ae H. L. Smith on a new Binocular Eye-piece. 
somewhat blurred or doubled, and also from a sort of parallax, 
which causes a movement of the different parts of the image, 
readily seen as one looks alternately through the field by mov- 
ing the head from side to side; the pulsation of the arteries 
causes movement. J have found sometimes this movement a 
seen under very high powers. e fact of using both eyes, 
with two fields illuminated exactly alike, gives great physical 
per 
ece at . Of course a plate accurate ound would be 
"better ; the sides of common plates of Ae glass as I have 
-_ ae & acne less wavy. The thickness of the 
; ri orm 1s Imm, it is so slightly wedged-sha 
that the difference in thickness of the two ends very come 
