Oliver.] • ^^^ [Dec. 15, 



Stage, of wliicli the axis passed through the object observed, so that the 

 object is in the focus of the illumination in every position. This remark- 

 ably ingenious plan of swinging the substage and the mirror soas to have 

 the object as its centre, induced numerous foreign and domestic makers to 

 employ this important principle in optical construction. 



Two years later, a third and most important honor was added to the list 

 by the Committee of Awards on Microscopes at the Paris Exhibition, who 

 found fit to give a silver medal and a diploma to Mr. Zentmayer for the 

 superiorit}'', manifold value and simplicity of his workmanship. 



Recognizing the value and convenience of the Abbe system of condens- 

 ing lenses or illuminator in stands that are provided with substages, he 

 modified the ordinary form by so placing the carrier that the diaphragms 

 can be readily changed and arranging the contrivance so that the dia- 

 phragm cannot only be moved over the field by rack and pinion, but that 

 it can be revolved. How much we must praise his exquisitely simple, 

 single-prism, total-reflecting camera lucida wliich is so contrived as to be 

 used either in the upright, angular or horizontal positions of the draw- tube 

 of the microscope. 



How exasperalingly easy of comprehension and yet how excellently 

 adapted for their purpose are his contrivances of the life current and 

 siphon-slides so arranged in accordance with Mr. S. D. Holman's ideas 

 that varying degrees of circulation in animalculaj can be made visible, not 

 only to the individual student at work with his highest powers, but 

 actually made recognizable to large audiences during class-work instruc- 

 tion and lecture-room demonstration. Again, the wonderful mechanical 

 construction of Prof. John A. Ryder's automatic microtome, where, with 

 an ordinary razor, tissue-sections of .0025 mm. thickness can be cut by 

 the merest novice, and objects to the length of fifteen centimetres and two 

 centimetres wide can be completely cut serially into almost any desired 

 thickness. Further, the botanical dissecting microscope designed and 

 constructed to meet the requirements of Prof. J. T. Rolhrock, of the Uni- 

 versity of Pennsylvania (a member of this Society), in his botanical class ; 

 his clinical stand for accurate examination of any object by a large class, 

 by being passed from hand to hand, that the memoirist has so often used 

 in his student-days ; the cheapening and simplification of the microscope so 

 as to bring a properly constructed and adetjuately workitig piece of appa- 

 ratus into the hands of the student of limited means, thus allowing him to 

 become an essential factor in scientific progress : these few contrivances 

 are but a limited number of the mechanical triumphs that resulted from 

 the employment of the never-ceaseless mind of Joseph Zentmayer (the 

 optician), as he proudly styled himself, for more than a half century. Is 

 it any wonder tliat we exclaim with Von Humboldt, " In the moral world 

 there is nothing impossible, if we bring a thorough will to it. Man can do 

 everything with himself." 



An interesting incident in his life is the history of the patent of his 

 doul)k't photographic lens, which is composed of two deep meniscus lenses 



