88 Br. E. Rose on the Doctrine 



It may here be remarked at once, not only that ultra-violet can 

 be seen indirectly in the objective spectrum by a lowering of the 

 refrangibility, but that I know a colleague who even in the sub- 

 jective spectrum sees the ultra-violet, and, accordingly, actually 

 sees it*, — a power of seeing ultra-violet which presupposes a 

 heightened sensitiveness of the retina, as in colour-blindness it 

 is diminished. In any case it was seen that the subjective spec- 

 trum alone could be used for investigating violet-blind persons. 



While thus the results with the objective solar spectrum were 

 not up to my expectations, the difficulties in its use were almost 

 insuperable. If the weather was fine, no one had time or wish 

 to take santonine ; several times when I took it myself a storm 

 followed immediately. If weather, leisure, and will were com- 

 bined the narcosis failed, or only occurred when hunger drove 

 away the person investigated. In addition to this was the trou- 

 ble of setting up, which renders useless this mode of investiga- 

 tion, however pleasant was the brightness or desirable the natu- 

 ral scale which is afforded by the Fraunhofer's lines. In further 

 experiments I subsequently found the following kind of self- 

 measurement the most convenient. 



It was established that yellow vision in the santonine intoxica- 

 tion depends upon a shortening of the spectrum, upon colour-blind- 

 ness, and that the shortening might take place at either end. 

 The greenish-yellow colour of all impure colours was easily ex- 

 plained by this want of sensitiveness to the complementary 

 colours in the mixture. The question was to determine with 

 still greater certainty whether the shortening was fixed or move- 

 able. 



For this purpose the most beautiful, but unequally long and 

 variable, solar spectrum was not so well fitted as an artificial 

 one ; only it is difficult to have an artificial spectrum with sharp 

 ends, and we lose, moreover, our natural scale. 



As the source of light, a spermaceti candle was used ; as spec- 

 trum, a diffraction-spectrum ; as scale, the intervals between its 

 separate bands of colour (spectra). It is known that, on looking at 

 a source of light through a grating of 2000-3000 lines to an inch 

 (diamond-ruled lines on glass) , the light is seen surrounded at some 

 distance on each side by a tolerably pure spectrum, followed at 

 some distance again by a band of colour which gradually shades off. 

 This band of colour is produced by the circumstance that the 

 dark intervals between the individual spectra decrease in breadth 

 on the outside ; hence the violet of the third covers the red of 

 the second spectrum to form a purple zone, and the others quite 



* Compare "The Visual Delusions in Jaundice," together with an Appen- 

 dix on the sense of colour in nocturnal blindness, and the action of picric 

 acid on the eye. Virehow's Archiv, vol, xxx. p. 442. 



