552 PROCEEDINGS OF THE SOCIETY. 



Amongst its special features was the very conveBient arrangement of 

 sliding plates, one white and the other black, either of which could 

 be used as a background. 



Mr. J. Beck said he saw this Microscope in use when he visited 

 the station a short time ago, and it seemed to him to be a very- 

 complete instrument for the purpose of dissecting. There was 

 abundance of play for the mirror, so that plenty of light could be 

 obtained in any direction ; but there was no means of rotating the 

 stage. Although this rotation was but rarely provided in a dissecting 

 Microscope, he thought it was a very desirable provision, as it was 

 much more inconvenient to have to move the mirror or lens, and 

 perhaps the source of light also, than it was to move the object. 

 He had pointed this out to Dr. Mayer, who agreed that it would be a 

 desirable improvement. 



Mr. E. M. Nelson read a note in explanation -of some models of 

 the markings of diatoms, which he exhibited. 



The President said that Mr. Nelson's communication was a most 

 interesting one, and the models had made the subject exceptionally 

 clear. 



Mr. Nelson also exhibited a new achromatic oil-immersion con- 

 denser of 1*28 N.A., made by Mr. Powell. He said that the great 

 advantage of it was that it allowed of the use of such a large central 

 solid cone of light. He had never previously been able to get a 

 condenser which had a greater angle than I'O N.A., and he had, 

 therefore, never before been able to examine test-objects as effectively 

 as was now possible, although it was not every objective which 

 would stand the full blaze of light from the whole aperture of the 

 condenser. 



Mr. Deby's letter was read, in which he stated that he was 

 prepared to open his library on Saturdays, from 10.30 a.m. to 10 p.m., 

 to all Fellows engaged in special scientific research. Besides the 

 principal standard works on the following subjects and most of the 

 principal periodicals, he had collected in the last thirty years the 

 following portfolios of pamphlets, &c. : — Bryozoa 10, Insect Ana- 

 tomy 12, Arachnida 5, Crustacea 10, Vermes 10, Eotifera 4, Ccelen- 

 terata 4, Protozoa 25, Desmids 5, Diatoms 36, and Microscopy 

 proper 15. 



The President said that the meeting had already, by the applause 

 which followed the reading of Mr. Deby's letter, expressed its 

 appreciation of the generosity of the writer in throwing open his 

 library. It appeared to be a specialized library of considerable 

 value, and the offer was therefore one well worthy of their appreciation 

 and thankfulness. 



Prof. Stewart, after remarking that' it was a well-known fact 

 that certain insects and others of the lower forms of animal life 

 possessed the means of producing sounds by which they could warn 



