﻿NO. II 



SMITHSONIAN EXPEDITIONS, I9IO-I9II 



California (4,420 meters). It is rather a new departure with the 

 bolometer, that delicate instrument which measures the millionth of 

 a degree rise of temperature, to use it out of doors, following the sun 

 in an equatorial telescope, but Mr. Abbot successfully used it so in 

 1908 at Flint Island in the South Pacific, in 1909 and 19 10 at Mount 

 Whitney, and now for several months in 191 1 in Algeria. 



A delay of about 2 weeks occurred in beginning observations, 

 owing to the miscarriage of one of the cases of apparatus. Consider- 

 able cloudy weather unfortunately prevailed in September and Octo- 

 ber, both at Bassour and at Mount Wilson, California, where Mr. L. 



Fig. 2. — Spectrobolometer. Photograph by Abbot. 



B. Aldrich was conducting similar observations. Messrs. Abbot and 

 Brackett observed on 44 days at Bassour, and discontinued observing 

 on November 18. Mr. Aldrich observed on 29 of these days at 

 Mount Wilson, and secured observations for about four more which 

 will be useful for the comparison of results between the two stations. 

 It takes about three days of computing to reduce one day's observa- 

 tions, so that the final results of the work are not yet known. If 

 further experiments are necessary, it is hoped to make them at the 

 same stations in June, July, and August of 19 12. 



Recent experiments of the Smithsonian Astrophysical Observatory 

 made principally at Mount Wilson, California, in the years 1905 to 



