Early studies in the nature of light
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Due to early studies in the nature of light, the science of optics has reached a very high stage. Through the spectroscope we can break light into its constituents. Characteristic lines belong to certain elements. An examination of the light emanating from the Sun and the stars tells directly their composition. By means of the spectroscope we know that the Sun has the same elements as the Earth. Every element which occurs in appreciable quantities upon the Earth, and has a characteristic spectrum, has also been found on the Sun. Conversely, almost every line in the solar spectrum has been identified with a terrestrial counterpart.
About 1880 an astronomer found in the solar spectrum a line which did not seem to correspond with any known element on Earth. He proclaimed his discovery, and public imagination ran riot over the possible nature of this unknown solar element. It might be the base from which all other elements were derived; it might be the long-sought philosopher's stone to be used in transmutation of the elements, or a precious metal more valuable than gold or platinum or the root of all evil. It might even be the root of all good, though that solution seemed less likely to the skeptical nineteenth-century minds.
Twenty years later, Sir William Ramsay obtained an unknown gas by heating rare minerals. Under a spectroscope he found it to be identical with the solar gas which had caused so much speculation. From its place of discovery it was named helium.
Unfortunately helium has solved no riddle of the universe. It has, however, some very remarkable properties. It refuses to combine with any other element, or any combination of elements. It is non-inflammable, and it is fire extinguishing. Next to hydrogen, there is no lighter gas known. Recently small quantities of helium have been found in some natural-gas wells. A government department separates it for use in balloons and dirigibles, and keeps a large stock on hand as a safeguard in case of war.
Most of the other elements found on Earth exist also in the Sun; but the solar residence is so much hotter than the terrestrial, that their state of existence varies greatly. In the Book of Daniel Shadrach, Meshach and Abednego were put into a fiery furnace; but their bodies were not consumed. Then the king ordered his servants to heat the furnace "seven times hotter than it was wont to be heated." If the previous temperature had been as high as the king's janitors knew how to create, then the increase would have heated the furnace almost to the temperature of the Sun; and, if Shadrach, Meshach, and Abednego remained completely unchanged after that, it was indeed a miracle.
We all know that the rays produce heat; but when we try to compute the amount of heat which they give off we are appalled. On this Earth, a good distance away, we have only to expose ordinarily protected parts of our bodies, and the resultant tan and blisters will demonstrate very effectively the power of the Sun's rays.
If we receive a definite quantity of light and heat from the Sun, we may fairly assume that the same amount is shooting forth in all directions, and we can form a reasonable estimate of the total energy dispersed. Astronomers have decided that the Sun must be losing weight continuously at the rate of four million tons per second. No other explanation will account for the terrific amount of energy expended over the universe. Yet so enormous is the Sun's mass that during the two thousand million years since the life of the Earth began, the Sun's shrinkage has been only a little over one one-hundredth of one percent.
All this heat does not have a very calming effect upon the place of its origin. Telescopic photographs show that the Sun is rampant with strife and turmoil. Under ordinary conditions this disorder gives the effect of granulations, but at times it appears as a London fog must appear to a distant observer--a dark spot on the face of the globe. Actually sunspots are quite bright, and appear dark only by contrast with the luminosity of the Sun; but they are the result of rather more inclement weather than even the city of London has ever experienced. When we see a sunspot we know that the turmoil has centered into a vast whirlpool storm with enormous gaping cavities which several earth-sized bodies could not fill.
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