478 PROCEEDINGS OF THE SOCIETY. 



struction of tlie three forms of instrument under discussion — (1) 

 Nacliet's, (2) Abbe-Zeiss's, (3) Grunow's. 



The Chairman thought that the variety of these instruments 

 showed that there had been considerable difficulty met with in 

 endeavouring to obtain good results. His own experience was that it 

 was better to keep to one form, and by constant use to acquire facility 

 in its manipulation. 



Mr. Crisp said one way which had been suggested for getting 

 over the difficulty of seeing the pencil was to draw on black paper 

 with a white bone pointer, the under surface of the black paper being 

 also blackened, and transferring the marks made upon its upper side 

 to a sheet of white paper underneath. 



Mr. Hitchcock, in reply to some remarks by Mr. Ingpen as to the 

 difficulty of seeing both the object and the pencil point at the same 

 time, said he thought that the most perfect form of camera was one in 

 which the pupil of the eye was divided, because w^hen they had objects 

 to deal with in which there was a great contrast between the light 

 from various portions, there would be some parts where the pencil 

 would be seen with great clearness under any conditions, but when, in 

 other portions, the light became stronger and the pencil point conse- 

 quently dimmed, all they had to do was to move the pujiil over the 

 edge sufficiently to equalize the light according to the requirements 

 of the altered conditions. 



Mr. Stewart was under the impression that any shifting of the 

 position of the pupil would be likely to involve an apparent shifting 

 of the image, which would be an inconvenience. 



Mr. Michael said he had a good deal of experience in this 

 matter, and had always found that if the pupil was moved the image 

 did certainly shift ; but he had got over all practical difficulty by 

 ■using two lamps, one to illuminate the object in the usual way, and 

 the other — the more powerful of the two — to illuminate the paper, 

 and in this manner, with a very little trouble, the apparatus could be 

 so arranged that neither the light on the object nor that on the pencil 

 would overbalance one another. 



Mr. Coppock exhibited a new and cheap form of Microtome, devised 

 by Mr. Cathcart, for freezing by means of ether spray, by means 

 of which a gum solution or paraffin can be frozen in one minute with 

 a consumption of 1-1 6th oz. of methylated sulphuric ether. 



Mr. Groves thought it a very nice instrument for the purpose, the 

 chief objection to it being that the vapour of the ether was discharged 

 into the room. 



Mr. "Watson exhibited and described a new form of Microscope 

 with swinging substage, the pattern having been suggested by Mr. 

 Bulloch's Biological Microscope. 



