This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
Thus the micrometer revealed to man the magnitude and general structure, together with the motions and revolutions of the sidereal heavens. Above all, it demonstrated that gravity extends throughout the universe. Still the longings of men were not appeased; they brought to view invisible suns sunk in space, and told their weight, yet the thirst for knowledge was not quenched. Men wished to know what all the suns are made of, whether of substances like those composing the earth, or of kinds of matter entirely different. Then was devised the spectroscope, and with it men audaciously questioned nature in her most secluded recesses. The basis of spectroscopy is the prism, which separates sunlight into seven colors and projects a band of light called a spectrum. This was known for three hundred years, and not much thought of it until Fraunhofer viewed it with a telescope, and was surprised to find it filled with hundreds of black lines invisible to the unaided eye. Could it be possible that there are portions of the solar surface that fail to send out light? Such is the fact, and then began a twenty years' search to learn the cause. The lines in the solar spectrum were unexplained until finally metals were vaporized in the intense heat of the electric arc and the light passed through a spectroscope, when behold the spectra of metals were filled with bright lines in the same places as were the dark lines in the spectrum of the sun. Another step: if when metals are volatilized in the arc, rays of light from the sun are passed through the vapor and allowed to enter the spectroscope, a great change is wrought; a reversal takes place, and the original black bands reappear. A new law of nature was discovered, thus: "Vapors of all elements absorb the same rays of light which they emit when incandescent." Every element makes a different spectrum with lines in different places and of different widths. These have been memorized by chemists, so that when an expert having a spectroscope sees anything burn he can tell what it is as well as read a printed page. Men have learned the alphabet of the universe, and can read in all things radiating light, the constituent elements. The black lines in the solar spectrum are there because in the atmosphere of the sun exist vapors of metals, and the light from the liquid metals below is unable to pass through and reach the earth, being absorbed kind for kind. Gaseous iron sifts out all rays emitted from melted iron, and so do the vapors of all other elements in the sun, radiating light in unison with their own. Sodium, iron, calcium, hydrogen, magnesium, and many other substances are now known to be incandescent in the sun and stars; and the results of the developments of the spectroscope may be summed up in the generalization that all bodies in the universe are composed of the same substance the earth is.
The sun is subject to terrific hurricanes and cyclones, as well as explosions, casting up jets to the height of 200,000 miles. In the early days of spectroscopy these protuberances could only be seen at a time of a total solar ellipse, and astronomers made long journeys to distant parts of the earth to be in line of totality. Now all is changed. Images of the sun are thrown into the observatory by an ingenious instrument run by clockwork, and called a heliostat. This is set on the sun at such an angle as to throw the solar image into the objective of the telescope placed horizontally in a darkened observatory, and the pendulum ball set in motion, when it will follow the sun without moving its image, all day if desired. At the eye end of the telescope is attached the spectroscope and the micrometer, and the whole set of instruments so adjusted that just the edge of the sun is seen, making a half spectrum. The other half of the spectroscope projects above the solar limb, and is dark, so if an explosion throws up liquid jets, or flames of hydrogen, the astronomer at once sees them and with the micrometer measures their height before they have time to fall. And the spectrum at once tells what the jets are composed of, whether hydrogen, gaseous iron, calcium, or anything else. Prof. C. A. Young saw a jet of hydrogen ascend a distance of 200,000 miles, measured its height, noted its spectrum and timed its ascent by a chronometer all at once, and was astonished to find the velocity one hundred and sixty miles per second--eight times faster than the earth flies on its orbit. By these improvements solar hurricanes, whirlpools, and explosions can be seen from any physical observatory on clear days.
The slit of the spectroscope can be moved anywhere on the disk of the sun; so that if the observer sees a tornado begin, he moves the slit along with it, measures the length of its tract and velocity. With the telescope, micrometer, heliostat, and spectroscope came desire for more complex instruments, resulting in the invention of the photoheliograph, invoking the aid of photography to make permanent the results of these exciting researches. This mechanism consists of an excessively sensitive plate, adjusted in the solar focus of the telespectroscope. In front of the plate in the camera is a screen attached to a spring, and held closed by a cord. The eye is applied to the spectroscopic end of the complex arrangement to watch the development of solar hurricanes.
Finally an appalling outburst occurs; the flames leap higher and higher, torn into a thousand shreds, presenting a scene that language is powerless to describe. When the display is at the height of its magnificence, the astronomer cuts the cord; the slide makes an exposure of one-three thousandth part of a second, and an accurate photograph is taken. The storm all in rapid motion is petrified on the plate; everything is distinct, all the surging billows of fire, boilings, and turbulence are rendered motionless with the velocity of lightning.
At Meudon, in France, M. Janssen takes these instantaneous photographs of the sun, thirty inches in diameter, and afterward enlarges them to ten feet; showing scenes of fiery desolation that appalls the human imagination. (See address of Vice President Langley, A. A. A. S., Proceedings Saratoga Meeting, p. 56.) This huge photograph can be viewed in detail with a small telescope and micrometer, and the crests of solar waves measured. Many of these billows of fire are in dimensions every way equal in size to the State of Illinois. Binary stars are photographed so that in time to come they can be retaken, when if they have moved, the precise amount can be measured.
Another instrument is the telepolariscope, to be attached to a telescope. It tells whether any luminous body sends us its own, or reflected light. Only one comet bright enough to be examined has appeared since its perfection. This was Coggia's, and was found to reflect solar from the tail, and to radiate its own light from the nucleus.
Still another intricate instrument is in use, the thermograph, that utilizes the heat rays from the sun, instead of the light. It takes pictures by heat; in other words, it sees in the dark; brings invisible things to the eye of man, and is used in astronomical and physical researches wherein undulations and radiations are concerned. And now comes the magnetometer, to measure the amount of magnetism that reaches the earth from the sun. It points to zero when the magnetic forces of the earth are in equilibrium, but let a magnetic storm occur anywhere in the world and the pointer will move by invisible power. It detects a close relation between the magnetism of the earth and sun. The needle is deflected every time a solar disturbance takes place. At Kew, England, an astronomer was viewing the sun with a telescope and observed a tongue of flame dart across a spot whose diameter was thirty-three thousand seven hundred miles. The magnetometer was violently agitated at once, showing that whatever magnetism may be, its influence traversed the distance of the sun with a velocity greater than that of light.
Not less remarkable is the new instrument, the thermal balance, devised by Prof. S. P. Langley, Pittsburgh. It will measure the one-fifty-thousandth part of a degree of heat, and consists of strips of platinum one-thirty-second of an inch wide and one-fourth of an inch long; and so thin that it requires fifty to equal the thickness of tissue paper, placed in the circuit of electricity running to a galvanometer. "When mounted in a reflected telescope it will record the heat from the body of a man or other animal in an adjoining field, and can do so at great distances. It will do this equally well at night, and may be said, in a certain sense, to give the power of seeing in the dark." (Science, issue of Jan. 8,1881, p. 12.) It is expected to reveal great facts concerning the heat of the stars.
Indeed, the thermopile in the hands of Lockyer has already made palpable the heat of the fixed stars. He placed the little detective in the focus of a telescope and turned it on Arcturus. "The result was this, that the heat received from Arcturus, when at an altitude of 55°, was found to be just equal to that received from a cube of boiling water, three inches across each side, at the distance of four hundred yards; and the heat from Vega is equal to that from the same cube at six hundred yards." (Lockyer's Star Gazing, p. 385.) Thus that inscrutable mode of force heat traverses the depths of space, reaches the earth, and turns the delicate balance of the thermopile. Another discovery was made with the spectroscope; thus, if a boat moves up a river, it will meet more waves than will strike it if going down stream. Light is the undulation of waves; hence if the spectroscope is set on a star that is approaching the earth, more waves will enter than if set on a receding star, which fact is known by displacement of lines in the spectroscope from normal positions. It is found that many fixed stars are approaching, while others are moving away from the solar system.
We cannot note the researches of Edison, Lockyer, or Tyndall, nor of Crookes, who has seemingly reached the molecules whence the universe is composed.
The modern observatory is a labyrinth of sensitive instruments; and when any disturbance takes place in nature, in heat, light, magnetism, or like modes of force, the apparatus note and record them.
Men are by no means satisfied. Insatiable thirst to know more is developing into a fever of unrest; they are wandering beyond the limits of the known, every day a little farther. They survey space, and interrogate the infinite; measure the atom of hydrogen and weigh suns. Man takes no rest, and neither will he until he shall have found his own place in the chain of nature.--Kansas Review.