Previous to the year 1859 a few meteors, composed chiefly of stone or iron, some of which had been actually seen to fall from the sky, had been subjected to chemical analysis; but outside of this naught was known of the physical constitution of other worlds than ours. Our ignorance on this point was complete. All our attempts to become better acquainted with the structure of the planets, the composition of the sun, and the nature of the fixed stars would probably have been in vain but for the invention of the spectroscope. This surprising instrument is a master-key with which to unlock many of Nature’s mysteries; her recesses are brought to view, and the farthest star is subjected to an accurate chemical analysis, so far as the light that comes from it is sufficient to disclose the materials of which it is composed.
[Illustration: THE LICK OBSERVATORY, MOUNT HAMILTON, CALIFORNIA.]
The wondrous use of electricity as an agent for the production of light, heat, and power is no greater achievement, in its way, than is Spectrum Analysis in bringing to our earthly laboratories the work of the Divine Hand performed in distant regions of space. Yet the story of the spectroscope is easily told. In its essential elements it is merely this: A ray of light, entering a darkened room through a hole in the window shutter, produces a bright beam on the opposite wall. A triangular glass prism held close to the crevice turns this beam into a band of rainbow hues. If the hole can be changed into a small slit, say one fourth of an inch high and one fiftieth of an inch wide, and if the light can further be made to pass in succession through several prisms, instead of through one, the band will be so elongated thereby that its various and surprising markings can be thoroughly traced and fully studied.
To this band of bright colors Sir Isaac Newton gave the name of the solar spectrum. The image formed by the light of any luminous body, after it has passed through a prism, is said to be the spectrum of that body.
The spectroscope consists essentially of three tubes joined in the form of the letter Y, one of which is a small telescope, in the focus of which a narrow slit is placed to admit the ray of light that is to be examined; a prism, or a ruled grating that disperses the light, so as to form a spectrum; and a view telescope, with which to observe the various parts of the spectrum.