634 



VERHOEFF AND BELL. 



plate. The reflection is a function as well of the angle of incidence, 

 but for the ordinary angles up to 30 degrees or so the variation is 

 negligible. At large angles of incidence such as would be presented, 

 for instance, by the marginal rays of a beam incident upon the cornea 

 the loss by reflection may be considerably more than doubled so as to 

 materially reduce the amount of energy absorbed. 



In any case the surface density of the energy received by the cornea 



80 

 70 



bn 

 ^ r.o 



c 



V 



> 



a: ■"« 



■20 

 10 



Distance from axis 

 Figure 2. Distribution of radiant energy on cornea. 



under such circumstances is diminished, following Lambert's law, in 

 direct proportion to the cosine of the angle of incidence. The net 

 result is that from parallel rays the cornea receives a much greater 

 incidence of energy per unit area in the centre than toward the margin, 

 which accounts for some of the results to be recorded later. Figure 2 

 shows for the average rabbit's cornea the approximate variation in the 

 intensity of energy per unit area from centre to periphery. 



Photophthalmia. 



Inasmuch as most of the pathological changes in the eye observed, 

 after exposure to light, either clinically or experimentally, have been 

 ascribed to the action of the ultra violet part of the spectrum, it is 

 with this that our work has chiefly been done, although we have also 



