﻿Visibility of Radiation. 



309 



acetylene, pentane, Hefner, Nernst (two efficiencies), tung- 

 sten and carbon (three efficiencies). The acetylene source 

 was a Mees standard burner (see above), the pentane and 

 Hefner were primary standard lamps, the Nernst was of 

 Westin_house make, 103x13 mm. filament, the tungsten 

 an old type evacuated Limp, and the carbon of the " gem ; ' 

 type. The quality determinations (means of three to six) 

 are as follows : — 





Obser 



rations. 



Stan dai 



•d quality. 



C/W. 



•1276 



•1144 



•598 



•570 



•484 



•903 



•216 

 •243 



•286 



Mean horizontal. 



Hefner 



M-W. 



6-84 

 14-2 



2-45 

 21-96 

 13-32 



5-48 



11-77 

 14-20 

 1606 



M-C. 



•871 

 1-625 



•731 

 12-42 

 6-46 

 4-94 



2-54 

 410 



4-58 



"W/C. 



7-84 



875 



167 



1-75 



206 



111 



4-64 

 4-12 

 3-51 



W/cm. 2 /C at 1 m. 

 6-24X10-5 watt 

 6 97 

 1-23 

 1'29 

 1-64 

 0-884 



Pentane 





Nernst - 80 amp. ... 



„ -67 „ ... 



Tungsten 1 -20 W/C. 



Carbon 40 



3-3 



27 





In calculating the illumination constant Y m , these quality 

 determinations and the above visibility curve (Y/Y m ) were 

 used. The required spectral energy curves available were, 

 however, found to be inadequate. Either the visible portion 

 is not known with sufficient precision or else the conditions 

 under which the whole curve was taken is not specified with 

 sufficient detail. After these curves have been freshly deter- 

 mined, for the sources whose luminous quality has been 

 determined, the constant Y m should be determinable to perhaps 

 two or three per cent. 



In the case of acetylene, spectral energy determinations 

 by Coblentz (B. S. Bull. vii. pp. 291-3) enable us to evaluate 

 Y m to about 5 per cent, uncertainty. We find for relative 

 integrals of energy and luminosity A/B = 62<>/5 , 66==110 , 6. 

 For C/W we obtained 0*598, hence Y m = 6G-2 candles inn- 

 watt. The uncertainty arises from the uncertainty in the 

 "saturation" of the infra-red part of the radiation for the 

 thickness of flame used. I hope soon to have a number of 

 more precise values of Y m . 



I am greatly indebted to friends in the Photographic and 

 Chemical divisions as well as to colleagues in the Physics 

 division, who so cheerfully served as. subjects in obtaining 

 visibility data. I am particularly indebted to Mr. Felix 

 Elliott, who recorded and reduced nearly all of the thousands 

 of observations. 



Research Laboratory, 

 Eastman Kodak Co. 



Rochester, N.Y., July 1014. 



