Page:In the high heavens.djvu/177

 for the successful application of this method. Nor is there the slightest prospect of any improvements in practical astronomy which would enable us to detect movements of stars in the line of sight in the way suggested. Certainly it offers no hope of a method which could compare for a moment in simplicity or precision with the beautiful spectroscopic process. Of course if a star were moving in the line of sight, there must be a certain change in its apparent lustre corresponding to the changes in its distance, and it might be supposed that by careful measurements of the brightness of a star conducted from time to time, conclusions could be drawn as to the speed with which it was moving.

But the application of such a process is beyond the sphere of available methods. It would take at least a thousand years before even the most rapidly-moving star would experience a change that would sensibly affect its lustre; and even if we had the means of measuring with precision the light emitted, our results would still be affected by the possible fluctuations in the star's intrinsic brightness.

It is thus manifest that the resources of the older astronomy were quite incapable of meeting the demands of astronomers when it became necessary to learn the