Browning, on the Spectroscope and Microscope. 107 
ance in polishing out a scratcli. This effect may also be 
exemplified by observing the marks left on a polished glass 
surface from the light blows of a steel centre-punch. The 
point of the punch drives in an atom of the glass, and the 
fracture extends some distance into the interior, expanding 
downwards in the form of a truncated cone. The polariscope 
shows that the conical centre is in a state of compression, 
and that the surrounding exterior portion of the glass is also 
under strain. 
The smooth, round edge of a glazier's diamond, when 
drawn over a polished glass surface, burnishes down and com- 
presses the glass beneath the cut, and in the case of thin 
sheets the wedge-like force of the compressed line splits the 
glass nearly through ; but when the glass is thick and rigid, 
as plate-glass, unless the sheet is bent back and broken 
through immediately after the cut, greater difficulty will be 
experienced if allowed to remain for a time, for the com- 
pressed line of glass will speedily tear up the portion on both 
sides, leaving a wide ragged groove in place of the original 
clean and scarcely visible line. 
On the Application of the Spectroscope to the Microscope. 
By John Browning, F.E.A.S. 
(Eead June 14, 1865.) 
In the last number of the ' Quarterly Journal of Science ^ 
appeared a valuable article on " The Application of the Spec- 
troscope to the Microscope,^^ by H. C. Sorby, Esq., F.R.S., 
which attracted considerable attention in the scientific world. 
After making some experiments in the same direction, I 
promised to communicate a paper on the subject to this 
Society, but, owing to pressure of business, the President 
desired me to defer it to the present meeting. 
Fig, 1 represents the kind of apparatus, top:ether with the 
optical arrangement, which I had found give the best results. 
It seems to me to possess some advantages over Mr. Sorby^s 
original contrivance. 
1st. In giving a black field round the spectrum, by exclud- 
ing all extraneous light, an advantage which will be at once 
appreciated by microscopists. This enables faint absorption- 
bands to be seen which might otherwise escape notice. 
