Part 15

What has just preceded will now help us to understand how it is that photography also succeeds so well in the incomparably fainter objects we are about to consider, and which have been produced not by short but by long exposures. We have just seen how sensitive the modern plate is, and we are next to notice a new and very important point in which photographic action in general differs remarkably from that of the eye. Seeing may be described, not wholly inaptly, as the recognition of a series of brief successive photographs, taken by the optic lens on the retina; but the important difference between seeing and photographing, which we now ask attention to, is this: When the eye looks at a faint object, such as the spectrum of a star, or at the still fainter nebula, this, as we know, appears no brighter at the end of half an hour than at the end of the first half-second. In other words, after a brief fraction of a second, the visual effect does not sensibly accumulate. But in the action of the photograph, on the contrary, the effect _does_ accumulate, and in the case of a weak light accumulates indefinitely. It is owing to this precious property, that supposing (for illustration merely) the lightning flash to have occupied the one-thousandth part of a second in impressing itself on the plate, to get a nearly similar effect from a continuous light one thousand times weaker, we have only to expose the ¡date a thousand times as long, that is, for one second; while from a light a million times weaker we should get the same result by exposing it a million times as long, that is, for a thousand seconds.

And now that we come to the stars, whose spectra occupy minutes in taking, what we just considered will help us to understand how we can advantageously thus pass from a thousandth of a second or less, to one thousand seconds or even more, and how we can even,--given time enough,--conceivably, be able to photograph what the eye _cannot see at all_.

We have on page 231 a photograph quite recently taken at Cambridge from a group of stars (the Pleiades) passing by the telescope. Every star is caught as it goes, and presented, not in its ordinary appearance to the eye, but by its spectrum. There is a general resemblance in these spectra from the same cluster; while in other cases the spectra are of all types and kinds, the essential distinction between individuals alike to the eve, being more strikingly shown, as stars apparently far away from one another are seen to have a common nature, and stars looking close together (but which may be merely in line, and really far apart) have often no resemblance; and so the whole procession passes through the field of view, each individual leaving its own description. This self-description will be better seen in the remarkable photographs of the spectra of Vega and Aldebaran, which are reproduced on page 235 from the originals by a process independent of the graver. They were obtained on the night of November 9, 1886, at Cambridge, as a part of the work pursued by Professor Pickering, with means which have been given from fitting hands, thus to form a memorial of the late Dr. Henry Draper. We are obliged to the source indicated, then, for the ability to show the reader here the latest, and as yet inedited, results in this direction; and they are such as fully to justify the remark made above, that minutes, by this new process, take the place of years of work by the most skilful astronomer’s eye and hand.

The spectrum of Vega (Alpha Lyræ) is marked only by a few strong lines, due chiefly to hydrogen, because these are all there are to be seen in a star of its class. Aldebaran (the bright star in Taurus), on the contrary, here announces itself as belonging to the family of our own sun, a probably later type, and distinguished by solar-like lines in its spectrum, which may be counted in the original photograph to the number of over two hundred. There is necessarily some loss in the printed reproduction; but is it not a wonderful thing, to be able to look up, as the reader may do, to Aldebaran in the sky, and then down upon the page before us, knowing that that remote, trembling speck of light has by one of the latest developments of the New Astronomy been made, without the intervention of the graver’s hand, to write its own autograph record on the page before him?

In the department of nebular astronomy, photography has worked an equal change. The writer well remembers the weeks he has himself spent in drawing or attempting to draw nebulæ,--things often so ghost-like as to disappear from view every time the eye turned from the white paper, and only to be seen again when it had recovered its sensitiveness by gazing into the darkness. The labors of weeks were, literally, only represented by what looked like a stain on the paper; and no two observers, however careful, could be sure that the change between two drawings of a nebula at different dates was due to an alteration in the thing itself, or in the eye or hand of the observer, though unfortunately for the same reason it is impossible fully to render the nebulous effect of the photograph in engraving. We cannot with our best efforts, then, do full justice to the admirable one of Orion, on page 239, which we owe to the particular kindness of Mr. Common, of Ealing, England, whose work in this field is as yet unequalled. The original enlargement measures nearly two square feet in area, with fine definition. It is taken by thirty-nine minutes’ exposure, and its character can only be indicated here; for it is not too much to say here of this original also, that as many years of the life of the most skilled artist could not produce so trustworthy a record of this wonder.

The writer remembers the interest with which he heard Dr. Draper, not long before his lamented death, speak of the almost incredible sensitiveness of these most recent photographic processes, and his belief that we were fast approaching the time when we should photograph what we could not even see. That time has now arrived. At Cambridge, in Massachusetts, and at the Paris Observatory, by taking advantage of the cumulative action we have referred to, and by long exposures, photographs have recently been taken showing stars absolutely invisible to the telescope, and enabling us to discover faint nebulæ whose previous existence had not been suspected; and when we consider that an hour’s exposure of a plate, now not only secures a fuller star-chart than years of an astronomer’s labor, but a more exact one, that the art is every month advancing perceptibly over the last, and that it is already, as we may say, not only making pictures of what we see, but of what we cannot see even with the telescope,--we have before us a prospect whose possibilities no further words are needed to suggest.

We have now, not described, but only mentioned, some division of the labors of the New Astronomy in its photometric, spectroscopic, and photographic stellar researches, on each of which as many books, rather than chapters, might be written, to give only what is novel and of current interest. But these are themselves but a part of the modern work that has overturned or modified almost every conception about the stellar universe which was familiar to the last generation, or which perhaps we were taught in our own youth.

* * * * *

In considering the results to be drawn from this glance we have taken at some facts of modern observation, if it be asked, not only what the facts are, but what lessons the facts themselves have to teach, there is more than one answer, for the moral of a story depends on the one who draws it, and we may look on our story of the heavens from the point of view either of our own importance or of our own insignificance. In the one case we behold the universe as a sort of reflex of our own selves, mirroring in vast proportions of time and space our own destiny; and even from this standpoint, one of the lessons of our subject is surely that there is no permanence in any created thing. When primitive man learned that with lapsing years the oak withered and the very rock decayed, more slowly but as surely as himself, he looked up to the stars as the types of contrast to the change he shared, and fondly deemed them eternal; but now we have found change there, and that probably the star clusters and the nebulæ, even if clouds of suns and worlds, are fixed only by comparison with our own brief years, and, tried by the terms of their own long existence, are fleeting like ourselves.

“We have often witnessed the formation of a cloud in a serene sky. A hazy point barely perceptible--a little wreath of mist increases in volume and becomes darker and denser, until it obscures a large portion of the heavens. It throws itself into fantastic shapes, it gathers a glory from the sun, is borne onward by the wind, and as it gradually came, so, perhaps, it gradually disappears, melting away in the untroubled air. But the universe is nothing more than such a cloud,--a cloud of suns and worlds. Supremely grand though it may seem to us, to the infinite and eternal intellect it is no more than a fleeting mist. If there be a succession of worlds in infinite space, there is also a succession of worlds in infinite time. As one after another cloud replaces clouds in the skies, so this starry system, the universe, is the successor of countless others that have preceded it,--the predecessor of countless others that will follow.”

These impressions are strengthened rather than weakened when we come back from the outer universe to our own little solar system; for every process which we know, tends to the dissipation, or rather the degradation, of heat, and seems to point, in our present knowledge, to the final decay and extinction of the light of the world. In the words of one of the most eminent living students of our subject, “The candle of the sun is burning down, and, as far as we can see, must at last reach the socket. Then will begin a total eclipse which will have no end.

‘Dies iræ, dies illa, Solvet sæclum in favilla.’”

Yet though it may well be that the fact itself here is true, it is possible that we draw the moral to it, unawares, from an unacknowledged satisfaction in the idea of the vastness of the funeral pyre provided for such beings as ourselves, and that it is pride, after all, which suggests the thought that when the sun of the human race sets, the universe will be left tenantless, as a body from which the soul has fled. Can we not bring ourselves to admit that there may be something higher than man and more enduring than frail humanity, in some sphere in which _our_ universe, conditioned as it is in space and time, is itself embraced; and so distrust the conclusions of man’s reason where they seem to flatter his pride?

May we not receive even the teachings of science, as to the “Laws of Nature,” with the constant memory that all we know, even from science itself, depends on our very limited sensations, our very limited experience, and our still more limited power of conceiving anything for which this experience has not prepared us?

* * * * *

I have read somewhere a story about a race of ephemeral insects who live but an hour. To those who are born in the early morning the sunrise is the time of youth. They die of old age while his beams are yet gathering force, and only their descendants live on to midday; while it is another race which sees the sun decline, from that which saw him rise. Imagine the sun about to set, and the whole nation of mites gathered under the shadow of some mushroom (to them ancient as the sun itself) to hear what their wisest philosopher has to say of the gloomy prospect. If I remember aright, he first told them that, incredible as it might seem, there was not only a time in the world’s youth when the mushroom itself was young, but that the sun in those early ages was in the eastern, not in the western, sky. Since then, he explained, the eyes of scientific ephemera had followed it, and established by induction from vast experience the great “Law of Nature,” that it moved only westward; and he showed that since it was now nearing the western horizon, science herself pointed to the conclusion that it was about to disappear forever, together with the great race of ephemera for whom it was created.

What his hearers thought of this discourse I do not remember, but I have heard that the sun rose again the next morning.

INDEX.

Abbe, Professor, 56.

Actinism, 71.

Adams, Professor, 195.

Africa, 116.

Ages, stellar, 238.

Air: dancing, 17; a medium, 33; continuous, 176; rarefied, 179; motes, 181; nimble, 191. (See _Atmosphere_.)

Airless Mountains, 160.

Air-wave, 185.

Aitken’s Researches, 181.

Alaska, 38.

Aldebaran, 222, 235, 236, 246.

Algot, 228.

Allegheny Observatory, 17, 19, 84, 86. (See _Langley_.)

Alphonsus Ring-plain, 156.

Alps, 39, 148, 151, 167, 181. (See _Apennines, Lunar_.)

American Astronomers, 227.

American Continents, 20, 21, 31. (See _South_.)

Andalusia, 53.

Animalculæ, 224.

Animals: food, 74; fright, 42. (See _Dog_.)

Antares, 238.

Ants, 223. (See _Insects_.)

Apennines, 151, 153, 155, 160, 167. (See _Alps, Lunar_.)

Apples, 171.

Arab Traditions, 194. (See _Moslem_.)

Arago, quoted, 41, 42.

Archimedes, 94.

Archimedes Crater, 151–153, 155.

Arctic Cold, 159.

Arctic Pole, 96.

Arcturus, 208, 211.

Aristillus Crater, 151.

Aristotelian Philosophy, 8.

Arzachel, 156, 161.

Asteroids, 128.

Astrology, 127.

Astronomers and Priests, 1–3. (See _American, New_, _Old_.)

Astronomical Day, 85, 86.

Atmosphere, 136, 180; as a shield, 216, 220. (See _Air_.)

Atolls, 152.

Auger, simile, 31.

Aurora Borealis, 35, 67, 212.

Autolycus Crater, 151.

Axis, 9, 10.

Babel, 96.

Bain Telegraph, 88.

Balloons, 176.

Bees, 124. (See _Insects_.)

Berkeley’s Theory, 70.

Berlin Observatory, 233.

Bernières’s Lens, 103.

Bessemer Steel, 104–108.

Birds, 172, 196, 197. (See _Animals_.)

Black Hole, 73.

Bond, Professor, 204.

Boston, Mass., 88, 132.

Bothkamp, observations at, 66.

Breadstuffs, 78, 79. (See _Grain_, _Sun-spots_, _Wheat_.)

Bridges, 20, 68.

Britain, Ancient, 1, 234. (See _England_.)

British Isles, 14, 25.

Brocken Spectre, 55.

Brothers, Mr., 50.

Bubbles, 168.

Buffer, the air as a, 216, 220.

Bunsen’s Researches, 12.

Burnham, W. S., 233.

Burning-glasses, 102–104.

Burning Heat, 160, 163.

Cactus, 14, 24.

Calcutta, 73.

California, 151, 180.

Cambric Needle (_q. v._), experiment, 132.

Cambridge Observations, 227, 245–247.

Camera Obscura, 63.

Campanus Crater, 163, 165.

Candle, simile, 39.

Cannon-ball, 5, 38, 41, 98, 135, 186, 211.

Canopus, 234.

Carbon, 72, 73, 107, 221.

Carbonic-acid Gas, 219.

Carpenter’s Studio, 140.

Carrington’s Work, 79, 87.

Carthage, 116.

Cassini, 42.

Cassiopeia, 229.

Cataclysm, 30.

Centimetres, 93.

Chacornac’s Drawing, 33.

Chambers, on sun-spots, 80.

Charleston Earthquake (_q. v._), 42.

Chemical Elements, 221, 223.

Cherry-stone, comparison, 196.

Chicago: great fire, 134; astronomer, 233.

China: lens, 103, 104; soil, 180.

Chlorophyl, 73.

Chocolate, simile, 107.

Cholera, 80.

Chromosphere, 7; clouds, 62; forms, 64–68.

Cinders, 171.

Clark’s Glasses, 123.

Cliffs, 164.

Clock, 135.

Cloud-ocean, 179.

Clouds: cirrous, 27, 28; beautiful, 54; and rain, 111; formed, 249.

Coal-beds, 115.

Coal: energy, 73–75, 111; destroyed, 97; wasted, 101; stock, 112.

Cobweb, simile, 26.

Cold: and eclipses, 40; in planets, 136.

Colorado, 50.

Colors: in eclipses (_q. v._), 65; mental, 70, 71; in Jupiter (_q. v._), 127; in moon (_q. v._), 168; in stars (_q. v._), 227; spectrum (_q. v._), 236.

Comet-hunters, 204, 207.

Comets: chapter, 199–220; Donati’s, 201, 204, 205, 207, 209, 217; one part, 203; parts and name, 208; tail (_q. v._), 208, 211; diameter and parts, 216; spectroscope, elements, dread, 219; numerous, stone, 219, 220; kernel, 220; (1858), 213–216; (1866), 200.

Common, A. A., 239, 247.

Compass, 86.

Connecticut Observations, 186, 242.

Converter, 104–108.

Coral, 151.

Corn, 111. (See _Grain_.)

Corona, 7, 36, 37, 40, 41, 43, 45–52, 55, 56, 59, 60–62.

Cotton-mill, 74.

Counting, 94.

Cracks, celestial, 163.

Craters, 164. (See special names.)

Crystalline Structure, 4, 23–27.

Cyclones, 24, 31, 32, 68.

Decay, 248, 249.

Delambre’s History, 207.

De la Rue’s Engraving, 125.

Delfthaven, 5.

Denning’s Theory, 197.

Diamonds, melted, 103.

Dies Iræ, 249.

Dipper, 207, 208. (See _Great Bear_, _Polar_.)

Diurnal Oscillation, 87.

Dog, anecdote of, 42. (See _Animals_.)

Donati, 201, 204, 205, 207, 209, 213, 217. (See _Comets_.)

Double Stars, 233.

Draper, Professor Henry, 128, 246, 247.

Ducks, noise, 188.

Dust, 34, 100, 101, 102, 105, 197.

Dynamite, 182, 185, 220.

Earth: relations, 3, 4; description difficult, 6; temperature (_q. v._), 34, 101; a string of earths, 96; stars like, 118; seen from outside, 133–135; craters, 148.

Earthquakes, 220. (See _Charleston_.)

Earth-shine, 167, 172.

Eclipses: total, 7, 37; screen, 36; three, 39, 55; partial, 40; singular gloom, 39–43; causing fright, 43; colors (_q. v._), 48, 56, 61, 65, 66; (1842), 41; (1857), 48; (1869), 39, 40; (1870), 44, 61; (1871), 50, 66, 68; (1878), 38, 50, 57, 58. (See _Total_.)

Egypt, 116, 234. (See _Pyramids_.)

Electricity, 13, 75, 76.

Electric Light, 7.

Electric Spark, 242. (See _Lightning_.)

Electric Storm, 84, 85, 88.

Elizabeth, Queen, 115.

Engine-power, 98, 111.

England: fleets, 2; coal, 115. (See _Britain_, _London_.)

Engraving, 17.

Enigma, 228.

Ephemera, 250, 251.

Equatorial Landscape, 13, 17, 18, 47.

Equatorial Telescope, 122.

Ericsson: engravings, 112, 113; discoveries, 163.

Eruptive Promontories, 66–68.

Etna, 164, 181.

Europe, size, 25.

Evolution, planetary, 139.

Explosive Forces, 182–194.

Eye, 71, 227.

Eye-pieces, 47, 63.

Fabricius’s Observations, 8.

Fact and Fancy, 175.

Factory, 73.

Faculæ, 32, 33.

Falling, 242, 243.

Falling Stars, 193. (See _Meteors_, _Shooting_.)

Faraday, Michael, 76.

Fault, technical term, 156.

Faust, 139.

Faye: theory, 29–32; on Comets’ Tails, 212.

Fern-like Forms, 25, 26.

Filaments, 25–27, 30, 55, 56, 65, 66, 68.

Fire, in sun (_q. v._), 92. (See _Flames_, _Heat_.)

Fixed Stars, 233.

Flame-like Appearances, 23, 24.

Flames, 65, 66, 69, 185.

Flashes, 189, 195.

Flax, 111.

Flowers, color (_q. v._), 70. (See _Rose_, _Plants_.)

Foliage-forms, 32.

Fontenelle’s Story, 133.

Forbes’s Observations, 38, 39.

Frankenstein, 221.

Franklin’s Discoveries, 76.

Fraunhofer Studies, 235.

French Institute, 186.

Frost-crystals (_q. v._), 23.

Furnaces, 101.

Galileo, 8, 121–123, 139, 140.

Gas: glowing, 44; in sun, 60.

Gas-jets, 40, 61, 68, 88.

Gassendi’s View, 172, 173.

Gelinck’s Observations, 80.

Geminids, 196.

Genii, 193.

Geographers and Geologists, 133.

Glare, 14, 18, 62–64.

Glass: spun, 26; globe, 145.

Glow-worms, 7, 117.

Good Hope Observations, 80.

Gould’s Researches, 80.

Grain, prices, 77, 80, 87. (See _Corn_, _Sun-spots_, _Wheat_.)

Gramarye, 92.

Grass-blades, 66, 72.

Grasses, 26.

Gravitation, 72, 203; negative, 215.

Great Bear, 207. (See _Dipper_, _Polar_.)

Green’s Maps, 130.

Greenwich Observatory, 2, 81, 82, 84, 85, 88, 89.

Gulliver’s Travels, 131, 132. (See _Swift_.)

Gunpowder, 186.

Guns, 135. (See _Cannon-ball_.)

Hall Island, 130.

Hall, Professor, 131.

Hand, illustration, 168.

Harkness’s Observations, 44.

Harvests, 90.

Hastings, Professor, 60.

Heat: development, 13; concentration, 19; loss, 29; confinement, 33; sensation, 71; vibrations, 72; energy, 91; amount, 92, 97; computation, 94–96; diminution, 101; emission, 102; storage, 111; in sugar, 188. (See _Flames_, _Sun_.)

Hecla, 164, 181.

Hedgehog-spines, simile, 68.

Helmholtz’s Estimates, 98.

Hengist and Horsa, 1. (See _Britain_.)

Hercules, 238.

Herschel, Sir John: sun-spots, 12–14; electric storms, 88; comet’s tail, 216.

Herschel, Sir William: avoidance of light, 18; prices, 79; sun-spots (_q. v._), 129.

Herschel’s Outlines, 11.

Holden, Professor, 124.

Honeycomb Structure, 30.

Huggins’s Experiment, 234, 235.

Humanity, deified, 172.

Human Race, 250.

Humboldt, 195.

Humming-bird, 70.

Hunt, Professor, 136, 219.

Hydrogen, 68, 99, 237.

Ibrahim, King, story, 194, 195.

Ice: melted, 95, 96; never melted, 163, 164.

Imbrian Sea, 151.

Insects, 224, 250. (See _Ants_, _Bees_.)

Iron: melting, 19, 107; appearance of cold, 25; in sun, 28; in man, 221; in stars, 236, 237. (See _Steel_.)

Ironstone, 188.

Ivy, 115.

Janssen’s Observations, 61.

Jevons, Professor, 80.

Joseph in Egypt, 90.

Jumping, 241, 242.

Jupiter, 79, 118, 124, 127–129, 156, 185, 229.

Kensington Museum, 221.

Kepler, on Comets, 219.

Kernels, 220.

Kew, 88.

Kirchoff’s Researches, 12.

Krakatao, 181, 185, 186.

La Harpe, quoted, 207.

Landscape, 169.

Langley, Prof. S. P.: drawings, 15, 16, 18, 19, 21, 22, 25, 28, 30; note-book, 24; expedition, 180; study of Reflection, 216. (See _Allegheny_, _Pittsburg_.)

Latent Power, 220.

Laws of Nature, 250, 251.

Leaf-like Appearances, 23. (See _Willow_.)

Lenses, 102, 103; Galileo’s, 123.

Leo, 195, 197.

Liais’s Drawing, 48, 50.

Lick Glass, 123.

Light: development, 13; day and night, 35; white (_q. v._), 48; mental (see _Eye_), 71; from balloon, 179; transmitted, 227. (See _Sun_.)

Lightning, 75, 76, 242, 244, 245. (See _Electric_.)

Lily, 73. (See _Flowers_.)

Limited Express Train, 5.

Loaf-sugar, experiment, 188.

Lockyer’s Land, 130.

Lockyer’s Solar Physics, 59, 61, 236, 238.

Lombardy, 151.

London, 111.

Lost Pleiad (_q. v._), 207.

Louis XV., 42.

Louis XVI., 221.

Lunar Alps (_q. v._), 148, 149. (See _Moon_.)

Lunar Apennines (_q. v._), 153.

Lunar Shadows, 36, 37, 39, 56.

Lyrids, 196, 200.

Macartney’s Lens, 103.

Maelstrom, 27.

Magic Lantern, simile, 220.

Magnesium, 236, 237.

Magnetic Needle, 81, 82, 84, 85, 87, 89.

Mammoth Cave, 40.

Man, chemistry of, 221, 233. (See _Humanity_.)

Manhattan Island, 111.

Mare Crisium, 143.

Mare Serenitatis, 143, 144.

Mars, 118, 128–132, 148.

Mason’s Publication, 137.

Matterhorn, 148, 167.

Mayflower, 5.

Meadows, 172.

Mecca, 175.

Medusa, 228.

Memnon, 234.

Mercator, 163, 165.

Mercury, 3, 118, 136, 229.

Messier, anecdote, 207.

Metals, melted, 103. (See _Iron_.)

Metaphysics, 70, 71.

Meteorites: around Saturn, 124; recent, 187; lawsuit, 187, 188; analyzed, 191, 192; in Iowa, 199, 200; swarm, 200; cracking, 211.

Meteors, 98, 175–198; (1868), 189. (See _Falling_, _Shooting_.)

Meunier’s Investigations, 192.

Mexican Gulf, 38.

Microcosm, 222.

Micromegas, 223.

Microscope, 224.

Middle Ages, 91, 175.

Milky Way, 224, 225.

Milton, quoted, 14, 38.

Mind-causation, 70, 71.

Mirror, 102, 107.

Mississippi, 134.

Mites, 224.

Mizar, 207.

M’Leod’s Drawing, 44.

Monochromatic Light (_q. v._), 63.

Montaigne of Limoges, 207.

Mont Blanc, 156.

Monte Rosa, 167.