,,the ,,children',s ,,book ,,of ,,stars ,,the ,,children',s ,,book ,,of ,,stars ,,mitton ,a4,c4 ,,black ,illustration3 ,,the ,,moon-,,child ,,must ,,keep ,,on ,,running ,,round ,,her4 ,p4 #aa4 ,,the ,,children',s ,,book ,,of ,,stars ---------------------------------------- --------- ,,by ,,the ,,same ,,author ,,children',s ,,book ,,of ,,london ,,containing #ab ,,full-,,page ,,illustrations ,,in ,,colour ,,by ,,john ,,williamson ,,price #fs4 ',the stories are told in a way that is bound to rivet attention1 and the historical sketches will leave a lasting impression on the minds of young readers which will be very useful when their studies in history become more advanced4'--,scotsman4 ,,animal ,,autobiographies ,,the ,,dog ,,with #ab ,,full-,,page ,,illustrations ,,in ,,colour ,,by ,j4 ,,williamson ,,price #fs4 ',a true life history1 written out of the fulness of first-hand knowledge by an author who is thoroughly acquainted with all the ways of the friend of man4'--,glasgow ,herald4 ',the story is admirably told in clear and fascinating language4'--,freeman's ,journal4 ,a4 ,c4 ,,black4 ,,soho ,,square4 ,,london1 ,w4 ---------------------------------------- --------- ,,agents ,,america ,,the ,,macmillan ,,company #fd #ff ,,fifth ,,avenue1 ,,new ,,york ,,canada ,,the ,,macmillan ,,company ,,of ,,canada1 ,,ltd4 #bg ,,richmond ,,street ,,west1 ,,toronto ,,india ,,macmillan ,,company1 ,,ltd4 ,,macmillan ,,building1 ,,bombay #cji ,,bow ,,bazaar ,,street1 ,,calcutta ,,the ,,children',s ,,book ,,of ,,stars ,,by ,g4 ,e4 ,,mitton ,,author ,,of ',,the ,,children',s ,,book ,,of ,,london1' ',,animal ,,autobiographies3 ,,the ,,dog1' ,,etc4 ,,london ,,adam ,,and ,,charles ,,black #aijg ,published ,september1 #aijg ,,preface ,it was the intention of the late ,agnes ,clerke to write the preface to this ',children's ,book of ,stars4' ,miss ,clerke took a warm and sympathetic interest in the authoress and her work1 but her lamented death occurred before this kindly intention could be fulfilled4 ,i cannot pretend to write adequately as her substitute1 but ,i could not resist the appeal made to me by the author1 in the name and for the sake of her dear friend and mine1 to write a few words of introduction4 ,i am in no way responsible either for the plan or for any portion of this work1 but ,i can commend it as a book1 written in a simple and pleasant style1 calculated to awaken the interest of intelligent children1 and to enable parents otherwise ignorant or astronomy to answer many of those puzzling questions which such children often put4 ,,david ,,gill4 ,,author',s ,,note ,this little work is the outcome of many suggestions on the part of friends who were anxious to teach their small children something of the marvels of the heavens1 but found it exceedingly difficult to get hold of a book wherein the intense fascination of the subject was not lost in conventional phraseology--a book in which the stupendous facts were stated in language simple enough to be read aloud to a child without paraphrase4 ,whatever merit there may be in the present work is due entirely to my friend ,agnes ,clerke1 the well-known writer on astronomy2 the faults are all my own4 ,she gave me the impetus to begin by her warm encouragement1 and she helped me to continue by hearing every chapter read as it was written1 and by discussing its successor and making suggestions for it4 ,thus she heard the whole book in ,,ms4 ,a week after the last chapter had been read to her ,i started on a journey lasting many months1 and while ,i was in the ,far ,east the news reached me of her death1 by which the world is the poorer4 ,for her sake1 as he has stated1 her friend ,sir ,david ,gill1 ,k4,c4,b41 kindly undertook to supply the missing preface4 ,g4 ,e4 ,,mitton4 ,,contents ,,chapter ,i ,,page ,,the ,,earth #a ,,chapter ,,ii ,,hanging ,,in ,,space #ac ,,chapter ,,iii ,,the ,,shining ,,moon #ba ,,chapter ,,iv ,,the ,,earth',s ,,brothers ,,and ,,sister #cb ,,chapter ,v ,,four ,,small ,,worlds #dh ,,chapter ,,vi ,,four ,,large ,,worlds #fg ,,chapter ,,vii ,,the ,,sun #hi ,,chapter ,,viii ,,shining ,,visitors #ajc ,,chapter ,,ix ,,shooting ,,stars ,,and ,,fiery ,,balls #abj ,,chapter ,x ,,the ,,glittering ,,heavens #ace ,,chapter ,,xi ,,the ,,constellations #adh ,,chapter ,,xii ,,what ,,the ,,stars ,,are ,,made ,,of #aei ,,chapter ,,xiii ,,restless ,,stars #agj ,,chapter ,,xiv ,,the ,,colours ,,of ,,the ,,stars #agf ,,chapter ,,xv ,,temporary ,,and ,,variable ,,stars #ahh ,,chapter ,,xvi ,,star ,,clusters ,,and ,,nebul #aig ,,illustrations ,,printed ,,in ,,colour ,,the ,,moon-,,child ,,must ,,keep ,,on ,,running ,,round ,,her ,frontispiece ,,facing ,,page ,,the ,,earth ,,and ,,moon ,,hanging ,,in ,,space #af ,,the ,,english ,,summer ,,and ,,winter #dj ,,jupiter ,,and ,,one ,,of ,,his ,,moons #gj ,,the ,,planet ,,saturn ,,and ,,two ,,of ,,his ,,moons #gh ,,flames ,,from ,,the ,,sun #ajj ,,the ,,comet ,,in ,,the ,,bayeux ,,tapestry #ajd ,a ,,stick ,,thrust ,,into ,,the ,,water ,,appears ,,crooked #aad ,,constellations ,,near ,,the ,,pole ,,star #aej ,,orion ,,and ,,his ,,neighbours #aed ,,the ,,spectrum ,,of ,,the ,,sun ,,and ,,sirius #afh ,,illustrations ,,in ,,black ,,and ,,white ,,page ,,the ,,moon facing #bd ,,an ,,eclipse ,,of ,,the ,,moon #bh ,,an ,,eclipse ,,of ,,the ,,sun #bi ,,the ,,moon ,,raising ,,the ,,tides #cj ,,comparative ,,sizes ,,of ,,the ,,planets #ce ,,different ,,phases ,,of ,,venus #ea ,,orbits ,,of ,,mars1 ,,the ,,earth1 ,,venus1 ,,and ,,mercury #ee ,,map ,,of ,,mars facing #ef ,,orbits ,,of ,,the ,,earth ,,and ,,mars #fc ,,jupiter ,,and ,,his ,,principal ,,moons #gb ,,sun-,,spots facing #ih ,a ,,great ,,comet #aah ,,the ,,great ,,nebula ,,in ,,andromeda #bjb ,,the ,,children',s ,,book ,,of ,,stars ,,chapter ,i ,,the ,,earth ,it is a curious fact that when we are used to things1 we often do not notice them1 and things which we do every day cease to attract our attention4 ,we find an instance of this in the curious change that comes over objects the further they are removed from us4 ,they grow smaller and smaller1 so that at a distance a grown-up person looks no larger than a doll2 and a short stick planted in the ground only a few feet away appears as long as a much longer one at ten times the distance4 ,this process is going on all round us every minute3 houses1 trees1 buildings1 animals1 all seem larger or smaller in proportion to their distance from us4 ,sometimes ,i have seen a row of raindrops hanging on a bar by the window4 ,when the sun catches one of them1 it shines so brilliantly that it is as dazzling as a star2 but my sense tells me it is a raindrop1 and not a star at all4 ,it is only because it is so near it seems as bright and important as a mighty star very1 very far away4 ,we are so much accustomed to this fact that we get into a habit of judging the distance of things by their size4 ,if we see two lights shining on a dark night1 and one is much larger than the other1 we think that the bright one must be nearer to us2 yet it need not necessarily be so1 for the two lights might possibly be at the same distance from us1 and one be large and the other small4 ,there is no way in which we can tell the truth by just looking at them4 ,now1 if we go out on any fine moonlight night and look up at the sky1 we shall see one object there apparently much larger than any other1 and that is the moon1 so the question that occurs to us at once is1 ,is the moon really very much larger than any of the stars1 or does it only seem so because it is very much nearer to us8 ,as a matter of fact1 the moon is one of the smallest objects in view1 only1 as it is our nearest neighbour1 it appears very conspicuous4 ,having learned this1 we shall probably look about to see what else there is to attract attention1 and we may notice one star shining very brilliantly1 almost like a little lamp1 rather low down in the sky1 in that part of it where the sun has lately set4 ,it is so beautifully bright that it makes all the others look insignificant in comparison1 yet it is not really large compared with the others1 only1 as it comes nearer to us than anything else in the sky except the moon1 it looks larger than it has any right to do in comparison with the others4 ,after this we might jump to the conclusion that all the bright large stars are really small and near to us1 and all the faintly shining ones large and far away4 ,but that would not be true at all1 for some bright ones are very far away and some faint ones comparatively near1 so that all we can do is to learn about them from the people who have studied them and found out about them1 and then we shall know of our own knowledge which of them seem bright only because they are nearer than the others1 and which are really very1 very brilliant1 and so still shine brightly1 though set in space at an almost infinite distance from us4 ,the sun1 as we all know1 appears to cross the sky every day2 he gets up in the east and drops down in the west1 and the moon does the same1 only the moon is unlike the sun in this1 that it changes its shape continually4 ,we see a crescent moon growing every night larger and larger1 until it becomes full and fat and round1 and then it grows thinner and thinner1 until it dies away2 and after a little while it begins again1 and goes through all the same changes once more4 ,i will tell you why this is so further on1 when we have a chapter all about the moon4 ,if you watch the stars quietly for at least five minutes1 you will see that they too are moving steadily on in the same way as the sun and moon4 ,watch one bright star coming out from behind a chimney-pot1 and after about five minutes you will see that it has changed its place4 ,yet this is not true of all1 for if we watch carefully we shall find that some1 fairly high up in the sky1 do not appear to move at all4 ,the few which are moving so slowly that they seem to us to stand still are at a part of the sky close to the ,pole ,star1 so called because it is always above the ,north ,pole of the earth4 ,i will explain to you how to find it in the sky for yourselves later on1 but now you can ask anyone to point it out4 ,watch it4 ,it appears to be fixed in one place1 while the other stars are swinging round it in circles4 ,in fact1 it is as if we on the earth were inside a great hollow globe or ball1 which continually turned round1 with the ,pole ,star near the top of the globe2 and you know that if you put your finger on the spot at the top of a spinning globe or ball1 you can hold it there while all the rest of the ball runs round4 ,now1 if you had to explain things to yourself1 you would naturally think3 ',here is the great solid earth standing still1 and the sun and moon go round it2 the stars are all turning round it too1 just as if they were fixed on to the inside of a hollow globe2 we on the earth are in the middle looking up at them2 and this great globe is slowly wheeling round us night by night4' ,in the childhood of the world men believed that this was really true--that the earth was the centre of the universe1 that the sun and moon and all the hosts of heaven were there solely to light and benefit us2 but as the world grew wiser the wonders of creation were fathomed little by little4 ,some men devoted their whole lives to watching the heavens1 and the real state of things was gradually revealed to them4 ,the first great discovery was that of the daily movement of the earth1 its rotation on its own axis1 which makes it appear as if all these shining things went round it4 ,it is indeed a very difficult matter to judge which of two objects is moving unless we can compare them both with something outside4 ,you must have noticed this when you are sitting in a train at a station1 and there is another train on the other side of yours4 ,for if one of the trains moves gently1 either yours or the other1 you cannot tell which one it is unless you look at the station platform2 and if your position remains the same in regard to that1 you know that your train is still standing1 while the other one beside it has begun to move4 ,and ,i am quite sure that there is no one of us who has not1 at one time or another1 stood on a bridge and watched the water running away underneath until we felt quite dizzy1 and it seemed as if the water were standing still and the bridge1 with ourselves on it1 was flying swiftly away backwards4 ,it is only when we turn to the banks and find them standing still1 that we realize the bridge is not moving1 and that it is the running water that makes it seem to do so4 ,these everyday instances show us how difficult it is to judge whether we are moving or an outside object unless we have something else to compare with it4 ,and the marvellous truth is that1 instead of the sun and moon and stars rolling round the earth1 it is the earth that is spinning round day by day1 while the sun and the stars are comparatively still2 and1 though the moon does move1 yet when we see her get up in the east and go down in the west that is due to our own movement and not to hers4 ,the earth turns completely round once in a day and night4 ,if you take an orange and stick a knitting-needle through it1 and hold it so that the needle is not quite straight up but a little slanting1 and then twirl it round1 you will get quite a good idea of the earth1 though of course there is no great pole like a gigantic needle stuck through it1 that is only to make it easy for you to hold it by4 ,in spinning the orange you are turning it as the earth turns day by day1 or1 as astronomers express it1 as it rotates on its axis4 ,there is a story of a cruel ,eastern ,king who told a prisoner that he must die if he did not answer three questions correctly1 and the questions were very difficult2 this is one of them3 ',how long would it take a man to go round the earth if he never stopped to eat or drink on the way8' ,and the prisoner answered promptly3 ',if he rose with the sun and kept pace with it all day1 and never stopped for a moment to eat or drink1 he would take just twenty-four hours1 ,your ,royal ,highness4' ,for in those days it was supposed that the sun went round the earth4 ,everyone is so remarkably clever nowadays that ,i am sure there will be someone clever enough to object that1 if what ,i have said is true1 there would be a great draught1 for the air would be rushing past us4 ,but1 as a matter of fact1 the air goes with us too4 ,if you are inside a railway carriage with the windows shut you do not feel the rush of air1 because the air in the carriage travels with you2 and it is the same thing on the earth4 ,the air which surrounds the earth clings to it and goes round with it1 so there is no continuous breeze from this cause4 ,but the spinning round on its own axis is not the earth's only movement1 for all the time it is also moving on round the sun1 and once in a whole year it completes its journey and comes back to the place from whence it started4 ,thus the turning round like a top or rotating on its axis makes the day and night1 and the going in a great ring or revolving round the sun makes the years4 ,our time is divided into other sections besides days and years4 ,we have1 for instance1 weeks and months4 ,the weeks have nothing to do with the earth's movements2 they are only made by man to break up the months2 but the months are really decided by something over which we have no control4 ,they are due to the moon1 and1 as ,i have said already1 the moon must have a chapter to herself1 so we won't say any more about the months here4 ,if any friend of ours goes to ,india or ,new ,zealand or ,america1 we look upon him as a great traveller2 yet every baby who has lived one year on the earth has travelled millions of miles without the slightest effort4 ,every day of our lives we are all flung through space without knowing it or thinking of it4 ,it is as if we were all shut up in a comfortable travelling car1 and were provided with so many books and pictures and companions that we never cared to look out of the windows1 so that hour by hour as we were carried along over miles of space we never gave them a thought4 ,even the most wonderful car ever made by man rumbles and creaks and shakes1 so that we cannot help knowing it is moving2 but this beautiful travelling carriage of ours called the earth makes never a creak or groan as she spins in her age-long journey4 ,it is always astonishing to me that so few people care to look out of the window as we fly along2 most of them are far too much absorbed in their little petty daily concerns ever to lift their eyes from them4 ,it is true that sometimes the blinds are down1 for the sky is thickly covered with clouds1 and we cannot see anything even if we want to4 ,it is true also that we cannot see much of the scenery in the daytime1 for the sun shining on the air makes a veil of blue glory1 which hides the stars2 but on clear nights we can see on every side numbers of stars quite as interesting and beautiful as any landscape2 and yet millions of people never look up1 never give a thought to the wonderful scenery through which their car is rushing4 ,by reason of the onward rush of the earth in space we are carried over a distance of at least eighteen miles every second4 ,think of it3 as we draw a breath we are eighteen miles away in space from the point we were at before1 and this goes on unceasingly day and night4 ,these astonishing facts make us feel how small and feeble we are1 but we can take comfort in the thought that though our bodies are insignificant1 the brain of man1 which has discovered these startling facts1 must in itself be regarded as one of the most marvellous of all the mysteries amid which we live4 ,well1 we have arrived at some idea of our earth's position2 we know that the earth is turning round day by day1 and progressing round the sun year by year1 and that all around lie the sentinel stars1 scattered on a background of infinite space4 ,if you take an older boy or girl and let him or her stand in the middle to represent the sun1 then a smaller one would be the earth1 and the smallest of all the moon2 only in truth we could never get anyone large enough to represent the sun fairly1 for the biggest giant that ever lived would be much too small in proportion4 ,the one representing the sun must stand in the middle1 and turn slowly round and round4 ,then let the earth-child turn too1 and all the time she is spinning like a top she must be also hastening on in a big ring round the sun2 but she must not go too fast1 for the little moon-child must keep on running round her all the time4 ,and the moon-child must keep her face turned always to the earth1 so that the earth never sees her back4 ,that is an odd thing1 isn't it8 ,we have never seen the other side of the moon1 which goes round us1 always presenting the same face to us4 ,the earth is not the only world going round the sun2 she has many brothers and a sister2 some are nearer to the sun than she is1 and some are further away1 but all circle round the great central light-giver in rings lying one outside the other4 ,these worlds are called planets1 and the earth is one of them1 and one of the smaller ones1 too1 nothing so great and important as we might have imagined4 ,,chapter ,,ii ,,hanging ,,in ,,space ,if you are holding something in your hand and you let it go1 what happens8 ,it falls to the ground1 of course4 ,now1 why should it do so8 ,you will say3 ',how could it do anything else8' ,but that is only because you are hampered by custom4 ,try to shake yourself free1 and think1 ,why should it go down instead of up or any other way8 ,the first man who was clever enough to find some sort of an answer to this question was the great philosopher ,sir ,isaac ,newton1 though he was not quite the first to be puzzled by it4 ,after years of study he discovered that every thing attracts every other thing in proportion to their masses 7which is what you know as weight7 and their distance from each other4 ,in more scientific language1 we should say every body instead of every thing1 for the word body does not only mean a living body1 but every lump or mass of matter in the universe4 ,the earth is a body in this sense1 and so is the table or anything else you could name4 ,now as the earth is immeasurably heavier than anything that is on it1 it pulls everything toward itself with such force that the little pulls of other things upon each other are not noticed4 ,the earth draws us all toward it4 ,it is holding us down to it every minute of the day4 ,if we want to move we have to exert another force in order to overcome this attraction of the earth1 so we exert our own muscles and lift first one foot and then the other away from the earth1 and the effort we make in doing this tires us4 ,all the while you are walking or running you are exercising force to lift your feet away from the ground4 ,the pull of the earth is called gravitation4 ,just remember that1 while we go on to something else which is almost as astonishing4 ,we know that nothing here on earth continues to move for ever2 everything has to be kept going4 ,anything left to itself has a tendency to stop4 ,why is this8 ,this is because here in the world there is something that fights against the moving thing and tries to stop it1 whether it be sent along the ground or thrown up in the air4 ,you know what friction is1 of course4 ,if you rub your hands along any rough substance you will quickly feel it1 but on a smooth substance you feel it less4 ,that is why if you send a stone spinning along a carpet or a rough road it stops comparatively soon1 whereas if you use the same amount of force and send it along a sheet of ice it goes on moving much longer4 ,this kind of resistance1 which we call friction1 is one of the causes which is at work to bring things to a standstill2 and another cause is the resistance of the air1 which is friction in another form4 ,it may be a perfectly still day1 yet if you are bicycling you are breaking through the air all the time1 just as you would be through water in swimming1 only the resistance of the air is less than that of water4 ,as the friction or the resistance of the air1 or both combined1 gradually lessens the pace of the stone you sent off with such force1 the gravitation of the earth begins to be felt4 ,when the stone first started the force you gave to it was enough to overcome the gravitation force1 but as the stone moves more slowly the earth-pull asserts itself1 and the stone drops down to the ground and lies still upon the surface4 ,now1 if there were no friction1 and therefore no resistance1 there would be no reason why anything once set moving should not go on moving for ever4 ,the force you give to any object you throw is enough to overcome gravitation2 and it is only when the first force has been diminished by friction that the earth asserts its authority and pulls the moving object toward it4 ,if it were possible to get outside the air and out of reach of the pull of the earth1 we might fling a ball off into space1 and it would go on in a straight line until something pulled it to itself by the force of gravity4 ,gravitation affects everything connected with the earth2 even our air is held to the earth by gravitation4 ,it grows thinner and thinner as we get further away from the earth4 ,at the top of a high mountain the air is so thin that men have difficulty in breathing1 and at a certain height they could not breathe at all4 ,as they cannot breathe in very fine air1 it is impossible for them to tell by personal experiment exactly where the air ends2 but they have tried to find out in other ways1 and though different men have come to different conclusions on the subject1 it is safe to say that at about two hundred miles above the earth there is nothing that could be called air4 ,thus we can now picture our spinning earth clothed in a garment of air that clings closely about her1 and grows thinner and thinner until it melts away altogether1 for there is no air in space4 ,illustration3 ,,the ,,earth ,,and ,,moon ,,hanging ,,in ,,space ,now in the beginning ,god made the world1 and set it off by a first impulse4 ,we know nothing about the details1 though further on you shall hear what is generally supposed to have taken place2 we only know that1 at some remote age1 this world1 probably very different from what it is now1 together with the other planets1 was sent spinning off into space on its age-long journey4 ,these planets were not sent off at random1 but must have had some particular connection with each other and with the sun1 for they all belong to one system or family1 and act and react on each other4 ,now1 if they had been at rest and not in movement1 they would have fallen right into the sun1 drawn by the force of gravitation2 then they would have been burned up1 and there would have been an end of them4 ,but the first force had imparted to them the impulse to go on in a straight line1 so when the sun pulled the result was a movement between the two3 the planets did not continue to move in a straight line1 neither did they fall on to the sun1 but they went on a course between the two--that is1 a circle--for the sun never let them get right away from him1 but compelled them to move in circles round him4 ,there is a very common instance of this kind of thing which we can see1 or perhaps feel1 every day4 ,if you try to sit still on a bicycle you tumble off1 because the earth pulls you down to itself2 but if1 by using the force of your own muscles1 you give the bicycle a forward movement this resists the earth-pull1 and the result is the bicycle runs along the ground4 ,it does not get right away from the earth1 not even two or three feet above ground2 it is held to the earth1 but still it goes forward and does not fall over1 for the movement is made up of the earth-pull1 which holds it to the ground1 and the forward movement1 which propels it along4 ,then again1 as another instance1 if you tie a ball to a string and whirl it round you1 so long as you keep on whirling it will not fall to the ground1 but the moment you stop down it drops1 for there is nothing to fight against the pull of gravitation4 ,thus we can picture the earth and all the planets as if they were swinging round the sun1 held by invisible strings4 ,it is the combination of two forces that keeps them in their places--the first force and the sun's pull4 ,it is very wonderful to think of4 ,here we are swinging in space on a ball that seems only large to us because we are so much smaller ourselves2 there is nothing above or below it but space1 yet it travels on day by day and year by year1 held by invisible forces that the brain of man has discovered and measured4 ,of course1 every planet gives a pull at every other planet too1 but these pulls are so small compared with that of the sun that we need not at present notice them4 ,then we come to another point4 ,we said that every body pulled every other body in proportion to their weights and their distance4 ,now1 gravity acts much more strongly when things are near together than when they are far away from each other2 so that if a smaller body is near to another somewhat larger than itself1 it is pulled by it much more strongly than by a very much larger one at a considerably greater distance4 ,we have an instance of this in the case of the earth and moon3 as the earth responds to the pull of the sun1 so the moon responds to the pull of the earth4 ,the moon is so comparatively near to the earth that the earth-pull forces her to keep on going round and round1 instead of leaving her free to circle round the sun by herself2 and yet if you think of it the moon does go round the sun too4 ,recall that game we had when the sun was in the middle1 and the two smaller girls1 representing the earth and moon1 went round it4 ,the moon-child turned round the earth-child1 but all the while the earth-child was going round the sun1 so that in a year's time the moon had been all round the sun too1 only not in a straight line4 ,the moon is something like a dog who keeps on dancing round and round you when you go for a walk4 ,he does go for the walk too1 but he does much more than that in the same time4 ,thus we have further completed our idea of our world4 ,we see it now hanging in space1 with no visible support1 held in its place by two mighty forces2 spinning on year after year1 attended by its satellite the moon1 while we run1 and walk1 and cry1 and laugh1 and play about on its surface--little atoms who1 except for the brain that ,god has given them1 would never even have known that they are continually moving on through endless space4 ,,chapter ,,iii ,,the ,,shining ,,moon ',once upon a time1' long1 long ago1 the earth was not a compact1 round1 hard body such as she is now1 but much larger and softer1 and as she rotated a fragment broke off from her2 it did not go right away from her1 but still went on circling round with the motion it had inherited from her4 ,as the ages passed on both the earth and this fragment1 which had been very hot1 cooled down1 and in cooling became smaller1 so that the distance between them was greater than it had been before they shrank4 ,and there were other causes also that tended to thrust the two further from each other4 ,yet1 compared with the other heavenly bodies1 they are still near1 and by looking up into the sky at night you can generally see this mighty fragment1 which is a quarter the diameter of the earth--that is to say1 a quarter the width of the earth measured from side to side through the middle4 ,it is--as1 of course1 you have guessed--the moon4 ,the moon is the nearest body to us in all space1 and so vast is the distance that separates us from the stars that we speak as if she were not very far off1 yet compared with the size of the earth the space lying between us and her is very great4 ,if you went right round the world at the thickest part--that is to say1 in the region of the ,equator--and when you arrived at your starting-point went off once again1 and so on until you had been round ten times1 you would only then have travelled about as far as from the earth to the moon6 ,the earth is not the only planet which has a moon1 or as it is called1 a satellite1 in attendance4 ,some of the larger planets have several1 but there is not one to compare with our moon4 ,which would you prefer if you had the choice1 three or four small moons1 some of them not much larger than a very big bright star1 or an interesting large body like our own moon8 ,i know which ,i should say4 ',you say that the moon broke off from the earth1 so perhaps there may be some people living on her1' ,i hear someone exclaim4 ,if there is one thing we have found out certainly about the moon1 it is that no life1 as we know it1 could exist there1 for there is neither air nor water4 ,whether she ever had any air or water1 and if so1 why they disappeared1 are questions we cannot answer4 ,we only know that now she is a dead world4 ,bright and beautiful as she is1 shedding on us a pale1 pure light1 in vivid contrast with the fiery yellow rays of the sun1 yet she is dead and lifeless and still4 ,we can examine her surface with the telescope1 and see it all very plainly4 ,even with a large opera-glass those markings which1 to the naked eye1 seem to be like a queer distorted face are changed1 and show up as the shadows of great mountains4 ,we can only see one side of the moon1 because as ,i have said1 she keeps always the same face turned to the earth2 but as she sways slightly in her orbit1 we catch a glimpse of sometimes a little more on one side and sometimes a little more on the other1 and so we can judge that the unseen part is very much the same as that turned toward us4 ,at first it is difficult to realize what it means to have no air4 ,besides supporting life in every breath that is drawn by living creatures1 the air does numerous other kind offices for us--for instance1 it carries sound4 ,supposing the most terrific volcano exploded in an airless world1 it could not be heard4 ,the air serves as a screen by day to keep off the burning heat of the sun's rays1 and as a blanket by night to keep in the heat and not let it escape too quickly4 ,if there were no air there could be no water1 for all water would evaporate and vanish at once4 ,imagine the world deprived of air2 then the sun's rays would fall with such fierceness that even the strongest tropical sun we know would be as nothing in comparison with it1 and every green thing would shrivel up and die2 this scorching sun would shine out of a black sky in which the stars would all be visible in the daytime1 not hidden by the soft blue veil of air1 as they are now4 ,at night the instant the sun disappeared below the horizon black darkness would set in1 for our lingering twilight is due to the reflection of the sun in the upper layers of air1 and a bitterness of deathly cold would fall upon the earth--cold fiercer than that of the ,arctic regions--and everything would be frozen solid4 ,it would need but a short time to reduce the earth to the condition of the moon1 where there is nothing to shrivel up1 nothing to freeze4 ,her surface is made up of barren1 arid rocks1 and her scenery consists of icy black shadows and scorching white plains4 ,illustration3 ,paris ,observatory4 ,,the ,,moon4 ,the black shadows define the mountains1 and tremendous mountains they are4 ,most of them have craters4 ,a crater is like a cup1 and generally has a little peak in the middle of it4 ,this is the summit of a volcano1 and when the volcano has burst up and vomited out floods of lava and dbris1 this has fallen down in a ring a little distance away from it1 leaving a clear space next to the peak1 so that1 as the mountain ceases vomiting and the lava cools down1 the ring hardens and forms a circular ridge4 ,the craters on the moon are immense1 not only in proportion to her size1 but immense even according to our ideas on the earth4 ,one of the largest craters in our own world is in ,japan1 and this measures seven miles across1 while in the moon craters of fifty1 sixty1 and even a hundred miles are by no means uncommon1 though there are also hundreds and thousands of smaller ones4 ,we can see the surface of the moon very plainly with the magnificent telescopes that have now been made1 and with the best of these anything the size of a large town would be plainly visible4 ,needless to say1 no town ever has been or ever will be seen upon the moon6 ,all these mountains and craters show that at one time the moon must have been convulsed with terrific disturbances1 far worse than anything that we have any knowledge of on our earth2 but this must have been ages ago1 while the moon still probably had an atmosphere of its own4 ,now it has long been quiet4 ,nothing changes there2 even the forces that are always at work on the earth--namely1 damp and mould and water--altering the surface and breaking up the rocks1 do not act there1 where there is no moisture of any sort4 ,so far as we can see1 the purpose of the moon is to be the servant of the earth1 to give her light by night and to raise the tides4 ,beautiful light it is1 soft and mysterious--light that children do not often have a chance of seeing1 for they are generally in bed before the moon rises when she is at the full4 ,we know that the moon has no heat of her own--she parted with all that long ago2 she cannot give us glowing light from brilliant flames1 as the sun does2 she shines only by the reflection of the sun on her surface1 and this is the reason why she appears to change her shape so constantly4 ,she does not really change2 the whole round moon is always there1 only part of it is in shadow4 ,sometimes you can see the dark part as well as the bright4 ,when there is a crescent moon it looks as if it were encircling the rest2 some people call it1 'seeing the old moon in the new moon's arms4' ,i don't know if you would guess why it is we can see the dark part then1 or how it is lighted up4 ,it is by reason of our own shining1 for we give light to the moon1 as she does to us4 ,the sun's rays strike on the earth1 and are reflected on to the moon1 so that the moon is lighted by earthshine as we are lighted by moonshine1 and it is these reflected earth-rays that light up the dark part of the moon and enable us to see it4 ,what a journey these rays have had6 ,they travel from the sun to the earth1 and the earth to the moon1 and then back to the earth again6 ,from the moon the earth must appear a much bigger and more glorious spectacle than she does to us--four times wider across and probably brighter--for the sun's light strikes often on our clouds1 which shine more brilliantly than her surface4 ,once again we must use an illustration to explain the subject4 ,set a lamp in the middle of a dark room1 and let that be the sun1 then take a small ball to represent the earth and a smaller one for the moon4 ,place the moon-ball between the lamp and the earth-ball4 ,you will see that the side turned to the earth-ball is dark1 but if you move the moon to one side of the earth1 then from the earth half of it appears light and half dark2 if you put it right away from the lamp1 on the outer side of the earth1 it is all gloriously lit up1 unless it happens to be exactly behind the earth1 when the earth's shadow will darken it4 ,this is the full explanation of all the changes of the moon4 ,illustration3 ,,an ,,eclipse ,,of ,,the ,,moon4 ,does it ever fall within the earth's shadow8 ,yes1 it does2 for as it passes round the earth it is not always at the same level1 but sometimes a little higher and sometimes a little lower1 and when it chances to pass exactly behind it enters the shadow and disappears4 ,that is what we call an eclipse of the moon4 ,it is nothing more than the earth's shadow thrown on to the moon1 and as the shadow is round that is one of the proofs that the earth is round too4 ,but there is another kind of eclipse--the eclipse of the sun2 and this is caused by the moon herself4 ,for when she is nearest to the sun1 at new moon--that is to say1 when her dark side is toward us1 and she happens to get exactly between us and the sun--she shuts out the face of the sun from us2 for though she is tiny compared with him1 she is so much nearer to us that she appears almost the same size1 and can blot him right out4 ,thus the eclipses of both sun and moon are not difficult to understand3 that of the moon can only happen at full moon1 when she is furthest from the sun1 and it is caused by the earth's shadow falling upon the moon2 and that of the sun at new moon1 when she is nearest to him1 and it is caused by the solid body of the moon coming between us and the sun4 ,illustration3 ,,an ,,eclipse ,,of ,,the ,,sun4 ,besides giving us light by night1 the moon serves other important purposes1 and the most important of all is the raising of the tides4 ,without the rising of the sea twice in every day and night our coasts would become foul and unwholesome1 for all the dead fish and rotting stuff lying on the beach would poison the air4 ,the sea tides scour our coasts day by day with never-ceasing energy1 and they send a great breath of freshness up our large rivers to delight many people far inland4 ,the moon does most of this work1 though she is a little helped by the sun4 ,the reason of this is that the moon is so near to the earth that1 though her pull is a comparatively small one1 it is very strongly felt4 ,she cannot displace the actual surface to any great extent1 as it is so solid2 but when it comes to the water she can and does displace that1 so that the water rises up in answer to her pull1 and as the earth turns round the raised-up water lags behind1 reaching backward toward the moon1 and is drawn up on the beach1 and makes high tide4 ,but it is stopped there1 and meantime1 by reason of the earth's movement1 the moon is left far behind1 and pulls the water to itself further on1 when the first high tide relapses and falls down again4 ,at length the moon gets round to quite the opposite side of the earth to that where she began1 and there she makes a high tide too2 but as she draws the water to herself she draws also the solid earth beneath the water to her in some degree1 and so pulls it away from the place where the first high tide occurred1 leaving the water there deeper than before1 and so causing a secondary high tide4 ,illustration3 ,,the ,,moon ,,raising ,,the ,,tides4 ,the sun has some influence on the tides too1 and when moon and sun are in the same line1 as at full and new moon1 then the tides are highest1 and are called spring tides2 but when they pull in different directions1 as when it is half-moon1 then the tides are lowest and are called neap tides4 ,,chapter ,,iv ,,the ,,earth',s ,,brothers ,,and ,,sister ,the earth is not the only world that1 poised in space1 swings around the sun4 ,it is one of a family called the ,solar ,system1 which means the system controlled and governed by the sun4 ,when we look up at the glorious sky1 star-studded night by night1 it might seem to us that the stars move only by reason of the earth's rotation2 but when men first began to study the heavens attentively--and this is so long ago that the record of it is not to be found--they noticed that1 while every shining object in the sky was apparently moving round us1 there were a few which also had another movement1 a proper motion of their own1 like the moon4 ,these curious stars1 which appeared to wander about among the other stars1 they called planets1 or wanderers4 ,and the reason1 which was presently discovered1 of our being able to see these movements was that these planets are very much nearer to us than any of the real stars1 and in fact form part of our own solar system1 while the stars are at immeasurable distances away4 ,of all the objects in the heavens the planets are the most intensely interesting to us2 for though removed from us by millions of miles1 the far-reaching telescope brings some of them within such range that we can see their surfaces and discover their movements in a way quite impossible with the stars4 ,and here1 if anywhere1 might we expect to find traces of other living beings like ourselves2 for1 after all the earth is but a planet1 not a very large nor a very small one1 and in no very striking position compared with the other planets2 and thus1 arguing by what seems common-sense1 we say1 ,if this one planet has living beings on its surface1 may not the other planets prove to be homes for living beings also8 ,counting our own earth1 there are eight of these worlds in our solar system1 and also a number of tiny planets1 called asteroids2 these likewise go round the sun1 but are very much smaller than any of the first eight1 and stand in a class by themselves1 so that when the planets are mentioned it is generally the eight large well-known planets which are referred to4 ,if we go back for a moment to the illustration of the large lamp representing our sun1 we shall now be able to fill in the picture with much more detail4 ,the orbits of the planets1 as their paths round the sun are called1 lie like great circles one outside another at various distances1 and do not touch or cut each other4 ,where do you suppose our own place to be8 ,will it be the nearest to the sun or the furthest away from him8 ,as a matter of fact1 it is neither1 we come third in order from the sun1 for two smaller planets1 one very small and the other nearly as large as the earth1 circle round and round the sun in orbits lying inside ours4 ,now if we want to place objects around our lamp-sun which will represent these planets in size1 and to put them in places corresponding to their real positions1 we should find no room large enough to give us the space we ought to have4 ,we must take the lamp out into a great open field1 where we shall not be limited by walls4 ,then the smallest planet1 named ,mercury1 which lies nearest of all to the sun1 would have to be represented by a pea comparatively close to the sun2 ,venus1 the next1 would be a greengage plum1 and would be about twice as far away2 then would come the earth1 a slightly larger plum1 about half as far again as ,venus4 ,after this there would be a lesser planet1 called ,mars1 like a marble4 ,these are the first four1 all comparatively small2 beyond them there is a vast gap1 in which we find the asteroids1 and after this we come to four larger planets1 mighty indeed as regards ourselves1 for if our earth were a greengage plum1 the first of these1 ,jupiter1 would have to be the size of a football at least1 and the next1 ,saturn1 a smaller football1 while ,uranus and ,neptune1 the two furthest out1 would be about the size of the toy balloons children play with4 ,the outermost one1 ,neptune1 would be thirty times as far from the sun as we are4 ,illustration3 ,,comparative ,,sizes ,,of ,,the ,,planets4 ,this is the solar system1 and in it the only thing that shines by its own light is the sun2 all the rest1 the planets and their moons1 shine only because the rays of light from the sun strike on their surfaces and are reflected off again4 ,our earth shines like that1 and from the nearer planets must appear as a brilliant star4 ,the little solar system is separated by distances beyond the realm of thought from the rest of the universe4 ,vast as are the intervals between ourselves and our planetary neighbours1 they are as nothing to the space that separates us from the nearest of the steady shining fixed stars4 ,why1 removed as far from us as the stars1 the sun himself would have sunk to a point of light2 and as for the planets1 the largest of them1 ,jupiter1 could not possibly be seen4 ,thus1 when we look at those stars across the great gulf of space1 we know that though we see them they cannot see us1 and that to them our sun must seem only a star2 consequently we argue that perhaps these stars themselves are suns with families of planets attached to them2 and though there are reasons for thinking that this is not the case with all1 it may be with some4 ,now if1 after learning this1 we look again at the sky1 we do so with very different eyes1 for we realize that some of these shining bodies are like ourselves in many things1 and are shining only with a light borrowed from the sun1 while others are mighty glowing suns themselves1 shining by their own light1 some greater and brighter1 some less than our sun4 ,the next thing to do is to learn which are stars and which are planets4 ,of the planets you will soon learn to pick out one or two1 and will recognize them even if they do change their places--for instance1 ,venus is at times very conspicuous1 shining as an evening star in the west soon after the sun goes down1 or us a morning star before he gets up1 though you are not so likely to see her then2 anyway1 she is never found very far from the sun4 ,jupiter is the only other planet that compares with her in brilliancy1 and he shines most beautifully4 ,he is1 of course1 much further away from us than ,venus1 but so much larger that he rivals her in brightness4 ,saturn can be quite easily seen as a conspicuous object1 too1 if you know where to look for him1 and ,mars is sometimes very bright with a reddish glow4 ,the others you would not be able to distinguish4 ,it is to our earth's family of these eight large planets going steadily round the same sun that we must give our attention first1 before going on to the distant stars4 ,many of the planets are accompanied by satellites or moons1 which circle round them4 ,we may say that the sun is our parent--father1 mother1 what you will--and that the planets are the family of children1 and that the moons are their children4 ,our earth1 you see1 has only one child1 but that a very fine one1 of which she may well be proud4 ,when ,i say that the planets go round the sun in circles ,i am only speaking generally2 as a matter of fact1 the orbits of the planets are not perfect circles1 though some are more circular than others4 ,instead of this they are as a circle might look if it were pressed in from two sides1 and this is called an ellipse4 ,the path of our own earth round the sun is one of the most nearly circular of them all1 and yet even in her orbit she is a good deal nearer to the sun at one time than another4 ,would you be surprised to hear that she is nearer in our winter and further away in our summer8 ,yet that is the case4 ,and for the first moment it seems absurd2 for what then makes the summer hotter than the winter8 ,that is due to an altogether different cause2 it depends on the position of the earth's axis4 ,if that axis were quite straight up and down in reference to the earth's path round the sun we should have equal days and nights all the year round1 but it is not2 it leans over a little1 so that at one time the ,north ,pole points towards the sun and at another time away from it1 while the ,south ,pole is pointing first away from it and then toward it in exactly the reverse way4 ,when the ,north ,pole points to the sun we in the ,northern ,hemisphere have our summer4 ,to understand this you must look at the picture1 which will make it much clearer than any words of mine can do4 ,the dark part is the night1 and the light part the day4 ,when we are having summer any particular spot on the ,northern ,hemisphere has quite a long way to travel in the light1 and only a very short bit in the dark1 and the further north you go the longer the day and shorter the night1 until right up near the ,north ,pole1 within the ,arctic ,circle1 it is daylight all the time4 ,you have1 perhaps1 heard of the 'midnight sun' that people go to see in the ,north1 and what the expression means is that at what should be midnight the sun is still there4 ,he seems just to circle round the horizon1 never very far above1 but never dipping below it4 ,when the sun is high overhead1 his rays strike down with much more force than when he is low4 ,it is1 for instance1 hotter at mid-day than in the evening4 ,now1 when the ,north ,pole is bowed toward the sun1 the sun appears to us to be higher in the sky4 ,in the ,british ,isles he never climbs quite to the zenith1 as we call the point straight above our heads2 he always keeps on the southern side of that1 so that our shadows are thrown northward at mid-day1 but yet he gets nearer to it than he does in winter4 ,look at the picture of the earth as it is in winter4 ,then we have long nights and short days1 and the sun never appears to climb very high1 because we are turned away from him4 ,during the short days we do not receive a great deal of heat1 and during the long night the heat we have received has time to evaporate to a great extent4 ,these two reasons--the greater or less height of the sun in the sky and the length of the days--are quite enough to account for the difference between our summer and winter4 ,there is one rather interesting point to remember1 and that is that in the ,northern ,hemisphere1 whether it is winter or summer1 the sun is south at mid-day1 so that you can always find the north then1 for your shadow will point northwards4 ,illustration3 ,,the ,,english ,,summer 7,,left7 ,,and ,,winter 7,,right74 ,new ,zealand and ,australia and other countries placed in the ,southern ,hemisphere1 as we are in the ,northern1 have their summer while we have winter1 and winter while we have summer1 and their summer is warmer than ours1 because it comes when the earth in its journey is three million miles nearer to the sun than in our summer4 ,all this seems to refer to the earth alone1 and this chapter should be about the planets2 but1 after all1 what applies to one planet applies to another in some degree1 and we can turn to the others with much more interest now to see if their axes are bowed toward the sun as ours is4 ,it is believed that in the case of ,mercury1 in regard to its path round the sun1 the axis is straight up and down2 if it is the changes of the seasons must depend on the nearness of ,mercury to the sun and nothing else1 and as he is a great deal nearer at one time than another1 this might make a very considerable difference4 ,some of the planets are like the earth in regard to the position of their axes1 but the two outermost ones1 ,uranus and ,neptune1 are very peculiar1 for one pole is turned right toward the sun and the other right away from it1 so that in one hemisphere there is continuous day all the summer1 in the other there is continuous night1 and then the process is reversed4 ,but these little peculiarities we shall have to note more particularly in the account of the planets separately4 ,there is a curious fact in regard to the distances of the planets from the sun4 ,each one1 after the first1 is1 very roughly1 about double the distance from the sun of the one inside it4 ,this holds good for all the first four1 then there is a great gap where we might expect to find another planet1 after which follow the four large planets4 ,now1 this gap puzzled astronomers greatly2 for though there seemed to be no reason why the planets should be at regular distances one outside the other1 yet there the fact was1 and that the series should be broken by a missing planet was annoying4 ,so very careful search was made1 and a thrill of excitement went all through the scientific world when it was known that a tiny planet had been discovered in the right place4 ,but this was not the end of it1 for within a few years three or four more tiny planets were observed not far from the first one1 and1 as years rolled on1 one after another was discovered until now the number amounts to over six hundred and others are perpetually being added to the list6 ,here was a new feature in the solar system1 a band of tiny planets not one of which was to be compared in size with the least of those already known4 ,the largest may be about as large as ,europe1 and others perhaps about the size of ,wales1 while there may be many that have only a few square miles of surface altogether1 and are too small for us to see4 ,to account for this strange discovery many theories were advanced4 ,one was that there had been a planet--it might be about the size of ,mars--which had burst up in a great explosion1 and that these were the pieces--a very interesting and exciting idea1 but one which proved to be impossible4 ,the explanation now generally accepted is a little complicated1 and to understand it we must go back for a bit4 ,when we were talking of the earth and the moon we realized that once long ago the moon must have been a part of the earth1 at a time when the earth was much larger and softer than she now is2 to put it in the correct way1 we should say when she was less dense4 ,there is no need to explain the word 'dense1' for in its ordinary sense we use it every day1 but in an astronomical sense it does not mean exactly the same thing4 ,everything is made up of minute particles or atoms1 and when these atoms are not very close together the body they compose is loose in texture1 while if they are closer together the body is firmer4 ,for instance1 air is less dense than water1 and water than earth1 and earth than steel4 ,you see at once by this that the more density a thing has the heavier it is2 for as a body is attracted to another body by every atom or particle in it1 so if it has more particles it will be more strongly attracted4 ,thus on the earth the denser things are really heavier4 ,but 'weight' is only a word we use in connection with the earth2 it means the earth's pulling power toward any particular thing at the surface1 and if we were right out in space away from the earth1 the pulling power of the earth would be less1 and so the weight would be less2 and as it would be impossible always to state just how far away a thing was from the earth1 astronomers talk about density1 which means the number of particles a body contains in proportion to other bodies4 ,thus the planet ,jupiter is very much larger than the earth1 but his density is less4 ,that does not mean to say that if ,jupiter were in one scale and the earth in the other he would weigh less1 because he is so very much bigger he would outweigh the earth still2 his total mass would be greater than that of the earth1 but it means that a piece of ,jupiter the same size as a piece of the earth would weigh less under the same conditions4 ,now1 before there were any planets at all or any sun1 in the place of our solar system was a vast gaseous cloud called a nebula1 which slowly rotated1 and this rotation was the first impulse or force which ,god gave it4 ,it was not at all dense1 and as it rotated a part broke off1 and inheriting the first impulse1 went on rotating too4 ,the impulse would have sent it off in a straight line1 but the pull of gravity from the nebula held it in place1 and it circled round2 then the nebula1 as it rotated1 contracted a little1 and occupied less space and grew denser1 and presently a second piece was thrown off1 to become in time another planet4 ,the same process was repeated with ,saturn1 and then with the huge ,jupiter4 ,the nebula was always rotating and always contracting4 ,and as it behaved1 so did the planets in their turn2 they spun round and cooled and contracted1 and the moons were flung off from them1 just as they--the planets--had been flung off from the parent nebula4 ,now1 after the original nebula had parted with the mighty mass of ,jupiter1 it never again made an effort so great1 and for a long time the fragments that were detached were so small as hardly to be worth calling planets2 they were the asteroids1 little lumps and fragments that the nebula left behind4 ,but as it still contracted in time there came ,mars2 and having recovered a little1 the nebula with more energy got rid of the earth1 and next ,venus1 and lastly little ,mercury1 the smallest of the eight planets4 ,then it contracted further1 and perhaps you can guess what the remainder of it is--the sun2 and by spinning in a plastic state the sun1 like the earth1 has become a globe1 round and comparatively smooth2 and its density is now too great to allow of its losing any more fragments1 so1 as far as we can see1 the solar system is complete4 ,this theory of the origin of the planets is called the nebula theory4 ,we cannot prove it1 but there are so many facts that can only be explained by it1 we have strong reason for believing that something of the kind must have happened4 ,when we come to speak of the starry heavens we shall see that there are many masses of glowing gas which are nebul of the same sort1 and which form an object-lesson in our own history4 ,we have spoken rather lightly of the nebula rotating and throwing off planets2 but we must not think of all this as having happened in a short time4 ,it is almost as impossible for the human mind to conceive the ages required for such slow changes as to grasp the great gulfs of space that separate us from the stars4 ,we can only do it by comparison4 ,you know what a second is1 and how the seconds race past without ceasing day and night4 ,it makes one giddy to picture the seconds there are in a year2 yet if each one of those seconds was a year in itself1 what then8 ,that seems a stupendous time1 but it is nothing compared with the time needed to form a nebula into a planetary system4 ,if we had five thousand of such years1 with every second in them a year1 we should then only have counted one billion real years1 and billions must have passed since the sun was a gaseous nebula filling the outermost bounds of our system6 ,,chapter ,v ,,four ,,small ,,worlds ,what must the sun appear to ,mercury1 who is so much nearer to him than we are8 ,to understand that we should have to imagine our sun increased to eight or nine times his apparent size1 and pouring out far greater heat and light than anything that we have here1 even in the tropics4 ,it was at first supposed that ,mercury must have an extra thick covering of clouds to protect him from this tremendous glare2 but recent observations tend to prove that1 far from this1 he is singularly free from cloud4 ,as this is so1 no life as we know it could possibly exist on ,mercury4 ,his year--the time he takes to go round the sun and come back to the same place again--is eighty-eight days1 or about one-quarter of ours4 ,as his orbit is much more like an ellipse than a circle1 it follows that he is much nearer to the sun at one time than at another--in fact1 when he is nearest1 the size of the sun must seem three and a half times greater than when he is furthest away from it6 ,even at the best ,mercury is very difficult to observe1 and what we can learn about him is not much2 but1 as we have heard1 his axis is supposed to be upright4 ,if so his seasons cannot depend on the bend toward or away from the sun1 but must be influenced solely by the changes in his distance from the sun1 which are much greater than in our own ease4 ,there is some reason to believe1 too1 that ,mercury's day and year are the same length4 ,this means that as the planet circles round the sun he turns once4 ,if this is so the sun will shine on one half of the planet1 producing an accumulated heat terrific to think of2 while the other side is plunged in blackness4 ,the side which faces the sun must be heated to a pitch inconceivable to us during the nearer half of the orbit--a pitch at which every substance must be at boiling-point1 and which no life as we know it could possibly endure4 ,seen from our point of view1 ,mercury goes through all the phases of the moon1 as he shines by the reflected light of the sun2 but this point we shall consider more particularly in regard to ,venus1 as ,venus is nearer to us and easier to study4 ,for a long time astronomers had a fancy that there might be another planet even nearer to the sun than ,mercury1 perhaps hidden from us by the great glare of the sun4 ,they even named this imaginary planet ,vulcan1 and some thought they had seen it1 but it is tolerably certain that ,vulcan existed only in imagination4 ,mercury is the nearest planet to the sun1 and also the smallest1 of course excepting the asteroids4 ,it is about three thousand miles in diameter1 and as our moon is two thousand miles1 it is not so much bigger than that4 ,so far as we are concerned1 it is improbable we shall ever know very much more about this little planet4 ,but next we come to ,venus1 our beautiful bright neighbour1 who approaches nearer to us than any other heavenly body except the moon4 ,alas6 when she is nearest1 she like ,mercury1 turns her dark side toward us1 coming in between us and the sun1 so that we cannot observe her at all4 ,everyone must have noticed ,venus1 however carelessly they have looked at the sky2 but it is likely that far more people have seen her as an evening than a morning star1 for most people are in bed when the sun rises1 and it is only before sunrise or after sunset we can see ,venus well4 ,she is at her best from our point of view when she seems to us to be furthest from the sun1 for then we can study her best1 and at these times she appears like a half or three-quarter moon1 as we only see a part of the side from which the sunlight is reflected4 ,she shines like a little silver lamp1 excelling every other planet1 even ,jupiter1 the largest of all4 ,if we look at her even with the naked eye1 we can see that she is elongated or drawn out1 but her brilliance prevents us from seeing her shape exactly2 to do this we must use a telescope4 ,illustration3 ,,different ,,phases ,,of ,,venus4 ,it is a curious fact that some planets shine much more brightly than others1 without regard to their size--that is to say1 the surface on which the sun's rays strike is of greater reflecting power in some than in others4 ,one of the brightest things in ,nature that we can imagine is a bank of snow in sunlight2 it is so dazzling that we have to look away or wink hard at the sight2 and the reflective power of the surface of ,venus is as dazzling as if she were made of snow4 ,this is probably because the light strikes on the upper surface of the clouds which surround her4 ,in great contrast to this is the surface of ,mercury1 which reflects as dully as a mass of lead4 ,our own moon has not a high reflecting power1 as will be easily understood if we imagine what the world would be if condemned to perpetual moonlight only4 ,it would1 indeed1 be a sad deprivation if the mournful cold light of the moon1 welcome enough as a change from sunlight1 were to take the place of sunlight in the daytime4 ,for a very long time astronomers could not discover what time ,venus took in rotating on her own axis--that is to say1 what the length of her day was4 ,she is difficult to observe1 and in order to find out the rotation it is necessary to note some fixed object on the surface which turns round with the planet and comes back to the same place again1 so that the time it takes in its journey can be measured4 ,but the surface of ,venus is always changing1 so that it is impossible to judge at all certainly4 ,opinions differ greatly1 some astronomers holding that ,venus's day is not much longer than an earthly day1 while others believe that the planet's day is equal to her year1 just as in the case of ,mercury4 ,venus's year is #bbe days1 or about seven and a half of our months1 and if1 indeed1 her day and year are the same length1 very peculiar effects would follow4 ,for instance1 terrible heat would be absorbed by the side of the planet facing the sun in the perpetual summer2 and the cold which would be felt in the dreary winter's night would far exceed our bitterest ,arctic climate4 ,we cannot but fancy that any beings who might live on a planet of this kind must be different altogether from ourselves4 ,then1 there is another point3 even here on earth very strong winds are caused by the heating of the tropics2 the hot air1 being lighter than the cold air1 rises1 and the colder air from the poles rushes in to supply its place4 ,this causes wind1 but the winds which would be raised on ,venus by the rush of air from the icy side of the planet to the hot one would be tornadoes such as we could but faintly dream of4 ,it is1 of course1 useless to speculate when we know so little1 but in a subject so intensely interesting we cannot help guessing a little4 ,venus is only slightly smaller than the earth1 and her density is not very unlike ours2 therefore the pull of gravity must be pretty much there what it is here--that is to say1 things will weigh at her surface about the same as they do here4 ,her orbit is nearly a circle1 so that her distance from the sun does not vary much1 and the heat will not be much greater from this cause at one time of the year than another4 ,as her orbit is tilted up a little she does not pass between us and the sun at each revolution1 but occasionally she does so1 and this passing is called a transit4 ,many important facts have been learned by watching these transits4 ,mercury also has transits across the sun1 but as she is so much smaller than ,venus they are not of such great importance4 ,it was by the close observation of ,venus during her transits that the distance from the earth to the sun was first measured4 ,not until the year #bjjd will another transit of ,venus occur4 ,it is not difficult to imagine that the earth must appear a splendid spectacle from ,venus1 whence she is seen to great advantage4 ,when nearest to us she must see us like a little moon1 with markings as the continents and seas rotate1 and these will change as they are obscured by the clouds rolling over them4 ,at the ,north and ,south ,poles will be glittering ice-caps1 growing larger and smaller as they turn toward or away from the sun4 ,a brilliant spectacle6 ,illustration3 ,,orbits ,,of ,,mars1 ,,the ,,earth1 ,,venus1 ,,and ,,mercury4 ,we might say with a sigh1 ',if only we could see such a world6' ,well1 we can see a world--not indeed1 so large as ,venus1 yet a world that comes almost as near to us as ,venus does1 and which1 unlike her1 is outside us in order from the sun1 so that when it is nearest to us the full sunlight is on it4 ,this is ,mars1 our neighbour on the other side1 and of all the fascinating objects in the sky ,mars is the most fascinating1 for there1 if anywhere1 should we be likely to discover beings like ourselves6 ,mars takes rather more than half an hour longer to rotate than we do1 and as he is so much smaller than the earth1 this means that he moves round more slowly4 ,his axis is bent at nearly the same angle as ours is4 ,mars is much smaller than the earth1 his diameter is about twice that of the moon1 and his density is about three-quarters that of the earth1 so that altogether1 with his smaller size and less density1 anything weighing a hundred pounds here would only weigh some forty pounds on ,mars2 and if1 by some miraculous agency1 you were suddenly transported there1 you would find yourself so light that you could jump enormous distances with little effort1 and skip and hop as if you were on springs4 ,illustration3 ,memoirs of the ,british ,astronomical ,association4 ,,map ,,of ,,mars4 ,look at the map of ,mars1 in which the surface appears to be cut up into land and water1 continents and oceans4 ,the men who first observed ,mars with accuracy saw that some parts were of a reddish colour and others greenish1 and arguing from our own world1 they called the greenish parts seas and the reddish land4 ,for a long while no one doubted that we actually looked on a world like our own1 more especially as there was supposed to be a covering of atmosphere4 ,the so-called land and water are much more cut up and mixed together than ours1 it is true4 ,here and there is a large sea1 like that marked ',mare ,australe1' but otherwise the water and the land are strangely intermingled4 ,the red colour of the part they named land puzzled astronomers a good deal1 for our land seen at the same distance would not appear so red1 and they came at last to the conclusion that vegetation on ,mars must be red instead of green6 ,but after a while another disturbing fact turned up to upset their theories1 and that was that they saw canals1 or what they called canals1 on ,mars4 ,these were long1 straight1 dark markings1 such as you see on the map4 ,it is true that some people never saw these markings at all1 and disbelieved in their existence2 but others saw them clearly1 and watched them change--first go fainter and then darker again4 ,and quite recently a photograph has been obtained which shows them plainly1 so they must have an existence1 and cannot be only in the eye of the observer1 as the most sceptical people were wont to suggest4 ,but further than this1 one astronomer announced that some of these lines appeared to be double1 yet when he looked at them again they had grown single4 ,it was like a conjuring trick4 ,great excitement was aroused by this1 for if the canals were altered so greatly it really did look as if there were intelligent beings on ,mars capable of working at them4 ,in any case1 if these are really canals1 to make them would be a stupendous feat1 and if they are artificial--that is1 made by beings and not natural--they show a very high power of engineering4 ,imagine anyone on earth making a canal many miles wide and two thousand miles long6 ,it is inconceivable1 but that is the feat attributed to the ,martians4 ,the supposed doubling of the canals1 as ,i say1 caused a great deal of talk1 and very few people could see that they were double at all4 ,even now the fact is doubted1 yet there seems every reason to believe it is true4 ,they do not all appear to be double1 and those that do are always the same ones1 while others undoubtedly remain single all the time4 ,but the canals do not exhaust the wonders of ,mars4 ,at each pole there is an ice-cap resembling those found at our own poles1 and this tells us pretty plainly something about the climate of ,mars1 and that there is water there4 ,this ice-cap melts when the pole which it surrounds is directed toward the sun1 and sometimes in a hot summer it dwindles down almost to nothing1 in a way that the ice-caps at the poles of the earth never do4 ,a curious appearance has been noticed when it is melting3 a dark shadow seems to grow underneath the edge of it and extends gradually1 and as it extends the canals near it appear much darker and clearer than they did before1 and then the canals further south undergo the same change4 ,this looks as if the melting of the snow filled up the canals with water1 and was a means of watering the planet by a system totally different from anything we know here1 where our poles are surrounded by oceans1 and the ice-caps do not in the least affect our water-supply4 ,but1 then1 another strange fact had to be taken into consideration4 ,these straight lines called canals ran out over the seas occasionally1 and it was impossible to believe that if they were canals they could do that4 ,other things began to be discussed1 such as the fact that the green parts of ,mars did not always remain green4 ,in what is the springtime of ,mars they are so1 but afterwards they become yellow1 and still later in the season parts near the pole turn brown4 ,thus the idea that the greenish parts are seas had to be quite given up1 though it appeared so attractive4 ,the idea now generally believed is that the greenish parts are vegetation--trees and bushes and so on1 and that the red parts are deserts of reddish sand1 which require irrigation--that is to say1 watering--before anything can be grown on them4 ,the apparent doubling of the canals may be due to the green vegetation springing up along the banks4 ,this might form two broad lines1 while the canal itself would not be seen1 and when the vegetation dies down1 we should see only the trench of the canal1 which would possibly appear faint and single4 ,therefore the arrangements on ,mars appear to be a rich and a barren season on each hemisphere1 the growth being caused by the melting of the polar ice-cap1 which sends floods down even beyond the ,equator4 ,if we could imagine the same thing on earth we should have to think of pieces of land lying drear and dry and dead in winter between straight canal-like ditches of vast size4 ,a little water might remain in these ditches possibly1 but not enough to water the surrounding land4 ,then1 as summer progressed1 we should hear1 ',the floods are coming1' and each deep1 huge canal would be filled up with a tide of water1 penetrating further and further4 ,the water drawn up into the air would fall in dew or rain4 ,vegetation would spring up1 especially near the canal banks1 and instead of dreary wastes rich growths would cover the land1 gradually dying down again in the winter4 ,so far ,mars seems in some important respects very different from the earth4 ,he is also less favourably placed than we are1 for being so much further from the sun1 he receives very much less heat and light4 ,his years are #fhg of our days1 or one year and ten and a half months1 and his atmosphere is not so dense as ours4 ,with this greater distance from the sun and less air we might suppose the temperature would be very cold indeed1 and that the surface would be frost-bound1 not only at the poles1 but far down towards the ,equator4 ,instead of this being so1 as we have seen1 the polar caps melt more than those on the earth4 ,we can only surmise there must be some compensation we do not know of that softens down the rigour of the seasons1 and makes them milder than we should suppose possible4 ,of course1 the one absorbing question is1 ,are there people on ,mars8 ,to this it is at present impossible to reply4 ,we can only say the planet seems in every way fitted to support life1 even if it is a little different from our earth4 ,it is most certainly a living world1 not a dead one like the moon1 and as our knowledge increases we may some day be able to answer the question which so thrills us4 ,our opportunities for the observation of ,mars vary very greatly1 for as the earth's orbit lies inside that of ,mars1 we can best see him when we are between him and the sun4 ,of course1 it must be remembered that the earth and the other planets are so infinitely small in regard to the space between them that there is no possibility of any one of them getting in such a position that it would throw a shadow on any other or eclipse it4 ,the planets are like specks in space1 and could not interfere with one another in this way4 ,when ,mars1 therefore1 is in a line with us and the sun we can see him best1 but some of these times are better than others1 for this reason--the earth's orbit is nearly a circle1 and that of ,mars more of an ellipse4 ,illustration3 ,,orbits ,,of ,,the ,,earth ,,and ,,mars4 ,look at the illustration and remember that ,mars' year is not quite two of ours--that is to say1 every time we swing round our orbit we catch him up in a different place1 for he will have progressed less than half his orbit while we go right round ours4 ,sometimes when we overtake him he may be at that part which is furthest away from us1 or he may be at that part which is nearest to us1 and if he is in the latter position we can see him best4 ,now at these1 the most favourable times of all1 he is still more than thirty-five millions of miles away--that is to say1 one hundred and forty times as far as the moon1 yet comparatively we can see him very well4 ,he is coming nearer and nearer to us1 and very soon will be nearer than he has been since #ahib1 or fifteen years ago4 ,then many telescopes will be directed on him1 and much may be learned about him4 ,for a long time it was supposed that ,mars had no moons1 and when ,dean ,swift wrote ',gulliver's ,travels' he wanted to make the ,laputans do something very clever1 so he described their discovery of two moons attending ,mars1 and to make it quite absurd he said that when they observed these moons they found that one of them went round the planet in about ten hours4 ,now1 as ,mars takes more than twenty-four hours to rotate1 this was considered ridiculous1 for no moon known then took less time to go round its primary world than the primary world took to turn on its own axis4 ,our own moon1 of course1 takes thirty times as long--that is a month contains thirty days4 ,then one hundred and fifty years later this jest of ,dean ,swift's came true1 for two moons were really discovered revolving round ,mars1 and one of them does actually take less time to complete its orbit than the planet does to rotate--namely1 a little more than seven hours6 ,so the absurdity in ',gulliver's ,travels' was a kind of prophecy6 ,these two moons are very small1 the outer one perhaps five or six miles in diameter1 and the inner one about seven2 therefore from ,mars the outer one1 ,deimos1 cannot look much more than a brilliant star1 and the inner one would be but a fifth part the apparent width of our own moon4 ,so ,mars is not very well off1 after all4 ,still1 there is great variety1 for it must be odd to see the same moon appearing three times in the day1 showing all the different phases as it goes from new to full1 even though it is small6 ,such wonderful discoveries have already been made that it is not too much to say that perhaps some day we may be able to establish some sort of communication with ,mars1 and if it be inhabited by any intelligent beings1 we may be able to signal to them2 but it is almost impossible that any contrivance could bridge the gulf of airless space that separates us1 and it is not likely that holiday trips to ,mars will ever become fashionable6 ,,chapter ,,vi ,,four ,,large ,,worlds ,i have told you about the four lesser worlds of which our earth is one1 and you know that beyond ,mars1 the last of them1 there lies a vast space1 in which are found the asteroids1 those strange small planets circling near to each other1 like a swarm of bees4 ,after this there comes ,jupiter1 who is so enormous1 so superb in size compared with us1 that he might well serve as the sun of a little system of his own4 ,you remember that we represented him by a football1 while the earth was only a greengage plum4 ,but ,jupiter himself is far less in comparison with the sun than we are in comparison with him4 ,he differs from the planets we have heard about up to the present in that he seems to glow with some heat that he does not receive from the sun4 ,the illumination which makes him appear as a star to us is1 of course1 merely reflected sunlight1 and what we see is the external covering1 his envelope of cloud4 ,there is every reason to believe that the great bulk of ,jupiter is still at a high temperature4 ,we know that in the depths of the earth there is still plenty of heat1 which every now and then makes its presence felt by bursting up through the vents we call volcanoes1 the weak spots in the earth's crust2 but our surface long ago cooled1 for the outside of any body gets cool before the inside1 as you may have found if ever you were trying to eat hot porridge1 and circled round the edge of the plate with a spoon4 ,a large body cools more slowly than a small one1 and it is possible that ,jupiter1 being so much larger than we are1 has taken longer to cool4 ,one reason we have for thinking this is that he is so very light compared with his size--in other words1 his density is so small that it is not possible he could be made of materials such as the earth is made of4 ,as ,i said1 when we study him through telescopes we see just the exterior1 the outer envelope of cloud1 and as we should expect1 this changes continually1 and appears as a series of belts1 owing to the rotation of the planet4 ,jupiter's rotation is very rapid2 though he is so much greater than the earth1 he takes less than half the time the earth does to turn round--that is to say1 only ten hours4 ,his days and nights of five hours each seem short to us1 accustomed to measure things by our own estimates4 ,but we must remember that everything is relative2 that is to say1 there is really no such thing as fast or slow2 it is all by comparison4 ,a spider runs fast compared with a snail1 but either is terribly slow compared with an express train2 and the speed of an express train itself is nothing to the velocity of light4 ,in the same way there is nothing absolutely great or small2 it is all by comparison4 ,we say how marvellous it is that a little insect has all the mechanism of life in its body when it is so tiny1 but if we imagine that insect magnified by a powerful microscope until it appears quite large1 the marvel ceases4 ,again1 imagine a man walking on the surface of the earth as seen from a great distance through a telescope3 he would seem less than an insect1 and we might ask how could the mechanism of life be compressed into anything so small8 ,thus1 when we say enormous or tiny we must always remember we are only speaking by the measurements of our own standards4 ,there is nothing very striking about ,jupiter's orbit4 ,he takes between eleven and twelve of our years to get round the sun1 so you see1 though his day is shorter1 his year is longer than ours4 ,and this is not only because his path is much larger1 but because by the law of gravity the more distant a planet is from the sun the more slowly it travels1 so that while the earth speeds over eighteen miles ,jupiter has only done eight4 ,of course1 we must be careful to remember the difference between rotation and revolution4 ,jupiter rotates much quicker than the earth--that is to say1 he turns round more quickly--but he actually gets over the ground more slowly4 ,the sun appears much smaller to him than it does to us1 and he receives considerably less light and heat4 ,there are various spots on his surface1 and one remarkable feature is a dark mark1 which is called the 'great red spot4' ,if as we suppose what we see of the planet is merely the cloudy upper atmosphere1 we should not expect to find anything permanent there1 for the markings would change from day to day1 and this they do with this exception--that this spot1 dark red in colour1 has been seen for many years1 turning as the planet turned4 ,it was first noticed in #ahgh1 and was supposed to be some great mountain or excrescence peeping up through the clouds4 ,it grew stronger and darker for several years1 and then seemed to fade1 and was not so easily seen1 and though still remaining it is now pale4 ,but1 most startling to say1 it has shifted its position a little--that is1 it takes a few seconds longer to get round the planet than it did at first4 ,a few seconds1 you will say1 but that is nothing6 ,it does not seem much1 but it shows how marvellously accurate astronomers are4 ,discoveries of vast importance have been made from observing a few seconds' discrepancy in the time the heavenly bodies take in their journeys1 and the fact that this spot takes a little longer in its rotation than it did at first shows that it cannot be attached to the body of the planet4 ,it is impossible for it to be the summit of a mountain or anything of that sort4 ,what can it be8 ,no one has yet answered that question4 ,illustration3 ,,jupiter ,,and ,,one ,,of ,,his ,,moons ,when we get to the chapter on the sun1 we shall find curiosities respecting the spots there as well4 ,jupiter has seven moons1 and four of these are comparatively large4 ,they have the honour of having been the first heavenly bodies ever actually discovered1 for the six large planets nearest the sun have been known so long that there is no record of their first discovery1 and of course our own moon has always been known4 ,galileo1 who invented the telescope1 turned it on to the sky in #afaj1 when our ,king ,charles ,i4 was on the throne1 and he saw these curious bodies which at first he could not believe to be moons4 ,the four which he saw vary in size from two thousand one hundred miles in diameter to nearly three thousand six hundred4 ,you remember our own moon is two thousand miles across1 so even the smallest is larger than she4 ,they go round at about the same level as the planet's ,equator1 and therefore they cross right in front of him1 and go behind him once in every revolution4 ,since then the other three have been discovered in the band of ,jupiter's satellites--one a small moon closer to him than any of the first set1 and two others further out4 ,it was by observation of the first four1 however1 that very interesting results were obtained4 ,mathematicians calculated the time that these satellites ought to disappear behind ,jupiter and reappear again1 but they found that this did not happen exactly at the time predicted2 sometimes the moons disappeared sooner than they should have done1 and sometimes later4 ,then this was discovered to have some relation to the distance of our earth from ,jupiter4 ,when he was at the far side of his immense orbit he was much more distant from us than when he was on the nearer side--in fact1 the difference may amount to more than three hundred millions of miles4 ,and it occurred to some clever man that the irregularities in time we noticed in the eclipses of the satellites corresponded with the distance of ,jupiter from us4 ,the further he drew away from us1 the later were the eclipses1 and as he came nearer they grew earlier4 ,by a brilliant inspiration1 this was attributed to the time light took to travel from them to us1 and this was the first time anyone had been able to measure the velocity or speed of light4 ,for all practical purposes1 on the earth's surface we hold light to be instantaneous1 and well we may1 for light could travel more than eight times round the world in one second4 ,it makes one's brain reel to think of such a thing4 ,then think how far ,jupiter must be away from us at the furthest1 when you hear that sometimes these eclipses were delayed seventeen minutes--minutes1 not seconds--because it took that time for light to cross the gulf to us6 ,illustration3 ,,jupiter ,,and ,,his ,,principal ,,moons4 ,sound is very slow compared with light1 and that is why1 if you watch a man hammering at a distance1 the stroke he gives the nail does not coincide with the bang that reaches you1 for light gets to you practically at once1 and the sound comes after it4 ,no sound can travel without air1 as we have heard1 therefore no sound reaches us across space4 ,if the moon were to blow up into a million pieces we should see the amazing spectacle1 but should hear nothing of it4 ,light travels everywhere throughout the universe1 and by the use of this universal carrier we have learnt all that we know about the stars and planets4 ,when the time that light takes to travel had been ascertained by means of ,jupiter's satellites1 a still more important problem could be solved--that was our own distance from the sun1 which before had only been known approximately1 and this was calculated to be ninety-two millions seven hundred thousand miles1 though sometimes we are a little nearer and sometimes a little further away4 ,jupiter is marvellous1 but beyond him lies the most wonderful body in the whole solar system4 ,we have found curiosities on our way out3 we have studied the problem of the asteroids1 of the little moon that goes round ,mars in less time than ,mars himself rotates2 we have considered the 'great red spot' on ,jupiter1 which apparently moves independently of the planet2 but nothing have we found as yet to compare with the rings of ,saturn4 ,may you see this amazing sight through a telescope one day6 ,look at the picture of this wonderful system1 and think what it would be like if the earth were surrounded with similar rings6 ,the first question which occurs to all of us is what must the sky look like from ,saturn8 ,what must it be to look up overhead and see several great hoops or arches extending from one horizon to another1 reflecting light in different degrees of intensity8 ,it would be as if we saw several immense rainbows1 far larger than any earthly rainbow1 and of pure light1 not split into colours1 extending permanently across the sky1 and now and then broken by the black shadow of the planet itself as it came between them and the sun4 ,however1 we must begin at the beginning1 and find out about ,saturn himself before we puzzle ourselves over his rings4 ,saturn is not a very great deal less than ,jupiter1 though1 so small are the other planets in comparison1 that if ,saturn and all the rest were rolled together1 they would not make one mass so bulky as ,jupiter6 ,saturn is so light--in other words1 his density is so small--that he is actually lighter than water4 ,he is the lightest1 in comparison with his size1 of any of the planets4 ,therefore he cannot be made largely of solid land1 as our earth is1 but must be to a great extent1 composed of air and gaseous vapour1 like his mighty neighbour4 ,he approaches at times as near to ,jupiter as ,jupiter does to us1 and on these occasions he must present a splendid spectacle to ,jupiter4 ,he takes no less than twenty-nine and a half of our years to complete his stately march around the sun1 and his axis is a little more bent than ours2 but1 of course1 at his great distance from the sun1 this cannot have the same effect on the seasons that it does with us4 ,saturn turns fast on his axis1 but not so fast as ,jupiter1 and in turning his face1 or what we call his surface1 presents much the same appearance to us that we might expect1 for it changes very frequently and looks like cloud belts4 ,the marvellous feature about ,saturn is1 of course1 the rings4 ,there are three of these1 lying one within the other1 and separated by a fine line from each other4 ,the middle one is much the broadest1 probably about ten thousand miles in width1 and the inner one1 which is the darkest1 was not discovered until some time after the others4 ,as the planet swings in his orbit the rings naturally appear very different to us at different times4 ,sometimes we can only see them edgewise1 and then even in the largest telescope they are only like a streak of light1 and this shows that they cannot be more than fifty or sixty miles in thickness4 ,the one which is nearest to ,saturn's surface does not approach him within ten thousand miles4 ,saturn has no less than ten satellites1 in addition to the rings1 so that his midnight sky must present a magnificent spectacle4 ,the rings1 which do not shine by their own light but by reflected sunlight1 are solid enough to throw a shadow on the body of the planet1 and themselves receive his shadow4 ,sometimes for days together a large part of ,saturn must suffer eclipse beneath the encircling rings1 but at other times1 at night1 when the rings are clear of the planet's body1 so that the light is not cut off from them1 they must appear as radiant arches of glory spanning the sky4 ,the subject of these rings is so complicated by the variety of their changes that it is difficult for us even to think about it4 ,it is one of the most marvellous of all the features of our planetary system4 ,what are these rings8 what are they made of8 ,it has been positively proved that they cannot be made of continuous matter1 either liquid or solid1 for the force of gravity acting on them from the planet would tear them to pieces4 ,what1 then1 can they be8 ,it is now pretty generally believed that they are composed of multitudes of tiny bodies1 each separate1 and circling separately round the great planet1 as the asteroids circle round the sun4 ,as each one is detached from its neighbour and obeys its own impulses1 there is none of the strain and wrench there would be were they all connected4 ,according to the laws which govern planetary bodies1 those which are nearest to the planet will travel more quickly than those which are further away4 ,of course1 as we look at them from so great a distance1 and as they are moving1 they appear to us to be continuous4 ,it is conjectured that the comparative darkness of the inside ring is caused by the fact that there are fewer of the bodies there to reflect the sunlight4 ,then1 in addition to the rings1 enough themselves to distinguish him from all other planets1 there are the ten moons of richly-endowed ,saturn to be considered4 ,it is difficult to gather much about these moons1 on account of our great distance from them4 ,the largest is probably twice the diameter of our own moon4 ,one of them seems to be much brighter--that is to say1 of higher reflecting power--on one side than the other1 and by distinguishing the sides and watching carefully1 astronomers have come to the conclusion that it presents always the same face to ,saturn in the same way as our own moon does to us2 in fact1 there is reason to think that all the moons of large planets do this4 ,illustration3 ,,the ,,planet ,,saturn ,,with ,,two ,,of ,,his ,,moons4 ,all the moons lie outside the rings1 and some at a very great distance from ,saturn1 so that they can only appear small as seen from him4 ,yet at the worst they must be brighter than ordinary stars1 and add greatly to the variations in the sky scenery of this beautiful planet4 ,in connection with ,saturn's moons there is another of those astonishing facts that are continually cropping up to remind us that1 however much we know1 there is such a vast deal of which we are still ignorant4 ,so far in dealing with all the planets and moons in the solar system we have made no remark on the way they rotate or revolve1 because they all go in the same direction1 and that direction is called counter-clockwise1 which means that if you stand facing a clock and turn your hand slowly round the opposite direction to that in which the hands go1 you will be turning it in the same way that the earth rotates on its axis and revolves in its orbit4 ,it is1 perhaps1 just as well to give here a word of caution4 ,rotating of course means a planet's turning on its own axis1 revolving means its course in its orbit round the sun4 ,mercury1 ,venus1 ,earth1 ,mars1 ,jupiter1 and all their moons1 as well as ,saturn himself1 rotate on their axes in this one direction--counter-clockwise--and revolve in the same direction as they rotate4 ,even the queer little moon of ,mars1 which runs round him quicker than he rotates1 obeys this same rule4 ,nine of ,saturn's moons follow this example1 but one independent little one1 which has been named ,phoebe1 and is far out from the planet1 actually revolves in the opposite way4 ,we cannot see how it rotates1 but if1 as we said just now1 it turns the same face always to ,saturn1 then of course it rotates the wrong way too4 ,a theory has been suggested to account for this curious fact1 but it could not be made intelligible to anyone who has not studied rather high mathematics1 so there we must just leave it1 and put it in the cabinet of curiosities we have already collected on our way out to ,saturn4 ,for ages past men have known and watched the planets lying within the orbit of ,saturn1 and they had made up their minds that this was the limit of our system4 ,but in #agha a great astronomer named ,herschel was watching the heavens through a telescope when he noticed one strange object that he was certain was no star4 ,the vast distance of the stars prevents their having any definite outline1 or what is called a disc4 ,the rays dart out from them in all directions and there is no 'edge' to them1 but in the case of the planets it is possible to see a disc with a telescope1 and this object which attracted ,herschel's attention had certainly a disc4 ,he did not imagine he had discovered a new planet1 because at that time the asteroids had not been found1 and no one thought that there could be any more planets4 ,yet ,herschel knew that this was not a star1 so he called it a comet6 ,he was actually the first who discovered it1 for he knew it was not a fixed star1 but it was after his announcement of this fact that some one else1 observing it carefully1 found it to be a real planet with an orbit lying outside that of ,saturn1 then the furthest boundary of the solar system4 ,herschel suggested calling it ,georgius ,sidus1 in honour of ,george ,,iii41 then ,king2 but luckily this ponderous name was not adopted1 and as the other planets had been called after the ,olympian deities1 and ,uranus was the father of ,saturn1 it was called ,uranus4 ,it was subsequently found that this new planet had already been observed by other astronomers and catalogued as a star no less than seventeen times1 but until ,herschel's clear sight had detected the difference between it and the fixed stars no one had paid any attention to it4 ,uranus is very far away from the sun1 and can only sometimes be seen as a small star by people who know exactly where to look for him4 ,in fact1 his distance from the sun is nineteen times that of the earth4 ,yet to show at all he must be of great size1 and that size has actually been found out by the most delicate experiments4 ,if we go back to our former comparison1 we shall remember that if the earth were like a greengage plum1 then ,uranus would be in comparison about the size of one of those coloured balloons children play with2 therefore he is much larger than the earth4 ,in this far distant orbit the huge planet takes eighty-four of our years to complete one of his own4 ,a man on the earth will have grown from babyhood to boyhood1 from boyhood to the prime of life1 and lived longer than most men1 while ,uranus has only once circled in his path4 ,but in dealing with ,uranus we come to another of those startling problems of which astronomy is full4 ,so far we have dealt with planets which are more or less upright1 which rotate with a rotation like that of a top4 ,now take a top and lay it on one side on the table1 with one of its poles pointing toward the great lamp we used for the sun and the other pointing away4 ,that is the way ,uranus gets round his path1 on his side6 ,he rotates the wrong way round compared with the planets we have already spoken of1 but he revolves the same way round the sun that all the others do4 ,it seems wonderful that even so much can be found out about a body so far from us1 but we know more3 we have discovered that ,uranus is made of lighter material than the earth2 his density is less4 ,how can that be known8 ,well1 you remember every body attracts every other body in proportion to the atoms it contains4 ,if1 therefore1 there were any bodies near to ,uranus1 it could be calculated by his influence on them what was his own mass1 which1 as you remember1 is the word we use to express what would be weight were it at the earth's surface2 and far away as ,uranus is1 the bodies from which such calculations may be made have been discovered1 for he has no less than four satellites1 or moons4 ,considering now the peculiar position of the planet1 we might expect to find these moons revolving in a very different way from others1 and this is indeed the case4 ,they turn round the planet at about its ,equator--that is to say1 if you hold the top representing ,uranus as was suggested just now1 these moons would go above and below the planet in passing round it4 ,only we must remember there is really no such thing as above and below absolutely4 ,we who are on one side of the world point up to the sky and down to the earth1 while the people on the other side of the earth1 say at ,new ,zealand1 also point up to the sky and down to the earth1 but their pointings are directly the opposite of ours4 ,so when we speak of moons going above and below that is only because1 for the moment1 we are representing ,uranus as a top we hold in our hands1 and so we speak of above and below as they are to us4 ,it was ,herschel who discovered these satellites1 as well as the planet1 and for these great achievements he occupies one of the grandest places in the rle of names of which ,england is proud4 ,but he did much more than this3 his improvements in the construction of telescopes1 and his devotion to astronomy in many other ways1 would have caused him to be remembered without anything else4 ,of ,uranus's satellites one1 the nearest1 goes round in about two and a half days1 and the one that is furthest away takes about thirteen and a half days1 so both have a shorter period than our moon4 ,the discovery of ,uranus filled the whole civilized world with wonder4 ,the astronomers who had seen him1 but missed finding out that he was a planet1 must have felt bitterly mortified1 and when he was discovered he was observed with the utmost accuracy and care4 ,the calculations made to determine his path in the sky were the easier because he had been noted as a star in several catalogues previously1 so that his position for some time past was known4 ,everybody who worked at astronomy began to observe him4 ,from these facts mathematicians set to work1 and1 by abstruse calculations1 worked out exactly the orbit in which he ought to move2 then his movements were again watched1 and behold he followed the path predicted for him2 but there was a small difference here and there3 he did not follow it exactly4 ,now1 in the heavens there is a reason for everything1 though we may not always be clever enough to find it out1 and it was easily guessed that it was not by accident that ,uranus did not precisely follow the path calculated for him4 ,the planets all act and react on one another1 as we know1 according to their mass and their distance1 and in the calculations the pull of ,jupiter on ,saturn and of ,saturn on ,uranus were known and allowed for4 ,but ,uranus was pulled by some unseen influence also4 ,a young ,englishman named ,adams1 by some abstruse and difficult mathematical work far beyond the power of ordinary brains1 found out not only the fact that there must be another planet nearly as large as ,uranus in an orbit outside his1 but actually predicted where such a planet might be seen if anyone would look for it4 ,he gave his results to a professor of astronomy at ,cambridge4 ,now1 it seems an easy thing to say to anyone1 ',look out for a planet in such and such a part of the sky1' but in reality1 when the telescope is turned to that part of the sky1 stars are seen in such numbers that1 without very careful comparison with a star chart1 it is impossible to say which are fixed stars and which1 if any1 is an intruder4 ,there happened to be no star chart of this kind for the particular part of the sky wanted1 and thus a long time elapsed and the planet was not identified4 ,meantime a young ,frenchman named ,leverrier had also taken up the same investigation1 and1 without knowing anything of ,adams' work1 had come to the same conclusion4 ,he sent his results to the ,berlin ,observatory1 where a star chart such as was wanted was actually just being made4 ,by the use of this the ,berlin astronomers at once identified this new member of our system1 and announced to the astonished world that another large planet1 making eight altogether1 had been discovered4 ,then the ,english astronomers remembered that they too held in their hands the means for making this wonderful discovery1 but1 by having allowed so much time to elapse1 they had let the honour go to ,france4 ,however1 the names of ,adams and ,leverrier will always be coupled together as the discoverers of the new planet1 which was called ,neptune4 ,the marvel is that by pure reasoning the mind of man could have achieved such results4 ,if the observation of ,uranus is difficult1 how much more that of ,neptune1 which is still further plunged in space6 ,yet by patience a few facts have been gleaned about him4 ,he is not very different in size from ,uranus4 ,he also is of very slight density4 ,his year includes one hundred and sixty-five of ours1 so that since his discovery in #ahdf he has only had time to get round less than a third of his path4 ,his axis is even more tilted over than that of ,uranus1 so that if we compare ,uranus to a top held horizontally1 ,neptune will be like a top with one end pointing downwards4 ,he rotates in this extraordinary position1 in the same manner as ,uranus--namely1 the other way over from all the other planets1 but he revolves1 as they all do1 counter-clockwise4 ,seen from ,neptune the sun can only appear about as large as ,venus appears to us at her best1 and the light and heat received are but one nine-hundreth part of what he sends us4 ,yet so brilliant is sunshine that even then the light that falls on ,neptune must be very considerable1 much more than that which we receive from ,venus1 for the sun itself glows1 and from ,venus the light is only reflected4 ,the sun1 small as it must appear1 will shine with the radiance of a glowing electric light4 ,to get some idea of the brilliance of sunlight1 sit near a screen of leaves on some sunny day when the sun is high overhead1 and note the intense radiance of even the tiny rays which shine through the small holes in the leaves4 ,the scintillating light is more glorious than any diamond1 shooting out coloured rays in all directions4 ,a small sun the apparent size of ,venus would1 therefore1 give enough light for practical purposes to such a world as ,neptune1 even though to us a world so illuminated would seem to be condemned to a perpetual twilight4 ,,chapter ,,vii ,,the ,,sun ,so far we have referred to the sun just so much as was necessary to show the planets rotating round him1 and to acknowledge him as the source of all our light and heat2 but we have not examined in detail this marvellous furnace that nourishes all the life on our planet and burns on with undiminished splendour from year to year1 without thought or effort on our part4 ,to sustain a fire on the earth much time and care and expense are necessary2 fuel has to be constantly supplied1 and men have to stoke the fire to keep it burning4 ,considering that the sun is not only vastly larger than all the fires on the earth put together1 but also than the earth itself1 the question very naturally occurs to us1 ,who supplies the fuel1 and who does the stoking on the sun8 ,before we answer this we must try to get some idea of the size of this stupendous body4 ,it is not the least use attempting to understand it by plain figures1 for the figures would be too great to make any impression on us--they would be practically meaningless2 we must turn to some other method4 ,suppose1 for instance1 that the sun were a hollow ball2 then1 if the earth were set at the centre1 the moon could revolve round her at the same distance she is now1 and there would be as great a distance between the moon and the shell of the sun as there is between the moon and the earth4 ,this gives us a little idea of the size of the sun4 ,again1 if we go back to that solar system in which we represented the planets by various objects from a pea to a football1 and set a lamp in the centre to do duty for the sun1 what size do you suppose that lamp would have to be really to represent the sun in proportion to the planets8 ,well1 if our greengage plum which did duty for the earth were about three-quarters of an inch in diameter we should want a lamp with a flame as tall as the tallest man you know1 and even then it would not give a correct idea unless you imagined that man extending his arms widely1 and you drew round him a circle and filled in all the circle with flame6 ,if this glorious flame burnt clear and fair and bright1 radiating beams of light all around1 the little greengage plum would not have to be too near1 or it would be shrivelled up as in the blast of a furnace4 ,to place it at anything resembling the distance it is from the sun in reality you would have to walk away from the flaming light for about three hundred steps1 and set it down there2 then1 after having done all this1 you would have some little idea of the relative sizes of the sun and the earth1 and of the distance between them4 ,of course1 all the other planets would have to be at corresponding distances4 ,on this same scale1 ,neptune1 the furthest out1 would be three miles from our artificial sun6 ,it seems preposterous to think that some specks so small as to be quite invisible1 specks that crawl about on that plum1 have dared to weigh and measure the gigantic sun2 but yet they have done it1 and they have even decided what he is made of4 ,the result of the experiments is that we know the sun to be a ball of glowing gas at a temperature so high that nothing we have on earth could even compare with it4 ,of his radiating beams extending in all directions few indeed fall on our little plum1 but those that do are the source of all life1 whether animal or vegetable4 ,if the sun's rays were cut off from us1 we should die at once4 ,even the coal we use to keep us warm is but sun's heat stored up ages ago1 when the luxuriant tropical vegetation sprang up in the warmth and then fell down and was buried in the earth4 ,at night we are still enjoying the benefit of the sun's rays--that is1 of those which are retained by our atmosphere2 for if none remained even the very air itself would freeze1 and by the next morning not one inhabitant would be left alive to tell the awful tale4 ,yet all this life and growth and heat we receive on the whole earth is but one part in two thousand two hundred millions of parts that go out in all directions into space4 ,it has been calculated that the heat which falls on to all the planets together cannot be more than one part in one hundred millions and the other millions of parts seem to us to be simply wasted4 ,for untold ages the sun has been pouring out this prodigal profusion of glory1 and as we know that this cannot go on without some sort of compensation1 we want to understand what keeps up the fires in the sun4 ,it is true that the sun is so enormous that he might go on burning for a very long time without burning right away2 but1 then1 even if he is huge1 his expenditure is also huge4 ,if he had been made of solid coal he would have been all used up in about six thousand years1 burning at the pace he does4 ,now1 we know that the ancient ,egyptians kept careful note of the heavenly bodies1 and if the sun were really burning away he must have been very much larger in their time2 but we have no record of this2 on the contrary1 all records of the sun even to five thousand years ago show that he was much the same as at present4 ,it is evident that we must search elsewhere for an explanation4 ,it has been suggested that his furnace is supplied by the number of meteors that fall into him4 ,meteors are small bodies of the same materials as the planets1 and may be likened to the dust of the solar system4 ,it is not difficult to calculate the amount of matter he would require on this assumption to keep him going1 and the amount required is so great as to make it practically impossible that this is the source of his supply4 ,we have seen that all matter influences all other matter1 and the quantity of meteoric stuff that would be required to support the sun's expenditure would be enough to have a serious effect on ,mercury1 an effect that would certainly have been noticed4 ,there can1 therefore1 be no such mass of matter near the sun1 and though there is no doubt a certain number of meteors do fall into his furnaces day by day1 it is not nearly enough to account for his continuous radiation4 ,it seems after this as if nothing else could be suggested2 but yet an answer has been found1 an answer so wonderful that it is more like a fairy tale than reality4 ,to begin at the beginning1 we must go back to the time when the sun was only a great gaseous nebula filling all the space included in the orbit of ,neptune4 ,this nebula was not in itself hot1 but as it rotated it contracted4 ,now1 heat is really only a form of energy1 and energy and heat can be interchanged easily4 ,this is a very startling thing when heard for the first time1 but it is known as surely as we know anything and has been proved again and again4 ,when a savage wants to make a fire he turns a piece of hard wood very very quickly between his palms--twiddles it1 we should say expressively--into a hole in another piece of wood1 until a spark bursts out4 ,what is the spark8 ,it is the energy of the savage's work turned to heat4 ,when a horse strikes his iron-shod hoofs hard on the pavement you see sparks fly2 that is caused by the energy of the horse's leg4 ,when you pump hard at your bicycle you feel your pump getting quite hot1 for part of the energy you are putting into your work is transformed into heat2 and so on in numberless instances4 ,no energetic action of any kind in this world takes place without some of the energy being turned into heat1 though in many instances the amount is so small as to be unnoticeable4 ,nothing falls to the ground without some heat being generated4 ,now1 when this great nebula first began its remarkable career1 by the action of gravity all the particles in it were drawn toward the centre2 little by little they fell in1 and the nebula became smaller4 ,we are not now concerned with the origin of the planets--we leave that aside2 we are only contemplating the part of the nebula which remained to become the sun4 ,now these particles being drawn inward each generated some heat1 so as the nebula contracted its temperature rose4 ,throughout the ages1 over the space of millions and millions of miles1 it contracted and grew hotter4 ,it still remained gaseous1 but at last it got to an immense temperature1 and is the sun as we know it4 ,what then keeps it shining8 ,it is still contracting1 but slowly1 so slowly that it is quite imperceptible to our finest instruments4 ,it has been calculated that if it contracts two hundred and fifty feet in diameter in a year1 the energy thus gained and turned into heat is quite sufficient to account for its whole yearly output4 ,this is indeed marvellous4 ,in comparison with the sun's size two hundred and fifty feet is nothing4 ,it would take nine thousand years at this rate before any diminution could be noticed by our finest instruments6 ,here is a source of heat which can continue for countless ages without exhaustion4 ,thus to all intents and purposes we may say the sun's shining is inexhaustible4 ,yet we must follow out the train of reasoning1 and see what will happen in the end1 in eras and eras of time1 if nothing intervenes4 ,well1 some gaseous bodies are far finer and more tenuous than others1 and when a gaseous body contracts it is all the time getting denser2 as it grows denser and denser it at last becomes liquid1 and then solid1 and then it ceases to contract1 as of course the particles of a solid body cannot fall freely toward the centre1 as those of a gaseous body can4 ,our earth has long ago reached this stage4 ,when solid the action ceases1 and the heat is no more kept up by this source of energy1 therefore the body begins to cool--surface first1 and lastly the interior2 it cools more quickly the smaller it is4 ,our moon has parted with all her heat long ago1 while the earth still retains some internally4 ,in the sun1 therefore1 we have an object-lesson of the stages through which all the planets must have passed4 ,they have all once been glowing hot1 and some may be still hot even on the surface1 as we have seen there is reason to believe is the case with ,jupiter4 ,by this marvellous arrangement for the continued heat of the sun we can see that the warmth of our planets is assured for untold ages4 ,there is no need to fear that the sun will wear out by burning4 ,his brightness will continue for ages beyond the thoughts of man4 ,besides this1 a few other things have been discovered about him4 ,he is1 of course1 exceptionally difficult to observe2 for though he is so large1 which should make it easy1 he is so brilliant that anyone regarding him through a telescope without the precaution of prepared glasses to keep off a great part of the light would be blinded at once4 ,one most remarkable fact about the sun is that his surface is flecked with spots1 which appear sometimes in greater numbers and sometimes in less1 and the reason and shape of these spots have greatly exercised men's minds4 ,sometimes they are large enough to be seen without a telescope at all1 merely by looking through a piece of smoked or coloured glass1 which cuts off the most overpowering rays4 ,when they are visible like this they are enormous1 large enough to swallow many earths in their depths4 ,at other times they may be observed by the telescope1 then they may be about five thousand miles across4 ,sometimes one spot can be followed by an astronomer as it passes all across the sun1 disappears at the edge1 and after a lapse of time comes back again round the other edge4 ,this first showed men that the sun1 like all the planets1 rotated on his axis1 and gave them the means of finding out how long he took in doing so4 ,but the spots showed a most surprising result1 for they took slightly different times in making their journey round the sun1 times which differed according to their position4 ,for instance1 a spot near the equator of the sun took twenty-five days to make the circuit1 while one higher up or lower down took twenty-six days1 and one further out twenty-seven2 so that if these spots are1 as certainly believed1 actually on the surface1 the conclusion is that the sun does not rotate all in one piece1 but that some parts go faster than others4 ,no one can really explain how this could be1 but it is certainly more easily understood in the case of a body of gas than of a solid body1 when it would be simply impossible to conceive4 ,the spots seem to keep principally a little north and a little south of the equator2 there are very few actually at it1 and none found near the poles1 but no reason for this distribution has been discovered4 ,it has been noted that about every eleven years the greatest number of spots appears1 and that they become fewer again1 mounting up in number to the next eleven years1 and so on4 ,all these curious facts show there is much yet to be solved about the sun4 ,the spots were supposed for long to be eruptions bursting up above the surface1 but now they are generally held to be deep depressions like saucers1 probably caused by violent tempests1 and it is thought that the inrush of cooler matter from above makes them look darker than the other parts of the sun's surface4 ,but when we use the words 'cooler' and 'darker1' we mean only by comparison1 for in reality the dark parts of the spots are brighter than electric light4 ,illustration3 ,royal ,observatory1 ,greenwich4 ,,sun-,,spots4 ,the fact that the spots are in reality depressions or holes is shown by their change of appearance as they pass over the face of the sun toward the edge2 for the change of shape is exactly that which would be caused by foreshortening4 ,it sounds odd to say that the best time for observing the sun is during a total eclipse1 for then the sun's body is hidden by the moon4 ,but yet to a certain extent this is true1 and the reason is that the sun's own brilliance is our greatest hindrance in observing him1 his rays are so dazzling that they light up our own atmosphere1 which prevents us seeing the edges4 ,now1 during a total eclipse1 when nearly all the rays are cut off1 we can see marvellous things1 which are invisible at other times4 ,but total eclipses are few and far between1 and so when one is approaching astronomers make great preparations beforehand4 ,a total eclipse is not visible from all parts of the world1 but only from that small part on which the shadow of the moon falls1 and as the earth travels1 this shadow1 which is really a round spot1 passes along1 making a dark band4 ,in this band astronomers choose the best observatories1 and there they take up their stations4 ,the dark body of the moon first appears to cut a little piece out of the side of the sun1 and as it sails on1 gradually blotting out more and more1 eager telescopes follow it2 at last it covers up the whole sun1 and then a marvellous spectacle appears1 for all round the edges of the black moon are seen glorious red streamers and arches and filaments of marvellous shapes1 continually changing4 ,these are thrown against a background of pale green light that surrounds the black moon and the hidden sun4 ,in early days astronomers thought these wonderful coloured streamers belonged to the moon2 but it was soon proved that they really are part of the sun1 and are only invisible at ordinary times1 because our atmosphere is too bright to allow them to be seen4 ,an instrument has now been invented to cut off most of the light of the sun1 and when this is attached to a telescope these prominences1 as they are called1 can be seen at any time1 so that there is no need to wait for an eclipse4 ,illustration3 ,,the ,,earth ,,as ,,it ,,would ,,appear ,,in ,,comparison ,,with ,,the ,,flames ,,shooting ,,out ,,from ,,the ,,sun4 ,what are these marvellous streamers and filaments8 ,they are what they seem1 eruptions of fiery matter discharged from the ever-palpitating sun thousands of miles into surrounding space4 ,they are for ever shooting out and bursting and falling back1 fireworks on a scale too enormous for us to conceive4 ,some of these brilliant flames extend for three hundred thousand miles1 so that in comparison with one of them the whole world would be but a tiny ball1 and this is going on day and night without cessation4 ,look at the picture where the artist has made a little black ball to represent the earth as she would appear if she could be seen in the midst of the flames shooting out from the sun4 ,do not make a mistake and think the earth really could be in this position2 she is only shown there so that you may see how tiny she is in comparison with the sun4 ,all the time you have lived and your father1 and grandfather1 and right back to the beginnings of ,english history1 and far1 far further into the dim ages1 this stupendous exhibition of energy and power has continued1 and only of late years has anyone known anything about it2 even now a mere handful of people do know1 and the rest1 who are warmed and fed and kept alive by the gracious beams of this great revolving glowing fireball1 never give it a thought4 ,i said just now a pale green halo surrounded the sun1 extending far beyond the prominences2 this is called the corona and can only be seen during an eclipse4 ,it surrounds the sun in a kind of shell1 and there is reason to believe that it too is made of luminous stuff ejected by the sun in its burning fury4 ,it is composed of large streamers or filaments1 which seem to shoot out in all directions2 generally these are not much larger than the apparent width of the sun1 but sometimes they extend much further4 ,the puzzle is1 this corona cannot be an atmosphere in any way resembling that of our earth2 for the gravitational force of the sun1 owing to its enormous size1 is so great that it would make any such atmosphere cling to it much more densely near to the surface1 while it would be thinner higher up1 and the corona is not dense in any way1 but thin and tenuous throughout4 ,this makes it very difficult to explain2 it is supposed that some kind of electrical force enters into the problem1 but what it is exactly we are far from knowing yet4 ,,chapter ,,viii ,,shining ,,visitors ,our solar system is set by itself in the midst of a great space1 and so far as we have learnt about it in this book everything in it seems orderly3 the planets go round the sun and the satellites go round the planets1 in orbits more or less regular2 there seems no place for anything else4 ,but when we have considered the planets and the satellites1 we have not exhausted all the bodies which own allegiance to the sun4 ,there is another class1 made up of strange and weird members1 which flash in and out of the system1 coming and going in all directions and at all times--sometimes appearing without warning1 sometimes returning with a certain regularity1 sometimes retiring to infinite depths of space1 where no human eye will ever see them more4 ,these strange visitors are called comets1 and are of all shapes and sizes and never twice alike4 ,even as we watch them they grow and change1 and then diminish in splendour4 ,some are so vast that men see them as flaming signs in the sky1 and regard them with awe and wonder2 some cannot be seen at all without the help of the telescope4 ,from the very earliest ages those that were large enough to be seen without glasses have been regarded with astonishment4 ,men used to think that they were signs from heaven foretelling great events in the world4 ,timid people predicted that the end of the world would come by collision with one of them4 ,others1 again1 fancifully likened them to fishes in that sea of space in which we swim--fishes gigantic and terrifying1 endowed with sense and will4 ,it is perhaps unnecessary to say that comets are no more alive than is our own earth1 and as for causing the end of the world by collision1 there is every reason to believe the earth has been more than once right through a comet's tail1 and yet no one except scientific men even discovered it4 ,these mysterious visitors from the outer regions of space were called comets from a ,greek word signifying hair1 for they often leave a long luminous trail behind1 which resembles the filaments of a woman's hair4 ,it is not often that one appears large and bright enough to be seen by the naked eye1 and when it does it is not likely to be soon forgotten4 ,in the year #aiaj such a comet is expected1 a comet which at its former appearance compelled universal attention by its brilliancy and strangeness4 ,at the time of the ,norman ,conquest of ,england a comet believed to be the very same one was stretching its glorious tail half across the sky1 and the ,normans seeing it1 took it as a good omen1 fancying that it foretold their success4 ,the history of the ,norman ,conquest was worked in tapestry--that is to say1 in what we should call crewels on a strip of linen--and in this record the comet duly appears4 ,look at him in the picture as the ,normans fancied him4 ,he has a red head with blue flames starting from it1 and several tails4 ,the little group of men on the left are pointing and chattering about him4 ,we can judge what an impression this comet must have made to be recorded in such an important piece of work4 ,illustration3 ,,the ,,comet ,,in ,,the ,,bayeux ,,tapestry4 ,but we are getting on too fast4 ,we have yet to learn how anyone can know that the comet which appeared at the time of the ,norman ,conquest is the same as that which has come back again at different times1 and above all1 how anyone can tell that it will come again in the year #aiaj4 ,all this involves a long story4 ,before the invention of telescopes of course only those comets could be seen which were of great size and fine appearance4 ,in those days men did not realize that our world was but one of a number and of no great importance except to ourselves1 and they always took these blazing appearances in the heavens as a particular warning to the human race4 ,but when astronomers1 by the aid of the telescope1 found that for one comet seen by the eye there were hundreds which no mortal eye unaided could see1 this idea seemed1 to say the least of it1 unlikely4 ,yet even then comets were looked upon as capricious visitors from outer space2 odd creatures drawn into our system by the attraction of the sun1 who disappeared1 never to return4 ,it was ,newton1 the same genius who disclosed to us the laws of gravity1 who first declared that comets moved in orbits1 only that these orbits were far more erratic than any of those followed by the planets4 ,so far we have supposed that the planets were all on what we should call a level--that is to say1 we have regarded them as if they were floating in a sea of water around the sun2 but this is only approximately correct1 for the orbits of the planets are not all at one level4 ,if you had a number of slender hoops or rings to represent the planetary orbits1 you would have to tilt one a little this way and another a little that way1 only never so far but that a line through the centre of the hoop from one side to another could pass through the sun4 ,the way in which the planetary orbits are tilted is slight in comparison with that of the orbits of comets1 for these are at all sorts of angles--some turned almost sideways1 and others slanting1 and all of them are ellipses long drawn out and much more irregular than the planetary orbits2 but erratic as they are1 in every case a line drawn through the sun and extended both ways would touch each side of the orbits4 ,a great astronomer called ,halley1 who was born in the time of the ,commonwealth1 was lucky enough to see a very brilliant comet1 and the sight interested him so much that he made all the calculations necessary to find out just in what direction it was travelling in the heavens4 ,he found out that it followed an ellipse which brought it very near to the sun at one part of its journey1 and carried it far beyond the orbit of the earth1 right out to that of ,neptune1 at the other4 ,then he began to search the records for other comets which had been observed before his time4 ,he found that two particularly bright ones had been carefully noted--one about seventy-five years before that which he had seen1 and the other seventy-five years before that again4 ,both these comets had been watched so scientifically that the paths in which they had travelled could be computed4 ,a brilliant inspiration came to ,halley4 ,he believed that instead of these three1 his own and the other two1 being different comets1 they were the same one1 which returned to the sun about every seventy-five years4 ,this could be proved1 for if this idea were correct1 of course the comet would return again in another seventy-five years1 unless something unforeseen occurred4 ,but ,halley was in the prime of life3 he could not hope to live to see his forecast verified4 ,the only thing he could do was to note down exact particulars1 by means of which others who lived after him might recognize his comet4 ,and so when the time came for its return1 though ,halley was in his grave1 numbers of astronomers were watching eagerly to see the fulfilment of his prediction4 ,the comet did indeed appear1 and since then it has been seen once again1 and now we expect it to come back in the year #aiaj1 when you and ,i may see it for ourselves4 ,when the identity of the comet was fully established men began to search further back still1 to compare the records of other previous brilliant comets1 and found that this one had been noticed many times before1 and once as ,i said1 at the time of the ,norman ,conquest4 ,halley's comet is peculiar in many ways4 ,for instance1 it is unusual that so large and interesting a comet should return within a comparatively limited time4 ,it is the smaller comets1 those that can only be seen telescopically1 that usually run in small orbits4 ,the smallest orbits take about three and a half years to traverse1 and some of the largest orbits known require a period of one hundred and ten thousand years4 ,between these two limits lies every possible variety of period4 ,one comet1 seen about the time ,napoleon was born1 was calculated to take two thousand years to complete its journey1 and another1 a very brilliant one seen in #ahhb1 must journey for eight hundred years before it again comes near to the sun4 ,but we never know what might happen1 for at any moment a comet which has traversed a long solitary pathway in outer darkness may flash suddenly into our ken1 and be for the first time noted and recorded1 before flying off at an angle which must take it for ever further and further from the sun4 ,everything connected with comets is mysterious and most fascinating4 ,from out of the icy regions of space a body appears2 what it is we know not1 but it is seen at first as a hairy or softly-glowing star1 and it was thus that ,herschel mistook ,uranus for a comet when he first discovered it4 ,as it draws nearer the comet sends out some fan-like projections toward the sun1 enclosing its nucleus in filmy wrappings like a cocoon of light1 and it travels faster and faster4 ,from its head shoots out a tail--it may be more than one--growing in splendour and width1 and always pointing away from the sun4 ,so enormous are some of these tails that when the comet's head is close to the sun the tail extends far beyond the orbit of the earth4 ,faster still and faster flies the comet1 for as we have seen it is a consequence of the law of gravitation that the nearer planets are to the sun the faster they move in their orbits1 and the same rule applies to comets too4 ,as the comet dashes up to the sun his pace becomes something indescribable2 it has been reckoned for some comets at three hundred miles a second6 ,but behold1 as the head flies round the sun the tail is always projected outwards4 ,the nucleus or head may be so near to the sun that the heat it receives would be sufficient to reduce molten iron to vapour2 but this does not seem to affect it3 only the tail expands4 ,sometimes it becomes two or more tails1 and as it sweeps round behind the head it has to cover a much greater space in the same time1 and therefore it must travel even faster than the head4 ,the pace is such that no calculations can account for it1 if the tail is composed of matter in any sense as we know it4 ,then when the sun is passed the comet sinks away again1 and as it goes the tail dies down and finally disappears4 ,the comet itself dwindles to a hairy star once more and goes--whither8 ,into space so remote that we cannot even dream of it--far away into cold more appalling than anything we could measure1 the cold of absolute space4 ,more and more slowly it travels1 always away and away1 until the sun1 a short time back a huge furnace covering all the sky1 is now but a faint star4 ,thus on its lonely journey unseen and unknown the comet goes4 ,this comet which we have taken as an illustration is a typical one1 but all are not the same4 ,some have no tails at all1 and never develop any2 some change utterly even as they are watched4 ,the same comet is so different at different times that the only possible way of identifying it is by knowing its path1 and even this is not a certain method1 for some comets appear to travel at intervals along the same path6 ,now we come to the question that must have been in the mind of everyone from the beginning of this chapter1 ,what are comets8 ,this question no one can answer definitely1 for there are many things so puzzling about these strange appearances that it is difficult even to suggest an explanation4 ,yet a good deal is known4 ,in the first place1 we are certain that comets have very little density--that is to say1 they are indescribably thin1 thinner than the thinnest kind of gas2 and air1 which we always think so thin1 would be almost like a blanket compared with the material of comets4 ,this we judge because they exercise no sort of influence on any of the planetary bodies they draw near to1 which they certainly would do if they were made of any kind of solid matter4 ,they come sometimes very close to some of the planets4 ,a comet was so near to ,jupiter that it was actually in among his moons4 ,the comet was violently agitated2 he was pulled in fact right out of his old path1 and has been going on a new one ever since2 but he did not exercise the smallest effect on ,jupiter1 or even on the moons4 ,and1 as ,i said earlier in this chapter1 we on the earth have been actually in the folds of a comet's tail4 ,this astonishing fact happened in ,june1 #ahfa4 ,one evening after the sun had set a golden-yellow disc1 surrounded with filmy wrappings1 appeared in the sky4 ,the sun's light1 diffused throughout our atmosphere1 had prevented its being seen sooner4 ,this was apparently the comet's head4 ,it is described as 'though a number of light1 hazy clouds were floating around a miniature full moon4' ,from this a cone of light extended far up into the sky1 and when the head disappeared below the horizon this tail was seen to reach to the zenith4 ,but that was not all4 ,strange shafts of light seemed to hang right overhead1 and could only be accounted for by supposing that they were caused by another tail hanging straight above us1 so that we looked up at it foreshortened by perspective4 ,the comet's head lay between the earth and the sun1 and its tail1 which extended over many millions of miles1 stretched out behind in such a way that the earth must have gone right through it4 ,the fact that the comet exercised no perceptible influence on the earth at all1 and that there were not even any unaccountable magnetic storms or displays of electricity1 may reassure us so that if ever we do again come in contact with one of these extremely fine1 thin bodies1 we need not be afraid4 ,there is another way in which we can judge of the wonderful tenuity or thinness of comets--that is1 that the smallest stars can be seen through their tails1 even though those tails must be many thousands of miles in thickness4 ,now1 if the tails were anything approaching the density of our own atmosphere1 the stars when seen through them would appear to be moved out of their places4 ,this sounds odd1 and requires a word of explanation4 ,the fact is that anything seen through any transparent medium like water or air is what is called refracted--that is to say1 the rays coming from it look bent4 ,everyone is quite familiar with this in everyday life1 though perhaps they may not have noticed it4 ,you cannot thrust a stick into the water without seeing that it looks crooked4 ,air being less dense than water has not quite so strong a refracting power1 but still it has some4 ,we cannot prove it in just the same way1 because we are all inside the atmosphere ourselves1 and there is no possibility of thrusting a stick into it from the outside6 ,the only way we know it is by looking at something which is 'outside' already1 and we find plenty of objects in the sky4 ,as a matter of fact1 the stars are all a little pulled out of their places by being seen through the air1 and though of course we do not notice this1 astronomers know it and have to make allowance for it4 ,the effect is most noticeable in the case of the sun when he is going down1 for the atmosphere bends his rays up1 and though we see him a great glowing red ball on the horizon1 and watch him1 as we think1 drop gradually out of sight1 we are really looking at him for the last moment or two when he has already gone1 for the rays are bent up by the air and his image lingers when the real sun has disappeared4 ,illustration3 ,a ,,stick ,,thrust ,,into ,,the ,,water ,,appears ,,crooked4 ,therefore in looking through the luminous stuff that forms a comet's tail astronomers might well expect to see the stars displaced1 but not a sign of this appears4 ,it is difficult to imagine1 therefore1 what the tail can be made of4 ,the idea is that the sun exercises a sort of repulsive effect on certain elements found in the comet's head--that is to say1 it pushes them away1 and that as the head approaches the sun1 these elements are driven out of it away from the sun in vapour4 ,this action may have something to do with electricity1 which is yet little understood2 anyway1 the effect is that1 instead of attracting the matter toward itself1 in which case we should see the comet's tails stretching toward the sun1 the sun drives it away6 ,in the chapter on the sun we had to imagine something of the same kind to account for the corona1 and the corona and the comet's tails may be really akin to each other1 and could perhaps be explained in the same way4 ,now we come to a stranger fact still4 ,some comets go right through the sun's corona1 and yet do not seem to be influenced by it in the smallest degree4 ,this may not seem very wonderful at first perhaps1 but if you remember that a dash through anything so dense as our atmosphere1 at a pace much less than that at which a comet goes1 is enough to heat iron to a white heat1 and then make it fly off in vapour1 we get a glimpse of the extreme fineness of the materials which make the corona4 ,here is ,herschel's account of a comet that went very near the sun3 ',the comet's distance from the sun's centre was about the #afjth part of our distance from it4 ,all the heat we enjoy on this earth comes from the sun4 ,imagine the heat we should have to endure if the sun were to approach us1 or we the sun1 to one #afjth part of its present distance4 ,it would not be merely as if #afj suns were shining on us all at once1 but1 #afj times #afj1 according to a rule which is well known to all who are conversant with such matters4 ,now1 that is #be1fjj4 ,only imagine a glare #be1fjj times fiercer than that of the equatorial sunshine at noon day with the sun vertical4 ,in such a heat there is no substance we know of which would not run like water1 boil1 and be converted into smoke or vapour4 ,no wonder the comet gave evidence of violent excitement1 coming from the cold region outside the planetary system torpid and ice-bound4 ,already when arrived even in our temperate region it began to show signs of internal activity2 the head had begun to develop1 and the tail to elongate1 till the comet was for a time lost sight of--not for days afterwards was it seen2 and its tail1 whose direction was reversed1 and which could not possibly be the same tail it had before1 had already lengthened to an extent of about ninety millions of miles1 so that it must have been shot out with immense force in a direction away from the sun4' ,we remember that comets have sometimes more than one tail1 and a theory has been advanced to account for this too4 ,it is supposed that perhaps different elements are thrust away by the sun at different angles1 and one tail may be due to one element and another to another4 ,but if the comet goes on tail-making to a large extent every time it returns to the sun1 what happens eventually8 ,do the tails fall back again into the head when out of reach of the sun's action8 ,such an idea is inconceivable2 but if not1 then every time a comet approaches the sun he loses something1 and that something is made up of the elements which were formerly in the head and have been violently ejected4 ,if this be so we may well expect to see comets which have returned many times to the sun without tails at all1 for all the tail-making stuff that was in the head will have been used up1 and as this is exactly what we do see1 the theory is probably true4 ,where do the comets come from8 ,that also is a very large question4 ,it used to be supposed they were merely wanderers in space who happened to have been attracted by our sun and drawn into his system1 but there are facts which go very strongly against this1 and astronomers now generally believe that comets really belong to the solar system1 that their proper orbits are ellipses1 and that in the case of those which fly off at such an angle that they can never return they must at some time have been pulled out of their original orbit by the influence of one of the planets4 ,illustration3 ,royal ,observatory1 ,cape of ,good ,hope4 ,a ,,great ,,comet4 ,to get a good idea of a really fine comet1 until we have the opportunity of seeing one for ourselves1 we cannot do better than look at this picture of a comet photographed in #aija at the ,cape of ,good ,hope4 ,it is only comparatively recently that photography has been applied to comets4 ,when ,halley's comet appeared last time such a thing was not thought of1 but when he comes again numbers of cameras1 fitted up with all the latest scientific appliances1 will be waiting to get good impressions of him4 ,,chapter ,,ix ,,shooting ,,stars ,,and ,,fiery ,,balls ,all the substances which we are accustomed to see and handle in our daily lives belong to our world4 ,there are vegetables which grow in the earth1 minerals which are dug out of it1 and elementary things1 such as air and water1 which have always made up a part of this planet since man knew it4 ,these are obvious1 but there are other things not quite so obvious which also help to form our world4 ,among these we may class all the elements known to chemists1 many of which have difficult names1 such as oxygen and hydrogen4 ,these two are the elements which make up water1 and oxygen is an important element in air1 which has nitrogen in it too4 ,there are numbers and numbers of other elements perfectly familiar to chemists1 of which many people never even hear the names4 ,we live in the midst of these things1 and we take them for granted and pay little attention to them2 but when we begin to learn about other worlds we at once want to know if these substances and elements which enter so largely into our daily lives are to be found elsewhere in the universe or are quite peculiar to our own world4 ,this question might be answered in several ways1 but one of the most practical tests would be if we could get hold of something which had not been always on the earth1 but had fallen upon it from space4 ,then1 if this body were made up of elements corresponding with those we find here1 we might judge that these elements are very generally diffused throughout the bodies in the solar system4 ,it sounds in the highest degree improbable that anything should come hurling through the air and alight on our little planet1 which we know is a mere speck in a great ocean of space2 but we must not forget that the power of gravity increases the chances greatly1 for anything coming within a certain range of the earth1 anything small enough1 that is1 and not travelling at too great a pace1 is bound to fall on to it4 ,and1 however improbable it seems1 it is undoubtedly true that masses of matter do crash down upon the earth from time to time1 and these are called meteorites4 ,when we think of the great expanse of the oceans1 of the ice round the poles1 and of the desert wastes1 we know that for every one of such bodies seen to fall many more must have fallen unseen by any human being4 ,meteors large enough to reach the earth are not very frequent1 which is perhaps as well1 and as yet there is no record of anyone's having been killed by them4 ,most of them consist of masses of stone1 and a few are of iron1 while various substances resembling those that we know here have been found in them4 ,chemists in analyzing them have also come across certain elements so far unknown upon earth1 though of course there is no saying that these may not exist at depths to which man has not penetrated4 ,a really large meteor is a grand sight4 ,if it is seen at night it appears as a red star1 growing rapidly bigger and leaving a trail of luminous vapour behind as it passes across the sky4 ,in the daytime this vapour looks like a cloud4 ,as the meteor hurls itself along there may be a deep continuous roar1 ending in one supreme explosion1 or perhaps in several explosions1 and finally the meteor may come to the earth in one mass1 with a force so great that it buries itself some feet deep in the soil1 or it may burst into numbers of tiny fragments1 which are scattered over a large area4 ,when a meteor is found soon after its fall it is very hot1 and all its surface has 'run1' having been fused by heat4 ,the heat is caused by the friction of our atmosphere4 ,the meteor gets entangled in the atmosphere1 and1 being drawn by the attraction of the earth1 dashes through it4 ,part of the energy of its motion is turned to heat1 which grows greater and greater as the denser air nearer to the earth is encountered2 so that in time all the surface of the meteor runs like liquid1 and this liquid1 rising to a still higher temperature1 is blown off in vapour1 leaving a new surface exposed4 ,the vapour makes the trail of fire or cloud seen to follow the meteor4 ,if the process went on for long the meteor would be all dissipated in vapour1 and in any case it must reach the earth considerably reduced in size4 ,numbers and numbers of comparatively small ones disappear1 and for every one that manages to come to earth there must be hundreds seen only as shooting stars1 which vanish and 'leave not a wrack behind4' ,when a meteor is seen to fall it is traced1 and1 whenever possible1 it is found and placed in a museum4 ,men have sometimes come across large masses of stone and iron with their surfaces fused with heat4 ,these are in every way like the recognized meteorites1 except that no eye has noted their advent4 ,as there can be no reasonable doubt that they are of the same origin as the others1 they too are collected and placed in museums1 and in any large museum you would be able to see both kinds--those which have been seen to come to earth and those which have been found accidentally4 ,the meteors which appear very brilliant in their course across the sky are sometimes called fire-balls1 which is only another name for the same thing4 ,some of these are brighter than the full moon1 so bright that they cause objects on earth to cast a shadow4 ,in #ahjc a fiery ball was noticed above a small town in ,normandy2 it burst and scattered stones far and wide1 but luckily no one was hurt4 ,the largest meteorites that have been found on the earth are a ton or more in weight2 others are mere stones2 and others again just dust that floats about in the atmosphere before gently settling4 ,of course1 meteors of this last kind could not be seen to fall like the larger ones1 yet they do fall in such numbers that calculations have been made showing that the earth must catch about a hundred millions of meteors daily1 having altogether a total weight of about a hundred tons4 ,this sounds enormous1 but compared with the weight of the earth it is very small indeed4 ,now that we have arrived at the fact that strange bodies do come hurtling down upon us out of space1 and that we can actually handle and examine them1 the next question is1 ,where do they come from8 ,at one time it was thought that they were fragments which had been flung off by the earth herself when she was subject to violent explosions1 and that they had been thrown far enough to resist the impulse to drop down upon her again1 and had been circling round the sun ever since1 until the earth came in contact with them again and they had fallen back upon her4 ,it is not difficult to imagine a force which would be powerful enough to achieve the feat of speeding something off at such a velocity that it passed beyond the earth's power to pull it back1 but nothing that we have on earth would be nearly strong enough to achieve such a feat4 ,imaginative writers have pictured a projectile hurled from a cannon's mouth with such tremendous force that it not only passed beyond the range of the earth's power to pull it back1 but so that it fell within the influence of the moon and was precipitated on to her surface6 ,such things must remain achievements in imagination only2 it is not possible for them to be carried out4 ,other ideas as to the origin of meteors were that they had been expelled from the moon or from the sun4 ,it would need a much less force to send a projectile away from the moon than from the earth on account of its smaller size and less density1 but the distance from the earth to the moon is not very great1 and any projectile hurled forth from the moon would cross it in a comparatively short time4 ,therefore if the meteorites come from the moon1 the moon must be expelling them still1 and we might expect to see some evidence of it2 but we know that the moon is a dead world1 so this explanation is not possible4 ,the sun1 for its part1 is torn by such gigantic disturbances that1 notwithstanding its vast size1 there is no doubt sufficient force there to send meteors even so far as the earth1 but the chances of their encountering the earth would be small4 ,both these theories are now discarded4 ,it is believed that the meteors are merely lesser fragments of the same kind of materials as the planets1 circling independently round the sun2 and a proof of this is that far more meteorites fall on that part of the earth which is facing forward in its journey than on that behind1 and this is what we should expect if the meteors were scattered independently through space and it was by reason of our movements that we came in contact with them4 ,there is no need to explain this further4 ,everyone knows that in cycling or driving along a road where there is a good deal of traffic both ways the people we meet are more in number than those who overtake us1 and the same result would follow with the meteors2 that is to say1 in travelling through space where they were fairly evenly distributed we should meet more than we should be overtaken by4 ,you remember that it was suggested the sun's fuel might be obtained from meteors1 and this was proved to be not possible1 even though there are no doubt unknown millions of these strange bodies circling throughout the solar system4 ,there are so many names for these flashing bodies that we may get a little confused3 when they are seen in the sky they are meteors1 or fire-balls2 when they reach the earth they are called meteorites1 and also aerolites4 ,then there is another class of the same bodies called shooting stars1 and these are in reality only meteors on a smaller scale2 but there ought to be no confusion in our thoughts1 for all these objects are small bodies travelling round the sun1 and caught by the earth's influence4 ,when you watch the sky for some time on a clear night1 you will seldom fail to see at least one star flash out suddenly in a path of thrilling light and disappear1 and you cannot be certain whether that star had been shining in the sky a minute before1 or if it had appeared suddenly only in order to go out4 ,the last idea is right4 ,we must get rid at once of the notion that it would be possible for any fixed star to behave in this manner4 ,to begin with1 the fixed stars are many of them actually travelling at a great velocity at present1 yet so immeasurably distant are they that their movement makes no perceptible difference to us4 ,for one of them to appear to dash across the heavens as a meteor does would mean a velocity entirely unknown to us1 even comparing it with the speed of light4 ,no1 these shooting stars are not stars at all1 though they were so named1 long before the real motions of the fixed stars were even dimly guessed at4 ,as we have seen1 they belong to the same class as meteors4 ,i remember being told by a clergyman1 years ago1 that one night in ,november he had gone up to bed very late1 and as he pulled up his blind to look at the sky1 to his amazement he saw a perfect hail of shooting stars1 some appearing every minute1 and all darting in vivid trails of light1 longer or shorter1 though all seemed to come from one point4 ,so marvellous was the sight that he dashed across the village street1 unlocked the church door1 and himself pulled the bell with all his might4 ,the people in that quiet country village had long been in bed1 but they huddled on their clothes and ran out of their pretty thatched cottages1 thinking there must be a great fire1 and when they saw the wonder in the sky they were amazed and cried out that the world must be coming to an end4 ,the clergyman knew better than that1 and was able to reassure them1 and tell them he had only taken the most effectual means of waking them so that they might not miss the display1 for he was sure as long as they lived they would never see such another sight4 ,a star shower of this kind is certainly well worth getting up to see1 but though uncommon it is not unique4 ,there are many records of such showers having occurred in times gone by1 and when men put together and examined the records they found that the showers came at regular intervals4 ,for instance1 every year about the same time in ,november there is a star shower1 not comparable1 it is true1 with the brilliant one the clergyman saw1 but still noticeable1 for more shooting stars are seen then than at other times1 and once in every thirty-three years there is a specially fine one4 ,it happened in fact to be one of these that the village people were wakened up to see4 ,not all at once1 but gradually1 the mystery of these shower displays was solved4 ,it was realized that the meteors need not necessarily come from one fixed place in the sky because they seemed to us to do so1 for that was only an effect of perspective4 ,if you were looking down a long1 perfectly straight avenue of tree-trunks1 the avenue would seem to close in1 to get narrower and narrower at the far end until it became a point2 but it would not really do so1 for you would know that the trees at the far end were just the same distance from each other as those between which you were standing4 ,now1 two meteors starting from the same direction at a distance from each other1 and keeping parallel1 would seem to us to start from a point and to open out wider and wider as they approached1 but they would not really do so2 it would only be1 as in the case of the avenue1 an effect of perspective4 ,if a great many meteors did the same thing1 they would appear to us all to start from one point1 whereas really they would be on parallel lines1 only as they rushed to meet us or we rushed to meet them this effect would be produced4 ,therefore the first discovery was that these meteors were thousands and thousands of little bodies travelling in lines parallel to each other1 like a swarm of little planets4 ,to judge that their path was not a straight line but a circle or ellipse was the next step1 and this was found to be the case4 ,from taking exact measurements of their paths in the sky an astronomer computed they were really travelling round the sun in a lengthened orbit1 an ellipse more like a comet's orbit than that of a planet4 ,but next came the puzzling question1 ,why did the earth apparently hit them every year to some extent1 and once in thirty-three years seem to run right into the middle of them8 ,this also was answered4 ,one has only to imagine a swarm of such meteors at first hastening busily along their orbit1 a great cluster all together1 then1 by the near neighbourhood of some planet1 or by some other disturbing causes1 being drawn out1 leaving stragglers lagging behind1 until at last there might be some all round the path1 but only thinly scattered1 while the busy1 important cluster that formed the nucleus was still much thicker than any other part4 ,now1 if the orbit that the meteors followed cut the orbit or path of the earth at one point1 then every time the earth came to what we may call the level crossing she must run into some of the stragglers1 and if the chief part of the swarm took thirty-three years to get round1 then once in about thirty-three years the earth must strike right into it4 ,this would account for the wonderful display4 ,so long drawn-out is the thickest part of the swarm that it takes a year to pass the points at the level crossing4 ,if the earth strikes it near the front one year1 she may come right round in time to strike into the rear part of the swarm next year1 so that we may get fine displays two years running about every thirty-three years4 ,the last time we passed through the swarm was in #ahii1 and then the show was very disappointing4 ,here in ,england thick clouds prevented our seeing much1 and there will not be another chance for us to see it at its best until #aicb4 ,these ,november meteors are called ,leonids1 because they seem to come from a group of stars named ,leo1 and though the most noticeable they are not the only ones4 ,a shower of the same kind occurs in ,august too1 but the ,august meteors1 called ,perseids1 because they seem to come from ,perseus1 revolve in an orbit which takes a hundred and forty-two years to traverse6 ,so that only every one hundred and forty-second year could we hope to see a good display4 ,when all these facts had been gathered up1 it seemed without doubt that certain groups of meteors travelled in company along an elliptical orbit4 ,but there remained still something more--a bold and ingenious theory to be advanced4 ,it was found that a comet1 a small one1 only to be seen with the telescope1 revolved in exactly the same orbit as the ,november meteors1 and another one1 larger1 in exactly the same orbit as the ,august ones2 hence it could hardly be doubted that comets and meteors had some connection with each other1 though what that connection is exactly no one knows4 ,anyway1 we can have no shadow of doubt when we find the comet following a marked path1 and the meteors pursuing the same path in his wake1 that the two have some mysterious affinity4 ,there are other smaller showers besides these of ,november and ,august1 and a remarkable fact is known about one of them4 ,this particular stream was found to be connected with a comet named ,biela's ,comet1 that had been many times observed1 and which returned about every seven years to the sun4 ,after it had been seen several times1 this astonishing comet split in two and appeared as two comets1 both of which returned at the end of the next seven years4 ,but on the next two occasions when they were expected they never came at all1 and the third time there came instead a fine display of shooting stars1 so it really seemed as if these meteors must be the fragments of the lost comet4 ,it is very curious and interesting to notice that in these star showers there is no certain record of any large meteorite reaching the earth2 they seem to be made up of such small bodies that they are all dissipated in vapour as they traverse our air4 ,,chapter ,x ,,the ,,glittering ,,heavens ,on a clear moonless night the stars appear uncountable4 ,you see them twinkling through the leafless trees1 and covering all the sky from the zenith1 the highest point above your head1 down to the horizon4 ,it seems as if someone had taken a gigantic pepper-pot and scattered them far and wide so that some had fallen in all directions4 ,if you were asked to make a guess as to how many you can see at one time1 no doubt you would answer ',millions6' ,but you would be quite wrong1 for the number of stars that can be seen at once without a telescope does not exceed two thousand1 and this1 after the large figures we have been dealing with1 appears a mere trifle4 ,with a telescope1 even of small power1 many more are revealed1 and every increase in the size of the telescope shows more still2 so that it might be supposed the universe is indeed illimitable1 and that we are only prevented from seeing beyond a certain point by our limited resources4 ,but in reality we know that this cannot be so4 ,if the whole sky were one mass of stars1 as it must be if the number of them were infinite1 then1 even though we could not distinguish the separate items1 we should see it bright with a pervading and diffused light4 ,as this is not so1 we judge that the universe is not unending1 though1 with all our inventions1 we may never be able to probe to the end of it4 ,we need not1 indeed1 cry for infinity1 for the distances of the fixed stars from us are so immeasurable that to atoms like ourselves they may well seem unlimited4 ,our solar system is set by itself1 like a little island in space1 and far1 far away on all sides are other great light-giving suns resembling our own more or less1 but dwindled to the size of tiny stars1 by reason of the great void of space lying between us and them4 ,our sun is1 indeed1 just a star1 and by no means large compared with the average of the stars either4 ,but1 then1 he is our own2 he is comparatively near to us1 and so to us he appears magnificent and unique4 ,judging from the solar system1 we might expect to find that these other great suns which we call stars have also planets circling round them1 looking to them for light and heat as we do to our sun4 ,there is no reason to doubt that in some instances the conjecture is right1 and that there may be other suns with attendant planets4 ,it is however a great mistake to suppose that because our particular family in the solar system is built on certain lines1 all the other families must be made on the same pattern4 ,why1 even in our own system we can see how very much the planets differ from each other3 there are no two the same size2 some have moons and some have not2 ,saturn's rings are quite peculiar to himself1 and ,uranus and ,neptune indulge in strange vagaries4 ,so why should we expect other systems to be less varied8 ,as science has advanced1 the idea that these faraway suns must have planetary attendants as our sun has been discarded4 ,the more we know the more is disclosed to us the infinite variety of the universe4 ,for instance1 so much accustomed are we to a yellow sun that we never think of the possibility of there being one of another colour4 ,what would you say then to a ruby sun1 or a blue one2 or to two suns of different colours1 perhaps red and green1 circling round each other2 or to two such suns each going round a dark companion8 ,for there are dark bodies as well as shining bodies in the sky4 ,these are some of the marvels of the starry sky1 marvels quite as absorbing as anything we have found in the solar system4 ,it requires great care and patience and infinite labour before the very delicate observations which alone can reveal to us anything of the nature of the fixed stars can be accomplished4 ,it is only since the improvement in large telescopes that this kind of work has become possible1 and so it is but recently men have begun to study the stars intimately1 and even now they are baffled by indescribable difficulties4 ,one of these is our inability to tell the distance of a thing by merely looking at it unless we also know its size4 ,on earth we are used to seeing things appear smaller the further they are from us1 and by long habit can generally tell the real size2 but when we turn to the stars1 which appear so much alike1 how are we to judge how far off they are8 ,two stars apparently the same size and close together in the sky may really be as far one from another as the earth is from the nearest2 for if the further one were very much larger than the nearer1 they would then appear the same size4 ,at first it was natural enough to suppose that the big bright stars of what we call the first magnitude were the nearest to us1 and the less bright the next nearest1 and so on down to the tiny ones1 only revealed by the telescope1 which would be the furthest away of all2 but research has shown that this is not correct4 ,some of the brightest stars may be comparatively near1 and some of the smallest may be near also4 ,the size is no test of distance4 ,so far as we have been able to discover1 the star which seems nearest is a first magnitude one1 but some of the others which outshine it must be among the infinitely distant ones4 ,thus we lie in the centre of a jewelled universe1 and cannot tell even the size of the jewels which cover its radiant robe4 ,i say 'lie1' but that is really not the correct word4 ,so far as we have been able to find out1 there is no such thing as absolute rest in the universe--in fact1 it is impossible2 for even supposing any body could be motionless at first1 it would be drawn by the attraction of its nearest neighbours in space1 and gradually gain a greater and greater velocity as it fell toward them4 ,even the stars we call 'fixed' are all hurrying along at a great pace1 and though their distance prevents us from seeing any change in their positions1 it can be measured by suitable instruments4 ,our sun is no exception to this universal rule4 ,like all his compeers1 he is hurrying busily along somewhere in obedience to some impulse of which we do not know the nature2 and as he goes he carries with him his whole cortge of planets and their satellites1 and even the comets4 ,yes1 we are racing through space with another motion1 too1 besides those of rotation and revolution1 for our earth keeps up with its master attractor1 the sun4 ,it is difficult1 no doubt1 to follow this1 but if you think for a moment you will remember that when you are in a railway-carriage everything in that carriage is really travelling along with it1 though it does not appear to move4 ,and the whole solar system may be looked at as if it were one block in movement4 ,as in a carriage1 the different bodies in it continue their own movements all the time1 while sharing in the common movement4 ,you can get up and change your seat in the train1 and when you sit down again you have not only moved that little way of which you are conscious1 but a great way of which you are not conscious unless you look out of the window4 ,now in the case of the earth's own motion we found it necessary to look for something which does not share in that motion for purposes of comparison1 and we found that something in the sun1 who shows us very clearly we are turning on our axis4 ,but in the case of the motion of the solar system the sun is moving himself1 so we have to look beyond him again and turn to the stars for confirmation4 ,then we find that the stars have motions of their own1 so that it is very difficult to judge by them at all4 ,it is as if you were bicycling swiftly towards a number of people all walking about in different directions on a wide lawn4 ,they have their movements1 but they all also have an apparent movement1 really caused by you as you advance toward them2 and what astronomers had to do was to separate the true movements of the stars from the false apparent movement made by the advance of the sun4 ,this great problem was attacked and overcome1 and it is now known with tolerable certainty that the sun is sweeping onward at a pace of about twelve miles a second toward a fixed point4 ,it really matters very little to us where he is going1 for the distances are so vast that hundreds of years must elapse before his movement makes the slightest difference in regard to the stars4 ,but there is one thing which we can judge1 and that is that though his course appears to be in a straight line1 it is most probably only a part of a great curve so huge that the little bit we know seems straight4 ,when we speak of the stars1 we ought to keep quite clearly in our minds the fact that they lie at such an incredible distance from us that it is probable we shall never learn a great deal about them4 ,why1 men have not even yet been able to communicate with the planet ,mars1 at its nearest only some thirty-five million miles from us1 and this is a mere nothing in measuring the space between us and the stars4 ,to express the distances of the stars in figures is really a waste of time1 so astronomers have invented another way4 ,you know that light can go round the world eight times in a second2 that is a speed quite beyond our comprehension1 but we just accept it4 ,then think what a distance it could travel in an hour1 in a day2 and what about a year8 ,the distance that light can travel in a year is taken as a convenient measure by astronomers for sounding the depths of space4 ,measured in this way light takes four years and four months to reach us from the nearest star we know of1 and there are others so much more distant that hundreds--nay1 thousands--of years would have to be used to convey it4 ,light which has been travelling along with a velocity quite beyond thought1 silently1 unresting1 from the time when the ,britons lived and ran half naked on this island of ours1 has only reached us now1 and there is no limit to the time we may go back in our imaginings4 ,we see the stars1 not as they are1 but as they were4 ,if some gigantic conflagration had happened a hundred years ago in one of them situated a hundred light-years away from us1 only now would that messenger1 swifter than any messenger we know1 have brought the news of it to us4 ,to put the matter in figures1 we are sure that no star can lie nearer to us than twenty-five billions of miles4 ,a billion is a million millions1 and is represented by a figure with twelve noughts behind it1 so--#a1jjj1jjj1jjj1jjj2 and twenty-five such billions is the least distance within which any star can lie4 ,how much farther away stars may be we know not1 but it is something to have found out even that4 ,on the same scale as that we took in our first example1 we might express it thus3 ,if the earth were a greengage plum at a distance of about three hundred of your steps from the sun1 and ,neptune were1 on the same scale1 about three miles away1 the nearest fixed star could not be nearer than the distance measured round the whole earth at the ,equator6 ,all this must provoke the question1 ,how can anyone find out these things8 ,well1 for a long time the problem of the distances of the stars was thought to be too difficult for anyone to attempt to solve it1 but at last an ingenious method was devised1 a method which shows once more the triumph of man's mind over difficulties4 ,in practice this method is extremely difficult to carry out1 for it is complicated by so many other things which must be made allowance for2 but in theory1 roughly explained1 it is not too hard for anyone to grasp4 ,the way of it is this3 ,if you hold up your finger so as to cover exactly some object a few feet distant from you1 and shut first one eye and then the other1 you will find that the finger has apparently shifted very considerably against the background4 ,the finger has not really moved1 but as seen from one eye or the other1 it is thrown on a different part of the background1 and so appears to jump2 then if you draw two imaginary lines1 one from each eye to the finger1 and another between the two eyes1 you will have made a triangle4 ,now1 all of you who have done a little ,euclid know that if you can ascertain the length of one side of a triangle1 and the angles at each end of it1 you can form the rest of the triangle2 that is to say1 you can tell the length of the other two sides4 ,in this instance the base line1 as it is called--that is to say the line lying between the two eyes--can easily be measured1 and the angles at each end can be found by an instrument called a sextant1 so that by simple calculation anyone could find out what distance the finger was from the eye4 ,now1 some ingenious man decided to apply this method to the stars4 ,he knew that it is only objects quite near to us that will appear to shift with so small a base line as that between the eyes1 and that the further away anything is the longer must the base line be before it makes any difference4 ,but this clever man thought that if he could only get a base line long enough he could easily compute the distance of the stars from the amount that they appeared to shift against their background4 ,he knew that the longest base line he could get on earth would be about eight thousand miles1 as that is the diameter of the earth from one side to the other2 so he carefully observed a star from one end of this immense base line and then from the other1 quite confident that this plan would answer4 ,but what happened8 ,after careful observations he discovered that no star moved at all with this base line1 and that it must be ever so much longer in order to make any impression4 ,then indeed the case seemed hopeless1 for here we are tied to the earth and we cannot get away into space4 ,but the astronomer was nothing daunted4 ,he knew that in its journey round the sun the earth travels in an orbit which measures about one hundred and eighty-five millions of miles across1 so he resolved to take observations of the stars when the earth was at one side of this great circle1 and again1 six months later1 when she had travelled to the other side4 ,then indeed he would have a magnificent base line1 one of one hundred and eighty-five millions of miles in length4 ,what was the result8 ,even with this mighty line the stars are found to be so distant that many do not move at all1 not even when measured with the finest instruments1 and others move1 it may be1 the breadth of a hair at a distance of several feet6 ,but even this delicate measure1 a hair's-breadth1 tells its own tale2 it lays down a limit of twenty-five billion miles within which no star can lie6 ,this system which ,i have explained to you is called finding the star's parallax1 and perhaps it is easier to understand when we put it the other way round and say that the hair's-breadth is what the whole orbit of the earth would appear to have shrunk to if it were seen from the distance of these stars6 ,many1 many stars have now been examined1 and of them all our nearest neighbour seems to be a bright star seen in the ,southern ,hemisphere4 ,it is in the constellation or star group called ,centaurus1 and is the brightest star in it4 ,in order to designate the stars when it is necessary to refer to them1 astronomers have invented a system4 ,to only the very brightest are proper names attached2 others are noted according to the degree of their brightness1 and called after the letters of the ,greek alphabet3 alpha1 beta1 gamma1 delta1 etc4 ,our own word 'alphabet' comes1 you know1 from the first two letters of this ,greek series4 ,as this particular star is the brightest in the constellation ,centaurus1 it is called ,alpha ,centauri2 and if ever you travel into the ,southern ,hemisphere and see it1 you may greet it as our nearest neighbour in the starry universe1 so far as we know at present4 ,,chapter ,,xi ,,the ,,constellations ,from the very earliest times men have watched the stars1 felt their mysterious influence1 tried to discover what they were1 and noted their rising and setting4 ,they classified them into groups1 called constellations1 and gave such groups the names of figures and animals1 according to the positions of the stars composing them4 ,some of these imaginary figures seem to us so wildly ridiculous that we cannot conceive how anyone could have gone so far out of their way as to invent them4 ,but they have been long sanctioned by custom1 so now1 though we find it difficult to recognize in scattered groups of stars any likeness to a fish or a ram or a bear2 we still call the constellations by their old names for convenience in referring to them4 ,supposing the axis of the earth were quite upright1 straight up and down in regard to the plane at which the earth goes round the sun1 then we should always see the same set of stars from the ,northern and the same set of stars from the ,southern ,hemispheres all the year round4 ,but as the axis is tilted slightly1 we can1 during our nights in the winter in the ,northern ,hemisphere1 see more of the sky to the south than we can in the summer2 and in the ,southern ,hemisphere just the reverse is the case1 far more stars to the north can be seen in the winter than in the summer4 ,but always1 whether it is winter or summer1 there is one fixed point in each hemisphere round which all the other stars seem to swing1 and this is the point immediately over the ,north or the ,south ,poles4 ,there is1 luckily1 a bright star almost at the point at which the ,north ,pole would seem to strike the sky were it infinitely lengthened4 ,this is not one of the brightest stars in the sky1 but quite bright enough to serve the purpose1 and if we stand with our faces towards it1 we can be sure we are looking due north4 ,how can we discover this star for ourselves in the sky8 ,go out on any starlight night when the sky is clear1 and see if you can find a very conspicuous set of seven stars called the ,great ,bear4 ,i shall not describe the ,great ,bear1 because every child ought to know it already1 and if they don't1 they can ask the first grown-up person they meet1 and they will certainly be told4 7,see map47 ,illustration3 ,,constellations ,,near ,,the ,,pole ,,star4 ,having found the ,great ,bear1 you have only to draw an imaginary line between the two last stars forming the square on the side away from the tail1 and carry it on about three times as far as the distance between those two stars1 and you will come straight to the ,pole ,star4 ,the two stars in the ,great ,bear which help one to find it are called the ,pointers1 because they point to it4 ,the ,great ,bear is one of the constellations known from the oldest times2 it is also sometimes called ,charles's ,wain1 the ,dipper1 or the ,plough4 ,it is always easily seen in ,england1 and seems to swing round the ,pole ,star as if held by an invisible rope tied to the ,pointers4 ,besides the ,great ,bear there is1 not far from it1 the ,little ,bear1 which is really very like it1 only smaller and harder to find4 ,the ,pole ,star is the last star in its tail2 from it two small stars lead away parallel to the ,great ,bear1 and they bring the eye to a small pair which form one side of a square just like that in the ,great ,bear4 ,but the whole of the ,little ,bear is turned the opposite way from the ,great ,bear1 and the tail points in the opposite direction4 ,and when you come to think of it1 it is very ridiculous to have called these groups ,bears at all1 or to talk about tails1 for bears have no tails6 ,so it would have been better to have called them foxes or dogs1 or almost any other animal rather than bears4 ,now1 if you look at the sky on the opposite side of the ,pole ,star from the ,great ,bear1 you will see a clearly marked capital ,w made up of five or six bright stars4 ,this is called ,cassiopeia1 or the ,lady's ,chair4 ,in looking at ,cassiopeia you cannot help noticing that there is a zone or broad band of very many stars1 some exceedingly small1 which apparently runs right across the sky like a ragged hoop1 and ,cassiopeia seems to be set in or on it4 ,this band is called the ,milky ,way1 and crosses not only our northern sky1 but the southern sky too1 thus making a broad girdle round the whole universe4 ,it is very wonderful1 and no one has yet been able to explain it4 ,the belt is not uniform and even1 but it is here and there broken up into streamers and chips1 having the same appearance as a piece of ribbon which has been snipped about by scissors in pure mischief2 or it may be compared to a great river broken up into many channels by rocks and obstacles in its course4 ,the ,milky ,way is mainly made up of thousands and thousands of small stars1 and many more are revealed by the telescope2 but1 as we see in ,cassiopeia1 there are large bright stars in it too1 though1 of course1 these may be infinitely nearer to us1 and may only appear to us to be in the ,milky ,way because they are between us and it4 ,now1 besides the few constellations that ,i have mentioned1 there are numbers of others1 some of which are difficult to discover1 as they contain no bright stars4 ,but there are certain constellations which every one should know1 because in them may be found some of the brightest stars1 those of the first magnitude4 ,magnitude means size1 and it is really absurd for us to say a star is of the first magnitude simply because it appears to us to be large1 for1 as ,i have explained already1 a small star comparatively near to us might appear larger than a greater one further away4 ,but the word 'magnitude' was used when men really thought stars were large or small according to their appearance1 and so it is used to this day4 ,they called the biggest and brightest first magnitude stars4 ,of these there are not many1 only some twenty1 in all the sky4 ,the next brightest--about the brightness of the ,pole ,star and the stars in the ,great ,bear--are of the second magnitude1 and so on1 each magnitude containing stars less and less bright4 ,when we come to stars of the sixth magnitude we have reached the limit of our sight1 for seventh magnitude stars can only be seen with a telescope4 ,now that we understand what is meant by the magnitude1 we can go back to the constellations and try to find some more4 ,if you draw an imaginary line across the two stars forming the backbone of the ,bear1 starting from the end nearest the tail1 and continue it onward for a good distance1 you will come to a very bright star called ,capella1 which you will know1 because near it are three little ones in a triangle4 ,now1 ,capella means a goat1 so the small ones are called the kids4 ,in winter ,capella gets high up into the sky1 and then there is to be seen below her a little cluster called the ,pleiades4 ,there is nothing else like this in the whole sky4 ,it is formed of six stars1 as it appears to persons of ordinary sight1 and these stars are of the sixth magnitude1 the lowest that can be seen by the naked eye4 ,but though small1 they are set so close together1 and appear so brilliant1 twinkling like diamonds1 that they are one of the most noticeable objects in the heavens4 ,a legend tells that there were once seven stars in the ,pleiades clearly visible1 and that one has now disappeared4 ,this is sometimes spoken of as 'the lost ,pleiad1' but there does not seem to be any foundation for the story4 ,in old days people attached particular holiness or luck to the number seven1 and possibly1 when they found that there were only six stars in this wonderful group1 they invented the story about the seventh4 ,as the ,pleiades rise1 a beautiful reddish star of the first magnitude rises beneath them4 ,it is called ,aldebaran1 and it1 as well as the ,pleiades1 forms a part of the constellation of ,taurus the bull4 ,in ,england we can see in winter below ,aldebaran the whole of the constellation of ,orion1 one of the finest of all the constellations1 both for the number of the bright stars it contains and for the extent of the sky it covers4 ,four bright stars at wide distances enclose an irregular four-sided space in which are set three others close together and slanting downwards4 ,below these1 again1 are another three which seem to fall from them1 but are not so bright4 ,the figure of ,orion as drawn in the old representations of the constellations is a very magnificent one4 ,the three bright stars form his belt1 and the three smaller ones the hilt of his sword hanging from it4 ,illustration3 ,,orion ,,and ,,his ,,neighbours4 ,if you draw an imaginary line through the stars forming the belt and prolong it downwards slantingly1 you will see1 in the very height of winter1 the brightest star in all the sky1 either in the ,northern or ,southern ,hemisphere4 ,this is ,sirius1 who stands in a class quite by himself1 for he is many times brighter than any other first magnitude star4 ,he never rises very high above the horizon here1 but on crisp1 frosty nights may be seen gleaming like a big diamond between the leafless twigs and boughs of the rime-encrusted trees4 ,sirius is the ,dog ,star1 and it is perhaps fortunate that1 as he is placed1 he can be seen sometimes in the southern and sometimes in the northern skies1 so that many more people have a chance of looking at his wonderful brilliancy1 than if he had been placed near the ,pole star4 ,in speaking of the supreme brightness of ,sirius among the stars1 we must remember that ,venus and ,jupiter1 which outrival him1 are not stars1 but planets1 and that they are much nearer to us4 ,sirius is so distant that the measures for parallax make hardly any impression on him1 but1 by repeated experiments1 it has now been proved that light takes more than eight years to travel from him to us4 ,so that1 if you are eight years old1 you are looking at ,sirius as he was when you were a baby6 ,not far from the ,pleiades1 to the left as you face them1 are to be found two bright stars nearly the same size2 these are the ,heavenly ,twins1 or ,gemini4 ,returning now to the ,great ,bear1 we find1 if we draw a line through the middle and last stars of his tail1 and carry it on for a little distance1 we come fairly near to a cluster of stars in the form of a horseshoe2 there is only one fairly bright one in it1 and some of the others are quite small1 but yet the horseshoe is distinct and very beautiful to look at4 ,this is the ,northern ,crown4 ,the very bright star not far from it is another first-class star called ,arcturus4 ,to the left of the ,northern ,crown lies ,hercules1 which is only mentioned because near it is the point to which the sun with all his system appears at present to be speeding4 ,for other fascinating constellations1 such as ,leo or the ,lion1 ,andromeda and ,perseus1 and the three bright stars by which we recognize ,aquila the ,eagle1 you must wait awhile1 unless you can get some one to point them out4 ,those which you have noted already are enough to lead you on to search for more4 ,perhaps some of you who live in towns and can see only a little strip of sky from the nursery or schoolroom windows have already found this chapter dull1 and if so you may skip the rest of it and go on to the next4 ,for the others1 however1 there is one more thing to know before leaving the subject1 and that is the names of the string of constellations forming what is called the ,zodiac4 ,you may have heard the rhyme3 ',the ,ram1 the ,bull1 the ,heavenly ,twins1 ,and next the ,crab1 the ,lion shines1 ,the ,virgin and the ,scales2 ,the ,scorpion1 ,archer1 and ,he-goat1 ,the ,man that holds the watering-pot1 ,the ,fish with glittering tails4' ,this puts in a form easy to remember the signs of the constellations which lie in the ,zodiac1 an imaginary belt across the whole heavens4 ,it is very difficult to explain the ,zodiac1 but ,i must try4 ,imagine for a moment the earth moving round its orbit with the sun in the middle4 ,now1 as the earth moves the sun will be seen continually against a different background--that is to say1 he will appear to us to move not only across our sky in a day by reason of our rotation1 but also along the sky1 changing his position among the stars by reason of our revolution4 ,you will say at once that we cannot see the stars when the sun is there1 and no more we can4 ,but the stars are there all the same1 and every month the sun seems to have moved on into a new constellation1 according to astronomers' reckoning4 ,if you count up the names of the constellations in the rhyme1 you will find that there are just twelve1 one for each month1 and at the end of the year the sun has come round to the first one again4 ,the first one is ,aries the ,ram1 and the sun is seen projected or thrown against that part of the sky where ,aries is1 in ,april1 when we begin spring2 this is the first month to astronomers1 and not ,january1 as you might suppose4 ,perhaps you will learn to recognize all the constellations in the ,zodiac one day2 a few of them1 such as the ,bull and the ,heavenly ,twins1 you know already if you have followed this chapter4 ,,chapter ,,xii ,,what ,,the ,,stars ,,are ,,made ,,of ,how can we possibly tell what the stars are made of8 ,if we think of the vast oceans of space lying between them and us1 and realize that we can never cross those oceans1 for in them there is no air1 it would seem to be a hopeless task to find out anything about the stars at all4 ,but even though we cannot traverse space ourselves1 there is a messenger that can1 a messenger that needs no air to sustain him1 that moves more swiftly than our feeble minds can comprehend1 and this messenger brings us tidings of the stars--his name is ,light4 ,light tells us many marvellous things1 and not the least marvellous is the news he gives us of the workings of another force1 the force of gravitation4 ,in some ways gravitation is perhaps more wonderful than light1 for though light speeds across airless space1 it is stopped at once by any opaque substance--that is to say1 any substance not transparent1 as you know very well by your own shadows1 which are caused by your bodies stopping the light of the sun4 ,light striking on one side of the earth does not penetrate through to the other1 whereas gravitation does4 ,you remember1 of course1 what the force of gravitation is1 for we read about that very early in this book4 ,it is a mysterious attraction existing between all matter4 ,every atom pulls every other atom towards itself1 more or less strongly according to distance4 ,now1 solid matter itself makes no difference to the force of gravitation1 which acts through it as though it were not there4 ,the sun is pulling the earth toward itself1 and it pulls the atoms on the far side of the earth just as strongly as it would if there were nothing lying between it and them4 ,therefore1 unlike light1 gravitation takes no heed of obstacles in the way1 but acts in spite of them4 ,the gravitation of the earth holds you down just the same1 though you are on the upper floor of a house1 with many layers of wood and plaster between you and it4 ,it cannot pull you down1 for the floor holds you up1 but it is gravitation that keeps your feet on the ground all the same4 ,a clever man made up a story about some one who invented a kind of stuff which stopped the force of gravitation going through it1 just as a solid body stops light2 when this stuff was made1 of course1 it went right away off into space1 carrying with it anyone who stood on it1 as there was nothing to hold it to the earth6 ,that was only a story1 and it is not likely anyone could invent such stuff1 but it serves to make clear the working of gravitation4 ,these two tireless forces1 light and gravitation1 run throughout the whole universe1 and carry messages of tremendous importance for those who have minds to grasp them4 ,without light we could know nothing of these distant worlds1 and without understanding the laws of gravity we should not be able to interpret much that light tells us4 ,to begin with light1 what can we learn from it8 ,we turn at once to our own great light-giver1 the sun1 to whom we owe not only all life1 but also all the colour and beauty on earth4 ,it is well known to men of science that colour lies in the light itself1 and not in any particular object4 ,that brilliant blue cloak of yours is not blue of itself1 but because of the light that falls on it4 ,if you cannot believe this1 go into a room lighted only by gas1 and hey1 presto6 the colour is changed as if it were a conjuring trick4 ,you cannot tell now by looking at the cloak whether it is blue or green6 ,therefore you must admit that as the colour changes with the change of light it must be due to light1 and not to any quality belonging to the material of the cloak4 ,but1 you may protest1 if the colour is solely due to light1 and light falls on everything alike1 why are there so many colours8 ,that is a very fair question4 ,if the light that comes from the sun were of only one colour--say blue or red--then everything would be blue or red all the world over4 ,some doors in houses are made with a strip of red or blue glass running down the sides4 ,if you have one in your house like that1 go and look through it1 and you will see an astonishing world made up of different tones of the same colour4 ,everything is red or blue1 according to the colour of the glass1 and the only difference in the appearance of objects lies in the different shades1 whether things are light or dark4 ,this is a world as it might appear if the sun's rays were only blue or only red4 ,but the sun's light is not of one colour only1 fortunately for us2 it is of all the colours mixed together1 which1 seen in a mass1 make the effect of white light4 ,now1 objects on earth are only either seen by the reflected light of the sun or by some artificial light4 ,they have no light of their own4 ,put them in the dark and they do not shine at all2 you cannot see them4 ,it is the sun's light striking on them that makes them visible4 ,but all objects do not reflect the light equally1 and this is because they have the power of absorbing some of the rays that strike on them and not giving them back at all1 and only those rays that are given back show to the eye4 ,a white thing gives back all the rays1 and so looks white1 for we have the whole of the sun's light returned to us again4 ,but how about a blue thing8 ,it absorbs all the rays except the blue1 so that the blue rays are the only ones that come back or rebound from it again to meet our eyes1 and this makes us see the object blue2 and this is the case with all the other colours4 ,a red object retains all rays except the red1 which it sends back to us2 a yellow object gives back only the yellow rays1 and so on4 ,what an extraordinary and mysterious fact6 ,imagine a brilliant flower-garden in autumn4 ,here we have tall yellow sunflowers with velvety brown centres1 clustering pink and crimson hollyhocks1 deep red and bright yellow peonies1 slender fairy-like ,japanese anemones1 great bunches of mauve ,michaelmas daisies1 and countless others1 and mingled with all these are many shades of green4 ,yet it is the light of the sun alone that falling on all these varied objects1 makes that glorious blaze of colour2 it seems incredible4 ,it may be difficult to believe1 but it is true beyond all doubt4 ,each delicate velvety petal has some quality in it which causes it to absorb certain of the sun's rays and send back the others1 and its colour is determined by those it sends back4 ,well then how infinitely varied must be the colours hidden in the sun's light1 colours which1 mixed all together1 make white light6 ,yes1 this is so1 for all colours that we know are to be found there4 ,in fact1 the colours that make up sunlight are the colours to be seen in the rainbow1 and they run in the same order4 ,have you ever looked carefully at a rainbow8 ,if not1 do so at the next chance4 ,you will see it begins by being dark blue at one end1 and passes through all colours until it gets to red at the other4 ,we cannot see a rainbow every day just when we want to1 but we can see miniature rainbows which contain just the same colours as the real ones in a number of things any time the sun shines4 ,for instance1 in the cut-glass edge of an inkstand or a decanter1 or in one of those old-fashioned hanging pieces of cut-glass that dangle from the chandelier or candle-brackets4 ,of course you have often seen these colours reflected on the wall1 and tried to get them to shine upon your face4 ,or you have caught sight of a brilliant patch of colour on the wall and looked around to see what caused it1 finally tracing it to some thick edge of shining glass standing in the sunlight4 ,now1 the cut-glass edge shows these colours to you because it breaks up the light that falls upon it into the colours it is made of1 and lets each one come out separately1 so that they form a band of bright colours instead of just one ray of white light4 ,this is perhaps a little difficult to understand1 but ,i will try to explain4 ,when a ray of white light falls on such a piece of glass1 which is known as a prism1 it goes in as white light at one side1 but the three-cornered shape of the glass breaks it up into the colours it is made of1 and each colour comes out separately at the other side--namely1 from blue to red--like a little rainbow1 and instead of one ray of white light1 we have a broad band of all the colours that light is made of4 ,who would ever have thought a pretty plaything like this could have told us what we so much wanted to know--namely1 what the sun and the stars are made of8 ,it seems too marvellous to be true1 yet true it is that for ages and ages light has been carrying its silent messages to our eyes1 and only recently men have learnt to interpret them4 ,it is as if some telegraph operator had been going steadily on1 click1 click1 click1 for years and years1 and no one had noticed him until someone learnt the code of dot and dash in which he worked1 and then all at once what he was saying became clear4 ,the chief instrument in translating the message that the light brings is simply a prism1 a three-cornered wedge of glass1 just the same as those hanging lustres belonging to the chandeliers4 ,when a piece of glass like this is fixed in a telescope in such a way that the sun's rays fall on it1 then there is thrown on to a piece of paper or any other suitable background a broad coloured band of lovely light like a little rainbow1 and this is called the sun's spectrum1 and the instrument by which it is seen is called a spectroscope4 ,but this in itself could tell us little2 the message it brings lies in the fact that when it has passed through the telescope1 so that it is magnified1 it is crossed by hundreds of minute black lines1 not placed evenly at all1 but scattered up and down4 ,there may be two so close together that they look like one1 and then three far apart1 and then some more at different distances4 ,when this remarkable appearance was examined carefully it was found that in sunlight the lines that appeared were always exactly the same1 in the same places1 and this seemed so curious that men began to seek for an explanation4 ,someone thought of an experiment which might teach us something about the matter1 and instead of letting sunlight fall on the prism1 he made an artificial light by burning some stuff called sodium1 and then allowed the band of coloured light to pass through the telescope2 when he examined the spectrum that resulted1 he found that1 though numbers of lines to be found in the sun's spectrum were missing1 there were a few lines here exactly matching a few of the lines in the sun's spectrum2 and this could not be the result of chance only1 for the lines are so mathematically exact1 and are in themselves so peculiarly distributed1 that it could only mean that they were due to the same cause4 ,what could this signify1 then1 but that away up there in the sun1 among other things1 stuff called sodium1 very well known to chemists on earth1 is burning8 ,after this many other substances were heated white-hot so as to give out light1 in order to discover if the lines to be seen in their spectra were also to be found in the sun's spectrum4 ,one of these was iron1 and1 astonishing to say1 all the many little thread-like lines that appeared in its spectrum were reproduced to a hair's-breadth1 among others1 in the sun's spectrum4 ,so we have found out beyond all possibility of doubt some of the materials of which the sun is made4 ,we know that iron1 sodium1 hydrogen1 and numerous other substances and elements1 are all burning away there in a terrific furnace1 to which any furnace we have on earth is but as the flicker of a match4 ,it was not1 of course1 much use applying this method to the planets1 for we know that the light which comes from them to us is only reflected sunlight1 and this1 indeed1 was proved by means of the spectroscope4 ,but the stars shine by their own light1 and this opened up a wide field for inquiry4 ,the difficulty was1 of course1 to get the light of one star separated from all the rest1 because the light of one star is very faint and feeble to cast a spectrum at all4 ,yet by infinite patience difficulties were overcome4 ,one star alone was allowed to throw its light into the telescope2 the light passed through a prism1 and showed a faint band of many colours1 with the expected little black lines cutting across it more or less thickly4 ,examinations have thus been made of hundreds of stars4 ,in the course of them some substances as yet unknown to us on earth have been encountered1 and in some stars one element--hydrogen--is much stronger than in others2 but1 on the whole1 speaking broadly1 it has been satisfactorily shown that the stars are made on the same principles as our own sun1 so that the reasoning of astronomers which had argued them to be suns was proved4 ,illustration3 ,,the ,,spectrum ,,of ,,the ,,sun ,,and ,,sirius4 ,we have here in the picture the spectrum of the sun and the spectrum of ,arcturus4 ,you can see that the lines which appear in the band of light belonging to ,sirius are also in the band of light belonging to the sun1 together with many others4 ,this means that the substances flaming out and sending us light from the far away star are also giving out light from our own sun1 and that the sun and ,sirius both contain the same elements in their compositions4 ,this1 indeed1 seems enough for the spectroscope to have accomplished2 it has interpreted for us the message light brings from the stars1 so that we know beyond all possibility of mistake that these glowing1 twinkling points of light are brilliant suns in a state of intense heat1 and that in them are burning elements with which we ourselves are quite familiar4 ,but when the spectroscope had done that1 its work was not finished1 for it has not only told us what the stars are made of1 but another thing which we could never have known without it--namely1 if they are moving toward us or going away from us4 ,,chapter ,,xiii ,,restless ,,stars ,you remember we have already remarked upon the difficulty of telling how far one star lies behind another1 as we do not know their sizes4 ,it is1 to take another similar case1 easy enough to tell if a star moves to one side or the other1 but very difficult by ordinary observation to tell if it is advancing toward us or running away from us1 for the only means we have of judging is if it gets larger or smaller1 and at that enormous distance the fact whether it advances or recedes makes no difference in its size4 ,now1 the spectroscope has changed all this1 and we can tell quite as certainly if a star is coming toward us as we can if it moves to one side4 ,i will try to explain this4 ,you know1 perhaps1 that sound is caused by vibration in the air4 ,the noise1 whatever it is1 jars the air and the vibrations strike on our ears4 ,it is rather the same thing as the result of throwing a stone into a pond3 from the centre of the splash little wavelets run out in ever-widening circles2 so through the air run ever-widening vibrations from every sound4 ,the more vibrations there are in a second the shriller is the note they make4 ,in a high note the air-vibrations follow one another fast1 pouring into one's ear at a terrific speed1 so that the apparatus in the ear which receives them itself vibrates fiercely and records a high note1 while a lower note brings fewer and slower vibrations in a second1 and the ear is not so much disturbed4 ,have you ever noticed that if a railway engine is sweeping-toward you and screaming all the time1 its note seems to get shriller and shriller8 ,that is because the engine1 in advancing1 sends the vibrations out nearer to you1 so more of them come in a second1 and thus they are crowded up closer together1 and are higher and higher4 ,now1 light is also caused by waves1 but they are not the same as sound waves4 ,light travels without air1 whereas sound we know cannot travel without air1 and is ever so much slower1 and altogether a grosser1 clumsier thing than light4 ,but yet the waves or rays which make light correspond in some ways to the vibrations of sound4 ,what corresponds to the treble on the piano is the blue end of the spectrum in light1 and the bass is the red end4 ,now1 when we are looking at the spectrum of any body which is advancing swiftly toward us1 something of the same effect is observed as in the case of the shrieking engine4 ,take any star and imagine that that star is hastening toward us at a pace of three hundred miles a second1 which is not at all an unusual rate for a star2 then1 if we examine the band of light1 the spectrum1 of such a star1 we shall observe an extraordinary fact--all these little lines we have spoken of are shoved up toward the treble or blue end of the spectrum4 ,they still remain just the same distances from each other1 and are in twos and threes or single1 so that the whole set of lines is unaltered as a set1 but everyone of them is shifted a tiny fraction up toward the blue end of the spectrum1 just a little displaced4 ,now if1 instead of advancing toward us1 this same star had been rushing away from us at a similar pace1 all these lines would have been moved a tiny bit toward the red or bass end of the spectrum4 ,this is known to be certainly true1 so that by means of the spectroscope we can tell that some of these great sun-stars are advancing toward us and some receding from us1 according to whether the multitudes of little lines in the spectrum are shifted slightly to the blue or the red end4 ,you remember that it has been surmised that the pace the sun moves with his system is about twelve miles a second4 ,this seems fast enough to us1 who think that one mile a minute is good time for an express train1 but it is slow compared with the pace of many of the stars4 ,as ,i have said1 some are travelling at a rate of between two hundred and three hundred miles a second2 and it is due to the spectroscope that we know not only whether a star is advancing toward us or receding from us1 but also whether the pace is great or not2 it even tells us what the pace is1 up to about half a mile a second1 which is very marvellous4 ,it is a curious fact that many of the small stars show greater movement than the large ones1 which mayor may not mean that they are nearer to us4 ,it may be taken as established that there is no such thing as absolute rest in the universe3 everything1 stars and nebul alike1 are moving somewhere2 in an infinite variety of directions1 with an infinite variety of speed they hasten this way and that4 ,it would be impossible for any to remain still1 for even supposing it had been so 'in the beginning1' the vast forces at work in the universe would not let it remain so4 ,out of space would come the persistent call of gravitation3 atoms would cry silently to atoms4 ,there could be no perfect equality of pull on all sides2 from one side or another the pull would be the stronger4 ,slowly the inert mass would obey and begin falling toward it2 it might be an inch at a time1 but with rapid increase1 until at last it also was hastening some whither in this universe which appears to us to be infinite4 ,it must be remembered that these stars1 even when moving at an enormous pace1 do not change their places in the sky when regarded by ordinary observers4 ,it would take thousands of years for any of the constellations to appear at all different from what they are now1 even though the stars that compose them are moving in different directions with a great velocity1 for a space of many millions of miles1 at the distance of most of the stars1 would be but as the breadth of a fine hair as seen by us on earth4 ,so thousands of years ago men looked up at the ,great ,bear1 and saw it apparently the same as we see it now2 yet for all that length of time the stars composing it have been rushing in this direction and that at an enormous speed1 but do not appear to us on the earth to alter their positions in regard to each other4 ,i know of nothing that gives one a more overwhelming sense of the mightiness of the universe and the smallness of ourselves than this fact4 ,from age to age men look on changeless heavens1 yet this apparently stable universe is fuller of flux and reflux than is the restless ocean itself1 and the very wavelets on the sea are not more numerous nor more restless than the stars that bestrew the sky4 ,,chapter ,,xiv ,,the ,,colours ,,of ,,the ,,stars ,has it ever occurred to you that the stars are not all of the same colour8 ,it is true that1 just glancing at them casually1 you might say they are all white2 but if you examine them more carefully you cannot help seeing that some shine with a steely blue light1 while others are reddish or yellowish4 ,these colours are not easy to distinguish with the naked eye1 and might not attract any attention at all unless they were pointed out2 yet when attention is drawn to the fact1 it is impossible to deny the redness of some1 such as ,aldebaran4 ,but though we may admit this1 we might add that the colours are so very faint and inconspicuous1 that they might be1 after all1 only the result of imagination4 ,to prove that the colours are constant and real we must use a telescope1 and then we need have no further doubt of their reality1 for instead of disappearing1 the colours of some stars stand out quite vividly beyond the possibility of mistake4 ,red stars are a bright red1 and they are the most easily seen of all1 though the other colours1 blue and yellow and green1 are seen very decidedly by some people4 ,the red stars have been described by various observers as resembling 'a drop of blood on a black field1' 'most magnificent copper-red1' 'most intense blood-red1' and 'glowing like a live coal out of the darkness of space4' ,some people see them as a shining red1 like that of a glowing cloud at sunset4 ,therefore there can be no doubt that the colours are genuine enough1 and are telling us some message4 ,this message we are able to read1 for we have begun to understand the language the stars speak to us by their light since the invention of the spectroscope4 ,the spectroscope tells us that these colours indicate different stages in the development of the stars1 or differences of constitution--that is to say1 in the elements of which they are made4 ,our own sun is a yellow star1 and other yellow stars are akin to him2 while red and blue and green stars contain different elements1 or elements in different proportions4 ,stars do not always remain the same colours for an indefinite time2 one star may change slowly from yellow to white1 and another from red to yellow2 and there are instances of notable changes1 such as that of the brilliant white ,sirius1 who was stated in old times by many different observers to be a red star4 ,all this makes us think1 and year by year thought leads us on to knowledge1 and knowledge about these distant suns increases4 ,but though we know a good deal now1 there are still many questions we should like to ask which we cannot expect to have answered for a long time yet1 if ever4 ,the star colours have some meanings which we cannot even guess2 we can only notice the facts regarding them4 ,for instance1 blue stars are never known to be solitary--they always have a companion1 but why this should be so passes our comprehension4 ,what is it in the constitution of a blue star which holds or attracts another8 ,whatever it may be1 it is established by repeated instances that blue stars do not stand alone4 ,in the constellation of ,cygnus there are two stars1 a blue and a yellow one1 which are near enough to each other to be seen in the same telescope at the same time1 and yet in reality are separated by an almost incredible number of billions of miles4 ,but as we know that a blue star is never seen alone1 and that it has often as its companion a yellowish or reddish star1 it is probable that these two1 situated at an enormous distance from one another1 are yet in some mysterious way dependent on each other1 and are not merely seen together because they happen to fall in the same field of view4 ,many double stars show most beautifully contrasted colours3 among them are pairs of yellow and rose-red1 golden and azure1 orange and purple1 orange and lilac1 copper-colour and blue1 apple-green and cherry-red1 and so on4 ,in the ,southern ,hemisphere there is a cluster containing so many stars of brilliant colours that ,sir ,john ,herschel named it 'the ,jewelled ,cluster4' ,i expect most of you have seen an advertisement of ,pear's ,soap1 in which you are asked to stare at some red letters1 and then look away to some white surface1 such as a ceiling1 when you will see the same letters in green4 ,this is because green is the complementary or contrasting colour to red1 and the same thing is the case with blue and yellow4 ,when any one colour of either of these pairs is seen1 it tends to make the other appear by reaction1 and if the eye gazed hard at blue instead of red1 it would next see yellow1 and not green4 ,now1 many people to whom this curious fact is known argue that perhaps the colours of the double stars are not real1 but the effect of contrast only2 for instance1 they say a red star near a companion white one would tend to make the companion appear green1 and so1 of course1 it would4 ,but this does not account for the star colours1 which are really inherent in the stars themselves1 as may be proved by cutting off the light of one star1 and looking only at the other1 when its colour still appears unchanged4 ,another argument equally strong against the contrast theory is that the colours of stars in pairs are by no means always those which would appear if the effect was only due to complementary colours4 ,it is not always blue and yellow or red and green pairs that we see1 though these are frequent1 but many others of various kinds1 such as copper and blue1 and ruddy and blue4 ,we have therefore come to the conclusion that there are in this astonishing universe numbers of gloriously coloured suns1 some of which apparently lie close together4 ,what follows8 ,why1 we want to know1 of course1 if these stars are really pairs connected with each other1 or if they only appear so by being in the same line of sight1 though one is infinitely more distant than the other4 ,and that question also has been answered4 ,there are now known thousands of cases in which stars1 hitherto regarded as single1 have been separated into two1 or even more1 by the use of a telescope4 ,of these thousands1 some hundreds have been carefully investigated1 and the result is that1 though there are undoubtedly some in which the connexion is merely accidental1 yet in by far the greater number of cases the two stars thus seen together have really some connexion which binds them to one another2 they are dependent on one another4 ,this has been made known to us by the working of the wonderful law of gravitation1 which is obeyed throughout the whole universe4 ,we know that by the operation of this law two mighty suns will be drawn toward each other with a certain pull1 just as surely as we know that a stone let loose from the hand will fall upon the earth2 so by noting the effect of two mighty suns upon each other many facts about them may be found out4 ,by the most minute and careful measurements1 by the use of the spectroscope1 and by every resource known to science1 astronomers have1 indeed1 actually found out with a near approach to exactness how far some of these great suns lie from each other1 and how large they are in comparison with one another4 ,the very first double star ever discovered was one which you have already seen1 the middle one in the tail of the ,great ,bear4 ,if you look at it you will be delighted to find that you can see a wee star close to it1 and you will think you are looking at an example of a double star with your very own eyes2 but you will be wrong1 for that wee star is separated by untold distances from the large one to which it seems so near4 ,in fact1 any stars which can be seen to be separate by the naked eye must lie immeasurably far apart1 however tiny seems the space between them4 ,such stars may possibly have some connexion with each other1 but1 at any rate in this case1 such a connexion has not been proved4 ,no1 the larger star itself is made up of two others1 which can only be seen apart in a telescope4 ,since this discovery double stars have been plentifully found in every part of the sky4 ,the average space between such double stars as seen from our earth is--what do you think8 ,it is the width of a single hair held up thirty-six feet from our eyes6 ,this could not1 of course1 be seen without the use of a telescope or opera-glasses4 ,it serves to give some impression of star distances when we think that the millions and millions of miles lying between those stars have shrunk to that hair's-breadth seen from our point of view4 ,twin stars circle together round a common centre of gravity1 and are bound by the laws of gravitation just as the planets are4 ,our sun is a solitary star1 with no companion1 and therefore such a state of things seems to us to be incredible4 ,fancy two gigantic suns1 one topaz-yellow and the other azure-blue1 circling around in endless movement6 ,where in such a system would there be room for the planets8 ,how could planets exist under the pull of two suns in opposite directions8 ,still more wonders are unfolded as the inquiry proceeds4 ,certain irregularities in the motions of some of these twin systems led astronomers to infer that they were acted upon by another body1 though this other body was not discernible4 ,in fact1 though they could not see it1 they knew it must be there1 just as ,adams and ,leverrier knew of the existence of ,neptune1 before ever they had seen him1 by the irregularities in the movements of ,uranus4 ,as the results showed1 it was there1 and was comparable in size to the twin suns it influenced1 and yet they could not see it4 ,so they concluded this third body must be dark1 not light-giving like its companions4 ,we are thus led to the strange conclusion that some of these systems are very complicated1 and are formed not only of shining suns1 but of huge dark bodies which cannot be called suns4 ,what are they1 then8 ,can they be immense planets8 ,is it possible that life may there exist8 ,no fairy tale could stir the imagination so powerfully as the thought of such systems including a planetary body as large or larger than its sun or suns4 ,if indeed life exists there1 what a varied scene must be presented day by day6 ,at one time both suns mingling their flashing rays may be together in the sky2 at another time only one appears1 a yellow or blue sun1 as the case may be4 ,the surface of such planets must undergo weird transformations1 the foliage showing one day green1 the next yellow1 and the next blue2 shadows of azure and orange will alternate6 ,but fascinating as such thoughts are1 we can get no further along that path4 ,to turn from fancy to facts1 we find that telescope and spectroscope have supplied us with quite enough matter for wonder without calling upon imagination4 ,we have discovered that many of the stars which seem to shine with a pure single light are double1 and many more consist not only of two stars1 but of several1 some of which may be dark bodies4 ,the ,pole ,star was long known to be double1 and is now discovered to have a third member in its system4 ,these multiple systems vary from one another in almost every case4 ,some are made up of a mighty star and a comparatively small one2 others are composed of stars equal in light-giving power--twin suns4 ,some progress swiftly round their orbits1 some go slowly2 indeed1 so slowly that during the century they have been under observation only the very faintest sign of movement has been detected2 and in other systems1 which we are bound to suppose double1 the stars are so slow in their movements that no progress seems to have been made at all4 ,the star we know as the nearest to us in the heavens1 ,alpha ,centauri1 is composed of two very bright partners1 which take about eighty-seven years to traverse their orbit4 ,they sometimes come as near to each other as ,saturn is to the sun4 ,in the case of ,sirius astronomers found out that he had a companion by reason of his irregularities of movement before they discovered that companion1 which is apparently a very small star1 only to be discerned with good telescopes4 ,but here1 again1 it would be unwise to judge only by what we see4 ,though the star appears small1 we know by the influence it exercises on ,sirius that it is very nearly the same size as he is4 ,thus we judge that it is poor in light-giving property2 in fact1 its shining power is much less than that of its companion1 though its size is so nearly equal4 ,this is not wonderful1 for ,sirius's marvellous light-giving power is one of the wonders of the universe2 he shines as brilliantly as twenty-nine or thirty of our suns6 ,in some cases the dark body which we cannot see may even be larger than the shining one1 through which alone we can know anything of it4 ,here we have a new idea1 a hint that in some of these systems there may be a mighty earth with a smaller sun going round it1 as men imagined our sun went around the earth before the real truth was found out4 ,so we see that1 when we speak of the stars as suns comparable with our sun1 we cannot think of them all as being exactly on the same model4 ,there are endless varieties in the systems2 there are solitary suns like ours which may have a number of small planets going round them1 as in the solar system2 but there are also double suns going round each other1 suns with mighty dark bodies revolving round them which may be planets1 and huge dark bodies with small suns too4 ,every increase of knowledge opens up new wonders1 and the world in which we live is but one kind of world amid an infinite number4 ,in this chapter we have learnt an altogether new fact--the fact that the hosts of heaven comprise not only those shining stars we are accustomed to see1 but also dark bodies equally massive1 and probably equally numerous1 which we cannot see4 ,in fact1 the regions of space may be strewn with such dark bodies1 and we could have no possible means of discovering them unless they were near enough to some shining body to exert an influence upon it4 ,it is not with his eyes alone1 or with his senses1 man knows of the existence of these great worlds1 but often solely by the use of the powers of his mind4 ,,chapter ,,xv ,,temporary ,,and ,,variable ,,stars ,it is a clear night1 nearly all the world is asleep1 when an astronomer crosses his lawn on his way to his observatory to spend the dark hours in making investigations into profound space4 ,his brilliant mind1 following the rays of light which shoot from the furthest star1 will traverse immeasurable distances1 while the body is forgotten4 ,just before entering the observatory he pauses and looks up2 his eye catches sight of something that arrests him1 and he stops involuntarily4 ,yet any stranger standing beside him1 and gazing where he gazes1 would see nothing unusual4 ,there is no fiery comet with its tail stretching across from zenith to horizon1 no flaming meteor dashing across the darkened sky4 ,but that there is something unusual to be seen is evident1 for the astronomer breathes quickly1 and after another earnest scrutiny of the object which has attracted him1 he rushes into the observatory1 searches for a star-chart1 and examines attentively that part of the sky at which he has been gazing4 ,he runs his finger over the chart3 here and there are the well-known stars that mark that constellation1 but here8 ,in that part there is no star marked1 yet he knows1 for his own eyes have told him but a few moments ago1 that here there is actually blazing a star1 not large1 perhaps1 but clear enough to be seen without a telescope--a star1 maybe1 which no eye but his has yet observed6 ,he hurries to his telescope1 and adjusts it so as to bring the stranger into the field of view4 ,a new star6 ,whence has it come8 ,what does it mean8 ,by the next day at the latest the news has flown over the wires1 and all the scientific world is aware that a new star has been detected where no star ever was seen before4 ,hundreds of telescopes are turned on to it2 its spectrum is noted1 and it stands revealed as being in a state of conflagration1 having blazed up from obscurity to conspicuousness4 ,night after night its brilliance grows1 until it ranks with the brightest stars in heaven1 and then it dies down and grows dim1 gradually sinking--sinking into the obscurity from whence it emerged so briefly1 and its place in the sky knows it no more4 ,it may be there still1 but so infinitely faint and far away that no power at our command can reveal it to us4 ,and the amazing part of it is that this huge disaster1 this mighty conflagration1 is not actually happening as it is seen1 but has happened many hundreds of years ago1 though the message brought by the light carrier has but reached us now4 ,there have not been a great many such outbursts recorded1 though many may have taken place unrecorded1 for even in these days1 when trained observers are ceaselessly watching the sky1 'new' stars are not always noticed at once4 ,in #ahib a new star appeared1 and shone for two months before anyone noticed it4 ,this particular one never rose to any very brilliant size4 ,i twas situated in the constellation of ,auriga1 and was noticed on ,february #a4 ,it remained fairly bright until ,march #f1 when it began to die down2 but it has now sunk so low that it can only be seen in the very largest telescopes4 ,photography has been most useful in recording these stars1 for when one is noticed it has sometimes been found that it has been recorded on a photographic plate taken some time previously1 and this shows us how long it has been visible4 ,more and more photography becomes the useful handmaid of astronomers1 for the photographic prepared plate is more sensitive to rays of light than the human eye1 and1 what is more useful still1 such plates retain the rays that fall upon them1 and fix the impression4 ,also on a plate these rays are cumulative--that is to say1 if a very faint star shines continuously on a plate1 the longer the plate is exposed1 within certain limits1 the clearer will the image of that star become1 for the light rays fall one on the top of the other1 and tend to enforce each other1 and so emphasize the impression1 whereas with our eyes it is not the same thing at all1 for if we do not see an object clearly because it is too faint1 we do not see it any better1 however much we may stare at the place where it ought to be4 ,this is because each light ray that reaches our eye makes its own impression1 and passes on2 they do not become heaped on each other1 as they do on a photographic plate4 ,one variable star in ,perseus1 discovered in #aija1 rose to such brilliancy that for one night it was queen of the ,northern ,hemisphere1 outshining all the other first-class stars4 ,it rose into prominence with wonderful quickness1 and sank equally fast4 ,at its height it outshone our sun eight thousand times6 ,this star was so far from us that it was reckoned its light must take about three hundred years to reach us1 consequently the great conflagration1 or whatever caused the outburst1 must have taken place in the reign of ,james ,i41 though1 as it was only seen here in #aija1 it was called the new star of the new century4 ,when these new stars die down they sometimes continue to shine faintly for a long time1 so that they are visible with a telescope1 but in other cases they may die out altogether4 ,we know very little about them1 and have but small opportunity for observing them1 and so it is not safe to hazard any theories to account for their peculiarities4 ,at first men supposed that the great flame was made by a violent collision between two bodies coming together with great velocity so that both flared up1 but this speculation has been shown by the spectroscope to be improbable1 and now it is supposed by some people that two stars journeying through space may pass through a nebulous region1 and thus may flare up1 and such a theory is backed up by the fact that a very great number of such stars do seem to be mixed up in some strange way with a nebulous haze4 ,all these new stars that we have been discussing so far have only blazed up once and then died down1 but there is another class of stars quite as peculiar1 and even more difficult to explain1 and these are called variable stars4 ,they get brighter and brighter up to a certain point1 and then die down1 only to become bright once more1 and these changes occur with the utmost regularity1 so that they are known and can be predicted beforehand4 ,this is even more unaccountable than a sudden and unrepeated outburst1 for one can understand a great flare-up1 but that a star should flare and die down with regularity is almost beyond comprehension4 ,clearly we must look further than before for an explanation4 ,let us first examine the facts we know4 ,variable stars differ greatly from each other4 ,some are generally of a low magnitude1 and only become bright for a short time1 while others are bright most of the time and die down only for a short time4 ,others become very bright1 then sink a little bit1 but not so low as at first2 then they become bright again1 and1 lastly1 go right down to the lowest point1 and they keep on always through this regular cycle of changes4 ,some go through the whole of these changes in three days1 and others take much longer4 ,the periods1 as the intervals between the complete round of changes are called1 vary1 in fact1 between three days and six hundred6 ,it may seem impossible that changes covering so long as six hundred days could be known and followed1 but there is nothing that the patience of astronomers will not compass4 ,one very well-known variable star you can see for yourselves1 and as an ounce of observation is worth a pound of hearsay1 you might take a little trouble to find it4 ,go out on any clear starlight night and look4 ,not very far from ,cassiopeia 7,w471 to the left as you face it1 are three bright stars running down in a great curve4 ,these are in the constellation called ,perseus1 and a little to the right of the middle and lowest one is the only variable star we can see in the sky without a telescope4 ,this is ,algol4 ,for the greater part of three days he is a bright star of about the second magnitude1 then he begins to fade1 and for four and a half hours grows steadily dimmer4 ,at the dimmest he remains for about twenty minutes1 and then rises again to his ordinary brightness in three and a half hours4 ,how can we explain this8 ,you may possibly be able to suggest a reason4 ,what do you say to a dark body revolving round ,algol1 or1 rather1 revolving with him round a common centre of gravity8 ,if such a thing were indeed true1 and if such a body happened to pass between us and ,algol at each revolution1 the light of ,algol would be cut off or eclipsed in proportion to the size of such a body4 ,if the dark body were the full size of ,algol and passed right between him and us1 it would cut off all the light1 but if it were not quite the same size1 a little would still be seen4 ,and this is really the explanation of the strange changes in the brightness of ,algol1 for such a dark body as we are imagining does in reality exist4 ,it is a large dark body1 very nearly as large as ,algol himself1 and if1 as we may conjecture1 it is a mighty planet1 we have the extraordinary example of a planet and its sun being nearly the same size4 ,we have seen that the eclipse happens every three days1 and this means1 of course1 that the planetary body must go round its sun in that time1 so as to return again to its position between us and him1 but the thing is difficult to believe4 ,why1 the nearest of all our planets to the sun1 the wee ,mercury1 takes eighty-seven days to complete its orbit1 and here is a mighty body hastening round its sun in three6 ,to do this in the time the large dark planet must be very near to ,algol2 indeed1 astronomers have calculated that the surfaces of the two bodies are not more than about two million miles apart1 and this is a trifle when we consider that we ourselves are more than forty-six times as far as that from the sun4 ,at this distance ,algol1 as observed from the planet1 will fill half the sky1 and the heat he gives out must be something stupendous4 ,also the effects of gravitation must be queer indeed1 acting on two such huge bodies so close together4 ,if any beings live in such a strange world1 the pull which draws them to their mighty sun must be very nearly equal to the pull which holds them to their own globe2 the two together may counteract each other1 but the effect must be strange6 ,from irregularities in the movements of ,algol it has been judged that there may be also in the same system another dark body1 but of it nothing has been definitely ascertained4 ,but all variable stars need not necessarily be due to the light being intercepted by a dark body4 ,there are cases where two bright stars in revolving round each other produce the same effect2 for when seen side by side the two stars give twice as much light as when one is hidden behind the other1 and as they are seen alternately side by side and in line1 they seem to alter regularly in lustre4 ,,chapter ,,xvi ,,star ,,clusters ,,and ,,nebul ,could you point out any star cluster in the sky8 ,you could if you would only think for a minute1 for one has been mentioned already4 ,this is the cluster known as the ,pleiades1 and it is so peculiar and so different from anything else1 that many people recognize the group and know where to look for it even before they know the ,great ,bear1 the favourite constellation in the northern sky1 itself4 ,the ,pleiades is a real star cluster1 and the chief stars in it are at such enormous distances from one another that they can be seen separately by the eye unaided1 whereas in most clusters the stars appear to be so close together that without a telescope they make a mere blur of brightness4 ,for a long time it was supposed that the stars composing the ,pleiades could not really be connected because of the great distances between them2 for1 as you know1 even a hair's-breadth apparently between stars signifies in reality many millions of miles4 ,light travelling from the ,pleiades to us1 at that incomprehensible pace of which you already know1 takes a hundred and ninety years to reach us6 ,at this incredibly remote distance lies the main part of the cluster from us2 but it is more marvellous still that we have every reason to believe that the outlying stars of this cluster are as far from the central ones as the nearest star we know of1 ,alpha ,centauri1 is from us6 ,little wonder was it1 then1 that men hesitated to ascribe to the ,pleiades any real connection with each other1 and supposed them to be merely an assemblage of stars which seemed to us to lie together4 ,with the unaided eye we see comparatively few stars in the ,pleiades4 ,six is the usual number to be counted1 though people with very good sight have made out fourteen4 ,viewed through the telescope1 however1 the scene changes3 into this part of space stars are crowded in astonishing profusion2 it is impossible to count them1 and with every increase in the power of the telescope still more are revealed4 ,well over a thousand in this small space seems no exaggerated estimate4 ,now1 it is impossible to say how many of these really belong to the group1 and how many are seen there accidentally1 but observations of the most prominent ones have shown that they are all moving in exactly the same direction at the same pace4 ,it would be against probability to conceive that such a thing could be the result of mere chance1 considering the infinite variety of star movements in general1 and so we are bound to believe that this wonderful collection of stars is a real group1 and not only an apparent one4 ,so splendid are the great suns that illuminate this mighty system1 that at least fifty or sixty of them far surpass our own sun in brilliancy4 ,therefore when we look at that tiny sparkling group we must in imagination picture it as a vast cluster of mighty stars1 all controlled and swayed by some dominant impulse1 though separated by spaces enough to make the brain reel in thinking of them4 ,if these suns possess also attendant planets1 what a galaxy of worlds1 what a universe within a universe is here6 ,other star clusters there are1 not so conspicuous as the ,pleiades1 and most of these can only be seen through a telescope1 so we may be thankful that we have one example so splendid within our own vision4 ,there are some clusters so far and faintly shining that they were at first thought to be nebul1 and not stars at all2 but the telescope gradually revealed the fact that many of these are made up of stars1 and so people began to think that all faint shining patches of nebulous light were really star clusters1 which would be resolved into stars if only we had better telescopes4 ,since the invention of the spectroscope1 however1 fresh light has been thrown on the matter1 for the spectrum which is shown by some of the nebulous patches is not the same as that shown by stars1 and we know that many of these strange appearances are not made up of infinitely distant stars4 ,we are talking here quite freely about nebul because we have met one long ago when we discussed the gradual evolution of our own system1 and we know quite well that a nebula is composed of luminous faintly-glowing gas of extreme fineness and thinness4 ,we see in the sky at the present time what we may take to be object-lessons in our own history1 for we see nebul of all sorts and sizes1 and in some stars are mixed up1 and in others stars are but dimly seen1 so that it does not require a great stretch of the imagination to picture these stars as being born1 emerging from the swaddling bands of filmy webs that have enwrapped them2 and other nebul seem to be gas only1 thin and glowing1 with no stars at all to be found in it4 ,we still know very little about these mysterious appearances1 but the work of classifying and resolving them is going on apace4 ,nebul are divided into several classes1 but the easiest distinction to remember is that between white nebul and green nebul4 ,this is not to say that we can see some coloured green1 but that green appears in the spectrum of some of the nebul1 while the spectrum of a white nebula is more like that of a star4 ,it is fortunate for us that in the sky we can see without a telescope one instance of each of the several objects of interest that we have referred to4 ,we have been able to see one very vivid example of a variable star2 we have seen one very beautiful example of a star cluster2 and it remains to look for one very good example of a white nebula4 ,just as in finding ,algol you were doing a little bit of practical work1 proving something of which you had read1 so by seeing this nebula you will remember more about nebul in general than by reading many chapters on the subject4 ,this particular nebula is in ,andromeda1 and is not far from ,algol2 and it is not difficult to find4 ,it is the only one that can be well seen without a telescope1 and was known to the ancients2 it is believed to have been mentioned in a book of the tenth century6 ,if you take an imaginary line down from the two left-hand stars of ,cassiopeia1 and follow it carefully1 you will come before long to a rather faint star1 and close to it is the nebula4 ,when you catch sight of it you will1 perhaps1 at first be disappointed1 for all you will see is a soft blur of white1 as if someone had laid a dab of luminous paint on the sky with a finger2 but as you gaze at it night after night and realize its unchangeableness1 realize also that it is a mass of glowing gas1 an island in space1 infinitely distant1 unsupported and inexplicable1 something of the wonder of it will creep over you4 ,illustration3 ,dr4 ,max ,wolf4 ,,the ,,great ,,nebula ,,in ,,andromeda4 ,thousands of telescopic nebul are now known1 and have been examined1 and they are of all shapes4 ,roughly1 they have been divided up into several classes--those that seem to us to be round and those that are long ovals1 like this one in ,andromeda2 but these may1 of course1 be only round ones seen edgewise by us2 others are very irregular1 and spread over an enormous part of the sky4 ,the most remarkable of these is that in ,orion1 and if you look very hard at the middle star in the sword-hilt of ,orion1 you may be able to make out a faint mistiness4 ,this1 when seen through a telescope1 becomes a wonderful and far-spreading nebula1 with brighter and darker parts like gulfs in it1 and dark channels4 ,it has been sometimes called the ,fish-mouth ,nebula1 from a fanciful idea as to its shape4 ,indeed1 so extraordinarily varied are these curious structures1 that they have been compared with numbers of different objects4 ,we have some like brushes1 others resembling fans1 rings1 spindles1 keyholes2 others like animals--a fish1 a crab1 an owl1 and so on2 but these suggestions are imaginative1 and have nothing to do with the real problem4 ,in ,the ,system of the ,stars ,miss ,clerke says3 ',in regarding these singular structures we seem to see surges and spray-flakes of a nebulous ocean1 bewitched into sudden immobility2 or a rack of tempest-driven clouds hanging in the sky1 momentarily awaiting the transforming violence of a fresh onset4 ,sometimes continents of pale light are separated by narrow straits of comparative darkness2 elsewhere obscure spaces are hemmed in by luminous inlets and channels4' ,one curious point about the ,orion ,nebula is that the star which seems to be in the midst of it resolves itself under the telescope into not one but six1 of various sizes4 ,nebul are in most cases too enormously remote from the earth for us to have any possible means of computing the distance2 but we may take it that light must journey at least a thousand years to reach us from them1 and in many cases much more4 ,therefore1 if at the time of the ,norman ,conquest a nebula had begun to grow dim and fade away1 it would1 for all intents and purposes1 still be there for us1 and for those that come after us for several generations1 though all that existed of it in reality would be its pale image fleeting onward through space in all directions in ever-widening circles4 ,that nebul do sometimes change we have evidence3 there are cases in which some have grown indisputably brighter during the years they have been under observation1 and some nebul that have been recorded by careful observers seem to have vanished4 ,when we consider that these strange bodies fill many1 many times the area of our whole solar system to the outermost bounds of ,neptune's orbit1 it is difficult to imagine what force it is that acts on them to revive or quench their light4 ,that that light is not the direct result of heat has long been known2 it is probably some form of electric excitement causing luminosity1 very much as it is caused in the comets4 ,indeed1 many people have been tempted to think of the nebul as the comets of the universe1 and in some points there are1 no doubt1 strong resemblances between the two4 ,both shine in the same way1 both are so faint and thin that stars can be seen through them2 but the spectroscope shows us that to carry the idea too far would be wrong1 as there are many differences in constitution4 ,we have seen that there are dark stars as well as light stars2 if so1 may there not be dark nebul as well as light ones8 ,it may very well be so4 ,we have seen that there are reasons for supposing our own system to have been at first a cool dark nebula rotating slowly4 ,the heavens may be full of such bodies1 but we could not discern them4 ,their thinness would prevent their hiding any stars that happened to be behind them4 ,no evidence of their existence could possibly be brought to us by any channel that we know4 ,it is true that1 besides the dark rifts in the bright nebul1 which may themselves be caused by a darker and non-luminous gas1 there are also strange rifts in the ,milky ,way1 which at one time were conjectured to be due to a dark body intervening between us and the starry background4 ,this idea is now quite discarded2 whatever may cause them1 it is not that4 ,one of the most startling of these rifts is that called the ,coal-,sack1 in the ,southern ,hemisphere1 and it occurs in a part of the sky otherwise so bright that it is the more noticeable4 ,no possible explanation has yet been suggested to account for it4 ,thus it may be seen that1 though much has been discovered1 much remains to be discovered4 ,by the patient work of generations of astronomers we have gained a clear idea of our own position in the universe4 ,here are we on a small globe1 swinging round a far mightier and a self-luminous globe1 in company with seven other planets1 many of which1 including ourselves1 are attended by satellites or moons4 ,between the orbits of these planets is a ring or zone of tiny bodies1 also going round the sun4 ,into this system flash every now and then strange luminous bodies--some coming but once1 never to return2 others returning again and again4 ,far out in space lies this island of a system1 and beyond the gulfs of space are other suns1 with other systems3 some may be akin to ours and some quite different4 ,strewn about at infinite distances are star clusters1 nebul1 and other mysterious objects4 ,the whole implies design1 creation1 and the working of a mighty intelligence2 and yet there are small1 weak creatures here on this little globe who refuse to believe in a ,god1 or who1 while acknowledging ,him1 would believe themselves to know better than ,he4 ,,the ,,end ,,billing ,,and ,,sons1 ,,ltd41 ,,printers1 ,,guildford