Action of Badium Salts on Glass. 
361 
nature of the glass. Further experiments are being proceeded with on 
various kinds of glass and other materials. 
Professor Joly, in the Phil. Mag. for Feb., 1910, gives an account 
of an appearance similar to that just described, in a specimen of greisen. 
From the description of the sets of halos, it seems that a structure must 
exist in the crystal section similar to that occurring in the glass tube of 
my observations, but here again the action is limited to a small distance. 
A piece of glass tubing, owing to the method of manufacture, will probably 
be in a state of strain between the two surfaces, from which relief may be 
obtained by the zonal structure being formed. In the case of the crystal 
Fig. 4. 
M = 12 Diameters. 
referred to by Professor Joly, since it separated from the magma, it would 
have been subject to some severe strain when the whole mass had become 
solid, on which a zonal structure may have been developed. The two 
surfaces of adjacent zones would naturally form boundaries to materials 
which are in some slightly different physical state, and so the a or other 
particles might experience a difficulty in crossing the boundaries. If the 
surface layers of the different zones were in a state of great tension they 
might act as though their densities were much greater than that of the mass 
of the material enclosed between their surfaces, and thus the a particles 
would experience a check to their velocity on crossing the boundary. 
