302 
PROCEEDINGS OP THE SOCIETY. 
Meeting of 16th March, 1892, at 20, Hanover Square, W., 
the President (Dr. Braithwaite, F.L.S.) in the Chair. 
The Minutes of the meeting of 17th February last were read and 
confirmed, and were signed by the President. 
The following Donations (exclusive of exchanges and reprints) 
received since the last meeting was submitted, and the thanks of the 
Society given to the donors. 
From 
Monograph of the Palaeontographical Society, 1891 Mr. Crisp 
Mr. G. C. Karop read a short paper descriptive of Messrs. Swift’s 
new fine-adjustment for the substage of the Microscope, exhibited in the 
room, one complete revolution of which is equivalent to a vertical move- 
ment of the 1/125 part of an inch. 
The thanks of the meeting were, on the motion of the President, 
voted to Mr. Karop for his communication. 
Mr. E. M. Nelson gave a resume of the contents of two papers, the 
first of which was entitled “ Virtual Images and Initial Magnifying 
Power,” and the other “ On Penetration in the Microscope.” 
The President expressed the thanks of the Society to Mr. Nelson for 
these papers. He was very glad to find that Mr. Nelson was making 
these matters very much more simple than was usually the case, it being 
too often assumed that the Fellows of a scientific society were able to 
understand at once what was really only clear to those whose time and 
attention had been specially devoted to such subjects. 
Dr. Dallinger said they had received from Prof. Czapski an im- 
portant communication “ On the Calculable Limit of Microscopic Vision.” 
Considering its technical character, it would be unwise to read the 
whole of this paper at the meeting, but he might mention that its 
purpose was to show why it was that great numerical aperture was of 
such high value in the determination of minute structure, and to inquire 
whether — seeing that a numerical aperture of 1 • 60 was so utterly 
unavailable in the case of living objects or of such as did not admit of 
being put into media of sufficiently high refractive index — there was 
any method of making these high numerical apertures available for such 
objects ? The author’s attention had turned in this inquiry towards the 
value of monochromatic light for such a purpose — not simply coloured 
light, but that which was in a strict sense purely monochromatic, such 
as was recently shown at one of their meetings by Mr. Nelson — and the 
latter part of his paper went to show that by using blue rays of such 
light with large apertures, it was possible to increase the aperture so as 
to obtain the relatively great advantage which would result from a 
difference between 1'40 and l - 75. The paper was in itself so 
thoroughly valuable, and the matter was worked out in a way that was 
