I ()-i 



RADIATION mOLOGY 



Icr or photoelectric cell. The determination reciuire.s that the atmos- 

 pheric attenuation a remain unchanged for several hours as Z changes. 

 Several sets of data obtained hy this method are plotted in Fig. 3-3. 

 They include the data of the Smithsonian Institution (Ahl)ott et al., 

 1923; Fowle, 1934h) of Pettit (1940) at Mt. Wilson, and of Gotz and 

 Schonmann (1948) at Arosa. The curve of Moon (1940) is an average 

 of all data existing in 1940. The data at an altitude of 55 km were 

 obtained in 1947 i)y Durand ci al. (1949) of the Naval Research Labora- 

 tory with a spectrograph on a rocket; at 55 km the pressure was 2 X 10~' 

 too 



90 



80 - 



70 - 



t 60 



z 



H 



? 50 



UJ 



> 



40 



30 



20 



10 



0.2 



0.4 



0.6 



0.8 



1.0 



2.0 



2.2 



2.4 



2.6 



1.2 1.4 1.6 1.8 



WAVE LENGTH, /Z 



Fig. 3-3. Solar-spectrum curves on top of tlio atniosphore. 



atm, and the spectrograph had risen through 4999 5000 of tlie atmosphere 

 and had only 1/5000 al)o\^e it. The solid-line curve of Fig. 3-3 is the 

 spectral intensity of a l)lack body at 6000° K. All the curves of Fig. 3-3 

 were arbitrarily adjusted to have their maxima at 100. It is seen that 

 the ()000°K curve lies abov^e the solar values in the ultraviolet and also in 

 the red and infrared to 1.4 m- 



In Figs. 3-1 and 2 are reproduced perhaps the best photographs which 

 have been made of the ultraviolet portions of the solar spectrum. The 

 spectrum of Fig. 3-1 was taken by Giitz and Casparis (1942) at Arosa, 

 Switzerland, using all po.ssible care to reduce the scattered light which 

 always veils the short-wave-length limit of the solar spectrum l)elow the 

 ozone layer. The spectrum of Fig. 3-2 is a composite made from four of 

 a series of spectra obtained by F. S. Johnson, .1. 1). Purcell, and W. 



