PROCEEDINGS OF THE SOCIETY. 395 



of a living pallida, but to do this properly a reflex camera would be re- 

 quired ; however, he had obtained one or two fairly good photographs. 



The Chairman said that anything of a labour saving nature was of 

 value he felt sure all would allow, but one so simple as had just been 

 mentioned commended itself very strongly, and he felt sure those present 

 would be desirous to thank Dr. Hebb for bringing the matter before 

 their notice, and he felt equally certain the Meeting would like to convey 

 their congratulations to Dr. Burri for his simple, useful, and ingenious 

 method. 



Dr. Hebb said they ought to thank Mr. Chopping instead, as what 

 had been shown was entirely due to his energy and ingenuity. 



Mr. 0. W. Wentz exhibited some transparent specimens of animal 

 substances prepared so as to show the internal structure without the 

 removal or alteration of the exterior. A bone, a crayfish, a mouse and 

 other objects so treated were exhibited to the Meeting. 



The Chairman thought that these were very beautiful as museum 

 specimens, but being in liquid they could not safely be handed round 

 for inspection. 



Mr. W. R. Traviss exhibited and described a small iris-diaphragm 

 to be applied to high-power objectives — the one shown being made to 

 suit Leitz' high-power objectives so as to regulate the size of the aper- 

 ture as might be required. It could be made to suit any maker's objec- 

 tives where they mount the optical system in one part, as in Continental 

 powers. The iris-diaphragm can be made very short to suit medium 

 high powers when used for the Binocular. 



The Chairman said that Mr. Traviss had very kindly sent him one 

 of these diaphragms to look at and try. It was certainly very useful 

 for adaptation to Leitz' two-millimetre objectives, but he did not feel 

 quite certain as to whether the results effected by its means were quite 

 as good as when using the special diaphragm supplied by the makers. 

 He thought the iris was a little too far off the back-lens, although, 

 doubtless, that could very easily be altered. 



Mr. Traviss explained that the first one was made by way of experi- 

 ment, but in future they would be made to go nearly down to the lens. 



Dr. Hebb read some portions of a paper by Mr. E. M. Nelson en- 

 titled, " What did our Forefathers see in a Microscope ?" 



Mr. F. Shillington Scales read a further paper by Mr. Nelson, "On 

 Critical Microscopy," illustrated by a diagram showing the appearance of 

 the back lens of an objective under different conditions. 



Mr. A. E. Conrady said he had no doubt that this paper would be 

 warmly welcomed by the younger members, as it supplied detailed and 

 safe instructions for regulating the illumination of microscopic objects. 

 The reference in the paper to the late Professor Abbe suggested some 



