"It is a wonderful imitation," I responded, my awestruck eyes wandering over the mysterious tracts of the Milky Way and the familiar constellations of the mimic heavens. "May I ask how it is done--how you produce that impression of infinite distance?"

"By means of translucent sh.e.l.ls illuminated from behind. The stars, of course, are electric lamps, and some of them, as you see, have a tinge of red or blue."

Most of the light, however, came from a brilliant globe of a bluish l.u.s.tre, which appeared to occupy the centre of the crystal sphere, and was surrounded by a number of smaller and fainter orbs that shone by its reflected rays.

"This, again, is a model of the solar system," said Gazen. "The central luminary is, of course, the sun, and the others are the planets with their satellites."

"They seem to float in air."

"That is because their supports are invisible, or nearly so. Both their lights and periodic motions are produced by the electric current."

"Surely they are not moving now?"

"Oh, yes, and with velocities proportionate to those of the real bodies; but you know that whilst the actual movements of the sun and planets are so rapid, the dimensions of the system are so vast that if you could survey the whole from a standpoint in s.p.a.ce, as we are supposed to do, it would appear at rest. Let us look at them a little closer."

I followed Gazen along the gangway which encircled the orrery, and allowed us to survey each of the planets closer at hand.

"This kind of place would make a good theatre for a cla.s.s in astronomy,"

said I, "or for the meetings of the Interplanetary Congress of Astronomers, in the year 2000. You can turn on the stars and planets when you please. I wish you would give me a lecture on the subject now.

My knowledge is a little the worse for wear, and a man ought to know something of the worlds around him--especially if he intends to visit them."

"I should only bore you with an old story."

"Not at all. You cannot be too simple and elementary. Regard me as a small boy in the stage of

"'Twinkle, twinkle, little star, How I wonder what you are!'"

"Very well, my little man, have you any idea how many stars you can see on a clear night?"

"Billions."

"No, Tommy. You are wrong, my dear boy. Go to the foot of your cla.s.s.

With the naked eye we can only distinguish three or four thousand, but with the telescope we are able to count at least fifty millions. They are thickest in the Milky Way, which, as you can see, runs all round the heavens, over your head, and under your feet, like an irregular tract of hazy light, a girdle of stars in short. Of course we cannot tell how many more there are beyond the range of vision, or what other galaxies may be scattered in the depths of s.p.a.ce. The stars are suns, larger or smaller than our own, and of various colours--white, blue, yellow, green, and red. Some are single, but others are held together in pairs or groups by the force of gravitation. From their immense distance they appear fixed to us, but in reality they are flying in all directions at enormous velocities. Alpha, of the constellation Cygnus, for example, is coming towards us at a speed of 500 million leagues per annum, and some move a great deal faster. Most of them probably have planets circling round them in different stages of growth, but these are invisible to us.

Here and there amongst them we find luminous patches or 'nebulae,' which prove to be either cl.u.s.ters of stars or stupendous clouds of glowing gases. Our sun is a solitary blue star on the verge of the Milky Way, 20 billion miles from Alpha Centauri his next-door neighbour. He is travelling in a straight line towards the constellation Hercules at the rate of 20,000 miles an hour, much quicker than a rifle bullet; and, nevertheless, he will take more than a million years to cover the distance. Eight large or major planets, with their satellites, and a flock of minor planets or planetoids, are revolving round him as their common centre and luminary at various distances, but all in the same direction. The orbits, or paths, about the sun are ovals or ellipses, almost circular, of which the sun occupies one focus, and they are so nearly in one plane, or at one level, that if seen from the sun, they would appear to wander along a narrow belt of the heavens, called the zodiac, which extends a few degrees on each side of the Elliptic or apparent course of the sun against the stars. The planets are all globes, more or less flat at the poles, like an orange, and each is turning and swaying on its axis, thus exposing every part to the light and warmth of the sun. They are divided by the planetoids into an inner and an outer band. The inner four are Mercury, Venus, the Earth, and Mars; the outer four are Jupiter, Saturn, Ura.n.u.s, and Neptune. Moreover, a number of comets and swarms of meteoric stones or meteorites are circulating round the sun in eccentric paths, which cross those of the planets. Such is the solar system--a lonely archipelago in the ethereal ocean--a little family of worlds."

"Not without its jars, I'm afraid."

"The sun is chief of the clan," continued Gazen, "and keeps it together by the mysterious tie of gravitation. While flying through s.p.a.ce, he turns round his own axis like a rifle bullet in 25 or 26 days. His diameter is 860,000 miles, and although he is not much denser than sea-water, his ma.s.s is over 700 times greater than the combined ma.s.s of all his retinue. Gravity on his surface being 28 times stronger than on the earth, a piece of timber would be as heavy as gold there, and a stone let fall would drop 460 feet the first second instead of 16 feet as here. He is built of the same kind of matter as the earth and other planets, but is hotter than the hottest electric arc or reverberatory furnace. Apparently his glowing bulk is made up of several concentric sh.e.l.ls like an onion. First there is a kernel or liquid nucleus, probably as dense as pitch. Above it is the photosphere, the part we usually see, a jacket of incandescent clouds, or vapours, which in the telescope is seen to resemble 'willow leaves,' or 'rice grains in a plate of soup,' and in the spectroscope to reveal the rays of iron, manganese, or other heavy elements. What we call 'faculae' (or little torches), are brighter streaks, not unlike some kinds of coral. The 'Sunspots' are immense gaps or holes in the photosphere, some of them 150,000 miles in diameter, which afford us a peep at the glowing interior. There are different theories as to their nature, hence they provide rival astronomers with an excellent opportunity of spotting each other's reputations. For instance, I look upon them as eruptions, and Professor Sylva.n.u.s Pettifer Possil (my pet aversion) regards them as cyclonic storms; consequently we never lose an opportunity of erupting and storming at each other. Above the photosphere comes a stratum of cooler vapours and gases, namely, hydrogen and helium, a very light element recently found on the earth, along with argon, in the rare mineral cleveite. Tremendous jets of blazing hydrogen are seen to burst through the clouds of the photosphere, and play about in this higher region like the flames of a coal fire. These are the famous 'red flames'

or 'prominences,' which are seen during a total eclipse as a ragged fringe of rosy fire about the black disc of the moon. Some of them rush through the chromosphere to a height of 80,000 miles in 15 minutes.

"Higher still is the 'corona,' an aureole of silvery beams visible in a total eclipse, and resembling the star of a decoration. The streamers have been traced for hundreds of thousands of miles beyond the solar disc. It appears to consist of meteoric stones, illuminated by the sunlight as well as of incandescent vapours of 'coronium,' a very light element unknown on the earth, and probably, too, of electrical discharges. The 'zodiacal light,' that silvery glow often seen in the west after sunset, or in the east before sunrise, may be a prolongation of it."

"I daresay these meteorites are swarming about the sun like midges about a lamp," said I.

"And just as eager to get burnt up," replied Gazen, with a smile. "Let us pa.s.s now to the planets. The little one next the sun is Mercury, who can be seen as a rosy-white star soon after sunset or before sunrise. He is about 36 million miles, more or less, from the sun; travels round his...o...b..t in 88 days, the length of his year; and spins about his axis in 24 hours, making a day and night. His diameter is 3,000 miles, and his ma.s.s is nearly seven times that of an equal volume of water. The attraction of gravity on his surface is barely half that on the earth, and a man would feel very light there. Mercury seems to have a dense atmosphere, and probably high mountains, if not active volcanoes. The sunshine is from four to nine times stronger there than on the earth, and as summer and winter follow each other in six weeks, he is doubtless rather warm.

"Venus, the 'Shepherd's Star,' and the brightest object in the heavens after the moon, can sometimes be seen by day, and casts a distinct shadow at night. She is about 67 million miles from the sun, revolves round him in 225 days, and rotates on her axis in 23 to 24 hours, or as Schiaparelli believes, in 224 days. Her diameter is 7,600 miles, and her ma.s.s nearly five times that of an equal volume of water. Gravity is rather less there than it is here. Like Mercury, she appears to have a cloudy atmosphere, and very high mountains. On the whole she resembles the earth, but is, perhaps, a younger as well as a warmer planet.

"The green ball, next to Venus, is, I need hardly say, our own dear little world. Terra, or the earth, is 93 million miles from the sun, goes round him in 365 days, and turns on her axis in 24 hours less four minutes. Her diameter is 7,918 miles, and her density is 5.66 times that of water. She is attended by a single satellite, the moon, which revolves round her in 27.3 days, at a distance of 238,000 miles. The moon rotates on her axis in about the same time, and hence we can only see one side of her. She is 2,160 miles in diameter, but her ma.s.s is only one-eightieth that of the earth. A pound weight on the moon would scale six pounds on the earth. Having little or no atmosphere or water, she is apparently a dead world.

"The red planet beyond the earth is Mars, who appears in the sky as a ruddy gold or coppery star. He is 141 million miles from the sun, travels his...o...b..t in 687 days, and wheels round his axis in 24 hours 37 minutes. His diameter is 4,200 miles, and his ma.s.s about one-ninth that of the earth. A body weighing two pounds on the earth would only make half a pound on Mars. As you know, his atmosphere is clear and thin, his surface flat, and subject to floods from the melting of the polar snows.

Mars is evidently a colder and more aged planet than the earth.

"He is accompanied by two little moons, Phobos (Fear), which is from ten to forty miles in diameter, and revolves round him in 7 hours 39 minutes, at a distance of 6,000 miles, a fact unparalleled in astronomy; and Deimos (Rout), who completes a revolution in 30 hours 18 minutes, at a distance of 14,500 miles.

"About 400 planetoids have been discovered up to now, but we are always catching more of them. Medusa, the nearest, is 198 million miles, and Thule, the farthest, is 396 million miles from the sun. Vesta, the brightest and probably the largest, a pale yellow, or, as some say, bluish white orb, visible with the naked eye, is from 200 to 400 miles in diameter. It is impossible to say which is the smallest. Probably the ma.s.s of the whole is not greater than one quarter that of the earth.

"Jupiter, surnamed the 'giant planet,' who almost rivals Venus in her splendour, is 480 million miles from the sun; travels round his...o...b..t in 12 years less 50 days; and is believed to whirl round his axis in 10 hours. His diameter is 85,000 miles, and his bulk is not only 1,200 times that of the earth, but exceeds that of all the other planets put together. Nevertheless, his ma.s.s is only 200 to 300 times that of the earth, for his density is not much greater than that of water. What we see is evidently his vaporous atmosphere, which is marked by coloured spots and bands or belts, probably caused by storms and currents, especially in the equatorial regions. Jupiter is thought to be self luminous, at least in parts, and is, perchance, a cooling star, not yet entirely crusted over.

"Four or five numbered satellites, about the size of our moon and upwards, are circulating round him in orbits from 2,000 to 1,000,000 miles distant in periods ranging from 11 hours to 16 days 18 hours.

"Saturn, the 'ringed planet,' who appears as a dull red star of the first magnitude, is the most interesting of all the planets. He is 884 million miles from the sun; his period of revolution is 29 years, and he turns on his axis in 10 hours 14 minutes. His diameter is 75,000 miles, but his ma.s.s is only 94 times that of the earth, for he is lighter than pinewood. His atmosphere is marked with spots and belts, and on the whole his condition is like that of Jupiter.

"Two flat rings or hoops, divided by a dark s.p.a.ce, encircle his ball in the plane of his equator. The inner ring is over 18,000 miles from the ball, and nearly 17,000 miles broad. The gap between is 1,750 miles wide, and the outer ring is over 10,000 miles broad. The rings are banded, bright or dark, and vary in thickness from 40 to 250 miles. They consist of innumerable small satellites and meteoric stones, travelling round the ball in rather more than ten hours, and are brightest in their densest parts. Of course they form a magnificent object in the night sky of the planet, and it may be that our own zodiacal light is the last vestige of a similar ring, and not an extension of the solar corona.

"Saturn has eight moons outside his rings, the nearest, Mimas, being 115,000, and the farthest, j.a.petus, 220,400 miles from his ball. With the exception of j.a.petus, they revolve round him in the plane of his rings, and when these are seen edgewise, appear to run along it like beads on a string.

"Ura.n.u.s, the next planet visible, is a pale star of the sixth magnitude, 1,770 million miles from the sun, and completes his round in 84 years.

His axis, differing from those of the foregoing planets, lies almost in the plane of his...o...b..t, but we cannot speak as to his axial rotation. He is 31,000 miles in diameter, and somewhat heavier, bulk for bulk, than water. Four satellites revolve round him, the nearest, Ariel, being 103,500, and the farthest, Oberon, 347,500 miles distant. Unlike the orbits of the foregoing satellites, which are nearly in the same plane as the orbits of their primaries, those of the satellites of Ura.n.u.s are almost perpendicular to his own. They are travelled in periods of two and a half to thirteen and a half days.

"Neptune, invisible to the naked eye, but seen as a pale blue star in the telescope, is 2,780 million miles from the sun, and makes a revolution in 165 years. His diameter is about 35,000 miles, and his density rather less than that of water.

"Neptune has one satellite, at a distance of 202,000 miles, which, like those of Ura.n.u.s, revolves about its primary in an orbit at a considerable angle to his own in five days twenty-one hours. Both Neptune and Ura.n.u.s are probably dying suns.

"Comets of unknown number travel in long elliptical or parabolic orbits round the sun at great velocities. They seem to consist partly of glowing vapours, especially hydrogen, and partly of meteoric stones.

'Shooting stars,' that is to say, stones which fall to the earth, are known to swarm in their wake, and are believed to be as plentiful in s.p.a.ce as fishes in the sea."

"The trash or leavings of creation," said I reflectively.

"And the raw material, for nothing is lost," rejoined Gazen. "Now, in spite of all its diversity, there is a remarkable symmetry in the solar system. The planets are all moving round the sun in one direction along circular paths. As a rule each is nearly as far again from the sun as the next within it. Thus, if we take Mercury as inch from the sun, Venus is about 1 inches, the Earth 2, Mars 2, the planetoids 5, Jupiter 9, Saturn 14, Ura.n.u.s 36, and Neptune 60 inches. On the same scale, by the way, Enckes' comet at Aphelion, its farthest distance from the sun, would be about 12 feet; Donatis almost a mile; and Alpha Centauri, a near star in the Milky Way, some ten miles.

"The stately march of the planets in their orbits becomes slower the farther they are from the sun. The velocity of Mercury in its...o...b..t is thirty, that of Jupiter is eight, and that of Neptune is only three miles a second. On the other hand, the inner planets, as a rule, take some twenty-four hours, and the outer only ten hours to spin round their axis. The inner planets are small in comparison with the outer. If we represent the sun by a gourd, 20 inches in diameter, Mercury will seem a bilberry (?16 inch) Venus, a white currant, the Earth a black currant ( inch), Mars a red currant (? inch), the planetoids as fine seed, Jupiter an orange or peach (2 inches), Saturn a nectarine or greengage (1 inch), Ura.n.u.s a red cherry ( inch), and Neptune a white cherry (barely 1 inch in diameter). By putting the sun and planets in a row, and drawing a contour of the whole, we obtain the figure of a dirk, a bodkin, or an Indian club, in which the sun stands for the k.n.o.b (disproportionately big), the inner planets for the handle, and the outer for the blade or body. Again, the average density of the inner planets exceeds that of the outer by nearly five to one, but the ma.s.s of any planet is greater than the combined ma.s.ses of all which are smaller than it. The inner planets derive all their light and heat from the sun, and have few or no satellites; whereas the outer, to all appearance, are secondary suns, and have their own retinue of worlds. On the similitude of a clan or house we may regard the inner planets as the immediate retainers of the chief, and the outer as the chieftains of their own septs or families."

"How do you account for the symmetrical arrangement?" I enquired.

"The origin of the solar system is, you know, a mystery," replied the astronomer. "According to the nebular hypothesis we may imagine that two or more dark suns, perhaps encircled with planets, have come into collision. Burst into atoms by the stupendous shock they would fill the surrounding region with a vast nebula of incandescent gases in a state of violent agitation. Its luminous fringes would fly immeasurably beyond the present orbit of Neptune, and then rush inwards to the centre, only to be driven outwards again. Surging out and in, the fluid ma.s.s would expand and contract alternately, until in course of ages the fiery tides would cease to ebb and flow. If the impact had been somewhat indirect it would rotate slowly on its axis, and under the influence of gravity and centrifugal force acquire a globular shape which would gradually flatten to a lenticular disc. As it cooled and shrank in volume it would whirl the faster round its axis, and grow the denser towards its heart. By and by, as the centrifugal force overcame gravity, the nebula would part, and the lighter outskirts would be shed one after another in concentric rings to mould the planets. The inner rings, being relatively small and heavy, would probably condense much sooner than the large, light, outer rings. The planetoids are apparently the rubbish of a ring which has failed to condense into one body, perhaps through its uniformity or thinness. The separation of so big a ma.s.s as Jupiter might well attenuate the border."

"If the planetoids were born of a single small ring, might not several planets be condensed from a large one?"

"I see nothing to hinder it. A large ring might split into smaller rings, or condense in several centres."

"Because it seems to me that might explain the distinction between the inner and the outer planets. Perhaps the outer were first thrown off in one immense ring, and then the inner in a smaller ring. Before separation the nebula viewed edgewise might resemble your Indian club."

"A 'dumb-bell nebula,' like those we find in the heavens," observed Gazen. "Be that as it may, the rings would collect into b.a.l.l.s, and some of these, especially the outer, would cast off rings which would condense into moons, always excepting the rings of Saturn, which, like the planetoids, are evidently a failure. The solar system would then appear as a group of suns, a cl.u.s.ter of stars, in short, a constellation. Each would be what we call a 'nebulous star,' not unlike the sun at present; that is to say, it would be surrounded by a glowing atmosphere of vapours, and perhaps meteoric matter. Under the action of gravity, centrifugal force, and tidal r.e.t.a.r.dation, their orbits would become more circular, they would gradually move further apart, rotate more slowly on their axes, and a.s.sume the shapes they have now. In cooling down, new chemical compounds, and probably elements would be formed, since the so-called elements are perhaps mere combinations of a primordial substance which have been produced at various temperatures.

The heavier elements, such as platinum, gold, and iron, would sink towards the core; and the lighter, such as carbon, silicon, oxygen, nitrogen, and hydrogen, would rise towards the surface. A crust would form, and portions of it breaking in or bursting out together with eruptions and floods of molten lava, would disturb the poise of the planet, and give rise to inequalities of surface, to continents, and mountains. When the crust was sufficiently stable, sound, and cool, the mists and clouds would condense into rivers, lakes, or seas, and the atmosphere would become clear. In due course life would make its appearance."

"Can you account for that mystery?"

"No. Science is bound in honour, no doubt, to explain all it can without calling in a special act of creation; but the origin of life and intelligence seems to go beyond it, so far. Spontaneous generation from dead matter is ruled out of court at present. We believe that life only proceeds from life. As for the hypothesis that meteoric stones, the 'moss-grown fragments of another world' may have brought life to the earth, I hardly know what to think of it."