104 On the Aperture of Object Glasses. 
te, distinguished himself; and I am willing to admit that i 
refraction of the balsam and glass cover (the indices being about 
1:54 and 1:53) total reflection would take place from the upper | 
the extreme limit has been about 78°. This statement is not the 
result of mere hypothesis, but admits of ocular demonstration, 
by experiments that will prove it at least half a dozen different 
ways, and is so true in theory, that to endeavor to disprove It 
will be to take the difficult course of attempting to undermine 
the ground upon which I stand, by denying the first laws of re- 
fraction upon which my assertion is based. 
Prof. Bailey has, no doubt, experienced the advantage of the 
ighest powers are to be used only for viewing thin and flat 
r 
considering all the requirements and perhaps more useful applt 
cation of the object glass, I am still of opinion that beyond 130° 
there is no real advantage to be gained. I have expended mu 
time and taken special delight in the cultivation of the larg 
