486 



The forty-third annual report of the Committee was read by 

 the Hon. Secretary, Mr. W. B. Stokes. During 1908 there had 

 been a net gain of sixteen members, the total on December 31st 

 being 469. The average attendance at the ordinary meetings 

 was 95 "9. A list of papers read, lectures and exhibitions given, 

 and of new apparatus brought forward followed. Special thanks 

 were expressed to the editor of The English Mechanic for the 

 publication of lengthy reports of the meetings in the issue of the 

 second Friday in the month. 



The Hon. Treasurer, Mr. F. J. Perks, presented his report for 

 the year 1908, showing a slightly increased balance in hand. 

 The investments remain as in the previous year. He considered 

 the financial position of the Club satisfactory. 



The usual votes of thanks were made to the officers and 

 members of committees for their services. 



Dr. Duncan J. Eeid, M.B., CM., gave a lecture on " A 

 Method of Estimating the Exposure required in Photomicro- 

 graphy with Axial Cone Illumination." He said that it was 

 generally admitted that to obtain a perfect negative it was 

 necessary that the exposure should be correct. In ordinary 

 photography there are tables of many kinds, and various forms 

 of actinometers, to help in the matter ; and in photomicrography 

 he had no doubt that every one has, as he used to have himself, 

 some more or less reliable method of calculating what the ex- 

 posure for a certain magnification, etc., should be ; but until he 

 had worked out the method about to be described he had not 

 come across any S3 r stematic method of calculation. Dr. Bousfield 

 had described a method of estimating exposures by the use of 

 a sensitometer on the ground glass ; but that appeared to be only 

 suitable for low powers and for a lamp-fiame. Reference was 

 also made to a paper read on October 16th, 1907, before the 

 Royal Microscopical Society by Dr. A. Letherby ; but the 

 lecturer thought that the details there given were insufficient. 

 His own method was intended to give the exposure required to 

 obtain a fully exposed negative with what might be called an 

 average slide, under varying apertures and magnifications. The 

 method also enables the conditions under which an exposure has 

 been made to be recorded with such accuracy as to make it 

 possible to repeat it under absolutely similar conditions. In 

 photomicrography the same series of factors have to be taken 



