the planet, he has branded the object, so that it can ever afterwards be identified. Had he been only able to report that he had seen a black point, his observation would have been of little value, and no one would know where to look for it again. By simply ascertaining how long it took to cross an ascertained portion of the sun's disc, its distance from the sun and its period of revolution could at once be deduced, and thus the chief elements of identity would be determined. These essential points were not observed when the knock was heard, and we can well conceive the painful suspense of the observer, till his eye was once more applied to the tube.
This reminds one of the interruptions of Sir William Herschel, when pursuing his musical avocations in the pump-room at Bath. He had a small workshop close at hand, and when the exacting loungers in the pump-room admitted of a pause in the music, he slipped off to complete the polishing of a speculum, or the grinding of a lens. But he was always ready, when he heard the signal, to snatch up his instrument, and be the first in the orchestra. He did not permit his astronomical tastes to interfere with the duties of his calling. He was allowed to be one of the best drummers in the Hanoverian army, and few in Bath could match him on the fiddle, the flute, or the cornet-à-piston. While his fellow-musicians spent their pauses in drinking and gossiping, he
