212 CARNEGIE INSTITUTION OF WASHINGTON. 



Hooker telescope. Excellent preliminary results were obtained, and it 

 is hoped that he may be able to continue this work at some time in the 

 near future. 



The 100-inch telescope affords an exceptional opportunity for meas- 

 uring the radiation of faint stars and of determining the spectral- 

 energy curves of brighter ones. Dr. Abbot's long experience with the 

 bolometer especially qualifies him for this work, which he will under- 

 take as soon as his other duties permit. Meanwhile, the problem has 

 been approached from a different direction with the aid of a thalofide 

 cell, a new device for the measurement of radiation in which the sen- 

 sitive substance, fused on a quartz disk and mounted in an evacuated 

 tube, is composed of thallium, oxygen, and sulphur. The maximum 

 sensitiveness of this cell, which makes it especially useful for certain 

 observations, is at 10,000 angstroms. The preliminary tests made by 

 Messrs. Shapley and Benioff V\^ith the 100-inch telescope are promising 

 and the w^ork will be continued with improved instrumental arrange- 

 ments. 



In connection with the experiments made last year by Messrs. Ander- 

 son and Babcock on the polarization of the light of the sky by day and 

 night, an extremely sensitive means of detecting very slight traces of 

 polarized light was developed. This device is being used with the 

 Hooker telescope by Mr. Hubble in an attempt to determine whether 

 the light of certain nebulse shows any indication of polarization. 



Finally, although no new instrumental accessory has been required 

 for the purpose, a word may be added regarding the striking phenomena 

 rendered visible on the moon's surface by the aid of the stereoscope. 

 The very sharp lunar photographs made at the 134-foot focus of the 

 Hooker telescope by Mr. Pease serve admirably for this purpose when 

 pairs representing the same phase, but differing in libration, are com- 

 bined. The distinct appearance of relief thus brought out should aid 

 materially in the solution of lunar problems. 



Other additions to the equipment of the Hooker telescope are in pros- 

 pect, and the development of this instrument has already advanced so 

 far that we are now able to complete the details of our general research 

 program, some of the chief elements of which were indicated in the last 

 annual report. WTiile considering the most promising lines of attack 

 on stars and nebulse, the possibilities of the solar and laboratory work 

 have been re-examined, \^dth the object of perfecting a homogeneous 

 and well-balanced general scheme. In this connection the completion 

 of the remodeled Snow telescope and its accessories for work with the 

 Fabry-Perot interferometer, and the addition of several important 

 instruments to our laboratory equipment, have been essential factors. 



Full details of the work of the year may be found in the body of this 



report, but the chief investigations in progress may be briefly summar- 



zed here. Of exceptional current interest is the bearing of the solar 



