Page:The Moon (Pickering).djvu/130

90 of silver on glass, eighteen inches in diameter and about four inches thick. Owing to the length of the instrument, it was decided to drive it by electric motors capable of control from the eye end of the tube, instead of by clockwork actuated by gravity, as has heretofore always been done. The plan proved very successful.

On our arrival in Jamaica in October, 1900, we proceeded at once to Mandeville, where we had decided to locate the station. There we hired an estate called Woodlawn, situated about two miles to the east of the town, in latitude +18° 01′, longitude 5$h$ 10$m$ 02.′5, altitude 2,080 feet above sea level. In Plate K is given a view of the instrument. On the extreme left is shown a part of the dwelling-house, which was built in the form of a bungalow. The long inclined tube of the telescope consisted of a wooden frame covered with wire netting and supported on posts driven into the ground. The netting was covered at first with builder's paper, and later with cotton cloth. In the bottom of the tube were strung twelve insulated copper wires, permitting the operator at the upper end of the tube to control the motions of the mirror at the lower end. The small building at the upper end contained the observing room, the laboratory, the computing and dark rooms. The building at the lower end had a movable roof, divided in the middle. This could be slid apart, exposing the mirror and lens to the sky. The light of the Moon was reflected from the mirror up through the lens to the observer at the upper end of the tube. By turning the mirror the observer could see the Moon, no matter in what part of the sky it chanced to be, and it always appeared below him, and in the same direction. This was an important advantage, as when observing with an ordinary telescope it is very difficult to do good work when the Moon is directly overhead. This is a position that it frequently assumes to an observer located in the tropics.

We obtained our first view through the telescope a few minutes after midnight on December 31, 1900, the beginning of the new century. Eight days later our first photograph was taken, and from then until August 31st, when the telescope was dismounted, not a clear night passed when the Moon was visible but that some observations or photographs were secured. Our first satisfactory photograph of the Moon was taken on January 29, 1901. Our last photograph was taken August 31, so that the material for the present volume was collected in about seven months.

In planning the work, it was decided to divide the Moon's equatorial diameter into