midnight
They say it held due east for several minutes , '' continued Evarts , hoping to engage his senior in conversation -- almost an impossibility , as he well knew . Thornton did not reply . He was carefully observing the infinitesimal approach of a certain star to the meridian line , marked by a thread across the circle 's aperture . When that point of light should cross the thread it would be midnight , and July 22 , 1916 , would be gone forever . Every midnight the indicating stars crossed the thread exactly on time , each night a trifle earlier than the night before by a definite and calculable amount , due to the march of the earth around the sun . So they had crossed the lines in every observatory since clocks and telescopes had been invented . Heretofore , no matter what cataclysm of nature had occurred , the star had always crossed the line not a second too soon or a second too late , but exactly on time .