EFFECTS OF RADIANT ENERGY ON THE EYE. 



705 



complicated for complete analysis since fully to understand them 

 would require a knowledge not only of the chemical changes originally 

 produced, but of the vital processes of the cells. An interesting 

 question in regard to them is that concerning latency of their appear- 

 ance. In the case of abiotic action, as has been pointed out, abso- 

 lutely no visible change either histological or clinical takes place 

 immediately after the exposure, and usually not for several hours. 

 This is no doubt due to the fact that time is required for the chemical 

 changes to produce physical alterations. In the case of heat effects, 

 it is a matter of common experience that latency also occurs and that 

 the time interval varies with the intensity of the exposure, but it is a 

 far less striking phenomenon than in the case of abiotic effects. This 

 may be due, among other causes, to the fact that the energy required 

 to produce chemical changes by heat is so great owing to the rapid 

 dissipation of the latter, that under ordinary conditions the critical 

 point is quickly passed and an excessive effect produced. 



Abiotic Energy in the Solar Spectrum. 



As has already been noted the solar spectrum when filtered through 

 a thick layer of atmosphere as at sea level when the sun is low fades 

 out at about 305 njx. At high altitudes and with the sun running 



700 800 900 



Mt. Whitney z. d. 



1300 yU/U 



0° 



h. Mt. Whitney z. d. = 60° 

 Figure 5. Distribution of energy in solar spectrum. 



high, it extends to about 295 /x^t- Under extremely favorable condi- 

 tions some very faint traces of the spectrum were registered by 

 Cornu ^^ down nearly to 292 ix\x. 



