310 
PKOCEEDINGS OF THE SOCIETY. 
claim tlie invention merely of a right-angled prism for illuminating 
objects under the microscope, but obviously the particular application 
of such a method for the special purposes dealt with by his paper. 
As Dr. Edmunds had said, the right-angled prism was undoubtedly 
not “ new ” — indeed it had become very difficult to substantiate a 
claim to actual novelty as regards the mere form of any illuminating 
apparatus, as things seemed to be re-invented over and over again in 
more or less regular cycles. Mr. Wenham, who was admittedly the 
‘‘ first and true inventor ” of the right-angled prism, used it, however, 
entirely for the illumination of objects under high powers by total 
internal reflection from the upper surface of the covering glass. 
Those curious in the matter would find a summary of the various 
analogous devices of Mr. Wenham and others in the second German 
edition of Harting’s ‘ Das Mikroskop,’ the figures in which he 
showed to the meeting. Canada balsam or other medium was in- 
terposed between the prism and the slide in Mr. Wenham’s arrange- 
ment for the purpose of preventing the rays from being reflected from 
the back of the prism instead of passing on to the covering glass. 
Mr. Crisp (Secretary) said that a Congress of American Micro- 
scopists had been held in August at Indianapolis, at which the 
subject of a “ Unit of Micrometry ” had been taken into considera- 
tion, and he read the Resolutions which had been passed by the 
Congress recommending the use of the of a millimetre (see 
p. 254). 
Mr. Beck inquired if it was intended to take any action with 
reference to the Resolutions. The desirability of a uniform standard 
had always been appreciated in this country, and it would be a very 
desirable thing if the Society would now give the weight of its 
influence towards the establishment of such a standard. Some time 
ago the adoption of a single thread for the screws of all objectives 
was due to the action of the Society, and though perhaps the one 
decided upon might not be the best, yet the adoption of a uniform 
gauge had been of very great advantage in the way of getting rid 
of those horrible nuisances, the adapters. He merely threw out the 
suggestion because he thought the idea was worth their consideration, 
and he should like to know whether or not the Council were prepared 
to take any action in the matter. 
Mr. Crisp added that at the Congress a paper had been read by 
Professor W. A. Rogers, of Harvard University, in which it was 
understood that he had explained the application of a machine he was 
using for the production of “ standard ” micrometer scales, and by 
means of which he believed that he could rule any number of micro- 
meters precisely alike and with exceptional accuracy. It should not 
be forgotten that, as Mr. Reeves reminded him, the subject of a 
uniform micrometric standard had been very completely dealt with 
by Dr. Cooke in a paper read before the Quekett Microscopical 
Club, and printed in their J ournal on p. 1 of vol. i. 
Mr. Bock, in reply to the President, said there would be no dif- 
ficulty whatever in obtaining scales ruled as required for the adoption 
of the proposed standard. 
