640 PROCEEDINGS OF THE SOCIETY. 



carrier, with arrangement for rotating the diaphragms, for demonstrat- 

 ing the effects of diffraction on the formation of microscopical images ; 

 and (4) the identical Zeiss "a</. " objective used by Professor Abbe in 

 demonstrating his diffraction theory. Dr. Edmunds exhibited his 

 immersion paraboloid at a meeting of the Quekett Microscopical Club 

 on October 6th, 1877. The top of the paraboloid was cut off by an 

 exactly calculated distance below its focus, the distance varying, in the 

 four lenses constituting the set, the plane top being made optically con- 

 tinuous with the slide by means of a fluid of high refractive index, such 

 as glycerin, castor oil, oil of cloves, etc. No. 1 lens was calculated for 

 use with a slide of ordinary thickness, say ^^tli of an inch. No. 2 lens 

 was calculated for use with a slide not exceeding j-Jot-t of an inch 

 in thickness. The thickness of slide for which the others were pro- 

 portioned is not stated. The example presented to the Society was 

 presumably a No. 1 ; it belonged to Dr. Carpenter, and was probably 

 made by Powell and Lealand. Dr. Edmunds claimed to have obtained 

 highly satisfactory results, but Dr. Dallinger, in his edition of Carpenter, 

 criticized it severely. He (the speaker) had not yet succeeded in finding 

 a description of the sub-stage condenser for oblique illumination ; and 

 although Mr. Ingpen assured him it was made by Powell and Lealand, 

 Mr. Powell did not recognize this particular accessory. It was probably 

 of the same date as the paraboloid. 



Coming to tlie accessories illustrating the Abbe diffraction theory, 

 Mr. Parsons referred to a paper by J. W. Stephenson, entitled 

 " Observations on Professor Abbe's Experiments illustrating his Theory 

 of Microscopic Vision," in the Transactions of the Society in the 

 "Monthly Microscopical Journal" for February, 1877, and a translation 

 by Dr. H. S. Fripp of Professor Abbe's " Contribution to the Theory of 

 the Microscope and the Nature of Microscopic Vision," which appeared 

 in the Proceedings of the Bristol Naturalists' Society, n.s., vol. i., pt. 2. 

 (Both papers are in the Society's Library.) 



The President proposed a vote of thanks to Mr. Parsons for having 

 influenced this gift, aud for having brought it forward in this way. 

 The occasion gave him an opportunity of proposing another vote of 

 thanks to Mr. Parsons. It would be known to Fellows that the 

 Assistant-Secretary was called up some months ago, with the suddenness 

 with which such things happened, and the Society was, consequently, 

 placed in considerable difficulty. Mr. Parsons, who was formerly 

 Assistant-Secretary for many years, and was the steerer of their ship 

 through a good many troubled waters, was good enough to come back 

 at once and assist the lady who took the reins of government into her 

 hands, but who, unfortunately, had been prevented from carrying on 

 those duties by the illness of her husband. Although the Society was 

 fortunate in having now secured the services of one whom he was sure 

 would prove an extremely efficient Assistant-Secretary, they must not 

 lose sight of the fact that they owed a very great debt of gratitude to 

 Mr. Parsons. The Council, at their meeting that evening, decided that 

 this vote of thanks should be proposed from the chair at this meeting. 

 .They also voted an inadequate — but in war times all good impulses must, 

 ex facto, be inadequate — honorarium to Mr. Parsons, which would reach 



