PROCEEDINGS OF THE SOCIETY. 375 



should SO entirely fail on account of want of balance between tbe 

 fluids. 



Mr. White said he could quite corroborate what Dr. Matthews had 

 said with regard to objects mounted in the way he had described, but 

 so far as he had been able to judge, he concluded that the action of 

 the carbolic acid was not of a bleaching character. 



Mr. Stewart mentioned that objects kept for some time in oil of 

 cloves were exceedingly prone to bleach, and suggested that this 

 might also be an effect of long exposure to carbolic acid. 



Mr. Crisp called attention to a series of mycological preparations 

 made by Dr. Zimmermann of Chemnitz, of which a list was laid on 

 the table. 



Mr. Swift said he should like to ask a question with regard to the 

 gaiiges for the "Society" screw now supplied by the Society. He 

 found it was taper from end to end, and should therefore be glad to 

 know which part of it was the correct standard. 



Mr. Crisp said that he was unable to answer that question at the 

 moment, as the matter had been placed, by arrangement with the 

 Council, in the hands of Mr. Bevington, who was not now present. 



Mr. Beck considered that the only way to have a standard screw 

 would be by turning off the thread and seeing what was the diameter 

 of the plain cylinder. He knew from personal experience how 

 difficult it was to work to such a pattern as that referred to by 

 Mr. Swift. 



Some discussion ensued, in which Mr. Beck, Mr. Powell, and 

 others took part, as to the standards produced by the Assistant- 

 Secretary, and which it was stated had been presented to the Society 

 by the late Mr. Charles Brooke. 



Mr. Curties said the question was one of so much importance to 

 opticians that it would be desirable to have it settled, and he suggested 

 that it should be fully discussed at the next meeting, which was 

 arranged to be done. 



Mr. Crisp explained the result of M. W. Prinz's observations 

 on diatoms found in thin plates of " roche de Nykjobing" (Jutland). 

 The author had been able to obtain sections of the diatoms in a 

 great variety of planes, and had, he considered, established that the 

 valves of Coscinodiscus Oculus-Iridis and Trinacria Megina were tra- 

 versed by small openings. 



Mr. Stewart considered this was an additional confirmation of the 

 view propounded by Mr. Stephenson some time ago.* 



Mr. Crisp referred also to the result arrived at by Dr. Gunther's 

 photographs.f 



Mr. A. D. Michael's paper, " On a Species of Acarus, believed to be 

 Unrecorded," was read by Mr. Stewart (see p. 212). 



The President said that one found these creatures in such strange 



* See Mon. Micr. Journ., x. (1873) p. 4. 

 t See this Journal, iii. (1880) p. 891. 



