C 187 3 
XL On the Affections of Light transmitted through crystallized 
Bodies. By David Brewster, LL.D. F. R. S. Edin. and 
F. S. A. Edin. In a Letter to Sir Humphry Davy, LL.D. 
F. R. S. 
Read December 23, 1813. 
Dear Sir, 
In a former paper* on ‘‘ Some Properties of Light,'" which I 
took the liberty of addressing to 3^11, and which the Royal 
Society honoured with a place in their Transactions, I attempted 
to give a brief abstract of a set of experiments on the Pro- 
perties of transparent Bodies in refracting, dispersing, and 
polarising the rays of Light. An account of the instruments 
and methods employed in these experiments has since that 
time been published in my “ Treatise on new philosophical 
Instruments." 
From the general object of these researches, however, I have 
been allured into a new field of inquiry, by the discovery of 
a singular property of light transmitted through the agate, and 
the prosecution of the views which it suggested has led to 
some very extraordinary results, which, while they seem to 
conduct us into the very mysteries of physical optics, exhibit at 
the same time a series of appearances which far surpass, both in 
splendour and variety , all the phenomena of light under its usual 
transformations. In again soliciting you to communicate these 
observations to the Royal Society, I trust I need offer no apo- 
logy. They are closely allied with that science which you 
have so widely extended by the most profound and brilliant 
* Phil. Trans, for the year 1813, p. loi. 
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