EFFECTS OF RADIANT ENERGY ON THE EYE. 647 



source is enormously rich in lines due to a complex mixture of those 

 belonging to iron and titanium, reaching down to v/aves below 230 mi. 

 Moreover, the spectrum is particularly rich in lines between 330 n^i 

 and 290 jiix. Beyond this the intensity falls oflF noticeably. The 

 source is thus particularly well adapted for work in the region here 

 investigated. The lamp used took approximately 9 amperes at the 

 arc which consumed approximately 750 watts. The energy in the 

 ultra violet from wave length 390 mm. was about 15,000 ergs per 

 second per square cm. at .5 meter standard distance, of which approxi- 

 mately 3500 ergs was below 300 ^l^t, as against very nearly 5700 ergs 

 per second per square cm. for the quartz lamp in the same region. 

 The latter source, however, as just pointed out has relatively more 

 energy in the shorter wave lengths. Plate 5 shows side by side the 

 spectra of the two sources in the ultra violet. 



For determining the wave length at which abiotic effects on the 

 cornea and lens cease, the use of suitable screens is very much prefer- 

 able to attempts at using the spectrum formed by a quartz prism as the 

 source of energy. This is for the reason that with screens one can 

 obtain an enormously greater amount of energy than it is practicable 

 to get by passing the radiation through a slit, coUimating lens and 

 prism, especially in cases where a considerable area like that of the 

 cornea must be covered. In our experiments seven screens were 

 employed of which the absorption was definitely ascertained by the 

 spectrograph. These screens were of various sorts of optical glass 

 and mostly in the form of discs 43 mm. in diameter and 2 mm. thick. 

 They were as follows: — 



Limits of absorption 



1. Extra dense flint Nd 1.69 335 ju/x 



2. Medium flint Nd 1.62 315 mm 



3. Medium flint Nd 1.616, 1 mm. thick. 310 mm 



4. Light flint Nd 1.57 305 mm 



5. Medium crown Nd approximately 1.52 300 mm 



6. Extra light flint Nd 1.54 298 mm 



7. Light crown Nd 1.51 295 mm 



The absorption of these seven glasses for the magnetite spectrum 

 is shown in Plate 6 with the scale of wave lengths subjoined. These 

 limits are taken at the point where the transmission somewhat ab- 

 ruptly ceases. They do not run to the last lines of which traces are 

 visible, since these are so immensely reduced by the absorption as to 

 have little if any effect bearing on the experiments. In any case the 



