PROCEEDINGS OF THE SOCIETY. 
499 
Mr. C. Beck inquired if these photographic lenses were single un- 
corrected lenses, or were they not the same as the periscope introduced 
by Steinheil in 1865? He should have thought — looking at them 
casually — that it had an aperture of // 16, and was nothing more than 
two uncorrected meniscus lenses. In what way was it corrected for 
aberration ? 
Mr. J. E. Ingpen was glad to hear that Zeiss had taken to making 
low-power objectives again. When Prof. Abbe was over here the first 
time he brought with him an objective of 32 mm. which was an extremely 
good one, and showed a distinct advance upon much work done at that 
date. Zeiss’s firm went back however to their 24 mm., but he was very 
pleased to find they were again making a low power, having come back 
to their right mind. 
The Chairman said that the photographic lens was not corrected at 
all, but he thought there must be some difference in the glasses, because 
he found that the correction for astigmatism was perfect. It worked at 
F/13, and he found he could take instantaneous views with it, outside, 
quite perfectly. He had not taken it to pieces to see what the combina- 
tion might consist of, but so far as he could judge by reflection, the 
lenses were single. 
Mr. Beck said it would be a rather curious optical problem if with 
such a construction the lens was corrected. Of course, it would be un- 
derstood at once that a photographic lens always had a very great 
advantage over a microscopic objective, because it had to produce an 
image which was much smaller than the original, whereas a lens for the 
Microscope had to produce a magnified image, and the correction was 
necessarily of a more accurate character. 
On the motion of Prof. F. J. Bell, a vote of thanks was passed to 
Mr. E. M. Nelson for bringing to the meeting these very interesting 
exhibits. 
Mr. W. C. Bosanquet read a paper on Nyctotherus ovalis , a parasite 
of the Cockroach, illustrating the subject by a diagram upon the black 
board. 
The Chairman said he was glad to welcome on that occasion the 
presence of a new worker amongst them in that room, and moved a 
hearty vote of thanks to Mr. Bosanquet, which was carried unani- 
mously. 
Dr. Bruce’s paper, “ On a new Microtome for cutting sections in 
spirit,” was read to the meeting, in the absence of the author, by 
Mr. Karop (see p. 487). 
Mr. G. C. Karop said that by reading a technical description it was 
hardly possible at once to grasp all the features of an instrument such 
as this, but so far as he could judge there was not any special novelty 
about it. As regarded the cutting of sections under spirit, this had been 
done long ago by Katsch of Munich, and others. Supporting the knife 
at both ends had also been done before, but, as indeed the author admitted 
towards the end of his paper, this was really quite unnecessary except 
in the case of very large sections. The idea of changing the obliquity 
of the knife as desired was also an old contrivance. As a combination 
