Page:Popular Science Monthly Volume 3.djvu/141

Rh (the sun and fixed stars), of scoriæ or gradual formation of a cold and non-luminous surface (the earth and planets), and finally of complete gelation and torpidity (the moon), or whether they exist as a complete and separate system of worlds; telescopes have only widened the problem, and have neither simplified nor solved its difficulties.

That which was beyond the power of the most gigantic telescopes has been accomplished by that apparently insignificant, but really delicate, and almost infinitely sensitive instrument—the spectroscope; we are indebted to it for being able to say with certainty that luminous nebulae actually exist as isolated bodies in space, and that these bodies are luminous masses of gas.

The splendid edifice already planned by Kant in his "Theory of the Heavens" (1755), and erected by Laplace forty-one years later, in his "System of the Universe," has received its topmost stone through the discoveries of the spectroscope. The spectroscope, in combination with the telescope, affords means for ascertaining even now some of the phases through which the sun and planets have passed in their process of development or transition from masses of luminous nebulae to their present condition.



Great variety is observed in the forms of the nebulæ: while some are chaotic and irregular, and sometimes highly fantastic, others exhibit the pure and beautiful forms of a curve, a crescent, a globe, or a circle. A number of the most characteristic of these forms have been photographed on glass at the suggestion of Mr. Huggins; to these have been added a few others, taken from accurate drawings by Lord