200 



be, it would have some variations in density, the effects of which would be 

 greatly aggravated by striae 5 he believed it was absolutely impossible to 

 get one uniformly dense throughout. As to the appearance of the hair, 

 he thought this was very likely a question of the angle of the lens. Dr. 

 Carpenter had recommended for the purpose a low-angled ^in. 



Mr. Hardy understood Mr. Nelson to say that some of these appearances 

 were equally seen with the monocular • if so, had he tried rotating the 

 object glass so as to ascertain if the fault was in any way due to that ? 



Mr. Nelson said he did not mean to imply that there was anything like 

 this distortion with the monocular, but only that with the binocular the 

 blur was seen in the vertical position of the object. He had tried various 

 objectives, as a |in. of 80°, a £in. of 40°, a lin. of 30°, and a fin. of 35°. 

 He had also tried those of various makers, so that he did not think there 

 was anything in them to cause the error; he had also tried a different 

 prism and several different instruments on the pseudo-trachea. He had 

 noticed an imperfect diffusion of the light as it passed through the prism, 

 and he did not suppose it was possible to put any piece of glass in the 

 course of the rays without affecting them in a greater or less degree. 



The Chairman said that in practice a number of prisms were worked to- 

 gether, so as to obtain a better and flatter surface, but he maintained that it 

 was not possible by any process of grinding to produce surfaces which were 

 absolutely flat. 



Mr. Hailes said there was one source of error which had not been noticed, 

 and that was that in using the Wenham binocular they looked through the 

 prism with one eye, but not with the other ; he should like to hear if Mr, 

 Nelson had tried these experiments with the Stephenson binocular, where 

 there were two prisms, and each eye saw the object under the same 

 conditions. 



Mr. Nelson said he had tried the Stephenson binocular and found that 

 there was no image at all worth comparing with that shown by the 

 Wenham instrument, whilst the loss of light was very considerable. For 

 convenience of working it might be a useful form ; but he had never seen 

 an object shown by it in a manner he considered worth looking at. 



Mr. Parsons gave some account of an organism which he had found at the 

 Royal Botanic Society's Gardens in Regent's Park — he thought it was some 

 kind of Acincta, and made a rough drawing of it upon the board in order 

 that the members might be able to assist him in identifying it. 



The President having requested the members present to help Mr. Parsons 

 to a diagnosis of the creature, a vote of thanks was passed to him for his 

 communication. 



Members were reminded that at the next ordinary meeting they would be 

 asked to nominate and elect an auditor of the accounts, and also to nominate 

 some of their number for election as members of Committee at the forth- 

 coming annual meeting. 



Announcements of meetings, excursions, and of the excursionists' annual 

 dinner were then made, and the proceedings terminated with the usual con- 

 versazione, and the following objects were exhibited : — 



