1864. | Microscopical Science. 183 
thickness of the mechanical and sub-stages. A still further improve- 
ment has been made by adding an additional tube, and thereby adapt- 
ing the instrument to the binocular arrangement. Moreover, Mr. Ross 
has graduated the circular parts of both the upper and lower stages so 
as to enable the observer to use the instrument as a goniometer. 
ll 
_ jam TTT 
We shall now pass on to the consideration of our next head, 
namely, the diminished cost of instruments for the use of students 
and others. 
At our public institutions where there are large microscopical 
classes, as, for'example, at University College, London, and at the 
University of Edinburgh, the great majority of the students have 
hitherto been supplied with the foreign instruments of Nachet and 
Oberhauser, costing about 8. each. Now, however, English opticians 
are cutting the ground from beneath the foreigner’s feet, by producing 
really good useful instruments at similar prices. The most recently 
constructed microscope of the kind, is that just brought out by Parkes 
of Birmingham. 
