432 PHILOSOPHICAL SOCIETY OP WASHINGTON. 
1 . • 
had been suggested by Dr. G. F. Becker, and is found to satisfy 
with high accuracy observations on india rubber and metallic 
wires. The paper was illustrated with lantern views. [Not 
published.] 
A letter was read by Mr. Day from Dr. Becker expressing his 
appreciation of this investigation. 
Mr. C. W. Waidner then gave the results of numerous deter¬ 
minations by himself and Mr. G. K. Burgess of The temper¬ 
ature of the electric arc; they were made by photometric methods 
based on Wien’s law, the instruments being calibrated at the 
highest practicable temperatures; the results were very accordant, 
and gave about 3700° absolute. An increase of 70° to 80° C. 
was found when the current forming the arc was raised from 
15 to 30 amperes. The apparatus used was shown by lantern- 
views. [Published in Physical Review, vol. 19, p. 241, 1904, 
and in Bulletin, Bureau of Standards, No. 1, p. 109, 1904.] 
590th Meeting. November 12, 1904. 
President Marvin in the chair. 
% 
Thirty-one persons present. 
Mr. Marsden Manson, of San Francisco, read by invitation 
a paper on The evolution of climate. The ordinary explanations 
of the glacial epoch attribute it to solar control; the speaker 
sought to show that it was due to a plvysical change in the con¬ 
ditions of the earth and its atmosphere. At the beginning of 
geological time, when the earth-ball had a relatively high tem¬ 
perature, there must have been a great amount of aqueous vapor 
in the atmosphere and dense clouds, both of which trapped the 
heat radiated from the ball and prevented the solar radiation 
from reaching the surface. The isothermal surfaces were ap¬ 
proximately spheroidal and non-zonal; as they contracted and the 
evaporation diminished, they cut the earth’s surface, beginning 
at the poles, and the solar rays could also reach the surface; so a 
zonal distribution began; the two periods respectively of earth- 
controlled and sun-controlled surface temperatures were sepa¬ 
rated by an ice age; this could occur in a complete form only 
once. [Published in fuller form in the American Geologist, 
