THE NEW DRIVING SYSTEM OF THE CROSSLEY REFLECTOR

Abstract

The Crossley reflector has recently been equipped with an electrical driving clock. The apparatus is similar to that in use at the McMath-Hulbert Observatory, which has been described by Robert R. McMath and Walter A. Greig.1 The new equipment has been in service for several months. It appears to have improved the accuracy of following of the telescope in a considerable degree, and the strain on the observer has been lessened. This paper contains a general description of the driving system, in which it is thought there might be some interest. For some time, with the old mechanical clock, the following of the Crossley telescope has been unsatisfactory. The instrument is provided with two sectors instead of with the more common worm wheel. These sectors function alternately, one driving the telescope while the other is being returned to the starting position. The changing of these sectors is done automatically. The system involves a rather complex arrangement of gears, and there are numerous points of varying friction in the mechanism. The driving clock was a standard type of conical pendulum, brake-controlled. The unsteady frictional loads reacted upon the clock, an effect undoubtedly made worse by the circumstance that many of the gears, after long service, were badly worn. There resulted a drive that was subject to annoying and erratic changes in rate. To improve the following of the Crossley telescope, a reconstruction of the driving clock seemed to be an obvious first step. This does not necessarily involve changing the sector mechanism, or the slow-motion gears. The McMath-Hulbert drive seemed attractive from several points of view: (1) The rate of the clock, being determined by the frequency of a vacuum-tube oscillator, is nearly or quite independent of any variable load demands upon the driving motor, such as those caused