Page:Popular Science Monthly Volume 71.djvu/339

Rh Depot of Charts and Instruments. It was given charge of the unused charts and instruments of the navy. It distributed these necessary articles to the naval ships. It repaired and rated the chronometers. For the latter purpose simple meridian observations were necessary. Lieutenant Charles Wilkes, who was made superintendent of the depot in 1833, removed it to Capitol Hill. Here he erected a small observatory, 14 feet long, 13 feet wide, and 10 feet high. He installed in it one of the five-foot transit instruments, which Hassler had procured for the Coast Survey.

In 1836 Gilliss was detailed to duty at the Depot of Charts and Instruments. He shortly began to make astronomical observations in addition to those necessary for the rating of the chronometers. In the winter of 1837-8 he observed certain culminations of the moon and stars. In August, 1838, the Wilkes exploring expedition sailed from the United States on its famous voyage to the Pacific and Antarctic seas. Wilkes suggested to the secretary of the navy that in determining the longitude of the various stations of his expedition, observations made in the United States would be of the greatest value. Accordingly, Secretary of the Navy Paulding issued instructions to Gilliss to observe, during the absence of the exploring expedition, culminations of the moon and stars, eclipses of the moon, sun and Jupiter's satellites, falling stars, and any striking astronomical phenomena. He was to make also meteorological and magnetic observations.

Gilliss immediately made thorough preparations for his new work. He procured a 42-inch achromatic telescope mounted parallactically, a variation transit, an 8-inch dip circle, and a sidereal chronometer. He imported several new meteorological and magnetic instruments, to accommodate which he erected a small frame building fifty feet south of the observatory on Capitol Hill. Three or four additional passed midshipmen were attached to the depot to assist in its new work. This began in September, 1838, and did not end until June, 1842. All the astronomical observations, with the exception of those for two days in May, 1841, when Gilliss was sick, and a part of those for two other days, were made personally by Gilliss. The average time of his daily employment throughout the period was twelve hours, and he was often on his feet twenty hours out of twenty-four. The number of transits recorded exceeded ten thousand, and embraced those of the moon, planets, and about eleven hundred stars. The average number of lunar culminations observed was one hundred and ten, and of lunar occultations about twenty. The meteorological and magnetic observations were made bi-hourly day and night. All these observations were reduced by Gilliss, and were published by the government in 1845 and 1846 in two octavo volumes containing more than thirteen hundred