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y remarkable meteor systems--the system which produces the November shooting-stars, or Leonides, and that which produces the August shooting-stars, or Perseides. It chanced that the year 1866 was the time when a great display of November meteors was expected by astronomers, Hence, in the years 1865 and 1866 considerable attention was directed to the whole subject of shooting-stars, More-
over, so many astronomers watched the display of 1866, that very exact information was for the first time obtained as to the apparent track of these meteors. It is necessary to mention that such information was essential to success in the main inquiry. Now it had chanced that in 1862 a fine comet had been seen, whose path approached the earth's path very closely indeed. This led the Italian astronomer Schiaparelli to inquire whether there might not be some connection between this comet and the August shooting-stars, which cross the earth's path at the same place. He was able, by comparing the path of the comet and the apparent paths of the meteors, to render this opinion highly probable. Then came inquiries into the real paths of the November meteors, these inquiries being rendered just practicable by several coincidences, as --(1) the exact observations just mentioned; (2) the existence of certain old accounts of the meteor shower; (3) the wonderful mastery obtained by Professor Adams over all problems of perturbation (for the whole question depended on the way in which the November meteors had been perturbed); and (4) the existence of a half-forgotten treatise by Gauss, supplying formulas which reduced Adams' labor by one-half. The path having been determined (by Adams alone, I take this opportunity of insisting), the
Leverrier, Schiaparelli, and others calculated the path on the assumption that the occurrence of displays three times per century implies a periodic circulation around the sun in about thirty-three years and a quarter; but Adams alone proved that this period, and no other, must be that of the November meteors.
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