PKOCEED[NCrS OF THE SOCIETY. 357 



AN ORDINARY MEETING 



OF THE Society was Held at 20 Hanover Squaee, London, on 

 Wednesday, May 17th, 1916, Mr. E. Heron-Allen, F.L.S., etc., 

 President, in the Chair. 



The Minutes of the preceding Meeting, having been circulated, 

 were confirmed and signed by the President. 



The Hon. Secretary announced the donation of two historical 

 Microscopes of the Ellis aquatic type, presented by Mr. C. E. Heath, 

 F.R.M.S., and a copy of " Practical Principles of Plain Photo-micro- 

 graphy," presented by the author, Mr. G. West. The thanks of the 

 Society were accorded to the Donors. 



The President announced the resignation by ]Mr. Rousselet of the 

 office of Cuiator of the Society's Instruments, and, in the name of 

 the Council and of the Society, paid a warm tribute to the excellent 

 work which this distinguished Fellow had carried out for the Society. 

 A very hearty vote of thanks was accorded, and ordered to be entered 

 upon the Minutes, to Mr. Rousselet for his services to the Society. 



Mr. Julius Rheinberg then read a paper by Mr. J. W. Purkiss, 

 entitled " Some Suggestions regarding Visual Efficiency in the Use of 

 the Microscope and other Optical Instruments," in which the author 

 said that, from experience of work with tlie spectrophotometer and 

 other comparative instruments for measuring colour absorptions, he 

 had arrived at the conclusion that the observer's visual efficiency and 

 accuracy over prolonged periods depends very largely on adjusting the 

 light in which he was working, so that it should be approximate to 

 the light-intensity in the field of the observing instrument. He de- 

 yeloped this principle in its application to the Microscope and other 

 optical instruments, and showed how the more or less rapid succession 

 of efforts of the eye to accommodate itself to changes of luminosity was 

 usually a much more potent cause of eye fatigue or strain than the 

 actual conditions of light in the field of the instrument itself. This 



