. APPENDIX V. 
REPORT ON THE ASTROPHYSICAL OBSERVATORY. 
Sr: I have the honor to present the following report on the operations of 
the Astreyhysical Observatory during the fiscal year ending June 30, 1907: 
During the past year the cost of the necessary repairs and repainting of the 
Observatory ineclosure and buildings has been $300. Plans have been prepared 
and contracts awarded, incurring a total liability of $2,000, for the installation 
of electric lighting, power, and laboratory service currents, to replace the pres- 
ent inadequate facilities. These improvements are not as yet completed. 
Apparatus for research has been procured at a cost of $600. 
The usual scientific periodicals have been continued, and books of reference 
purchased at a total cost to the Observatory of $600. 
No losses of property have occurred. 
Personnel.—C. G. Abbot was promoted to be acting director July 1, 1906, and 
Director March 1, 1907. 
FEF. E. Fowle was promoted to be aid March 1, 1907. 
J. C. Dwyer was promoted to be messenger March 1, 1907. 
DR: Ingersell served as temporary bolometric assistant from July 1 to Sep- 
tember 10, 1906. 
Miss CG. V. Barber served as temporary computer January 2 to June 25, 1907. 
P. k. Tavenner, fireman, was transferred to the Department of Agriculture 
June 15, 1907. 
WorkK OF THE OBSERVATORY. 
The work of the Observatory has consisted as follows: 
1. Observations at Mount Wilson and Washington. 
2. Preparation of Volume II of the Observatory Annals. 
OBSERVATIONS AT MOUNT WILSON. 
The staff of the Mount Wilson expedition, mentioned in last year’s report, 
continued observations for determining the “solar constant” of radiation until 
October 22, 1906, when the apparatus was packed and in part returned to Wash- 
ington. During the stay of the expedition in 1906 about seventy days were 
devoted to “solar constant” observations, and with generally excellent results. 
Much attention was paid to the observation of the intensity of light reflected 
from clouds, with a view to the determination of the albedo, or total reflection 
of the earth. The quality and amount of light of the sky was also measured 
on several days. Very successful trials were made with the continuously record- 
ing standard pyrheliometer mentioned in former reports, and the other instru- 
ments used on Mount Wilson were compared carefully with each other and with 
it. Krom these comparisons, made on different days and with widely differing 
conditions, it appears that the scale of values heretofore employed in the reduc- 
tion of Mount Wilson observations is probably 1.5 per cent too high. But it 
has been decided not to make a correction for this until the completion and trial 
of a new continuously recording pyrheliometer, now partly done, of different 
dimensions and improved construction. 
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