8 Dr. Brewster's additional observations, &c. 
ment, till at a certain temperature the crystallization is com- 
plete. As the temperature diminishes, the particles approach 
one another, and gradually recover their former arrangement. 
The crystallization which is thus produced in drops of melted 
glass, is rendered permanent by the sudden immersion of the 
drop in water, which arrests the particles in that particular 
position that constitutes the crystalline state of the body. 
Hence it follows that the particles of glass, when separated 
to a certain distance by the expansive energy of heat, assume 
a crystalline arrangement and, unless they are fixed in this 
state, by a sudden diminution of temperature, the crystalliza- 
tion is gradually destroyed by the approximation of the par- 
ticles which takes place during the operation of slow cooling. 
During my experiments on depolarisation, which I shall 
soon have the honour of submitting to your notice, I discovered 
another species of crystallization, which is the effect of time 
alone, and which is produced by the slow action of corpus- 
cular forces. This kind of crystallization appears, in general, 
to accompany the consolidation of many vegetable and animal 
products, and will probably be found to have had an exten- 
sive influence in those vast arrangements which must have 
attended the formation of our globe. 
I have the honour to be, 
Dear Sir, 
your most obedient humble servant, 
DAVID BREWSTER, 
To the Right Hon. Sir Joseph Banks, Bart. K. B. P. R .S, 
