186 Dr. Hersghel's Experiments for investigating 
observation where he saw these rings by transmission, in 
consequence of which I have again multiplied and varied the 
method of producing them that way, as follows : 
First Method. On a slip of plain glass highly polished on 
both sides place the same double convex lens of 26 inches, 
which had already been used when the rings were seen by re- 
flection. Take them both up together and hold them against 
the light of a window, in witch position the concentric rings 
will be seen with great ease by transmitted light. But as the 
use of an eye-glass will not be convenient in this situation, it 
will be necessary to put on a pair of spectacles with glasses of 
5, 6 > or 7 inches focus, to magnify the rings in order to see 
them more readily. 
Second Method. It would be easy to construct an apparatus 
for viewing the rings by transmission fitted with a proper eye- 
glass ; but other methods of effecting the same purpose are 
preferable. Thus, if the two glasses that are to give the rings 
be laid upon a hollow stand, a candle placed at a proper angle 
and distance under them will show the rings conveniently by 
transmitted light, while the observer and the apparatus remain 
in the same situation as if they were to be seen by reflection. 
Third Method. A still more eligible way is to use daylight 
received upon a plain metalline mirror reflecting it upwards to 
the glasses placed over it, as practised in the construction of the 
common double microscope ; but I forbear entering into a far- 
ther detail of this last and most useful way of seeing rings by 
transmission, as I shall soon have occasion to say more on the 
same subject. 
Generalization. Every combination of glasses that has been 
explained in the first, third, and fifth methods qf seeing rings 
