80 REPORTS ON INVEiSTIGATlOXS AND PROJECTS. 



effective means of continuing this work would be through the establish- 

 ment of a mountain station in the southern hemisphere. In this way a 

 continuous series of observations could be carried through that part of 

 the year which corresponds to our rain)^ season. The joint work of three 

 stations — one at Washington, one at Mount Wilson, and one in the 

 southern hemisphere — would undoubtedly permit the solution of the most 

 important problem involved in the comparative study of solar and ter- 

 restrial phenomena. 



In undertaking cooperative observations on the solar constant, the 

 International Union for Cooperation in Solar Research will doubtless 

 devote special attention to the methods which Mr. Abbot is employing. 

 It would seem essential, if pyrheliometric observations are to be freed 

 from the effects of atmospheric absorption, that the holographic method, 

 or some analogous plan, should be adopted. The new forms of p3^rheliom- 

 eter which Mr. Abbot has devised and tested should also receive most 

 careful consideration by all who are interested in this field of research. 



COMPUTING DIVISION. 



Much attention has been devoted to the question of the best organiza- 

 tion of the computing division. While there would be certain advantages 

 in having photographs measured and reduced on Mount Wilson, the dis- 

 advantage of quartering a large force of computers there seems to out- 

 weigh them. With the completion of the Mount Wilson road and the 

 rapid means of communication thus afforded, there should be no prac- 

 tical difficulty in carrying on this work at our Pasadena offices. This 

 agrees with the general principle, adopted at the outset, that the work 

 on Mount Wilson should be confined, so far as possible, to observations. 



Accordingly, our Pasadena building was enlarged last spring by a 

 brick addition, adjoining on the east side the long hall used for optical 

 testing purposes. The addition is divided into a series of rooms, includ- 

 ing a library, an office for the superintendent of the computing division, 

 Mr. Adams, and six small rooms, each serving as an office for one com- 

 puter. Cases for the storage of photographs are placed in the hall into 

 which the offices open. The optical testing hall, which is entered by a 

 door from the computing quarters, serves admirably for the globe-measur- 

 ing machine, or "heliomicrometer," which is installed there. The use of 

 the hall for this purpose, and also for the Littrow spectrograph of i8 

 feet focal length, and the transformer and electric furnace employed with 

 it, does not interfere in the least with its employment for testing mirrors 

 of great focal length. 



The equipment of the computing division now includes a Toepfer 

 measuring machine, capable of measuring spectra 6 inches long; a 

 Gaertner measuring machine, for spectra i8 inches long, or for the meas- 



