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London makers of microscopes, that 135 was the largest angular pencil 

 which could be passed through a microscopic object glass. But long before 

 this an American optician had made a -| object glass having an angular 

 aperture of 146 , the same glass which he now held in his hand. Since that 

 time the same maker has made glasses with an angular aperture, thirty de- 

 grees and more, larger than this. Mr. Wefcb will shew you in connection 

 with his beautiful binocular a glass having an angle of 178 , which, as he 

 says, and as we should expect, is equal to the resolution of the most difficult 

 tests. 



This audacious American who carried the angle of aperture more than 

 forty degrees beyond the limits of the possible (according to the highest Eng- 

 lish authority) was Mr. Charles Spencer of Canastota, a small town in the 

 midst of half-burned stumps of the forest in the interior of the State of New 

 York. 



2. Next on the list of American inventions and improvements, comes 

 the inverted microscope of Dr. J. Lawrence Smith, of Louisiana, a form 

 of instrument universally approved and very widely adopted by chemists 

 as particularly fitted for their investigations. 



3. The binocular microscope of Professor Kiddell, of New Orleans 

 which, variously improved and modified, is now extensively employed both 

 in England and on the continent as well as in this country. 



4. Tolles' binocular eye-piece, which bids fair to supersede the double 

 body heretofore used. 



5. The objective mirror, if we may so call it, of Professor Hamilton 

 Smith, which most of us know only by report as yet, but which promises to 

 do for the highest powers what the " Lieberkuhn" does for the lower ones. 



The best known American microscope makers are Mr. Spencer, the pio- 

 neer among them, whose inventive genius has stimulated the opticians of the 

 old world to attempt feats which they considered impossible until he shewed 

 they could be and had been done ; Mr. Tolles, his worthy successor, whose 

 glasses challenge competition with any in the world ; Mr. Wales, not so long 

 known among us, but making first rate objectives ; Mr. Griinow, whose in- 

 struments of moderate cost are perhaps the best the American student can 

 buy, and who can make excellent microscopes of costlier pattern when requi- 

 red ; Mr. Zentmayer, whose stands are equal, if not superior in elegance and 

 workmanship to the finest of European make. 



Dr. Holmes next proceeded to speak of microscopic photography. He 

 referred to the very remarkable photographs made by Dr. John Dean, of 

 Boston, from his own sections of the spinal cord. 



He then shewed some specimens of the art sent him a week or two since 

 by Dr. Woodward, in charge of the medical department of the Army Museum 

 at Washington. These micro-photographs made by Dr. Edward Curtis, are 

 the most extraordinary in many respects Dr. Holmes had ever seen. The 

 object chosen was the well known test Pleurosigma angulatum. Two nega- 



