C. M. Wetherill on the Crystalline Nature of Glass. 25 
etching to give an appearance of crystals having in reality no ex- 
Istence, - 
the acid was constantly stirred upon the plate with the platinum 
oat employed for dropping it, the crystalline etching resulted 
a8 before, 
| of 
the residue. In this case the acid was slightly diluted, but still 
which were combined with smaller needles forming rene = 
‘i 
edly in intaglio, The depression could be distinctly felt with a 
needle when observing under the microscope, and fine powder 
of vermilion filled the rays. When first viewed, before the glass 
retard the corrosive effect of the acid under it, it is impossible to 
See how such a crystal could eat away the glass beneath it and 
th sink itself under the surface. : ; on ei 
_ =n some of the other specimens these starry groups were per- 
ceived 2 but in no case as distinctly as in this one. There hap- 
