3092 M. C. White on the Microscope. 
The Nicol’s prism above the object-glass, used for an analyser, 
requires to be large, otherwise the lateral portions of each pencil 
of light are cut off, the object seen in the microscope appears 
insufficiently illuminated, and the definition becomes very im- 
perfect. ‘ 
On the other hand, if the Nicol’s prism is very large its 
object-glass a Nicol’s prism for an analyser, measuring two and 
one-fifth inches in thick 
same dimensions (obtained from Rossie, N. Y.) in a reversed po- 
not be distinguished. ese facts prove conclusively, as I think, 
the great value of the compensating prism here described, which 
has : ever app. ied 
