C 219 : 
XII. On the Polarisation of Light by oblique transmission through 
all Bodies i zvhether crystallized or uncry stalUzed. By David 
Brewster, LL,D. F. R. S. Edin. and F. S. A. Edin. In a 
Letter addressed to Taylor Combe, Esq. Sec. R. S. 
Read January 27, 1814. 
Sir, 
In a letter on ‘‘ the Affections of Light in its passage through 
crystallized Bodies,’' which I had the honour of transmitting 
a few days ago to the Royal Society through Sir Humphry 
Davy, I alluded to a series of experiments which I had in view 
for the purpose of generalising the various phenomena which 
had been described. At the very commencement of this en- 
quiry I have been led to the important general result “ that 
“ light transmitted obliquely through all transparent bodies, 
“ whether crystallized or uncrystallized, suffers polarisation 
like one of the pencils formed by doubly refracting crystals,” 
and I hasten to communicate to you a brief sketch of the nature 
and consequences of this discovery. 
In examining if any change was produced upon common 
light during its passage along the oblique depolarising axis of 
'mica, I observed, in one position of the mineral, some appear- 
ances which indicated a partial polarisation of the incident rays. 
Upon turning the mica round, so as to preserve its obliquity 
to the incident pencil, the same phenomena presented them- 
selves in every part of the revolution of the mica, and the 
quantity of polarised light was found to increase with the 
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