560 PROFESSOR STOKES ON THE CHANGE OF REFRANGIBILITY OF LIGHT. 
part of the new region contains many lines remarkable both for their strength and for their arrange- 
ment. I hope to make a careful drawing of these lines as shown by the complete train with a 
summer’s sun. 
I have some reasons for believing that the photographic action of these highly refrangible rays is 
feeble, perhaps almost absolutely null. In the second of the papers referred to in Note A. (p. 300), 
M. Becquerel describes an experiment in which a prism of quartz was employed to form a spec- 
trum ; and yet the impressed spectrum formed by rays which had traversed the quartz alone was 
hardly longer than that formed by rays which, in addition to the quartz, had traversed a screen of 
pure flint-glass a centimetre in thickness. It is possible, I am inclined to think probable, that glass 
made with perfectly pure materials would be transparent like quartz, but aU the specimens I have 
examined were decidedly defective in transparency. Besides, M. Becquerel, who maybe allowed 
to be the best judge of his own experiments, considered the result just mentioned as a proof that the 
impressed spectrum formed by rays which had traversed quartz only did not extend, except a very 
trifling distance, beyond that formed by his train of glass ; and yet his map, formed by means of the 
latter, does not take in the line p. 
However, among the multitude of preparations capable of being acted on by light, it is probable 
that there may be some which are acted on mainly by rays of unusually high refrangibility, and which, 
on that very account, would not be suitable for the ordinary purposes of photography. With these 
it is possible that the new region of the solar spectrum might be taken photographically. 
Note I. Art. 213. 
I have since examined the salt, or product, whatever it may be, in the dry state, and under more 
favourable circumstances, and have found it sensitive, though not by any means in a high degree. 
It exhibits also the absorption bands which seem to run through the salts of peroxide of uranium. 
In connexion with the insensibility of a solution of nitrate of uranium in ether, it seems interest- 
ing to mention a fact which I have since observed, namely, that the sensibility of a solution of 
nitrate of uranium in water is destroyed by the addition of a little alcohol. 
Note J. Art. 217- 
On repeating this experiment on a subsequent occasion, I could not satisfactorily make out the 
difference of character of a strong and of a weak spark from the prime conductor, perhaps because 
the machine was in less vigorous action ; but the difference between the effects of a mere spai'k and 
of the discharge from a Leyden jar was plainly evident. I would here warn the reader, that in order 
to perform the experiment in such a manner as to obtain a striking and perfectly decisive result, it 
is essential to employ an excessively weak solution. The reason of this is evident. 
A severe thunder-storm which visited Cambridge on the evening of July 16, 1852, afforded me a 
good opportunity of observing the effect of lightning on a solution of quinine, and other sensitive 
media. From the copiousness of the dispersed light, it was evident that the proportion of the active, 
and therefore highly refrangible rays to the visible rays was very far greater in the radiation from 
lightning than in daylight. A difference of character was observed between the effects of a weak 
distant flash, and of a bright flash nearly overhead, similar to that which has been described with 
reference to the effects of a spark from a machine, and of the discharge from a Leyden jai*. In 
