[Ill.u.s.tration: Fig. 62.
[Greek: e] Lyrae. A double-binary star. Each couple revolves, and the couples probably also revolve round each other. (After Chambers.)]
Let us turn the telescope for a short time upon a few of the double stars and we shall have a great treat, for one of the most interesting facts about them is that both stars are rarely of the same colour. It seems strange at first to speak of stars as coloured, but they do not by any means all give out the same kind of light. Our sun is yellow, and so are the Pole-star and Pollux; but Sirius, Vega, and Regulus are dazzling white or bluish-white, Arcturus is a yellowish-white, Aldebaran is a bright yellow-red, Betelgeux a deep orange-red, as you may see now in the telescope, for he is full in view; while Antares, a star in the constellation of the Scorpion, which at this time of year cannot be seen till four in the morning, is an intense ruby red.
[Ill.u.s.tration: _Plate II._]
COLOURED DOUBLE STARS.
[Ill.u.s.tration: [Greek: g] _Andromedae_.]
[Ill.u.s.tration: [Greek: e] _Bootis_.]
[Ill.u.s.tration: [Greek: d] _Geminorum_.]
[Ill.u.s.tration: [Greek: a] _Herculis_.]
[Ill.u.s.tration: [Greek: b] _Cygni_.]
[Ill.u.s.tration: [Greek: e] _Ca.s.siopeiae_.]
It appears to be almost a rule with double stars to be of two colours.
Look up at Almach ([Greek: g] Andromedae), a bright star standing next to Algol the Variable in the sweep of four bright stars behind Ca.s.siopeia (see Fig. 58). Even to the naked eye he appears to flash in a strange way, and in the telescope he appears as two lovely stars, one a deep orange and the other a pale green, while in powerful telescopes the green one splits again into two (Plate II.) Then again, [Greek: e]
Ca.s.siopeae, the sixth star lying between the two large ones in the second V of Ca.s.siopeia, divides into a yellow star and a small rich purple one, and [Greek: d] Geminorum, a bright star not far from Pollux in the constellation Gemini, is composed of a large green star and a small purple one. Another very famous double star ([Greek: b] Cygni), which rises only a little later in the evening, lies below Vega a little to the left. It is composed of two lovely stars; one an orange yellow and the other blue; while [Greek: e] Bootis, just visible above the horizon, is composed of a large yellow star and a very small green one.[1]
[1] The plate of coloured stars has been most kindly drawn to scale and coloured for me by Mr. Arthur Cottam, F.R.A.S.
There are many other stars of two colours even among the few constellations we have picked out to-night, as, for example, the star at the top of the tailboard of Charles"s Waggon and the second horse Mizar. Rigel in Orion, and the two outer stars of the belt, [Greek: a]
Herculis, which will rise later in the evening, and the beautiful triple star ([Greek: z] Cancer) near the Beehive (see Fig. 54), are all composed of two or more stars of different colours.
Why do these suns give out such beautiful coloured light? The telescope cannot tell us, but the spectroscope again reveals the secrets so long hidden from us. By a series of very delicate experiments, Dr. Huggins has shown that the light of all stars is sifted before it comes to us, just as the light of our sun is; and those rays which are least cut off play most strongly on our eyes, and give the colour to the star. The question is a difficult one but I will try to give you some idea of it, that you may form some picture in your mind of what happens.
We learnt in our last lecture (p. 131) that the light from our sun pa.s.ses through the great atmosphere of vapours surrounding him before it goes out into s.p.a.ce, and that many rays are in this way cut off; so that when we spread out his light in a long spectrum there are dark lines or s.p.a.ces where no light falls.[1] Now in sunlight these dark lines are scattered pretty evenly over the spectrum, so that about as much light is cut off in one part as in another, and no one colour is stronger than the rest.
[1] See No. 1 in Table of Spectra, Plate I.
Dr. Huggins found, however, that in coloured stars the dark s.p.a.ces are often crowded into particular parts of the long band of colour forming the spectrum; showing that many of those light-rays have been cut off in the atmosphere round the star, and thus their particular colours are dimmed, leaving the other colour or colours more vivid. In red stars, for example, the yellow, blue, and green parts of the spectrum are much lined while the red end is strong and clear. With blue stars it is just the opposite, and the violet end is most free from dark lines. So there are really brilliantly coloured suns shining in the heavens, and in many cases two or more of these revolve round each other.
And now I have kept your attention and strained your eyes long enough, and you have objects to study for many a long evening before you will learn to see them plainly. You must not expect to find them every night, for the lightest cloud or the faintest moonlight will hide many of them from view; and, moreover, though you may learn to use the telescope fairly, you will often not know how to get a clear view with it. Still, you may learn a great deal, and before we go in I want to put a thought into your minds which will make astronomy still more interesting. We have seen that the stronger our telescopes the more stars, star-cl.u.s.ters, and nebulae we see, and we cannot doubt that there are still countless heavenly bodies quite unknown to us. Some years ago Bessel the astronomer found that Sirius, in its real motion through the heavens, moves irregularly, travelling sometimes a little more slowly than at other times, and he suggested that some unseen companion must be pulling at him.
Twenty-eight years later, in 1862, two celebrated opticians, father and son, both named Alvan Clark, were trying a new telescope at Chicago University, when suddenly the son, who was looking at Sirius, exclaimed, "Why, father, the star has a companion!" And so it was. The powerful telescope showed what Bessel had foretold, and proved Sirius to be a "binary" star--that is, as we have seen, a star which has another moving round it.
It has since been proved that this companion is twenty-eight times farther from Sirius than we are from our sun, and moves round him in about forty-nine years. It is seven times as heavy as our sun, and yet gives out so little light that only the keenest telescopes can bring it into view.
Now if such a large body as this can give so very faint a light that we can scarcely see it, though Sirius, which is close to it, shines brightest of any star in the heavens, how many more bodies must there be which we shall never see, even among those which give out light, while how many there are dark like our earth, who can tell?
Now that we know each of the stars to be a brilliant sun, many of them far, far brighter than ours, yet so like in their nature and laws, we can scarcely help speculating whether round these glorious suns, worlds of some kind may not be moving. If so, and there are people in them, what a strange effect those double coloured suns must produce with red daylight one day and blue daylight another!
Surely, as we look up at the myriads of stars bespangling the sky, and remember that our star-sun has seven planets moving round it of which one at least--our own earth--is full of living beings, we must picture these glorious suns as the centres of unseen systems, so that those twinkling specks become as suggestive as the faint lights of a great fleet far out at sea, which tell us of mighty ships, together with frigates and gunboats, full of living beings, though we cannot see them, nor even guess what they may be like. How insignificant we feel when we look upon that starlit sky and remember that the whole of our solar system would be but a tiny speck of light if seen as far off as we see the stars! If our little earth and our short life upon it were all we could boast of we should be mites indeed.
But our very study to-night lifts us above these and reminds us that there is a spirit within us which even now can travel beyond the narrow bounds of our globe, measure the vast distances between us and the stars, gauge their brightness, estimate their weight, and discern their movements. As we gaze into the depths of the starlit sky, and travel onwards and onwards in imagination to those distant stars which photography alone reveals to us, do not our hearts leap at the thought of a day which must surely come when, fettered and bound no longer to earth, this spirit shall wander forth and penetrate some of the mystery of those mighty suns at which we now gaze in silent awe.
CHAPTER VIII
LITTLE BEINGS FROM A MINIATURE OCEAN
[Ill.u.s.tration]
In our last lecture we soared far away into boundless s.p.a.ce, and lost ourselves for a time among seen and unseen suns. In this lecture we will come back not merely to our little world, nor even to one of the widespread oceans which cover so much of it, but to one single pool lying just above the limits of low tide, so that it is only uncovered for a very short time every day. This pool is to be found in a secluded bay within an hour"s journey by train from this college, and only a few miles from Torquay. It has no name, so far as I know, nor do many people visit it, otherwise I should not have kept my little pool so long undisturbed. As it is, however, for many years past I have had only to make sure as to the time of low tide, and put myself in the train; and then, unless the sea was very rough and stormy, I could examine the little inhabitants of my miniature ocean in peace.
The pool lies in a deep hollow among a group of rocks and boulders, close to the entrance of the cove, which can only be entered at low water; it does not measure more than two feet across, so that you can step over it, if you take care not to slip on the ma.s.ses of green and brown seaweed growing over the rocks on its sides, as I have done many a time when collecting specimens for our salt-water aquarium. I find now the only way is to lie flat down on the rock, so that my hands and eyes are free to observe and handle, and then, bringing my eye down to the edge of the pool, to lift the seaweeds and let the sunlight enter into the c.h.i.n.ks and crannies. In this way I can catch sight of many a small being either on the seaweed or the rocky ledges, and even creatures transparent as gla.s.s become visible by the thin outline gleaming in the sunlight. Then I pluck a piece of seaweed, or chip off a fragment of rock with a sharp-edged collecting knife, bringing away the specimen uninjured upon it, and place it carefully in its own separate bottle to be carried home alive and well.
Now though this little pool and I are old friends, I find new treasures in it almost every time I go, for it is almost as full of living things as the heavens are of stars, and the tide as it comes and goes brings many a mother there to find a safe home for her little ones, and many a waif and stray to seek shelter from the troublous life of the open ocean.
You will perhaps find it difficult to believe that in this rock-bound basin there can be millions of living creatures hidden away among the fine feathery weeds; yet so it is. Not that they are always the same. At one time it may be the home of myriads of infant crabs, not an eighth of an inch long, at another of baby sea-urchins only visible to the naked eye as minute spots in the water, at another of young jelly-fish growing on their tiny stalks, and splitting off one by one as transparent bells to float away with the rising tide. Or it may be that the whelk has chosen this quiet nook to deposit her leathery eggs; or young barnacles, periwinkles, and limpets are growing up among the green and brown tangles, while the far-sailing velella and the stay-at-home sea-squirts, together with a variety of other sea-animals, find a nursery and shelter in their youth in this quiet harbour of rest.
And besides these casual visitors there are numberless creatures which have lived and multiplied there, ever since I first visited the pool.
Tender red, olive-coloured, and green seaweeds, stony corallines, and acorn-barnacles lining the floor, sea-anemones clinging to the sides, sponges tiny and many-coloured hiding under the ledges, and limpets and mussels wedged in the cracks. These can be easily seen with the naked eye, but they are not the most numerous inhabitants; for these we must search with a magnifying-gla.s.s, which will reveal to us wonderful fairy-forms, delicate crystal vases with tiny creatures in them whose transparent lashes make whirlpools in the water, living crystal bells so tiny that whole branches of them look only like a fringe of hair, jelly globes rising and falling in the water, patches of living jelly clinging to the rocky sides of the pool, and a hundred other forms, some so minute that you must examine the fine sand in which they lie under a powerful microscope before you can even guess that they are there.
[Ill.u.s.tration: Fig. 63.
Group of seaweeds (natural size).
1, _Ulva Linza._ 2, _Sphacelaria filicina._ 3, _Polysiphonia urceolata._ 4, _Corallina officinalis._]
So it has proved a rich hunting-ground, where summer and winter, spring and autumn, I find some form to put under my magic gla.s.s. There I can watch it for weeks growing and multiplying under my care; moved only from the aquarium, where I keep it supplied with healthy sea-water, to the tiny transparent trough in which I place it for a few hours to see the changes it has undergone. I could tell you endless tales of transformations in these tiny lives, but I want to-day to show you a few of my friends, most of which I brought yesterday fresh from the pool, and have prepared for you to examine.
[Ill.u.s.tration: Fig. 64.
_Ulva lactuca_, a green seaweed, greatly magnified to show structure.
(After Oersted.)
_s_, Spores in the cells. _ss_, Spores swimming out. _h_, Holes through which spores have escaped.]
Let us begin with seaweeds. I have said that there are three leading colours in my pool--green, olive, and red--and these tints mark roughly three kinds of weed, though they occur in an endless variety of shapes.
Here is a piece of the beautiful pale green seaweed, called the Laver or Sea-lettuce, _Ulva Linza_ (1, Fig. 63), which grows in long ribbons in a sunny nook in the water. I have placed under the first microscope a piece of this weed which is just sending out young seaweeds in the shape of tiny cells, with lashes very like those we saw coming from the moss-flower, and I have pressed them in the position in which they would naturally leave the plant (_ss_, Fig. 64.).[1] You will also see on this slide several cells in which these tiny spores _s_ are forming, ready to burst out and swim; for this green weed is merely a collection of cells, like the single-celled plants on land. Each cell can work as a separate plant; it feeds, grows, and can send out its own young spores.
[1] The slice given in Fig. 64 is from a broader-leaved form, _U. lactuca_, because this species, being composed of only one layer of cells, is better seen. _Ulva linza_ is composed of two layers of cells.
This deep olive-green feathery weed (2, Fig. 63), of which a piece is magnified under the next microscope (2, Fig. 65), is very different. It is a higher plant, and works harder for its living, using the darker rays of sunlight which penetrate into shady parts of the pool. So it comes to pa.s.s that its cells divide the work. Those of the feathery threads make the food, while others, growing on short stalks on the shafts of the feather make and send out the young spores.
[Ill.u.s.tration: Fig. 65.
Three seaweeds of Fig. 63 much magnified to show fruits. (Harvey.)