262 REPORT—1852. 
On the Chemical Action of the Solar Radiations. 
By Rosert Hunt. 
(1). Tue following results are offered as a small instalment of an exten- 
sive system of examination which I have undertaken. The object in view 
is to determine, with all the accuracy possible, the relation which each 
coloured ray of the prismatic spectrum bears to the chemical action which 
takes place upon the different agents employed in the production of the 
sensitive surface. Since different media exhibit very various degrees of 
absorbent action upon the chromatic rays, as well as on the chemical rays, of 
the spectrum, by employing them we obtain indications by which we may 
determine the relation in which these phenomena stand to each other. 
(2). The plan upon which I am proceeding is this. Having obtained a 
very extensive series of coloured glasses, and by the solution of chemical 
compounds, procured a still more varied set of transparent ccloured solu- 
tions, I analyse the luminous spectrum of a well-formed vertical opening be- 
tween two knife-edges, by passing the spectrum through a particular absorb- 
ent medium. The spectra are obtained, first, by means of an excellent flint- 
glass prism ; again, by one of crown-glass of faultless purity, the manufac- 
ture of Messrs. Chance, Brothers, of Birmingham; and, thirdly, by a hollow 
prism, in which I have the means of employing fluids of very different re- 
fracting powers. For obtaining the chemical impression of the spectrum, I 
procure a flame-like chromatic image of great intensity, 1 inch in length, from 
a vertical opening in my steel plate. I have adopted this as my measure 
throughout, dividing it into 100 equal parts: thus, all the numbers employed 
are intended to express inches, or the one-hundredth part of an inch. 
(3). The first part of the present Report is devoted to the examination of 
the prismatic spectrum by coloured glasses of various kinds. ‘The numbers 
affixed may appear somewhat irregular, but as they correspond with a very 
extensive series, over many of which I have no control, but which are well 
known to me by these numbers, and can always be obtained, I have thought 
it best to retain them. I have however adopted the plan of numbering my 
paragraphs, so that in referring back there will be no difficulty in comparing 
the chemical with any particular luminous spectrum. 
As I hope to present to the next meeting a far more complete examina- 
tion of this subject, I refrain from offering a single speculation, contenting 
myself for the present with the record of careful observations and exact 
experiments. 
The lines a a! indicate throughout the length of the normal spectrum. 
ANALYSIS OF SPECTRUM BY ABSORBENT Mep1A.—No. 1. 
(A.) Series of Yellow Glasses. 
(4) 16. Deer yELLow. Colouring matter Carbon, fig. 1.-The Fig. 1. 
ordinary red raysvery intense, but partaking more of ascarlet colour 
from the mixture of yellow than a pure red ; the orange and red rays 
blend so perfectly that it is difficult to define their boundaries. 
Combined, these rays occupy ‘12. The yellow rays are reduced to 
a line of bright light equal to‘10. Beyond these the green rays ap- 
pear very intense, and occupy a well-defined space equal to *25. 
Blue and violet rays, confined within a space equal to *38, appear 
somewhat more luminous than the green, presenting no decided 
colour, but appearing rather as a patch of a pale neutral tint. 
(5) 15. StRAw-yELLow. Silver stain upon one surface only.—Shortens 
the spectrum by two-thirds of the violet, so that its entire length is reduced 

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