PHILOSOPHICAL 
TRANSACTION S. 
I. Additional observations on the optical properties and structure 
of heated glass and unannealed glass drops. By David 
Brewster, LL. D. F. R. S. Edin. and F. S. A. Edin . In a 
Letter addressed to the Right Hon. Sir Joseph Banks, Bart. 
K. B. P. R. S. 
Read November 10, 1814. 
Dear Sir, 
Edinburgh, April 8, 1814. 
I n a former paper on the optical properties of heated glass 
and unannealed glass drops, I have briefly described the 
leading phenomena which they exhibit in their action upon 
polarised light. These experiments I have frequently repeated 
with the same results, and I have the satisfaction also of 
stating, that as soon as they were known in France, they were 
repeated and verified by M. Biot of the National Institute, to 
whose active genius this branch of optics owes great obli- 
gations. 
Having ascertained that glass melted and suddenly cooled, 
possessed all the optical properties of crystallized bodies, I 
was anxious to determine if it exhibited any other marks of 
y ' mdcccxv. B 
