Notes . 
696 
objeCt mounted in balsam in the ratio of 11 to 67, and greatly 
exceeding the visibility of the same objects mounted in air. In 
this latter medium they could not be examined with any advan- 
tage under the recently construdted objectives, having a nume- 
rical aperture exceeding i*o. Ttje practical difficulties of mounting 
in a solution of phosphorus are very great, owing to the inflam- 
mability of the medium, so that, good as the results are, it will 
probably be but seldom employed. 
The new “ Periscopic ” eye-piece of Mr. Gundlach consists of 
a triple eye-lens and a double-convex field-lens, the latter being 
situated within the focal distance of the former, and a diaphragm 
placed in the focus of the equivalent of the two lenses. The 
field of the new eye-piece is larger than that of Kellner, and the 
image is sharply defined to the extreme edge. As the focus of 
the eye-piece lies behind the field-lens it is particularly suitable 
for micrometers, especially as the divisions are distinctly visible 
to the extreme edge, which is not the case with Ramsden’s eye- 
piece. 
Note. — Absence from London having prevented Mr. Reichenbach from seeing 
proof-sheets of his article in Nos. 93 and 94, he apologises for the 
errata therein. 
