Mr Herschel’s Experirtients on Circular Polarisation* S7S 
cohurless amethyst, of which we are in possession of several spe- 
cimens. 
Another experiment of Mr Herschel is, in our opinion, equal- 
ly hostile to M. Biot’s notion, that circular polarisation is an 
inherent property of the ultimate particles of matter^. He 
prepared the Liquor Silicum, (a solution of silica in potash), 
from a portion of a plagiedral crystal, which turned the plane of 
polarisation to the left ; but it possessed no circular polarisa^ 
Mon* 
Arguments of a similar kind had been urged by Dr Bi'etvstei’ 
against the opinion of the French philbsopher. When he dis- 
covered more than five years ago the double system of rings in 
crystallized sugar, he observed that there was no circular po- 
larisation at the two poles, although solutions of sugar were 
known to possess that property ; and in his paper on the Ame- 
thyst, he states, that neither Opal nor Tabasheer (which is no- 
thing more than the Liquor silicum solidified,) have the rotatory 
property of quartz. Another argument still more convincing 
will be found in our Scientific Intelligence, from which it ap- 
pears, that Dr Brewster has examined a piece of Melted Quartz, 
which had been entirely deprived of its ordinary polarising struc- 
ture, and has found that it ewhihits no traces erf' circular polari- 
sation. Each of these facts we regard as an eooperimentum cru- 
CIS sufiicient to decide the question; and we have brought them 
forward at present, because Mr Herschel seems to think it pos- 
sible that the rotatory property m^y be inseparable from the 
ultimate particles of the body which exhibits ifc. 
* Faculte qu’eUes ne peuvent perdre que lorsqu’ elles cessent d^etre elles-memes, 
par leur decomposition. — Mem. Inst. 1818, 
