A few years previous to the display of 1866 it was shown by Professor Newton, of Yale College, that the distribution of meteoric matter around the ring or orbit is far from uniform; that the motion is retrograde; that the node of the orbit has an annual forward motion of 102´´.6 with respect to the equinox, or of 52´´.4 with respect to the fixed stars; that the periodic time must be limited to five accurately determined periods, viz.: 180.05 days, 185.54 days, 354.62 days, 376.5 days, or 33.25 years; and that the inclination of the orbit to the ecliptic is about 17°. Professor Newton, for reasons assigned, regarded the third period named as the most probable. He remarked, however, that by computing the secular motion of the node for each periodic time, and comparing the result with the known precession, it was possible to determine which of the five periods is the correct one. For the application of this crucial test,--a problem of more than ordinary interest,--we are indebted to Professor J. C. Adams, of Cambridge, England. By an elegant analysis it was first shown that for either of the first four periods designated by Professor Newton, the annual motion of the node, resulting from planetary perturbation, would be considerably less than one half of the observed motion. It only remained, therefore, to examine whether the period of 33-1/4 years would give a motion of the node corresponding with observation. Professor Adams found that in this time the longitude of the node is increased 20´ by the action of Jupiter, 7´ by the action of Saturn, and 1´ by that of Uranus. The effect of the other planets is scarcely perceptible. The _calculated_ motion in 33-1/4 years is therefore 28´. The _observed_ motion in the same time, according to Professor Newton, as previously stated, is 29´. This remarkable accordance was at once accepted by astronomers as satisfactory evidence that the period is about 33.25 years. Having determined the periodic time, the mean distance, or semi-axis major, is found by Kepler's third law to be 10.34. The aphelion is consequently situated at a comparatively short distance beyond the orbit of Uranus. The orbit is represented in Fig. 4. [Illustration: Fig. 4.] It was stated at the close of Chapter VI. that shooting-stars are the dissevered fragments of cometic matter, which, penetrating our atmosphere, are rendered luminous by the resistance so encountered. The discovery that comets and meteors are actually moving in the same orbits was first announced by Signor Schiaparelli in 1867. The coincidence of the orbits of Tempel's comet[23] as computed by Dr. Oppolzer, and the meteors of November 14 as determined by Schiaparelli, is too close to be regarded as merely accidental. These elements are as follows: