The Astronomical Department.
A large portion of the investigatory work has been in the field of stellar spectra. Professor Pickering, in conjunction with others, has derived a new method of determining the relative motion of two stars in the line of sight. The method depends on the calculation, by means of photographic plates, of the relative variation in the position of the spectra of the two moving stars. There is reasonable belief that this method will enable such calculations to be made with a degree of accuracy hitherto unobtainable. The spectra of many obscure stars have been carefully studied, and in some cases, peculiar spectrum lines have been noticed which point to the presence of some unknown elements.
A new eight-inch photographic telescope for the observatory is in process of construction. It is called a doublet, or rectilinear instrument, from the fact that it is to contain two object glasses, by which the linear distortions caused by ordinary lenses are nearly eradicated. The new telescope differs from the present Draper instrument in that it will take successive stellar photographs automatically, changing and exposing the plates according to the particular programme decided upon. The charts produced will be about eight inches square.
The station at Arequipa, Peru, where the Bruce telescope was moved last winter, is now under the personal direction of Professor Bailey. The difficulties met with in setting up the instrument, owing to its great size and weight, have been finally overcome. Professor Bailey has photographed a large number of excellent stellar charts of which some very fine specimens have been received in Cambridge. The main station at Arequipa controls many meteorological posts in the neighboring country. The most important of these is situated on the summit of the volcano El Misti, 19200 feet above the level of the sea. At this high post there has recently been set up an automatic meteorograph which runs without care for months at a time. This records the direction and velocity of the wind, and registers continuously the barometric pressure, the temperature, and the humidity of the atmosphere.