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��THE SCIENTIFIC MONTHLY

��tion, they would move in ellipses so elongated that we could not hope to distinguish them from parabolas. Their periods of revolution would be nearly one hundred and fifty thousand years. Yet they would be members of our solar system, subject to the sun's attraction, and unless disturbed by some other body or bodies, they would return again and again to the center of the system.

The work of Carrington, Schiaparelli, Fabry, Fayet, Stromgren and Leuschner and of many others has left no room for doubt that comets are bona fide members of our solar system. The materials com- posing the great majorit}^ of comets spend most of their time in regions far removed from the sun and its planets, as our little distances in the planetary system go, but close to the sun in terms of the magnificent distances which separate our sun from the other suns. They are mov- ing in closed orbits around our sun and traveling through space along with our sun.*

Besides the comets which go out on extremely elongated orbits to great distances from the sun, there are about fifty elliptic comets which

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��Fig. 2. Jupiteb's Family of Comets (up to 1893).

strongly advised to read Schiaparelli 's paper on "Orbites eom^taireSy Gourants cosmiques, M^t^rites," in Bulletin Astronomique, toI. 27, pp. 194-205 and 241- 254, 1910. It embodies some points of view slightly different from those pre- sented by me. The technical contributions by Fabry, Fayet and Stromgren are extensive and of a high order of merit; and students of comets cannot afford to neglect them. — W. W. C.
 * Thof'e who would like to look more thoroughly into this question are

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