On an Improved Method , &c. By Sir W. Sendall. 709 
degrees, halves, and quarters. The least division therefore contains 
fifteen minutes ; and by help of the vernier, readings may he taken 
to a minute and a half of arc ; the linear value of which, to a radius 
of ten inches, is less than the 1 /200 of an inch. 
When constructed upon this scale the instrument requires a 
somewhat massive stand to support it ; hut it could easily be made 
smaller and lighter, though with some loss of range in the graduation. 
The black face of the speculum will be found useful, in cases 
where the field of the Microscope is feebly illuminated ; it being often 
easier in such cases to catch the outlines of the image upon a dark 
surface, than upon a light one. 
