NATURAL HISTORY MISCELLANY. 691 
ment is costly, and apart from this vin it has for some reason or 
other failed to become a favorite with those who have used it. 
t is now two or three years since Mr. We nham suggested the emet 
cability of constructing a binocular for high powers, by means of a co 
trivance which should reflect one-half the light of each pencil iid 
transmit the other half. is plan was to take a glass prism with par- 
On this account, or for some other reason not stated, Mr. Wenham did 
not pens up his invention 
In the January number of ‘¢Silliman’s Journal" for 1868, Professor 
Hamilton L. Smith, now of Hobart College, described a binocular arrange- 
in the body or the microscope: As both surfaces of such a mirror will 
tant saving of light. Hitherto Professor spent binocular has not been 
constructed by regular opticians, and its merits are not fully known. 
e oonstruetions by Professor eise himself perform very well, but 
have a rather limited field. 
MR and Lealand, of London, have patented a binocular 
t 
mirror are parallel, and the image from the second surface is got rid of 
by giving to the glass considerable thickness. The reflected rays are re- 
flected a second time by means of a right angled prism. As this arrange- 
when very high p 
cally unavailable for any useful purpose. This evil might be remedied 
by increasing the angle of incidence at which the rays from the Penn 
fall upon the first reflecting surface ; but this expedient would be attended 
AMER. NATURALIST, VOL. IV. 88 
