170 



THE AMEKICAN MONTHLY 



[September, 



form of the lens would much nearer 

 fulfil the conditions of minimum 

 spherical aberration. But then, of 

 course, the flint-glass lens will no 

 longer have the proper form as a cor- 

 recting lens ; it would now over cor- 

 rect the aberrations of the crown-glass 

 lens, and therefore a more flat, long- 

 curved form oi" the same would be 

 required. If the exact form or curv- 

 ature of minimum aberration of the 

 crown-glass lens, as well as that of 

 the correcting flint-glass lens, as 

 found by calculation, is compared 

 with the present objective, it will be 

 found that the aberrations of higher 

 order in the new objective are reduced 

 to about one-third of the old one, and 

 a corresponding gain in the definition 

 and reduction of color, or otherwise 

 an extension of the limit of aperture 

 must be the result. 



' In my foregoing description I 

 have, for the purpose of avoiding 

 complications and giving a clearer 

 understanding, referred to the tele- 

 scope only ; but as the construction 

 of this instrument is submitted to the 

 same theoretical laws as that of the 

 microscope, little remains to be said 

 about the application of the described 

 new principle to the microscope.' 



Mr. H. F. Atwood followed with 

 a paper on ' New Apparatus for Pho- 

 to-micrography.' The paper was as 

 follows : — 



' At our meeting last year at Chi- 

 cago Mr. Walmsley, of Philadelphia, 

 read a valuable paper on photo-mi- 

 crography. No doubt many others 

 have, like myself, become enthusi- 

 astic on the subject, and have done 

 much work in that direction. Benefit- 

 ing from the hints derived from Mr. 

 Walmsley's paper, I some months 

 ago attached my Griffith Club micro- 

 scope to a camera, and with it did 

 some very creditable work. It was 

 not, however, satisfactory to me 

 wholly, and the thought occurred to 

 me that if a combination of camera 

 and microscope could be produced at 

 a reasonable cost it would, like a 

 country newspaper, fill a long-felt 



want. I finally submitted to Edward 

 Bausch a drawing that, besides con- 

 veying an idea of what I wanted, 

 represented the consumption of an 

 unknown quantity of brain tissue. 

 He went to work on it, corrected my 

 errors, added new ideas, and as a re- 

 sult I have the pleasure of presenting 

 and describing to you to-day an ap- 

 paratus capable of doing any work in 

 photo - micrography perfectly, and 

 that can be put in the hands of the 

 mici^oscopist at an expense less than 

 that of ordinary camera attachment 

 for his microscope. As the apparatus 

 is before you there is hardly a neces- 

 sity for me to describe it in detail.' 



Mr. Atwood explained the appa- 

 ratus in detail, and showed specimens 

 of photo-micrography. A discussion 

 followed as to whether it was advisa- 

 ble to work with or without eye- 

 pieces. Mr. Atwood said he ob- 

 tained a denser and clearer plate 

 without an eye-piece. President Cox 

 said he had obtained the best results 

 with an eye-piece. Dr. Blackham 

 took the same ground. He thought 

 the microscope had been manufac- 

 tured with the intention that the eye- 

 piece should be used in photo-micro- 

 graphic work. He thought the prej- 

 udice against eye-pieces unreasona- 

 ble. After an image had been 

 focussed the instrument was thrown 

 out of adjustmfent if the eye-piece was 

 removed. Prof. Burrell said he had 

 started out with a prejudice against 

 eye-pieces, but, notwithstanding, he 

 had found that better photo-micro- 

 graphic work could be executed by 

 their use. 



President Cox announced that he 

 had communicated to Dr. Dallinger 

 that the latter had been elected a per- 

 manent honorary inember of the or- 

 ganization. Dr. Dallinger said: 

 ' Not only on my own account, but 

 on behalf of the society I represent, I 

 accept the honor with the greatest 

 pleasure. While I have been among 

 you I have felt that my interest in 

 microscopy has widened. I feel that 

 there is more earnest work being; 



