Prof. Miller on the Form of Crystals of Tin. 263 
perpendicular incidence, the reflected ray will be deft-handed, 
and vice versd. 
I have been prevented for some time from attending to the 
subject, but having now done so, and not observing that any 
of your other correspondents have taken up the subject, I beg 
to announce that I have succeeded in verifying by experi- 
ment the above theoretical prediction. 
My experiment was conducted by the use of Mr. Airy’s ‘new 
analyser” described in the Cambridge Transactions, 1832, 
which does the same for right- and left-handed circular light, 
as the common analyser does for light polarized in opposite 
planes; that is, it stops one kind and transmits the other. This 
affords a ready test whether any given ray is right- or left- 
handed. I procured the circular light by means of the 
Fresnel-rhomb, and on ascertaining that the light emerging 
from it was stopped by the Airy-analyser, I examined the same 
light after reflexion from glass at an incidence as near the 
perpendicular as possible, and found it transmitted by the 
analyser ; thus proving its change from right- to left-handed. 
I remain, Gentlemen, 
Your most obedient Servant, 
Oxford, March 5, 1843, B. PowE Lt. 
XLV. On the Form of Crystals of Tin. By W.H. MItter, 
M.A., F.RS., Professor of Mineralogy in the University of 
Cambridge*. 
LTHOUGH crystals of tin have been not unfrequently 
observed when the metal has been permitted to cool 
slowly after fusion, and also when it has been reduced by gal- 
vanic action, they appear to have been too imperfect to admit 
of the determination of their forms by measurement with the 
reflective goniometer. If however a feeble galvanic current, 
produced by one of Daniell’s constant cells weakly charged, 
be transmitted through a solution of tin in hydrochloric acid, 
kept nearly saturated by suspending in the solution a piece of 
metallic tin connected with the copper element of the cell, in 
the course of four or five days very perfect crystals may be 
obtained, 
These crystals belong to the pyramidal system. 
The Syrnbots of the different simple forms which have been 
observed, in the notation adopted in my treatise on Crystallo- 
graphy, will be as follows :—the letter denoting one of the faces 
of each form being prefixed to the symbol of the form, 
a{100}, m{110}, p {111}, s {101}, r {301}, ¢ {331}. 
* Communicated by the Author. 
