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The compression downward of gaseous strata on the moon should, in any case, proceed very gradually, owing to the slight power of lunar gravity, and they might hence play an important part in the economy of our satellite while evading spectroscopic and other tests. Thus as Mr.
Two volumes of the Publications of the Astronomical Observatory, dealing with the spectroscopic investigations for which the Observatory is now particularly well equipped, have also appeared. A "History of the Chemical Laboratory," by Professor E.D. Campbell, should also be mentioned. From time to time there have been issued compilations of the publications of members of the University Faculties.
But the oval was not perfect; at my right a screen cut it a screen that gleamed with fugitive, fleeting luminescences stretching from the side of our standing place up to the tip of the chamber; slightly convex and crisscrossed by millions of fine lines like those upon a spectroscopic plate, but with this difference that within each line I sensed the presence of multitudes of finer lines, dwindling into infinitude, ultramicroscopic, traced by some instrument compared to whose delicacy our finest tool would be as a crowbar to the needle of a micrometer.
A small star, numbered 1,830 in Groombridge's Circumpolar Catalogue, "devours the way" at the rate of at least 150 miles a second a speed, in Newcomb's opinion, beyond the gravitating power of the entire sidereal system to control; and Mu Cassiopeiæ possesses above two-thirds of that surprising velocity; while for both objects, radial movements of just sixty miles a second were disclosed by Professor Campbell's spectroscopic measurements.
It should also show itself in the measures of all spectroscopic binaries. A third method of great promise depends on a remarkable investigation carried on in the physical laboratory of the Case School of Applied Science.
Instead of a single measure for each star, in the case of the so-called spectroscopic binaries, we must make enough measures to determine the dimensions of the orbit, its form and the period of revolution. What has been said of the motions of the stars applies also, in general, to the determination of their distances. A vast amount of labor has been expended on this problem.
The telegram read: What's Happening on Mars? "Professor Barnard, watching Mars to-night with the forty-inch telescope, saw a sudden outburst of reddish light, which we think indicates that something has been shot from the planet. Spectroscopic observations of this moving light indicated that it was coming earthward, while visible, at the rate of not less than one hundred miles a second."
Ambition as regards telescopic power is by no means yet satisfied. Nor ought it to be. The advance of astrophysical researches of all kinds depends largely upon light-grasp. For the spectroscopic examination of stars, for the measurement of their motions in the line of sight, for the discovery and study of nebulæ, for stellar and nebular photography, the cry continually is "more light."
Around the poles are plainly to be seen rounded white areas, which vary in extent with the Martian seasons, nearly vanishing in summer and extending widely in winter. The most recent spectroscopic determinations indicate that Mars has an atmosphere perhaps as dense as that to be found on our loftiest mountain peaks, and there is a perceptible amount of watery vapor in this atmosphere.
Of many ingenious improvements in spectroscopic appliances the most fundamentally important relate to what are known as "gratings." These are very finely striated surfaces, by which light-waves are brought to interfere, and are thus sifted out, strictly according to their different lengths, into "normal" spectra.
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