Page:Gods Glory in the Heavens.djvu/280

246 starry night, and observing how the stars that were in the east at one hour, are in the west at another. But this is a matter of inference. It is not a direct, sensible proof. You do not see the stars moving as you do the trees and houses when you travel along in a carriage. But in the transit instrument, so sensible is the motion, that it is a most nervous business to note the precise moment when the star passes across the various wires; but it is needful to do this, in order to determine, more accurately, the moment when it passes the central line. This applies, however, only to the most rapid stars; for, as you approach the pole, the motion becomes slower and slower, till it is imperceptible. The observer must be within hearing of the clock, and as he silently counts the seconds, he must note down when the star passes each line; and as the star may take but a very few seconds to travel from one line to another, he has no sooner noted the one transit, than he has to note another. This would be all comparatively easy if the star passed each line precisely at the beat of each second; but this rarely occurs, and, consequently, the observer has to make a hurried estimate of the fraction of a second; and the requirements of science are such, that he must be able to appreciate the tenth of a second. Listen to the beat of a clock, and if you attempt to divide the interval between two beats into ten smaller intervals, you will have some idea of the difficulty of transit observation.