Chemistry and Physics. 149 
mercury unit.—Annalen der Physik und Chemie, No. 13, 1882, 
PP. 773-816 5. f, 
Approx azimate Photometric Measurements of Sun lak 
Cloud, Sky, Electric and other artificial lights.—Sir Win 
Taomson having referred to the experiments of Pouillet, float 
eve oceed 
calculation: Take, however, instead of the sun an ideal radiating 
surface of a solid globe of 440 ,000 miles radius. The distance of 
the earth being 93,000,000 miles, the radius of the sun is equal to, 
in round n umbers, 1-200th of the earth’s dista ance; hence the 
area at sfie: earth’s ‘distance, corresponding to rn square foot o 
the sun’s surface, is equal to 40,000 square feet. The radiation 
on this surface is 40 ,000 X 86 or 3,440,000 eckiniatsl which is 
therefore the amount of radi ation from each s square foot of the 
ce. m 
fourths of a horse power per square inch ence the activity of 
the sun’s radiation is about sixty-seven times greater than that of 
a Swan lamp per eee are mn ference Electrical 
two or three per cent of accuracy. rago has compare¢ 
luminous intensity of the sun with that of a candle and estimates 
it as equal to about 15,000 times that of a candle flame. Seidel 
estimated the luminous intensity of the moon as about equal to 
mately one-third of the light = upon it. The observation 
on moonlight taken at York—about midnight at the time of full 
moon-—showed that the caeania was equal to the light of a 
