Page:Popular Science Monthly Volume 76.djvu/15

Rh

would be very promptly disposed of. Of course, all computers are not like the late Professor Safford, who used to compute such an orbit in one hour, but we should probably not find it necessary to search long for one who would undertake to do the work in ten or twelve days. But the method developed by Newton seems now very cumbersome and its application laborious. It was, moreover, so far from completion

that no means were found for computing the elliptic elements of a periodic comet unless it had been observed at a second return. The identification, therefore, depended on the similarity of the elements, a very uncertain criterion, as we shall see.

It is not at all improbable that if Halley had known more of the chances of failure which beset this method of identification he would hardly have ventured to predict another return of his comet. The step,