PROCEEDINGS OP THE SOCIETY. 
303 
so clear and convincing, that it was well worth the attention of the 
practical microscopist. 
Mr. Crisp thought it should be pointed out that the broad fact dealt 
with in this paper was one which had long ago been explained — cer- 
tainly ten years ago — though perhaps it had not been worked out in the 
same manner. 
Dr. Dallinger said he had himself worked it out some time ago, 
obtaining as a result the difference between 1*40 and l 1 70, which came 
remarkably near to that mentioned in the paper. 
Mr. Crisp said that the aperture table, which was printed with every 
number of the Journal, gave them the difference in resolving power 
between white light and monochromatic blue light with objectives of 
various apertures. 
Prof. Bell called attention to the fact that in the December number 
of the Journal there was an abstract of what appeared to be the same 
paper as that just read ; the account ran to something like five pages 
of the Journal, and if it really referred to the same thing, they could not 
of course publish it now in the Journal, after its previous publication 
elsewhere. 
Dr. Dallinger said that the subject was no doubt the same so far as 
the main facts were concerned, and it was also one which was not new to 
English observers, though the results were, in the paper before them, 
more completely worked out than they had hitherto been, and were put 
before them much more simply. 
Prof. Bell said they also had a paper by Mr. H. L. Brovoort entitled 
“ Observations on the Brownian Movement ” ; after giving a brief outline 
of its contents he pointed out that whilst the general conclusion arrived 
at by the author was that light had some influence in the matter, he 
did not seem to have taken any precautions as to temperature, so that 
he had not really eliminated from his calculations an element which 
was usually considered to be an active agent in the production of the 
observed phenomena. 
Dr. Dallinger read a letter received from the Hon. J. G. P. Yereker, 
taking notice of some points raised during the discussion of his paper 
“ On the Resolution of Podura Scales ” read at the December meeting of 
the Society. 
Dr. A. C. Mercer then read his paper on Photomicrography as illus- 
trated by a collection of 73 lantern slides exhibited upon the screen 
by Messrs. Nelson and C. L. Curties. Among the slides exhibited was 
a group which illustrated a mooted point in Podura scale structure, the 
author showing that the so-called featherlets on Podura scales are only 
inflations of the membrane. A number of slides also proved the value 
of the Microscope as a means of detection in cases of forgery, or when 
alterations were alleged to have been made in promissory notes. A 
further group of slides was devoted to the illustration of photomicro- 
graphic apparatus. 
