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explain the usefulness of these apertometers in determining the 

 kind of stop to be used in obtaining dark ground illumination. 

 To get the best possible results, the stop in the sub-stage must 

 have a definite relation to the apertometer measurement of 

 the angle of the lens. He thought it was not sufficiently realised 

 that the size of the stop to be used varied under different con- 

 ditions — tube length, trough, and other things would affect it, but 

 it was only by measuring and working out these conditions that 

 what was the true relation between them could be ascertained. 



Mr. Karop was sure the Club was very much indebted to Mr. 

 Angus for the exhibition of these examples, and for his explana- 

 tion of them, and he expressed a hope that this communication 

 might be put into a form in which it could appear in the Journal 

 with diagrams in illustration. Some time ago it was proposed to 

 get an Abbe apertometer for the use of the Club, but it was 

 thought that as very few members would be likely to use it the 

 expense could very well be spared. As regarded stops, various 

 contrivances had been recommended, but he thought sticking a 

 piece of paper on the condenser was not at all satisfactory : it was 

 almost impossible to get a true centring, and it got out of shape ; 

 he therefore strongly recommended that stops should be made of 

 thin sheet-metal. 



The Chairman said they had heard Mr. Angus's useful and 

 instructive paper with great pleasure, and he had no doubt they 

 would desire not only to thank him for the explanations which he 

 had given them in language which all could understaind, but vvould 

 join with Mr. Karop in expressing a hope that he would have 

 them put into the Journal. 



The thanks of the meeting were unanimously voted to Mr. 

 Angus for his communication. 



Mr. Karop called attention to a microtome by Reichert which 

 had been brought to the meeting for exhibition by Mr. Curties. 

 It was at first sight an instrument which could only be regarded 

 with some apprehension, but on closer inspection it certainly 

 appeared to be a very marvellous and beautiful piece of 

 mechanism. 



The Chairman did not know if any one had examined this 

 microtome before the meeting, so as to be able to explain its 

 working : it certainly looked a rather formidable instrument. 



Mr. C. L. Curties said that, although this microtome was not 



