Page:Popular Science Monthly Volume 15.djvu/467

Rh would add to this 7', Uranus would add 1'; the effect of the earth and other planets would be insensible. Adding these numbers together, the whole effect, according to Mr. Adams's computation, is 28', almost exactly the same as the observed amount which had been determined by Professor Newton, which was 29'. But, if the meteors were in any of the other four possible orbits, the total amount would never exceed 12'. Here, then, we have reached the final result: the long orbit is the orbit of the meteors. This great discovery was published in March, 1867.

Meanwhile Signor Schiapparelli, of Milan, was laboring in another direction. It was evident from the observations that the meteors were drawn out into a long stream. What was the cause of this? Signor Schiapparelli pointed out that if a cloud of meteors were started under conditions which are not quite the same, each meteor would pursue its own orbit, which would differ from the others. If they were treated almost exactly, although not quite, alike at starting, their various orbits would lie excessively close to one another, and would be undistinguishable in most respects. But if there be any effect which goes on accumulating from revolution to revolution, such an effect would in the end become very sensible. And such an effect there is. The periodic times differ a little in these different orbits. At the end of the first revolution those meteors which have the longest periodic times are the last to get back to the starting-point, and have, therefore, already fallen a little into the rear of the group, while those with the shortest periodic time have gone a little ahead. At the end of the second revolution the separation is doubled, and in each successive revolution the column is still more lengthened out. After a sufficient number of revolutions it will be spread out over the whole length of the orbit, and form a complete oval ring. This has not yet happened to the November meteors, and we are thus assured that it can not be any enormous period, speaking cosmically, since the time when they first started on their present path. On the other hand, the August meteors, which have returned punctually every year since they were first observed, are probably a complete ring, and are at all events of far greater antiquity than the November meteors. But they are also, as might be expected, more scattered, so that the sprinkling of meteors they discharge upon the earth as it passes through them has nothing like the splendor of the great November shower. Signor Schiapparelli also pointed out that there is a comet moving in the track of the August meteors, and another in the track of the November meteors. We shall presently see the significance of this observation.

The next great step was made by M. Le Verrier, the late Director of the Paris Observatory. Acting on the suggestion made by Signor Schiapparelli, M. Le Verrier pointed out that the orbit of the meteors intersects the orbit of Uranus, as represented in the diagram. From