WHAT THE WORLDS ARE MADE OF.
The present century was already well advanced before there was any solid ground for the belief that the worlds of space are made of analogous or identical materials. It was only with the invention of the spectroscope and the analysis of light that the material identity of universal nature was proved by methods which could not be doubted. The proof came by the spectroscope.
This little instrument, though not famed as is its lordly kinsman the telescope, or even regarded with the popular favor of the microscope, has nevertheless carried us as far, and, we were about to say, taught us as much, as either of the others. It is one thing to see the worlds afar, to note them visibly, to describe their outlines, to measure their mass and determine their motions. It is another thing to know their constitution, the substances of which they are composed, the material condition in which they exist and the state of their progress in worldhood. The latter work is the task of the spectroscope; and right well has it accomplished its mission.
The solar spectrum has been known from the earliest ages. When the sun-bow was set on the background of cloud over the diluvial floods, the living beings of that age saw a spectrum—the glorious spectrum of rain and shine. Wherever the rays of light have been diffracted under given conditions by the agency of water drops, prism of glass or other such transparent medium, and the ray has fallen on a suitable screen, lo! there has been the beautiful spectrum of light.
The artificial, intentional production of this phenomenon of light has long been known, and both novice and scientist have tested and improved the methods of getting given results. The child's soap-bubble shows it in miniature splendor. The pressure of one wet pane of glass against another reveals it. The breakage of nearly all crystalline substances brings something of the colored effects of light; but the triangular prism of glass, suitably prepared, best of all displays the analysis of the sun-beam into the colors of which it is composed.
The spectroscope is the improved instrument by which the diffracting prism is best employed in producing the spectrum. The reader no doubt has seen a spectroscope, and has observed its beautiful work. In this place we pass, however, from the instrument of production to the spectrum, or analyzed result, as the same is shown on a screen. There the pencil of white light falling from the sun is spread out in the manner of a fan, presenting on the screen the following arrangement of colors: red, orange, yellow, green, blue, indigo and violet.
This order of colors, beginning with red, starts from that side of the spectrum which is least bent from the right line in which the white ray was traveling. The violet rays are most bent. The red rays are thus said to be at the lower edge of the prism, and the violet rays at the upper edge. Below the red rays there are now known to be certain invisible rays, as of heat and electricity. Above the violet rays are other invisible rays, such as the actinic influence. In fact, the spectrum, beginning invisibly, passes by way of the visible rays to the invisible again. Nor can any scientist in the world say at the present time how much is really included in the spread-out fan of analyzed sunlight.
Thus much scientists have known for some time. Certain other facts, however, in connection with the solar spectrum are of greater importance than are its more sensible phenomena. It was in the year 1802 that the English physicist, William Hyde Wollaston, discovered that the solar spectrum is crossed with a large number of dark lines. He it was who first mapped these lines and showed their relative position. He it was also who discovered the existence of invisible rays above the violet. Twelve years afterward Joseph von Fraunhofer, of Munich, a German optician of remarkable talents, took up the examination of the Wollaston lines, and by his success in the investigation succeeded in attracting the attention of the world.
This second stage in scientific discovery is generally that which receives the plaudits of mankind. It was so in the case of Fraunhofer. His name was given to the dark lines in the solar spectrum, and the nomenclature is retained to the present time. They are called the "Fraunhofer lines." It was soon discovered that the lines in question as produced in the spectrum are due to the presence of gases in the producing flame or source of light. It was also discovered that each substance in, the process of combustion yields its own line or set of lines. These appear at regular intervals in the spectrum. When several substances are consumed at the same time; the lines of each appear in the spectrum. The result is a system of lines, becoming more and more complex as the number of elements in the consuming materials is increased.
The lines in a narrow spectrum fall so closely together that they cannot be critically examined; but when more than one prism is used and the spectrum by this means spread out widely, the dark lines are made to stand apart. They are then found to number many thousands. We speak now of the analysis of sunlight. Experimentation was naturally turned, however, to terrestrial gases and solids on fire, and it was found that these also produce like series of dark lines in the spectrum. Or when the substances are consumed as solids, then the spectral effects are reversed, and the lines that would be dark lines in the luminous colored spectrum become themselves luminous lines on the screen; but these lines hold the same relation in mathematical measurement, etc., as do the dark lines in the colored spectrum.