,,flowers ,,of ,,the ,,sky ,,flowers ,,of ,,the ,,sky ,,by ,,richard ,a4 ,,proctor ,,author ,,of ,,the ,,expanse ,,of ,,heaven1 ,,the ,,infinities ,,around ,,us1 ,,the ,,universe ,,of ,,stars1 ,,the ,,sun1 ,,the ,,moon1 ,,etc41 ,,etc4 ,,with ,,fifty-,,four ,,illustrations ,illustration ,new ,york ,a4 ,c4 ,,armstrong ,,and ,,son #gad1 ,,broadway ,all rights reserved ,spirit of nature6 here1 ,in this interminable wilderness ,of worlds1 at whose immensity ,even soaring fancy staggers1 ,here is thy fitting temple4 ,yet not the lightest leaf ,that quivers to the passing breeze ,is less instinct with thee4--,shelley4 ,,contents4 ,,page ,i4 ,,light #a ,,ii4 ,,space #ag ,,iii4 ,,the ,,infinitely ,,minute #ca ,,iv4 ,,the ,,mystery ,,of ,,gravity #dc ,v4 ,,the ,,end ,,of ,,many ,,worlds #ef ,,vi4 ,,the ,,aurora ,,borealis #ia ,,vii4 ,,the ,,lunar ,,halo #aad ,,viii4 ,,moonlight #abe ,,ix4 ,,the ,,planet ,,mars #adi ,x4 ,,the ,,planet ,,jupiter #aia ,,xi4 ,,the ,,ringed ,,planet ,,saturn #bae ,,xii4 ,,fancied ,,figures ,,among ,,the ,,stars #bcf ,,xiii4 ,,transits ,,of ,,venus #bgc ,illustration ,i4 ,,light4 ,what soul was his1 when1 from the naked top ,of some bold headland1 he beheld the sun ,rise up and bathe the world in light6 ,he looked-- ,ocean and earth1 the solid frame of earth ,and ocean's liquid mass1 beneath him lay ,in gladness and deep joy4 ,we live in a mighty ocean whose waves are ever rushing hither and thither1 always according to law1 with velocity inconceivable1 almost immeasurable4 ,these waves lave the shore of that island of space which is our home1 travelling to it from remotest regions1 and making known to us all that we know of what lies outside our small abode4 ,we call these waves1 or rather their effects1 by the name of ,light4 ,we recognise in light-- offspring of ,heav'n's first-born ,and of th' ,eternal co-eternal beam-- the antecedent of all else that exists in the universe2 or1 as ,sir ,john ,herschel said1 the superior in point of rank and conception to all other products or results of creative power in the physical world4 ,it is light which alone can give1 and does give us1 the assurance of a uniform and all-pervading energy--a mechanism almost beyond conception1 complex1 minute1 and powerful1 by which that influence1 or rather that movement1 is propagated4 ,our evidence of the existence of gravitation fails us beyond the region of the double stars1 or leaves at best only a presumption amounting to moral conviction in its favour4 ,but the argument for a unity of design and action afforded by light stands unweakened by distance1 and is co-extensive with the universe itself4 ,what1 then1 is light8 ,what is that mysterious movement of some essence pervading all space1 whereby1 from remotest depths1 news is brought to us1 after journeys lasting many years1 though space is traversed at a rate exceeding more than ten million times the velocity of the swiftest express train8 ,light is in reality the result of undulations in what is called the ether of space1 a perfectly transparent1 almost perfectly elastic medium1 occupying not only void space1 but flowing as freely through the densest solids as the summer breeze flows through the forest trees4 ,the waves of light cannot in this way pass through solid or liquid1 or even aerial bodies1 but either they are sooner or later brought to rest1 or else they are more or less gradually deflected2 just as the waves which traverse the ocean come to their end1 or are deflected1 when they meet the shore or shallows near the shore4 ,all light1 however1 has its real origin1 not in the ethereal ocean itself1 but in the movements of the minute particles of which all forms of matter known to us are composed4 ,a tiny atom1 far too small to be perceived with a microscope1 even though one should be made ten thousand times more powerful than any yet constructed1 when set in rapid vibration1 raises minute waves in the ethereal ocean1 just as a small body1 vibrating on the surface of a sheet of water1 would generate waves there4 ,and as the water-waves would travel radially away from the place of their birth1 so do the light-waves generated by the vibrations of one of the atoms composing a luminous body radiate forth in all directions through the ethereal ocean until1 encountering some obstacle1 they are sent 7reduced in size7 in a new direction4 ,in some luminous bodies there are atoms vibrating in many different periods 7all very small7 so as to cause light-waves of many different kinds to proceed from the body4 ,in other cases the atoms all vibrate at one rate1 or at two or three or some definite number of rates1 so that only light-waves of certain kinds proceed from the body4 ,but in all cases these light-waves only cause us to see the body when they flow in through the pupil of the eye1 and falling upon the retina 7or the choroid membrane1 or whatever part of the eye it may be which finally receives the waves71 convey to the optic nerve1 and thence to the brain1 the information that such and such a body1 so coloured1 so shaped1 so moving1 exists towards that direction from which the light-waves seem to come4 ,the body so seen1 as we call it1 may be the original source of light1 or may be a body on which light has been reflected to us4 ,it is in this way that we receive information from light-waves4 ,it will be conceived how minute they must be1 how perfectly they must retain their separate character1 multitudinous though they are1 in traversing the ether 7even when that ether is clogged by the gross matter of our ordinary air71 if we remember how through the tiny eye-pupil we often receive light-waves telling us of all the details1 all the varieties of colour and brightness1 all the movements in a rich landscape4 ,even more startling are the thoughts suggested by a view of the starlit heavens4 ,from hundreds of suns at once the light-waves which have traversed varying but all enormous distances pour in upon the small circle of the eye-pupil1 waves of many kinds coming in together from each sun4 ,the waves which thus reach the eye from one bright star have been but a few years upon their journey2 all that time they have been traversing an ocean swept in every part by untold millions of other waves1 and yet they arrive as perfect in order and regularity as rollers which have traversed a wide sea pour in upon a level shore4 ,from another star1 as bright as the first1 they have been years in travelling2 from some among the fainter stars1 hundreds1 perhaps thousands of years4 ,yet still they flow on1 each order of waves in perfect uniformity as when they first left their parent sun4 ,but even this is not all4 ,among the waves which reach the eye many1 nay1 most1 are so small that ordinary vision cannot perceive their action4 ,take1 however1 a telescope1 and so gather them together as to intensify this action1 and they are rendered perceptible1 just as the unnoticed heaving of ocean becomes a manifest wave-motion when it reaches a regularly narrowing inlet4 ,thus1 from stars so remote that their light has required thousands1 or1 even in some cases1 perhaps1 hundreds of thousands of years in reaching us1 the light-waves flow steadily in upon us4 ,so small are these waves1 that the breadth of from forty to sixty thousand of them would occupy but a single inch4 ,through every point in space waves from all the hundred millions of stars are at all times simultaneously rushing at the rate of one hundred and eighty-five thousand miles in every second of time3 yet they travel on altogether undisturbed1 and each tells its story as distinctly as though the ether had conveyed no other message1 and that message but for a short distance4 ,it would be difficult to say which thought1 considered in its real significance1 is more striking1--the thought of what is done for us by light regarded as a terrestrial phenomenon1 or the thought of what light is doing1 and has done1 in presenting to us a view of the starlit heavens4 ,when the sun rises in splendour above the eastern horizon1 tinting the sky with varied colours1 lighting up the clouds which till then have been but dark patches on the heavens1 bringing out the colours of hill and dale1 rock and river1 fields and woods1 the heart gladdens at the spectacle4 ,a pleasing melancholy falls on us as the light fades away at eventide1 tint after tint vanishing1 until at length the gloom of night enshrouds all4 ,the full splendour of mid-day1 the chastened splendour of a moonlit night1 and the glory of the heavens when all the stars shine1 and the shepherd gladdens in his heart1 stir the soul in like manner2 and it might seem to many that to analyse these glories1 to explain their scientific meaning1 would be to rob the mind of the pleasure it had before found in such scenes4 ,many would be disposed to think that a purer enjoyment is expressed by ,augustine than any student of science could find in the wonders of light1 in those words in which he expresses his sense of the loveliness of fair forms and brilliant colours4 ,for light1 queen of the colours1 he says1 bathing all ,i can look upon1 from morning till evening1 let me go where ,i will1 will still keep gliding by me in unnumbered guises1 and soothe me whilst ,i am busy at other things1 and am thinking nothing of her4 ,but the sensuous pleasure afforded by light is enhanced1 while a purer and higher enjoyment is superadded1 when the real meaning of the display is understood4 ,as the astronomer sees in the sun a more glorious object than the sun of the poet1 recognising in imagination not only the visible splendour of that orb1 but the mighty energy with which it is swaying the motions of a scheme of circling worlds1 the wondrous activities at work throughout its entire frame1 the inconceivable tumult which must prevail in that seemingly silent globe1 so the glories of light1 rightly understood1 are far more impressive than as they appeal simply to the senses4 ,illustration3 ,fig4 #a4--,sunrise on the ,righi4 ,consider1 for instance1 the real meaning of sunrise4 ,the orb seemingly rising above the horizon1 but1 in reality1 at rest1 is the source of all the glory which is spreading over the fair face of earth4 ,the atoms of that remote body1 vibrating with intensest activity1 send forth in all directions ethereal waves1 and of these relatively but a very few1 about one in two thousand millions1 fall upon our earth1 producing the phenomena of sunlight4 ,they have been little more than eight minutes on the road1 but in that short time they have traversed more than #ij1jjj1jjj of miles4 ,were they to fall directly upon our earth1 we should see few of the splendours which attend the uprising of the sun4 ,the deep air clothing our earth receives the onward rushing waves1 and reflects them in all directions4 ,to use ,biot's simile1 ,the air is a sort of brilliant veil1 which multiplies and diversifies the sunlight by an infinity of repercussions4 ,nor is the wonder of the scene1 or its effect in filling the mind with solemn and poetic thoughts1 diminished--on the contrary1 it is enhanced--by the recollection that the gradually growing glory of day is brought about by the slow turning of the mighty earth1-- that spinning sleeps ,on her soft axle1 as she paces even1 ,and bears us soft with the smooth air along4 ,but if this is true of a scene of terrestrial splendour1 how much more fully may it be said of the glories of the heavens8 ,no poet1 if unaware of the real meaning of modern discoveries respecting the celestial bodies1 can be moved by the starlit depths as the astronomer is1 at least the astronomer whose study of science is not limited to mere observation and calculation4 ,hundreds of bright points of light sparkling1 and sometimes varying strangely in colour1 form1 no doubt1 a beautiful scene2 but the scene is not less beautiful1 and certainly it is far more impressive1 when we remember that every one of these points of light is a sun1 mighty in attractive energy like ours1 its whole surface glowing with fiery heat1 and every particle of its substance constantly in motion1 if not always in the fierce rush of cosmic hurricanes1 yet with the ceaseless vibrations which generate the ethereal light-waves telling us of the star's existence4 ,there is one strange thought connected with the motion of light-waves through the ether of space which has not1 ,i think1 received the attention it deserves4 ,every one knows that when we look at the heavens we do not see the celestial bodies where they are1 but where they were1 and again1 not where they were at any one moment of time1 but some where they were a short time ago1 others where they were very long ago4 ,but it is not so generally known1 or remembered by those who do know it1 that if light were not so active as it is the result would be that utterly incorrect pictures of the celestial depths would continually be presented to us4 ,as matters actually are no orb in space can appear very far from its true place4 ,we see the sun1 for instance1 at any moment1 not where he is1 but where he was 7or rather towards the direction in which he lay7 about eight minutes before4 ,but as the real velocity of the earth1 and therefore the apparent velocity of the sun1 amounts only to about eighteen miles per second1 the sun is only thrown about #ijjj miles out of his true position1 which is but about the ninetieth part of his diameter3 so that we see the sun very nearly in his right place4 ,now it might seem that a star whose light takes1 say1 twenty years in reaching us1 must be seen very far from its true place1 supposing the star to be travelling along very quickly2 and1 in one sense1 this is true4 ,if such a star is moving at the rate of fifty miles per second1 athwart the line of sight1 it will be out of place by so considerable a distance as #cae1jjj1jjj1jjj of miles4 ,yet the star will appear very nearly in its true position1 simply because1 at the star's enormous distance from us1 even the great distance just named is reduced to a very small apparent amount4 ,such a star would1 in fact1 be displaced by only about the thirtieth part of the sun's or moon's apparent diameters1 or by about a fifteenth part of the distance separating the middle star of the ,great ,bear's tail from its small companion1 sometimes called ,jack by the ,middle ,horse4 ,thus the stellar heavens present very truly to us the positions of the stars2 for such athwart motion as ,i have just imagined would be very much larger than the motion of far the greater number of the stars4 ,but we only thus see the heavens truly pictured because of the enormous velocity with which light travels4 ,if light swept along only at the rate of a hundred miles in a second 7a velocity still far beyond our powers of conception71 there would be no believing what we should see1 for every star1 and our own sun1 and all the planets1 and even our own companion planet1 the moon1 would be thrown in appearance very far from their true positions4 ,if they were all shifted in position by the same amount and in the same direction the picture would still be true1 in a sense1 just as we see a true picture of an object at the bottom of a clear lake1 though the picture is displaced by the refractive action of the water on the rays of light4 ,but1 in the imagined case1 the sun1 and moon1 and planets1 and stars would be shifted by different amounts and in different ways1 simply because they are moving at different rates and in different directions4 ,the scene presented to us would have been utterly untrue4 ,astronomy as a science could probably have had no existence in such a case4 ,assuredly it could have had no existence until students of the heavenly bodies had learned to accept as the first axiom of their science the doctrine that ,seeing is not believing4 ,illustration3 ,fig #b4--,sunset at ,sea4 ,a strange thought truly1 that so active are the orbs peopling space1 so swiftly do they rush onwards upon their orbits1 that light1 carrying its message at a rate exceeding six thousand times the velocity of the swiftest express train1 would be utterly unable to give a true account of the position and movements of the celestial bodies4 ,fortunately light gives a true record1 because the qualities of the cosmic ether are such that the message of light is transmitted hundreds of times more swiftly than the swiftest bodies in the universe travel onwards upon their orbits around each other or in space4 ,illustration ,,ii4 ,,space ,although astronomy tells us in clearest words of the vast depths of space which surround our earth on all sides1 we are not thereby enabled to realize their enormous extension4 ,it is not merely that the unknown depths beyond the range of our most powerful telescopes are inconceivable1 but that the parts of space which we can examine are on too large a scale for us to conceive their real dimensions4 ,it is hardly going too far to say that our powers of actual conception are limited to the extent of space over which the eye seems to range in the daytime4 ,of course in the daytime1 at least in clear weather1 there is one direction in which the eyesight ranges over a distance of many millions of miles1--namely1 where we see the sun4 ,but the sense of sight is not cognisant of that enormous distance1 and simply presents the sun to us as a bright disc in the sky1 or perhaps rather nearer to us than the sky4 ,even the distance of the sky itself is under-estimated4 ,a portion of the light we receive from the sky on a clear day comes from parts of the atmosphere distant more than thirty or forty miles from us2 but the eye does not recognise the fact4 ,the blue sky seems a little farther off than the clouds1 but not much2 the light clouds of summer seem a little but not much farther off than the heavier clouds of a winter sky2 a cloud-covered winter sky seems a little farther off than heavy rain-clouds4 ,the actual varieties of distance among clouds of various kinds are not much more clearly discerned than the actual varieties of distance among the heavenly bodies4 ,the estimate formed of the distance of a cloud-covered sky overhead probably amounts to little more than a mile1 and it is very doubtful whether the mind presents the remotest depths of a blue sky overhead at more than two miles4 ,towards the horizon the distance seems greater1 and probably on a cloudy day the sky near the horizon is unconsciously regarded as at a distance of about five miles1 while blue sky near the horizon may be regarded as lying at a distance of six or seven miles1 the arch of a blue sky seeming to be far more deeply curved than that of a cloud-covered sky4 ,it is to distances such as these that the mind unconsciously refers the celestial bodies4 ,we know that the moon is about #b1jjj miles in diameter1 but the mind refuses to present her to us as other than a round disc much smaller than those other objects in sight which occupy a much larger portion of the field of vision4 ,the sun cannot be conceived to exceed the moon enormously in size1 seeing that he appears no larger2 and all the multitude of stars are judged by the sight to be mere bright points of light in reality as they appear to be4 ,how1 then1 can we hope to appreciate the vastness of space whereof astronomy tells us8 ,to the student of science attempting to conceive the immensities of whose existence he is assured1 the same lesson might be taught in parable which the child of ,st4 ,augustine's vision taught the ,numidian theologian4 ,as reasonably might an infant hope to pour the waters of ocean into a hollow1 scooped with his tiny fingers in the sand1 as man to picture in his narrow mind the length and breadth and depth of the abysses of space in which our earth is lost4 ,yet1 as a picture of a great mansion may be so drawn on a small scrap of paper as to convey just ideas of its proportions1 so may the great truths which astronomy has taught us about the depths of space be so presented that just conceptions may be formed of the proportions of at least those parts of the universe which lie within the range of scientific vision1 though it would be hopeless to attempt to conceive their real dimensions4 ,thus1 when we learn that a globe as large as our earth1 suspended beside the moon1 would seem to have a diameter exceeding hers nearly four times1 so that the globe would cover a space in the heavens about thirteen times as large as the moon covers1 we form a just conception of the size of the moon as compared with the earth1 though the mind cannot conceive such a body as the moon or the earth really is4 ,when1 in turn1 we are told that if a globe as large as the earth1 but glowing as brightly as the sun1 were set beside the sun1 it would look a mere point of light1 we not only learn to picture rightly to ourselves how largely the sun exceeds the earth1 but also how enormous must be the real distance of the sun4 ,another step leads us to a standpoint whence we can form a correct estimate of the vast distance of the fixed stars2 for we learn that so enormous is the distance of even the nearest fixed star1 that the tremendous space separating the earth from that star sinks in turn into the merest point1 insomuch that if a globe as bright as the sun had the earth's orbit as a close fitting girdle1 then this glorious orb 7with a diameter of some #ahd1jjj1jjj of miles7 would look very much smaller than such a globe as our earth would look at the sun's distance--would1 in fact1 occupy but about one-fortieth part of the space in the sky which she1 though she would then look a mere point1 would occupy if viewed from that distance4 ,but there is a way of viewing the immensities of space which1 though not aiding us indeed to conceive them1 enables the mind to picture their proportions better than any other4 ,the dimensions of the earth's path around the sun sink into insignificance beside those of the outermost planets2 but these in their turn dwindle into nothingness beside those of some among the comets4 ,from the paths of these comets1 if only sentient and reasoning beings could trace out in a comet's company those mighty orbits1 and could have for the duration of their existence not the brief span of time which measures the longest human life1 but many circuits of their comet home around the same ruling orb 7as we live during many circuits of our globe around the sun71 the dimensions of the star-depths1 which even to scientific insight are all but immeasurable1 would be directly discernible4 ,not only would the proportions of that mighty system be perceived1 whose fruits and blossoms are suns and worlds1 but even the gradually changing arrangement of its parts could be discerned4 ,some comets1 indeed1 as ,i pointed out in an essay on comets several months ago 7see ,expanse of ,heaven1 p4 #adi71 do not travel around the sun1 but flit from sun to sun on journeys lasting millions of years1 paying each sun but a single visit4 ,a being inhabiting such a comet1 and having these interstellar journeys as the years of his existence1 so that he could live through many of them1 would have a wonderful insight into the economy of the stellar system4 ,if his powers of conception as far exceeded ours as the range of his travels and the duration of his existence1 he would be able to recognise the proportions of a large part of the stellar universe as clearly as we recognise the proportions of the solar system4 ,but leaving these wonderful wanderers1 whose journeys are as far beyond our powers of conception as the immensity of the regions of star-strewn space1 we may find1 among the comets belonging to the sun's domain1 bodies whose range of travel would give their inhabitants far clearer views of the architecture of the heavens than even the profoundest terrestrial astronomer can possibly obtain4 ,such a comet as ,halley's 7fig4 #c7 for instance1 though one of comparatively limited range in space1 yet travels so far from the sun that1 from the extreme part of its path1 it sees the stars displaced nearly twenty times as much 7owing to its own change of position7 as they are from the earth on opposite sides of her comparatively narrow orbit4 ,and the length of this comet's year1 if it indicated the length of the lives of all creatures travelling along with it1 would suggest a power of patiently watching the progress of changes lasting not a few of our years only1 but for centuries4 ,seventy-five or seventy-six years elapse between each return of this comet to the sun's neighbourhood1 and one who should have lived during sixty or seventy circuits of this body around its mighty orbit would have been able to watch the rush of stars1 with their velocities of many miles per second1 until visible displacements had taken place in their positions4 ,illustration3 ,fig4 #c4--;,halley's ,comet of #ahce4 ,this1 however1 is as nothing compared with the mighty range in space and the enormous period of the orbit of the great comet of the year #ahaa 7fig4 #d74 ,this comet is1 on the whole1 the most remarkable ever known4 ,it was visible for nearly seventeen months1 and though it did not approach the sun within #ajj1jjj1jjj miles1 and was therefore not subject to that violence of action which has caused enormous tails to be thrown out from comets which have come within a few million miles of him1 or even within less than a quarter of his own diameter1 it flourished forth a tail #abj1jjj1jjj of miles in length4 ,its orbit has1 according to the calculations of the astronomer ,argelander1 a space exceeding the earth's distance from the sun #baa times1 and thus surpassing even the mighty distance of ,neptune fully seven times4 ,it occupies in circuiting this mighty path no less than #cjfe of our years 7with a possible error either way of about forty-three years74 ,so that1 according to ,bible chronology1 this comet's last appearance probably occurred during the rule of the judge ,tola1 son of ,puah1 son of ,dodo1 over the children of ,israel1 though it may have occurred during the rule of his predecessor ,abimelech1 or during that of his successor ,jair4#a ,during one half of the enormous interval between that time and #ahaa the comet was rushing outwards into space1 reaching the remotest part of its path somewhere about the year #bgh 7,a4,d471 and from that time to #ahaa it was on its return journey4 ,it is strange to think1 however1 that though the remotest part of its path lay #baa times farther from the sun than the earth's orbit1 yet even this mighty path1 requiring more than #cjjj years for a single circuit1 cannot be said to have carried the comet into the star-depths4 ,if the earth were to shift its position by the same enormous amount the nearest fixed star would have its apparent position changed only by about an eighth part of the apparent diameter of the sun or moon1 or by about one-quarter of the distance separating the middle star of the ,bear's tail from its close companion4 ,illustration3 ,fig4 #d4--;,comet of #ahaa4 ,but this fact of itself is most strikingly suggestive of the vast distance of the stars4 ,for consider what it means4 ,imagine the middle star of the ,bear's tail to be the really nearest of all the stars instead of lying probably twenty or thirty times farther away4 ,conceive a comet belonging to that sun after making its nearest approach to it to travel away upon an orbit requiring #cjjj years for each circuit4 ,then 7supposing that star equal to our sun in mass71 the comet1 though rushing away from its sun with inconceivable velocity during #aejj years1 would1 at the end of that vast period1 seem to be no farther away than one-fourth of the distance separating the sun from its near companion4 ,look at the middle star of the ,bear's tail on any clear night1 and on its small satellite1 remembering this fact1 and the awful immensity of the star depths are strongly impressed upon the mind4 ,but the observer must not fail to remember that the star really is many times more remote than we have here for a moment supposed1 and that such a comet's range of travel would be proportionately reduced4 ,moreover1 many among the stars are1 doubtless1 hundreds1 even thousands1 of times still farther away4 ,illustration3 ,fig4 #e--,six-tailed ,comet of #agdd4 ,let us turn lastly to the amazing comet of the year #agdd1 pictured1 at the time1 as shown in fig4 #e 7though probably the drawing is greatly exaggerated74 ,we find that though it had the longest period of any which has ever been assigned to a comet as the result of actual mathematical calculation1 yet its range in space would scarcely suffice to change the position of the stars in such sort that the aspect of the familiar constellations would be materially altered4 ,euler1 the eminent mathematician1 calculated for this comet a period of #abb1fhc years1 which would correspond1 ,i find1 to a distance of recession equal to #bdfi times the distance of the earth from the sun1 or about eighty times the distance of ,neptune4 ,yet this is but little more than twelve times the greatest distance of the comet of #ahaa4 ,probably the actual range of such an orbit from the middle star of the ,bear's tail would be equal in appearance to the range described above on the supposition that the star is no farther from us than the nearest known star 7,alpha ,centauri74 ,that is1 such a comet1 if it could be seen and watched during a period of about #abb1jjj years1 would seem to recede from the star to a distance equal to about one-fourth the space separating it from its close companion1 and then to return to the point of nearest approach to its ruling sun4 ,such are the immensities of star-strewn space6 ,the journey of a comet receding from the sun with inconceivable velocity during hundreds of thousands of years carries it but so small a distance from him compared with the distance of the nearest star as scarcely to change the appearance of the celestial landscape2 and yet the distances separating the sun from the nearest of his fellow suns are but as hair-breadths to leagues when compared with the proportions of the scheme of suns to which he belongs4 ,these distances1 though so mighty that by comparison with them the inconceivable dimensions of our own earth sink into utter nothingness1 do not bring us even to the threshold of the outermost court of that region of space to which the scrutiny of our telescopes extends4 ,yet the whole of that region is but an atom in the infinity of space4 ,,footnotes3 #a ,it might be suggested that the appearance of this blazing comet among the stars drove the more superstitious of the ,israelites at that time to the worship of star-gods1 as we read how1 during the judgeship of ,jair1 they served ,baalim1 and ,ashtaroth1 and the gods of ,syria1 and the gods of ,moab1 and the gods of the ,philistines1 and forsook the ,lord and served not ,him4 ,to a people like the ,jews1 who seem to have been in continual danger of returning to the ,sabaistic worship of their ,chaldean ancestors1 the appearance of a blazing comet may have been a frequent occasion of backsliding4 ,illustration ,,iii4 ,,of ,,the ,,infinitely ,,minute4 ,when ,i speak of the infinitely minute1 ,i use the word infinitely not in its absolute sense1 but relatively4 ,actual infinity of minuteness is as utterly beyond our conceptions as actual infinity of vastness4 ,but we may speak of what is very much less than the least object of which our senses can make us directly conscious as for us infinitely minute4 ,among the greatest wonders science has to deal with are those relating to bodies and movements thus beyond the direct ken of our senses4 ,there is a universe within the universe which our senses reveal to us1--a universe whose structure is so fine that the minutest particle which the microscope can reveal to us is1 by comparison1 like one of the suns which people our universe compared with the unseen particles constituting matter4 ,it is a strange thought that the objects constituting our universe1 so long regarded by man as the only universe1 are in a sense pervaded by the materials of an utterly different universe1--which yet is as essential to our very existence as what we commonly call matter4 ,we cannot live without light and heat1 for instance1 and again1 light and heat affect matter as we know it2 but they thus exist and affect such matter by means only of a form of matter unlike any which we can conceive4 ,it is certain that if absolute vacancy separated our earth from the sun1 even by the narrowest imaginable gap1 his heat and light could never reach us4 ,they could no more pass that vacant space than the wave-motion of water can cross a space where water itself is wanting4 ,it is because of relations such as these that it has been said1 and justly1 that matter is the less important half of the material constituting the physical universe4 ,our knowledge of this universe within our universe has been obtained within comparatively recent years4 ,men were unwilling or at least they spoke and thought as if they were unwilling1 to believe that the universe of matter which they had so long recognised was dependent on another universe for its chief if not all its properties4 ,they regarded heat as some sort of substance1 which might1 with more delicate means than they possessed1 admit of being dealt with as chemists had dealt with the gases4 ,the sun was full of this fluid1 this phlogiston1 as it was called4 ,light1 in so far as it could be distinguished from heat1 was another fluid2 electricity was another4 ,these were the imponderables1 or unweighable substances of last century's science1--not as with us1 the effects of modes of motion taking place in a universe which1 though material1 is yet not made of matter such as we know1 or even such as we can at present conceive4 ,this is the greatest of all human scientific marvels1--the greatest because it includes all others4 ,we know of a universe which is as infinite in extent1 and doubtless in duration1 as our own universe2 which pervades all forms of matter3 and yet we know of this universe only indirectly2 by the effects of movements taking place within it1 not by any perception of these movements themselves4 ,waves are ever beating upon the shores of our material universe1 and constantly changing the form and condition of the coast line1 but the waves themselves are unseen4 ,we only know of their existence through the changes wrought by them4 ,we speak of the ether of space1 and of waves traversing it1 as though the ether were simply some fluid very much more attenuated than the rarest gas1 even in a so-called vacuum4 ,but in reality1 so soon as we attempt to apply to the movements taking place in such an ether the mechanical considerations which suffice for the motions of all ordinary forms of matter1 we perceive that it must of necessity be utterly unlike any kind of substance known to us4 ,for instance1 we find that though it is like a gas in being elastic1 its elasticity is infinite compared with that of any material gas4 ,again1 it is like a solid in retaining each of its particles always very near to a fixed position2 but again1 no solid we know of can be compared with it for a moment as respects this kind of rigidity4 ,it is at once infinitely elastic and infinitely rigid4 ,we cannot1 for example1 explain the phenomena of light unless we suppose the elasticity of the ether at least #hjj1jjj1jjj1jjj times greater than the elasticity of air at the sea-level2 and yet1 as ,sir ,j4 ,herschel long since pointed out1 every phenomenon of light points strongly to the conclusion that none of the particles of the ether can be supposed capable of interchanging places1 or of bodily transfer to any measurable distance from their own special and assigned localities in the universe4 ,again1 how are we to explain the continuance of the ether in its present condition1 when we recognise the fact that a gas of similar elastic power would expand in all directions with irresistible force1 diminishing correspondingly in density2 yet the ether of space remains always1 so far as we can judge1 absolutely unchanged in position4 ,its characteristics certainly remained unchanged4 ,light travels at the same rate now as it did last year1 last century1 a million years ago4 ,the ether1 then1 that bears it has presumably remained unchanged4 ,if it were gaseous1 and bounded on all sides by vacuum1 it would expand with inconceivable velocity4 ,to suppose it infinite in extent is to get rid of the difficulty perfectly2 but only by introducing a difficulty far greater4#b ,a wonderful feature of the infinitely tenuous ether is1 that while its ultimate particles must be inconceivably more minute than the ultimate atoms of ordinary matter1 the movements taking place in it are transmitted with enormous velocities4 ,the structure of our universe is on a grander scale2 its least atom may comprise millions of millions of the largest component portions of that infinitely tenuous ether4 ,but amid that ether motions are transmitted with velocities transcending all but infinitely those which take place among the particles of matter composing the universe in which we live and move and have our being4 ,the planets1 immense aggregates of matter such as we know it1 sweep onwards upon their immense orbits1 traversing many thousands of miles in an hour2 but light and heat sweep along the ether of space1 and by virtue of motions taking place within that ether at the rate of many tens of thousands of miles per second4 ,the suns which people space rush onwards with mightier momentum1 but less swiftly than the planets in their orbits4 ,comets attain the greatest velocities of all the bodies that science deals with1 rushing sometimes1 in their periastral swoop1 with a velocity of hundreds of miles per second1--though yet in mid-space the comets of widest orbital range lag slowly enough1 insomuch that some of those which1 when nearest our sun1 travel at the rate of two or three hundred miles per second1 move more slowly when very far from him than many of our rivers4 ,taking even the swiftest rush of a comet within the solar domain1 we find that light speeds along five hundred times more quickly1--so that if we represent the velocity of light by that of an express train 7reducing light's velocity in scale to about one-#aj1jjj1jjjth part of its real value71 the velocity of the most swiftly-moving comet would be represented by that of a walk at the rate of one-eighth of a mile per hour1--a very slow walk indeed4 ,it is not only amid the depths of space that these wonderfully swift motions take place in the ethereal universe4 ,as ,i have said1 that universe pervades ours throughout its entire extent4 ,the densest of our solids is as freely traversed by the ether as a forest by the summer breeze4 ,as the foliage of a thick forest may prevent the passage of fierce winds1 so may a solid body prevent the passage of light-waves--though all solid bodies1 as we know1 do not prevent1 and some scarcely even modify1 the passage of light4 ,but substances which prevent the passage of light are yet found capable of transmitting ethereal motions of similar velocity4 ,according to ,wheatstone's experiments electricity travels at the rate of more than #bjj1jjj miles per second along stout copper wire4 ,fizeau's experiments gave a lower speed2 but they did not negative ,wheatstone's1 the conditions not being the same4 ,can anything be more wonderful than the thought of the transmission of electricity with this enormous velocity8 ,what really happens we do not know4 ,perhaps if we were told what really takes place between and among the particles of the wire1 we should find ourselves utterly unable to conceive it--for1 as we have seen1 the properties of the ether1 and1 therefore1 the processes taking place in the ethereal universe1 are probably unlike any within our experience4 ,but this we know--a certain condition of the molecules of the wire is transmitted1 by virtue of the ethereal medium pervading the wire1 at a rate so enormous that1 if the wire itself could move at that rate1 the force required to bring its mass to rest would suffice to generate enough heat to turn many times as much metal into the vaporous state4 ,nay1 even as regards the energy of their action on the matter of our universe1 these movements in the ethereal universe enormously exceed the forces we are accustomed to regard as most powerful4 ,the effects produced by gravity1 for instance1 are almost evanescent compared with those produced by heat4 ,the sun's rays poured on a piece of metal for a few minutes produce motions in every one of the ultimate particles of the metal4 ,each particle vibrates with inconceivable rapidity 7referring to the rate at which the vibrations succeed each other71 and with great actual velocity of motion4 ,summing up the energy thus pervading the piece of metal1 we find that it incalculably exceeds the energy represented by the velocity which the sun's attraction would communicate in the same interval to that piece of metal1 supposed to be entirely under its influence at the earth's distance from the sun4 ,or take another instance4 ,think for a moment1 say the authors of the ,unseen ,universe1 of the fundamental experiments in electricity and magnetism1 known to men for far more than #bjjj years1--the lifting of light bodies in general by rubbed amber and of iron filings by a loadstone4 ,to produce the same effect by gravitation-attraction1--at least1 if the attracting body had the moderate dimensions of a hand-specimen of amber or loadstone1--we should require it to be of so dense a material as to weigh1 at the very least1 #a1jjj1jjj1jjj pounds1 instead of 7as usual7 a mere fraction of a pound4 ,hence it is at once obvious that the imposing nature of the force of gravity1 as usually compared with other attractive forces1 is due1 not to its superior qualitative magnitude1 but to the enormous masses of the bodies which exercise it4 ,we may put this illustration in another form4 ,when we place a powerful magnet near a piece of iron1 say at a distance of one inch1 and the magnet lifts that piece of iron by virtue of its attractive power1 a contest has been waged1 if one may so speak1 between the attractive powers of the small magnet and of the mighty earth1 and the magnet has conquered the earth4 ,now the magnet has been much nearer than the earth to the piece of iron1 for we know that the earth's attractive influence has been the same as though the entire mass of the earth were gathered at its centre1 say #djjj miles from the piece of iron4 ,a distance of #djjj miles contains #djjj times #agfj times thirty-six inches1 or1 roughly1 #bej millions of inches4 7,this is in truth very near the true number of inches in the earth's radius1 insomuch that many suppose the inch to have been originally taken as the #ejj1jjj1jjjth part of the earth's diameter4 ,a ,british inch is about one-#ejj1jjj1jjjth part of the polar diameter of the earth47 ,since attraction diminishes as the square of the distances increases1 and vice vers1 it follows that if the earth's entire mass could act on the piece of iron1 at a distance of one inch1 the attraction would exceed that actually exerted by the earth #bej million times #bej million times1 or #fb1ejj millions of millions of times4 ,in this degree1 then1 the earth is at a disadvantage compared with the magnet as respects distance4 ,and one-#fb1ejj1jjj1jjj1jjj1jjjth part of the earth's mass would be capable of attracting the piece of iron as strongly as the earth actually attracts it1 if that fraction of the earth's mass could exert its pull from a distance of only one inch4 ,but a #fb1ejj1jjj1jjj1jjj1jjjth part of the earth would be an enormous mass4 ,it would weigh about #ig1ejj tons1 or some #bah millions of pounds4 ,thus a magnet which a child can lift exerts a greater attraction on the piece of iron at the same distance than a mass at least #ajjj million times its weight could exert by its gravity only4 ,in fact we see from this illustration that gravity1 though it produces effects so tremendous1 though it sways the moon round the earth1 the earth and all the other planets around the sun1 and urges the sun and his fellow-suns through space1 is1 after all1 but a puny force in itself4 ,a child can lift his own weight against the attraction of the mighty earth2 and by combined strength as many children as would have a weight equal to the earth's would easily bear a weight exceeding the earth's1 if the force could be wholly and directly applied to such work4#c ,the attraction of gravity must1 however1 be regarded as only one manifestation of the energies of the infinitely minute4 ,it is in this sense well worthy of careful study4 ,i propose to present in a future paper some of the strange thoughts which are suggested by the action of this wonderful force1 the range of whose activity is seemingly co-extensive with the material universe4 ,,footnotes3 #b ,i do not say we can in any way avoid this far greater difficulty4 ,our own material universe cannot even be conceived as limited in any way save by void space of infinite extent2 and it is as impossible for us to conceive an infinite void as to conceive the infinite extension of matter4 ,some modern mathematicians1 indeed1 assert that space is not necessarily infinite1 but they accompany the assertion 7very justly7 with the admission that we cannot possibly conceive any boundary to space2 and as one of the things they ask mathematicians to admit is the possibility that a straight line indefinitely produced both ways will at length re-enter into itself1 while another is the possibility that in other parts of the universe two and two may make three or five1 they are not likely1 ,i conceive1 to persuade most mathematicians 7profoundly mathematical though they are themselves7 that the mystery of infinity has been as yet entirely expounded4 #c ,of course the reader will understand that when ,i here speak of the earth's weight1 ,i mean simply the pressure which would be exerted by the quantity of matter contained in the earth1 if each portion were only subjected to an attractive force equal to that of gravity at the earth's surface4 ,the actual force with which the earth is drawn in any direction1 as a weight at the earth's surface is drawn downwards1 depends on the distance and mass of the attracting body as well as on the mass of the earth2 and strictly speaking1 we ought not to say that the earth weighs so many millions of tons1 but that she contains so many million times as much matter as a mass which at her surface weighs a ton4 ,illustration ,,iv4 ,,the ,,mystery ,,of ,,gravity4 ,the law of gravity1 or of the mutual attraction of masses of matter upon each other1 accounts so perfectly for all the observed motions of the heavenly bodies1 that we are apt to regard ,newton's discovery of the great law as though it had finally solved the mystery of these motions4 ,many accept the verdict given by the poet ,pope in the famous epitaph which he suggested for ,newton1-- ,nature and ,nature's laws lay hid in night3 ,god said1 ,let ,newton be6 and all was ,light4 ,but ,newton1 who probably knew as much about his work as ,pope1 was of another opinion4 ,every one knows how he compared himself to a child who had picked up a few shells on the shore1 while the ocean of truth lay unexplored before him4 ,he has1 however1 spoken definitely of the great discovery which has rendered his name illustrious1 in terms which show that he did not find that all was light4 ,among the questions which he specially would have had answered1 amongst the secrets of nature concealed beneath the ocean of truth1 the mystery of gravity was probably the chief4 ,when ,newton asked of the ,ocean of ,truth what ,mrs4 ,hemans later said1 and in another sense1 of the natural sea-- ,what hidest thou in thy treasure-caves and cells1 ,thou hollow-sounding and mysterious main8 he had in his thoughts the very power which he is commonly supposed to have explained1 but which was in truth for him1 more than for any man that had ever lived1 the mystery of mysteries4 ,it may be well to consider the very words of the great philosopher1 so far at least as our more diffuse language can present the concise expressions of the original ,latin3 ,hitherto we have explained1 he says1 the phenomena of the heavens and of our sea by the power of gravity1 but have not yet assigned the cause of this power4 ,this is certain 7we must hearken attentively here1 for when a man like ,newton speaks of aught as certain1 we have sure ground to go upon71--this is certain1 that it must proceed from a cause that penetrates to the very centres of the sun and planets1 without suffering the least diminution of its forces2 that operates1 not according to the quantity of surfaces of particles on which it acts 7as mechanical causes usually do71 but according to the quantity of the solid matter which they contain1 and propagates its virtue on all sides to immense distances1 decreasing always as the squares of the distances4 ,gravitation towards the sun is made up of the gravitations towards the several particles of which the body of the sun is composed1 and in receding from the sun decreases accurately as the square of the distances as far as the path of ,saturn4441 nay1 and even to the remotest parts of the paths of comets4444 ,but hitherto ,i have not been able to discover the cause of those properties of gravity from phenomena2 and ,i frame no hypotheses3#d for1 whatever is not deduced from phenomena is to be called an hypothesis2 and hypotheses1 whether metaphysical or physical1 whether of occult qualities or mechanical1 have no place in experimental philosophy4444 ,to us it is enough that gravity does really exist1 and act according to the laws which we have explained1 and abundantly serves to account for all the motions of the celestial bodies and of our sea4 ,hitherto ,i have not been able to discover the cause of the properties of gravity4 ,such is the simple statement of the man who discovered those properties4 ,and now let us inquire a little into this law of gravity1 not with the hope of explaining this great mystery of nature1--though1 for my own part1 ,i believe that the time is not far distant when the progress of discovery will enable man to make this approach towards the mystery of mysteries1--but in order to recognise the real nature of the mystery1 which is a very different thing from explaining it4 ,in the first place the study of gravity brings us at once to the consideration of the infinitely minute1--at least of what is for us practically infinite in its minuteness4 ,if we consider the above quotation attentively1 we perceive that this quality of gravity was recognised by ,newton4 ,it is not the quantity of the surfaces of particles1 he says1 but the quantity of solid matter which they contain1 that gives to gravity its power4 ,gravity resides in the ultimate particles of matter4 ,we cannot conceive of matter so divided1 no matter how finely1 that non-gravitating particles could be separated from gravitating particles4 ,without entering into the question what atoms are1 we perceive that these ultimate constituents of matter must contain1 each according to the quantity of matter in it1 the gravitating energy4 ,only1 observe how incongruously we are compelled to speak4 7,it is always so when we deal with the infinite1 whether the infinitely great or the infinitely minute47 ,we are speaking of atoms as the ultimate constituents of matter1 and yet we are compelled1 in describing their gravitating energy1 to speak of the quantity of matter contained in each atom1--in other words1 we speak in the same breath of an atom as not admitting of being divided or diminished1 and of its containing matter by quantity1 that is1 by more or less4 ,may we not1 however1 reasonably accept both views8 ,the reasoning is sound by which science has proved that1 so far as our material universe is concerned1 there is a limit beyond which the division of matter cannot be supposed to go1--insomuch that ,sir ,w4 ,thomson has indicated the actual limits of size of the atoms composing matter4 ,yet1 passing in imagination beyond the bounds of our visible universe1 and so entering into the next order of universe below it 7in scale of construction71--the ether of space1--the atoms of our universe may be infinitely divisible in that universe1 may be1 in fact1 compared with its particles1 as the suns and worlds of our universe are to our atoms and molecules4 ,but while gravity thus draws us to the contemplation of the infinitely minute1 it also leads us to the consideration of what is for us the infinitely vast4 ,newton was only able to speak confidently of the action of gravity at the distance of ,saturn1 the remotest planet known in his day4 ,he did1 indeed1 refer to the comets as probably obeying1 even in the remotest parts of their paths1 the force of the sun's gravity2 but he could not be certain on that point1 because in his time no comet had been proved to travel back to the sun after receding to the remotest portion of its track4 ,we now know not only that the sun's attraction extends to the farthest parts of the solar system1 having thus a domain in space nearly thirty times larger than the sphere of ,saturn1 but we perceive that many among the stars exert a similar force2 for around them travel other stars even as the planets travel around the sun4 ,thus we know that gravity is exerted in regions lying hundreds of thousands of times farther from the sun than ,saturn is4 ,we have1 indeed1 every reason to believe1 not only that star unto star extendeth this mysterious attractive influence1 but that the least particle in the inmost depths of sun or world exerts in full force on each particle1 even of suns lying millions of times beyond the range of the most powerful telescope yet constructed by man1 the full energy corresponding 7i47 to the quantity of matter in itself and such particle1 and 7ii47 to the distance separating each from each4 ,this is amazing enough2 but there is something more perplexing and mysterious in gravity even than this4 ,not only does gravity lead us to consider the infinitely minute in space on the one hand1 and the infinitely vast in space on the other1 but also it leads us to consider the infinitely minute and the infinitely vast in time also1 and this in such a way as to suggest a difficulty which1 as yet1 no man has been able to solve4 ,light travels1 as we know1 with a velocity so enormous1 that1 by comparison with it1 all the velocities we are familiar with seem absolutely as rest4 ,but gravity acts so quickly that even the velocity of light becomes as rest by comparison with the velocity of the propagation of gravity4 ,laplace had occasion1 now nearly a century ago1 to inquire whether a certain change in the moon's motion1 by which she seemed to be gradually hastening her motion round the earth1 might not be caused by the circumstance that gravity requires time for its action to be propagated over great distances4 ,he found that if the whole of that change had to be explained in this way1 which would be giving to gravity the slowest admissible rate of transmission1 the velocity with which gravity is propagated would be eight million times greater than the velocity of light4 ,if1 on the other hand1 that change in the moon's motion could be satisfactorily explained in some other way1 then the velocity of gravity must be at least #af1jjj1jjj times greater than the velocity of light4 ,he himself soon after discovered what was in his day regarded as a complete explanation of the hastening of the moon's motion2 and though in our own time ,adams of ,cambridge has shewn that only half the hastening can be accounted for by ,laplace's reasoning1 the general explanation of the remaining half is that it is not a real hastening of the moon1 but is only an apparent hastening caused by the gradual slowing of the earth's rate of turning on her axis4 ,this makes the day by which we measure the moon's motion seem longer 7very slightly1 however74#e ,supposing1 however1 half the moon's hastening were left unexplained1 and that the non-instantaneous transmission of gravity were the only way of accounting for it1 even then it would be certain that gravity is propagated at a rate exceeding #ab1jjj1jjj times the velocity of light4 ,indeed1 at present1 owing to the more exact observations available1 and the greater range of time over which they extend1 it may safely be said that the rate of propagation of gravity is far greater than this4 ,it is even held by some that gravity acts instantaneously over any distance1 however vast4 ,illustration3 ,fig4 #f4 ,although ,i cannot here indicate the exact nature of the reasoning by which the enormous rapidity of the action of gravity is inferred1 ,i must briefly indicate the general argument1 that the reader may not suppose the matter to be merely speculative4 ,suppose that the action of gravity were propagated at the same rate as light4 ,then the earth would feel the pull of the sun eight minutes or so after she had been in the place where the sun began to exert that particular pull4 ,the direction of the pull then would not be that of the straight line connecting the earth and sun at the moment when the pull was felt1 but that of the straight line connecting the sun and the earth eight minutes or so before4 ,for instance1 when the earth is at ,e#a1 fig4 #f1 the sun at ,s would begin to exert a pull in the line ,e#a ,s1 but the earth would only feel this pull when she got to ,e#b1 her place eight minutes later1 when it would act upon her in the direction ,e#b ,f1 parallel to ,e#a ,s4 ,now this pull1 ,e#b ,f1 may be divided into two parts1 one along ,e#b ,s1 pulling the earth towards the sun ,s1 the other along ,e#b ,t in the earth's course1 hastening her therefore4 ,but the maintenance by the earth of the same constant track depends entirely on the action of gravity sunwards4 ,if there is any action in addition1 hastening the earth1 then she will not keep her course1#f but will travel in a constantly widening path1--or1 in a sort of spiral1 very slowly retreating from the sun1 but retreating constantly4 ,the change of distance would not be measurable in millions of years2 but the increase in the length of the year would1 before long1 be observable4 ,because there is no such increase1 astronomers feel well assured that gravity is not only propagated more swiftly than light1 but many times1 even1 as we have seen1 many millions of times1 more swiftly4 ,it is then in an infinitely minute time that the action of gravity traverses all ordinary distances4 ,the earth's pull on the moon takes less than the #ej1jjj1jjjth part of a second in reaching the moon1--and the particles constituting the mass of the earth act on ourselves1 and on all the objects which lie near the earth's surface1 in far less than the #aj1jjj1jjjth part even of this utterly minute time-interval4 ,yet age after age has passed during which this infinitely active force has been at work without diminution1 and age after age will continue to pass without any change in its activity4 ,for millions of millions of ons it has lasted and will last1 so permanent is it2 while its operation is felt simultaneously at points millions of millions of star-distances apart4 ,what infinities of distance has this wonderful attractive force traversed6 ,but even these considerations do not present the greatest of the marvels of gravity4 ,it is wonderful1 indeed1 to consider a form of attraction possessed by the infinitely minute1 and exerted over the infinitely vast1 operating in portions of time immeasurably small1 and extending its operations throughout time infinite4 ,but the mystery of mysteries is not here4 ,the marvel of marvels is this1 that1 so far as we can perceive1 the force of gravity is exerted without any material connection with the objects moved by it4 ,matter seems to act where it is not1 to use the phraseology of the schools4 ,of this action at a distance1 ,newton himself said1 that it is inconceivable1 that in point of fact it is impossible4 ,no man1 he said1 who has1 in philosophical matters1 a competent faculty of thinking1 can for a moment believe that a body can act through a vacuum1 without the intervention of anything else by or through which the force may be conveyed from one body to another4 ,yet this is precisely what gravity seems to do4 ,the ether occupies1 indeed1 all space2 but there is nothing at present known to us by which we can understand how the ether can transmit the force of gravity4 ,the power of the ether in the rapid transmission of undulations seems to attain its limit in the propagation of light and heat and electricity at the rate of nearly #bjj1jjj miles per second4 ,how the ether can act so as to serve as a medium of communication between bodies at all distances1 transmitting impressions #aj1jjj1jjj times faster1 at least1 than light travels1 nothing at present known to us enables us to say4 ,i have1 in a lecture which ,i gave in ,america upon the mysteries of the universe1 indicated a way in which gravity may be conceived to be generated and transmitted2 and ,i may hereafter describe the conception 7based partly on the views of ,le ,sage74 ,but it is only a conception4 ,there is no phenomenon 7except the very form of attraction which has to be explained7 tending to show that the conception is correct ,and even if it be accepted1 it brings us face to face with only greater marvels4 ,at present1 however1 let this simply be said in conclusion--that the apparent action of gravity at a distance is1 of all physical wonders1 the greatest yet known to man4 ,if we accept the opinion of ,newton1 which1 indeed1 seems to me indisputable1 that matter cannot act through a vacuum1 then we must admit the existence of properties1 as yet unthought of1 in the ether of space1 or in some still more subtle universe permeating that ether4 ,if1 on the other hand1 we accept the belief that matter can act at a distance1 then is there no miracle1 either of those believed in by mankind generally1 or of those more generally rejected1 which exceeds in marvellousness this wonder of all the wonders of physical science4 ,,footnotes3 #d ,the words of ,newton1 ,hypotheses non fingo1 have been often quoted in such sort as to give an entirely incorrect idea of his real opinion as to the relation between theoretical and practical science4 ,as too commonly understood1 they would1 in fact1 make his discovery of gravitation a great exception to his own rule4 ,they must be taken in connection with his definition of a hypothesis1 as whatsoever is not deduced from phenomena4 ,it is a part of true science1 nay1 it is the highest office of the student of science to deduce theories from phenomena4 ,such research stands as high above the simple observation of phenomena as architecture stands above brick-making or stone-cutting4 ,but to frame hypotheses as the old ,greeks did1 trusting to the power of the understanding independently of the observation of phenomena1 is to make bricks without straw and to build with them upon the sand4 #e ,the point is explained in a paper called ,our ,chief ,timepiece ,losing ,time1 in the first series of my ,light ,science for ,leisure ,hours4 #f ,in the popular1 but incorrect way of speaking1 the balance between the centrifugal and the centripetal force will no longer be maintained3 the increase of velocity will give the centrifugal force the advantage1 and it will slowly draw the body away from the centre4 ,in reality there is no centrifugal force1 the only force acting on the earth in her course round the sun being the sun's attraction upon her1 which1 however1 must keep bending her course from the straight line1 if she is to maintain her distance4 ,in the case above imagined it would not bend her course actively enough4 ,illustration ,v4 ,,the ,,end ,,of ,,many ,,worlds4 ,a sign has recently appeared in the heavens which has been interpreted in a way suggesting that many worlds like our own have undergone a terrible catastrophe1 every living creature upon them being consumed as by fire4 ,i propose briefly to consider some of the thoughts suggested by this strange event4 ,it is difficult when we look at the star-lit heavens1 suggestive as they are of solemn peace1 to conceive the stupendous energy1 the fierce uproar and tumult1 of which even the faintest visible star in reality tells us4 ,pythagoras spoke of the harmony of the celestial spheres1 which we are only prevented from hearing by its continuity4 ,there's not the smallest orb which thou beholdest1 said the science of the middle ages1 ,but in his motion like an angel sings1 ,still quiring to the young-eyed cherubim4 ,the science of our own time tells us a still stranger story4 ,there's not the smallest orb which thou beholdest1 she says1 but in his motion throbs like a mighty heart1 still pulsating life to the worlds which circle round it4 ,but while our powers of vision are limited to the narrow range of our present telescopes1 we cannot watch the action of these great centres of energy1 nor can we hope that the uproar of those remote fires will ever reach mortal ears1 though to the mind's ear clear and distinct4 ,it is no longer a mere fancy that each star is a sun4 ,science has made this an assured fact1 which no astronomer thinks of doubting4 ,we know that in certain general respects each star resembles our sun4 ,each is glowing like our sun with an intense heat4 ,around each1 as around our sun1 are the vapours of many elements4 ,in each the fires are maintained1 as they are maintained in our sun1 in some way which may be partly mechanical1 partly chemical1 but which certainly does not in the least resemble combustion4 ,we know that in each star processes resembling in violence those taking place in our own sun must be continually in progress1 and that such processes must be accompanied by a noise and tumult compared with which all the forms of uproar known upon our earth are as absolute silence4 ,the crash of the thunderbolt1 the bellowing of the volcano1 the awful groaning of the earthquake1 the roar of the hurricane1 the reverberating peals of loudest thunder1 any of these1 or all combined1 are as nothing compared with the tumult raging over every square mile1 every square yard1 of the surface of each one among the stars4 ,if we remember this when we hear of stars varying in brightness1 we shall perceive that the least change which could be recognised from our remote stand-point must represent an accession or falling off of energy corresponding to far more than all the energies existing on our earth1 or indeed on all the members of the solar system taken together4 ,astronomers recognise our sun as in one sense a variable star2 for we can hardly suppose that he shines with the same degree of brilliancy when many spots mark his surface as when he is quite free from spots2 and astronomers know that these changes in the sun's condition correspond to wonderful changes in his activity4 ,when spots are most numerous1 the coloured flames rage with fierce energy over his whole globe1 metallic vapours are shot forth from below his visible surface with velocities of many miles per second4 ,whereas1 when he has no spots1 the coloured flames sink down from their former height of tens of thousands of miles1 till they are but a few thousand miles in height2 while metallic vapours are seldom emitted1 and never to the same height1 or with the same velocity1 as when the spots are most numerous4 ,but though the sun thus varies in condition1 and probably in his total brightness1 we cannot suppose that such variations could be recognised from the distance of even the nearest among the fixed stars4 ,what1 then1 must be the nature of changes taking place in a star1 that we1 at our enormous distance1 should be able to recognise them6 ,we may well believe that the entire aspect of such a star must be changed to the inhabitants1 if such there are1 of worlds circling around them4 ,if1 however1 the changes taking place in stars1 whose variations of brightness can just be recognised1 must be amazing1 how stupendous must be the changes affecting a star which alternates from brightness to invisibility1 like ,mira1 the ,star ,wonderful1 in the constellation of the ,whale6 how destructive those affecting a star like ,eta1 of the ship ,argo1 which has varied from the fourth magnitude to a lustre nearly equalling that of ,sirius1 and thence to the lowest limit of visibility1 in the course of the last hundred years6 ,even these changes1 however1 though justly regarded as among the chief wonders and mysteries of the star-depths1 seem in turn to sink into nothingness by comparison with the sudden appearance of a new star1 as interpreted by modern scientific observations4 ,of old1 when a new star appeared1 it was thought for awhile to be a fresh creation2 a new sun set in the centre of a new system of worlds1--a thought which was not then so startling as in our own times it would be reckoned4 ,when the new star was seen slowly to die out until at last it became invisible1 men were content to regard it as a sign set in the heavens for a special purpose4 ,nor did they find much difficulty in associating such a phenomenon with some event of importance occurring during its continuance1 or soon after the new star had died out4 ,such were the explanations offered respecting the exceedingly bright star which made its appearance in the constellation ,cassiopeia in the year #aegb4 ,the place in which it appeared is shown in fig4 #g4 ,it must have sprung into its full glory in a very short time1 for ,tycho ,brah1 the celebrated astronomer1 tells us that1 returning on ,november #a1 #aegb1 from his laboratory to his dwelling-house1 he saw the new star1 which he was certain had not been visible an hour before1 shining more brightly than any before seen4 ,it surpassed all the stars in the heavens in brilliancy1 and even ,jupiter when that planet is at its brightest4 ,only ,venus at her brightest was superior to the new star4 ,for three weeks it shone with full lustre1 after which it began slowly to decline4 ,being situated in a part of the heavens always above the horizon 7for ,european observatories71 the star's entire history could be followed4 ,it remained for sixteen months steadfast in its position like the other stars4 ,as it decreased in size it varied in colour4 ,at first1 says an old writer2 its light was white and extremely bright2 it then became yellowish2 afterwards of a ruddy colour like ,mars2 and finished with a pale1 livid white1 resembling the colour of ,saturn4 ,illustration3 ,fig4 #g4--;,cassiopeia2 showing where a new star appeared in the year #aegb4 ,in passing it may be remarked that there are reasons for expecting the return of ,tycho ,brah's star in the course of a few years4 ,for other new stars have been recorded as seen in the same part of the heavens in the years #ide and #abfd1 and though the interval from #ide to #abfd 7or #cai years7 exceeds by #aa years the interval from #abfd to #aegb 7or #cjh years71 yet the difference is but small by comparison with either entire interval2 and we may not unreasonably believe that the three new stars seen in ,cassiopeia have been only three apparitions of one and the same star1 which shines out1 with superior lustre1 for a few months1 once in a period averaging about #cac years4 ,it seems to me not at all unlikely that1 some time during the next twenty years1 astronomers will have an opportunity of examining1 with the telescope and spectroscope1 a star which last appeared before either instrument had been invented4 ,already facts are known respecting the so-called new stars which will not permit us to accept the explanations of old so readily offered and admitted1 simply because so little was certainly known4 ,in the year #ahff a star appeared suddenly in the constellation of the ,northern ,crown1 where no star had before been visible to the naked eye4 ,it was a little below the arc of stars forming the celestial coronet4#g ,it shone as a second magnitude star when first seen1 but very rapidly diminished in lustre4 ,it increased our knowledge in two important respects4 ,first1 on examining ,argelander's charts of the northern heavens1 the new star was found to have been observed and charted as a tenth magnitude star1 that is1 four magnitudes below the lowest limit of naked eye vision4 ,it was not1 then1 a new sun1 though it might still truly be called a new star1 in this sense1 that it was a new member of the set of stars which adorn our skies as seen by ordinary vision4 ,in the second place1 the star was subject to the searching scrutiny of spectroscopic analysis1 with results of a most interesting character4 ,the reader is no doubt aware that when the light of a star is analysed into its component colours by the instrument called the spectroscope1 it is found that all the colours of the rainbow are present1 as in the case of solar light1 but 7also in the sun's case7 not all the tints of these colours4 ,certain dark lines athwart the rainbow-tinted streak1 called the spectrum of the star1 indicate the presence of absorbing vapours in the star's atmosphere4 ,this general statement is true of every fixed star1 though the dark lines of some stars differ in number and position from the dark lines of others1 showing that other absorbing vapours are present4 ,in the case of the new star in the ,crown1 the usual stellar spectrum was shewn1--a rainbow-tinted streak crossed by a number of dark lines4 ,but besides these1 there were seen four very bright lines1--lines so bright that the rainbow-tinted streak appeared as a dark background4 ,the meaning of this is well understood by spectroscopists4 ,it signifies that besides the vapours which1 being cooler than the star1 absorbed a portion of its light1 and produced the dark lines1 some vapours were present in the star's atmosphere which were a great deal hotter than the star1 and so produced bright lines4 ,now two of the lines corresponded in position with two of the well known lines of the gas hydrogen1 showing that this was one of the gases which had been raised to an unusual degree of heat4 ,it was inferred that there had been some tremendous disturbance in that remote star1 by which the hydrogen and some other vapours present in its atmosphere had been intensely heated4 ,but astronomers were unable to decide whether the disturbance was of the nature of a conflagration1 the hydrogen actually burning1 or whether the heat was occasioned in some other way1 as by the downfall of some immense mass upon that remote sun4 ,for burning hydrogen and glowing hydrogen1 though either could give the observed bright lines1 are very different things4 ,in the former case a chemical change is taking place1 as in the case of burning wood or coal2 the latter case resembles that of redhot iron1 which is not burning itself 7not changing into a different form as everything does which burns71 though it will burn other things1--in the ordinary1 and incorrect1 use of the expression4 ,the general belief was that there had been a downfall of matter on the star in the ,crown1 by which the whole globe of that sun had been excited to an intense degree of heat1 especially at the surface1 near which lies the hydrogen atmosphere of the star4 ,i must leave1 however1 to the next part1 the further consideration of the strange thoughts suggested by the outburst of this star4 ,i wish to use the small space remaining at present to indicate the place where another new star burst forth last ,november1 so that any readers of these pages who have telescopes may know where to look for a sun which is now dying out1 but was shining a few weeks ago as a third magnitude star4 ,fig4 #h presents a portion of the well-known constellation ,cygnus or the ,swan4 ,any star atlas will indicate the place of the lettered stars shown in the figure4 ,the constellation itself does not show at all well at this season of the year4#h ,the part shown in the figure is close to the horizon1 and directly under the pole-star1 at about half-past ten in the middle of ,february2 but a little higher up1 between north and north-east1 at midnight4 ,professor ,schmidt1 of the ,athens ,observatory1 noticed a new star1 in the place shown1 on ,november #bdth last4 ,it must have shone out suddenly1 for ,schmidt had been observing in that region on the night of ,november #bbnd 7the last preceding clear night74 ,it has since gradually faded1 until now a small telescope is required to show it1 shining as a seventh magnitude star1 with a well-marked orange tint4 ,illustration3 ,fig4 #h4--,part of ,cygnus1 showing the place of new star 7,november #bd1 #ahgf74 ,we have now to consider the history of this star1 and discuss the general questions suggested by the sudden blazing out of suns which had for many years1 and probably for many centuries1 shone continuously with a far feebler lustre4 ,it is clear that we have good reason to be interested in these questions1 seeing that1 for aught we know1 our sun may be one of those exposed to sudden great increase of lustre4 99 99 99 99 99 ,it seems certain1 in the first place1 that this star leapt very suddenly to its full splendour4 ,schmidt had been observing the same regions of the heavens only two evenings before1 and is sure the star was not then shining visibly to the naked eye4 ,again1 astronomy is now studied by so many persons1 and so many more who are not students of astronomy are now well acquainted with the constellations1 that it is very difficult for a new star to shine many hours without being detected4 ,for example1 the new star in the ,crown1 which appeared in ,may1 #ahff1 though not so well placed for observation1 was detected by many observers at widely distant stations within a few hours of each other4 ,it is probable that the star acquired its full lustre in a few hours at the utmost1 and quite possible that1 had any one been watching the place where the star appeared1 he would have been able to see the star grow into full brightness by visible change of lustre1 just as the lustre of a revolving light in a distant lighthouse visibly waxes and wanes4 ,it may be1 of course1 that the increase of the star from its ordinary lustre1 up to the stage when first it was visible to the naked eye1 occupied many days1 or even many months or years2 but it seems more likely that as the later stages of increase were rapid1 so also was the entire development of the new lustre4 ,in that case1 if there were inhabited worlds circling around that remote sun1 they had but brief warning of the fate in store for them1 as presently to be described4 ,like the star in the ,northern ,crown1 the new star in ,cygnus was subjected to the searching scrutiny of the spectroscope4 ,the results1 though similar in general respects1 were even more interesting than in the case of the brighter new star4 ,in the interval between #ahff and #ahgf spectroscopic analysis has developed largely4 ,it has thus become possible to analyse more completely the light even of faint stars than the light of bright stars could be analysed a decade of years since4 ,the spectrum of the new star as examined by ,m4 ,cornu1 of the ,paris ,observatory1 showed the bright lines of hydrogen1 indicating the presence of enormous quantities of glowing hydrogen1 in a state of intense heat4 ,but beside these bright lines1 others also could be seen4 ,one of these was an orange-yellow line4 ,it will be understood that the faint spectrum of a star cannot be so readily lengthened by increasing the dispersion as a bright spectrum2 for with too great dispersion the light fades out altogether4 ,and though this is not strictly the case with the bright lines1 which are merely thrown farther apart by dispersion1 yet still it remains true that one cannot deal with a star spectrum even of bright lines as one can with the solar spectrum4 ,so that ,m4 ,cornu was not able to determine whether the orange-yellow line belonged to sodium1 or to that other substance1 whatever it may be1 which produces the orange-yellow line seen in the spectrum of a solar prominence4#i ,another bright line1 green in colour1 agreed in position with a triple line belonging to the metal magnesium4 ,lastly1 a bright yellowish-green line was seen1 which is known to be present in the spectrum of the sun's corona and of the low-lying ruddy matter round the sun1 called the sierra by some1 and by others 7apparently unfamiliar with the ,greek language7 the chromosphere4 ,now all this agrees very well with what had been noticed in the case of the star in the ,northern ,crown4 ,for1 unquestionably1 if a sun increases so much in heat and lustre that the hydrogen outside it glows more brightly than the body of the star1 then other matter outside that sun might also be expected to share the great increase of heat4 ,we see that1 outside our own sun1 hydrogen1 a certain unknown vapour of an orange yellow colour1 magnesium1 and another unknown vapour of greenish-yellow colour are present in enormous quantities2 and it seems1 therefore1 reasonable to believe that other suns have these gases extending far outside the rest of their substance4 ,it is certain that1 if our sun were caused to glow with far more than its present degree of heat1 the gases whose increase of brightness would be most discernible from a distant station 7as a world circling around some remote star7 would be just those gases which were glowing so resplendency around the star in ,cygnus last ,november--or rather at the time when that light which reached us last ,november set out from the remote star in the ,swan4 ,when we view the outburst of that remote sun in this way the thoughts suggested are not altogether satisfactory4 ,that sun shows far too much resemblance to our own1 and behaved1 so far as can be judged1 far too much as our own sun would behave if roused to many times its present degree of heat and splendour4 ,when we hear of a railway accident it is a matter of special interest to us 7if we travel much7 to learn whether the conditions under which the accident took place resembled those under which the trains proceed by which we chiefly travel4 ,when an express train suffers in such a way as to show some special danger arising from great velocity1 we find ourselves to some degree concerned personally in the investigation which follows1 if we travel generally by quick trains4 ,if a bridge breaks down1 and we have often to traverse bridges in railway journeying1 we are similarly concerned1 especially if any of the bridges we have to cross resemble in structure the one which has given way4 ,so also of many other special forms of danger in railway travelling4 ,now1 on the same principle1 we cannot but regard with considerable interest the circumstance that1 apparently1 a catastrophe has taken place in the star in ,cygnus1 which has not only affected a sun resembling our own very closely in constitution1 but has produced effects very closely corresponding to those which would affect our own sun if1 through any cause1 he were excited to many times his present degree of heat4 ,let us pause a little to reflect upon the effects which would follow a great increase of the sun's lustre4 ,a change in our own sun1 such as affected the star in ,cygnus1 or that other star in the ,northern ,crown1 would unquestionably destroy every living creature on the face of this earth2 nor could any even escape which may exist on the other planets of the solar system4 ,the star in the ,northern ,crown shone out with more than #hjj times its former lustre3 the star in ,cygnus with from #ejj to many thousand times its former lustre1 according as we take the highest possible estimate of its brightness before the catastrophe1 or consider that it may have been very much fainter4 ,now1 if our sun were to increase tenfold in brightness1 all the higher forms of animal life and nearly all vegetable life would inevitably be destroyed on this earth4 ,a few stubborn animalcules might survive1 and1 possibly1 a few of the lowest forms of vegetation1 but naught else4 ,if the sun increased a hundredfold in lustre his heat would doubtless sterilise the whole earth4 ,the same would happen in other planets4 ,the heat falling on the remotest members of the solar system would not1 indeed1 be excessive according to our conceptions4 ,but if we regard ,neptune1 ,uranus1 ,saturn1 and ,jupiter as the abode of life 7which1 for my own part1 ,i consider altogether improbable71 we cannot but suppose the orders of living creatures in each of these planets to be well fitted to exist under the conditions subsisting around them4 ,if this is so--as who can for a moment doubt8--a sudden enormous increase in the sun's heat1 though not making the supply received by those planets much greater than1 or even equal to1 the supply which we receive from the sun1 would prove as fatal to living creatures there as to living creatures on our earth4 ,if1 then1 the sun increased in splendour as the stars have increased which the astronomers call new stars or temporary stars1 there would be an end of life upon this earth2 and nothing short of either the spontaneous development of life1 or of the creation of various forms of life1 could people our earth afresh4 ,science knows nothing of spontaneous generation1 and believers in revelation reject the doctrine4 ,science knows nothing of the creation of living forms1 but believers in revelation accept the doctrine4 ,certain it is that if our sun ever undergoes the baptism of fire which has affected some few among his brother suns1 one or other of these processes 7if creation can be called a process7 must come into operation1 or else our earth and her companion worlds would for ever after remain absolutely devoid of life4 ,but if our sun1 without suffering so great a change1 underwent a change of less degree1 it might well happen that though there would be enormous destruction of life upon the earth and other planets1 some life 7presumably the strongest and best7 would survive4 ,in that case1 after a long period of time1 the earth would again be well peopled1 and it might even be that the various races of terrestrial creatures would be improved1 by the desolation which the great solar conflagration had wrought4 ,it is somewhat curious1 considering how little there is in the ordinary progress of events to suggest the idea1 that most of the ancient systems of cosmogony recognised the periodical destruction of living creatures on the earth by fire as well as by water4 ,each form of destruction was supposed to be brought about by planetary influences4 ,the ,ecpyrosis1 or destruction by fire1 was effected when all the planets were in conjunction with ,cancer2 the ,cataclysm1 or destruction by flood1 when all the planets were in conjunction with ,capricorn4 ,each form of destruction was supposed also to purify the human race4 ,towards the termination of each era1 writes ,lyell1 speaking of these old ideas1 the gods could no longer bear with the wickedness of men1 and a shock of the elements or a deluge overwhelmed them2 after which calamity ,astrea again descended on the earth1 to renew the golden age4 ,the ,greeks undoubtedly borrowed all such doctrines from the ,egyptians1 who believed the world to be subject to occasional conflagrations and deluges1 whereby the gods arrested the career of human wickedness1 and purified the earth from guilt4 ,after each regeneration mankind was in a state of virtue and happiness1 from which they gradually degenerated again into vice and immorality4 ,considering that we have every reason to believe the records of great floods to relate to events which actually occurred1 however imperfectly remembered1 it seems not unreasonable to believe that the tradition of great heats had its origin in observed phenomena4 ,as neither ordinary conflagrations nor volcanic outbursts would have suggested traditions of the kind1 it would seem not impossible that at certain times our sun may have acquired for a time unusual lustre and heat1 causing great and widely spread destruction among all forms of animal and vegetable life4 ,this idea may possibly seem to many1 especially at a first view1 too wild to be entertained for a moment4 ,our sun shines1 so far as appears to ordinary observation1 with steadfast lustre from year to year1 and also from age to age4 ,if an occasional hot season suggests for a while to some that the sun has grown hotter1 or a cool season that he has grown cooler1 the restoration of cool or warmer weather1 as the case may be1 causes the thought to be quickly cast on one side that a change of either kind has taken place4 ,again1 if we examine the historical records of past ages1 we find little to suggest the idea1 or even the possibility1 that the sun in former times shone with greater splendour or with less than at present4 ,the men of those days were formed like the men of our own day1 and could not have supported any much greater degree of heat or of cold than men can support at present4 ,any sudden accession 7or diminution7 of solar light and heat1 such as we are considering1 would certainly have attracted marked attention1 and have been recorded for the benefit of future ages4 ,the geologic record1 again1 does1 indeed1 suggest variations in the sun's emission of heat as constituting one among the few available explanations of the existence of tropical forms of life in certain strata and of arctic forms in other strata4 ,but even if this explanation be the true one1 which is by no means established1 such variations must of necessity have been slow1 the condition of increased heat continuing for many ages in succession1 and the like with the condition of diminished heat4 ,we have no evidence1 historical or geological1 of the occurrence of any sudden accession of solar heat1 followed by a quick return to the normal temperature1 unless we find such evidence in the tradition prevalent among ,egyptian1 ,indian1 and ,chinese cosmogonists1 that at certain recurring epochs in the past our earth has undergone destruction and renovation by fire4 ,yet1 as ,i shall now show1 it appears that the one only natural interpretation which can be given of the outburst of a new or temporary sun indicates an event which might happen to our own sun1 and an event which if it happened at all would happen periodically4 ,moreover1 while it will appear that there is no reason for fearing the possible occurrence 7which would1 in such case1 be really the recurrence7 of such a catastrophe in the case of our own sun as has affected the stars in the ,crown and in ,cygnus1 there is no reason for rejecting as incredible the idea that catastrophes very serious in their character may have affected our sun2 and there is abundant reason for believing that small alterations in the sun's total emission of light and heat take place very often1 in some cases periodically2 in others--so far as we can yet judge--periodically4 ,lastly1 it will be seen that there is always a possibility that our own or any other sun may undergo precisely such a change as the stars in ,cygnus and the ,northern ,crown4 ,some indeed1 even among men of science 7as the ,abb ,moigno1 for example7 believe that it was an event of this sort which ,st4 ,peter predicted when he wrote1 that as the old world1 being overflowed with water1 perished1 so the heavens and the earth which are now1 by the same word are kept in store1 reserved unto fire4 ,according to that view1 the day of destruction will come as a thief in the night2 in the which the heavens shall pass away with a great noise1 and the elements shall melt with fervent heat1 the earth also1 and the works that are therein shall be burned up4 99 99 99 99 99 ,let us consider how the sudden brightness of a new star may be explained4 ,i must confess that for my own part ,i do not attach much weight to the suggestion once made by ,mr4 ,huggins1 that an actual conflagration had taken place in the case of the new star in the ,northern ,crown4 ,it does not seem to me that any process of mere burning could account for the enormous accession of light and heat which that sun underwent4 ,consider the case of our own sun4 ,his heat is very far beyond that which would be given out by any matter known to us undergoing any known process of true combustion4 ,that is to say1 if a mass as large as the sun of any known substance were caused to burn1 under any conditions we can imagine1 the momentary emission of heat by that mass would be very much less than the momentary emission of heat by the sun4 ,now it is quite conceivable that by some great accession of combustible matter1 some supply of fuel exceeding many times his entire mass1 the sun's entire emission of heat might be very largely increased4 ,but though such an idea is conceivable1 it seems altogether far-fetched4 ,the conception is1 in fact1 inadmissible as an explanation of the increase of heat of a temporary star1 not because of the improbability of the sudden accession of so enormous a quantity of matter 7though that improbability is very great71 but because if so enormous a quantity of matter fell upon the sun1 many times as much heat would be generated by the mechanical effect of the impact as by the combustion of the freshly received matter4 ,so that even with the daring assumption here made1 combustion would account for only a small portion of the increase of light and heat4 ,huggins' idea was indeed somewhat different4 ,he supposed that in consequence of some great internal convulsion of the sun in the ,northern ,crown a large volume of hydrogen and other gases was evolved from the interior1 the hydrogen then by burning giving out the light corresponding to the bright lines4 ,at the same time1 the mass of the sun would be intensely heated by the surrounding mass of glowing hydrogen4 ,when the liberation of gas from the interior ceased the flame would die out1 and the sun's surface would gradually cool4 ,but if we judge by the case of our own sun1 the heat of the burning hydrogen would be nothing near so great as the heat of the glowing hydrogen already outside and within the visible globe of a sun4 ,on the whole it seems altogether more probable that the accession of splendour observed in the case of temporary stars is due to the downfall of enormous masses of matter upon the surface of these suns4 ,it is1 no doubt1 well known to most of my readers that the downfall of meteoric matter upon the surface of our own sun has been considered a sufficient explanation of the sun's entire emission of light and heat4 ,the theory that the sun's heat and light are thus excited has long since been abandoned2 but not because the cause would be insufficient4 ,it has been abundantly proved that a downfall of meteors1 not sufficient in quantity to add appreciably to the sun's size in many thousands of years1 would generate more heat and light than he emits in that time4 ,the meteoric theory has been abandoned simply because it has been shown that no such downfall is taking place4 ,the reason why meteoric impact would suffice to warm the sun to his present temperature if the meteoric showers were heavy1 and to warm him far beyond his present temperature if for a few days very heavy meteoric showers fell upon him1 is simply that his attraction upon matter approaching him from without is capable of generating a tremendous velocity4 ,we know that when a cannon-ball strikes a metal target1 with a velocity perhaps of some #djj yards per second1 great heat is excited1 and there is a momentary flash of light4 ,if the velocity were doubled1 the quantity of heat would be doubled also4 ,conceive1 then1 the tremendous heat which would be excited if a cannon-ball could be caused to strike a target with a velocity exceeding that just named some #aejj times6 ,the ball and target would both be vaporised by the shock1 if--which1 however1 could never happen--the target resisted the blow and brought the ball to rest4 ,now matter which reaches the sun from without1 under the influence of his tremendous attraction1 strikes his globe with a velocity #aejj times greater than that of a cannon ball striking a target at a distance of two or three hundred yards4 ,the heat excited is1 therefore1 very intense2 and if meteors were showering at all times and in dense flights upon the sun's surface1 we should require no other explanation of the sun's heat4 ,but it appears that meteoric systems are neither so numerous nor so rich as to account for the sun's uniform emission of heat1 though occasional meteoric showers upon the sun may be heavy enough to increase appreciably the amount of heat he emits4 ,it would seem1 from experiments which have been made by ,professor ,piazzi ,smyth1 of the ,edinburgh ,observatory1 and later by the ,astronomer ,royal at ,greenwich1 that from time to time the sun's emission of heat really is greater than usual4 ,it seems not at all improbable that the increase is due to the occasional fall of large masses of meteors in great numbers upon the sun4 ,again1 it seems that such falls occur periodically1 or rather that at regular intervals great meteoric streams pour upon the sun's surface4 ,for instance1 the periodic increase and decrease in the number of sun-spots is accompanied 7so far as we can judge by the observations made at ,edinburgh and ,greenwich7 by an accession and diminution of the solar heat2 and if the change is attributed to the passage of a meteoric stream athwart the sun1 we should have to assign to such a stream a period of rather more than eleven years4 ,this1 from what we know about the association between meteors and comets1 would correspond simply to the existence of a comet whose path intersects the sun's globe1 and which is followed by a train of millions of large meteoric masses1 many of which are consumed at each passage of the rich portion of the train athwart the globe of the sun4 ,this comet must of necessity be inconspicuous1 since it has hitherto escaped detection4 ,in fact1 its head and nucleus must long since have been entirely destroyed4 ,only the meteoric train1 far more widely scattered1 remains1 simply because at each passage past the sun1 though many are captured1 far greater numbers get safely past4 ,i am careful to remind the reader that though ,i have1 for convenience1 used the indicative mood in describing these matters1 ,i am in reality presenting merely a theory4 ,it may be that the solar spots and the accessions of heat are produced in some other way4 ,but ,i must admit ,i find strong reasons for regarding as probable the general theory1 that the alternations of solar activity 7not the solar activity itself be it noted7 are excited from without4 ,and since we know1 as a matter of fact1 that meteors exist in enormous numbers within the solar system1 and that they aggregate with rapidly increasing density in the sun's neighbourhood1 we must believe that they fall upon the sun in enormous numbers4 ,we also perceive that the supply cannot be uniform1 but must vary greatly from time to time2 while what we know about the periodicity of meteoric showers on our own earth suggests the belief1 we may almost say the certainty1 that there must be periodic downfalls of very heavy meteoric showers upon the sun's surface4 ,we have1 then1 strong probability in favour of the belief that events may occur which1 if they occurred1 might be expected1 with a high degree of probability1 to produce effects resembling those actually observed1--viz41 the production of a heat more intense than usual1 accompanied by signs of great disturbance like the sun-spots4 ,it does1 therefore1 seem at least not improbable that these accessions of heat and these signs of great disturbance really are brought about in the way supposed4 ,a further argument in favour of the meteoric origin of solar alternations of heat is to be found in the fact that1 on one occasion at least1 a solar phenomenon1 corresponding precisely to what we should expect to see1 if great meteoric masses fell upon the sun1 has been followed by precisely the same signs of terrestrial disturbance which accompany and follow the formation of great solar spots4 ,i refer to the remarkable occurrence witnessed by ,carrington and ,hodgson 7at different observatories7 in ,september1 #ahei1 when two intensely bright points of light were seen travelling beside each other at the rate of about #abj miles per second along a short arc of the sun's surface1--an arc only equal in length to some four-and-a-half times the diameter of our earth4 ,on that occasion the emission of solar heat may or may not have been increased in an appreciable degree for several minutes4 ,my own belief is that it must have been2 but we certainly have no means of proving that it was4 ,what we do know certainly is1 that on that day all the phenomena which usually accompany the existence of many and large sun-spots showed themselves with exaggerated intensity4 ,the magnetic needle was greatly disturbed1 auroras displayed their coloured streamers in both hemispheres1 telegraphic communication was interrupted1 and everything tended to show that a disturbance of the same general character as that which produces sun-spots1 but much more active while it lasted1 had affected the sun4 ,it seems1 then1 altogether reasonable to infer that sun-spots are due to the same cause as the disturbance which then occurred4 ,so that if we conclude1 with most astronomers competent to form an opinion1 that the disturbance witnessed by ,carrington and ,hodgson was due to the downfall of two very large meteoric masses upon the sun1 it would follow that sun-spots are due to more wide-spread meteoric showers1 not consisting of masses so large4 ,the reader will long since have guessed1 no doubt1 to what all this tends4 ,if the periodical variations of the sun's surface are due to meteoric and cometic systems whose orbits intersect the sun's globe1 their periods being short 7that is1 lasting but a few years71 it may well be that more important meteoric and cometic systems intersecting the sun's globe exist1 which have much longer periods4 ,when next one of these makes its passage athwart the sun1 far more important solar disturbances may take place than those which occur when the regularly recurring systems salute the sun4 ,two or three times in the history of science comets have approached very close to the surface of the sun1 as in #afhj1 and again in #ahdc1 but without actually impinging upon it4 ,very slight changes in the motions of those comets1 owing to the disturbing influences of the planets1 would cause their very nuclei to strike the sun1 and their meteoric trains to pour afterwards in a full stream upon him for many days1 or even for many months and years in succession4 ,now ,i do not think our sun would necessarily suffer very much from any of these known comets4 ,they may long since have parted with the greater quantity of their substance4 ,but it is quite possible that even one of those well-known comets of the solar system might cause very serious outbursts of solar heat and light2 and it is certainly not only possible but extremely probable that other comets1 such as have visited the solar system on paths fortunately not bringing them near to the sun1 would have worked much mischief had their paths been differently situated4 ,we know that ,newton held this opinion4 ,he considered the real danger from comets to reside1 not in the possibility that one might strike our earth1 but in the possibility that one1 falling upon the sun1 might excite that orb to a degree of heat so intense that all life on this earth would be destroyed4 ,it is true that1 in ,newton's time1 physical laws were not so well understood as at present1 and a considerable portion of ,newton's reasoning was consequently inexact4 ,but nothing which is now known opposes itself to the belief which ,newton adopted on this subject4 ,on the contrary1 whereas ,newton only recognised the danger arising from the consumption of a comet as fuel for the sun1 we now recognise a far more serious danger1 from the force of meteoric impact1 and the heat excited as the thermal equivalent of the destroyed velocities4 ,of this part of the danger ,newton had no clear conception1 the relations between mechanical energy and heat not having been established until quite recent times4 ,it appears to me1 however1 that the danger in the case of our own sun--or may we not say our danger8--arises only from the possibility that some one of the comets which visit us from the star-depths may make straight for the sun2 and this danger is exceedingly small4 ,almost certainly a comet which1 leaving the domain of another sun1 falls under the attractive influence of our own1 would approach him on a path passing many millions of miles from his surface4 ,the chances against a more direct approach are so great that they may be regarded as1 to all intents and purposes1 overwhelming4 ,a comet might visit us from the star-depth on a destructive course1 just as a single black ball might be drawn at the first trial from a bag containing a million white balls and only that single black one4 ,but the danger is exceedingly small4 ,we see1 indeed1 that other suns have suffered in this way1 assuming cometic downfall to be the true cause of stellar outbursts4 ,there are so many millions of suns1 however1 in the region of space to which telescopic survey extends that the occurrence of ten or twelve such outbursts in the course of four or five centuries need not be regarded as implying any serious danger4 ,moreover1 all the suns which have thus suffered lie within a particular region of the heavens1--viz41 in the ,milky ,way1 and in that half of the ,milky ,way which is most irregular1 one may almost say ragged1 in structure4 7,with one exception--the star in the ,northern ,crown1 which1 nevertheless1 lies on a faint outlying streamer of the ,milky ,way not discernible to ordinary vision47 ,if then our sun belongs to this region of space1 the danger for him and for us is somewhat greater than my previous argument would indicate4 ,for1 in that case1 we must compare the number of outbursts1 not with the total number of stars within telescopic range1 but with the number of those stars which lie within this particular region of space4 ,on the other hand1 if our sun does not lie within that region of space1 the danger for him and for us is very much less2 for instead of a certain small number of accidents among his fellow suns1 there have been no such accidents1 only accidents affecting other suns which must be differently classed4 ,the case may be compared to the estimation of the dangers1 let us say1 of travelling by ocean steamships on a particular route4 ,if we take the total number of accidents1 for instance1 to steamships travelling between ,england and the ,united ,states1 we should estimate the risk of the journey as very small1 the number of passengers who have lost their lives being very small compared with the number who have made the journey4 ,but even this small risk is diminished if we estimate the danger for a passenger by ,cunard steamships1 simply because no passenger has yet lost his life through accident to one of these ,cunard vessels4 ,so in the case of our sun1 the danger of an outburst such as has affected the stars in the ,northern ,crown and ,cygnus is small enough when we estimate it by comparing the number of such accidents with the total number of stars1 but vanishes almost into nothingness when we note that no insulated star like our sun seems hitherto to have undergone one of these tremendous catastrophes4 ,but as regards the fate of worlds circling round suns which have suffered in this way1 we can form but one opinion4 ,beyond all doubt1 if such worlds existed and were inhabited when their central orb blazed forth with many hundred times its former lustre1 all life must have perished from their surface4 ,we may believe1 as many do1 that no conditions are too unlike those we are familiar with on earth to render life impossible2 that the creatures subsisting in a world exposed to the most fiery heat or to the most intense cold are adapted as perfectly to the conditions under which they subsist as we are to the circumstances of terrestrial life4 ,but even adopting this view1 though it seems to accord ill with what we know of our own earth1--where life ceases towards the polar and over large tracts of the equatorial regions1--we could not believe that creatures thus adapted to the conditions prevailing around them could endure an entire change of those conditions4 ,with the accessions of heat in the stars in ,cygnus and the ,crown1 such change must inevitably have taken place4 ,therefore1 as ,i think1 we must regard the catastrophes affecting those remote suns as assuredly involving ,the ,end of many ,worlds4 ,note4--,what is stated in the latter portion of this chapter applies now only to the star in the ,northern ,crown2 for the star in ,cygnus has not faded into a small star1 but into a small nebula6 ,for the further history of this star1 the reader is referred to my forthcoming treatise entitled1 ,pleasant ,ways in ,science4 ,,footnotes3 #g ,its place is indicated in my ,school ,atlas1 as well as 7of course7 in my ,library ,atlas1 from the latter of which the small maps illustrating the present article have been pricked off4 ,the new star is marked ,t in the ,crown 7,map ,,viii471 and must not be confounded with the star 1 as in ,roscoe's ,treatise on ,spectral ,analysis1 and in some astronomical works4 ,the star is a well known fifth magnitude star1 which has shone with no perceptible increase or diminution of splendour since ,bayer's time certainly1 and probably for thousands of years before4 #h ,this chapter was first published in ,february1 #ahgg1 when the star was already invisible to the naked eye4 #i ,it will be remembered by those familiar with the history of solar observation1 that when the spectrum of the solar prominence was first observed1 the orange-yellow bright line was supposed to be the well-known double sodium line4 ,it is so near to this pair of lines1 that while they are called ,d #a and ,d #b1 it has been called ,d #c2 and in a spectroscope of small dispersive power the three would be seen as one4 ,illustration ,,vi4 ,,the ,,aurora ,,borealis4 ,among the objects in view1 when the recent ,polar expedition was fitted out1 was the hope that during the winter of #ahge-gf the scientific observers who accompanied the expedition might be able to study the ,aurora ,borealis under unusually favourable conditions4 ,this hope was1 as most of my readers doubtless know1 disappointed4 ,few auroras were seen1 and those seen were not remarkable either for brilliancy or for beauty of colour4 ,yet in the very disappointment of the hope which had been entertained on this subject there was very significant evidence respecting the aurora1 as will presently be shown4 ,the quiescence1 at that time1 of the forces which produce the auroral streamers had its meaning1 and a very strange one4 ,the aurora is one of those phenomena of nature which are characterized by exceeding beauty1 and sometimes by an imposing grandeur1 but are unaccompanied by any danger1 and indeed1 so far as can be determined1 by any influence whatever upon the conditions which affect our well-being4 ,comparing the aurora with a phenomenon akin to it in origin--lightning--we find in this respect the most marked contrast4 ,both phenomena are caused by electrical discharges2 both are exceedingly beautiful4 ,it is doubtful which is the more imposing so far as visible effects are concerned4 ,when the auroral crown is fully formed1 and the vault of heaven is covered with the auroral banners1 waving hither and thither silently1 now fading from view1 anon glowing with more intense splendour1 the mind is not less impressed with a sense of the wondrous powers which surround us than when1 as the forked lightnings leap from the thundercloud1 the whole heavens glow with violet light1 and then sink suddenly into darkness4 ,the solemn stillness of the auroral display is as impressive in its kind as the crashing peal of the thunderbolt4 ,but there is a striking contrast between the feelings with which we regard the safe splendours of the aurora and the terrible glory of the lightning flash4 ,one display we contemplate with the calmness engendered by absolute security2 the other--no matter how little the fear of death may affect the reason--cannot be regarded without exciting the consciousness of danger4 ,we witness in safety1 so far as itself is concerned1 the flash whose light illuminates the cloud masses above and around us1 but for aught we know it may be the last we shall ever see1 since no man killed by lightning ever saw the flash which brought his death4 ,i do not purpose to consider here at any length those facts respecting the aurora which properly find their place in text-books of science1 but those only which are less commonly dealt with1 and seem at once most suggestive and most perplexing4 ,the reader is no doubt aware that auroras1 or polar streamers1 as they are sometimes called1 are appearances seen not around the true poles of the earth1 but around the magnetic poles1 which lie very far away from those geographical poles which our arctic and antarctic seamen have in vain attempted to reach4 ,we in ,england1 though much nearer to the north pole than the inhabitants of ,canada1 see far fewer auroras than they do1 and those we see are far less splendid1 simply because we are farther away from the northern magnetic pole4 ,this will be seen from the accompanying pair of maps 7from my ,elementary ,physical ,geography71 showing where the northern and southern magnetic poles lie4 ,again1 you will see from the northern map1 that from ,england the northern magnetic pole lies towards the west of due north4 ,that is why when we see a fully developed auroral arch in this country its crown lies towards the west of north 7almost midway between north and north-west74 ,i may have occasion at another time to consider the curious changes which affect the actual position of the magnetic poles and lines2 in this place ,i merely note that what is now said respecting them only refers to the present time4 ,illustration3 ,fig4 #i4--,the ,northern ,magnetic ,meridians and ,lines of ,equal ,dip4 ,illustration3 ,fig4 #aj4--,the ,southern ,magnetic ,meridians and ,lines of ,equal ,dip4 ,the formation of auroral streamers around the magnetic poles of the earth shows that these lights are due to electrical discharges1 just as the general magnetic phenomena of the earth indicate the existence of electrical currents4 ,the earth1 in fact1 with its envelope of air1 moist and dense near the surface1 rare and dry above may be regarded as an enormous magnetic instrument1 a core surrounded by conducting matter1 in which electrical currents pass whenever the condition of the earth's magnetism changes4 ,the discharges of electricity1 though only visible at night1 take place in reality in the daytime also4 ,according to their extent and position1 varying with the varying conditions under which they take place1 their aspect changes4 ,moreover1 from different parts of the earth the appearance of the aurora is different4 ,from low latitudes 7,i speak now of magnetic latitudes as indicated by the closed curves around the magnetic poles in the maps71 the auroral arch is seen towards the north in our hemisphere1 towards the south in the other hemisphere4 ,from points nearer the magnetic pole it is seen overhead1 and when that pole is approached still nearer1 the crown of the arch is seen on the side remote from the pole1--that is1 towards the south in our hemisphere1 towards the north in the southern hemisphere4 ,remembering that the aurora is due to electrical discharges in the upper regions of the air1 it is interesting to learn what are the appearances presented by the aurora at places where the auroral arch is high above the horizon1--these being1 in fact1 places nearly under the auroral arch4 ,m4 ,ch4 ,martins1 who observed a great number of auroras at ,spitzbergen in #ahci1 thus writes 7as translated by ,mr4 ,glaisher7 respecting them3 ,at times they are simple diffused gleams or luminous patches2 at others1 quivering rays of pure white which run across the sky1 starting from the horizon as if an invisible pencil were being drawn over the celestial vault2 at times it stops in its course1 the incomplete rays do not reach the zenith1 but the aurora continues at some other point2 a bouquet of rays darts forth1 spreads out into a fan1 then becomes pale1 and dies out4 ,at other times long golden draperies float above the head of the spectator1 and take a thousand folds and undulations as if agitated by the wind4 ,they appear to be but at a slight elevation in the atmosphere1 and it seems strange that the rustling of the folds as they double back on each other is not audible4 ,generally1 a luminous bow is seen in the north2 a black segment separates it from the horizon1 the dark colour forming a contrast with the pure white or bright red of the bow1 which darts forth rays1 extends1 becomes divided1 and soon presents the appearance of a luminous fan1 which fills the northern sky1 and mounts nearly to the zenith1 where the rays1 uniting1 form a crown1 which in its turn darts forth luminous jets in all directions4 ,the sky then looks like a cupola of fire2 the blue1 the green1 the yellow1 the red1 and the white vibrate in the palpitating rays of the aurora4 ,but this brilliant spectacle lasts only a few minutes2 the crown first ceases to emit luminous jets1 and then gradually dies out2 a diffused light fills the sky2 here and there a few luminous patches1 resembling light clouds1 open and close with incredible rapidity1 like a heart that is beating fast4 ,they soon get pale in their turn1 everything fades away and becomes confused1 the aurora seems to be in its death-throes2 the stars1 which its light had obscured1 shine with a renewed brightness2 and the long polar night1 sombre and profound1 again assumes its sway over the icy solitudes of earth and ocean4 ,the association between auroral phenomena and those of terrestrial magnetism has long been placed beyond a doubt4 ,wargentin in #agej first established the fact1 which had been previously noted1 however1 by ,halley and ,celsius4 ,but the extension of the relation to phenomena occurring outside the earth--very far away from the earth--belongs to recent times4 ,the first point to be noticed1 as showing that the aurora depends partly on extra-terrestrial circumstances1 is the fact that the frequency of its appearance varies greatly from time to time4 ,it is said that the aurora was hardly ever seen in ,england during the seventeenth century1 though the northern magnetic pole was then much nearer to ,england than it is at present4 ,halley states that before the great aurora of #agaf none had been seen 7or at least recorded7 in ,england for more than eighty years1 and no remarkable aurora since #aegd4 ,in the records of the ,paris ,academy of ,sciences no aurora is mentioned between #afff and #agaf4 ,at ,berlin one was recorded in #agjg as a very unusual phenomenon2 and the one seen at ,bologna in #agbc was described as the first which had ever been seen there4 ,celsius1 who described in #agcc no less than three hundred and sixteen observations of the aurora in ,sweden between #agjf and #agcb1 states that the oldest inhabitants of ,upsala considered the phenomenon as a great rarity before #agaf4 ,anderson1 of ,hamburg1 states that in ,iceland the frequent occurrence of auroras between #agaf and #agcb was regarded with great astonishment4 ,in the sixteenth century1 however1 they had been frequent4 ,here1 then1 we seem to find the evidence of some cause external to the earth1 as producing auroras1 or at least as tending to make their occurrence more or less frequent4 ,the earth has remained to all appearance unchanged in general respects during the last three centuries1 yet in the sixteenth her magnetic poles have been frequently surrounded by auroral streamers2 during the seventeenth these streamers have been seldom seen2 during the last two-thirds of the seventeenth century auroras have again been frequent2 and during the present century they have occurred sometimes frequently during several years in succession1 at others very seldom4 ,let us inquire a little more closely into the circumstances attending auroral displays1 in order to ascertain what external cause it is which thus influences their occurrence4 ,connected as auroras are with the phenomena of terrestrial magnetism1 we may expect to find some help in our inquiry from the study of these phenomena4 ,now it appears certain that magnetic phenomena are partly influenced by changes in the sun's condition4 ,we may well believe that they are in the main due to the sun's ordinary action1 but the peculiarities which affect them seem to depend on changes in the sun's action4 ,it is found that the daily oscillation of the magnetic needle corresponds with the diurnal change in the position of the sun owing to the earth's rotation4 ,an annual change affecting that oscillation depends on the varying distance of the sun as the year proceeds4 ,the daily change is not only greater than the annual1 but is characterized by irregularities1 when the face of the sun shows the greatest number of spots4 ,it was found by ,general ,sabine1 says ,mr4 ,balfour ,stewart1 that the aggregate value of magnetic disturbances at ,toronto attained a maximum in #ahdh1 nor was he slow to remark that this was also ,schwabe's period of maximum sun-spots4 ,it was afterwards found1 by observations made at ,kew1 that #ahei 7another of ,schwabe's years7 was also a year of maximum magnetic disturbance4444 ,there is also some reason to believe that on one occasion our luminary was caught in the very act4 ,on the first of ,september1 #ahfi1 two astronomers1 ,carrington and ,hodgson1 were independently observing the sun's disc1 which exhibited at that time a very large spot1 when1 about a quarter past eleven1 they noticed a very bright star of light suddenly break out over the spot and move with great velocity across the sun's surface4 ,on ,mr4 ,carrington sending afterwards to ,kew ,observatory1 at which place the position of the magnet is recorded continuously by photography1 it was found that a magnetic disturbance had broken out at the very moment when this singular appearance had been observed4 ,the dip of the magnetic needle1 its deflection from the north1 the inferiority of its directive force1 were all three simultaneously and abruptly altered1 and continued so for many hours4 ,nor are we left in any doubt as to the connection between such well-marked disturbances of the magnetic needle4 ,while the needle was thus violently displaced1 vivid auroras occurred over the greater part of both the northern and southern 7magnetic7 hemispheres4 ,they were seen in latitudes where usually auroras are as infrequent as rain in ,peru1--at ,rome1 in the ,west ,indies1 even within eighteen degrees of the equator4 ,the disturbance of the earth's electrical condition was well shown in other ways4 ,mr4 ,c4 ,v4 ,walker1 the telegraphist1 found that strong electrical currents affected the various telegraphic lines throughout ,england4 ,these currents changed in direction every two or three minutes4 ,in many places it was impossible to send telegraphic messages4 ,in ,america some of the signalmen received severe electric shocks4 ,at a station in ,norway1 says ,sir ,j4 ,herschel1 the telegraphic apparatus was set fire to2 and at ,boston1 in ,north ,america1 a flame of fire followed the pen of ,bain's electric telegraph 7which writes down the message upon chemically prepared paper74 ,many of my readers will doubtless remember the auroras of ,may #ac1 #ahfi1 and ,october #bd1 #ahgj1 both of which occurred when the sun's surface was marked by many spots1 and both of which were accompanied by remarkable disturbance of the earth's magnetism4 ,it may1 then1 fairly be assumed that the occurrence of auroras depends in some way1 directly or indirectly1 on the condition of the sun4 ,but what the real nature of that connection may be is not to be easily determined4 ,it is clear that the eleven-year-period of sun-spots is not the only1 or even the chief period affecting auroras1 for we have seen that sometimes for a full century1 or even more1 very few auroras are seen4 ,it is not by any means certain that the connection between the sun's condition and the occurrence of auroras is of the nature of cause and effect2 quite probably sun-spots and auroras depend on some common cause as yet undetected1--and possibly never to be detected by man4 ,regarding the auroral streamers as terrestrial lights only1 but in some sense like the light reflected by planets in having their real source in the sun1 we can no longer speak1 as ,humboldt was wont to do1 of our planet possessing a power of emitting light of its own4 ,yet his manner of dealing with auroral light still possesses interest for us1 especially in relation to the question whether these polar lights are emitted by other planets and may possibly be discerned from our earth4 ,it results from the phenomena of the aurora1 said ,humboldt1 that the earth is endowed with the property of emitting a light distinct from that of the sun4 ,the intensity of this light is rather greater than that of the moon in its first quarter4 ,it is at times1 as on ,january #g1 #ahca1 strong enough to admit of one's reading printed characters without difficulty4 ,this light of the earth1 the emission of which towards the poles is almost continuous 7this1 however1 is not strictly the case71 reminds us of the light of ,venus1 the part of which not lighted by the sun often glimmers with a dim phosphorescent light4 ,other planets may also possess a light evolved out of their own substance4 ,i would venture1 however1 to express strong doubts as to the possibility of discerning1 either on ,venus or on any other planet1 the auroral gleams which may very probably illuminate at times their nocturnal skies4 ,it must be remembered that the aurora1 when at its brightest and covering a large part of the sky1 only gives about as much light as the moon in her first quarter1--that is1 as one half of a disc so small that #ahj1jjj such discs would not equal the entire sky4 ,the luminosity of the aurora is then in reality very small2 probably far less than that of the earth's surface when illuminated by the full moon4 ,a distant hill on which the rays of the full moon are falling seems strongly illuminated1 and yet its light is really so faint that we could scarcely discern it at all save for the favouring effect of contrast4 ,we know this1 because we often see portions of the moon's surface which are illuminated by earthshine 7when we see what is called the old moon in the new moon's arms71 and these portions are quite faint by comparison with the rest of the moon2 yet earthshine exceeds moonshine at least twelve times1 and probably more nearly twenty times in splendour4 ,the glimmering phosphorescent light1 supposed to have been seen on parts of ,venus not lighted by the moon1 is a phenomenon about which experienced telescopists are somewhat doubtful1 though ,webb speaks of the appearance as remarkably well attested1 quoting1 amongst others1 the following cases4 ,in #agae1 ,derham1 in his ,astro-,theology1 says that the sphericity or rotundity is manifest in our moon1 yea1 and in ,venus1 too1 in whose greatest falcations 7i4e41 when they appear as crescents7 the dark parts of their globes may be perceived1 exhibiting themselves under the appearance of a dull and rusty colour4 ,in #ahjf1 the phenomenon displayed itself beautifully to ,harding three times and to ,schrter once within five weeks4 ,guthrie and others noticed it a few years ago1 with small reflectors1 in ,scotland2 ,purchas1 at ,ross1 in ,england2 ,de ,vico and ,palomba1 many times in ,italy4 ,winnecke records a similar observation1 though very faint1 #ahga1 ,september #be1 a little before noon4 ,van ,hahn also says he saw it repeatedly1 by day as well as by night1 and with several instruments2 he was1 however1 an inferior observer4 ,the dark side is sometimes described as grey1 sometimes as reddish4 ,the phenomenon has1 on the other hand1 been looked for specially1 on several occasions1 by practised observers1 using very fine instruments1 who have failed to recognise any trace of it4 ,one of the most remarkable observations ever made on ,venus must here be mentioned4 ,mdler states that on one occasion1 when he was observing the planet1 he saw a number of brushes of light diverging from the circular side 7i4e41 the outside of the planet's crescent71 lasting as long as the planet could be seen that evening1 and remaining unchanged when he changed the position of the telescopic eye-piece1 or used a different one4 ,he attempts no explanation1 says ,webb1 but thinks it could not have been an optical illusion4 ,this is certainly possible1 but it is an instructive instance of the oversights which may be incidental even to great philosophers1 that it never seems to have occurred to him to try another telescope6 ,it cannot be doubted that the evidence would have been greatly strengthened had he changed telescope as well as eye-piece2 though it is not readily to be explained how a known telescope1 frequently used as well before as after this strange appearance was seen1 could for one evening only have played so strange a trick as ,mdler's must have done1 if what he saw was merely an instrumental illusion4 ,however1 whether we have telescopic evidence or not respecting auroral lights surrounding the polar regions of other planets1 we can have very little doubt that some among the planets1 if not all of them1 resemble our earth in this as in so many other respects4 ,the aurora is a cosmical phenomenon1 not one peculiar to our own earth4 ,it is not1 indeed1 altogether certain that our sun himself may not be girt round by mighty auroral streamers1 and that the light of these may not constitute a noteworthy portion of the corona of glory seen around him during the time of total eclipse4 ,this view1 indeed1 although it has not been definitely entertained as ,i have here expressed it1 has been suggested by reasoning which led others to suppose that the coloured prominences around the sun may be auroras4 ,perceiving the nature of the connection between terrestrial magnetism and auroras1 ,balfour ,stewart reasoned that we may extend our inquiries and ask1 ,if the sun's action is able to create a terrestrial aurora1 why may he not also create an aurora in his own atmosphere8 ,it occurred independently to ,general ,sabine1 ,prof4 ,challis1 and himself1 that the red flames visible during a total solar eclipse may be solar auror4 ,we now know that the solar flames are not auror1 nor1 properly speaking1 flames at all1 but great masses of glowing vapour4 ,it is not1 however1 by any means so clear that the solar corona is not auroral in its nature4 ,the following reasoning1 applied by ,balfour ,stewart to the sun's prominences1 applies with much greater force to the corona4 ,after mentioning the height 7from #gj1jjj to #hj1jjj7 which some prominences attain1 he proceeds1 ,considering the gravity of the sun1 we are naturally unwilling to suppose that there can be any considerable amount of atmosphere at such a distance from his surface2 and we are therefore induced to seek for an explanation of these red flames amongst those phenomena which require the smallest possible amount of atmosphere for their manifestation4 ,now the experiments of ,mr4 ,gassiot and the observed height of the terrestrial aurora alike convince us that this meteor will answer our requirements best4 ,and besides this1 the curved appearance of these red flames1 and their high actinic power1 in virtue of which one of them1 not visible to the eye1 was photographed by ,mr4 ,de la ,rue1 are bonds of union between these and terrestrial auror4 ,all this and much more may be said of the solar corona4 ,its streamers extend not #gj1jjj or #hj1jjj miles1 but #gjj1jjj or #hjj1jjj miles1 from the surface of the sun1 where the pressure must be far smaller than near the summits of even the loftiest prominences4 ,they are curved and striated1 like those of the aurora1 whereas the shapes of the prominences bear only a distant resemblance to auroral streamers4 ,they possess a high actinic 7i4e41 photographic7 power1 as is shewn by the readiness with which1 during the total eclipse of ,december1 #ahga1 they were photographed1 no less than six well-defined negatives being taken both by ,col4 ,tennant1 at ,ootacamund1 and by ,mr4 ,davis1 at ,baikal1 during the brief continuance 7only a few minutes7 of total obscuration4 ,in every respect the solar corona accords far better than do the solar coloured prominences with the appearance we should expect to recognise in solar auroras4 ,in particular1 it has always seemed to me that the curved1 especially the doubly curved1 streamers of the corona can only be well explained by regarding the corona as in the main an auroral phenomenon4 ,if mighty currents prevailed in the higher regions of a rare atmosphere1 extending hundreds of thousands of miles from the sun's surface1 appearances such as these curved streamers would undoubtedly be explained4 ,but no one who considers the effect of the sun's tremendous attractive power on such an atmosphere can fail to perceive that1 according to the known laws connecting gaseous pressure and density1 the density of that atmosphere would be enormously great1 even at a very great distance from the sun's surface1 if the curved streamers really were caused by atmospheric currents4 ,we know1 on the contrary1 from the behaviour of comets which have passed very near to the sun1 that the atmosphere above his visible surface must be very rare indeed4 ,it must not be understood1 however1 that ,i regard the corona as simply a great solar aurora4 ,it is certain that the whole region filled by the corona is occupied by immense numbers of scattered meteors1 and extremely probable that large quantities of cometic matter exist within the same region4 ,vaporous masses may also be there1 circling independently around the sun4 ,but that this region is illuminated constantly by auroral light1 varying greatly in intensity and position1 seems very strongly indicated by all that we know about the corona1 as seen during different total eclipses of the sun4 ,if we so viewed the solar corona1 and found our earth1 therefore1 in this respect resembling the great central orb of the solar system1 we could not but regard as extremely probable the theory that other planets also resemble the central body in this respect4 ,we might then picture to ourselves every orb in the solar system carrying onward its faintly luminous crowns of boreal and austral light1 not shining with constant lustre1 or in the same constant position1 but at one time leaping in coloured steamers to a great distance from the body they adorned1 and anon sinking down and growing fainter and fainter1 or occasionally disappearing altogether4 ,then1 when some great disturbance affected the central sun1 and caused his auroral banners to shine out more brilliantly and to attain a greater extension1 suddenly the auroral streamers of all the planets would leap out into new light and life1 playing around the northern and southern magnetic poles of those orbs1 even as electric brushes play around the positive and negative electrodes of a ,geissler's tube4 ,suddenly at least so far as each planet is concerned1 but not suddenly throughout the whole system4 ,for the magnetic influences1 like the light and heat of the sun1 require time for their transmission4 ,yet1 so rapidly do they travel that1 in a few hours1 the auroral illumination would extend from the central sun to the outermost limits of his system4 ,it remains that ,i should make a few remarks on the evidence which that wonderful instrument of research1 the spectroscope1 has afforded respecting the light of the aurora4 ,angstrm was the first to observe the spectrum of the aurora borealis4 ,he found that the greater part of the auroral light1 as observed in #ahfg1 was of one colour1 yellow1 but three faint bands of green and greenish blue colour were also seen4 ,the aurora of ,april #ae1 #ahfi1 was seen under very favourable conditions in ,america4 ,prof4 ,winlock1 observing it at ,new ,york1 found its spectrum to consist of five bright lines1 of which the brightest was the yellow line just mentioned4 ,one of the others seems to agree very nearly1 if not exactly1 in position with a green line1 which is the most conspicuous feature of the spectrum of the solar corona4 ,during the aurora of ,october #f1 #ahfi1 ,flgel noticed the strong yellow line and a faint green band4 ,schmidt1 on ,april #e1 #ahgj1 made a similar observation4 ,he saw the strong yellow line1 and from it there extended towards the violet end of the spectrum a faint greenish band1 which1 however1 at times showed three defined lines1 fainter1 than the yellow line4 ,it was not till the magnificent aurora of ,october #bd1 #be1 #ahgj1 that any red lines were seen in the spectrum of an aurora4 ,on that occasion the background of auroral light was ruddy1 and on the ruddy background there were seen three deep red streamers very well defined4 ,the ruddy streamers1 on the night of ,october #be1 converged towards the auroral crown1 which was on that occasion singularly well seen4 ,frster of ,berlin failed to see any red line or band despite the marked ruddiness of the auroral light4 ,but ,capron at ,guildford saw a faint line in the red part of the spectrum2 and ,elger at ,bedford observed a red band in the light of the red streamers1 the band disappearing1 however1 when the spectroscope was directed on the white rays of the aurora4 ,as yet the auroral spectrum has not been interpreted4 ,it is not a spectrum which can be 7at present7 artificially produced4 ,we understand the spectrum of the sun and stars1 because spectra of the same order can be produced in our laboratories4 ,the spectra of the planets1 so far as they differ from the spectrum of reflected sunlight in showing signs of the absorptive action of the planetary atmosphere1 have been similarly interpreted4 ,so also the spectra of the coloured solar prominences are understood1 while those of nebul and comets1 though not as yet thoroughly explained1 have been partly interpreted1 because of their partial agreement with the known spectra of earthly elements4 ,but as yet neither the spectrum of the aurora nor that of the solar corona has been explained4 ,the reason probably is1 that the conditions under which the light of the aurora as of the corona is formed are not such as have been or perhaps can be attained or even approached in laboratory experiments4 ,illustration ,,vii4 ,,the ,,lunar ,,halo4 ,there are some phenomena of nature which suggest false ideas4 ,for instance1 when we look at the broad expanse of ocean on a moonlit night1 and see a path of glory on its surface1 directed towards the moon's place1 we seem to be assured by the sense of sight that that broad track is illuminated while the waters all around are dark4 ,a little consideration1 however1 assures us that the impression is a false one1 that in this case seeing is not believing4 ,the moon's rays really illumine the whole surface which lies before us1 and we fail to receive light from other parts than the track below the moon1 not because they receive no light1 but because the light which they receive is not reflected towards us4 ,an observer1 stationed a mile or two towards the right or towards the left of our station1 sees a different track of light1 while the part which seems bright to us seems dark to him4 ,the rainbow is another phenomenon of this deceptive kind4 ,we seem to see an arch of many colours suspended in the air1--and when we learn that it is due to the presence of drops of water in the air1 we are apt to infer that where we see the red arch there are drops lit up with red light1 where the yellow1 green1 or violet arch1 that the drops are aglow with yellow1 green1 or violet light4 ,but in reality this is not so2 the same drops which seem green to us will seem red to another observer1 violet to another1 and to yet other observers will show none of the prismatic colours1 but only the dull grey colour of the cloud on which the rainbow is seen4 ,we have here a pretty emblem of the varied aspects which events of the same real nature present to different persons1 or according to the different circumstances under which the same person may see them4 ,one shall see events in rosy tints1 or with the freshness of spring hues1 or with the melancholy symbolled by the deeper indigo 7as when ,the heavy-skirted evening droops with frost7-- while to others the same events shall show only the ordinary tints of common-place life4 ,the lunar halo is one of the phenomena thus deceptive to the view4 ,we see all around the moon a circle or arc of light1 nearly white1 though sometimes faint tints of colour can be perceived in it1 while the space within the circle seems manifestly darker than the space outside4 ,the appearance of the halo as seen under favourable conditions is shown in fig4 #aa1 on the next page4 ,in this country the dark space round the moon is not generally so well seen as in countries where the air is clearer4 ,but this is in reality the characteristic feature of the halo1 as its name shows4 ,for the name is derived from a ,greek word signifying threshing-floor 7the old threshing-floors being round71 and thus naturally describes a round space relatively clear1 surrounded on all sides by a ring of aggregated matter4 ,we seem in looking at the lunar halo1 then1 to see the moon at the centre of a dark space1 surrounded by a ring of bright particles1 outside which again are particles not quite so brightly illuminated as those forming the ring1 but more brightly than those within the ring4 ,but in reality this impression1 which1 so far as the sense of sight is concerned1 seems forced upon the mind1 is entirely erroneous4 ,there is no real distinction between the space which looks dark all round the moon1 the space beyond which does not look dark1 and the ring between the two spaces which looks bright4 ,these are all equally illuminated by the moon1 in the same sense1 at least1 that we say the surface of a moonlit sea is all equally illuminated1 neglecting slight differences which do not concern the point we are specially dealing with4 ,precisely as the path of light on the ocean is not a real path of illumination1 bounded on either side by dark spaces1 so the ring of light round the moon is not a real ring of light1 bounded on one side by a less bright region1 and within by a dark space4 ,illustration3 ,fig4 #aa4--,lunar ,halo ,although my object in these essays is not specially to deal with scientific matters1 but rather with the thoughts 7much more important in my belief7 which they suggest--so that1 in dealing with my present subject1 ,i wish rather to call attention to the manifold ways in which our senses may deceive us unless their evidence is carefully cross-examined--yet it may be worth while to notice how the particular illusion here considered has deceived even the scientific elect4 ,it had been noticed by ,tyndall1 in certain experiments1 that a very sensitive measurer of heat1 when placed under the moon's rays1 gathered together by a powerful condenser1 seemed to indicate cooling rather than heating1 as we should expect4 ,on this a ,french student of science pointed to the darkening under the moon where the lunar halo is seen as evidence that our satellite possesses a certain power of clearing away vaporous matter from the air4 ,on peut dire1 he said1 speaking of the dark space within the halo1 que la lune ouvre alors une porte par laquelle s'chappe le calorique que l'action solaire a emmagasin dans les couches infrieures4 ,one may say1 that is1 that the moon then opens a door through which the heat escapes1 which the sun's action has stored up in the lower layers 7of the air74 ,it will be manifest1 if we remember that a lunar halo can often be seen at the same time from stations hundreds of miles apart1 that there can be no such opening of clear air4 ,for the cloud layer in which the halo is formed is but a few miles above the observer2 and therefore1 if one observer saw a circular opening in this layer1 with the moon at its centre1 another1 a hundred miles from him1 would see the space in a very different direction4 ,the moon would not only not be at the centre of the space for this second observer1 but would not be visible through the space at all4 ,moreover1 the space could not possibly seem round to both observers2 if it seemed round to one1 it would look like a very flat oval of darkness 7almost a mere line7 to the other4 ,the real explanation of the lunar halo is very different4 ,when you see such a halo1 you may be certain that there is1 high up in the air1 a layer of light feathery cloud--the cirrus cloud1 as it is called--composed of tiny crystals of ice4 ,these crystals1 as we know from those which in winter sometimes fall 7not as snow1 but as little ice-stars71 have all a definite shape4 ,they are in fact little prisms of ice1 with angles like those of an equilateral triangle4 ,these little prisms deflect the light which falls upon them1 just as one of the drops of a chandelier deflects any light which falls upon it4 ,if you hold a prism-drop of a chandelier between the eye and a light1 you will see that the prism looks dark2 it is really lit up1 but it sends the light away in such a direction that the eye receives none4 ,now move it gradually away from the line of sight to the light1 and at a certain distance it appears full of light2 or1 to speak more correctly1 it sends the light it receives directly towards your eye4 ,beyond that position it again looks dark1 but not so dark as when it was nearly between the eye and the light4 ,the little crystals of ice perform the same part with respect to the moon1 when we see a lunar halo4 ,those between us and the moon1 or within a certain distance from the line of sight to the moon1 are1 in reality1 lit up by the moon's rays2 but they send off those rays in such directions that we do not receive the light4 ,thus1 all the space lying towards the moon1 and for a certain distance all round1 looks dark4 ,but1 at a certain distance1 these little crystals send us light4 ,if we could see them separately1 they would seem to be full of light4 ,that is the distance where ice-crystals of their known shape act most favourably in deflecting light1--that is1 send off most for all the varying positions 7not places7 they can be in4 ,at greater distances1 a small proportion send us light4 ,thus1 at that distance we have a ring of light1 and outside the ring we have a gradual falling off in the quantity of light4 ,but the reader will be apt1 perhaps1 to say1 ,how can all this be proved8 ,no one has ever been among the ice-crystals of the feathery clouds when they are performing this work4 ,when ,coxwell and ,glaisher made their highest ascent1 the feather-clouds seemed almost as high above them as ever4 ,nor1 if any one could reach those clouds1 could he see the ice-crystals at their work4 ,yet there are few points about which science is more certainly assured than about this explanation of the halo4 ,for we know the shape constantly assumed by ice-crystals2 we know according to what precise law ice bends rays of light falling upon it2 hence we can calculate quite certainly where1 if ice-crystals make the halo1 its rings should be seen4 ,and the halo has the precise position thus calculated from the known laws of optics1 and the known facts about ice and ice-crystals4 ,the diameter of the halo should be1 and is1 about eighty times the apparent diameter of the moon1 or somewhat less than half the arc which separates the point overhead from the horizon4 ,there is1 however1 yet stronger evidence4 ,haloes form around the sun as well as round the moon1--in fact1 more frequently4 ,solar haloes have so much more light in them that we can recognise varieties of tint4 ,now1 it follows from the laws of optics that1 for the red part of the sun's light1 the halo ring should have a smaller diameter than the halo ring for the violet part1 intermediate colours having their corresponding intermediate halo rings4 ,thus1 the halo ring1 as a whole1 should be rainbow-tinted1 red on the inside1 then orange1 yellow1 green1 blue1 indigo1 and violet2 and these colours are shown 7under favourable conditions7 in this order4 ,the student looking out for haloes1 solar or lunar1 must be careful not to confound them with solar and lunar coronas1 that is1 not the corona of astronomy1 but rings of light around the sun and moon1 much smaller than the true halo rings4 ,what ,i have said above about the size of the true halo will suffice to prevent such a mistake4 ,coronas are not nearly so easily1 though they have been quite as thoroughly1 explained by science1 as haloes4 ,it is singular to observe how utterly unlike the interpretation of the halo by science is from the natural interpretation4 ,the observer would say1 ,there surely is a dark space all round the moon1 and round that a ring of light1--,i see these things1 and seeing is believing4 ,science says there is no dark space1 and there is no ring of light2 while the eye of science perceives something where the lunar halo shines which ordinary vision cannot recognise4 ,up yonder1 many miles above the earth1 science sees millions of crystals of ice1 carried hither and thither--so light are they--by every movement of the air4 ,science sees these ice crystals deflecting the rays of moonlight1 sifting the red rays from the orange1 and these from the yellow1 yellow from green1 green from blue1 blue from indigo1 and indigo from violet4 ,science1 in fine1 perceives processes taking place in those higher regions of air compared with which the most delicate analyses of the laboratory are utterly coarse and imperfect4 ,there is a purer and nobler poetry in the lunar halo as thus understood than in its mere visible phenomena1 attractive and beautiful though these are4 ,idle indeed is the fear that the interpretation of this special mystery of nature will leave the number of nature's mysteries diminished by one4 ,on the contrary1 for the one mystery explained many deeper mysteries are suggested4 ,the phenomena discernible by the sense of sight are explained1 but only by bringing into the range of a purer and more piercing vision phenomena infinitely more wonderful4 ,if one could see through some amazing extension of visual power1 or if even the imagination could adequately picture1 the rush of light waves of all orders of length upon the line of crystal breakers1 their deflection in all directions1 their separation into their various orders of wave-length2 if one could perceive the actual illumination of the ice-crystals1 even where they seem dark to us1 and the continual fluctuations of the troubled sea of ether between the crystal breakers and the earth below1--the scene would infinitely transcend in interest and mystery1 the picture would be infinitely more suggestive of solemn thoughts1 than the scene--beautiful though it doubtless is--presented by the halo-girt moon to ordinary vision4 ,truly they know little of the real meaning of science who regard it as depriving natural phenomena of their effect on the imagination1 as robbing ,nature of her poetic influence4 ,illustration ,,viii4 ,,moonlight4 ,the light of the moon and the changes of the moon were probably the first phenomena which led men to study the motions of the heavenly bodies4 ,in our times1 when most men live where artificial illumination is used at night1 we can scarcely appreciate the full value of moonlight to men who cannot obtain artificial light4 ,especially must moonlight have been valuable to the class of men among whom1 according to all traditions1 the first astronomers appeared4 ,the tiller of the soil might fare tolerably well without nocturnal light1 though even he1--as indeed the familiar designation of the harvest-moon shows us1--finds special value1 sometimes1 in moonlight4 ,but to the shepherd moonlight and its changes must have been of extreme importance as he watched his herds and flocks by night4 ,we can understand how carefully he would note the change from the new moon to the time when throughout the whole night1 or at least of the darkest hours1 the full moon illuminated the hills and valleys over which his watch extended1 and thence to the time when the sickle of the fast waning moon shone but for a short time before the rising of the sun4 ,to him1 naturally1 the lunar month1 and its subdivision1 the week1 would be the chief measure of time4 ,he would observe--or rather he could not help observing--the passage of the moon around the zodiacal band1 some twenty moon-breadths wide1 which is the lunar roadway among the stars4 ,these would be the first purely astronomical observations made by man2 so that we learn without surprise that before the present division of the zodiac was adopted the old ,chaldean astronomers 7as well as the ,indian1 ,persian1 ,egyptian1 and ,chinese astronomers1 who still follow the practice7 divided the zodiac into #bh lunar mansions1 each mansion corresponding nearly to one day's motion of the moon among the stars4 ,it is easy to understand how the first rough observations of moonlight and its changes taught men the true nature of the moon1 as an opaque globe circling round the earth1 and borrowing her light from the sun4 ,they perceived1 first1 that the moon was only full when she was opposite the sun1 shining at her highest in the south at midnight when the sun was at his lowest beneath the northern horizon4 ,before the time of full moon1 they saw that more or less of the moon's disc was illuminated as he was nearer or farther from the position opposite the sun1 the illuminated side being towards the west--that is1 towards the sun2 while after full moon the same law was perceived in the amount of light1 the illuminated side being still towards the sun1 that is1 towards the east4 ,they could not fail to observe the horned moon sometimes in the daytime1 with her horns turned directly from the sun1 and showing as plainly1 by her aspect1 whence her light was derived1 as does any terrestrial ball lit up either by a lamp or by the sun4 ,the explanation they gave was the explanation still given by astronomers4 ,let us briefly consider it4 ,in doing so ,i propose to modify the ordinary text-book illustration which has always seemed to me ingeniously calculated 7with its double set of diversely illuminated moons around the earth7 to make a simple subject obscure4 ,in fig4 #ab1 let ,e represent the earth one half in darkness1 the other half illuminated by the rays of the sun ,s1 which should be supposed placed at a much greater distance to the left1--in fact1 about five yards away from ,e4 ,to preserve the right proportions1 also1 the sun ought to be much smaller and the earth a mere point4 ,i mention this to prevent the reader from adopting erroneous ideas as to the size of these bodies4 ,in reality it is quite impossible to show in such figures the true proportions of the heavenly bodies and of their distances4 ,next let ,m#a1 ,m#b1 ,m#c1 etc41 represent the moon in different positions along her circuit around the earth at ,e4 ,illustration3 ,fig4 #ab4--;,explaining the ,moon's changes4 ,illustration3 ,fig4 #ac4--;,illustrating the ,moon's changes4 ,now1 it is clear that when the moon is at ,m#a1 her illuminated face is turned from the earth1 ,e4 ,she therefore cannot be seen2 and accordingly1 in fig4 #ab1 she is presented as a black disc at #a to correspond with her invisibility when she is as at ,m#a4 ,she passes on to ,m#b2 and now from ,e a part of her illuminated half can be seen towards the sun1 which would be towards the right1 if we imagine an eye at ,e looking towards ,m#b4 ,her appearance then is as shown at #b1 fig4 #ac4 ,in any intermediate portion between ,m#a and ,m#b1 the sickle of light is visible but narrower4 ,we see also that all this time the moon's place on the sky cannot be far from the sun's place1 for the line from ,e to ,m#b is not greatly inclined to the line from ,e to ,s4 ,when the moon has got round to ,m#c1 the observer on the earth sees as much of the dark half as of the bright half of the moon1 the bright half being seen1 of course1 towards the sun4 ,thus the moon appears as at #c1 fig4 #ac1 ,again as to position1 the moon is now a quarter of a circuit of the heavens from the sun1 for the line from ,e to ,m#c is square to the line from ,e to ,s4 ,we see similarly that when at ,m#d the moon appears as shown at #d1 fig4 #ac1 for now the observer at ,e sees as small a part of the moon's dark side as he had seen of her bright side when she was at ,m#b4 ,when she is at ,m#e the observer at ,e sees her bright face only1 the dark face being turned directly from him4 ,she1 therefore1 appears as at #e1 fig4 #ac4 ,also being now exactly opposite the sun1 as we see from fig4 #ab1 she is at her highest when the sun is at his lowest1 or at midnight2 and at this time she rules the night as the sun rules the day4#aj ,as the moon passes on to ,m#f1 a portion of her dark half comes into view1 the bright side being now towards the left1 as we look at ,m#e from ,e1 fig4 #ab4 ,her appearance1 therefore1 is as shown at #e4 ,when at ,m#g she is seen as at #g1 half-bright and half-dark1 as when she was at ,m#c1 but the halves interchanged4 ,at ,m#h she appears as at #h1 and1 lastly1 at ,m#a she is again undiscernible4 ,the ancient ,chaldean astronomers could have little doubt as to the validity of this explanation4 ,in fact1 while it is the explanation obviously suggested by observed facts1 one cannot see how any other could have occurred to them4 ,but if they had had any doubts for a while1 the occurrence of eclipses would soon have removed those doubts4 ,they must early have noticed that at times the full moon became first partly obscured1 then either wholly disappeared or changed in colour to a deep coppery red1 and after a while reappeared4 ,sometimes the darkening was less complete1 so that at the time of greatest darkness a portion of the moon seemed eaten out1 though not by a well defined or black shadow4 ,these phenomena1 they would find1 occurred only at the time of full moon4 ,and if they were closely observant1 they would find that these eclipses of the moon only occurred when the full moon was on or near the great circle round the stellar heavens1 which they had learned to be the sun's track4 ,they could hardly fail to infer that these darkenings of the moon were caused by the earth's shadow1 near which the moon must always pass when she is full1 and through which she must sometimes pass more or less fully2 in fact1 whenever1 at the time of full1 she is on or near the plane in which the earth travels round the sun4 ,solar eclipses would probably be observed later4 ,for though a total eclipse of the sun is a much more striking phenomenon than a total eclipse of the moon1 yet the latter are far more common4 ,a partial eclipse of the sun may readily pass unnoticed1 unless the sun's rays are so mitigated by haze or mist that it is possible to look at his disc without pain4 ,whenever solar eclipses came to be noted1 and we know from the ,chaldean discovery of the great eclipse period1 called the ,saros1 that they were observed at least two thousand years before the ,christian era1 the fact that the moon is an opaque body circling round the earth1 and much nearer to the earth than the sun is1 must be regarded as demonstrated4 ,not only would eclipses of the sun be observed to occur only when the moon was passing between the earth and the sun1 but in an eclipse of the sun1 whether total or partial1 the round black body cutting off the sun's light wholly or partially would be seen to have the familiar dimensions of the lunar orb4 ,leaving solar and lunar eclipses for description on another occasion1 ,i will now proceed to consider a peculiarity of moonlight which must very early have attracted attention1--,i mean the phenomenon called the harvest-moon4 ,the moon circuits the heavens in a path but slightly inclined to that of the sun1 called the ecliptic1 and for our present purpose we may speak of the moon as travelling in the ecliptic4 ,now we know that during the winter half of the year the sun is south of the equator1 the circle of the heavenly sphere which passes through the east and west points of the horizon1 and has its plane square to the polar axis of the heavens4 ,during the other or summer half of the year he is north of the equator4 ,in the former case the sun is above the horizon less than half the twenty-four hours1 day being so much shorter as the sun is farther south of the equator2 whereas in the latter case the sun is above the horizon more than twelve hours1 day being so much the longer as the sun is farther north of the equator4 ,precisely similar changes affect the moon1 only1 instead of taking place in a year 7the time in which the sun circuits the stellar heavens71 they occur in what is called a sidereal month1 the time in which the moon completes her circuit of the stellar heavens4 ,for about a fortnight the moon is above the horizon longer than she is below the horizon1 while during the next fortnight she is below the horizon longer than she is above the horizon4 ,now clearly when the length of what we may call the moon's diurnal path 7meaning her path above the horizon7 is lengthening most1 the time of her rising on successive nights must change least4 ,she comes to the south later and later each successive night by about #ej minutes1 because she is always travelling towards the east at such a rate as to complete one circuit in about four weeks2 and losing thus one day in #bh1 she losses about #ej minutes per day4 ,if the interval between her rising and her arriving to the south were always the same1 she would rise #ej minutes later night after night4 ,but if the interval is lengthening1 say by #aj minutes per night1 she would of course rise only #dj minutes later3 if the interval is lengthening #bj minutes per night1 she would rise only #cj minutes later1 and so forth4 ,but the lunar diurnal arc is lengthening all the time she is passing from her position farthest south of the equator to her position farthest north1 just in the same way as the solar day is lengthening from mid-winter to midsummer1 only to a much greater degree4 ,and as the solar day lengthens fastest at spring when the sun crosses the equator from south to north1 so the time the moon is above the horizon lengthens most1 day by day1 when the moon is crossing the equator from south to north4 ,it lengthens1 then1 from an hour to an hour and #bj minutes in one day1 that is1 the interval between moon-rise and moon-setting increases from #cj to #dj minutes4 ,at this time1 then1 whenever it happens in each lunar month1 the moon's time of rising changes least3 instead of the moon rising night after night #ej minutes later1 the actual difference varies only from #aj to #bj minutes4 ,now if this happens at a time when the moon is not nearly full1 it is not specially noticed1 because the moon's light is not then specially useful4 ,but if it happens when the moon is nearly full1 it is noticed1 because her light is then so useful4 ,a moon nearly full1 afterwards quite full1 and then for a day or two still nearly full1 rising night after night at nearly the same time1 remaining also night after night longer above the horizon1 manifestly serves man for the time being in the most convenient way possible4 ,but it is clear that as the full moon is opposite the sun1 and as to fulfil the condition described we have seen that she must be crossing the equator from south to north1 the sun1 opposite to her1 must be at the part of his path where he crosses the equator from north to south4 ,in other words1 the time of year must be the autumnal equinox4 ,thus the moon which comes to full nearest to ,september #bb or #bc will behave in the convenient way described4 ,at this time1 moreover1 when she rises night after night nearly at the same time1 the nights are lengthening fastest while the time the moon is above the horizon is lengthening still more1 and therefore1 in all respects1 the moon is then doing her best1 so to speak1 to illuminate the nights4 ,at this season the moon is called the harvest-moon1 from the assistance she sometimes renders to harvesters4 ,the moon which is full nearest to ,september #bb-bc may precede or follow that date4 ,in the former case only can it properly be called a harvest-moon4 ,in the latter it is sometimes called the hunter's moon4 ,the full moon occurring nearest to harvest time will always partake more or less of the qualities of a full moon occurring at the autumnal equinox3 and similarly of a full moon following the autumnal equinox4 ,so that1 in almost every year1 there may be said to be a harvest-moon and a hunter's moon4 ,but1 of course1 it will very often happen that in any particular agricultural district the harvest has to be gathered in during the wrong half of the lunar month1 that is1 during the last and first1 instead of the second and third quarters4 ,the reader must not fall into the mistake of supposing1 as ,i have seen sometimes stated in text-books of astronomy1 that we are more favoured in this respect than the inhabitants of the southern hemisphere4 ,it is quite true that the same full moon shines on us as on our friends in ,new ,zealand1 ,australia1 and ,cape ,colony1 and also that our autumn is their spring1 and their spring our autumn4 ,but the full moon we have in autumn behaves in the southern hemisphere not as with us1 but as our spring full moon behaves2 and the full moon of our spring1 which is their autumn1 behaves with them as our autumn moon behaves with us4 ,it is1 therefore1 for them a harvest-moon if it occur before the equinox1 and a hunter's moon if it occur after the equinox4 ,a very little consideration will show why this is4 ,in fact if1 in the explanation given above1 the words north and south be interchanged1 and ,march #ba-bb written for ,september #bb-bc1 the explanation will be precisely that which ,i should have given respecting the harvest 7or ,march7 moon of the southern hemisphere1 if ,i had been writing for southern readers4 99 99 99 99 99 ,having thus considered the moon as a light-giver1 both in respect of her monthly changes and of that yearly change which causes her services to be most useful in harvest time1 let us consider what science tells us of the orb which thus usefully reflects to us the solar rays4 ,the moon is a globe about #baei miles in diameter1 travelling round the earth at a mean distance of #bch1hah miles4 ,her path round the earth is not1 however1 a circle1 but an ellipse1 which itself is constantly varying in shape4 ,the average eccentricity of the moon's path is such that her greatest and least distances1 as she circuits round it1 are #bea1iec miles and #bbe1fhc miles respectively2 but when it is most eccentric1 her greatest and least distances are #beb1idh miles and #bba1eic miles respectively2 while1 when it is least eccentric1 they are respectively #bej1cbd miles and #bbg1cab miles4 ,the earth's surface exceeds the moon's nearly #ac times1 the actual number of square miles in the moon's surface amounting to #ad1fjj1jjj4 ,this is nearly equal to ,europe and ,africa together1 or1 more nearly still1 to ,north and ,south ,america together1 without their islands4 ,in volume our earth exceeds the moon rather more than #di times3 or1 more nearly1 if the earth's volume be represented by #aj1jjj1 the moon's will be represented by #bji4 ,the materials of the moon's globe are either lighter or 7more probably7 they are less closely compacted than those forming our earth1--for1 according to the best modern estimates1 the earth exceeds the moon in mass nearly #ha times4 ,assuming as the most probable value of the earth's mean density about #e-g_/aj times the density of water1 the moon's mean density is equal to #c-df_/ajj times that of water4 ,gravity at her surface is accordingly much less than at the surface of the earth2 a quantity of matter weighing six pounds at the surface of the earth would weigh almost exactly one pound at the surface of the moon4 ,the moon circuits once round the earth in #bg;d4 #g;h4 #dcm4 #aa4es4 ,this is the time in which1 viewed from the earth1 she seems to complete one circuit round the stellar heavens1 and is therefore called a sidereal month4 ,but as the earth is all the time travelling the same way round the sun1 the lunar month is longer4 ,thus1 suppose ,s 7fig4 #ad7 to be the sun1 ,e the earth at the beginning of a lunar month1 ,m#a ,m#b ,m#c ,m#d the moon's path1 and ,m#a the moon's place on the line joining ,e and ,s4 ,if the earth remained at rest while the moon went round the path ,m#a ,m#c1 then after completing one circuit the moon would again be at ,m#a on the line joining ,e and ,s1 or it would be new moon again4 ,but the earth is moving onwards along the arc ,,ee of her circuit round the sun4 ,so that when the moon has completed one circuit she is at ,m#d 7,em#a drawn parallel to ,,em#a7 and has still to travel some distance before she gets round to ,m on the line joining ,s and ,e4 ,the lunation1 or interval between successive new moons1 has an average duration of #bi;d4 #ab;h4 #ddm4 #chs41 exceeding a sidereal month by #b;d4 #e;h4 ,illustration3 ,fig4 #ad4--;,explaining the difference between a sidereal lunar month and a common lunar month or lunation4 ,it would not1 however1 be correct to regard the earth as the true centre of the moon's motion4 ,the moon is in reality a planet circling round the sun1 but largely perturbed by the attraction of its companion planet the earth4 ,if the moon's path in the course of a year were carefully drawn to scale1 or1 better1 were modelled by means of a fine wire1 it would scarcely be distinguishable from a similar picture or model of the earth's path round the sun4 ,or thus1 the entire width of the moon's track is about #dgg1fcf miles1 while the diameter of the orbit along which she and the earth both travel is nearly #ajd1jjj1jjj miles1 or #che times as great4 ,if we draw then a circle #c-he_/ajj inches in diameter to represent the earth's path round the sun1 somewhat eccentrically placed1 and the circular line is #a-ajjth of an inch wide1 the moon's track would be fairly represented by a curve touching alternately the inside and the outside edge of this circular line1 at equidistant points dividing the circle into about #bd parts4 ,regarding the moon as a planet1 she may be said to have a year1 and seasons1 and day and night1 as the earth has1 but very unlike our seasons and days4 ,her axis is inclined only #a degrees from uprightness to her path1 whereas our earth's axis is inclined #bc degrees4 ,the sun's range of mid-day altitude is in fact not quite equal to the range of our sun in mid-day height1 from four days before to four days after either spring or autumn4 ,the lunar day lasts a lunar month1 daytime and night-time each lasting rather more than a fortnight4 ,the lunar year of seasons is not1 as is commonly stated1 the same in length as ours4 ,she goes round the sun in the same time1 so that her sidereal year is the same as ours2 but owing to the swaying round of her axis her year of seasons or tropical year is shorter4 ,our tropical year is also shorter than the sidereal year1 but very little shorter1 because the earth's axis sways round once only in #be1hfh years4 ,the moon's axis sways round once in #ah years1 and accordingly the year of seasons is much more effectively shortened4 ,it lasts1 in fact1 only #cdf;d4 #ad;h4 #cdm4 of our time2 and contains only #aa lunar days4 ,so that ,i cannot altogether agree with ,sir ,w4 ,herschel's statement1 that the moon's situation with respect to the sun is much like that of our earth1 and by a rotation on its axis it enjoys an agreeable variety of seasons1 and of day and night4 ,when the moon is examined with a telescope her surface is seen to be marked by many irregularities4 ,there are large dark regions which were formerly thought to be seas1 but are now known to be land-surfaces4 ,some of these regions are singularly level1 and have been thought to be old sea-bottoms4 ,mountains and mountain ranges are another important feature of the moon's surface4 ,some1 like our ,rocky ,mountains and ,andes1 form long continuous chains2 others form elevated plateaus whence ridges extend in various directions4 ,a very striking form is that of narrow ridges little raised above the general level1 but reaching over enormous areas of the moon's globe4 ,it is a system of this kind1 radiating from a great lunar crater called ,tycho1 which gives to small photographs of the moon the appearance of a peeled orange4 ,they are supposed to indicate the action of tremendous forces of upheaval1 in past ages1 bursting open portions of the moon's crust4 ,but the most characteristic of all the lunar features are the crater mountains1 which exist on a scale not only much larger relatively to the moon's globe than the scale on which terrestrial craters are formed1 but much larger absolutely4 ,they are also far more numerous4 ,some parts of the moon's surface1 especially in the bright south-western quarter of her face1 are literally crowded with craters of various dimensions4 ,there are few signs of the former emission of lava from the lunar craters4 ,within some of them recent changes have been suspected4 ,a remarkable instance is that of the crater ,linn1 marked in ,mdler's map as a deep1 well-walled crater1 some four miles in diameter4 ,at present only a small crater can be seen in its place4 ,the surrounding region is rather conspicuously bright4 ,it is not necessary to infer that there has been any volcanic disturbance1 however4 ,far more probably the walls have been thrown down through the long-continued action of that alternate expansion and contraction1 which must affect the moon's crust as the long fortnightly day proceeds1 and then the equally long lunar night4 ,there are many well-marked valleys on the moon1 besides clefts and ravines4 ,the features called rilles are among the most perplexing objects on the moon's surface4 ,webb1 in his charming and most useful little book1 ,celestial ,objects for ,common ,telescopes1 thus describes them3 ,these most singular furrows pass chiefly through levels1 intersect craters 7proving a more recent date71 reappear beyond obstructing mountains1 as though carried through by a tunnel1 and commence and terminate with little reference to any conspicuous feature of the neighbourhood4 ,the idea of artificial formation is negatived by their magnitude2 they have been more probably referred to cracks in a shrinking surface4 ,some observations would seem to show that they have been formed from rows of closely-adjacent small craters4 ,faults1 also1 or closed cracks where the surface is higher on one side than on the other1 have been recognised from the careful study of the shadows on the moon's disc4 ,from measurements of the shadows of lunar mountains1 it appears that their average height is about five miles4 ,in comparing this elevation with that assigned to terrestrial mountains1 it must be remembered that these are measured from the sea-level2 if the average height of terrestrial mountains were determined with reference to the sea-bottom it would be far greater4 ,still1 even taking this circumstance into account1 the average height of the lunar mountains bears a far greater ratio to the diameter of the globe on which they stand than the average height of our mountains to the earth's diameter4 ,several circumstances agree in showing that the moon's atmosphere must be exceedingly rare4 ,the shadows of lunar mountains are either actually black or nearly so4 ,when the moon hides the sun in total eclipse1 no sign can be seen of any refractive effort exerted on the sun's rays4 ,when a star is hidden 7or occulted7 by the moon1 the star vanishes in an instant and reappears with equal suddenness4 ,it is certain from these phenomena that the moon has either no air1 or air exceedingly tenuous4 ,it is equally clear that she has no water1 for if she had we should undoubtedly be able to recognise the occasional formation or dissipation of mist and vapour over parts of the moon's surface4 ,no signs of such phenomena have ever been observed4 ,the moon is certainly at present a waterless globe1 so far at least as her surface is concerned4 ,it has been thought that though there is no water and very little air on the side of the moon turned towards the earth1 there may be both water and air on the farther unseen side4 ,the theory has been long since given up1 but the reasoning on which it depends is worth noting4 ,owing to the strange circumstance that the moon rotates on her axis in the same time in which she revolves round the earth1 she always presents the same face towards the earth1 or very nearly so4 ,if her axis were exactly square to the path in which she circuits the earth1 and if she revolved at a uniform rate1 we should have exactly the same side constantly turned towards us4 ,but as the axis is inclined about #f from uprightness to the path round the earth 7which1 be it remembered1 is not in the same plane as the path round the sun1 but inclined #e #h to it71 the northern and southern parts of the moon are alternately swayed over by about #f into view4 ,this apparent swaying is called a libration1 and the libration just described is called the libration in latitude4 ,again1 as the moon does not travel at a uniform rate round the earth1 but faster than her mean rate when nearer to us1 and slower when farther from us1 she alternately gains and loses in her motion of revolution as compared with her motion of rotation1 by a quantity varying between #e and #g1 to which varying extent the parts east and west of her mean disc are alternately swayed into view4 ,this is called the libration in longitude4 ,thus we see1 beyond the edge of the mean half turned towards us1 a considerable fringe of the other half4 ,if a globe1 as ,,pap,b1 fig4 #ae1 were divided into two halves to represent the farther and nearer halves of the moon1 and held so that that dividing circle were seen as ,,pep in the figure1 then ,ppep,p would represent the part brought into view at different times by the apparent swaying described above2 while ,ppep,p would represent the parts swayed out of view4 ,the regions thus alternately in view and out of view have their greatest breadth1 not at the poles or east and west1 but at m,mm and m,mm1 where the two librations act together4 ,the narrow fringe bordering these regions is that brought into or out of view by changes in the place of the observer on earth1 due to the earth's rotation4 ,it is called the parallactic fringe1 any change in the apparent position of a heavenly body1 or part of one1 on account of the earth's rotation1 being termed parallax4 ,illustration3 ,fig4 #ae4--;,illustrating lunar libration4 ,lastly1 let us return to the consideration of moonlight1 as depending on the condition of the moon's surface1 ,to one who observes the moon as seen on the sky1 her light appears white2 but it must not be supposed that she is a white body4 ,careful estimates of the quantity of light she reflects show that she is more nearly black than white1 though in reality she is neither one nor the other4 ,it has been said1 and truly1 that if the surface of the moon were covered with black velvet she would still appear white2 for even black velvet reflects some light1 and whatever light the moon reflected would show her by contrast with the blackness of the sky1 as a luminous body or white4 ,it follows from the observations made by ,zllner that if the moon's surface were covered with white snow she could give us about #d times as much light as she actually does4 ,if she were covered with white paper she would give more than #d times as much light as she does4 ,if she had a surface of white sandstone her light would be nearly half as great again as it is4 ,she gives rather more light than she would if her surface consisted entirely of weathered grey sandstone1 or of clay marl1 and more than twice as much light as she would give if her surface were of moist earth1 or dark grey syenite4 ,as some parts of her surface are obviously much brighter than others1 we must infer that some parts shine with much more1 and others with much less1 brightness than weathered grey sandstone4 ,probably some parts are much brighter than white sandstone1 and some much darker than dark grey syenite4 ,from the degree in which her lustre changes with her changing aspect1 ,zllner infers that her mountains have an average slope of about fifty-two degrees4 ,,footnotes3 #aj ,it has been thought by some that1 in the beginning1 the moon was always opposite the sun1 thus always ruling the night4 ,milton thus understood the account given in the first book of ,genesis4 ,for he says1-- ,less bright the morn1 ,but opposite in levell'd west was set ,his mirror1 with full face1 borrowing her light ,from him2 for other light she needed none ,in that aspect2 and still that distance keeps ,till night1 then in the east her turn she shines1 ,revolv'd on ,heav'n's great axle4 ,it was only as a consequence of ,adam's transgression that he conceives the angels sought to punish the human race by altering the movements of the celestial bodies-- ,to the blank moon ,her office they prescribe-- ,it is hardly necessary to say1 perhaps1 that this interpretation is not scientifically admissible4 ,illustration ,,ix4 ,,the ,,planet ,,mars4 ,every one who notices the stars at all1--and who that thinks and can see does not8--must have observed during the autumn of #ahgg two bright stars in the southern heavens4 ,one of these shone with a lustre which but for its ruddy hue would have caused the star to be taken for the planet ,jupiter2 the other shone with a somewhat yellowish light1 and was much fainter1 though surpassing most of the fixed stars in brightness4 ,the former was the planet ,mars1 the latter the ringed planet ,saturn4 ,the motions of these two stars with respect to each other and to the neighbouring stars were sufficiently conspicuous to attract attention4 ,during ,october these stars attracted still more attention1 because they drew nearer and nearer together1 to all appearance1 until on ,november #dth they were at their nearest1 when the distance separating them was about one-third the apparent diameter of the moon1 so that in a telescope showing at one view the whole disc of the moon1 ,mars and ,saturn on the night of ,november #dth appeared like a splendid double star1 the primary a fine red orb1 the companion a smaller body1 but attended by a splendid ring system and companion moons4 ,it was strange when we looked at these two stars1 the yellow one apparently much smaller than the brighter1 and the pair seemingly close together1 to consider how thoroughly the reality differed from these appearances4 ,the fainter and seemingly the smaller of the two stars was in reality some four thousand times larger than the brighter1 and had1 among eight orbs attending upon it1 one nearly as large as the ruddy planet which as actually seen so completely outshone ,saturn himself4 ,again1 instead of being near each other1 those two bodies were in reality separated by a distance exceeding some sixteen times that which separated us from the nearer of the two4 ,i propose now to consider some of the more interesting characteristics of these two planets1 presenting specially those features which mark ,saturn as the representative of one family of bodies1 and ,mars as the representative of another and an entirely different family4 ,illustration3 ,fig4 #af4--,the paths of ,mars and ,saturn during the autumn of #ahgg4 ,it will be well to consider ,mars first2 for although1 as will presently be seen1 ,saturn came earlier of the two to the portion of his path where he was most favourably seen1 there was nothing specially remarkable about the approach of ,saturn on that occasion1 whereas ,mars in the year #ahgg made a nearer approach to the earth than he has for thirty-two years past1 or will for some forty-seven years to come4 ,in the first place1 let us note the apparent paths on which the two planets have been and are now travelling4 ,fig4 #af presents that part of the zodiac along which lay the apparent paths of ,mars and ,saturn in #ahgg4 ,the stars marked with ,greek letters belong to the constellation ,aquarius1 or the ,water-,bearer 7his jar is formed by the stars in the upper right-hand corner of the picture71--with a single exception1 the star marked 1 which1 with those close to it not lettered1 belongs to the constellation ,pisces1 or the ,fishes4 ,thus the loops traversed by the two planets in #ahgg both fell in the constellation of the ,water-,bearer2 but1 as will be seen from the symbols on the ecliptic1 these loops lie in the zodiacal sign ,pisces1 which begins at and ends at 4 ,the signs have long since passed away1 in fact1 from the constellations to which they originally belonged4 ,it will be noticed that ,mars described a wide loop ranging to a considerable distance from the ecliptic 7or sun's track74 ,saturn1 on the other hand1 travelled on a narrow and shorter loop lying much nearer to the ecliptic1 his whole track1 except just where he was turning1--his stationary points1--lying nearly parallel to the ecliptic4 ,it may be well to mention the reason of this well-marked difference4 ,mars does not in reality range even quite so widely from the plane of the ecliptic as ,saturn does4 ,nay1 his path is even less inclined to the ecliptic4 7,this may sound like repetition1 but the inclination of a planet's path to the ecliptic is one thing1 the range of the planet north and south of the ecliptic1 in miles1 is another4 ,mercury1 for example1 has of all planets the path most inclined to the ecliptic1 but ,mercury never attains anything like the same distance from the plane of the ecliptic which is attained by the remote planet ,uranus1 whose path is of all others the least inclined to the plane of the ecliptic4 ,in fact1 none of the planets1 except ,venus and ,mars1 have so small a range from the ecliptic in actual distance as ,mercury has47 ,the reason why the range of ,mars from the ecliptic appeared so much greater than that of ,saturn1 in #ahgg1 is similar to the reason why ,mars1 though much smaller than ,saturn1 largely outshone him4 ,mars looked larger because he was nearer1 his loop looked larger because his real path was nearer4 ,for the same reason that a hut close by seems to stand higher above the horizon than a palace at a distance1 or a mountain yet further away1 so the displacement of ,mars from the ecliptic plane appeared greater than that of ,saturn1 though in reality much less4 ,let us consider how the paths of these planets are really situated4 ,i know of no better way of showing this than by drawing the paths of the two families of planets separately4 ,it is in fact utterly impossible to give an accurate yet clear view of the solar system in a single picture2 and the student may take it for granted that every drawing or plate in which this has ever been attempted is from one cause or another misleading4 ,in figs4 #ag and #ah the shape and position of the planetary paths are correctly shown4 ,very little description is necessary1 but it may be mentioned that on each orbit the point nearest to the sun is indicated by the initial letter of the planet1 while the point farthest from the sun is indicated by the same letter accented4 ,the places where each path crosses the plane of the earth's--which is supposed to be the plane of the paper--are marked and 1 the former sign marking where the planet in travelling round in the direction shown by the arrows crosses the plane of the earth's path from below upwards1 while the latter marks the place where the planet in travelling round crosses the plane of the earth's path from above downwards4 ,illustration3 ,fig4 #ag4--,the paths of ,mercury1 ,venus1 the ,earth1 and ,mars1 around the ,sun4 ,fig4 #ag shows the paths of the inner family of planets of which our earth is a member4 ,fig4 #ah shows the outer family of planets1 and inside of it the ring of small planets called asteroids4 ,inside that ring1 again1 we see the paths of the inner family of planets2 but they appear on a very small scale indeed4 ,in fact1 the scales appended to the two figures show that a length which represents #ej1jjj1jjj miles in fig4 #ag1 represents #a1jjj1jjj1jjj miles in fig4 #ah2 or1 in other words1 the scale of fig4 #ah is only one-twentieth of the scale of fig4 #ag4 ,on the scale of fig4 #ag the sun would be fairly represented by an ordinary pin-hole2 on the scale of fig4 #ah the sun would be scarcely visible4 ,the dots round the orbits show the planets' places at intervals of #aj days in fig4 #ag1 and of #ajjj days in fig4 #ah1 starting always from the left side of orbit 7on horizontal line through sun74 ,illustration3 ,fig4 #ah4--,the paths of ,jupiter1 ,saturn1 ,uranus1 and ,neptune1 around the ring of small planets4 ,now looking at fig4 #ah and noting how small is the distance of the path of ,mars from the earth's path1 compared with the distance of ,saturn's path1 we understand why ,saturn1 despite his far superior size1 shines far less brightly in our skies than ,mars does4 ,in fact1 in ,october1 #ahgg1 the ,earth and ,mars were on the parts of their tracks which lay nearest together1 that is1 the parts occupying the lower right-hand corner of fig4 #ag2 and turning to fig4 #ah1 we perceive that the distance separating the two paths here is very small indeed compared with ,saturn's distance4 ,so that1 when we looked at ,mars and ,saturn as they shone in conjoined splendour in our skies1 in #ahgg1 we saw in the bright orb of ,mars the planet whose track lies nearest to us in that direction1 whereas in looking at ,saturn the range of view passed athwart the track of ,mars1 through the ring of asteroids1 and past the orbit of ,jupiter1 before entering the wide and barren region which separates the orbits of the two giant members of the solar system4 ,we study ,mars under much more favourable conditions than either ,jupiter or ,saturn4 ,and yet1 at a first view1 the telescopic aspect of this interesting planet is exceedingly disappointing4 ,galileo1 who quite easily discovered the moons of ,jupiter with his largest telescope1 could barely detect with it the fact that ,mars is not quite round at all times1 but is seen sometimes in the shape of the moon two or three days before or after full4 ,i dare not affirm1 he wrote on ,december #cj1 #afaj1 to his friend ,castelli1 that ,i can observe the phases of ,mars2 yet1 unless ,i mistake1 ,i think ,i already perceive that he is not perfectly round4 ,but even in a large telescope one can see very little except under very favourable conditions4 ,it has only been by long and careful study1 and piecing together the information obtained at various times1 that astronomers have obtained a knowledge of the facts which appear in our text-books of astronomy4 ,the possessor of a telescope who should expect1 on turning the instrument towards ,mars1 to perceive what he has read in descriptions of the planet1 would be considerably disappointed4 ,first noticed among the features of the planet were two white spots of light occupying the northern and southern parts of his disc4 ,these are now known to be regions of snow and ice1 like those which surround the poles of our own earth4 ,but how different the reality must be from what we seem to see in the telescope6 ,these two tiny white specks represent hundreds of thousands of square miles covered over with great masses of snow and ice1 which doubtless are moved by disturbing forces similar to those which make our arctic regions for the most part impassable even for the most daring of our seamen4 ,the snow-caps of ,mars change in size as the planet circuits round the sun1 completing his year of seasons 7which lasts #fhg of our days74 ,they are largest in the winter of ,mars1 smallest in the ,martian summer2 so that1 as it is winter for one hemisphere when it is summer for the other1 one of the snow-caps is larger than the other at the winter and summer seasons4 ,in the same way1 our arctic snows extend more widely during our winter1 while the antarctic snows then retreat2 whereas1 during our summer1 when it is winter in the southern hemisphere1 the antarctic snows advance and our arctic snows retreat4 ,but we have still to learn why these white spots are known to be masses of snow4 ,they might well from analogy be considered to be snows1 since they behave like the snows of our polar regions4 ,yet that would be very different from proving them to be snow masses4 ,i shall now show how this has been done1 and afterwards describe the lands and seas of the planet1 and give a short account of the recent interesting discovery of two moons attending on the planet which ,tennyson had called the moonless ,mars4 99 99 99 99 99 ,even before the poles of ,mars had been discovered1 observers had perceived that the planet has marks upon its surface4 ,cassini1 in #afff1 at ,paris1 found by observing these spots that the planet turns on its axis once in about twenty-four hours forty minutes4 ,in the same year ,dr4 ,hooke observed ,mars4 ,he was in doubt whether the planet turned once round or twice round in about twenty-four hours2 for with his imperfect telescope two opposite faces of the planet seemed so much alike that he was doubtful whether they really were two different faces or the same4 ,fortunately he published two pictures of the planet1 taken on the same night in ,march1 #afff1 and we have been able to keep such good count of ,mars's turning on his axis1 that we know exactly how many times he has turned since that distant time4 ,however1 at present1 we need not further consider the turning motion of ,mars1 but rather what the telescope has shown us about him4 ,only1 let it be remembered that he has a day of about twenty-four hours thirty-seven minutes1 and is in this respect much like our earth4 ,maraldi1 ,cassini's nephew1 early in the last century observed several spots on ,mars1 and1 in particular1 one somewhat triangular dark spot1 which was one of ,hooke's markings1 but more clearly seen by ,maraldi4 ,about this time it was seen that the darker markings have a somewhat greenish colour2 and towards the end of last century1 or1 more exactly1 about a hundred years ago1 the idea was maintained by ,sir ,w4 ,herschel that the dark-greenish markings are seas1 while the lighter parts of ,mars1 to which the planet owes its somewhat ruddy colour1 are lands4 ,sir ,w4 ,herschel also was the first to show that ,mars1 like our earth1 has seasons4 ,it had been supposed by ,cassini1 ,maraldi1 and others1 that the axis of ,mars is upright to the level of the path in which he travels4 ,of course1 if this were so1 the light of the sun would always fall on the planet in the same way2 for the sun is in that level4 ,but the axis1 like that of our own earth1 is bowed considerably from uprightness2 so that at one part of his year the sun's rays fall more fully on his northern regions1 and his southern regions are correspondingly turned away from the sun2 then it is summer in his northern regions1 winter in his southern4 ,at the opposite season the reverse holds1 and then winter prevails over his northern and summer over his southern regions4 ,midway between these two seasons1 the sun's rays are equably distributed over both hemispheres of ,mars1 and then the days and nights are equal1 and it is spring in that hemisphere which is passing from winter to summer1 and autumn in the other hemisphere which is passing from summer to winter4 ,all these changes are precisely like those which take place in the case of our own earth4 ,only1 the year of ,mars1 and therefore his seasons1 are longer4 ,he takes #fhg days in travelling round the sun1 giving nearly #agb days1 or more than five and a half of our months1 for each season4 ,illustration3 ,fig4 #ai4 ,fig4 #bj4 ,fig4 #ba4 ,figs4 #ai-ba4--,three ,views of ,mars4 ,figs4 #ai1 #bj1 and #ba are three views of ,mars1 drawn by ,mr4 ,nathaniel ,green1 an excellent observer1 who has paid special attention to this planet4 ,fig4 #ai shows a faintly-marked sea running north and south 7the upper part of the picture being the south1 because that is the way in which the telescope used by astronomers inverts objects47 ,this is one of the markings which deceived ,hooke4 ,this picture was drawn on ,may #cj1 #ahgc1 at half-past seven in the evening4 ,the second picture was drawn two days earlier1 at eight in the evening2 but it shows the planet as it would have looked on ,may #cj at about a quarter past nine in the evening1 by which time the sea running north and south had been carried over to the right and lost to view4 ,but another north and south sea had come into view on the right4 ,the third picture shows a view taken three hours later1 or at eleven on ,may #bh1 when the planet appeared precisely as he would have appeared at a quarter past eleven in the early morning of ,may #ca1 had weather then permitted ,mr4 ,green to continue his observations4 ,you see in it the great north and south sea which ,maraldi had noticed1 the other of those two which had deceived ,hooke4 ,it will be seen from these drawings1 which1 be it remembered1 were taken at the telescope1 that it is possible from a great number of such drawings to make a chart of ,mars1 showing its lands and seas not as they are seen in the telescope1 but as they might be laid down by inhabitants of ,mars in a map or planisphere4 ,this has been done1 with gradually increasing accuracy1--first by ,sir ,w4 ,herschel1 next by ,beer and ,mdler1 then by ,phillips1 and lastly by myself4 7,in claiming for my own chart greater accuracy1 ,i am simply asserting the superior completeness of the list of telescopic drawings which ,i was able to consult47 ,the result is shown in the accompanying chart 7fig4 #bb71 which presents the whole surface of ,mars divided into lands and seas and polar snows1 with the names attached of various observers who have at sundry times contributed to our knowledge of the planet's features4 ,but now it will be asked by the thoughtful reader1 how can any one possibly be sure that the regions called continents and seas do really consist of land and water8 ,at any rate1 the doubt might well be entertained respecting the water4 ,for land is a wide term1 including all kinds of rock surface1 sand1 earthy soil1 and so forth2 but it may seem to require proof that the substance we call water really exists out yonder in space1 either in the form of snow and ice at the ,martian poles1 or as flowing water in the ,martian seas1 or in the vaporous form in the planet's air4 ,illustration3 ,fig4 #bb4--;,chart of ,mars1 from #bg drawings by ,mr4 ,dawes4 ,very strange1 then1 at first must the statement seem1 that we are as sure of the existence of water in all these forms on ,mars as if we had sent some messenger to the planet who had brought back for study by our chemists a block of ,martian ice1 a vessel full of ,martian water1 and a flask of ,martian air saturated with aqueous vapour4 ,indeed1 ,i do not know of any discovery effected by man which more strikingly displays the power of human ingenuity in mastering difficulties which1 at a first view1 seem altogether insuperable4 ,when we know that a mass of ice as large as ,great ,britain would appear at the distance of ,mars a mere bright point2 that a sea as large as the ,mediterranean would appear like a faint1 greenish-blue1 streak2 and that cloud masses such as would cover the whole of ,europe would only present the appearance of a whitish glare1 how hopeless seems the task of attempting to determine what is the real chemical constitution of objects thus seen6 ,it might well be thought that no possible explanation of the method used by astronomers could serve to establish its validity4 ,yet nothing can be simpler than the principle of the method1 or more satisfactory than its application in this special case4 ,first1 let the reader rid his mind of the difficulty arising from the enormous distance of the celestial bodies4 ,to do this let him note that there are some things which a body close by can tell us no more certainly than a remote body4 ,for instance1 we are just as certain that ,mars is a body capable of reflecting sunlight as we are that a cricket-ball is4 ,we know as certainly1 too1 that the quality of ,mars is such that more of the red of the sun's light is sent to us than of the other colours4 ,for we perceive that ,mars is a ruddy planet4 ,since distance in no way interferes with our perception of these general facts1 and others like them1 we need not necessarily find in mere distance any difficulty in the way of recognising some other facts4 ,all that we require to be shown before admitting the validity of the evidence is1 that it is of such a kind that distance does not affect its quality1 however much distance may and must affect the quantity of evidence4 ,now there is a means of taking the light which comes from a body shining either with its own or with reflected light1 and analyzing it into its component colours4 ,the spectroscope is the instrument by which this is accomplished4 ,i do not propose to describe here the nature of this instrument1 or the details of the various methods in which it is employed4 ,i note only that it separates the rays of different colour coming from an object1 and lays them side by side for us1--the red rays by themselves1 the orange rays by themselves1 and so with the yellow1 green1 blue1 indigo1 and violet4 ,and not only are the rays of these colours set by themselves1 but the red rays are sorted in order1 from the deepest brown-red#aa to a tint of red 7the lightest7 which must almost be called orange2 the orange in order1 from orange which must almost be called red to a tint 7the lightest orange7 which must almost be called yellow2 the yellow1 from an almost orange yellow to a yellow just beginning to be tinged with green2 the green1 from an almost yellow green 7the lightest7 to a green which may almost be called blue 7the darkest72 the blue1 from this tint to the beginning of the indigo2 the indigo1 from this tint to the first rays of the violet2 and lastly the violet1 through all the tints of this beautiful colour to a blackish-brown violet1 where the visible spectrum ends4 ,all these tints are sorted in order by the spectroscope1 just as a skilful colourist might range in due sequence a myriad tints of colour4 ,but this is only true of really white light1 such light as comes from a glowing mass of metal burning at a white heat4 ,in other cases 7even when the light may seem white to the eye7 some of the tints are found1 when the spectroscope spreads out the colours for us1 to be missing4 ,and we know that this may be caused in two ways4 ,either the source of light never gave out those missing tints2 or1 the source of light gave them out1 but some absorbing medium stopped them on their way before they reached the spectroscope with which we examine them4 ,there may be cases where we cannot tell very easily which of these is the true cause4 ,but sometimes we can1 as the instances ,i have now to deal with will show you4 ,the sun's own light shows under this method of spectroscopic analysis millions of tints1 in fact ,i might say millions of red tints1 and so forth1 right through the spectral list of colours4 ,but also many thousands of tints are wanting4 ,imagine a rainbow-coloured ribbon1 the colours ranged along its length1 so that the ribbon is black at both ends1 and that from the black of one end the colour merges into very deep red1 and thence by insensible gradations through orange1 yellow1 green1 blue1 indigo1 and violet1 into the black of the other end4 ,then suppose that tens of thousands of the fine threads which run athwart the ribbon--i4e41 the short cross threads--are drawn out4 ,then the ribbon1 laid on a dark background showing through the spaces where the threads were drawn out1 would represent the solar spectrum4 ,we know then that the light of the sun's glowing mass either wants particular tints originally1 or shines through vapours which prevent the free passage of rays of those colours4 ,both causes might be at work1 not one only4 ,at present we are not concerned with this particular point2 but ,i only mention that1 in reality1 no tints are actually wanting1 though some are very much enfeebled4 ,the sun's light falling on any opaque object is reflected4 ,if the object is white1 the light gives exactly the same spectrum1 only fainter4 ,thus1 ,i take a piece of white paper on which the sun's rays are falling1 and examine its light with one of ,browning's spectroscopes4 ,i get the ordinary solar spectrum4 ,the cold white paper gives me in fact a spectrum which speaks of a heat so intense that the most stubborn metals are not merely melted but vaporized in it4 ,but this heat resides in the sun1 not in the paper4 ,now1 speaking generally1 ,mars also sends us sunlight1 so that when we spread out with the spectroscope the rays coming from this planet1 we get the solar spectrum1 only of course very much enfeebled4 ,but close examination shows that other tints besides those missing from the solar spectrum are missing from the spectrum of ,mars4 ,he reflects to us the sunlight1 almost as it reaches him1 but he abstracts from it a few tints on his own account4 ,when we inquire what these tints are1 we find that they are tints which are sometimes wanting even from direct sunlight4 ,when the sun sinks very low and looks like a great red ball through the moisture-laden air1 his spectrum is not the same exactly as that of the sun shining high in the mid heaven4 ,it shows other gaps than those corresponding to the ordinary myriads of missing tints4 ,its red colour shows indeed that some thing has happened to the sunlight2 but1 oddly enough 7at first sight at least71 the gaps are chiefly in the red part of the spectrum1 just what one would expect if the sun's light showed a want instead of an excess of ruddy light4 ,the fact is1 however1 that the violet1 indigo1 and blue are weakened altogether1 not by the mere abstraction of tints here and there4 ,the red suffers under a few abstractions of tint1 but remains on the whole little weakened4 ,now the same gaps which at such times appear in the spectrum of the sun are found 7generally1 if not always7 in the spectrum of the planet ,mars1 even when he is shining high in the heavens1 so that his light is not at the time absorbed by the denser portions of our air4 ,in fact the gaps have been seen in the spectrum of ,mars when the planet has been shining higher in the heavens than the moon1 whose spectrum was found on trial 7at the time7 not to show the same gaps1--as of course it must have done1 and even more markedly1 if the missing tints had been abstracted by our own air4 ,no doubt can remain1 then1 that the sun's light1 which reaches us after falling on ,mars1 has suffered at ,mars the same absorption which our own air produces on the rays of the sun when he is low down4 ,but we know what it is in our air which causes this absorption4 ,it is the aqueous vapour4 ,we know this from several independent series of researches4 ,it was proved first by an ,american physicist1 ,professor ,cooke of ,harvard1 who found that these lines in the red are always darker when the air is moister4 ,then by ,janssen1 who observed the spectrum of great bonfires lit at a distance of many miles1 on the ,swiss mountains1 finding these same lines in the spectrum of the fire-light when the air was heavily laden with moisture4 ,wherefore we know that the air of ,mars must also contain the same substance--the vapour of water--which1 in our own air1 produces these dark lines4 ,we can1 indeed1 understand that the ruddy colour of ,mars is in part due to this moisture1 which1 precisely as in our own air it makes the sun and moon look red1 would1 in the air of a planet1 make the planet itself look red4 ,but how much follows from the discovery that there is moisture in the air of ,mars6 ,this moisture can only come from water in sufficient quantities4 ,there must1 therefore1 be seas on ,mars4 ,we should be sure of this from the spectroscopic evidence1 even without the evidence given by the telescope4 ,we cannot doubt for a moment1 however1 knowing as we do how the telescope shows greenish markings on ,mars1 that these really are the seas and oceans of the planet4 ,and again1 the white spots at the poles of ,mars can no longer be regarded doubtfully4 ,if we could not see them1 but knew only1 from the spectroscopic evidence1 that ,mars must have large seas1 we should be sure that his polar regions must be covered with everlasting ice and snow1 varying with the seasons1 but always surrounding1 in enormous masses1 the poles themselves4 ,seeing that the telescope presents spots to our view which1 long before the spectroscopic evidence had been obtained or hoped for1 had been regarded as analogues of our polar snows1 we can now entertain no manner of doubt that they really are so4 ,but again1 recognising the presence of enormous masses of snow and ice around the poles of ,mars1 and knowing that not only are there wide oceans1 seas1 and lakes1 but that there is an atmosphere capable of carrying mist and cloud1 how many circumstances1 corresponding to those which we associate with the wants of living creatures1 present themselves to our consideration6 ,it remains that ,i should now consider some of these points4 99 99 99 99 99 ,we have seen that ,mars has water in all its forms1 solid1 liquid1 and vaporous4 ,we perceive also that his polar regions do not extend very much farther towards his equator than do the polar ice and snows of our own earth4 7,of course the former do not extend so far in actual distance2 ,i refer to their extent compared with the globe they belong to47 ,it would appear then1 at a first view1 that the climate of ,mars cannot be very unlike that of our earth4 ,yet this is scarcely possible4 ,for ,mars is so much farther than we are from the sun that he receives less than half as much light and heat from that luminary4 ,and it is not easy to conceive that the deficiency can be compensated by any effects due to the nature of the ,martian air4 ,it is more likely by far that this air is much rarer than that it is much denser than ours4 ,for not only can it be shown that with the same relative quantity of air a smaller planet would have a smaller quantity above each square mile of its surface than would a larger one1#ab but the gravity at the surface of the smaller planet being less1 the air there is much less compressed by its own weight 7having in fact much less weight71 and is therefore rarer4 ,thus the probability is that the air of ,mars is like that at 7or even above7 the summits of our highest mountains1 where we know that an intense cold prevails4 ,it is not that the sun's rays do not fall there with as much heating power as at the sea-level1 for experiment shows that they fall with even greater power4 ,but there is less air to be warmed and to retain the heat4 ,the difference may be compared in fact to that between a well-watered country near the sea and an arid desert4 ,the sun's rays fall as fiercely on one as on the other1 but because there is no moisture in the desert to receive 7after the fashion characteristic of water7 the solar heat and retain it1 the heat passes away so soon as the sun has set1 and intense cold prevails1 while over the well-watered region the temperature is much more uniform1 and warm nights prevail4 ,so is it at the summits of lofty mountains4 ,the sun's rays are poured on them as hotly as elsewhere1 but there is little air to retain the moisture1 so that the heat passes away almost as quickly as it is received1 and during the night as much fresh snow is formed as had been melted during the day4 ,and so it would certainly be with ,mars1 if1 other things being the same1 the air were as rare as it is at the summits of our loftiest mountains4 ,if1 as seems probable1 the air is still rarer than this1 the cold would be still more intense4 ,it would seem1 then1 that either some important difference exists1 by which the ,martian air is enabled to retain the sun's heat even more effectively than our air does 7for the climate as indicated by the limits of the polar snows seems the same1 though the distance from the sun is greater72 or else there is some mistake in the supposition that the same general state of things prevails on ,mars as on our own earth4 ,i confess that though ,professor ,tyndall has shown clearly how the atmosphere of a more distant planet might make up for the deficient supply of solar heat1 by more effectively retaining the heat1 ,i know of nothing in either the telescopic or the spectroscopic evidence respecting any of the planets which tends to show1 or even renders it likely1 that any such arrangement exists1--excepting always the peculiarity in ,mars's case which we are now endeavouring to explain4 ,insomuch that should any other explanation of the difficulty be suggested1 and appear to have weight in its favour1 ,i apprehend that the mere possibility of an atmospheric arrangement1 such as has been suggested1 should not prevent our admitting this other explanation4 ,i am inclined to think that there is such an explanation4 ,it seems to me that there are good reasons for regarding ,mars as a planet which has passed to a much later stage of planetary life than that through which our earth is now passing1 and that in this circumstance some of the peculiarities of his appearance find their explanation4 ,as a planet outside the earth1 ,mars must probably be regarded as one formed somewhat before the earth4 ,as a much smaller planet1 he would be not only less heated when first found 7whatever theory of planetary formation we adopt71 but would also have parted much more rapidly 7relatively7 with his heat1 according to the same law which makes a small mass of metal cool more quickly than a large one4 ,if he has a rarer atmosphere he would be a colder planet on that account also4 ,being also remoter from the sun1 he receives less heat from that orb1 and we thus have a fourth reason for regarding ,mars as a much colder planet than our earth1 both as to inherent heat and as to heat received from without4 ,it seems to me that we may in this consideration find the real meaning of the comparatively limited extension of the ,martian snows4 ,it has been well pointed out by ,professor ,tyndall that for the formation of great glacial masses1 not great cold only1 but great heat also is required4 ,the snows which fall on mountain slopes1 to be compacted into ice and afterwards to form great glaciers1 were raised into the air by the sun's heat4 ,every ice particle represents the action of that heat upon the particles of water at the surface of ocean1 sea1 or lake1 or of wet soil4 ,if the sun's heat suddenly died out1 there would prevail an intense cold1 and the snows and ice now existing would assuredly remain4 ,the waters also of the earth would congeal4 ,but no new snows would fall4 ,the congealed seas viewed from some remote planet would appear unchanged4 ,for they would not be covered with snow and broken ice1 nor therefore white2 but would consist of pure ice throughout1 retaining the partial transparency and greenish colour of deep-sea water4 ,no winds would disturb the surface of the frozen seas1 for winds have their origin in heat1 and with the death of the solar heat the winds would utterly die out also4 ,if we are to choose between these two explanations1--one that the snows and ice have not the great range we should expect1 because the temperature is somehow raised despite ,mars's greater distance to the same temperature which we experience1 and the other that it is not heat but cold which diminishes the quantity of ,martian snow1 ,i conceive that there is every reason the case admits of for accepting the latter instead of the former explanation4 ,as extreme cold would certainly prevent glacial masses from being very large and deep1 simply because the stores whence the ice was gathered would be less1 the snow caps of a very cold planet would vary as readily with varying seasons as those of a planet like our earth4 ,for though less heat would be poured upon them with the returning summer1 less heat would be required to melt away their outskirts4 ,i think we may fairly regard ,mars as in all probability a somewhat old and decrepit planet4 ,he is not absolutely dead1 like our own moon1 where we see neither seas nor clouds1 neither snow nor ice1 no effects1 in fine1 of either heat or cold4 ,but ,i think he has passed far on the road towards planetary death1--that is1 towards that stage of a planet's existence when at least the higher forms of life can no longer exist upon the planet's surface4 ,there is one peculiarity of the planet's appearance which seems strikingly to accord with this view that ,mars holds a position intermediate between that of our earth and the moon1--as indeed we might fairly expect from his intermediate proportions4 ,the seas of our earth cover nearly three-quarters of her entire globe4 ,the moon has no visible water on her surface4 ,if we examine the chart of ,mars at page #afg1 we see that the seas and oceans of the planet are much smaller 7relatively as well as actually7 than are the seas of our own earth4 ,i have carefully estimated their relative extent in the following simple but effective way4 ,i drew a chart such as the above-mentioned1 but on a projection of my own invention1 in which equal surfaces on a globe are represented by equal surfaces on the planisphere4 ,then ,i cut out with a pair of scissors the parts representing land and the parts representing water 7leaving the polar parts as doubtful71 and carefully weighed these in a delicate balance4 ,i found that they were almost exactly equal3 whatever preponderance there was seemed to be in favour of the land4 ,thus1 if we assume that1 when in the same stage of planetary existence1 ,mars had as great a relative extent of water surface as our earth1 or that about #gb_/ajj of the surface of ,mars were originally water1 we should have to admit that the water had so far been withdrawn into the planet's interior as to diminish the water-surface by #bb_/ajj 7for there are now barely #ej_/ajj74 ,at a very fair assumption as to the slopes of the ,martian sea-bottoms1 it would follow that more than half the ,martian water originally existing above the surface had been withdrawn into the interior1 as the planet's mass gradually cooled4 ,i am aware the assumption above mentioned is in itself somewhat daring1 and is not supported by direct evidence4 ,but1 since we have very strong reasons for considering that the moon once had seas1 which have been withdrawn in the way suggested1 and since ,mars unquestionably holds a position midway between the earth and moon as to size and presumably as to age1#ac it seems not unreasonable to find in the character of her seas1--less extended relatively than the earth's1 but1 unlike the moon's1 still existing1--the evidence that she has gone partially through the process through which the moon has long since passed completely4 ,i think it very likely that the recent discovery of two ,martian satellites will lead many to look with more disfavour than ever on the idea that ,mars may not at present be the abode of life4 ,for moons seem so manifestly convenient additions to a planet's surroundings1 as light-givers1 time-measurers1 and tide-rulers1 that many will regard the mere fact that these conveniences exist as proof positive that they are at this present time subserving the purposes which they are capable of subserving4 ,i would point out1 however1 that our own moon must have existed for ages before any living creatures1 far less any reasoning beings1 could profit by her light1 or by the regularity of her motions1 or by her action in swaying the waters of ocean4 ,and doubtless she will continue to exist for ages after all life shall have passed away from the earth4 ,again1 there can be no question that our earth would present a most attractive scene if she were viewed from the moon1 and would be a most useful ornament of the lunar skies4 ,yet we have every reason to believe that there is not a living creature on the moon at present to profit by her light4 ,the case may well be the same 7apart from the actual evidence that it is the same7 with ,mars4 ,his satellites may long since have served most useful purposes to his inhabitants2 but it by no means follows that because if there were inhabitants on ,mars now the same purposes would still be subserved1 therefore there are inhabitants there4 ,let us1 however1 without considering the question whether the satellites of ,mars serve such special purposes for creatures living on the planet1 consider briefly the history of their discovery1 their nature1 and the laws of their motion around the planet4 ,astronomers had long examined the neighbourhood of ,mars with very powerful telescopes1 in the hope of discovering ,martian moons4 ,but the hope had so thoroughly been abandoned for many years that the planet had come to be known as moonless ,mars4 ,the construction1 however1 of the fine telescope which has been mounted at ,washington1 with an object-glass twenty-six inches in diameter1 caused at least ,american astronomers to hope that after all a ,martian moon or two might be discovered4 ,taking advantage of the exceptionally favourable opportunity presented during the planet's close approach to our earth in the autumn of #ahgg1 ,prof4 ,asaph ,hall1 of the ,washington ,observatory1 paid special attention to the search for ,martian moons4 ,at last1 on ,august #af1 #ahgg1 he detected close by the planet a faint point of light1 which he was unable to examine further at the time 7to see if it behaved as a satellite1 or as one of the fixed stars74 ,but on the #ahth he saw it again1 and determined its nature4 ,he also saw another still fainter point of light closer to the planet2 and subsequent observations shewed that this object also was a satellite4 ,during the next few weeks both the moons were observed as closely as possible1 in fact1 whenever weather permitted1 and the result is that we now know the true nature of their paths4 ,in fig4 #bc these paths are shown as they appeared in #ahgg4 ,of course the paths themselves are not seen2 but if the satellites left behind them a fine train or wake of light1 the shape of this train would be as shown in fig4 #bc4 ,the satellites themselves could not be shown at all in a picture on so small a scale--the diameter of either would certainly be less than the cross-breadth of the fine elliptical line representing its track4 ,the size of the planet is correctly indicated1 and the true pose of the planet in #ahgg is shown in the figure1 his southern pole being somewhat bowed towards the earth4 ,this is the uppermost pole2 for the figure represents the planet and his satellites' orbits as they would appear in an astronomical telescope1 which inverts objects4 ,illustration3 ,fig4 #bc4--,mars and the paths of the ,martian satellites as at present situated4 ,the outer satellite is probably not more than ten miles or so in diameter1 the inner one1 perhaps1 the same2 but neither can be measured4 ,in the most powerful telescopes they appear as mere points of light4 ,nor is it easy to determine1 from their lustre1 or rather from their faintness1 their true dimensions2 for we cannot compare them directly in this respect with objects of known size1 because their visibility is partly affected by the proximity of the planet1 whose overpowering light dims their feeble rays4 ,this remark applies with special force to the inner satellite4 ,the distance of the outer satellite from ,mars's centre is about #ad1cjj miles1 from ,mars's surface about #ab1jjj miles4 ,the inner travels at a distance of about #e1gej miles from the centre1 and about #c1dej miles from the surface of ,mars4 ,the motions of the satellites as seen from ,mars must be very different from those of our own moon4 ,thus1 our moon moves so slowly among the stars that she requires nearly an hour to traverse a distance equal to her own apparent diameter4 ,the outer moon of ,mars traverses a similar distance--that is1 not her own apparent diameter1 but an arc on the stellar heavens equal to our moon's apparent diameter--in about two and a half minutes1 while the inner moon moves so rapidly as to traverse the same distance in about forty seconds4 ,to both moons1 therefore1 but to the inner in particular1 ,job's description of our moon as walking in brightness would seem singularly applicable1 so far at least as the rapidity of their motions is concerned4 ,their brightness1 however1 cannot be comparable to our moon's4 ,for notwithstanding their much greater proximity1 it is easily shown that they must present much smaller discs1 and being illuminated by a more distant sun1 their discs cannot shine so brightly as our moon's4 ,that is1 not only are the discs smaller1 but their intrinsic brightness is less4 ,assuming the outer moon to be ten miles1 the inner fifteen miles in diameter1 it is easily shown that the two together1 if full at the same time1 can hardly give one-twelfth as much light to ,martians as our moon gives to us4 ,yet there can be no doubt that the ,martian moons must be 7or have been7 most useful additions to the ,martian skies4 ,they do not give a useful measure of time intermediate in length between the day and the year1 as our moon does2 for the outer travels round the planet in about thirty and a quarter hours1 the inner in about seven and a half hours4 ,nor can they exert an influence upon the ,martian seas corresponding to that exerted by our own moon in generating the lunar tidal wave4 ,but their motions must serve usefully to indicate the progress of time1 both by night and by day1 for they must be visible by day unless very close to the sun4 ,they must be even more useful than our moon in indicating the longitude of ships at sea1 seeing that the accuracy with which a moon indicates longitude is directly proportional to her velocity of motion among the stars4 ,i have said that there does not seem to be any valid reason for considering that now is the accepted time with these moons2 their services may have been of immense value in long past ages1 and now be valueless for want of any creatures to be benefited by them4 ,but those who not only believe that no object in nature was made without some special purpose1 but that we are able to assign to each object its original purpose1 should be well satisfied if they find reason for believing that1 during millions of years long1 long ago1 the moons lately discovered by our astronomers were measuring time for past races of ,martians1 swaying tides in wider seas than those which now lave the shores of ,martian continents1 and enabling ,martian travellers to guide their course over the trackless ocean and arid desert with far greater safety than can our voyagers by sea and land despite all the advances of modern science4 ,,footnotes3 #aa ,brown is not the right word for the tint of red where the visible spectrum begins4 ,i know1 however1 of no word properly expressing the colour4 #ab ,suppose there are two planets ,a and ,b of equal density1 of which ,a has a diameter twice as great as that of ,b4 ,then the volume of ,a is eight times greater than ,b's volume4 ,so that if the volume of its atmosphere exceed the volume of ,b's air in the same degree1 the planet ,a has eight times as much air as the planet ,b4 ,but the surface of ,a is only four times as great as the surface of ,b2 so that if ,a had only four times as much air as ,b1 there would be the same quantity of air above each square mile of ,a's surface as above each of ,b's surface4 ,since then ,a has eight times--not merely four times--as much air as ,b1 it follows that ,a has twice as much air over each square mile of surface as ,b has4 ,and similarly in all such cases1 the general law being that the larger planet has more air over each square mile of surface in the same degree that its diameter exceeds that of the other4 #ac ,by age here ,i do not mean absolute age1 but relative age4 ,i speak of ,mars and the ,moon as older than the earth in the same sense that ,i should speak of a fly in autumn as older than a five-year-old raven4 ,illustration ,x4 ,,the ,,planet ,,jupiter4 ,two or three years ago ,i had occasion to consider in the ,day of ,rest the giant planet ,jupiter1 the largest and most massive of all the bodies circling around the sun4 ,i then presented a new theory respecting ,jupiter's condition1 to which ,i had been led in #ahfi1 when ,i was visiting other worlds than ours4 ,since then1 in fact within the last few months1 observations have been made which place the new theory on a somewhat firm basis2 and ,i propose now briefly to reconsider the subject in the light of these latest observations4 ,in the first place ,i would call the reader's attention to the way in which modern science has altered our ideas respecting time as well as space1 though the change has only been noticed specially as it affects space4 ,in former ages men regarded the region of space over which they in some sense had rule as very extensive indeed4 ,this earth was the most important body in the universe1 all others being not only made for the service of the earth1 but being in all respects1 in size1 in range1 and so forth1 altogether subordinate to it4 ,step by step men passed from this to an entirely different conception of our earth's position in space4 ,shown first to be a globe within the domain of the heavenly bodies1 then to be a globe subordinate to the sun1 then to be a member of one family among thousands each with its ruling sun1 then to belong to a galaxy of suns which is but one among myriads of millions of such galaxies1 and lastly shown to the eye of reason1 though not to direct observation1 as belonging to a galaxy of galaxies itself but one among millions of the same order1 which in turn belong to higher and higher orders endlessly1 the earth has come to be regarded1 despite its importance to ourselves1 as but a point in space4 ,the minutest particle by which a mathematician might attempt to picture the conception of a mathematical point1 comparing that particle with any near object however large1 a house1 a mountain1 the earth itself1 would be but the grossest representation of a point1 by comparison with the massive earth1 when she is considered with reference to the universe of the fixed stars or rather to that portion of the universe1 itself but a point in space1 over which the survey of the astronomer extends4 ,all this has been admitted4 ,men have fully learned to recognise1 though they are quite unable to conceive1 the utter minuteness1 one may say the evanescence1 of their abode in space4 ,but along with the extension of our ideas respecting space1 a corresponding extension has been made1 or should have been made1 in our conceptions respecting time4 ,we have learned to recognise the time during which our earth has been and will be a fit abode for living creatures as exceedingly short compared with the time during which she was being fashioned into fitness for that purpose1 and with the ons of ons to follow1 after life has disappeared from her surface4 ,this1 however1 is but one step towards the eternities to which modern science points4 ,the earth is but one of many bodies of a system2 and though it has been the custom to regard the birth of that system as if it had been effected1 if one may so speak1 in a single continuous effort 7lasting millions of millions of years1 mayhap1 but bringing all the planets and their central sun simultaneously into fitness for their purpose71 there is no reason whatever for supposing this to have been really the case1 while there are many reasons for regarding it as utterly unlikely4 ,it seems as though men could not divest themselves of the idea that our earth's history is the history of the solar system and of the universe4 ,precisely as children can hardly be brought to understand1 for a long time1 what history really means1 how generation after generation of their own race has passed away1 and how their own race has succeeded countless others1 so science1 still young1 seems scarcely to appreciate the real meaning of its own discoveries4 ,it follows directly from these that world after world like our earth1 in this our own system or among the millions peopling space1 has had its day1 and that the systems themselves1 on which such worlds attend1 are but the existent representatives of their order1 and succeed countless other systems which have long since served their purpose4 ,yet1 strangely enough1 students of science continue for the most part to speak of other worlds1 and other suns1 and other systems1 as though this present era1 this bank and shoal of time1 were the sole period to which to refer in considering the condition of those worlds and suns and systems4 ,it does not seem to occur to them that1--not possibly or probably1 but most certainly1--myriads among the celestial bodies must be passing through stages preceding those which are compatible with the existence or support of life1 while myriads of others must long since have passed that stage4 ,and thus ideas appear strange and fanciful to them which1 rightly apprehended1 are alone in strict accordance with analogy4 ,to consider ,jupiter or ,saturn as in the extreme youth of planetary existence1 still glowing with such heat as pervaded the whole frame of our earth before she became a habitable world1 still enveloped in cloud masses containing within them the very oceans of those future worlds1 all this is regarded as fanciful and sensational4 ,yet those who so regard such theories do not hesitate to admit that every planet must once in its life pass through the fiery stage of planetary existence1 nor are they prepared to show any reason why the stage must be regarded as past in the case of every planet or even of most of the planets4 ,seeing that1 on the other hand1 there are abundant reasons for believing that planets differ very widely as regards the duration of the various stages of their life1 and that our earth is by no means one of the longest lived1 we may very fairly expect to find among the planets some which are very much younger than our earth1--not younger1 it will be understood1 in years1 but younger in the sense of being less advanced in development4 ,when we further find that all the evidence accords with this view1 we may regard it as the one to which true science points4 ,all that we know about the processes through which our earth has passed suggests the probability1 ,i will even say the certainty1 that planets so much larger than she is as are ,jupiter and ,saturn must require much longer periods for every one of those processes4 ,a vast mass like ,jupiter would not cool down from the temperature which our earth possessed when her surface was molten to that which she at present possesses in the same time as the earth1 but in a period many times longer4 ,supposing ,bischoff to be right in assigning #cdj1jjj1jjj years to that era of our earth's past1 ,i have calculated that ,jupiter would require about seven times and ,saturn nearly five times as long1 or about #b1chj1jjj1jjj and #a1ejj1jjj1jjj years respectively1 and by these respective periods would they be behind the earth as respects this stage of development4 ,suppose1 however1 on the other hand1 that ,bischoff has greatly overrated the length of that era--and ,i must confess that experiments on the cooling of small masses of rock1 such as he dealt with1 seem to afford very unsatisfactory evidence respecting the cooling of a great globe like our earth4 ,say that instead of #cdj1jjj1jjj years we must assign but a tenth part of that time to the era in question4 ,even then we find for the corresponding era of ,jupiter's existence about #bch1jjj1jjj years1 and for that of ,saturn's #aej1jjj1jjj years1 or in one case more than #bjj1jjj1jjj years longer1 in the other more than #aaj1jjj1jjj years longer than in our earth's case4 ,this relates to but one era only of our earth's past4 ,that era was preceded by others which are usually considered to have lasted much longer4 ,the earth1 according to the nebular theory of ,laplace1 was once a mighty ring surrounding the sun1 and had to contract into globe form1 a process requiring many millions of years4 ,when first formed into a globe she was vaporous1 and had to contract--forming the moon in so doing--until she became a mass1 first of liquid1 then of plastic half solid matter1 glowing with fire and covered with tracts of fluent heat4 ,here was another stage of her past existence1 requiring probably many hundreds of millions of years4 ,jupiter and ,saturn had to pass through similar stages of development1 and required many times as many years for each of them4 ,is it then reasonable to suppose that they have arrived at the same stage of development as our earth1 or indeed as each other4 ,supposing for a moment that we were fully assured that ,jupiter and ,saturn had separate existence1 hundreds of millions of years before our earth had been separated from the great glowing mass of vapour formerly constituting the solar system1 and that having this enormous start1 so to speak1 they need not necessarily be regarded as now very greatly in arrear as respects development1 or might even be in advance of the earth1 it is altogether improbable that either of them1 and far more improbable that both of them1 are passing through precisely the same stage of development4 ,if we knew only of two ships1 that one had to travel from ,new ,york to ,london1 and another from ,canton to ,liverpool1 some time during the year1 and that the one which had to make the longer journey was likely to start several weeks before the other1 would it not be rather unsafe to conclude1 when the former had entered the mouth of the ,thames1 that in all probability the other was sailing up the ,mersey8 ,yet something like this1 or in reality much wilder than this1 is the reasoning which permits the student of science to believe1 independently of the evidence1 or altogether against all evidence1 that ,jupiter and ,saturn are necessarily passing through the very stage of planetary existence through which the one planet we know much about is passing4 ,it seems to me that the student of science should be prepared to widen his conceptions of time even as he has been compelled to widen his conceptions of space4 ,as he knows that the planets are not1 as was once supposed1 mere attendants upon our earth and belonging to her special domain in space1 so should he understand that neither do the other planets appertain of necessity to the domain of time in which our earth's existence has been cast1 or only do so in the same sense that like her they occupy a certain domain in space1 not her domain1 but the sun's4 ,their history in time1 like hers1 doubtless belongs to the history of the solar system1 but the duration of that system enormously surpasses the duration of the earth as a planet1 and immeasurably surpasses the duration of that particular stage of life through which she is now passing4 ,prepared thus to view the other planets independently of preconceived ideas as to their resemblance to our own earth1 we shall not find much occasion to hesitate1 ,i think1 in accepting the conclusion that ,jupiter is a very much younger planet4 ,we have seen already that the enormous mass of ,jupiter1 surpassing that of our earth #cdj times1 is suggestive of the enormous duration of every stage of his existence1 and therefore of his present extreme youth4 ,his bulk yet more enormously exceeds that of our earth1 as1 according to the best measurements1 no less than #abcj globes1 as large as our earth1 might be formed out of the mighty volume of the prince of planets4 ,in this superiority of bulk1 nearly four times greater than his vast superiority of mass1 we find the first direct evidence from observation in favour of the theory that ,jupiter is still intensely hot4 ,how can a mass so vast1 possessing an attractive power in its own substance so great that1 under similar conditions1 it should be compressed to a far greater degree than our earth1 and be1 therefore1 considerably more dense1 come to be considerably rarer8 ,we no longer believe that there is any great diversity of material throughout the solar system4 ,we cannot suppose1 as ,whewell once invited us to do1 that ,jupiter consists wholly or almost wholly of water4 ,nor can we imagine that any material much lighter than ordinary rocks constitutes the chief portion of his bulk4 ,we are1 to all intents and purposes1 forced to believe that the contractive effect due to his mighty attractive energy is counteracted by some other force4 ,nor can we hesitate1 since this is admitted1 to look for the resisting force in the expansive effects due to heat4 ,we know that in the case of the sun1 where a much mightier contractive power is at work1 a much more intense heat so resists it that the sun has a mean density no greater than ,jupiter's4 ,we have every reason1 then1 which bulk and mass can supply1 to believe that ,jupiter is far hotter than the earth--that in fact1 as the sun1 exceeding ,jupiter more than #ajjj times in volume1 is many times hotter than he is1 so ,jupiter1 exceeding our earth #abjj times in volume1 is very much hotter than the earth4 ,illustration3 ,fig4 #bd4--,the ,planet ,jupiter4 ,but when we consider the aspect of ,jupiter we find that similar reasoning applies to his atmosphere4 ,the telescope shows ,jupiter as an orb continually varying in aspect1 so as to assure us that we do not see his real surface4 ,the variable envelope we do see presents1 further1 all the appearance of being laden with enormously deep clouds4 ,the figure 7#bd7 shows the planet as seen by ,herr ,lohse on ,february #e1 #ahgb1 and serves to illustrate the rounded clouds often seen in ,jupiter's equatorial zone1 as though floating in the deep atmosphere there4 ,although rounded clouds such as these are not constantly present1 they are very often seen2 their appearance1 even on a few occasions only1 would suffice for the argument ,i now propose to draw from them4 ,it is impossible to regard them as flat round clouds4 ,manifestly they are globular4 ,now they may not be quite as deep as they are long1 or even broad1 but supposing them only half as deep as they are broad1 that would correspond to much more than a third of the diameter of our earth1 shown in the same picture4 ,the atmosphere in which they float would necessarily be deeper still1 but that depth alone would be about #c1jjj miles4 ,now an atmosphere #c1jjj miles deep under the tremendous attraction of ,jupiter's mass would be compressed near its base to a density many times exceeding that of the densest solids if 7which of course is impossible7 it could remain in the gaseous form with such density4 ,the fact1 then1 that an atmosphere1 certainly gaseous1 exists around ,jupiter to this enormous depth at least1 proves to demonstration that there must be some power resisting its attractive energy2 and again1 we have little choice but to admit that that power is no other than the planet's intense heat4 ,as we extend our scrutiny into the evidence from direct observation1 we find still other proofs independent of those just considered4 ,one proof alone1 be it remembered1 is all that is required1 but it will be found that there are many4 99 99 99 99 99 ,we have found reasons for believing that the planet ,jupiter is expanded by heat in such sort that the contractive or condensing power of his own mighty attractive energy is overcome4 ,we know certainly that1 regarding the planet we see as a whole1 its globe is of very small density4 ,we have every reason to believe that it is made of the same materials1 speaking generally1 as our earth4 ,we know that its mass as a whole possesses many times the gravitating power of our earth's mass4 ,it is highly probable1 therefore1 that the condition of its substance is very different from that of our earth's substance4 ,and as we know of no cause save heat which could keep the planet in this state1 it is altogether probable that the planet is extremely hot4 ,the argument1 be it noticed1 is independent of that based on the probability that ,jupiter1 owing to his enormous mass1 has not cooled nearly so much as our earth has4 ,we then noticed another very powerful argument1 similar in kind1 but also quite independent1 derived from the aspect of the planet4 ,jupiter's appearance indicates clearly that he has a deep cloud-laden atmosphere1 and we know that such an atmosphere1 if of the same temperature as our earth's1 would be compressed enormously1 whereas the observed mobility of ,jupiter's cloud-envelope1 and other circumstances1 indicate that this enormous compression does not exist4 ,we infer1 then1 that some cause is at work expanding the atmosphere2 and we know of no other cause but heat which could do so effectively4 ,but now let us consider certain details which the telescope has brought to our knowledge4 ,in the first place1 a number of circumstances indicate a tremendous activity in that deep cloud-laden air4 ,the cloud-belts sometimes change remarkably in appearance and shape in a very short time4 ,mr4 ,webb1 in his excellent little treatise1 ,celestial ,objects for ,common ,telescopes1 gives instances from the observations of ,south1 which ,i here translate into non-technical terms3--,on ,june #c1 #ahci1 at about nine in the evening1 ,south saw with his large telescope1 just below the principal belt of ,jupiter1 a spot of enormous size4 ,it was dark1 and therefore probably represented an opening in a great cloud-layer by which a lower or inner layer was brought into view4 7,for though the planet's real globe may be so intensely hot as to emit a great deal of light1 it is probable that most of the light so emitted is concealed by the enwrapping cloud masses1 and that the greater part of the light we receive from the planet is reflected sunlight2 so that the inner cloud-layers would be the darker47 ,south estimated this spot as about #bj1jjj miles in diameter4 ,i showed it1 he says1 to some gentlemen who were present2 its enormous extent was such that on my wishing to have a portrait of it1 one of the gentlemen1 who was a good draughtsman1 kindly undertook to draw me one2 whilst ,i1 on the other hand1 extremely desirous that its actual magnitude should not rest on estimation1 proposed1 on account of the scandalous unsteadiness of the large instrument1 to measure it with my five-feet telescope4 ,having obtained for my companion the necessary drawing instruments1 ,i went to work1 he preparing himself to commence his4 ,but on looking into the telescope1 ,south was astonished to find that the large dark spot1 except at its eastern and western edges1 had become much whiter than any of the other parts of the planet2 and thirty-four minutes after these observations had commenced1 these query three8 miserable scraps were the only remains of a spot which but a few minutes before had extended over at least #bj1jjj miles1--or two and a half times the diameter of the earth4 ,the cloud envelope1 then1 of ,jupiter is certainly not in a state of quiescence4 ,of course we need not suppose that winds had carried cloud masses athwart the tremendous opening seen by ,south4 ,that would imply a motion of #aj1jjj miles in the half-hour or so of observation1--supposing contrary winds to have rushed towards the centre1--or double that velocity if the entire breadth of the spot had been traversed in that time4 ,a velocity of #bj1jjj miles1 and still more of #dj1jjj miles per hour1 may fairly be regarded as incredible4 ,it would exceed more than a hundred-fold 7taking the least number7 the velocity of our most tremendous hurricanes4 ,and although the solar hurricanes would seem to have a velocity1 at times1 of #cjj1jjj or #djj1jjj miles per hour1 we have no reason for supposing that winds of tens of thousands of miles per hour could be raised in the atmosphere of ,jupiter4 ,as ,i have said1 however1 it is not necessary to suppose this4 ,we may conceive that clouds had formed very rapidly at the higher elevation where before they had been wanting4 ,clouds may form as readily and quickly over an area a thousand miles across as over an area two or three miles across4 ,indeed ,webb1 referring to such changes as ,south witnessed1 says that ,sir ,j4 ,herschel once observed a cloud-bank in our own air1 which formed so rapidly that it crossed the sky at the rate of #cjj miles an hour1 not moving1 of course1 at that rate1 but being formed along different parts of its apparent progress almost simultaneously1 so as to appear to travel with this enormous velocity4 ,but now ,i wish the reader specially to notice how this observation of ,south's may serve to explain another1 equally remarkable and at first sight far more perplexing2 and how1 when the two observations are brought together1 a very singular piece of information is obtained respecting ,jupiter's cloud-envelope4 ,let a b1 fig4 #be1 represent the great dark space seen by ,south1 just below the principal belt1 and let us suppose the planet turned round until this dark space1 or rather this opening in the planet's outer cloud-envelope1 is brought to the edge as at a c d1 fig4 #bf4 ,then this opening would really cause a depression in the planet's outline at d c1 the shaded part being depressed4 ,the depression might not be observable in any ordinary telescope4 ,for at the edge of ,jupiter the features of the belt are generally lost1 and the outline is at all times smoothed in appearance by that peculiarity of vision which makes all bright objects seen on a dark background appear somewhat larger than they actually are4 7,this is really due to a fringing1 as it were1 of the image on the retina of the eye47 ,but though the depression might not be recognisable1 it would exist1 and1 as we shall presently see1 it might be detected in another way than by being actually seen4 ,when the clouds formed which concealed the spot1--we do not know how quickly1 but certainly in less than thirty-four minutes1--the depression1 had the spot been at the edge1 would have been removed4 ,this change1 however1 like the existence of the depression1 would doubtless not have been discernible by ordinary vision4 ,illustration3 ,fig4 #be4 ,fig4 #bf4 ,now1 let us consider the second observation mentioned above4 ,illustration3 ,fig4 #bg4 ,fig4 #bh4 ,fig4 #bi4 ,on ,thursday1 ,june #bf1 #ahbh1 the second satellite of ,jupiter was about to make a passage across the planet's face4 ,it was observed1 just before this passage or transit began1 in the position shown in fig4 #bg by the late ,admiral ,smyth4 ,he was using an excellent telescope4 ,it gradually made its entry1 looking for a few minutes like a small white mountain on the edge of the planet1 and finally disappeared4 ,the reader must understand that the moon was not hiding itself behind the planet1 but was on this side of it1 and simply lost to view because its brightness was the same1 or very nearly the same1 as that of the planet's edge4 7,its place is shown in fig4 #bh1 but of course the little dark ring was not so seen47 ,at least #ab or #ac minutes must have elapsed1 says ,smyth1 when1 accidentally turning to ,jupiter again1 to my astonishment ,i perceived the same satellite outside the disc1 as shown in fig4 #bi4 ,it remained visible there for at least four minutes1 and then suddenly vanished4 ,to show that the observation was not due to any local or personal peculiarity1 it is only necessary to mention that two other astronomers1 ,mr4 ,maclear at ,biggleswade1 and ,dr4 ,pearson at ,south ,kilworth1 observed the same extraordinary behaviour of ,jupiter's second satellite4 ,the three telescopes are thus described by ,admiral ,smyth1-- ,mr4 ,maclear's1 #c inches in opening1 #c feet long2 ,dr4 ,pearson's1 #f inches in opening1 #ab feet long2 ,adm4 ,smyth's1 #c inches in opening1 #e feet long2 all good observing telescopes4 ,now1 of course1 the satellite did not really stop4 ,nothing short of a miracle could have stopped the satellite1 or1 if the satellite could have stopped1 have set it travelling on again as usual4 ,for the satellite did not lose one mile1 or change its velocity by the thousandth part of a mile per hour or even per annum4 ,but suppose such a change had taken place at the edge of ,jupiter as we have seen would certainly have taken place there if the changes affecting the spot which ,south saw had occurred to a region at the edge1 as in fig4 #bf1 instead of the middle1 as in fig4 #be4 ,then ,smyth's observation would be perfectly explained4 ,we require1 indeed1 to suppose the change occurring in a different order1 the outer cloud-layer being in the first instance well-developed and very rapidly becoming dissipated1 so that the outline which had at first been at its usual level1 was very rapidly depressed to the inner cloud-layer4 ,but1 of course1 if the rapid formation of clouds by condensation can occur on ,jupiter1 so also can the rapid dissipation occur1 especially at that particular part where ,smyth saw the satellite behave so strangely4 ,for that part is being carried1 by the planet's swift rotation1 into sunlight1 and the extra heat to which it is thus exposed might readily effect the dissipation of widely extended cloud strata1 supposing the temperature near that critical value at which clouds form or are dissipated4 ,here1 then1 is an explanation of a phenomenon which otherwise seems utterly inexplicable4 ,the explanation requires only that a process like one which has been observed to occur on ,jupiter's disc should occur at a part of his surface forming at the moment a portion of his outline4 ,if we had never known of such changes as ,south and other observers have noted in the markings of ,jupiter1 we should be compelled by ,smyth's observation to admit their possibility4 ,if we had never known of ,smyth's observation we should be compelled by ,south's to admit that such a change of outline as is indicated by ,smyth's observation must be possible1--must1 in fact1 occur whenever cloud-masses form or are dissipated over wide areas at the apparent edge of the planet4 ,when we have both forms of evidence it seems altogether unreasonable to entertain any further doubt on this point4 ,but ,smyth's observation1 thus interpreted1 indicates an enormous distance between the outer and inner cloud-layers which formed the planet's edge near the satellite in figs4 #bh and #bi respectively4 ,i find after making every possible allowance for errors in his estimate of time1 not taken it would seem from his observatory clock1 that the distance separating these cloud-layers cannot have been less than #c1ejj miles1 or not far from half the diameter of our earth4 ,it is the startling nature of this result which perhaps deters many from accepting the explanation of ,smyth's observation here advanced4 ,but there is no other explanation4 ,the satellite cannot have stopped in its course2 ,jupiter cannot have shifted his place bodily2 the satellite was on this side of the planet1--therefore no effects of the planet's atmosphere on the line of sight from the planet can help us2 three observers at different stations saw the phenomenon1--therefore neither effects of our earth's atmosphere nor personal peculiarities can account for the strange phenomenon4 ,explanation is set at defiance1 says ,webb2 demonstrably neither in the atmosphere of the earth nor ,jupiter1 where and what could have been the cause8 ,the explanation ,i have advanced is the only possible answer to this question4 ,i might occupy twenty times the space here available to me in detailing various other phenomena all pointing in the same way1--that is1 all tending to show that ,jupiter is a planet glowing with intense heat1 surrounded by a deep cloud-laden atmosphere1 intensely hot in its lower portions1 but not necessarily so in the parts we see1 and undergoing changes 7consequences of heat7 of a stupendous nature1 such as the small heat of the remote sun1 which shines on ,jupiter with less than the #bgth part of the heat we receive1 could not by any possibility produce4 ,but partly because space will not permit1 partly because most of these phenomena have been described in my ,orbs ,around ,us1 and ,other ,worlds1 ,i content myself by describing a singular observation recently made1 which1 with ,south's and ,smyth's1 seems to place the theory ,i have advanced beyond the possibility of doubt or cavil4 ,mr4 ,todd of ,adelaide has recently obtained for his observatory a fine #h-;inch telescope by ,mr4 ,cooke4 ,with this instrument1 mounted in ,december1 #ahgd1 he has made many valuable observations of the motions of ,jupiter's satellites4 ,ordinarily1 of course1 the entry of each satellite on the planet's face and the egress therefrom1 the disappearance of each satellite behind the planet or in the planet's shadow 7not necessarily the same thing7 and the reappearance1 are effected in what may be called the normal way2 and ,mr4 ,todd's experience in this respect has been like that of other observers4 ,but on two occasions he and his assistant1 ,mr4 ,ringwood1 observed that a satellite1 when passing behind the planet's edge1 did not disappear at once1 but remained visible as if seen through the edge1 for about two minutes4 ,the same satellite behaved thus on each occasion1--viz4 the satellite nearest the planet4 ,as this satellite travels at the rate of about #fde miles per minute1 it would follow that the satellite was seen through a depth of nearly #acjj miles1 or1 after making all possible allowance for optical illusions1 some #ijj or #ajjj miles4 ,the effect of refraction cannot then be great in the air of ,jupiter1 to this depth below the usual limit of the upper clouds1--for otherwise the satellite would have been altogether distorted4 ,and this very fact1 that for #ajjj miles or so below the highest clouds the change of atmospheric density is not sufficient to produce any noticeable refractive effects1 implies that the true base of the atmosphere of ,jupiter lies very far lower yet--perhaps many hundreds of miles lower4 ,if the reader now look again at the picture at page #bja1 he will understand1 ,i think1 how those great round white clouds in the chief belt1--clouds thousands of miles long and broad1--are probably hundreds of miles deep also1 and float in an atmosphere still deeper4 ,all that we know about ,jupiter1 in fine1 from direct observation1 as well as all that we can infer respecting the past history of the solar system1 tends to show that he is still an extremely young planet4 ,he is the giant of the solar family in bulk1 and probably he is far older than our earth in years2 but in development he is1 in all probability1 the youngest of the sun's family of planets1 and certainly far younger than the earth on which we live4 ,illustration ,,xi ,,the ,,ringed ,,planet ,,saturn4 ,very different from the ruddy planet which approached so closely to him in ,november1 #ahgg1 is ,saturn1 the ringed world1 the most wonderful of all the planets if the complexity of the system attending on him is considered1 and in size inferior only to the giant ,jupiter4 ,it will have been noticed1 perhaps1 by those who are familiar with the aspect of the planets1 that the contrast between ,mars and ,saturn during their late approach to us was not only greater than usual1 but greater than was to be expected even when account was taken of the unusual lustre of ,mars4 ,i have often wondered whether the ancient astronomers were ever perplexed by the varying lustre of ,saturn4 ,they recognised the fact that ,mars has an orbit of great eccentricity 7see the picture of the orbits of ,mars1 ,venus1 etc41 at page #aef72 and there was nothing in the varying lustre of ,mars which could not be perfectly well explained by his known variations of distance1 whether the ,ptolemaic or the ,copernican system were accepted4 ,but with ,saturn the case is different4 ,his distance at successive returns to our midnight skies is subject to moderate changes only4 ,yet his brilliancy varies in a remarkable manner4 ,we now know that those changes are due to the opening and closing of that marvellous system of rings which renders this planet the most beautiful of all the objects of telescopic observation which the heavens present to us4 ,when the edge of the rings is turned towards the earth1 we see only the most delicate thread of light on either side of the planet's disc4 ,but when the rings are opened out to their full extent they reflect towards us as much light as we receive from the disc4 ,at such times the planet presents a much more brilliant appearance than when the ring is turned nearly edgewise2 in fact to the naked eye he seems very nearly twice as bright4 ,now at present the rings are turned nearly edgewise towards the earth4 ,in ,july and ,august1 #ahfi1 the planet presented in the telescope the appearance presented in fig4 #cj1 where it will be seen that the shorter axis of the oval into which any one of the ring-outlines is thrown is nearly equal to half the larger axis4 ,since then the rings have been slowly closing up2 and at present the rings are so little open that the corresponding shorter axis1 if it could be directly seen1 would appear to be about one-sixteenth only of the larger axis4 ,the rings were turned exactly edgewise towards the sun at two in the afternoon1 on ,st4 ,valentine's day1 #ahgh1 according to calculations which ,i made in #ahfd1 and published in a table under the head ,passages of the ,rings plane through the ,sun between the years #afjj and #bjjj1 in my treatise entitled ,saturn and its ,system4 ,the ,nautical ,almanac for #ahgh1 indeed makes the passage of the rings plane through the sun occur somewhat earlier1 stating that at noon on ,february #ad the sun's centre would pass south of the ring's horizon by about one-fifth of its apparent diameter 7as seen by us74 ,but my own calculation took into account certain small details which1 in matters of this sort1 the ,nautical ,almanac computers neglect4 ,after all1 it mattered very little to terrestrial observers whether the sun's light passed from the northern to the southern side of the rings a few hours earlier or later3 the moment when it passed could not possibly be observed1 even if it had occurred during the night hours4 ,in the present instance it occurred at midday1 and unfortunately none of the interesting phenomena presented in powerful telescopes when the rings are turned edgewise to the sun or earth could be observed1 for they occurred when ,saturn and the sun were nearly in the same part of the heavens1 and when the planet therefore was utterly lost in the splendour of the solar rays4 ,illustration3 ,fig4 #cj4--,the planet ,saturn in ,july and ,august1 #ahfi4 ,but now let us briefly consider what is known or may be surmised respecting the noble planet which was so far outshone in ,november1 #ahgg1 by the comparatively minute orb of ,mars4 ,saturn travels at a distance from the sun exceeding rather more than nine and a half times that of our own earth4 ,the second figure of orbits 7see page #aeg7 shows the wide span of his orbit compared with the earth's1 and yet it will be seen that the orbits of ,uranus and ,neptune1 planets unknown to the ancients1 are so wide that the path of ,saturn becomes in turn small by comparison4 ,saturn has a globe about #gj1jjj miles in diameter1 where it bulges out at the equator2 but he is somewhat flattened at his poles1 so that his polar diameter is about #gjjj miles less than the equatorial diameter4 ,in volume he exceeds our earth about #gjj times2 but in mass only about ninety times3 for his mean density is but about #ac_/ajj of the earth's4 ,in fact1 if we could imagine an ocean of water wide enough and deep enough for the planets to be all set in it1 ,saturn would float with about one-fourth of his bulk out of water1--always supposing that no change took place in his density directly after he was immersed4 ,saturn1 indeed1 would float highest of all the planets1 or rather all of them would sink except ,saturn and ,neptune1 and ,saturn would float higher than ,neptune4 ,uranus would just sink4 ,jupiter is half as heavy again as he should be to float4 ,all the terrestrial planets1 ,mercury1 ,venus1 the ,earth1 and ,mars1 would go to the bottom at once4 ,it is almost impossible to regard any feature of ,saturn as better deserving to be considered first than his ring system4 ,yet for the sake of preserving a due sequence of ideas we must first consider his globe4 ,we find ourselves at once in presence of difficulties like those we encountered when we considered the planet ,jupiter4 ,how is it that the mighty mass of a planet like ,saturn1 constructed1 we have every reason to believe1 of materials resembling those which constitute our earth1 has so failed to gather in its substance that the mean density is much less than that of the earth's globe8 ,it must be remembered that gravity prevails throughout the frame of ,saturn as throughout our earth's frame4 ,every particle of that enormous globe is drawn towards the centre with a force almost exactly the same as would be exerted by the attraction of the entire mass of that portion of the planet which lies nearer to the centre than the particle1 if this mass were collected at the centre4 ,but this is not all4 ,it is not merely the attraction exerted on each particle of ,saturn's mass which has to be considered1 but the entire weight of all the superincumbent matter4 ,the distinction between attraction and weight1 by the way1 is very commonly overlooked in considering the planets' interiors4 ,i think it was ,sir ,david ,brewster who argued that as attraction can easily be shown to diminish downwards towards the centre1 it is possible to conceive that the interior of a planet may be hollow4 ,the error is readily perceived1 if we take a familiar instance where the attraction is the same yet the effect of pressure very much greater4 7,without voyaging to the centre of the earth1 which is troublesome1 and certainly not a familiar experience1 we cannot reach places where the attraction of gravity is greatly less than at the surface47 ,take a massive arch of brickwork3 the bricks near the top are subject to the same attraction as those belonging to the foundation2 but the pressure to which the foundation bricks are exposed is very much greater than that affecting the upper bricks4 ,so again with a deep sea3 the particles at the bottom of such a sea are subject to no greater attraction than the particles near the top2 but we know that a strong hollow case of metal which near the top of such a sea would be scarcely pressed at all1 and would suffer no change of shape1 will be crushed perfectly flat under the tremendous pressure to which it will be exposed when sunk to the bottom4 ,there is1 in fact1 no escape from the conclusion that the interior portions of a planet like ,saturn or ,jupiter1 nay1 even of a body like our earth or the moon1 must be subject to tremendous pressure1 a pressure exceeding many hundred-fold the greatest which we can obtain experimentally1 and that under that enormous pressure the density of the materials composing those central parts must be increased4 ,how is it then that ,saturn is of much smaller density than the earth8 ,i can imagine no other explanation at once so natural and so complete as this1 that an intense heat pervading the entire frame of the planet enables it to resist the tremendous pressure due to mere weight4 ,the planet's mass is expanded by the heat2 large portions which at ordinary temperatures would be solid are liquified or even vaporised2 matters which are liquid on our earth are vaporised2 and1 in fine1 the planet assumes 7as seen from our distant station7 the appearance of being very much larger than it really is4 ,we measure not the true globe1 which1 for aught that is known1 may be exceedingly dense1 but the dimensions of cloud-layers floating high in the planet's atmosphere4 ,in describing ,jupiter1 ,i considered the changes which have been noticed in that planet's outline1 and observed that it is impossible adequately to explain the evidence1 without assuming that the changes of outline are real4 ,the outline is not that of a solid globe1 however1 but of cloud-layers surrounding such a globe1 and probably at a great distance from its surface4 ,illustration3 ,fig4 #ca4--,saturn's square-shouldered aspect4 ,in ,saturn's case we have very singular evidence to the same purpose4 ,it was observed by ,sir ,w4 ,herschel in ,april1 #ahje1 that ,saturn occasionally appears distorted1 as though bulging out in the latitudes midway between the pole and the equator of the planet4 ,fig4 #ca represents the appearance of the planet so far as shape is concerned1 but the ring was not1 when ,sir ,w4 ,herschel observed it1 so narrow as it is shown in fig4 #ca4 ,in fact the ring had been turned edgewise to the earth two years before2 and when ,herschel noticed the abnormal appearance of ,saturn1 the rings had begun to open out1 though their outermost outline was still far within the regions of the planet which seemed to project as shown4 ,fig4 #ca in fact represents ,saturn as seen by ,schrter in #ahjc1 when1 as he said1 the planet did not seem to present a truly spheroidal figure4 ,herschel tested his observations by using several telescopes of different dimensions1--ten1 seven1 twenty1 and forty feet in length4 ,in #ahah1 when the rings were scarcely visible1 ,kitchener saw the planet as shown in fig4 #ca1 or square-shouldered1 as some have called it4 ,on one occasion the present ,astronomer-,royal saw the planet of that figure4 ,in ,january1 #ahee1 ,coolidge1 using the fine refractor of the ,cambridge ,u4,s4 ,observatory1 noticed that the equatorial diameter was not the greatest2 on the #ith the planet seemed of its usual shape2 but on ,december #f1 ,coolidge writes1 ,i cannot persuade myself that it is an optical illusion which makes the maximum diameter of the ball intersect the limb half-way between the northern edge of the equatorial belt1 and the inner ellipse of the inner bright ring4 ,this was at a time when the rings were nearly at their greatest opening2 so that1 including ,schrter's observation1 we have ,saturn out of shape when his ring has presented every shape between that shown in fig4 #cj and that shown in fig4 #ca4 ,again1 in the report of the ,greenwich ,observatory for #ahfj-fa1 when the ring was nearly closed1 it is stated that ,saturn has sometimes appeared to assume the square-shouldered aspect4 ,lastly1 the eminent observers1 ,g4 ,bond and ,g4 ,p4 ,bond1 father and son1 have seen ,saturn abnormally shaped1 flattened unduly in the north polar regions in #ahdh1 when the ring was turned edgewise towards us1 and unsymmetrical in varying ways in #ahee-eg1 when the ring was most widely opened4 ,yet the planet's outline is usually a perfect oval1 and has been shown to be so by careful measurements effected in some instances by the same observers1 who1 making equally careful measurements1 have found the planet to be distorted4 ,does it not seem abundantly clear that the great cloud-layers which float in the atmosphere of ,saturn have a widely varying range in height1 and that therefore as we see and measure the outline of the cloud-layers1 we see and measure in effect a planet which is variable in figure8 ,this seems so natural and complete an explanation of the observed peculiarities that it appears idle on the one hand to reject the evidence of some among the most skilful observers who have ever lived2 or1 on the other1 to imagine that the solid frame of the planet has undergone changes so tremendous as would be involved by the observed variations of outline if they really signified that a solid planet had changed in shape4 99 99 99 99 99 ,the mighty globe of ,saturn turns upon its axis nearly as quickly as ,jupiter4 ,it will be remembered that the ,jovian day lasts only #i of our hours1 and as the diameter of ,jupiter is about ten times the earth's1 the equatorial parts of the giant planet travel some twenty-six or twenty-seven times as fast as those of our own earth1 which move 7rotationally7 at the rate of more than a thousand miles an hour4 ,saturn's equatorial parts do not move quite so fast1--in fact1 in this respect1 ,jupiter comes first of all the members of the solar system1 including the sun himself4 ,saturn's equatorial circuit being almost nine times the earth's1 while his day is little more than five-twelfths of the earth's1 it follows that his equatorial parts move twelve-fifths of nine times1 or nearly twenty-two times faster than the earth's4 ,their actual rotational rate is rather more than #bb1jjj miles an hour1 or #cfg miles a minute1 or more than six miles a second4 ,this is a wonderful rate of motion4 ,it always seems to me one of the most striking results of modern astronomical research that we have to recognise in bodies like that dull looking star1--the heavy slow-moving ,saturn1 as the ancients called him1#ad--motions of such tremendous swiftness4 ,the planet is not only rushing bodily along through space with a velocity of nearly six miles per second1 but his equatorial parts are being carried round with a velocity somewhat exceeding six miles per second4 7,the coincidence must be regarded as accidental1 but it has this curious effect1 that the equatorial parts of ,saturn near the middle of the disc we see are actually almost at rest with respect to the sun1 being carried forward with the planet at the rate of about five miles and nine-tenths per second1 and backward round the planet at the rate of about six miles and one-tenth per second4 ,in fact there are always two points on the disc which are almost exactly at rest with respect to the sun1 viz41 those two points north and south of the equator where the rotational velocity is about five miles and nine-tenths per second1 the velocity of ,saturn in his orbit47#ae ,but let us turn from the contemplation of ,saturn's globe1 interesting though it undoubtedly is1 to study those marvellous objects1 the ,saturnian rings4 ,the history of their discovery is interesting1 but must not here detain us long4 ,briefly1 it runs as follows3-- ,galileo1 in ,july1 #afaj1 observing the planet ,saturn with a telescope not powerful enough to show the rings1 imagined at first that ,saturn had two companion planets1 one on either side of him1 as though helping the planet along upon his road4 7,from a table relating to the rings1 in my treatise on ,saturn and its ,system1 the aspect of the ring1 at the time of any such observation1 can at once be inferred4 ,in the present case1 for example1 it will be seen from the table that the rings were closing up as the time of their disappearance1 ,december #bh1 #afab1 drew near47 ,a year and a half later1 ,galileo looked again at ,saturn1 and lo6 the companion planets were gone4 ,he was perplexed beyond measure4 ,what is to be said concerning so strange a metamorphosis8 he asked4 ,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 an illusion or fraud1 with which the glasses have so long deceived me1 as well as many others to whom ,i have shown 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 mistaken1 have greatly confounded me4 ,hevelius was similarly perplexed by the constantly varying appearance of the planet4 ,saturn1 he informed his contemporaries1 presents five various figures to the observer1 to wit--first1 the mono-spherical2 secondly1 the tri-spherical2 thirdly1 the spherico-ansated2 fourthly1 the elliptico-ansated2 fifthly1 and finally1 the spherico-cuspidated2 of which we can only say1 like ,mr4 ,gilbert's ,ferdinando1 that we know it's very clever2 but we do not understand it4 ,it was not till #afei that ,huyghens1 using a telescope forty yards long1 was able to make out the real meaning of the appendages which had so perplexed ,galileo and ,hevelius4 ,he announced to the world1 in an anagram1 his discovery that ,saturn is girdled about by a flat ring nowhere touching the planet4 ,huyghens also discovered the largest of ,saturn's moons4 ,he looked for no more1 having the idea that1 since six planets and six moons were now known1 no more moons existed4 ,in #affc the ,brothers ,ball discovered that the rings are divided into two1 or1 at any rate1 that a broad black stripe1 such as is shown in fig4 #cj1 separates the outer portion of the ring from the inner4 ,two years later these observers saw the stripe on the northern side of the rings1 when the rings had so shifted in position that observers saw their southern side4 ,dominic ,cassini recognised a corresponding stripe on the southern side4 ,this was regarded as proving that there is a real division between the rings4 ,the width of the gap thus separating the outside of the inner ring from the inside of the outer cannot be less than #a1fjj miles4 ,cassini also detected another ,saturnian moon in ,october1 #afga1 and1 later1 he discovered three others1 making five ,saturnian moons in all4 ,sir ,w4 ,herschel observed the rings with great care4 ,he confirmed the discovery of the great division between the rings2 but rejected the idea which was beginning to be entertained in his time1 that there are many divisions4 ,he found reasons for suspecting1 but never actually proved1 that the outer ring turns round in about #aj hours4 ,he also detected two small moons close to the outer ring4 ,one other moon1 detected independently by ,bond at the ,harvard ,observatory1 ,cambridge1 ,u4,s41 and by ,lassell in this country in #ahdh1 completes the set of eight moons now known to revolve around the planet ,saturn4 ,we need not here say much more about these moons1 saving1 perhaps1 to note that the span of the entire ,saturnian system of moons amounts to about #d1djj1jjj miles1 nearly double that of the ,jovian system4 ,this is the largest system of satellites known to us4 ,it is wonderful to reflect1 when we look at the dull1 slow-moving ,saturn1 that not only is the planet itself #gjj times larger than the earth1 not only is it girdled about by a ring system having a span exceeding more than #bj times the diameter of this earth on which we live1 but that the entire span of the system over which that distant planet rules exceeds more than eighteen-fold the distance separating our earth from the moon4 ,return we now1 however1 to the consideration of the ,saturnian ring-system4 ,in #ahej a singular discovery was made4 ,it was found by ,bond1 in ,america1 and1 a few days later1 independently1 by ,dawes1 in ,england1 that inside the inner bright ring there is a dark ring almost as wide as the outer bright ring4 ,one of the strangest circumstances about this inner ring is that where it crosses ,saturn's disc the outline of the planet can be distinctly traced through the dark ring1 which is thus1 in a sense1 a semi-transparent body4 ,i say in a sense1 because it does not follow that it really consists of semi-transparent matter any more than it follows from our being able to see through a gauze veil that the individual threads forming the gauze are made of a semi-transparent material4 ,on examining recorded observations of the planet evidence was found that this dark ring is not1 as was at first supposed1 a recent formation4 ,where it crosses ,saturn it had been mistaken in former times for a dark belt4 ,it had always been supposed that the rings are solid1 or at any rate continuous bodies4 ,the younger ,cassini1 indeed1 ventured to express doubts on the subject1 but with this solitary exception1 no suspicion had ever existed among astronomers that the rings are otherwise than continuous1 until the discovery of the dark ring4 ,when the singular fact was discovered that the body of the planet can be seen through the slate-coloured ring1 the solidity of this ring1 at any rate1 began naturally to be questioned4 ,the idea was suggested that this formation may be fluid4 ,mathematicians applied rigorous processes of investigation to the question whether a fluid ring can possibly exist in such a position4 ,the inquiry led to a re-examination of the whole subject of the ring-system and its stability4 ,mathematicians took up the question where ,laplace had left it more than half a century before4 ,he had decided that solid rings might1 under certain conditions1 revolve around a planet without being broken4 ,but his inquiry had not been carried to a conclusion4 ,now1 when the work was completed1 it was found that the requisite conditions are certainly not fulfilled by the ,saturnian ring-system4 ,the rings should be situated eccentrically1 and heavier at one side than the opposite4 ,in fact they should have a perceptible bias4 ,they exhibit1 on the contrary1 the most perfect symmetry of figure--this symmetry1 indeed1 constitutes the great charm of ,saturn's telescopic appearance2 and although1 occasionally1 the ball has not seemed to be quite in the middle of the ring-system1 the displacement has never approached that which theory requires4 ,the conclusion to which mathematicians arrived was accordingly the following3-- ,the rings may be held to be formed of a multitude of tiny satellites1 travelling nearly in one plane1 each pursuing its own course around ,saturn1 according to the laws of satellite motion1 though of course disturbed by the attraction of its fellow-satellites4 ,we owe this theory principally to the labours of ,professor ,j4 ,clerk ,maxwell1 who gained the ,adams ,prize offered by the ,university of ,cambridge for the best mathematical essay upon the conditions under which a ring-system such as ,saturn's can exist4 ,but ,professor ,pierce1 of ,america1 had 7somewhat earlier7 supplied a complete refutation of the idea that the rings are solid and continuous bodies4 ,when the rings are fully open1 as in fig4 #cj1 the ,saturnian system affords as charming an object for telescopic observation as the astronomer can desire4 ,the rings are then exhibited in their full beauty4 ,the divisions1 the dark ring1 and the strange shading of the middle ring1 can be well seen in a telescope of adequate power4 ,the telescopic view is still more interesting when 7as in fig4 #cj7 the planet throws a well-marked shadow upon the rings4 ,but perhaps the most beautiful of all the features which ,saturn presents to the telescopist is the strange variety of colour to be observed upon his surface1 and upon that of the rings4 ,mr4 ,browning1 the eminent optician1 thus describes the colours which the planet presents in his #ab-;inch reflector3-- ,the colours ,i have used1 he says1 referring to a painting of the planet1 were--for the rings1 yellow-ochre 7shaded with the same7 and sepia2 for the globe1 yellow ochre and brown madder1 orange and purple1 shaded with sepia4 ,the great division in the rings is coloured sepia 7not black as commonly described74 ,the pole and the narrow belts situated near it on the globe are pale cobalt blue4 ,these tints1 he adds1 are the nearest ,i could find to those seen on the planet2 but there is a muddiness about all terrestrial colours when compared with the colours of the objects seen in the heavens4 ,these colours could not be represented in all their brilliancy and purity1 unless we could dip our pencil in a rainbow1 and transfer the prismatic tints to our paper4 ,i can corroborate these remarks from observations made upon the planet with an #h-;inch reflector4 ,it is1 indeed1 a circumstance worthy of note1 that the colours of the planets are much more strikingly exhibited by reflecting telescopes than by refractors1 insomuch that1 while ,sir ,w4 ,herschel and ,messrs4 ,de la ,rue and ,lassell1 making use of the former class of instruments1 have all recorded the marked impression which the colours of ,saturn and ,jupiter have made upon them1 we find that few corresponding observations have been made by observers who have been armed with even the most perfect specimens of the refracting telescope4 ,it must be noticed1 however1 that the colours of ,saturn and his ring-system can only be seen in the most favourable observing weather4 ,,footnotes3 #ad ,who assigned to him1 as his representative metal1 lead--a metal heavy1 dull1 and slow1 as ,don ,armado puts it1 in ,love's ,labour's ,lost4 #ae ,attention has lately been called1 by the astronomers of the ,washington ,observatory1 to the fact that the statement usually made in our books of astronomy1 that ,sir ,w4 ,herschel's latest determination of ,saturn's rotation period was #aj;h4 #bim41 is incorrect4 ,his only determination of the period gave #aj;h4 #afm4 #dds4 for the ,saturnian day4 ,illustration ,,xii4 ,,fancied ,,figures ,,among ,,the ,,stars4 ,i ,,think that every thoughtful student of the stars must have wondered how the figures of the various objects now pictured in our star-maps came to be imagined in the heavens themselves4 ,it is a convenient answer to inquiries of the sort to say that it became necessary at an early stage in the progress of astronomy to have some means of identifying and naming star-groups1 and that the arrangement into constellations was as suitable as any other that could have been desired4 ,but it seems to me altogether unlikely that1 in the infancy of a science1 a mere arbitrary arrangement1 such as this explanation supposes1 should have been adopted4 ,if we try to imagine the position of the first observers of the stars1 what they wanted1 and what they were likely to do1--and this a priori method of dealing with such questions is1 ,i believe1 the only safe one1--we perceive that the division of the stars into sets named after animals and other objects1 without any real resemblance to suggest such nomenclature1 is as unlikely a course as could possibly be conceived4 ,beyond all question1 ,i think1 the first watchers of the skies 7they can scarcely be called astronomers7 would have taken advantage of imagined similarity1 more or less close1 between each remarkable group of stars and some known object1 to identify the group1 and to obtain a name by which to speak of it4 ,yet it must be admitted that1 as the constellations are at present arranged and figured1 it is very difficult1 in the great majority of cases1 to imagine the least resemblance between a constellation and the object from which it derives its name4 ,this is not only true of the modern constellations1 the preposterous pneumatic machines1 printing presses1 microscopes1 and so forth1 with which ,hevelius and his successors foolishly crowded the heavens4 ,even the oldest of the old constellations of ,ptolemy1 nay1 some even of those which are found among all nations1 present1 according to their present configuration1 scarce any resemblance to their antitypes4 ,for instance1 it is well known that the ,great ,bear was recognised by many nations besides the ,greeks and those1 whoever they may have been1 from whom the ,greeks derived the constellation4 ,we learn that when ,america was discovered the ,iroquois ,indians called this constellation ,okouari1 or the ,bear4 ,so the inhabitants of ,northern ,asia1 the ,phoenicians1 the ,persians1 and others1 called this constellation the ,bear4 ,the ,egyptians1 not knowing the bear1 called the constellation the ,hippopotamus1 an animal resembling the bear in several respects1 as in its heavy body1 short inconspicuous tail1 small head1 and short ears4 ,yet the constellation1 as at present figured1 is certainly not in the remotest degree like a bear4 ,apart from the enormous tail given in the pictures to the bear 7almost tailless in reality71 it is impossible for the liveliest imagination to recognise a bear as the constellation is at present formed4 ,flammarion says that1 even if we take in the smaller stars that stand in the feet and head1 no ingenuity can make it in this or any other way resemble a bear1 adding the absurd explanation given by ,aristotle1 that the name is derived from the fact that of all human animals the bear was thought to be the only one that dared to venture into the frozen regions of the north1 and tempt their solitude and cold4 ,as though the shepherds and tillers of the soil1 who first gave names to the stars1 were likely to consider such far-fetched reasons1 even if they had known either the habits of the polar bears or had considered the relation of the northern star-groups to the polar regions of the earth4 ,now the question whether any real resemblance attracted the attention of the earlier observers in such cases as this is by no means without interest4 ,if such a resemblance formerly existed1 and does not now exist1 it would follow that quite a considerable proportion of the stars have changed in brightness4 ,considering that each star is a sun1 the centre1 most probably1 of a system like that which circles around our own sun1 such a conclusion would be very startling indeed4 ,it would have a special interest for ourselves1 somewhat in the same way that the news that many railway accidents occur has an interest for those who travel much by rail4 ,if accidents frequently happen to those other suns1 in such sort that they either lose or gain greatly in brightness1 an accident of one or other kind might well happen to our own sun1 in which case the inhabitants of this earth would perish4 ,for many of the stars1 by our supposition1 would have changed so much as either to lose their character as the defining stars of a constellation or by accession of brightness to acquire that character which in old times they had not possessed4 ,now1 assuredly1 a change of brightness competent to affect our sun's character 7as viewed from any remote star system7 in equal degree1 would be destructive to the inhabitants of the earth4 ,none at least of the higher races of animals or plants could bear the intense cold resulting from a change of the former kind1 or the intense heat resulting from a change of the latter kind4 ,yet1 if the constellations were once named because of their imagined resemblance to various objects1 and if no such resemblance can now be even imagined1 a change of one or other kind in the condition of our sun must be regarded as probable1--much in the same way that a regular traveller by train on any line must be regarded as exposed to danger1 if accidents are known to be continually happening on that line4 ,what ,i now propose to do is to inquire whether we may not find the true figures and proportions of the ancient constellations in another way--viz41 not by looking for them among the constellations as at present bounded and figured in our star-maps1 but by searching the heavens themselves for them4 ,this general method of search occurred to me very long ago while ,i was preparing various star-atlases1 but the special mode of illustration here adopted occurred to me lately1 while preparing for young astronomers in the ,united ,states a series of monthly maps showing the skies towards the north1 south1 east1 and west1 at different times of the night all the year round1 and in various latitudes within the limits of the ,states4 ,when ,i was in ,america ,i noticed1 as ,i travelled about over a tolerably wide range of latitude1 that the varying attitudes assumed by several of the constellations suggested features of resemblance to different objects4 ,in constructing maps1 simple in appearance1 but based in reality on careful calculations1 this characteristic came out more clearly4 ,adopting a particular way of presenting the connection between the various stars of a constellation1 ,i often found the figure suggested which had actually been associated with the group of stars thus connected4 ,lastly1 the idea of extending this method to other cases naturally occurred to me1 and some of the results are presented in the present essay4 ,the method of delineation referred to is simply that of connecting the stars of a group by lines1 ad libitum1 that is1 not merely introducing so many lines as will connect all the stars into a single set1 but where necessary to complete the delineation of the imagined figure1 adding other lines connecting pairs of stars belonging to the group1 yet not so many that every pair of stars is connected by a line4 ,the lines1 again1 need not be straight4 ,on the contrary1 where a group of stars forms a stream1 the natural way of joining them is by lines so curved as to follow the serpentine course thus suggested4 ,and in other cases a slight curvature of the lines joining pairs of stars will seem permissible1 because corresponding to a configuration suggested by the stars themselves4 ,it is easily seen that in some of the simplest cases1 the figure associated with a constellation is at once suggested by this method of delineation4 ,for instance1 take the case of the ,northern ,crown4 ,illustration3 ,fig4 #cb4--,the ,northern ,crown4 ,illustration3 ,fig4 #cc4--,the ,dolphin4 ,in this constellation we have a group which1 while consisting of only a few stars1 yet suggests very naturally the idea of a coronet of gems1 as shown in fig4 #cb4 ,the same is true also1 though perhaps in less degree1 of the ,dolphin1 as shown in fig4 #cc4 ,it is noteworthy1 by the way1 that this constellation can hardly have been invented by landsmen4 ,for though in our own time when the pictures of sea-creatures are accurately drawn1 so that persons who have never been to sea may have a correct idea of the figure of such creatures1 in old times it was exceedingly unlikely that any but sailors would have such familiar knowledge of the dolphin as to be reminded of that creature by a group of stars4 ,illustration3 ,fig4 #cd4--,the ,scorpion4 ,a much more complex constellation than either of those just mentioned--the ,scorpion1--is even better represented by lineation1 as shown in fig4 #cd4 ,it is not1 however1 with cases so remarkable as these that the difficulty suggested at the outset is really connected4 ,the instances of really remarkable resemblance are so few that they must be regarded as altogether exceptional4 ,the best proof that the ,scorpion is unmistakably pictured by the stars is to be found in the fact that the modern map-makers have not in this case departed much from the older delineations4 ,no one1 in fact1 who knows what a ,scorpion is like1 could have any doubt as to the configuration of the body1 at least1 of the celestial ,scorpion4 ,so that though such a case illustrates well the way in which the method of delineation ,i have suggested may be made to picture the object seen by the ancient observers in the heavens1 it does not afford any answer to the difficulty indicated by those who assert that the ,great ,bear1 the ,lion1 the ,ship1 and other of the old constellation figures1 have no real existence among the stars4 ,before leaving the ,scorpion1 however1 ,i must call attention to one or two points which this remarkable constellation seems to establish4 ,first1 it is clear that in its case real resemblance suggested the association of a group of stars with a familiar object4 ,since this resemblance remains1 we infer that the group of stars presents now an appearance closely resembling that which it presented four or five thousand years ago4 ,and as there is no special reason why the stars of the ,scorpion more than those of other constellations should retain their lustre unchanged1 we gain a certain probability for the belief that all the constellations are now very much as they were when first named4 ,indeed1 it so happens that the region occupied by the ,scorpion is perhaps that part of the heavens where changes would on the whole most probably occur1 the region of the ,milky ,way crossed by the ,scorpion being exceptionally irregular4 ,we may note also that the part of the earth where the observers lived who called this constellation the ,scorpion must have been one where the reptile is well known1 a conclusion which seems to dispose of the belief that the first astronomers lived in high latitudes4 ,let us1 now1 however1 take some of the more difficult cases4 ,we cannot do better1 perhaps1 than take at the very outset the ,great ,bear1 a constellation of which many astronomers have asserted that it no longer presents and probably never did present the slightest resemblance to a bear4 ,i would lay down1 in the first place1 the hypothesis that the stars in the region of the heavens now occupied by the ,great ,bear must have reminded the earliest observers of a large1 heavily-bodied1 small-headed1 short-eared1 and short-tailed creature1 such as either a bear or a hippopotamus4 ,next1 it may be taken for granted that the creature of which they were thus reminded was one with which they were familiar2 and as we have already seen that the inventors of the oldest constellations cannot have lived in very high latitudes1 we may conclude with great probability that the bear imagined in the heavens was not the ,polar bear1 but the bear from which the first shepherd astronomers had to defend their herds and flocks1--the ,syrian bear1 as it is commonly called1 though the species inhabited also the greater part of ,asia ,minor in former times4 ,the ,indians may be supposed to have seen the grizzly bear1 not the smaller black bear1 in the heavens4 ,the features to be looked for1 then1 among the stars1 are those common to the bears of comparatively low latitudes--not those of the polar bear4 ,so much premised we may proceed to inquire whether the region of the heavens occupied by the ,great ,bear presents such a creature with sufficient distinctness to suggest the idea of the animal to persons familiar with its aspect4 ,it is perhaps hardly necessary to remark that we must not expect to find a complete far less a perfect picture of a bear1 or lion1 or ship1 in a large region of the heavens such as is occupied by these constellations4 ,if some characteristic feature of a bear could be recognised in a group of stars1 the ancient observer would be content to recognise the region of the heavens which would be occupied by the entire figure of the animal1 as belonging to a ,great ,bear1 unless some marked peculiarity in the stars of that region absolutely prevented the most lively imagination from conceiving a bear's body there4 ,as an instance of the latter kind may be mentioned the ,bull and the ,ship1 both of which constellation figures are seen only in part4 ,the ,bull's head is exceedingly well marked1 as is the stern of the ship ,argo1 but the liveliest imagination cannot recognise the body and tail of a bull1 or the fore-part of a ship1 where these should be4 ,consequently the ancients always regarded the ,bull as a half bull1 and 7as ,aratus is careful to mention7 they recognised only the stern of the good ship ,argo4 ,but in general1 where only some marked feature of an object could be imagined1 or perhaps two or three1 they yet conceived the whole object to be shown in the heavens1 though it may have been altogether impossible to distribute the other stars over the remaining portion of the object in such a way as to show any natural association4 ,illustration3 ,fig4 #ce4--,the ,great ,bear4 ,the ,great ,bear seems to have been a constellation of this sort4 ,one can recognise the head of an animal like the bear or the hippopotamus1 and also the feet of such a creature1 but the proper disposal of the stars forming the animal's body is not so easy4 ,this would not interfere1 however1 with the choice of the bear to represent the region of stars occupied by the constellation4 ,every one who has seen faces and figures in the fire--and who has not8--knows that one or two features will suffice to suggest a resemblance2 either the imagination does all the rest1 or else the idea is suggested that some other object partially conceals that portion of the imagined figure which is wanting4 ,fig4 #ce shows how1 as ,i conceive1 a bear was figured in the heavens by those who1 in various nations1 gave to the stars of this part of the sky the name of the ,great ,bear4 ,illustration3 ,fig4 #cf4--,the ,bear's ,head4 ,it will be noticed in the first place that the famous ,septentriones 7the seven stars of the ,plough1 as in ,england the set is called1 the ,dipper as it is called in ,america1 the ,corn-measurer as it was called by the ancient ,chinese7 has little or nothing to do with the configuration of the ,bear1 though forming a part of the constellation4 ,it is the set of small stars forming the head which seems to have suggested the idea of a bear1 though two of the paws are also well defined by the stars4 ,but the outlining of the head of a bear or hippopotamus is really sufficiently close to require no very lively imagination to fill it in4 ,fig4 #cf1 giving these stars only1 serves to show this1 ,i think4 ,that the entire figure of a bear or hippopotamus was not recognised seems further shown by the figure assigned to the constellation in the ,zodiac of ,tentyra1 or ,denderah1 where it appears as in fig4 #cg4 ,the smaller figure is supposed to represent the ,little ,bear4 ,illustration3 ,fig4 #cg4--,the constellations of the ,bears1 represented as a hippopotamus 787 and wolf 787 in the ,denderah ,zodiac4 ,in the second place1 the reader familiar with the constellations will perceive that several stars not at present appertaining to the ,great ,bear are included within the configuration itself of the animal in fig4 #ce4 ,thus the third magnitude star behind the right ear belongs to the constellation of the ,dragon2 the third magnitude star near the hind quarters is ,cor ,caroli1 the chief star of the modern constellation ,canes ,venatici1 or the ,hunting ,dogs4 ,it appears to me that we ought not to expect that the first observers of the heavens1 in recognising imaginary features of resemblance between a group of stars and some known object1 would be careful to inquire whether some among those stars were included in a group which they had compared or might afterwards compare with another object4 ,it is very necessary for the astronomer of our time1 nay1 it may have even been very necessary for the astronomers of the times of ,hipparchus1 ,ptolemy1 etc41 to have the limits of the constellations clearly defined1 and to let no conspicuous star be common to different constellations4 ,but as regards the figures fancied in the heavens by the first observers of the stars1 considerations of that sort would be of no importance whatever4 ,indeed1 it is worthy of notice that even so late as the time of ,bayer1 who gave to the stars their ,greek letters1 the constellations were not separated from each other4 ,he called the star now known as ,beta ,tauri only1 ,gamma ,auriga also1 so that now ,auriga has stars ,alpha1 ,beta1 ,delta1 and so forth1 but no ,gamma4 ,similarly1 we look in vain for any star ,delta in the constellation ,pegasus1 simply because ,bayer called one and the same star ,alpha ,andromed and ,delta ,pegasi1 the astronomers of our own time retaining only the former name for this star1--the bright one adorning the head of ,andromeda4 ,even in our time it has been found impossible properly to separate the older constellations from each other1 so that to this day the ,scorpion remains entangled with the legs of ,ophiuchus1 who is further inextricably mixed up with the ,serpent4 ,in fact1 the ,serpent is divided into two separate parts by the body of ,ophiuchus1 map-makers having no choice but either to allow ,ophiuchus to divide the ,serpent1 or the ,serpent to divide ,ophiuchus4 ,illustration3 ,fig4 #ch4--,the ,original ,constellation of the ,lion4 ,in the next case1 that of the ,great ,lion1 we have still further to depart from the modern configuration of the constellation4 ,no one can imagine the remotest resemblance between any part of a lion and the grouping of stars falling on the corresponding portion of ,leo in the modern constellation4 ,the nose of the ,lion now falls near 7fig4 #ch72 and forming the outline of the mane1 the end of the tail1 the nearer fore-paw1 the nearer hind-paw4 ,the original ,lion1 ,i cannot doubt1 was imagined somewhat as pictured in fig4 #ch4 ,the head and mane are unmistakably pictured among the stars1 the paws fairly1 the relatively small quarters and the tufted tail exceedingly well--always remembering that anything like very close resemblance is not to be looked for between a widely extended group of stars and the figure of an animal or other large object4 ,if we remember also that uncultured nations1 like children1 are much quicker in imagining resemblances than those carefully trained to recognise the artistic delineation of objects1 we cannot be surprised to find that nearly all those nations who were acquainted with the lion imagined a large leonine figure in the part of the heavens now centrally occupied by our modern and most puny ,lion1 but including portions of ,cancer1 the whole of ,leo ,minor 7one of ,hevelius's absurd inventions71 the ,hair of ,berenice1 and a star or two belonging to ,virgo4 ,illustration3 ,fig4 #ci4--,the ,original ,ship ,argo4 ,we have to treat in a similar way the constellation ,argo of our present maps1 to get the good ship ,argo1 as the ancients must have conceived the constellation4 ,fig4 #ci shows the ,ship as ,i imagine she was originally pictured4 ,the stars which mark her curved poop belong in part at present 7as doubtless they have long belonged7 to the ,larger ,dog1 while those which mark the steering-oar belong to the modern constellation ,columba ,noachi1 or ,noah's ,dove4 ,it must be observed that the bright star ,canopus1 shown in the water1 was not visible in the time of the first observers in the latitude where they probably dwelt4 ,the mighty gyrating motion of the earth has caused these stars to be brought five or six degrees further from the southern pole of the heavens4 ,but ,canopus and a few of the small stars near it are the only stars which have thus been added to the constellation as seen from the regions inhabited by the first observers4 7,canopus was known to the ,arabian and ,egyptian astronomers47 ,this introduces another point which seems worth noticing4 ,at present the ship ,argo is never seen from any part of the earth's surface as pictured in fig4 #ci4 ,when due south1 the position whence in all northern latitudes the constellation is most favourably seen1 the ship is always tilted up at the stern3 one would say1 in more nautical phrase1 she is down by the head1 if the ship had any fore-part2 but from time immemorial she has been a half-ship only4 ,some #d1jjj years ago1 however1 ,argo stood nearly on an even keel when due south4 ,again1 it is to the mighty gyrational motion of the earth that we have to look for the cause of the great change in the apparent position of the ship4 ,the sphere of the fixed stars has remained all the time unchanged1 or very nearly so1 but the direction in which the earth's axis of rotation points has swayed round 7much as the axis of a reeling top sways round7 through about one-sixth part of a complete gyration4 ,in the regions where astronomy first began as a science1 ,argo not only stood on an even keel but almost on the horizon when due south2 and the features of resemblance to a ship1 which ,i have endeavoured to portray in fig4 #ci1 must have seemed much more striking there 7and then7 than now4 ,the fore-part of the ship1 or rather that region of the heavens where the fore-part should be1 is occupied by great masses of the ,milky ,way in one of its brightest and most remarkable portions4 ,i have sometimes fancied that in some of the old ,zodiac temples of star-worshippers the constellation ,argo was depicted as a mighty ship1 gemmed with stars1 and heavily laden in its fore-part with great masses of gilded cloud to represent the ,milky ,way1 and that from such representations of the constellation came the tradition of the ship ,argo and its cargo of golden fleece4 ,many parts of the story of ,jason and his companions seem to relate to objects depicted in the old constellation-domes1--as those relating to the ,dragon1 to ,hercules1 ,castor and ,pollux1 the ,centaur1 etc4 ,there is also a curious reference1 in the tradition1 to the stern of the ship1 which is much like what we can imagine as resulting from an attempt to explain the appearance of this part only1 in the set of constellation figures4 ,we read that the entrance to the ,euxine ,sea was fabled to be closed up by certain rocks called ,symplegades 7the ,clashers71 which floated on the water1 and when anything attempted to pass through came together with such velocity that not even birds could escape4 ,phineas advised them to let a bird fly through1 and if the bird passed safely1 to venture the passage4 ,it passed with only the loss of its tail2 and the ,argo1 favoured by ,juno1 and impelled by the utmost efforts of its heroic crew1 passed also1 though so narrowly that the meeting rocks carried away part of her stern-works1 which remained fixed there thenceforward4 ,for my own part1 ,i think we may not only regard the story of the ship ,argo as in reality a version1 though much modified1 of the account of ,noah's deluge1 but consider the series of constellations1 ,aquarius1 ,cetus1 ,eridanus1 ,argo1 ,corvus1 ,centaurus1 ,ara1 and ,sagittarius1 as typifying the same narrative4 ,it is somewhat curious that if we place these constellations in their original position1--that is1 as they were before the changes which the earth's great gyration has introduced during the last four thousand years or so1--we find the following coincidences with the account of the deluge4 ,first comes ,aquarius 7whose beginning would correspond with the sun's position on or about the seventeenth day of the second month of the old ,pleiades year7 pouring water4 ,his range on the ecliptic 7or the space he occupies in the annual range represented in the zodiac temple7 is about forty days4 ,then came the watery constellations ,eridanus1 the river1 and ,cetus1 the sea monster1 having1 with the ship ,argo1 a range of about #aej days of the annual circuit4 ,about forty days later in the circuit we find ,corvus1 the raven1 whose feet rest on ,hydra1 the great celestial sea-serpent1 as though no dry land could be found by the bird4 ,a dove also1 if we accept the interpretation above given of the ,argo narrative1 may have been represented in this part of the star temple4 ,next we have the ,centaur1 originally we know represented as a man only1 offering an animal as sacrifice on the altar ,ara4 ,there is a cloud of stars rising from the altar3 we may recall ,manilius's account of the constellation1-- ,ara1 ferens thuris1 stellis imitantibus1 ignem4#af ,in this cloud is the ,bow of ,sagittarius1 the bow being originally alone shown1 as it is indeed the only figure which can be imagined among the stars of this region4 ,so that these constellation figures seem to typify ,noah offering sacrifice on the ,altar1 and the ,bow of ,promise set in the cloud above the altar4 ,it is curious1 too1 that while the time of ,noah's leaving the ark was a year and ten days from the beginning of the rains1 the constellation ,sagittarius overlaps the conjoined watery signs ,capricornus and ,aquarius 7running south of them7 by about so much as would correspond to ten days of the annual circuit of the heavens4 ,the objections to the view of matters above indicated are1 first1 that the constellations referred to seem to have been formed because of real resemblance between the star-groups and the figures associated with them2 and1 secondly1 that the ,zodiac temples were probably erected by star-worshippers1 and would scarcely have been employed to typify such a narrative as that of the ,deluge4 ,the theory that the narrative itself was an attempt to interpret pictures represented on a ,zodiac temple will1 of course1 be objectionable to many readers2 though they may not be unwilling to believe that the fable of the ,argonautic expedition had its origin in some such way4 99 99 99 99 99 ,it will have been noticed that in the figures which ,i have given of the ,great ,bear1 ,lion1 and ,ship1 ,i have not altogether adhered to my idea of simply connecting the stars of a group by lines4 ,to say the truth1 although a rough notion of a bear1 lion1 or ship may thus be given1 the figure so presented is not altogether satisfactory to the mind4 ,in any case1 as for instance even in the ,scorpion 7of all these figures the best marked71 the line-figure is very imperfect4 ,but in some cases it does suggest the idea of an animal or figure1 or a part of either1 much in the same way that the idea of a human figure can be suggested by a few lines forming a skeleton figure1 such as our old friend ,tommy ,traddles used to draw4 ,now the ,lion1 ,bear1 and ,ship are not well suited for this sort of delineation1 as anyone will find who tries to suggest the idea of a bear1 lion1 or ship 7of the old-fashioned heavily-sterned sort7 by means of a few lines4 ,in order1 however1 to show that in some cases a skeleton figure can be formed by joining the stars of a constellation1 and that the figure thus formed represents 7of course in an utterly inartistic sort of way7 the object associated with those stars1 ,i will now take one or two instances in which such resemblance suggested itself to me without being specially sought for4 ,i might add to the ,crown1 ,dolphin1 and ,scorpion1 the ,chair of ,cassiopeia1 the figure of ,orion1 and the constellation of the ,cup2 ,i omit these1 however1 not because they are unfit for my purpose1 but because they so obviously illustrate my argument4 ,no one1 with the least power of imagination1 can fail to see how a chair1 a belted giant1 and a cup1 are pictured1 as it were1 in these constellations4 ,i will take others where the resemblance is less obvious4 ,thus1 ,i think scarcely anyone who is acquainted with the constellation ,andromeda can have failed to be perplexed by the association of the figure of a chained lady with this group of stars4 ,in the arrangement of the stars themselves1 without lines drawn to connect them1 no such figure can be imagined2 at least ,i fail utterly for my own part when ,i attempt to picture such a figure1 even now that ,i recognise how the figure is formed1 skeleton-wise1 by connecting lines4 ,i cannot but think this figure must have been imagined from pictures of the groups of stars with lines connecting them1 and not from the stars themselves4 ,there is this reason1 among others1 for so thinking4 ,the lady's head is represented by a single star1 ,alpherat4 ,now a single star in the sky1 however bright1 is not large enough to represent the head of a human figure like ,andromeda's4 ,but the representation of a bright star like ,alpherat in a chart or sculpture has sufficient size to serve for a head1 because size is the only way in which brightness can be indicated4 ,in fig4 #dj the stars forming the constellation ,andromeda are shown2 also the chair of ,cassiopeia2 and1 on the right1 one of the fishes and the triangle4 ,a group of stars in the upper left-hand corner marks the place of the rock to which the chains are fastened which bind ,andromeda's right hand4 ,illustration3 ,fig4 #dj4--;,andromeda4 ,it cannot be said that the skeleton picture shewn in fig4 #dj is very graceful or artistic2 but1 on the other hand1 it cannot1 ,i think1 be doubted that there is enough in it to suggest the idea of a chained person4 ,the fish naturally suggests the idea that the place is by the sea-shore4 ,and the chair suggests the idea of some one on the shore waiting and watching4 ,in our own time1 probably1 the idea suggested would be that of a person taking a bath1 while some one sat in a chair on the sands and waited for their turn4 ,but to the old observers of the heavens1 unfamiliar as they were with sea-side diversions1 the notion would more naturally occur of a woman chained to a rock1 ,lifting her long white arms1 widespread1 to the walls of the basalt2 while not far off was imagined among the stars the monster ,cetus coming onward1 bulky and black as a galley1 ,lazily coasting along1 as the fish fled leaping before it4 ,one of these fish is seen close by the figure of the chained ,andromeda4 ,near at hand they imagined the father and mother of the lady2 ,cassiopeia sitting close to the shore2 but ,cepheus far in the palace ,sat in the midst of his hall1 on his throne1 like a shepherd of people1 ,choking his woe dry-eyed1 while the slaves wailed loudly around him4 ,the story of ,andromeda1 as the reader doubtless knows1 is not of ,greek origin4 ,its real origin is lost in a far antiquity4 ,the ,indians have the same story in their astronomical mythology1 and almost the same names4 ,thus ,wilford1 in his ,asiatic ,researches1 relating his conversation with an ,indian astronomer1 says1 ,i asked him to show me in the heavens the constellation of ,antarmada1 and he immediately pointed to ,andromeda1 though ,i had not given him any information about it beforehand4 ,he afterwards brought me a very rare and curious work in ,sanscrit1 which contained a chapter devoted to ,upanachatras1 or extra-zodiacal constellations1 with drawings of ,capuja 7,cepheus71 and of ,casyapi 7,cassiopeia71 seated and holding a lotus flower in her hand2 of ,antarmada1 chained1 with the fish beside her2 and last1 of ,parasiea 7,perseus71 who1 according to the explanation of the book1 held the head of a monster which he had slain in combat2 blood was dropping from it1 and for hair it had snakes4 ,as another illustration of the method ,i have described1 ,i give the constellation ,pegasus1 or1 as it was sometimes called1 the ,half-horse4 ,i do not assert that fig4 #da presents a very well shaped steed1 any more than that in fig4 #dj a lady of exquisite proportions is pictured4 ,but one can perceive how the stars suggest the idea of a horse in one case1 and of a human figure with upraised fastened arms in the other4 ,it is commonly stated that ,pegasus is one of the constellations showing no resemblance at all to the figure associated with it4 ,i think fig4 #da suffices to show that there is some slight resemblance at least4 ,illustration3 ,fig4 #da4--,pegasus4 ,it may be mentioned1 in passing1 that all the nations of antiquity would not be likely to form equally clear conceptions of figures in the heavens4 ,there are marked differences between the various races of the human family in this respect1 just as there are marked differences between various persons in the power of imagining figures under different conditions4 ,some persons see figures at once in a cloud1 in the outline of a tree1 in a fire1 in a group of accidental markings1 and so forth2 while others not only do not see such figures1 but cannot imagine them even when their outlines are indicated4 ,so it is with different races of men4 ,there have been some which1 even when only just emerging from the utterly savage state1 possessed so much of the imaginative power as to be able to picture for themselves1 by lines cut with rude flint instruments on pieces of bone1 horn1 or ivory1 the animals with which they were familiar4 ,we have even among such pictures some belonging to an age so remote that the mammoth 7or hairy elephant7 had not yet entirely disappeared from ,europe2 for1 in the cave of ,la ,madeleine1 at ,dordogne1 among other relics of the stone age1 there has actually been found a drawing of the mammoth scratched on a piece of mammoth tusk4 ,on the other hand1 there are some races in existence at the present day1 in a more advanced stage of civilization1 who cannot perceive even in well-executed coloured drawings any resemblance to the objects pictured4 ,an aboriginal ,new ,hollander1 says ,oldfield1 being shown a coloured engraving of a member of his own tribe1 declared it to be a ship1 another a kangaroo1 and so on2 not one of a dozen identifying the portrait as having any connection with himself4 ,a rude drawing1 with all the lesser parts much exaggerated1 they can realise4 ,thus1 to give them an idea of a man1 the head must be drawn disproportionately large4 ,dr4 ,collingwood tells us that when he showed a copy of the ,illustrated ,london ,news to the ,kibalaus of ,formosa1 he found it impossible to interest them by pointing out the most striking illustrations1 which they did not appear to comprehend4 ,denham 7,i quote throughout from ,lubbock's most valuable and interesting work on the ,origin of ,civilization7 says that ,bookhaloum1 a man otherwise of considerable intelligence1 though he readily recognised figures1 could not understand a landscape4 ,i could not1 he says1 make him understand the print of the sand-wind in the desert1 which is really so well described by ,captain ,lyons' drawing4 ,he would look at it upside down2 and when ,i twice reversed it for him he exclaimed1 ',why6 why6 it's all the same4' ,a camel or a human figure was all ,i could make him understand1 and at these he was all agitation and delight4 ',gieb6 ,gieb6--wonderful6 wonderful6' ,the eyes first took his attention1 then the other features2 at the sight of the sword1 he exclaimed1 ',allah6 ,allah6' and1 on discovering the guns1 instantly exclaimed1 ',where is the powder8' ,we have in the consideration of this diversity of character between different races and nations1 as respects the power as well of imagining as of delineating figures 7the two are closely connected71 one means of judging to what race we owe the original constellations4 ,for although some figures in the heavens are manifest enough1 others require a considerable power of imagination4 ,and it should be noted that this must have been true even if we suppose 7which ,i think ,i have succeeded in showing we need not do7 that many of the stars have changed in brightness1 and that thus resemblances have disappeared which formerly existed4 ,for1 in any case1 the heavens four1 ten1 or twenty thousand years ago1 or at whatever remote period we set the original invention of the constellations1 must have presented the same characteristics as at present4 ,it can never have been the case that all the star-groups could be compared at once1 obviously1 with the figures of men and animals4 ,so that only a race of lively imagination could have found figures for all the star-groups1 as was certainly done in very remote times by some race4 ,the race1 then1 to whom we owe the general system of constellations1 was probably one with so much talent for artistic delineation that in later ages this people would have become distinguished for skill in painting and sculpture4 ,i think the sculptures found in ,babylon1 and the traditions left of the artistic skill of the ,babylonians1 correspond well with the belief that the constellations had their origin1 and astronomy its first development1 among that people or a kindred race4 ,but the chief lesson to be derived 7and ,i think it may fairly be derived7 from the study of the constellation-groups is1 that enough resemblance still remains1 if only the arbitrary boundaries invented for the constellation figures in recent times are overlooked1 to assure us that no very great changes have taken place in the aspect of the heavens for thousands of years4 ,a few stars here and there have certainly changed greatly in brightness1 and some few have changed considerably even in position2 while a considerable number have probably changed slightly in brightness1 and all1 or very nearly all1 have changed somewhat in position4 ,but on the whole the aspect of the stellar heavens now is the same as it was when the constellation figures were first imagined4 ,this thought not only assures us of the permanence of our own sun 7seeing that among the thousands of his fellow-suns which spangle the heavens so few have changed in lustre71 but seems to me to give to the study of the stars a singular charm4 ,our antiquaries and archologists present for our study the relics of long past ages1 and we may often rest assured that the objects thus gathered for us were really used in old times1 though probably in a manner not understood by us1 and when in a condition very unlike that in which they have reached our times4 ,in nearly all such instances1 however1 doubt exists as to the antiquity of the relic1 as to the race to whom it really belonged1 and as to its real use and purport4 ,but as regards the stellar heavens we have no doubt4 ,of all the objects on which the eyes of remote races have rested1 the celestial bodies are undoubtedly the most ancient1 while at the same time they and they alone were most certainly contemplated by all mankind4 ,from the very earliest ages1 from the time when the child-man first turned his thoughts from mere animal wants to the wonders of nature1 the stars1 and the sun and moon and planets must have drawn to themselves the attention of all who had eyes to see even though they had no power to understand the glories of the star-depths4 ,men pictured among the stars the objects most familiar to them1 the herds and flocks which they tended1 the herdsman himself1 the waggoner1 the huntsman1 the birds of the air1 the beasts of the field1 the fishes of the sea1 the ship1 the altar1 the bow1 the arrow1 and1 one may say1 all that according to their knowledge existed in the heavens above1 in the earth beneath1 and in the waters under the earth4 ,imperfect and anomalous as these meanings are1 in relation to modern astronomy1 with its exact methods1 elaborate instruments1 and profound investigations into the meaning of all the phenomena of the heavens1 they nevertheless retain their place1 and are likely long to do so1 in virtue of the hold which they took1 in remote ages1 on the imagination of mankind in general4 ,,footnotes3 #af ,the altar1 bearing fire of incense1 pictured by stars4 ,a remarkably bright and complex portion of the ,milky ,way lies near the constellation ,ara1 giving the appearance of smoke ascending from the altar1 only the altar must be set upright1 as in my ,gnomonic ,atlas1 not inverted as in all the modern maps4 7,it is shown properly in the old ,farnese globe74 ,illustration ,,xiii4 ,,transits ,,of ,,venus4 ,as a transit of ,venus1 visible in this country1 occurs in ,december1 #ahhb1 my readers1 although they may not care for an account of the mathematical relations involved in the observation and calculation of a transit1 will probably be interested by a simple explanation of the reasons why transits of ,venus are so important in astronomy4 ,of course it is known that a transit of ,venus is the apparent passage of the planet across the face of the sun1 when1 in passing between the earth and sun1 as she does about eight times in thirteen years1 she chances to come so close to the imaginary line joining the centres of those bodies that1 as seen from the earth1 she appears to be upon the face of the sun4 ,we may compare her to a dove circling round a dovecot1 and coming once in each circuit between an observer and her house4 ,if in her circuit she flew now higher1 now lower1 or1 in other words1 if the plane of her path were somewhat aslant1 she would appear to pass sometimes above the cot1 and sometimes below it1 but from time to time she would seem to fly right across it4 ,so ,venus1 in circuiting round the sun1 appears sometimes1 when she comes between us and the sun1 to pass above his face1 and sometimes to pass below it2 but occasionally passes right across it4 ,in such a case she is said to transit the sun's disc1 and the phenomenon is called a transit of ,venus4 ,she has a companion in these circuiting motions1 the planet ,mercury1 though this planet travels much nearer to the sun4 ,it is as though1 while a dove were flying around a dovecot at a distance of several yards1 a sparrow were circling round the cot at a little more than half the distance1 flying a good deal more quickly4 ,it will be understood that ,mercury also crosses the face of the sun from time to time--in fact1 a great deal oftener than ,venus2 but1 for a reason presently to be explained1 the transits of ,mercury are of no great importance in astronomy4 ,one occurred in #ahfa1 another in #ahfh2 another in ,may1 #ahgh2 yet very little attention was paid to those events2 and before the next transit of ,venus1 in #ahhb1 there will be a transit of ,mercury1 in ,november1 #ahha2 yet no arrangements have been made for observing ,mercury in transit on these occasions2 whereas astronomers began to lay their plans for observing the transit of ,venus in #ahhb1 as far back as #aheg4 ,the illustration which ,i have already used will serve excellently to show the general principles on which the value of a transit of ,venus depends2 and as1 for some inscrutable reasons1 any statement in which ,venus1 the sun1 and the earth are introduced1 seems by many to be regarded as1 of its very nature1 too perplexing for anyone but the astronomer even to attempt to understand1 my talk in the next few paragraphs shall be about a dove1 a dovecot1 and a window1 whereby1 perhaps1 some may be tempted to master the essential points of the astronomical question who would be driven out of hearing if ,i spoke about planets and orbits1 ascending nodes and descending nodes1 ingress and egress1 and contacts internal and external4 ,suppose ,d1 fig4 #db1 to be a dove flying between the window ,a ,b and the dovecot ,c c1 and let us suppose that a person looking at the dove just over the bar ,a sees her apparently cross the cot at the level a1 at the foot of one row of openings1 while another person looking at the dove just over the bar ,b sees her cross the cot apparently at the level b1 at the foot of the row of openings next above the row a4 ,now suppose that the observer does not know the distance or size of the cot1 but that he does know in some way that the dove flies just midway between the window and the cot2 then it is perfectly clear that the distance a b between the two rows of openings is exactly the same as the distance ,a ,b between the two window-bars2 so that our observers need only measure ,a ,b with a foot-rule to know the scale on which the dovecot is made4 ,if ,a ,b is one foot1 for instance1 then a b is also one foot2 and if the dovecot has three equal divisions1 as shown at the side1 then ,c c is exactly one yard in height4 ,illustration3 ,fig4 #db4 ,thus we have here a case where two observers1 without leaving their window1 can tell the size of a distant object4 ,and it is quite clear that wherever the dove may pass between the window and the house1 the observers will be equally able to determine the size of the cot1 if only they know the relative distances of the dove and dovecot4 ,illustration3 ,fig4 #dc4 ,illustration3 ,fig4 #dd4 ,illustration3 ,fig4 #de4 ,thus1 if ,d a is twice as great as ,d ,a1 as in fig4 #dc1 then a b is twice as great as ,a ,b1 the length which the observers know2 and if ,d a is only equal to half ,d ,a1 as in fig4 #dd1 then a b is only equal to half the known length ,a ,b4 ,in every possible case the length of a b is known4 ,take one other case in which the proportion is not quite so simple3--,suppose that ,d a is greater than ,d ,a in the proportion of #ah to #g1 as in fig4 #de2 then b a is greater than ,a ,b in the same proportion2 so that1 for instance1 if ,a ,b is a length of #g inches1 b a is a length of #ah inches4 ,we see from these simple cases how the actual size of a distant object can be learned by two observers who do not leave their room1 so long only as they know the relative distances of that object and of another which comes3 between it and them4 ,we need not specially concern ourselves by inquiring how they could determine this last point3 it is enough that it might become known to them in many ways4 ,to mention only one4 ,suppose the sun was shining so as to throw the shadow of the dove on a uniformly paved court between the house and the dovecot1 then it is easy to conceive how the position of the shadow on the uniform paving would enable the observers to determine 7by counting rows7 the relative distances of dove and dovecot4 ,now1 ,venus comes between the earth and sun precisely as the dove in fig4 #de comes between the window ,a ,b and the dovecot b a4 ,the relative distances are known exactly1 and have been known for hundreds of years4 ,they were first learned by direct observation2 ,venus going round and round the sun1 within the path of the earth1 is seen now on one side 7the eastern side7 of the sun as an evening star1 and now on the other side 7the western side7 as a morning star1 and when she seems farthest away from the sun in direction ,e ,v 7fig4 #df7 in one case1 or ,e v in the other case1 we know that the line ,e ,v or ,e v1 as the case may be1 must just touch her path2 and perceiving how far her place in the heavens is from the sun's place at those times1 we know1 in fact1 the size of either angle ,s ,e ,v or ,s ,e v1 and1 therefore1 the shape of either triangle ,s ,e ,v or ,s ,e v4 ,but this amounts to saying that we know what proportion ,s ,e bears to ,s ,v--that is1 what proportion the distance of the earth bears to the distance of ,venus4#ag ,illustration3 ,fig4 #df4 ,this proportion has been found to be very nearly that of #ajj to #gb2 so that when ,venus is on a line between the earth and sun1 her distances from these two bodies are as #bh to #gb1 or as #g to #ah4 ,illustration3 ,fig4 #dg4 ,these distances are proportioned precisely then as ,d ,a to ,d a in fig4 #de2 and the very same reasoning which was true in the case of dove and dovecot is true when for the dove and dovecot we substitute ,venus and the sun respectively1 while for the two observers looking out from a window we substitute two observers stationed at two different parts of the earth4 ,it makes no difference in the essential principles of the problem that in one case we have to deal with inches1 and in the other with thousands of miles2 just as in speaking of fig4 #de we reasoned that if ,a ,b1 the distance between the eye-level of the two observers1 is #g inches1 then b a is #ah inches1 so we say that if two stations1 ,a and ,b1 fig4 #dg1 on the earth ,e1 are #gjjj miles apart 7measuring the distance in a straight line71 and an observer at ,a sees ,venus' centre on the sun's disc at a1 while an observer at ,b sees her centre on the sun's disc at b1 then b a 7measured in a straight line1 and regarded as part of the upright diameter of the sun7 is equal to #ah1jjj miles4 ,so that if two observers1 so placed1 could observe ,venus at the same instant1 and note exactly where her centre seemed to fall1 then since they would thus have learned what proportion b a is of the whole diameter ,s ,s' of the sun1 they would know how many miles there are in that diameter4 ,suppose1 for instance1 they found1 on comparing notes1 that b a is about the #dgth part of the whole diameter1 they would know that the diameter of the sun is about #dg times #ah1jjj miles1 or about #hdf1jjj miles4 ,now1 finding the real size of an object like the sun1 whose apparent size we can so easily measure1 is the same thing as finding his distance4 ,any one can tell how many times its own diameter the sun is removed from us4 ,take a circular disc an inch in diameter1--a halfpenny1 for instance--and see how far away it must be placed to exactly hide the sun4 ,the distance will be found to be rather more than #ajg inches1 so that the sun1 like the halfpenny which hides his face1 must be rather more than #ajg times his own diameter from us4 ,but #ajg times #hdf1jjj miles amounts to #ij1ebb1jjj miles4 ,this1 therefore1 if the imagined observations were correctly made1 would be the sun's distance4 ,i shall next show how ,halley and ,delisle contrived two simple plans to avoid the manifest difficulty of carrying out in a direct manner the simultaneous observations just described1 from stations thousands of miles apart4 ,we have seen that the determination of the sun's distance by observing ,venus on the sun's face would be a matter of perfect simplicity if we could be quite sure that two observations were correctly made1 and at exactly the same moment1 by astronomers stationed one far to the north1 the other far to the south4 ,illustration3 ,fig4 #dh4 ,the former would see ,venus as at ,a1 fig4 #dh1 the other would see her as at ,b2 and the distance between the two lines a a and b b along which her centre is travelling1 as watched by these two observers1 is known quite certainly to be #ah1jjj miles1 if the observers' stations are #g1jjj miles apart in a north-and-south direction 7measured in a straight line74 ,thence the diameter ,s ,s of the sun is determined1 because it is observed that the known distance a b is such and such a part of it4 ,and the real diameter in miles being known1 the distance must be #ajg times as great1 because the sun looks as large as any globe would look which is removed to a distance exceeding its own diameter 7great or small7 #ajg times4 ,but unfortunately it is no easy matter to get the distance a b1 fig4 #dh1 determined in this simple manner4 ,the distance #ah1jjj miles is known2 but the difficulty is to determine what proportion the distance bears to the diameter of the sun ,s ,s4 ,all that we have heard about ,halley's method and ,delisle's method relates only to the contrivances devised by astronomers to get over this difficulty4 ,it is manifest that the difficulty is very great4 ,illustration3 ,fig4 #di4 ,for1 first1 the observers would be several thousand miles apart4 ,how then are they to ensure that their observations shall be made simultaneously8 ,again1 the distance a b is really a very minute quantity1 and a very slight mistake in observation would cause a very great mistake in the measurement of the sun's distance4 ,accordingly1 ,halley devised a plan by which one observer in the north 7or as at ,a1 fig4 #dg7 would watch ,venus as she traversed the sun's face along a lower path1 as a a fig4 #di2 while another in the south 7or as at ,b1 fig4 #dg7 would watch her as she traversed a higher path1 as b b fig4 #di4 ,by timing her they could tell how long these paths were1 and therefore how placed on the sun's face1 as in fig4 #di2 that is1 how far apart1 which is the same thing as determining b a1 fig4 #dh4 ,this was ,halley's plan1 and as it requires that the duration of the transit should be timed1 it is called the method of durations4 ,delisle proposed another method--viz41 that one observer should time the exact moment when ,venus1 seen from one station1 began to traverse the path a a1 while another should time the exact moment when she began to traverse the path b b2 this would show how much b is in advance of a1 and thence the position of the two paths can be determined4 ,or two observers might note the end of the transit1 thus finding how much a is in advance of b ,this is ,delisle's method1 and it has this advantage over ,halley's--that an observer is only required to see either the beginning or the end of the transit1 not both4 ,i shall not here consider1 except in a general way1 the various astronomical conditions which affect the application of these two methods4 ,of course1 all the time that a transit lasts1 the earth is turning on her axis2 and as a transit may last as long as eight hours1 and generally lasts from four to six hours1 it is clear that the face of the earth turned towards the sun must change considerably between the beginning and end of a transit4 ,so that ,halley's method1 which requires that the whole duration of a transit should be seen1 is hampered with the difficulty arising from the fact that a station exceedingly well placed for observing the beginning of the transit might be very ill placed for observing the end1 and vice vers4 ,delisle's method is free from this objection1 because an observer has only to note the beginning or the end1 not both4 ,but it is hampered by another4 ,two observers who employ ,halley's method have each of them only to consider how long the passage of ,venus over the sun's face lasts2 and they are so free from all occasion to know the exact time at which the transit begins and ends1 that theoretically each observer might use such an instrument as a stop-watch1 setting it going 7right or wrong as to the time it showed7 when the transit began1 and stopping it when the transit was over4 ,but for ,delisle's method this rough-and-ready method would not serve4 ,the two observers have to compare the two moments at which they severally saw the transit begin1--and to do this1 being many thousand miles apart1 they must know the exact time4 ,suppose they each had a chronometer which had originally been set to ,greenwich time1 and which1 being excellently constructed and carefully watched1 might be trusted to show exact ,greenwich time1 even though several months had elapsed since it was set4 ,then all the requirements of the method would be quite as well satisfied as those of the other method would be if the stop-watches just spoken of went at a perfectly true rate during the hours that the transit lasted4 ,but it is one thing to construct a time-measure which will not lose or gain a few seconds in a few hours1 and quite another to construct one which will not lose or gain a few seconds in a journey of many thousand miles1 followed perhaps by two or three months' stay at the selected station4 ,an error of five seconds would be perfectly fatal in applying ,delisle's method1 and no chronometer could be trusted under the conditions described to show true time within ten or twelve seconds4 ,hence astronomers had to provide for other methods of getting true time 7say ,greenwich time7 than the use of chronometers2 and on the accuracy of these astronomical methods of getting true time depended the successful use of ,delisle's method4 ,illustration3 ,fig4 #ej4 ,illustration3 ,fig4 #ea4 ,then another difficulty had to be considered1 which affected both methods4 ,it was agreed by both ,halley and ,delisle that the proper moment to time the beginning or end of transit was the instant when ,venus was just within the sun's disc1 as in fig4 #ej1 either having just completed her entry1 or being just about to begin to pass off the sun's face4 ,if at this moment ,venus presented a neatly defined round disc1 exactly touching the edge of the sun1 also neatly defined1 this plan would be perfect4 ,at the very instant when the contact ceased at the entry of ,venus1 the sun's light would break through between the edges of the two discs1 and the observer would only have to note that instant2 while1 when ,venus was leaving the sun1 he would only have to notice the instant when the fine thread of light was suddenly divided by a dark point4 ,but unfortunately ,venus does not behave in this way1 at least not always4 ,with a very powerful and very excellent telescope1 in perfectly calm1 clear weather1 and with the sun high above the horizon1 she probably behaves much as ,halley and ,delisle expected4 ,but under less favourable conditions1 she presents at the moment of entry or exit some such appearance as is shown in figures #ea1 #eb1 and #ec1 while with a very low sun she assumes all sorts of shapes1 continually changing1 being for one moment1 perhaps1 as in one or other of figs4 #ea1 #eb1 and #ec1 and in the next distorted into some such pleasing shape as is pictured in fig4 #ed4 ,illustration3 ,fig4 #eb4 ,illustration3 ,fig4 #ec4 ,accordingly1 many astronomers are disposed to regard both ,halley's method and ,delisle's as obsolete1 and to place reliance on the simple method of direct observation first described4 ,they would1 however1 of course bring to their aid all the ingenious devices of modern astronomical observation in order to overcome the difficulties inherent in that method4 ,one of the contrivances naturally suggested to meet such difficulties is to photograph the sun with ,venus upon his face4 ,the ,american astronomers1 in particular1 consider that the photographic results obtained during the transit of #ahgd will outweigh those obtained by all the other methods4 ,the ,german and ,russian astronomers1 as well as those of ,lord ,lindsay's expedition1 while placing great reliance on photography1 employed also a method of measuring the position of ,venus on the sun's disc1 by means of a kind of telescope specially constructed for such work1 the peculiarities of which need not be here considered4 ,illustration3 ,fig4 #ed4 ,the observations made in #agfi were so imperfect that astronomers deduced a distance fully #c1jjj1jjj miles too great4 ,of late1 other methods of observation had set them much nearer the true distance1 which has been judged to lie certainly between #ia1hjj1jjj miles and #ib1fjj1jjj miles--a tolerably wide range4 ,but it may perhaps occur to some that the distance of the sun may be changing4 ,the earth might be drawing steadily in towards the sun1 and so all our measurements might be deceptive4 ,nay1 the painful thought might present itself that when the observations of #agfi were made1 the sun really was farther away than at present by more than #c1jjj1jjj of miles4 ,if this were so1 the earth would1 in the course of a century1 have reduced her distance by fully one-thirtieth part1 so that1 supposing the approach to continue1 she would in #c1jjj years fall into the sun1 while1 long before that period had elapsed1 the increased heat to which she would be exposed would render life impossible4 ,fortunately1 we know quite certainly that no such approach is taking place4 ,it is known that the distance of the earth from the sun cannot change without a corresponding change in her period of revolution--that is1 in the length of the year4 ,the law connecting these two 7indicated in the note1 page #bgi7 is such that1 on the reduction of the distance by any moderate portion the period would be reduced by a portion half as great again4 ,for instance3 if the distance of the earth from the sun were reduced by a thirtieth part 7or about #c1jjj1jjj miles7 the length of the year would be reduced by a thirtieth and half a thirtieth--that1 is1 by a twentieth part1 or by more than eighteen days4 ,we know that no such change has taken place during the last century1 or since the beginning of history4 ,nay1 from the ,chaldean estimate of the length of the year1 which only exceeded ours by about two minutes1 it is easily shown that the distance of the earth from the sun has not diminished #bjj miles within the last #b1ejj years4 ,so that1 assuming even that the earth is approaching the sun at this rate1 or eight miles in a century1 it would be #a1bej1jjj years before the distance would be diminished by #ajj1jjj miles1 which is the probable limit of error in the determination of the sun's distance4 ,if1 finally1 it be asked1 ,what1 after all1 is the use of determining the sun's distance8 the answer we shall give must depend on the answer given to the question1 ,what1 after all1 is the use of knowing any facts in astronomy other than those useful in navigation1 surveying1 and so on8 ,and ,i think that this question would introduce another and a wider one--viz41 ,what is the use of that quality in man's nature which makes him seek after knowledge for its own sake8 ,i certainly do not propose to consider this question1 nor do ,i think that the reader will find any difficulty in understanding why ,i do not4 ,but accepting the facts3 7#a7 that we are so constituted as to seek after knowledge2 and 7#b7 that knowledge about the celestial orbs is interesting to us1 quite apart from the use of such knowledge in navigation and surveying1 it is easy to show that the determination of the sun's distance is a matter full of interest4 ,for on our estimate of the sun's distance depend our ideas as to the scale1 not only of the solar system1 but of the whole of the visible universe4 ,the size of the sun1 his mass1 and therefore his might1 the scale of those wonderful operations which we know to be taking place upon1 and within1 and around the sun2 all these relations1 as well as our estimate of the size and mass of every planet1 and therefore our estimate of the earth's relative importance in the solar system1 depend absolutely and directly on the estimate we form of the sun's distance4 ,such being the case 7this being in point of fact the cardinal problem of dimensional astronomy7 it cannot but be thought that1 great as were the trouble and expense of the expeditions sent out to observe the transit of #ahgd1 they were devoted to an altogether worthy cause4 ,,footnotes3 #ag ,there is1 however1 a much more perfect way of determining this proportion1 by applying the law which ,kepler found to connect the distances of the planets from the sun with the times in which they complete the circuits of their orbits4 ,the law is that1 if we take any two planets1 and write down the numbers expressing their periods of circuit 7say in days71 and the numbers expressing their distances from the sun 7say in miles7 in the same order2 then if we multiply each number of the first pair into itself1 and each number of the second pair twice into itself1 the four numbers thus obtained will be proportional2 that is to say1 as the first is to the second1 so will the third be to the fourth4 ,now1 as every one knows who has worked sums in the rule of three1 when any three are given out of four proportionals1 the fourth can always be found2 but we know the periods of circuit both of the earth and ,venus 7#cfebefd days and #bbdgjjh days respectively7 very exactly indeed1 because they have traversed their orbits so many times since they began to be observed by astronomers4 ,we can call the earth's distance #ajj1 and then applying the rule just stated1 we get ,venus' distance relatively to the earth's4 ,the reader who cares to work out this little sum will find no difficulty whatever--if at least he is able to extract the cube roots of any number4 ,the proportion runs thus3-- #cfebefd #cfebefd 3 #bbdgjjh #bbdgjjh 33 #ajj #ajj #ajj 3 7,venus' distance cubed47 ,work out this sum and we get for ,venus' distance #gbccc4 ,the ratio of ,venus' distance to the earth's is almost exactly expressed by the numbers #bag and #cjj4 ,hazell1 ,watson1 and ,viney1 ,printers1 ,london and ,aylesbury4 99 99 99 99 99 ,transcriber's ,notes3 ,italic text is denoted by underscores4 ,obvious printer's errors corrected4 ,every effort has been made to replicate this text as faithfully as possible1 including non-standard punctuation1 inconsistently hyphenated words1 and other inconsistencies4