558 PROFESSOR STOKES ON THE CHANGE OF REFRANGIBILITY OP LIGHT. 
f 
the spectrum. M. Becquerel expressly states that lines were seen beyond the last he has repre- 
sented, though they were hardly distinct; and on comparing together his map, Mr. Kingsley’s 
photographs, and my own map, I think hardly any doubt can remain as to the identification. 
I take this opportunity of referring to another very interesting paper of M. Becquerel’s, entitled 
‘ Des etfets produits sur les corps par les rayons solaires,’ which is published in the Annales de 
Chimie, tom. ix. (1843) p. 257, '"'ith which I was not acquainted till lately, or I should have refeired 
to it before. This paper contains, among other things, an investigation of the effects of trans- 
parent and coloured screens on the luminous, chemical, and phosphorogenic rays, in which it is 
shown, that, notwithstanding the great difference in the action of a given screen on the three classes 
of rays, when we study the effect of the incident rays as a whole, its action is the very same when 
we confine our attention to rays of any one refrangibility. Among the media employed by M. Bec- 
querel, are some whose absorbing effect I have mentioned in the present paper, as having been 
determined by methods depending upon the change of refrangibility. In such cases my own results, 
as might have been anticipated, are in perfect harmony with those of M. Becquerel. With 
respect to the results at which 1 have arrived regarding the nature of the phosphorogenic rays of an 
electric spark, which are mentioned towards the end of the paper, I have been in a good measure 
anticipated by M. Becquerel. Yet I do not think that even he was aware that so much of the 
effect of the spark was due to rays of such high refrangibility. 
Note B. Art. 105. 
I have since succeeded, by a particular arrangement, in seeing so far into the “ lavender ” rays as 
to make out the groups of fixed lines m, n, p by means of light received directly into the eye, and 
even to perceive light beyond that. 
As to the colour of these rays when they are w'ell isolated, I think the corolla of the lavender 
gives as good an idea of it as could be expected from the circumstances. They seem to me to want 
the luminousness of the blue and the ruddiness of the violet. No doubt much error and uncertainty 
has hitherto existed both as to the colour and as to the illuminating power of these rays, because 
the gray prolongation of a spectrum formed on paper by projection has been mistaken for the 
lavender rays. 
Note C. Art. 154. 
On adding common phosphoric acid to a solution of nitrate of uranium no effect seemed to be 
produced, but on examining the vessel some days afterwards, a precipitate was found to have fallen. 
This precipitate proved to be sensitive in a very high degree. 
Note D. Art. 158. 
I have since observed in a mineral solution a system of absorption bands so remarkable, and so 
closely resembling in many respects those found in the salts of peroxide of uranium, though they 
occur in a totally different part of the spectrum, that I think no apology is needed for mentioning 
the circumstance. The medium referred to is a solution of permanganate of potassa, in fact, red 
solution of mineral chameleon. In order to see the bands, it is essential to employ a dilute solution. 
