereby furnishing another link of proof to support the statement made at the commencement of this chapter that1 taken all in all1 ,mars is the planet which bears most resemblance to the ,earth4 ,the apparent absence of satellites in the case of ,mars was long a matter of regret to astronomers2 they seemed to think that such a planet ought to have at least one companion4 ,at last1 in #ahhg1 two were found by ,hall at ,washington1 ,u4 ,s41 using a very fine refractor of #bf inches aperture4 ,these satellites1 which have been named ,phobos and ,deimos1 are1 however1 very small1 for ,phobos at its best only resembles a star of mag4 #aa1 whilst ,deimos is no brighter than a star of mag4 #ac2 from this it will be understood that only very large telescopes will show either of them4 ,phobos revolves round ,mars in #g hours at a distance of about #fjjj miles1 whilst ,deimos revolves in #cj hours at a distance of about #ae1jjj miles4 ,it has been thought that neither of them can be more than about #f or #g miles in diameter1 and therefore that they can not afford much light to their primary4 ,mars revolves round the ,sun in #fhf;d4 #bc;h4 #cjm41 at a mean distance of #ada million of miles1 which the eccentricity of its orbit may increase to #aed millions or diminish to #abh millions4 ,the planet's apparent diameter varies between #d in conjunction and #cj in opposition4 ,owing to the great eccentricity of the orbit the planet's apparent diameter as seen from the ,earth varies very much at different oppositions4 ,the real diameter is rather more than #djjj miles4 ,,chapter ,,viii4 ,,the ,,minor ,,planets4 ,in #aggb a ,german astronomer named ,bode1 of ,berlin1 drew attention to certain curious numerical relations subsisting between the distances of the various planets4 ,this 8law10 as it has been sometimes called1 usually bears ,bode's name1 though it was not he but ,j4 ,d4 ,titius of ,wittemberg who really first discovered it4 ,take the numbers-- #j1 #c1 #f1 #ab1 #bd1 #dh1 #if1 #aib1 #chd2 each of which 7the second excepted7 is double the preceding2 adding to each of these numbers #d we obtain-- #d1 #g1 #aj1 #af1 #bh1 #eb1 #ajj1 #aif1 #chh2 which numbers approximately represent the distances of the planets from the sun expressed in radii of the ,earth's orbit4 ,a little table will make the matter more clear4 ,planets4 ,distance3 ,bode's ,law4 ,true distance from ,sun4 ,mercury #d #c4i ,venus #g #g4b ,earth #aj #aj4j ,mars #af #ae4b ,ceres #bh #bg4g ,jupiter #eb #eb4j ,saturn #ajj #ie4d ,uranus #aif #aia4h ,neptune #chh #cjj4j ,bode having examined these relations and noticing the void between #af and #eb 7,ceres and the other minor planets1 and ,uranus and ,neptune also1 being then unknown7 ventured to predict the discovery of new planets1 and this idea stimulated him to organise a little company of astronomers to hunt for new planets4 ,before1 however1 this scheme was got into working order1 ,piazzi1 director of the ,observatory at ,palermo1 on ,january #a1 #ahja1 noted an #hth magnitude star in ,taurus1 which on the next and succeeding nights he saw again1 and found had moved4 ,he observed the strange object for #f weeks1 when illness interrupted him4 ,however he wrote letters announcing what he had seen1 one of them to ,bode himself2 but this letter1 though dated ,jan4 #bd1 did not reach ,bode at ,berlin1 till ,march #bj--;a striking illustration of the state of the ,postal service on the ,continent less than #ajj years ago4 ,the new body1 at first assumed to be a tailless comet1 was eventually recognised to be a new planet2 and the name of ,ceres1 the tutelary goddess of ,sicily1 was at ,piazzi's instance bestowed upon it4 ,looking for ,ceres in ,march1 #ahjb1 ,olbers at ,bremen1 came upon another new planet1 which was afterwards named ,pallas4 ,at first he thought he had got hold of a new variable star1 but two hours sufficed to show that the object under notice was in motion4 ,the two new bodies were found to be so much alike in size and appearance1 and in their orbits1 that ,olbers suggested both were but fragments of some larger body which had been shattered by some great convulsion of nature4 ,the idea was a daring one1 and it was an attractive one1 though now regarded as untenable4 ,however it served the purpose of stimulating research1 and the discovery of ,pallas was followed by that of ,juno1 by ,harding1 at ,lilienthal #ahjd2 and of ,vesta1 by ,olbers1 at ,bremen in #ahjg4 ,the organised search for minor planets was relinquished in #ahaf1 presumably because no more planets seemed to be forthcoming1 and it does not appear that any further attempts were made by anybody till about #ahcj1 when a ,prussian amateur1 named ,hencke of ,driessen1 profiting by the publication of some new star maps put forth by the ,berlin ,academy1 commenced a methodical search for small planets4 ,these ,berlin maps1 one for each hour of ,r4 ,a41 were only completed in #ahei1 and1 therefore1 ,hencke had only a small number of them at his command during the early years of his labours4 ,still it is strange that #ae years elapsed before his zeal and perseverance were rewarded1 his first discovery1 the planet ,astra1 not taking place till ,december #ahde4 ,once however the ice was broken new planets followed with considerable rapidity1 and beginning with #ahdg1 no year has elapsed without several or many having been found4 ,during the last decade the number detected annually has been very great--sometimes as many as #bj in a year1 but this has been the result of photography being brought to bear on the work4 ,it is obvious that if a photograph of a given field taken on any one day is compared with a photograph taken a few days earlier or later1 and any of the objects photographed have moved1 their change of place will soon be noticed and will be a distinct proof of their planetary nature4 ,it seems quite certain that all the larger of these planets have now been found1 for the average brilliancy 7and this no doubt means the average size7 of those recently discovered has been steadily diminishing year by year1 and it looks as if the limit of visibility will soon be reached1 if it has not been reached already4 ,the three largest of these bodies1 in order of size1 have generally been thought to be ,vesta1 ,ceres1 and ,pallas2 but ,barnard1 from observations made in #ahid1 concluded that ,ceres is #ebj miles in diameter2 ,pallas1 #cjd miles2 and ,vesta1 #bda miles4 ,as to all the rest of the minor planets1 excepting ,juno1 ,hornstein is of opinion that those having a greater diameter than #be geographical miles are few in number1 and that the majority of them are no larger than from #e to #ae miles in diameter4 ,from what has gone before the reader will readily infer that these minor planets are of no sort of interest to the casual amateur who dabbles in ,astronomy2 and indeed that they are of very little interest to anybody4 ,with a few general statistics1 therefore1 this chapter may be concluded4 ,the total number of minor planets now known nearly reaches #ejj1 and every year increases the list2 but not1 however1 at as rapid a rate as was once the case1 because the ,german mathematicians1 who alone latterly have been willing to trouble themselves with the computation of the orbits1 are understood to have announced that they are no longer able to keep pace with the discoveries made4 ,those who care to investigate in detail the circumstances of these planets will find great extremes in the nature of the orbits4 ,whilst the planet nearest to the ,sun has a period of only #c years1 the most distant occupies nearly #i years in performing its journey round the ,sun4 ,so1 also1 there are great differences in the eccentricities of the orbits and in their inclinations to the ecliptic4 ,whilst one planet revolves almost in the plane of the ecliptic1 another 7,pallas7 has an orbit which is inclined no less than #cd to the ecliptic4 ,one word1 in conclusion1 as to the names applied to these bodies4 ,at the outset the names given were1 without exception1 chosen from the mythologies of ancient ,greece and ,rome1 but1 latterly1 the most fantastic and ridiculous names have in many cases been selected1 names which in too many instances have served no other purpose than that of displaying the national or personal vanity of the astronomers who applied them to the several planets4 ,the ,french are great offenders in this matter4 ,,chapter ,,ix4 ,,jupiter4 ,the planet ,jupiter occupies1 in one sense1 the first position in the planetary world1 it being the largest of all the planets4 ,moreover1 with the exception of ,venus1 it is the brightest of the planets4 ,as with ,mars1 and for the like reason1 ,jupiter1 when in the positions known as the ,quadratures 7or near thereto71 exhibits a slight phase1 but owing to the far greater distance from the ,sun of ,jupiter1 compared with ,mars1 the deviation of the illuminated surface from that of a complete circle is very small2 it is1 however1 perceptible at or near the time of quadrature1 a slight shading off of the limb farthest from the ,sun being traceable4 ,jupiter is noteworthy on account of two features1 both of them more or less familiar1 at least by name1 to most people--its belts and its satellites1--both of which will be described in due course4 ,the belts are dusky streaks1 which vary from time to time both in breadth and number3 most commonly two broad belts will be seen with two or three narrower ones on either side2 but sometimes all are rather narrow1 and their narrowness is made up for by an increase in their number4 ,illustration3 ,fig4 #ad4--;,jupiter1 ,november #bg1 #aheg 7,dawes74 ,under all circumstances they lie practically parallel1 or nearly so1 to the planet's equator4 ,it is generally thought that the planet1 whatever may be its actual structure or constitution1 is surrounded by a dense cloudy envelope1 and that the shaded streaks which we call belts are rifts in this atmosphere1 which expose to view the solid body of the planet underneath4 ,whether1 however1 the term 8solid body0 is an accurate one to be used in this connection is thought by some to be open to doubt4 ,the laws which regulate the existence of these belts are quite unknown2 indeed it seems doubtful whether any laws exist at all1 for the belts at one time appear to undergo constant change1 whilst at another time they remain almost unchanged for several months4 ,it has been suggested that when the changes are rapid it must be presumed that great atmospheric storms are to be considered as in progress1 and possibly this may be the true explanation4 ,belts are commonly non-existent immediately under the equator2 whilst north and south of this void space it most usually happens that there is one broad belt and several narrower ones in each hemisphere4 ,at each pole the planet's brightness is less than the average brightness1 but it cannot exactly be said that this is due to the existence there of belts properly so called4 ,it was formerly considered that no tinges of colour could be traced on ,jupiter except a silvery gray of different degrees of intensity2 but during the last thirty years there can be no doubt that shades of brown1 red1 and orange1 of no great depth1 but yet quite definite have been traceable4 ,many observers concur in this opinion4 ,whether this detection of colour is due to an absolute development of colour during the period in question2 or whether its detection is merely the result of more careful scrutiny with better instruments is a matter as to which the evidence is not clear4 ,though the general position of the belts is such that they are parallel to the planet's equator1 yet there are sometimes exceptions to this rule1 for in a few very rare instances a streak in the nature of a narrow belt has been seen1 inclined to the equator at a decided angle1 perhaps #bj or even more4 ,it occasionally happens that spots are seen on ,jupiter's belts4 ,sometimes these remain visible for a considerable period4 ,they are either dark or luminous1 and their origin is unknown4 ,besides these casual spots1 which are always small in size1 there was visible during many years following #ahgh a very remarkable and conspicuous large spot1 strongly red in colour for several years1 though it afterwards became much fainter4 ,this spot exhibited an oval outline and was about #bg1jjj miles long and #hjjj miles broad4 ,for about #d years it maintained its intense red colour and its shape almost unaltered2 but after #ahhb1 the shape remaining1 the colour sensibly faded4 ,the observations which were made on this spot during #ahhf by ,professor ,hough at ,chicago1 ,u4 ,s41 with an #ah-;inch refractor1 led him to the opinion that the persistence of the red spot for so many years rendered untenable the generally accepted theory that the phenomena seen on the surface of the planet are due to atmospheric causes4 ,some astronomers have thought that a relationship subsists between the spots on the ,sun and the spots on ,jupiter4 ,there certainly seems an apparent identity in point of time between the two classes of spots1 and on the assumption that the spots on ,jupiter are indicative of disturbances on the planet1 ,ranyard broached the idea that both classes of phenomena are dependent on some extraneous cosmical change2 and are not related as cause and effect4 ,browning suggested many years ago that the red colour of the belts is a periodical phenomenon coinciding with the epoch of the greatest display of sunspots1 but this thought does not appear to have been followed up by any one4 ,spots on ,jupiter seem to have been first recorded by ,robert ,hooke in #affd4 ,in the following year ,cassini saw a spot which he found to be in motion1 and by following it attentively he inferred that the planet rotated on its axis in #i;h4 #efm4 ,it is a remarkable illustration of the great care bestowed by ,cassini on his astronomical work that the best modern determinations of ,jupiter's rotation-period differ from ,cassini's estimate by only half a minute4 ,bearing in mind the enormous size of ,jupiter compared with the ,earth1 whilst its period of rotation is considerably less than half the ,earth's1 it will be at once seen that the velocity of matter at the planet's equator is immensely great--#dff miles per minute against the ,earth's #ag miles per minute4 ,one result of this is the great intensity of the centrifugal force at the equator1 and likewise the greatness of the compression of the planet's body at the poles4 ,hind has suggested that the great velocity which thus evidently exists may have the effect1 by reason of the development of the heat which it gives rise to1 of compensating the planet for the small amount of heat which owing to its distance it receives from the ,sun4 ,on favourable occasions the brilliancy of ,jupiter is very considerable2 so much so that it rivals ,venus and ,mars4 ,and besides this1 there appears to be something special in the nature of ,jupiter's surface1 for not only does it seem to radiate a much larger proportion of the solar light which falls on it than do the planets generally1 but some observers have expressed the opinion that it possesses inherent light of its own4 ,speculations1 however1 such as this must always be received with reserve1 because of the evident difficulty of making sure of the facts on which they must be based4 ,one thing1 however1 seems less open to doubt4 ,bearing in mind the small amount of heat which reaches ,jupiter from the ,sun1 there is reason to infer that the clouds which certainly exist on ,jupiter must owe their origin to the influence of some other heat than solar heat2 in other words that ,jupiter possesses sources of heat within itself4 ,jupiter has satellites1 #e in number4 ,the discovery of four of these1 was one of the first fruits of the invention of the telescope1 for they were found by ,galileo in ,january1 #afaj4 ,the #eth satellite is so small that it escaped notice until as recently as #ahib1 having been discovered on ,september #i of that year by ,professor ,barnard1 with the great ,lick telescope in ,california4 ,it is1 however1 so minute that one can count on one's fingers the telescopes capable of showing it4 ,the four old satellites of ,jupiter shine as stars of about the #gth magnitude2 in other words1 they are sufficiently bright to be visible with telescopes however small3 indeed several instances are on record of persons gifted with very good sight1 having been able to see them with the naked eye4 ,for the study of their physical appearance very powerful optical assistance is necessary1 but their movements are so rapid1 and the phenomena which result from those movements are so interesting1 that these bodies may be considered to occupy the first place in the stock-in-trade of every amateur astronomer1 who lays himself out for planet-gazing1 with the object of profiting himself or his friends4 ,the phenomena here alluded to are known as eclipses1 transits1 and occultations4 ,the four old satellites do not bear any names1 but are numbered from the innermost outwards1 and are always alluded to by their numbers as ,i1 ,,ii1 ,,iii and ,,iv4 ,an eclipse of a ,jovian satellite is identical in principle with an eclipse of the ,moon2 that is to say1 just as an eclipse of the ,moon happens when the ,moon passes into and is lost in the ,earth's shadow1 so an eclipse of a ,jovian satellite happens when such satellite becomes lost in the shadow cast by the planet into space4 ,the ,ist ,i,ind and ,i,i,ird satellites in consequence of the smallness of the inclination of their orbits1 undergo eclipse once in every revolution round their primary1 but the ,i,vth is less often eclipsed1 owing to the joint effect of its considerable orbital inclination1 and of the distance to which it recedes from its primary4 ,an occultation of a ,jovian satellite is akin in principle to an occultation of a star by the ,moon4 ,as the ,moon moving forwards suddenly covers a star1 so the planet1 on occasions1 suddenly covers one of its satellites4 ,if the satellite in question is the ,i,vth1 its disappearance behind the planet and its reappearance from behind the planet will both be visible in due succession4 ,this is often true also of the ,i,i,ird satellite1 but for reasons connected with the proximity to their primary of the ,ist and ,i,ind satellites1 only their disappearance or reappearance 7not both7 can1 as a rule1 be observed on the same occasion4 ,the most interesting1 by far1 however1 of the phenomena connected with ,jupiter's satellites are their transits in front of1 that is across1 the visible disc of the planet4 ,though these transits are of frequent occurrence1 yet they are always interesting because of the diverse appearances which the satellites exhibit at different times1 and which cannot be said to be in accordance with any recognised laws4 ,moreover1 in observing the transit of a satellite1 we may often see the black shadow cast by the satellite on the planet's disc2 and this shadow will sometimes precede and sometimes follow the satellite itself4 ,from the fact that the satellite generally appears as a bright spot on a bright background whilst the shadow is black1 or blackish1 an inexperienced observer is apt to look at the shadow and think he is seeing the satellite4 ,jupiter revolves round the ,sun in not quite #ab years at a mean distance of #dhc millions of miles4 ,its apparent diameter varies between #ej and #cj according to its position with respect to the ,earth4 ,its true diameter is about #hh1jjj miles4 ,owing to its large size and rapid rotation1 as has already been mentioned1 ,jupiter is very much flattened at the poles4 ,the amount of this 7the polar 8compression0 as it is called7 is about #a_/af4 ,,chapter ,x4 ,,saturn4 ,next beyond ,jupiter1 proceeding outwards from the ,sun1 we reach the planet ,saturn1 which beyond any doubt is the most beautiful and most interesting of all the planets4 ,nobody who has ever had a fairly good chance of seeing it can have the least doubt that this is the case4 ,briefly stated the three main features which constitute its claims are3--7#a7 ,its belts1 7#b7 its rings1 7#c7 its satellites4 ,the belts of ,saturn resemble generally those of ,jupiter1 but they are more faint and less changeable4 ,their physical cause1 however1 may be assumed to be the same4 ,taking the planet as a whole1 it may be said that its ordinary colour is yellowish white1 the belts inclining to grayish white2 though the dark belts have often been thought to exhibit a greenish hue4 ,lassell considered that the south pole is generally darker than the north pole and more blue in tinge4 ,illustration3 ,fig4 #ae4--,saturn1 ,jan4 #bf1 #ahhi 7,antoniadi74 ,there is one important particular in which the belts of ,saturn differ from those of ,jupiter4 ,jupiter's belts are straight1 whereas ,saturn's are sensibly curved4 ,supposing1 as is probable1 that ,saturn's belts are parallel to the planet's equator1 then we must assume that the plane of this equator makes a rather considerable angle with the ecliptic4 ,spots on ,saturn are very rare4 ,whether ,saturn has an atmosphere seems uncertain1 or perhaps it may be said that one has not been proved to exist but may exist4 ,the question of polar snow is also uncertain1 but ,sir ,w4 ,herschel thought he could trace changes of hue at the poles which might be due to the melting of snow4 ,it is usual to speak of the planet itself under the name of the 8,ball0 when it is not a question of referring to the whole ,saturnian system collectively4 ,in consequence of its distance from the ,sun1 ,saturn undergoes no equivalent to a phase2 or to be more exact1 no phase can be detected1 though theoretically when the planet is in quadrature the disc must undergo an infinitesimally small loss of light4 ,though the point has now-a-days no scientific importance1 it may perhaps be desirable just to make a brief allusion to ,sir ,w4 ,herschel's curious theory that ,saturn was seen by him to be compressed not only at the poles but at the equator1 so that it resembled a parallelogram with the corners rounded off4 ,it is difficult to imagine what could have given rise to this strange idea1 though1 of course1 ,herschel's good faith in advancing it cannot be called in question4 ,i refer to it because it will be found mentioned in so many books on astronomy1 often under the name of the 8square-shouldered0 figure of ,saturn4 ,as a theory it may be regarded as quite exploded in consequence of accurate measures by ,bessel1 ,main and others having conclusively shown that the form of the ball does not depart from that of a regular spheroid4 ,in referring to ,saturn generally1 we speak of its ring in the singular number1 but1 in point of fact1 there are several rings--three in particular4 ,the principal bright ring is really double1 and within the innermost bright ring there is a dusky one1 perfect as a ring1 but not luminous as the outer rings are4 ,by way of distinguishing one ring from another1 it is usual to adopt ,struve's nomenclature1 whereby the outermost bright ring is called ,a1 the inner bright ring ,b1 and the dusky ring ,c4 ,a good engraving will convey more fully and more clearly an idea of what the ,saturnian system consists of than the fullest verbal description will do4 7,see ,frontispiece47 ,to the earliest astronomers who possessed telescopes1 ,saturn proved a great puzzle1 because it seemed to undergo changes of shape which were quite inexplicable on any principles then known4 ,galileo1 when first he saw it1 thought it presented an oval outline which might be due to a central planet having a smaller planet on each side of it1 and accordingly he announced to his friend1 ,kepler1 that the most distant planet was tergeminum or tri-form4 ,but greater magnifying power led him to arrive at the conclusion that the planet was not a triple combination of spheres1 but one body1 either oblong or oval in outline4 ,this conclusion1 however1 was soon found to be untenable1 because the two 7supposed7 tributary bodies gradually decreased in size until they entirely disappeared4 ,galileo writing to his friend1 ,welser1 in ,december #afab1 thus expressed himself3-- 8,what is to be said concerning so strange a metamorphosis8 ,are the two lesser stars consumed after the manner of the solar spots8 ,have they vanished or suddenly fled8 ,has ,saturn1 perhaps1 devoured his own children8 ,or were the appearances indeed illusion or fraud1 with which the glasses have so long deceived me1 as well as many others to whom ,i have shewn them8 ,now1 perhaps1 is the time come to revive the well-nigh withered hopes of those who1 guided by more profound contemplations1 have discovered the fallacy of the new observations1 and demonstrated the utter impossibility of their existence4 ,i do not know what to say in a case so surprising1 so unlooked for1 and so novel4 ,the shortness of the time1 the unexpected nature of the event1 the weakness of my understanding1 and the fear of being mistaken have greatly confounded me40 ,illustration3 ,fig4 #af4--;,general view of the ,phases of ,saturn's ,rings4 ,galileo seems to have become so out of heart in consequence of the difficulty of determining what these changes really meant1 that he gave up altogether observing ,saturn4 ,in the course of time1 but by very gradual steps1 astronomers came to realise what the facts were4 ,the next idea that was broached1 was that the planet consisted of simply one central ball1 and that the excrescences which ,galileo had been puzzled by were merely handles as they were called1 7ans7 projecting like the handles1 say of a soup tureen1 though why they should vary in size at stated intervals remained as great a mystery as ever4 ,it was not until about #afef that the true explanation was arrived at by a ,dutchman1 named ,christopher ,huygens4 ,it was the fashion in those days for scientific men to intimate to the world discoveries which they had made by resort to mysterious anagrams1 which served in some degree the purpose which in the present day is served by the law regulating copyright or patent rights4 ,accordingly ,huygens published the following singular memorandum3-- aaaaaaa cccc d eeeee g h i iiiiii llll mm nnnnnnnnn oo oo pp q rr s ttttt uuuuu4 ,these letters arranged in their proper order furnish the following ,latin sentence3-- ,annulo cingitur1 tenui1 plano1 nusquam cohaerente1 ad eclipticam inclinato2 which ,latin sentence becomes in the ,english tongue3-- 8,the planet is surrounded by a slender flat ring inclined to the ecliptic1 but which nowhere touches the body of the planet40 ,huygen's discovery was not a mere piece of guesswork1 for he spent several years carefully observing the alterations of form which ,saturn underwent1 before he came to the conclusion that it was only the existence of a ring surrounding the planet which would explain the various observed changes4 ,it was by way of guarding himself from being robbed of the fruits of his discovery whilst he was accumulating the necessary proof of its truth1 that he buried his thoughts in the logogriph or anagram just quoted4 ,having arrived at the conclusion which he did1 he thought himself sufficiently sure of his facts to predict that in ,july or ,august #afga1 the planet would again appear round1 the ring becoming invisible4 ,this surmise proved practically correct1 in so far1 that in ,may #afga1 or within #b months of the time predicted by ,huygens1 ,cassini saw the planet as a simple ball unaccompanied by any ring4 ,this is a convenient place at which to offer a brief explanation of the changes of appearance as regards the ball and rings which ,saturn undergoes4 ,these changes depend jointly on ,saturn's motion in its orbit round the ,sun1 and on the corresponding motion of the ,earth in its orbit4 ,neither ,saturn nor the ,earth revolve round the ,sun exactly in the ecliptic1 and this want of coincidence results in the fact1 that twice in the #bi years occupied by ,saturn in journeying round the ,sun1 the plane of its ring is seen edgeways by us on the ,earth2 whilst at two other periods intermediate but equi-distant the ring is seen opened out to the widest possible extent2 that is1 so far as we on the ,earth can by any possibility have a chance of seeing it4 ,illustration3 ,fig4 #ag4--,phases of ,saturn's ,rings at specified dates4 ,the appearances presented by the rings when undergoing the transformations to which they are subject1 will be readily understood by an inspection of the annexed engravings4 ,fig4 #ag1 indicates the actual appearances in the years specified1 and these years may be considered as carried forward and brought up to date by substituting #ahgg for #ahdh1 #ahhe for #ahee1 #ahia for #ahfb1 and #ahih for #ahfi4 ,adverting to fig4 #af1 it will suffice to remark that the two central phases of the rings1 opened wide1 are to be deemed co-related1 or indeed identical in a geometrical sense 7so to speak7 the difference being that one of them is to be deemed to show the northern side of the ring 7which is now in view and will continue in view till #aijg7 whilst the other represents the southern side1 which was in view from #ahgg till #ahia4 ,the foregoing is a brief statement of the general principle involved in the changes which take place1 but the motions of the two planets introduce certain technical complications into the details which would be seen by an observer using a large telescope2 with these1 however1 the ordinary reader will not care to concern himself1 and need not do so4 ,a great deal might be said with respect to the rings treated descriptively4 ,i will now mention a few matters of general interest4 ,huygens regarded the appendage to ,saturn1 whose existence he established1 to be a single ring1 but as far back as #afge1 ,cassini determined that ,huygen's single ring was really made up of two1 one lying inside the other4 ,cassini in this conclusion outstepped not only all the observers of his own century1 but those of the succeeding century1 for ,sir ,w4 ,herschel even #ajj years after ,cassini1 was for a long time unable to satisfy himself1 even with his superior telescopes1 that the black streaks seen in the ring by ,cassini1 and regarded by him as indicative of a severance of the ring into two parts1 really implied a severance4 ,it is now1 however1 accepted as a fact that not only are the rings which are known as ,a and ,b absolutely distinct1 but that ,a also is itself certainly duplex1 that is1 that it certainly consists of two independent rings4 ,in addition to this many competent observers armed with powerful telescopes have obtained traces of other sub-divisions1 both in ,a and ,b2 and though there is some want of harmony in the details1 as stated by the different observers1 yet undoubtedly we must speak of ,saturn's rings collectively as forming a multiple system4 ,what the rings are is a highly debatable point1 but the preponderating idea is that they are not what they appear to be1 namely solid masses of matter1 but are swarms of independent fragments of matter4 ,yet 8fragment0 is not the best word to use1 because it implies that something has been broken up to make the fragments4 ,rather1 perhaps1 we should say with ,professor ,young1 that the rings are 8composed of a swarm of separate particles1 each a little independent moon pursuing its own path around the planet4 ,the idea was suggested long ago1 by ,j4 ,cassini in #agae1 and by ,wright in #agej1 but was lost sight of until ,bond revived it in connection with his discovery of the dusky ring4 ,professor ,benjamin ,pierce soon afterwards demonstrated that the rings could not be continuous solids2 and ,clerk ,maxwell finally showed that they can be neither solid nor liquid sheets1 but that all the known conditions would be answered by supposing them to consist of a flock of separate and independent bodies1 moving in orbits nearly circular1 and in one plane--in fact1 a swarm of meteors40 ,the thickness of the rings seen edgeways has been variously estimated4 ,sir ,j4 ,herschel suggested #bej miles as an outside limit1 which ,g4 ,p4 ,bond reduced to #dj miles4 ,it is generally considered1 however1 that #ajj miles is probably not far from the truth4 ,young has pointed out that if a model of them were constructed on the scale of #a inch to represent #aj1jjj miles1 so that the outer ring of such a model would be nearly #ag inches in diameter1 then the thickness of the ring would be represented by that of an ordinary sheet of writing paper4 ,considered as a system1 the rings are distinctly more luminous than the planet1 and of the two bright rings1 the inner one is brighter than the outer one2 and the inner one is less bright at its inner edge than elsewhere4 ,it is also to be noticed that when seen edgeways just about the time of the ,saturnian equinoxes1 when the ,sun is shifting over from one side of the ring to the other1 and the ring is dwindling down to a narrow streak1 its edges 7forming the ans as they are termed7 do not disappear and reappear at the same time1 and are not always of the same apparent extent4 ,one ansa1 indeed1 is sometimes visible without the other1 and most commonly it is the ,eastern one that is missing4 ,to what causes these various peculiarities are due is unknown4 ,many physical peculiarities have been either noticed or suspected with reference to the bright rings4 ,for instance1 on comparing one with another1 some persons have thought that their surfaces are convex1 and that they do not lie in the same plane4 ,the existence of mountains on their surface has more than once been suspected4 ,again1 it has been fancied that they are surrounded by an extensive atmosphere4 ,it seems hardly likely that the rings would have an atmosphere and not the ball 7or vice vers71 and1 therefore1 no wonder that we have no observations which countenance the idea that the ball does really possess an atmosphere4 ,this1 indeed1 seems to flow from ,trouvelot's observation1 that the ball is less luminous at its circumference than at its centre4 ,the circumstances of ring ,c1 otherwise called the 8,dusky0 or 8,crape0 ring are as curious historically1 as they are mysterious physically4 ,in #ahch1 ,galle of ,breslau1 noticed what he thought to be a gradual shading off of the interior bright ring towards the ball4 ,though he published a statement of what he saw1 the matter seems to have attracted little or no notice4 ,in #ahej1 ,g4 ,p4 ,bond in ,america perceived something luminous between the ring and the ball1 and after repeated observations in concert with his father1 came to the conclusion that the luminous appearance which he saw1 was neither less nor more than an independent and imperfectly illuminated ring lying within the old rings and concentric with them4 ,before1 however1 tidings of ,bond's discovery reached ,england1 but a few days after the discovery in point of actual date1 ,dawes suddenly noticed one evening as ,bond had done1 a luminous shading within the bright rings1 which he was not long in finding out to be in reality a complete ring1 except so far that a portion of it was of course hidden from view behind the ball4 ,he1 and ,o4 ,struve likewise1 noticed that this new ,dusky ,ring was occasionally to be seen divided into two or more rings4 ,the ,dusky ,ring is transparent1 though this fact was not ascertained until #aheb1 or two years after ,bond's discovery of the ring4 ,the ,dusky ,ring is now recognised as a permanent feature of ,saturn1 but how far it used to be permanent1 or how long it has been so1 is a matter wrapped in doubt4 ,recorded observations by ,picard in #afgc1 and by ,hadley in #agbc1 made of course with telescopes infinitely less powerful than those of the present day1 seem to suggest that both the observers named saw the ,dusky ,ring1 without1 however1 being able to form a clear conception that it was a ring4 ,it is strange that during the long period from #agbc to #ahch1 no one--not even ,sir ,w4 ,herschel1 with his various telescopes--should have obtained or at least have recorded any suspicion of its existence4 ,there is1 however1 direct evidence that the ,dusky ,ring is wider and less faint than formerly4 ,this was directly confirmed by ,carpenter in #ahfc1 who says he saw it 8nearly as bright as the illuminated ring1 so much so1 that it might easily have been mistaken for a part of it40 ,in #ahhc1 ,davidson found a marked difference in the brilliancy of the two ends 7ans7 of the ring4 ,in #ahhi ,barnard was fortunate enough to observe an eclipse of one of ,saturn's satellites by the ring1 but the eclipse1 that is the concealment of the satellite1 was only effected when it passed behind the bright rings2 the dusky ring did not obliterate it1 and hence there was obtained a conclusive proof of the transparency of the dusky ring4 ,barnard further concluded from his observations that there was no separating space or division between the inner bright ring and the dusky ring1 as has frequently been represented in drawings4 ,this transparency of the ,dusky ,ring1 as a matter of fact1 is therefore undoubted2 yet what are we to consider to be the meaning of an observation by ,wray in #ahfa1 that whilst looking at the dusky ring edgeways the impression was conveyed to his eye that that ring was very much thicker than the bright rings8 ,a very interesting question which has been much discussed has reference to the stability of the rings4 ,it is generally agreed that the constituent particles of the rings must be in motion round the primary or their equilibrium could not be maintained3 almost equally certain is it1 and for the like reason1 that the rings cannot be solid4 ,of actual change in the rings as regards their dimensions1 we have no satisfactory proof1 though authorities differ on the point1 some thinking that the rings are expanding inwards1 so that ultimately they will come into contact with the ball1 whilst others consider no proof whatever of such change can be obtained from any of the observations yet made in the way of measurements4 ,we must now proceed to consider the satellites of ,saturn4 ,these are #h in number1 #g of which move in orbits whose planes coincide nearly with the planet's equator1 whilst the remaining one is inclined about #ab thereto4 ,one consequence of this coincidence in the planes of these satellites1 which1 it should be stated1 are the #g innermost1 is that they are always visible to the inhabitants of both hemispheres when they are not actually undergoing eclipse in the shadow of ,saturn4 ,the satellites are of various sizes1 and succeed one another in the following order1 reckoning from the nearest1 outwards3--,mimas1 ,enceladus1 ,tethys1 ,dione1 ,rhea1 ,titan1 ,hyperion and ,iapetus4 ,any good #b-;inch telescope will show ,titan2 a #c-;inch will sometimes show ,iapetus2 a #d-;inch will show ,iapetus well1 together with ,rhea and ,dione1 but hardly ,tethys2 all the others require large telescopes4 ,if ,saturn has any inhabitants at all constituted like ourselves1 which is highly improbable1 they will have a chance of seeing celestial phenomena of the greatest interest4 ,what with the rings surrounding the planet and #h moons in constant motion1 there will be an endless succession of astronomical sights for them to study4 ,the amount of light received from the ,sun cannot be much--barely #a_/ajjth what the earth receives4 ,the ring and satellites will therefore be useful as supplementary sources of light2 yet the satellites will not furnish much1 for it has been calculated that the surface of the sky occupied by all the satellites put together would to a dweller on ,saturn only amount to #f times the area of the sky covered by our ,moon2 whilst the intrinsic brightness of all put together would be no more than #a_/afth part of the light which we receive from our ,moon4 ,the only physical fact worth noting here in connection with the satellites concerns ,iapetus4 ,cassini two centuries ago with his indifferent telescopes thought he had ascertained that this satellite was subject to considerable variations of brilliancy4 ,sir ,w4 ,herschel confirmed ,cassini as to this4 ,he found that it was much less brilliant when traversing the eastern half of its orbit than at other times4 ,two conclusions have been drawn from this fact4 ,one is that the satellite rotates once on its axis in the same time that it performs one revolution round its primary2 and that there are portions of its surface which are almost entirely incapable of reflecting the rays of the ,sun4 ,this last named supposition may perhaps be well founded1 but the former needs more proof than is as yet forthcoming4 ,iapetus on the whole may be said to shine as a star of the #ith magnitude4 ,to this it may be added that ,titan is of the #hth magnitude1 but all the others much smaller4 ,illustration3 ,fig4 #ah4--,saturn with the shadow of ,titan on it1 ,march #aa1 #ahib 7,terby74 ,saturn revolves round the ,sun in a little under #bi years at a mean distance of #hhf millions of miles4 ,its apparent diameter varies between #ae and #bj2 its true diameter may be put at #ge1jjj miles4 ,the flattening of the poles1 or 8polar compression0 as it is called1 is greater than that of any other planet1 but is usually less noticeable than in the case of ,jupiter1 because the ring is apt to distract the eye1 except when near the edgeways phase4 ,the compression may be taken at #a_/i4 ,,chapter ,,xi4 ,,uranus4 ,to the ,ancients ,saturn was the outermost planet of the ,system1 nothing beyond it being known4 ,nor indeed was it to be assumed that any more could possibly exist1 because ,mercury1 ,venus1 the ,earth1 ,mars1 ,jupiter1 and ,saturn1 with the ,sun1 made #g celestial bodies of prime importance2 and #g was the number of perfection2 and there was thus provided one celestial body to give a name to each of the days of the week4 ,but ,science is not sentimental2 and when men of ,science come upon what looks like a discovery they do their best to bring their discovery to a successful issue1 however much people's prejudices may seem to stand in the way at the moment4 ,on a certain evening in ,march1 #agha1 ,sir ,william ,herschel1 then gradually coming into notice as a practical astronomer1 was engaged in looking at different fields of stars in the constellation ,gemini when he lighted on one which at once attracted his special attention4 ,altering his eyepiece1 and substituting a higher magnifying power he found the apparent size of the mysterious object enlarged1 which conclusively proved that it was not a star2 for it is a well-known optical property of all stars that whatever be the size of telescope employed on them1 and however high the magnifying power no definite disc of light can be obtained when in focus4 ,herschel's new find1 therefore1 was plainly not a star1 and no idea having in those days come into men's minds of there being any new planets awaiting discovery1 he announced as a matter of course that he had found a new comet1 so soon as he ascertained that the new body was in motion4 ,the announcement was not made to the ,royal ,society till ,april #bf1 more than six weeks after the date of the actual discovery1 an indication1 by the way1 of the dilatory circulation of news a hundred years ago4 ,the supposed comet was observed by ,maskelyne1 the ,astronomer ,royal1 four days after ,herschel had first seen it1 and ,maskelyne seems to have at once got the idea into his head that he was looking at a planet and not at a comet4 ,as soon as possible after the discovery of a new comet the practice of astronomers is to endeavour to determine what is the shape of the orbit which it is pursuing4 ,all attempts to carry out this in the case of ,herschel's supposed new comet proved abortive1 because it was found impossible to harmonise1 except for a short period of time1 the movements of the new body with the form of curve usually affected by most comets1 namely1 the parabola4 ,it is true1 as we shall see later on in speaking of comets1 that a certain number of those bodies do revolve in the closed curve known as the ellipse1 but it is usual to calculate the parabolic form first of all1 because it is the easier to calculate2 and to persevere with it until it plainly appears that the parabola will not fit in with the observed movements of the new object4 ,this practice was carried out in the case of ,herschel's new body1 and it was eventually found that not only was its orbit not parabolic2 that not only was its orbit not an elongated ellipse of the kind affected by comets2 but that it was nearly a circle1 and as the body itself showed a defined disc the conclusion was inevitable3 it was in real truth a new planet4 ,it has not taken long to write this statement1 and it will take still less time for the reader to read what has been written1 but the result just mentioned occupied the attention of astronomers many months in working out1 step by step1 in such a way as to make sure that no mistake had been made4 ,when it was once clearly determined that ,herschel had added a new planet to the list of known planets it became an interesting matter of inquiry to find out whether it had ever been seen before2 and to settle the name it should bear4 ,a little research soon showed that the new planet had been seen and recorded as a fixed star by various observers on #bj previous occasions1 beginning as far back as ,dec4 #ac1 #afij1 when ,flamstead registered at ,greenwich as a star4 ,these various observations1 spread over a period of #ia years1 and all recorded by observers of skill and eminence materially helped astronomers in their efforts to calculate accurately the shape and nature of the new planet's orbit4 ,one observer1 a ,frenchman named ,le ,monnier1 saw the planet no less than #ab times between #agej and #agga1 and if he had had 7which it is known he had not7 an orderly and methodical mind1 the glory of this discovery would have been lost to ,england and obtained by ,france4 ,arago has left it on record that he was once shown one of these chance observations of ,uranus1 which had been recorded by ,le ,monnier on an old paper bag in which hair powder had been sold by a perfumer4 ,a long discussion took place on the question of a name for the new planet4 ,bode's suggestion of 8,uranus0 is now in universal use1 but it is within the recollection of many persons living that this planet bore sometimes the name of the 8,georgium ,sidus0 and sometimes the name of 8,herschel40 ,the former designation was proposed by ,herschel himself in compliment to his sovereign and patron ,george ,,iii4 of ,england2 whilst a ,french astronomer suggested the latter name4 ,however1 neither of these appellations was acceptable to the astronomers of the ,continent1 who declared in favour of a mythological name1 though it was a long time before they agreed to accept ,bode's 8,uranus40 ,the symbol commonly used to represent the planet is formed of ,herschel's initial with a little circle added below1 though the ,germans employ something else1 8made in ,germany10 to quote a too familiar phrase4 ,the visible disc of ,uranus is so small that none but telescopes of the very largest size can make anything of it4 ,a few sentences therefore will dispose of this part of the subject4 ,the disc is usually bluish in tinge1 and most observers who look at it consider it uniformly bright1 but there is satisfactory testimony to the effect that under the most favourable circumstances of instrument and atmosphere two or more belts1 not unlike the belts of ,jupiter1 may be traced4 ,from the position in which these belts have been seen it is inferred that the satellites of ,uranus 7presently to be mentioned7 are unusually much inclined to the planet's equator1 and revolve in a retrograde direction1 contrary to what is the ordinary rule of the planets and satellites4 ,it is assumed as the basis of these ideas1 7and by analogy it is reasonable to do this7 that the belts are practically parallel to the planet's equator1 and at right angles to the planet's axis of rotation4 ,to speak of the planet's axis of rotation is1 in one sense1 another assumption1 because available observations can scarcely be said to enable us to demonstrate that the planet does rotate on its axis1 yet we can have no moral doubt about it4 ,taylor has suggested grounds for the opinion that 8there can be very little doubt that ,uranus is to a very large extent self-luminous1 and that we do not see it wholly by reflected light40 ,to this ,gore adds the idea that there is 8strong evidence in favour of the existence of intrinsic heat in the planet40 ,uranus is attended by several satellites4 ,it was once thought that there were eight1 of which six were due to ,sir ,w4 ,herschel1 the other two being of modern discovery4 ,astronomers are1 however1 now agreed that no more than four satellites can justly be recognised as known to exist1 and they are so minute in size that only the very largest telescopes will show them2 and therefore our knowledge of them is extremely limited4 ,sir ,w4 ,herschel's idea that he had seen six satellites appears to have resulted from his having on some occasions mistaken some very small stars for satellites4 ,two only of his six are thought to have been real satellites4 ,the other two recognised satellites were found both in #ahdg1 one by ,lassell1 and the other by ,o4 ,struve4 ,uranus revolves round the ,sun in rather more than #hd years1 at a mean distance of #agha millions of miles4 ,its apparent diameter1 seen from the ,earth1 does not vary much from #c which corresponds to about #ca1jjj miles4 ,it has been calculated that the light received from the ,sun by ,uranus would be about the amount furnished by #cjj full ,moons seen by us on the ,earth1 though another authority increases this to #afgj full ,moons4 ,from ,uranus ,saturn can be seen1 and perhaps ,jupiter1 both as inferior planets1 just as we see ,venus and ,mercury2 but all the other inner planets1 including ,mars and the ,earth1 would be hopelessly lost to view1 because perpetually too close to the ,sun4 ,possibly1 however1 they might1 on rare occasions1 be seen in transit across the ,sun's disc4 ,neptune1 of course1 would be visible and be the only superior planet4 ,the ,sun itself would appear to an observer on ,uranus as a very bright star1 with a disc of #a of arc in diameter4 ,,chapter ,,xii4 ,,neptune4 ,we now come to the best known planet of the solar system1 reckoning outwards from the ,sun1 and though this planet itself1 as an object to look at1 has no particular interest for the general public1 yet the history of its discovery is a matter of extreme interest4 ,moreover1 it is very closely mixed up with the history of the planet ,uranus1 which has just been described4 ,after ,uranus had become fully recognised as a regular member of the solar system1 a ,french astronomer named ,alexis ,bouvard set himself the task of exhaustively considering the movements of ,uranus with a view of determining its orbit with the utmost possible exactness4 ,his available materials ranged themselves in two groups3--the modern observations between #agha and #ahbj1 and the early observations of ,flamsteed1 ,bradley1 ,mayer1 and ,le ,monnier1 extending from #afij to #agga4 ,bouvard found in substance that he could frame an orbit which would fit in with each group of observations1 but that he could not obtain an orbit which would reconcile both sets of observations during the #acj years over which they jointly extended4 ,he therefore rashly came to the conclusion that the earlier observations1 having been made when methods and instruments were alike relatively imperfect1 were probably inaccurate or otherwise untrustworthy1 and had better be rejected4 ,this seemed for awhile to solve the difficulty1 and results which he published in #ahba represented with all reasonable accuracy the then movements of the planet4 ,a very few years1 however1 sufficed to reveal discordances between observation and theory1 so marked and regular as to make it perfectly clear that it was not ,bouvard's work which was faulty but that ,uranus itself had gone astray through the operation of definite but as yet unknown causes4 ,what these causes were could only be a matter of surmise based upon the evident fact that there was some source of disturbance which was evidently throwing ,uranus out of its proper place and regular course4 ,first one and then another astronomer gave attention and thought to the matter1 and eventually the conclusion was arrived at that there existed1 more remote from the ,sun than ,uranus1 an undiscovered planet which was able to make its influence felt by deranging the movements of ,uranus in its ordinary journey round the ,sun every #hd years4 ,this conclusion on the part of astronomers becoming known1 a young ,cambridge student1 then at ,st4 ,john's ,college1 ,john ,couch ,adams by name1 resolved1 in ,july #ahda1 to take up the subject1 though it was not until #ahdc that he actually did so4 ,the problem to be solved was to suggest the precise place in the sky at a given time of an imaginary planet massive enough to push1 or pull1 out of its normal place the planet ,uranus1 which was evidently being pushed at one time and pulled at another4 ,it would also be part of the problem to predict the distance from the ,sun of the planet thus imagined to exist4 ,adams worked patiently and silently at this very profound and difficult problem for #a years when he found himself able to forward to ,airy1 who had become ,astronomer ,royal after being a ,cambridge ,professor1 some provisional elements of an imaginary planet of a size1 at a distance1 and in a position to meet the circumstances4 ,it is greatly to be regretted1 on more grounds than one1 that ,airy did nothing but pigeon-hole ,adams's papers4 ,had he done what might have been1 and probably was1 expected1 that is1 had he made them public1 or better still had he made telescopic use of them1 a long and unpleasant international controversy would have been avoided1 and ,adams would not have been robbed in part of the well-deserved fruits of his protracted labours4 ,we must now turn to consider something that was happening in ,france4 ,in the summer of #ahde1 just before ,adams had finished his work1 and one and a half years after he commenced it a young ,frenchman1 who afterwards rose to great eminence1 ,u4 ,j4 ,j4 ,le ,verrier1 turned his attention to the movements of ,uranus with a view of ascertaining the cause of their recognised irregularity4 ,in ,november #ahde he made public the conclusion that those irregularities did not exclusively depend upon ,jupiter or ,saturn4 ,he followed this up in ,june #ahdf by a second memoir to prove that an unknown exterior planet was the cause of all the trouble1 and he assigned evidence as to its position very much as ,adams had done #h months previously4 ,airy on receiving a copy of ,le ,verrier's memoir seems so far1 at last1 to have been roused that he took the trouble to compare ,le ,verrier's conclusions with those of ,adams so long in his possession neglected4 ,finding that a remarkably close accord existed between the conclusions of the two men1 he came to realise that both must be of value1 and he wrote a fortnight later to suggest to ,professor ,challis the desirability of his instituting a search for the suspected planet4 ,challis began within two days1 but was handicapped by not having in his possession any map of the stars in the neighbourhood suggested as the locale of the planet4 ,he lost no time however in making such a map1 but1 of course1 the doing so caused an appreciable delay1 and it was not until ,september #bi1 #ahdf1 that he found an object which excited his suspicions and eventually proved to be the planet sought for4 ,it was subsequently ascertained that the planet had been recorded as a star on ,august #d and #ab1 and that the star of ,august #ab was missing from the zone observed on ,july #cj4 ,the discovery of the planet was therefore just missed on ,august #ab because the results of each evening's work were not adequately compared with what had gone before4 ,meanwhile things had not been standing still in ,france4 ,in ,august #ahdf1 ,le ,verrier published a third memoir intended to develope information respecting the probable position of the planet in the heavens4 ,in ,september #bc a summary of this third memoir was received by ,encke at ,berlin1 accompanied by the request that he would cooperate instrumentally in the search for it4 ,encke at once directed two of his assistants named ,d',arrest and ,galle to do this1 and they were fortunately well circumstanced for the task4 ,unlike ,challis1 who1 as we have seen1 could do nothing until he had made a map for himself1 the ,berlin observers had one ready to hand1 which by good chance had just been published by the ,berlin ,academy for the part of the heavens which both ,adams and ,le ,verrier assigned as the probable locality in which the anxiously desired planet would be found4 ,galle called out the visible stars one by one whilst ,d',arrest checked them by the map1 and suddenly he came upon an unmarked object which at the moment looked like an #hth magnitude star4 ,the following night showed that the suspicious object was in motion1 and it was soon ascertained to be the trans-,uranian planet which was being searched for4 ,the discovery when announced excited the liveliest interest all over the world4 ,it did more2 it created a bitter feeling of resentment on the part of ,french astronomers that the laurels claimed by them should have been also claimed in an equal share by a young and unknown ,englishman1 and accordingly the old cry of 8perfide ,albion0 arose on all sides4 ,i have been particular in stating the various dates which belong to this narrative1 in order to make as clear as possible the facts of the case4 ,this is even now necessary1 because though the astronomers of ,england and ,germany are willing to give ,adams and ,le ,verrier each their fair share of this great discovery1 the same impartial spirit is not to be found in ,france1 for nothing is more common1 even in the present day1 in looking at ,french books of astronomy1 than to find ,adams's name either glossed over or absolutely suppressed altogether when the planet ,neptune is under discussion4 ,how remarkable a discovery this was1 will perhaps be realized1 when it is stated that ,adams was only #b out in assigning the position of the new planet1 whilst ,le ,verrier was even nearer1 being barely #a out4 ,we know practically nothing respecting the physical appearance of ,neptune1 owing to its immense distance from us1 and for the like reason the ,neptunian astronomers1 if there are any1 will know absolutely nothing about the ,earth2 indeed1 their knowledge of the ,solar ,system will be restricted to ,uranus1 ,saturn1 and the ,sun4 ,even the ,sun will only have an apparent diameter of about #a of arc1 and1 therefore1 will only seem to be a very bright star1 yielding light equal in amount1 according to ,zllner1 to about #gjj full moons4 ,there is one satellite belonging to ,neptune1 and as this has been calculated to exhibit a disc #aj in diameter1 a certain amount of light will no doubt be afforded by it especially if1 as is not unlikely1 ,neptune is itself possessed of some inherent luminosity independently of the ,sun4 ,the fact that ,neptune seems destitute of visible spots or belts1 results in our being ignorant of the period of its axial rotation1 though it should be stated that in #ahhc1 ,maxwell ,hall in ,jamaica1 observed periodical fluctuations in its light1 which he thought implied that the planet rotated on its axis in rather less than #h hours4 ,several observers thought #bj or #cj years ago1 that they had noticed indications of ,neptune being surrounded by a ring like ,saturn's ring1 but the evidence as to this is very inconclusive4 ,it is quite certain that none but the very largest telescopes in the world would show any such appendage1 and this planet seems to have been neglected of late years1 by the possessors of such telescopes4 ,moreover1 if a ring existed it would only open out to its full extent once in every #hb years1 being the half of the period of the planet's revolution round the ,sun 7just as ,saturn's ring only opens out to the fullest extent every #ad years71 so that1 obviously1 supposing suspicions of a ring dating back #cj or #dj years were well founded1 it might well be that another #cj or #dj years might need to elapse1 before astronomers would be in a position to see their suspicions revive4 ,neptune revolves round the ,sun in #afd years1 at a mean distance of #bgia millions of miles4 ,its apparent diameter scarcely varies from #b4 ,its true diameter is about #cg1jjj miles4 ,no compression of the ,poles is perceptible4 ,its one satellite revolves round ,neptune in #e days1 and in a retrograde direction1 at a mean distance of #bbc1jjj miles1 and shines as a star of the #adth magnitude4 ,this is a peculiarity which it only shares with the satellites of ,uranus1 so far as it regards the planetary members of the ,solar ,system1 though there are many retrograde ,comets4 ,the question has often been mooted1 whether there exists1 and belonging to the ,solar ,system1 a planet farther off than ,neptune4 ,there does seem some evidence of this1 as we shall better understand1 when we come to the subject of long-period ,comets1 though it cannot be said that much progress has yet been made in arriving at a solution of the problem4 ,unless there does exist a trans-,neptunian planet1 a ,neptunian astronomer will know very little about planets1 for ,uranus and ,saturn will alone be visible to him4 ,both will of course be what we call 8inferior planets10 and under the best of circumstances will cut a poor figure in the ,neptunian sky4 ,,chapter ,,xiii4 ,,comets4 ,i suppose that it is the experience of all those who happen to be in any sense1 however humble1 specialists in a certain branch of science1 that from time to time1 they are beset with questions on the part of their friends respecting those particular matters which it is known that they have specially studied4 ,there is no fault to be found with this thirst for information1 always supposing that it is kept within due bounds2 but my motive for alluding to it here1 is to see whether any well-marked conclusion can be drawn from it1 within my own knowledge as regards astronomical facts or events4 ,now in the case of the science of astronomy 7for which in this connection ,i1 for the moment1 will venture to speak71 there is certainly no one department which so unfailingly1 at all times and in all places1 seems to evoke such popular sympathy and interest as the department which deals with ,comets4 ,sun-spots may come and go2 bright planets may shine more brightly2 the ,sun or ,moon may be obscured by eclipses2 temporary stars may burst forth1--all these things are within the ken of the general public by means of newspapers or almanacs1 but it is a comet which evokes more questionings and conversations than all the other matters just referred to put together4 ,when a new and bright comet appears1 or even when any comet not very bright gets talked about1 the old question is still fresh and verdant--8,is there any danger to the ,earth to be apprehended from collision with a ,comet80 followed by 8,what is a ,comet80 8,what is it made of80 8,has it ever appeared before80 8,will it come back again80 and so on4 ,questions in this strain have more often than ,i can tell of been put to me4 ,they seem the stock questions of all who will condescend to replace for five minutes in the day the newest novel or the pending parliamentary election4 ,it may be taken as a fact 7though in no proper sense a rule7 that a bright and conspicuous comet comes about once in #aj years1 and a very remarkable comet every #cj years4 ,thus we have had during the present century bright comets in #ahaa1 #ahbe1 #ahce1 #ahdc1 #aheh1 #ahfa1 #ahgd and #ahhb1 whereof those of #ahaa1 #ahdc1 and #aheh were specially celebrated4 ,tested then by either standard of words 8bright and conspicuous10 or 8specially celebrated10 it may be affirmed that a good comet is now due1 so let us prepare for it by getting up the subject in advance4 ,i will not attempt to answer in regular order or in any set form the questions which ,i have just mentioned as being stock questions1 but they will be answered in substance as we go along4 ,there is one matter in connection with comets which has deeply impressed itself upon the public mind1 and that is the presence or absence of a 8tail40 ,it is not too much to say that the generality of people regard the tail of a comet as the comet2 and that though an object may be a true comet from an astronomer's point of view1 yet if it has no tail its claims go for nought with the mass of mankind4 ,we have here probably a remnant of ancient thought1 especially of that line of thought which in bygone times associated ,comets universally with the idea that they were especially sent to be portents of national disasters of one kind or another4 ,this is brought out by numberless ancient authors1 and by none more forcibly than ,shakespeare4 ,hence we have such passages as the following in ,julius ,csar 7,act ii41 sc4 #b73-- 8,when beggars die there are no comets seen1 ,the ,heavens themselves blaze forth the death of princes40 ,in ,henry ,,vi4 7,part ,i41 ,act i41 sc4 #a7 we find the well-known passage3-- 8,comets importing change of times and states ,brandish your crystal tresses in the sky1 ,and with them scourge the bad revolting stars ,that have consented unto ,henry's death40 ,there are in point of fact two distinct ideas evolved here3 7#a7 that comets are prophetic of evil1 and 7#b7 stars potential for evil4 ,there is another passage in ,henry ,,vi4 7,part ,i41 ,act iii41 sc4 #c7 even more pronounced3-- 8,now shine it like a ,comet of revenge1 ,a prophet to the fall of all our foes40 ,again2 in ,hamlet 7,act i41 sc4 #a7 we find3-- 8,as stars with trains of fire1 and dews of blood1 ,disasters in the ,sun40 ,once more2 in the ,taming of the ,shrew 7,act iii41 sc4 #b7 we have the more general1 but still emphatic enough1 idea expressed by the simple words of reference to-- 8,some ,comet or unusual prodigy40 ,shakespeare may be said to have lived at the epoch when astrology was in high favour1 and it may be that he only gave utterance to the current opinion prevalent among all classes in those still somewhat 8,dark ,ages0 7so called74 ,this1 however1 can hardly be said of the author of my next quotation--,john ,milton 7,paradise ,lost1 bk4 ,,ii473-- 8,satan stood ,unterrified1 and like a ,comet burned1 ,that fires the length of ,ophiuchus huge ,in th' ,arctic sky1 and from its horrid hair ,shakes pestilence and war40 ,jumping over a century we find the ancient theory still in vogue1 or ,thomson 7,seasons1 ,summer7 would never have written3-- 8,amid the radiant orbs ,that more than deck1 that animate the sky1 ,the life-infusing suns of other worlds2 ,lo6 from the dread immensity of space1 ,returning with accelerated course1 ,the rushing comet to the sun descends2 ,and1 as he sinks below the shading earth1 ,with awful train projected o'er the heavens1 ,the guilty nations tremble40 ,even ,napoleon ,i4 had servile flatterers who1 as late as #ahjh1 tried to extract astrological influence out of a comet by way of bolstering up 8,old ,bony40 ,but enough of poetry and fiction1 let us hasten back to prosaic fact4 ,illustration3 ,fig4 #ai4--,telescope ,comet with a nucleus4 ,comets as objects to look at may be classed under three forms1 though the same comet may undergo such changes as will at different epochs in its career cause it to put on each variety of form in succession4 ,thus the comet of #ahbe seen during that year as a brilliant naked-eye object1 after being lost in the sun's rays1 was again found on ,april #b1 #ahbf by ,pons4 ,lamentable were his cries at the miserable plight it was in4 ,he described it as totally destroyed3 without tail1 beard1 coma or nucleus1 a mere spectre4 ,the simplest form of comet is a mere nebulous mass1 almost always circular1 or perhaps a little oval1 in outline4 ,it may maintain this appearance throughout its visibility2 or1 growing brighter may become a comet of the second class1 with a central condensation1 which developing becomes a 8nucleus0 or head4 ,it may retain this feature for the rest of its career1 or may pass into the third class and throw out a 8coma0 or beard1 which will perhaps develop into a tail or tails4 ,doing this it will not unfrequently grow bright enough and large enough to become visible to the naked eye4 ,in exceptional cases the nucleus will become as bright as a #bnd or even #ast magnitude star1 and the tail may acquire a length of several or many degrees4 ,in the last named case of all the comet becomes1 par excellence according to the popular sentiment1 8a comet40 ,it will now be readily inferred that the astronomer in his observatory has to do with many comets which the public at large never hear of1 or if they do hear of1 treat with contempt1 because they are destitute of tails4 ,illustration3 ,fig4 #bj4--,wells's ,comet of #ahhb1 seen in full daylight near the ,sun on ,sept4 #ah4 ,illustration3 ,fig4 #ba4--,quenisset's ,comet1 ,july #i1 #ahic 7,quenisset74 ,the tails of comets exhibit very great varieties not only of size but of form2 some are long and slender2 some are long and much spread out towards their ends1 like quill pens1 for instance2 some are short and stumpy1 mere tufts or excrescences rather than tails4 ,not unfrequently a tail seems to consist of two parallel rays with no cometary matter1 or it may be only a very slight amount of cometary matter traceable in the interspace2 some have one main tail consisting of a pair of rays such as just described1 together with one or more subsidiary or off-shoot tails4 ,the comet of #ahbe had five tails and the comet of #agdd had six tails4 ,it might be inferred from all this that the tails of comets are so exceedingly irregular1 uncertain and casual as to be amenable to no laws4 ,this was long considered to be the case2 but a ,russian observer named ,bredichin1 as the result of much study and research1 has arrived at the conclusion that all comet tails may be brought under one or other of three types2 and that each type is indicative of certain distinct differences of origin and condition which he considers himself able to define4 ,the first type comprises tails which are long and straight2 8they are formed0 7to quote ,young's statement of ,bredichin's views7 8of matter upon which the ,sun's repulsive action is from twelve to fifteen times as great as the gravitational attraction1 so that the particles leave the comet with a relative velocity of at least four or five miles a second2 and this velocity is continually increased as they recede1 until at last it becomes enormous1 the particles travelling several millions of miles in a day4 ,the straight rays which are seen in the figure of the tail of ,donati's ,comet1 tangential to the tail1 are streamers of this first type2 as also was the enormous tail of the comet of #ahfa4 ,the second type is the curved plume-like train1 like the principal tail of ,donati's ,comet4 ,in this type the repulsive force varies from #b4b times gravity 7for the particles on the convex edge of the tail7 to half that amount for those which form the inner edge4 ,this is by far the most common type of cometary train4 ,a few comets show tails of the third type--short1 stubby1 brushes violently curved1 and due to matter of which the repulsive force is only a fraction of gravity--from #a_/aj to 40 ,bredichin wishes it to be inferred that the tails of the #ast type are probably composed of hydrogen2 those of the #bnd type of some hydro-carbon gas2 and those of the #crd of the vapour of iron1 probably with some admixture of sodium and other substances4 ,bredichin1 as a reason for these conclusions1 supposes that the force which generates the tails of comets is a repulsive force1 with a surface action the same for equal surfaces of any kind of matter2 the effective accelerating force therefore measured by the velocity which it would produce would depend upon the ratio of surface to mass in the particles acted upon1 and so1 in his view1 should be inversely proportional to their molecular weights4 ,now it happens that the molecular weights of hydrogen1 of hydro-carbon gases1 and of the vapour of iron bear to each other just about the required proportion4 ,i am here stating the views and opinions of others without definitely professing to be satisfied with them1 but as they have met with some acceptance1 it is proper to chronicle them1 though we know nothing of the nature of the repulsive force here talked about4 ,it might be electric1 it might be anything4 ,the spectroscope certainly lends some countenance to ,bredichin's views1 but we need far more knowledge and study of comets before we shall be justly entitled to dogmatise on the subject4 ,illustration3 ,fig4 #bb4--;,holmes's ,comet1 ,nov4 #i1 #ahib 7,denning74 ,illustration3 ,fig4 #bc4--;,holmes's ,comet1 ,nov4 #af1 #ahib 7,denning74 ,this has been rather a digression4 ,i go back now to prosaic matters of fact1 of which a vast and interesting array present themselves for consideration in connection with comets4 ,let us consider a little in detail what they are1 to look at4 ,we have seen that a well-developed comet of the normal type usually comprises a nucleus1 a head or coma1 and a tail4 ,comets which have no tails generally exhibit heads of very simple structure2 and if there is a nucleus1 the nucleus is little else than a stellar point of light4 ,but in the case of the larger comets1 which are almost or quite visible to the naked eye1 the head often exhibits a very complex structure1 which in not a few cases seems to convey very definite indications of the operations going on at the time4 ,figs4 #bb and #bc may be taken as samples of a complex cometary head1 though no two comets resemble one another exactly in details4 ,fig4 #bd forcibly conveys the idea that we are looking at a process of development analogous to an uprush of water from a fountain1 or perhaps ,i might better say1 from a burst waterpipe4 ,there is a distinct idea of a jet4 ,this self-same idea1 in another form1 presents itself in the case of those comets which exhibit what astronomers are in the habit of calling 8luminous envelopes40 ,the jet in this case is not strictly a jet because it is not a continuous outflow1 or overflow1 of matter2 the idea rather suggests itself of an intermittent overflow resulting in accumulated layers1 or strata1 of matter becoming visible4 ,but with this we come to a standstill2 we cannot tell where the matter comes from1 and still less1 where it goes to2 we can only record what our eyes1 assisted by telescopes1 tell us4 ,there can1 however1 ,i think1 be no doubt that the matter of a comet becomes displayed to our senses as the result of a process of expulsion1 or repulsion1 from the nucleus2 and then1 having become launched into space1 it comes under the influence1 also repulsive1 of the ,sun4 ,all these things are visible facts4 ,as to causes1 we suggest little1 because we know so little4 ,anyone who has seen a comet and has watched the displays of jets and luminous envelopes1 such as ,i have endeavoured to set forth1 will realise at once how impossible it is to describe these things in words4 ,they must be seen either in actual being or in picture4 ,some further allusions to this branch of the subject may perhaps be more advantageously made after we have considered the movements and orbits of comets4 ,illustration3 ,fig4 #bd4--;,comet ,,iii4 of #ahfb1 on ,aug #bb1 showing jet of luminous matter 7,challis74 ,there is often a slight general resemblance between a planet and a comet1 as regards the path which each class of body pursues4 ,probably the least reflective person likely to be following me here understands the bare fact1 that all the planets revolve round the ,sun1 and are held to defined orbits by the ,sun's influence1 or attraction1 as it is called4 ,perhaps1 it is not equally realised1 that in a somewhat similar1 but not quite the same way1 comets are influenced and controlled by the ,sun4 ,comets must be considered as regards their motions to be divisible into two classes3--7#a7 ,those which belong to the ,solar ,system2 and 7#b7 those which do not4 ,each of these two classes must again be sub-divided1 if we would really obtain a just conception of how things stand4 ,by the ,comets which belong to the ,sun1 ,i mean those which revolve round the ,sun in closed orbits2#e and are1 or may be1 seen again and again at recurring intervals4 ,there are #b or #c dozen comets which present themselves to our gaze at stated intervals1 varying from about #c to #gj years4 ,there are again other comets which without any doubt 7mathematically7 are revolving round the ,sun in closed orbits1 but in orbits so large and with periods of revolution so long 7often many centuries71 that though they will return again to the sight of the inhabitants of the earth some day1 yet no second return having been actually recorded1 the astronomer's prediction that they will return1 remains at present a prediction based on mathematics but nothing more4 ,there is another class of ,comet of which we see examples from time to time1 and having seen them once shall never see again4 ,this is because these ,comets move in orbits which are not closed1 and which are known as parabolic or hyperbolic orbits respectively1 because derived from those sections of a cone which are called the ,parabola and the ,hyperbola4 ,it must be understood that what ,i am now referring to is purely a matter of orbit1 and that no relationship subsists between the size and physical features of a ,comet and the path it pursues in space4 ,the only sort of reservation1 perhaps1 to be made to this statement is1 that the comets celebrated for their size and brilliancy1 are often found to be revolving in elliptic orbits of great eccentricity1 which means that their periods may amount to many centuries4 ,it may be well to say something now as to what is the ordinary career of a comet1 so far as visibility to us1 the inhabitants of the ,earth1 is concerned4 ,though this might be illustrated by reference to the history of many comets1 perhaps there is no one more suitable for the purpose than ,donati's ,comet of #aheh4 ,in former times1 when telescopes were few or non-existent1 brilliant comets often appeared very suddenly1 just as a carriage or a man does1 as you turn the corner of a street4 ,such things even happen still3 for instance1 the great comet of #ahfa burst upon us all at once at a day's notice4 ,usually1 however1 now in consequence of the large size of the telescopes in use1 and the great number of observers who are incessantly on the watch1 comets are discovered when they are very small1 because remote both from the ,earth and ,sun1 and many weeks1 or even months1 it may be1 before they shine forth in their ultimate splendour4 ,now1 let us see how these statements are supported by the history of ,donati's comet in #aheh4 ,on ,june #b in that year1 it was first seen by ,donati at ,florence1 as a faint nebulosity1 slowly journeying northwards4 ,june passed away1 and ,july1 and ,august1 the comet all the while remaining invisible to the naked eye2 that is to say1 it first became perceptible to the naked eye on ,august #bi1 having put forth a faint tail about ,august #bj4 ,after the beginning of ,september its brilliancy rapidly increased4 ,on ,september #ag1 the head equalled in brightness a #bnd magnitude star1 the tail being #d long4 ,passing its point of nearest approach to the ,sun on ,september #bi1 it came nearest to the ,earth on ,october #aj2 though1 perhaps1 its appearance a few days previously1 namely on ,october #e1 is the thing best remembered by those who saw it1 because it was on that night that the comet passed over the #ast magnitude star ,arcturus4 ,for several days about this time1 the comet was an object of striking beauty in the ,western ,heavens1 during the hours immediately after sun-set4 ,after ,october #aj1 it rapidly passed away to the ,southern hemisphere1 diminishing in brightness1 as it did so1 because receding from the ,earth and the ,sun4 ,it continued its career through the winter2 became invisible to the naked eye2 and finally invisible altogether in ,march #ahei4 ,it remained in view1 therefore1 for more than nine months1 not to return again till about the year #caeh ,a4,d41 for its period of revolution was found to be about #bjjj years4 ,i have been particular in sketching somewhat fully the history of this comet so far as we are concerned1 because1 as ,i have already said1 it is typical of the visible career of many comets4 ,halley's comet in #ahce and #ahcf1 went through a somewhat similar series of changes4 ,this comet--a well-known periodical one of great historic interest and brilliancy--may be commended to the younger members of the rising generation1 because it is due to return again to these parts of space a few years hence1 or in #aiaj4 ,illustration3 ,fig4 #be4--,sawerthal's ,comet1 ,june #d1 #ahhh 7,charlois74 ,what is a comet made of8 ,men of ,science equally with the general public would like to be able to answer this question1 but they cannot do so with satisfactory certainty4 ,a great many years ago ,sir ,john ,herschel wrote thus3--8,it seems impossible to avoid the following conclusion1 that the matter of the nucleus of a comet is powerfully excited and dilated into a vaporous state by the action of the ,sun's rays escaping in streams and jets at those points of its surface which oppose the least resistance1 and in all probability throwing that surface or the nucleus itself into irregular motions by its reaction in the act of so escaping1 and thus altering its direction40 ,this passage was written of course before the spectroscope had been brought to bear on the observations of comets1 but so far as ,sir ,john ,herschel's remark implies the presence of vapour1 that is gas1 in a comet1 the surmise has been amply borne out by later discoveries4 ,the fact that as a comet approaches the ,sun some forces1 no doubt of solar origin1 come into operation to vaporise and therefore expand the matter composing the comet is sufficiently shown by the great developement which takes place as we have seen in the tails of comets1 but in regard to the heads of comets we are face to face with a strange enigma4 ,though the tails expand the heads contract as the comet approaches its position of greatest proximity to the ,sun4 ,having passed this point the head expands again4 ,this curious circumstance1 first pointed out by ,kepler in #afah1 has often been noticed since1 and noticed indeed not as the result of mere eye impressions1 but after careful micrometrical measurement with suitable instruments4 ,i think the confession must be made that we are hopelessly ignorant of the nature of comet's except that gases are largely concerned in their constitution4 ,it seems impossible to doubt that some tails of comets are hollow cylinders or hollow cones4 ,such a theory would account for the fact1 so often noticed1 that single tails are usually much brighter at their two edges than at the centre4 ,this is the natural effect of looking transversely at any translucent cylinder of measureable thickness4 ,it was long a moot point whether comets are self-luminous1 or whether they shine by reflected light2 but it is now generally admitted that whilst a part of the light of a comet may be derived by reflection from the ,sun yet as a rule they must be regarded as shining by their own intrinsic light4 ,it should be stated here by way of caution that the observations on this subject are not so consistent as one could wish1 and it seems necessary to assume that all comets are not constituted alike1 and that therefore what is true of one does not necessarily apply to another4 ,to those who possess telescopes 7not necessarily large ones7 opportunities for the study of comets have much multiplied during the last few years1 for we are now acquainted with a group of small comets which are constantly coming into view at short intervals of time4 ,the comets have now become so numerous that seldom a year passes without one or more of them coming into view4 ,whilst that known as ,encke's revolves round the ,sun in #c years1 ,tuttle's doing the same in #ac years1 there are four others whose periods average about #e years1 #e which average #f years1 together with one of #g years and one of #h years4 ,it is thus evident that there is a constant succession of these objects available for study1 and that very few months can ever elapse that some one or more of them are not on view4 ,they bear the names of the astronomers who either discovered them originally1 or who1 by studying their orbits1 discovered their periodicity4 ,the names run as follows1 beginning with the shortest in period and ending with the longest3-- ,encke's4 ,winnecke's4 ,temple's ,second 7#ahgc1 ,,ii47 ,brorsen's4 ,temple's ,first 7#ahfg1 ,,ii47 ,swift's 7#ahhj1 ,v47 ,wolf's 7#ahhd1 ,,iii47 ,barnard's 7#ahhd1 ,,ii47 ,faye's4 ,d',arrest's4 ,denning's4 ,finlay's4 ,tuttle's4 ,i cannot stay to dwell upon either the history or description of these comets separately1 but must content myself by saying generally that whilst as a rule they are not visible to the naked eye1 yet several of them may occasionally become so visible when they return to perihelion under circumstances which bring them more near than usual to the earth4 ,several other comets are on record which it was supposed at one time would certainly have been entitled to a place in the above list1 but three of them in particular have1 under very mysterious circumstances1 entirely disappeared from the ,heavens4 ,chief amongst the mysterious comets must be ranked that which goes by the name of ,biela4 ,this comet1 first seen in #aggb1 was afterwards found to have a period of about #f years1 and on numerous occasions it reappeared at intervals of that length down to #ahde1 when the mysterious part of its career seems to have commenced4 ,in ,december of that year this comet threw off a fragment of nearly the same shape as itself1 and the two portions travelled together side by side for four months1 the distance between the fragments slowly increasing4 ,at the end of the four months in question the comet passed out of sight owing to the distance from the earth to which it had attained4 ,the comet returned again to perihelion in #aheb1 remaining visible for three weeks4 ,the two portions of the comet noticed in #ahdf retained their individuality in #aheb1 but the distance between them had increased to about eight times the greatest distance noticed in #ahdf4 ,as a comet ,biela's ,comet has never been seen since #aheb1 and it must now be regarded as having permanently disappeared4 ,but what seems to have happened is this1 that ,biela's ,comet has become broken up into a mass of meteors4 ,on ,november #bg1 #ahgb1 and again in ,november #ahhe1 when the earth in travelling along its own orbit reached a certain point where its orbit intersected the former orbit of ,biela's ,comet the ,earth encountered1 instead of the comet which ought to have been there1 a wonderful mass of meteors2 and it is now generally accepted that these meteors1 which apparently are keeping more or less together as a fairly compact swarm1 are nought else than the disintegrated materials of what once was ,biela's ,comet4 ,illustration3 ,fig4 #bf4--;,biela's ,comet1 ,february #ai1 #ahdf4 ,it is extremely probable that as time goes on we shall be able to say that an intimate connection subsists between particular comets which have been and particular meteoric swarms4 ,we already possess proof that other comets which once came within our view were at that time revolving round the ,sun in orbits so comparatively small that they should have reappeared at intervals of half-a-dozen or so years1 yet they have not reappeared4 ,the question therefore suggests itself1 ,have they been subject to some great internal disaster which has led to their disintegration8 ,it may be said without doubt that this is in the highest degree probable2 but short of this1 that is short of total disintegration into small fragments1 we have several cases on record of what ,i may1 for the moment1 call ordinary comets breaking up into two or three fragments4 ,for a long while astronomers were naturally loath to believe that this was possible1 and therefore they discredited the statements to that effect which had been made4 ,though it would occupy too much space to give the particulars of these comets in full it may yet be worth while just to mention the names of some of them1 presumed to be of short period1 which seemed nevertheless to have eluded our grasp4 ,i would here specially mention ,liais's ,comet of #ahfj and the second comet of #ahha as seemingly having undergone some sort of disruption akin to what happened in the case of ,biela's ,comet4 ,there is another group of periodical comets to be mentioned4 ,these are six in number and seem to have periods of #gj years or a little more4 ,of these three have not yet given us the chance of seeing them again2 two have paid us a second visit1 and therefore their periods are not open to doubt2 whilst the most famous of this group1 8,halley's10 has been recorded to have shown itself to the ,earth no less than #be times1 beginning with the year #aa ,b4 ,c4 ,it was ,halley's comet which shone over ,europe in ,april #ajff1 and was considered the forerunner of the conquest of ,england by ,william of ,normandy4 ,it figures in the famous ,bayeux tapestry as a hairy star of strange shape4 ,it would seem that there exists in some inscrutable manner a connection between each of the three great exterior planets and certain groups of comets4 ,in the case of ,jupiter the association is so very pronounced as long ago to have attracted notice2 but the ,french astronomer1 ,flammarion1 has brought forward some suggestions that ,saturn has one comet 7and perhaps two7 with which it is associated2 ,uranus1 two 7and perhaps three72 and ,neptune1 six2 whilst farther off than ,neptune the fact that there are two comets1 supposed periodical1 without a known planet to run with them has inspired ,flammarion to look with a friendly eye on the idea 7often mooted7 that outside of ,neptune there exists another undiscovered planet revolving round the sun in a period of about #cjj years4 ,the ,jupiter group of comets deserves a few additional words4 ,there are certainly nine1 and perhaps twelve comets revolving round the ,sun in orbits of such dimensions that they either reach up to or slightly overreach the orbit of ,jupiter4 ,the effect of this condition of things is that on occasions ,jupiter and each of the comets may come into such proximity that the superior mass of ,jupiter may exercise a very seriously disturbing influence over a flimsy and ethereal body like a comet4 ,there is reason to suppose that some of the comets now belonging to the ,jupiter group have not done so for any great length of time1 but having been wandering about1 either in elliptic orbits of great extent1 or even in parabolic orbits1 have accidentally come within reach of ,jupiter1 and so have been1 as it were1 captured by him4 ,hence1 the origin of the term1 the 8capture theory10 as applied to these family groups of comets which ,i have just stated to exist1 each presided over1 as it were1 by a great planet4 ,it may be that at some future time this theory will help us to a clue to the fact that besides the comets of ,lexell of #aggj1 ,blainpain of #ahai1 and ,di ,vico of #ahdd1 short period comets unaccountably missing1 there are several others presumed to have been revolving in short period orbits when discovered1 and as to which it is very strange that they should not have been seen before their only recorded visit to us1 and equally strange that they should never have been seen since4 ,is there any reason to fear the results of a collision between a comet and the ,earth8 ,none whatever4 ,however vague may be1 and in a certain sense must be1 our answer to the question1 8,what is a comet80 certain is it that every comet is a very imponderable body--a sort of airy nothing1 a mass of gas or vapour4#f ,at the same time it always has been and perhaps still is difficult to persuade the public that whatever might be the effect on a comet if it were to strike the ,earth1 the effect on the ,earth1 were it to be struck by a comet1 would be nil4 ,this is not altogether a matter of speculation1 for according to a calculation by ,hind1 on ,june #cj1 #ahfa1 the ,earth passed into and through the tail of the great comet of that year at about two-thirds of its distance from the nucleus4 ,assuredly there was no dynamical result2 but it seems1 however1 not unlikely that there was an optical result2 at any rate1 traces of something of this sort were noted4 ,hind himself1 in ,middlesex1 observed a peculiar phosphorescence or illumination of the sky which he attributed at the time to an auroral glare4 ,lowe1 in ,nottinghamshire confirmed ,hind's statement of the appearance of the heavens on the same day4 ,the sky had a yellow auroral glare-like look1 and the ,sun1 though shining1 gave but feeble light4 ,the comet was plainly visible at #g4de p4 m4 7during sunshine71 and had a much more hazy appearance than on any subsequent evening4 ,lowe adds that his ,vicar had the pulpit candles lighted in the ,parish ,church at #g o'clock 7it was a ,sunday71 though only five days had elapsed since ,midsummer day1 which itself proves that some sensation of darkness was felt even while the ,sun was shining4 ,so far as ,i remember there has been no such thing as a comet panic during the present generation1 at any rate in civilised countries1 but it is on record that there was a very considerable panic in #ahcb in connection with the return of ,biela's ,comet in the winter of that year4 ,olbers as the result of a careful study in advance of the comet's movements found that the comet's centre would pass only #bj1jjj miles within the ,earth's orbit1 and that as the nebulosity of the comet had in #ahje been more than #bj1jjj miles in diameter1 it was certain1 unless its dimensions had diminished in the #bg years1 that some of the comet's matter would overlap the ,earth's orbit2 in other words would envelop the ,earth itself1 if the ,earth happened to be there4 ,this conclusion when it became public was quite enough to create a panic and make people talk about the forthcoming destruction of our globe4 ,it was nothing to the point 7in the public mind7 that astronomers were able to predict that the ,earth would not reach the place where the comet would cross the ,earth's orbit until four weeks after the comet had come and gone4 ,however1 we now know that nothing happened1 and ,i am justified in adding that even if there had been contact1 ,earth meeting comet face to face1 nothing 7serious7 would have occurred so far as the ,earth was concerned4 ,this seems a convenient place for referring to a matter which when it was first broached excited a great deal of interest1 but about which one does not hear much now-a-days4 ,the period of the small comet known as ,encke's 7which1 revolving as it does round the ,sun in a little more than three years1 has the shortest period of any of the periodical comets7 was found many years ago to be diminishing at each successive return4 ,that is to say1 it always attained its nearest distance from the ,sun at each apparition #b hours sooner than it ought to have done4 ,in order to account for this gradual diminution in the comet's period ,encke conjectured the existence of a thin ethereal medium sufficiently dense to affect a light flimsy body like a comet1 but incapable of obstructing a planet4 ,it has been remarked by ,hind that 8this contraction of the orbit must be continually progressing1 if we suppose the existence of such a medium2 and we are naturally led to inquire1 ,what will be the final consequence of this resistance8 ,though the catastrophe may be averted for many ages by the powerful attraction of the larger planets1 especially ,jupiter1 will not the comet be at last precipitated on the ,sun8 ,the question is full of interest1 though altogether open to conjecture40 ,astronomers are not altogether agreed as to the propriety of this explanation4 ,one argument against it is that with perhaps one exception none of the other short-period comets 7all of them small and presumably deficient in density7 seem affected as ,encke's is4 ,on the other hand ,sir ,john ,herschel favoured the explanation just given1 as also does ,hind who is the highest living authority on comets4 ,a ,german mathematician1 ,von ,asten1 who devoted immense labour to the study of the orbit of ,encke's ,comet1 thought there should be no hesitation in accepting the idea of a resisting medium1 subject to the limitation that it does not extend beyond the orbit of ,mercury4 ,von ,asten's allusion to ,mercury touches a subject which belongs more directly to the question of ,mercury's orbit and to that other very interesting question1 8,are there any planets1 not at present known1 revolving round the ,sun within the orbit of ,mercury40 ,which is the largest and most magnificent comet recorded in history8 ,it is virtually impossible to answer this question1 because of the extravagant and inflated language made use of by ancient and medieval 7,i had almost added1 and modern7 writers4 ,there is no doubt that the comet of #afhj1 studied by ,sir ,i4 ,newton1 the tail of which was curved1 and from #gj to #ij long1 must have been one of the finest on record1 as it was also the one which came nearest to the ,sun1 for it almost grazed the ,sun's surface4 ,the comet of #agdd1 visible as it was in broad daylight1 was1 no doubt1 the finest comet of the #ahth century1 though in size it has been surpassed2 yet its six tails must have made it a most remarkable object4 ,so far as the #aith century is concerned1 our choice lies between the comets of #ahaa1 #ahdc1 #aheh1 and #ahfa4 ,the comet of #ahaa is spoken of by ,hind as 8perhaps the most famous of modern times4 ,independently of its great magnitude1 the position of the orbit and epoch of perihelion passage1 were such as to render it a very splendid circumpolar object for some months40 ,the tail as regards its length was not so very remarkable1 for at its best1 in ,october #ahaa1 it was only about #be long1 its breadth1 however1 was very considerable2 at one time #f1 the real length of the tail1 about the middle of ,october1 was more than #ajj1jjj1jjj of miles1 and its breadth about #ae1jjj1jjj of miles4 ,the visibility of this comet was coincident with those events which proved to be the turning-point in the career of ,napoleon ,i41 and there were not wanting those who regarded the comet as a presage of his disastrous failure in ,russia4 ,owing to the long period 7#ag months71 during which this comet was visible1 it was possible to determine its orbit with unusual precision4 ,argelander found its period to be #cjfe years1 with no greater uncertainty than #dc years4 ,the great dimensions of its orbit will be realised when it is stated that this comet recedes from the ,sun to a distance of #ad times that of the planet ,neptune4 ,illustration3 ,fig4 #bg4--,the ,great ,comet of #ahaa4 ,donati's comet of #aheh1 has already received a good deal of notice at my hands1 but the question remains1 what are its claims1 to be regarded as the comet of the century1 compared with that of #ahdc8 ,it is not a little strange that though there must have been many persons who saw both1 yet it was only quite recently that ,i came across1 for the first time1 a description of both these comets from the same pen4 ,it ought1 however1 to be mentioned by way of explanation1 that the inhabitants of ,europe only saw the comet of #ahdc1 when its brilliancy and the extent of its tail had materially diminished1 about a fortnight after it was at its best4 ,the description of these two comets to which ,i have alluded1 will be found in ,general ,j4 ,a4 ,ewart's 8,story of a ,soldier's ,life10 published in #ahha4 ,writing first of all of the comet of #ahdc1 ,general ,ewart says3-- 8,it was during our passage from the ,cape of ,good ,hope to the ,equator1 and when not far from ,st4 ,helena1 that we first came in sight of the great comet of #ahdc4 ,in the first instance a small portion of the tail only was visible1 at right angles to the horizon2 but night after night as we sailed along1 it gradually became larger and larger1 till at last up came the head1 or nucleus1 as ,i ought properly to call it4 ,it was a grand and wonderful sight1 for the comet now extended the extraordinary distance of one-third of the heavens1 the nucleus being1 perhaps1 about the size of the planet ,venus40--7,vol4 i41 p4 #ge47 ,illustration3 ,fig4 #bh4--,the ,great ,comet of #ahhb1 on ,october #ai 7,artus74 ,as regards ,donati's comet of #aheh1 what the ,general says is3-- 8,a very large comet made its appearance about this time1 and continued for several weeks to be a magnificent object at night2 it was1 however1 nothing to the one ,i had seen in the year #ahdc1 when on the other side of the equator40--7,vol4 ii41 p4 #bje47 ,passing over the great comet of #ahfa1 on which ,i have already said a good deal1 ,i must quit the subject of famous comets by a few words about that of #ahhb1 which1 though by no means one of the largest1 was1 in some respects1 one of the most remarkable of modern times4 ,it was visible for the long period of nine months1 and was conspicuously prominent to the naked eye during ,september1 but these facts1 though note-worthy1 would not have called for particular remark1 had not the comet exhibited some special peculiarities which distinguished it from all others4 ,in the first place1 it seems to have undergone certain disruptive changes1 in virtue of which the nucleus became split up into four independent nuclei4 ,then the tail may have been tubular1 its extremity being not only bifid1 but totally unsymmetrical with respect to the main part4 ,the tubular character of the tail was suggested by ,tempel4 ,to other observers1 this feature gave the idea of the comet1 properly so-called1 being enclosed in a cylindrical envelope1 which completely surrounded the comet1 and overlapped it for a considerable distance at both ends4 ,finally 7and in this resembling ,biela's comet7 the comet of #ahhb seems to have thrown off a fragment which became an independent body4 ,what has gone before1 will1 ,i think1 have served abundantly to establish the position with which ,i started1 namely1 that comets occupy 7and deservedly so7 the front rank amongst those astronomical objects in which1 on occasions1 the general public takes an interest4 ,i have thus completed1 so far as the space at my disposal has permitted1 a popular descriptive ,survey of the ,solar ,system4 ,those who have perused the preceding pages1 however slight may have been their previous acquaintance with the ,science of ,astronomy taken as a whole1 will have no difficulty in realising that what ,i have said bears but a small proportion to what ,i have left unsaid4 ,they will equally1 ,i hope1 be able to see1 without indeed the necessity of a suggestion1 that all those wondrous orbs which we call the planets could neither have come into existence nor have been maintained in their allotted places for so many thousands of years1 except as the result of ,design emanating from an ,all-powerful ,creator4 ,,footnotes4 #a,the remark in the text applies to all the major planets and to a large number of the minor planets1 but certain of the minor planets travel in orbits which are considerably inclined to the ecliptic1 and therefore to all the other planets4 #b;,given in full in my ,handbook of ,astronomy1 #dth ed41 vol4 i41 p4 #bf4 #c8,recollections of ,past ,life10 #bnd ed41 p4 #cje4 #d;,for some information respecting these ,secchi 8,types0 of ,stars1 see my 8,story of the ,stars10 #bnd ed41 p4 #adj4 #e,the circle and the ellipse are what are called 8closed0 curves4 #f;,it is not a little singular that the ,chinese in bygone centuries have often alluded to comets under the name of vapours2 e4g41 the comet of #afah is recorded as having been 8a white vapour #bj cubits long40 ,,appendix4--,,tables ,,of ,,the ,,solar ,,system4 ,,the ,,sun ,,and ,,planets4 ,name4 ,sidereal ,mean ,diameter4 ,surface4 ,volume4 ,mass4 ,density4 ,axial ,force of ,velocity period4 distance ,miles4 ,earth#a4 ,earth#a4 ,earth#a4 ,earth#a4 ,rotation4 gravity4 in orbit4 from d4 h4 m4 ,fall3 ,miles per ,sun4 ,ft4 in #a hour ,millions sec4 of miles4 ,,sun 44444 44444 #hff1bjj #aa1idf #a1cje1jjj #ccb1jjj #j4be #be #g #dh #dfa h4 m4 s4 ,,mercury #hh days4 #cf #c1jjh #j4add #j4jee #j4jff #a4bf #bd #e #cj #g #ajg1jjj ,,venus #bbe #fg #g1dhj #j4hia #j4hda #j4ghb #j4ib #bc #ba #bc #ad #gh1jjj ,,earth #cfe #ic #g1ibf #a4jjj #a4jjj #a4jjj #a4jj #bc #ef #d #af #ff1jjj ,,mars #fhg #ada #e1jjj #j4cih #j4bea #j4ajg #j4de #bd #cg #bc #d #ec1jjj ,minor ,planets ,eros 7#dcc7 #a4gf 44444 #ah ,eros is the nearest to the ,sun of the ,minor ,planets1 part years4 of its orbit falling between the ,earth and ,mars4 ,vesta 7#d7 #c4f #bai #bad ,vesta is the largest of the ,minor ,planets4 ,thule 7#bgi7 #h4h #cif 44444 ,thule is the most distant from the ,sun of the ,minor ,planets4 ,,jupiter #aa4h #dhc #hh1dci #abd #a1chi #cag #j4bc #i #ee #ba #da #bi1jjj ,,saturn #bi4d #hhf #ge1jcf #hi #hdh #id #j4aa #aj #bi #ag #ah #ba1jjj ,,uranus #hd4j #aghb #cj1hge #ae #ei #ad #j4be 8 #ac #ae1jjj ,,neptune #afd4f #bgib #cg1bje #ba #ajc #ag #j4ag 8 #ab #ab1jjj ,,satellite ,,of ,,the ,,earth4 ,name4 ,sidereal ,distance ,diameter ,surface4 ,volume4 ,mass4 ,density4 ,axial ,force of ,velocity period4 from ,miles4 ,earth#a4 ,earth#a4 ,earth#a4 ,earth#a4 ,rotation4 gravity4 in orbit4 d4 h4 m4 ,earth4 d4 h4 m4 ,fall3 ,miles per ,miles4 ,feet in hour4 #a sec4 ,,moon #bg #g #dc #bcg1cjj #b1afj #j4jgd #j4jbjcd #j4jabh #j4fc #bg #g #dc #b4dh #b1bgc ,,satellites ,,of ,,mars4 ,name4 ,discoverer4 ,mean ,sidereal ,diameter4 ,maximum ,apparent distance period4 ,miles4 elongation4 star from d4 h4 m4 magnitude4 ,mars4 ,miles4 #a4 ,,phobos ,a4 ,hall1 ,august #f1jjj #j #g #ci #g #ab #aa #ag1 #ahgg4 #b4 ,,deimos ,a4 ,hall1 ,august #ae1jjj #a #f #ah #f #cb #ac #aa1 #ahgg4 ,,satellites ,,of ,,jupiter4 ,name4 ,discoverer4 ,mean ,sidereal ,diameter4 ,apparent ,apparent distance period4 ,miles4 diameter star from d4 h4 m4 of ,jupiter magnitude4 ,jupiter4 seen from ,miles4 satellite4 #e4 ,barnard 4444444 #j #aa #di 8 44444 4444 #a4 ,,io 444444444444444 #bfg1jjj #a #ah #bi #b1cij #ai #di #g #b4 ,,europa ,galileo1 ,january #dbe1jjj #c #ac #ac #b1abj #ab #be #g #g-ac1 #afaj4 #c4 ,,ganymede 444444444444444 #fgh1jjj #g #d #j #c1ihj #g #dg #f #d4 ,,callisto 444444444444444 #a1aib1jjj #af #ah #e #b1igj #d #be #g ,,satellites ,,of ,,saturn4 ,name4 ,discoverer4 ,mean ,sidereal ,diameter4 ,apparent ,apparent distance period4 ,miles4 diameter star from d4 h4 m4 of ,saturn magnitude4 ,saturn4 seen from ,miles4 satellite4 #a4 ,,mimas ,sir ,w4 ,herschel1 #aae1jjj #j #bb #cg #a1jjj #cc #ag ,sept1 #ag1 #aghi #b4 ,,enceladus ,aug4 #bh1 #aghi #adg1jjj #a #h #ec 8 #bf #ae #c4 ,,tethys ,j4 ,d4 ,cassini1 #ahc1jjj #a #ba #ah #ejj #ba #ac ,march1 #afhd #d4 ,,dione ,march1 #afhd #bcd1jjj #b #ag #da #ejj #af #ab #e4 ,,rhea ,dec4 #bc1 #afgb #cbg1jjj #d #ab #be #a1bjj #ab #aj #f4 ,,titan ,huygens1 ,mar4 #be1 #geh1jjj #ae #bb #da #c1cjj #e #h #afec #g4 ,,hyperion ,w4 ,bond #iaf1jjj #ba #g #g 8 #d #ag ,lassell1 ,sept1 #ai1 #ahdh #h4 ,,iapetus ,j4 ,d4 ,cassini1 #b1bba1jjj #gi #g #ec #a1hjj #b #i ,oct4 #be1 #afga ,,satellites ,,of ,,uranus4 ,name4 ,discoverer4 ,mean distance ,sidereal ,maximum from ,uranus4 period4 elongation4 ,miles4 d4 h4 m4 #a4 ,,ariel ,lassell1 ,september #abd1jjj #b #ab #bh #ab #ad1 #ahdg #b4 ,,umbriel ,o4 ,struve1 ,october #h1 #agc1jjj #d #c #bg #ae #ahdg #c4 ,,titania ,sir ,w4 ,herschel1 #bhe1jjj #h #af #ee #cc ,january #aa1 #aghg #d4 ,,oberon #cha1jjj #ac #aa #f #dd ,,satellite ,,of ,,neptune4 ,discoverer4 ,mean distance ,sidereal ,maximum ,apparent from ,neptune4 period4 elongation4 star ,miles4 d4 h4 m4 magnitude4 ,lassell1 ,october #bbc1jjj #e #ba #h #ah #ad #aj1 #ahdf ,,general ,,index4 ,a4 ,adams1 ,j4 ,c41 #ade4 ,airy1 ,sir ,g4 ,b41 #ade4 ,anagram on ,venus1 #fh2 on ,saturn1 #abg4 ,aphelion1 #aa1 #ajb4 ,apparent movements of the ,planets1 #ab1 #ad4 ,arago1 ,d4 ,j4 ,f41 #ii1 #abd1 #adj4 ,arctic regions of the ,earth1 #ge4 ,argelander1 ,f4 ,g4 ,a41 #agh4 ,aristarchus of ,samos1 #ga4 ,aristarchus 7,lunar ,mountain71 #ic1 #id4 ,asteroids1 #aaj4 ,aurora ,borealis and spots on the ,sun1 #ee2 and twinkling1 #hg4 ,autumnal ,equinox1 #gd4 ,axial rotation of the ,planets1 #ag1 #ahc4 ,b4 ,barnard4 ,e4 ,e41 #abj1 #acd4 ,barnard's ,comet1 #afh4 ,bayeux ,tapestry1 #aga4 ,beer and ,mdler2 their map of the ,moon1 #if4 ,belts on ,jupiter1 #aae1 #abc2 on ,saturn1 #abb4 ,bergeron's ,experiment1 #ic4 ,bessel1 ,w41 #abd4 ,biela's ,comet1 #afh4 ,bode's so-called 8,law10 #aaj4 ,bond1 ,g4 ,p41 #acb1 #acc4 ,bouvard1 ,a41 #adc4 ,bradley1 ,rev4 ,j41 #add4 ,bredechin's theory of ,tails of ,comets1 #aeg4 ,brorsen's ,comet1 #afg4 ,c4 8,canals0 on ,mars1 #ajf4 ,carpenter1 ,j41 #acd4 ,carrington1 ,r4 ,c41 #df1 #di4 ,cassini1 ,j4 ,d41 #cf1 #aah1 #abh1 #acj1 #acf4 ,ceres 7,minor ,planet71 #aab4 ,challis1 ,rev4 ,j41 #adf4 ,charts1 ,celestial1 #aab1 #adg4 ,chinese observations1 #be1 #agb4 ,clouds influenced by the ,moon1 #ih4 ,coggia's ,comet1 #ahgd1 #aea4 ,comets1 #aej2 periodic1 #afb1 #agj2 remarkable1 #agf4 ,comparative sizes of the ,planets1 #aa4 ,comparative size of the ,sun from the ,planets1 #ag4 ,compression of the ,planets1 #gj1 #abb1 #acg4 ,conjunction of the ,planets1 #ad1 #ae1 #ff4 ,copernican ,system1 #gb4 ,copernicus1 #gb1 #gc1 #gf4 ,d4 ,d',arrest1 #adg4 ,d',arrest's ,comet1 #afh4 ,dawes1 ,w4 ,r41 #ajf1 #acc4 ,day and night1 #ab4 ,day1 length of1 #gd4 ,de ,la ,rue1 ,w41 #ce1 #cf1 #di1 #eb4 ,denning's ,comet1 #afh4 ,density of the ,planets1 #ag1 #ahc4 ,diameter of the ,sun and ,planets1 #ahc4 ,di ,vico1 #fb1 #fc4 ,di ,vico's ,comet1 #agb4 ,distance of the ,planets from the ,sun1 #bj1 #ahc4 ,donati's ,comet of #aheh1 #aeg1 #afc1 #agh4 ,dufour on ,twinkling1 #hd4 ,e4 ,earth1 annual motion of1 #ge2 figure of1 #gj4 ,earthshine1 #ff1 #ic4 ,eccentricity of ,planetary orbits1 #aj1 #fj1 #ge4 ,eclipses of the ,sun1 #ef1 #eg2 of the ,moon1 #abj4 ,ecliptic1 plane of1 #i1 #aj1 #gd4 ,egyptian ,system1 #gb4 ,elliptic ,orbits1 #aj4 ,elongation of ,planets1 #ad4 ,encke1 ,j4 ,f41 #adg4 ,encke's ,comet1 #afg1 #agd1 #age4 ,equinoxes1 #gd4 ,ewart1 ,gen4 ,j4 ,a41 #agh4 ,f4 ,facul on the ,sun1 #db1 #dc4 ,faye's ,comet1 #afh4 ,finlay's ,comet1 #afh4 ,flammarion1 ,c41 #fb1 #ff1 #aga4 ,flamsteed1 ,rev4 ,j41 #adj1 #add4 ,g4 ,galileo1 #hi1 #aja1 #abj1 #abe4 ,galle1 ,j4 ,g41 #adg4 ,gassendi1 #gf4 ,geodesy1 #gj4 ,georgium ,sidus1 #ada4 ,goldschmidt1 ,h41 #d4 ,granules1 ,solar1 #ch4 ,gravity on the ,sun and ,planets1 #ahc4 ,h4 ,hall1 ,a41 #aji4 ,halley's ,comet1 #afd1 #aga4 ,heat rays of the ,sun1 #bj2 of the ,moon1 #if4 ,herschel1 ,sir ,w41 #cd1 #dj1 #dd1 #eh1 #ajj1 #ajc1 #acd1 #acg1 #ach1 #adb4 ,herschel1 ,sir ,j4 ,f4 ,w41 #bd1 #if1 #ii1 #ajc1 #acb1 #age4 ,hind1 ,j4 ,r41 #aai1 #agc1 #age4 ,holden1 ,e4 ,s41 #ajf4 ,holland1 ,sir ,h41 #gh4 ,holmes's ,comet1 #ahib1 #aei4 ,homer's ,iliad1 cited1 #fh4 ,howlett1 ,rev4 ,f41 #dg4 ,huggins1 ,w41 #dj4 ,huygens1 ,c41 #abg1 #acj4 ,hyperbola1 #afb4 ,hyperbolic ,comets1 #afb4 ,i4 ,inclination of planetary orbits1 #i4 ,inferior ,planets1 #i1 #ab4 ,j4 ,janssen ,j41 #dg4 ,juno 7,minor ,planet71 #aab4 ,jupiter3 its influence on ,sun-spots doubtful1 #ea1 #ec2 on ,comets1 #aga2 its light1 #g4 ,k4 ,kepler1 #ee1 #abe1 #aff4 ,kew ,observatory1 #dg4 ,l4 ,la ,hire1 #fc4 ,lalande1 #cd4 ,lassell1 ,w41 #abc1 #adb1 #ahe4 ,ledger1 ,rev4 ,e41 #hd4 ,le ,monnier1 #adj1 #add4 ,le ,verrier1 ,u4 ,j4 ,j41 #adg4 ,lexell's ,comet1 #agb4 ,liais's ,comet1 #agj4 ,logogriphs as to ,venus1 #fh2 as to ,saturn1 #abg4 ,m4 ,mdler1 ,j4 ,h41 #fc1 #if4 ,magnetism1 ,terrestrial1 #ee4 ,maps1 ,astronomical1 #aab1 #adg4 ,mars1 #ajj4 ,maskelyne1 ,rev4 ,n41 #aci4 ,mass of the ,sun1 and of the ,planets1 #bj1 #ahc4 ,medium1 ,resisting1 #age4 ,mercury1 #eg2 phases of1 #ae2 its influence on ,sun-spots1 #ea2 its luminosity1 #fg4 ,milton1 ,j41 ,paradise ,lost1 cited1 #aec4 ,minor ,planets1 #aaj4 ,montigny on ,twinkling1 #hd4 ,moon1 #hi4 ,moonlight1 ,brightness of1 #if4 ,motions of the ,planets1 #aj4 ,mountains of the ,moon1 #ij4 ,n4 ,napoleon ,i41 #aed1 #agf4 ,nasmyth1 ,j41 #dj4 ,needle1 ,magnetic1 #ee4 ,neptune1 #adc2 its influence on ,uranus1 #adc4 ,newton1 ,sir ,i41 #agf4 ,nubian after-glow1 #hc4 ,nucleus of a ,sun-spot1 #bb4 ,o4 ,obliquity of the ecliptic1 #gd4 ,occultations of ,jupiter's ,satellites1 #aba4 ,olbers1 ,w41 #aab1 #agd4 ,opposition of ,planets1 #ac4 ,orbits of the ,planets1 #i1 #aj2 of ,comets1 #afa4 ,p4 ,pallas 7,minor ,planet71 #aab1 #aac1 #aad4 ,parabola1 #afb4 ,penumbra of a ,sun-spot1 #bb4 ,perihelion1 #aa1 #ajb4 ,periodic ,comets1 #afb1 #agj4 ,perturbations of ,uranus by ,neptune1 #ade4 ,phases of an inferior ,planet1 #ae2 of a superior ,planet1 #af2 of ,mars1 #ajj2 of ,jupiter1 #aae4 ,piazzi1 ,g41 #aaa4 ,planets1 classification of1 #g2 comparative sizes of1 #aa2 movements of1 #aj4 ,plutarch1 #ga4 ,poles of ,mars1 snow at1 #ajd4 ,primary ,planets1 #g4 ,ptolemaic ,system1 #gb4 ,q4 ,quadrature of a ,planet1 #af4 ,quenisset's ,comet1 #ahic1 #aef4 ,r4 ,rays of the ,sun1 #bj4 ,refraction1 #gg2 effect of1 #gg4 ,red spot on ,jupiter1 #aah4 ,resisting ,medium1 #age4 ,retrograde motion of a ,planet1 #ae4 8,rice grains0 on the ,sun1 #ci1 #dj4 ,rings of ,saturn1 #abh4 ,rosse1 ,earl of1 #ic4 ,rotation of the ,sun1 #bd1 #bh2 of the planets1 #ag1 #ahc4 ,rotundity of the ,earth1 #gf4 ,s4 ,satellites of ,mars1 #af1 #ahd2 of ,jupiter1 #af1 #ahd2 of ,saturn1 #af1 #ahe2 of ,uranus1 #af1 #ahe2 of ,neptune1 #af1 #ahe4 ,saturn1 #abb4 ,sawerthal's ,comet1 #afe4 ,schiaparelli1 ,j4 ,v41 #ei1 #fb1 #fc1 #ajf4 ,schmidt1 ,j4 ,f4 ,f41 #if4 ,schrter1 ,j4 ,j41 #eh1 #fb1 #fc4 ,schwabe's observations of ,sun spots1 #df4 ,seas1 ,lunar1 #id4 ,seasons on the ,earth1 #ed1 #gd4 ,secchi1 ,a41 #bh1 #ce1 #db1 #ej1 #hd1 #hf1 #ajf4 ,secondary ,planets1 #h4 ,shakespeare1 citations from1 #aeb4 ,smyth1 ,c4 ,p41 #ib4 ,snow on ,venus1 #ff2 on ,mars1 #ajd2 doubtful on ,saturn1 #abc4 ,solstices1 #gd4 ,spherical form of the ,earth1 #gj4 ,sprer1 #df1 #ej4 ,spots on the ,sun1 #ba1 #aah2 on ,venus1 #fa2 on ,jupiter1 #aag2 on ,saturn1 #abc4 ,stewart1 ,b41 #eb1 #ef4 ,struve1 ,o41 #acd1 #adb4 ,sun1 #ah1 #ahc4 ,superior ,planets1 #h2 movements of1 #ae4 ,surfaces of the ,sun and ,planets1 #ahc4 ,swift's ,comet1 #afh4 ,systems of the ,universe1 #gb4 ,t4 ,tables of the ,major ,planets1 #ahc4 ,tails of ,comets1 #aed4 ,temple's ,periodical ,comets1 #afg4 ,terminator of the ,moon1 #ij4 ,thomson's ,seasons cited1 #aec4 ,tides1 #ih4 ,total ,eclipses of the ,sun1 #eg4 ,transits of inferior ,planets1 #ac1 #be1 #fe4 ,trouvelot1 #acc4 ,turtle's ,periodical ,comet1 #afg1 #afh4 ,twilight1 #hj4 ,twinkling1 #hc4 ,tycho 7,lunar ,mountains71 #id4 ,tycho ,brahe1 #gc4 ,tychonic ,system1 #gc4 ,u4 ,umbra of a ,sun-spot1 #bb4 ,uranus1 #ach2 the influence of ,neptune on1 #adc4 ,v4 ,velocity of the planets1 #ahc4 ,venus1 #fa2 phases of1 #ae2 its influence on ,sun-spots1 #ea1 #eb1 #ec4 ,vernal ,equinox1 #gd4 ,vesta 7minor planet71 #aab1 #aac4 ,virgil1 citation from1 #ej4 ,volume of the ,sun1 #bj2 of the ,planets1 #ahc4 ,w4 ,weather influences ascribed to the ,sun1 #dd2 to the ,moon1 #ih4 8,willow leaves0 on the ,sun1 #ci1 #dj4 ,wilson's theory of ,sun-spots1 #cb4 ,winnecke's ,periodical ,comet1 #afg4 ,wolf1 ,r41 observer of ,sun-spots1 #de1 #dh4 ,wolf's ,periodical ,comet1 #afh4 ,y4 ,young1 ,c4 ,a41 #aca4 ,z4 ,zodiac1 movement of ,planets in1 #ae4 ,,the ,,end4 ,transcriber's ,notes --,some palpable typographical errors were corrected4 --,copyright and publisher's information was included from the printed copy3 this e,book is public domain in the country of publication4