22 PROCEEDINGS OF THE AMERICAN ACADEMY. 



percentage relation of this energy to the whole input. It is quite clear 

 that in order to do anyinjury to the eye a certain amount of energy 

 must be spent upon it and must be delivered at a rate in excess of 

 the power of the eye to repair damages. One receives injury from 

 excessive exposure to ultra violet rays just as he receives it by exces- 

 sive exposure to heat rays. In either case the delivery of energy at 

 a very high rate for a considerable time does damage. 



TABLE I. 



Source Input Total u. v. u. v. per watt 



100 Watt G. E. M. 100 215 2.15 X 10" 



Glass Mercury Lamp (i length taken) 96 577 6*02 X 10"' 



Nernst (with globe) 91 640 7.03X10"' 



100 Watt Tungsten 103 670 6.50X10"' 



New Quartz Lamp (with Alba globe) 460 1305 2 .84 X 10"' 



Old Quartz Lamp (without globe) 260 5920 22.8 X 10"' 



Magnetite Arc (with globe) 530 7900 14.9 X 10"' 



Magnetite Arc (no globe) 530 10240 19.7 X 10"' 



New Quartz lamp (without globe) 350 11350 32.5 X 10"' 



Carbon Arc (quartz window) 495 26200 52.9 X 10"' 



At a moderate rate and for a moderate time the constructive forces 

 of the organism are not over balanced by the destructive forces of the 

 radiations. Hence the first application of the data obtained from the 

 sources investigated was to determine the actual rate at which ultra 

 violet energy was delivered by them. Table I shows for all the electric 

 sources of light, of which the input could be readily measured, the 

 gross input in watts at the lamp terminals, the total ultra violet radia- 

 tion in ergs per second per square cm. at the standard distance of 

 half a meter and finally, this ultra ^'iolet output in terms of ergs 

 square cm. per second per watt input. This last column is propor- 

 tional to the efficiency of the source as a producer of ultra violet 

 radiations in terms of the gross input. 



In Table I the highest ultra violet output per watt of input is reached 

 by the carbon arc operated in the manner already described. The 

 next highest figure is given l^y the quartz lamp operated without its 

 globe, a condition of relatively low luminous efficiency which would 

 only he found in cases where the arc was being used for bactericidal 

 purposes or other special tasks where ultra violet radiations are 



