1869.] 357 [Hagen. 



Section of Microscopy. March 10, 1869. 



Mr. R. C. Greenleaf in the chair. Six members present. 



Dr. H. Hagen made the following communication concern- 

 ing his exjjerience with the use of microscopes. 



Having worked with the microscope more than thirty years for 

 medical and scientific purposes, — tblloAving the gradual perfecting of 

 the instrument — I was anxious to examine the power of American 

 microscopes. But my occupation in the Museum and ignoi-ance of the 

 English language has prevented the accompHshment of my wishes. I 

 ordered a new microscope of M. Hartnack in Paris, which was kindly 

 forwarded to me by M. Milne-Edwards. The French instruments are 

 noted throughout Europe for their power and finish, and in order to 

 judge impartially, I chose one of these, rather than a German instru- 

 ment. It is well known that nearly every nation claims for itself the 

 highest degree of perfection in the manufacture of microscopes. No 

 Englishman would acknowledge the superiority of a French instru- 

 ment, nor a Frenchman that of an English instrument. In Germany 

 alone, Prussian, Austrian, Saxon and Bavarian manufacturers all claim 

 preeminence for their respective instruments, not only compared with 

 each other, but with those of American and English manufacture. 

 There has been no unanimity of opinion among scientific men in re- 

 gard to this question. I think these conflicting claims are based upon 

 something beyond mere national jiride. In fact, microscopes finished 

 by the most skillful opticians, have arrived at a high degree of perfec- 

 tion in nearly every country, and differ less than is generally sup- 

 posed. During the past ten years there has been great competition 

 among opticians, but in every case their progress has been arrested by 

 one insurmountable obstacle. Since the recent improvement in cor- 

 recting the objectives for the thickness of the covei'-glasses, compar- 

 atively little has been done. Indeed it is always stated and accepted 

 as a fact, that the proper means of obtaining a stronger power con- 

 sists in securing a higher power of the objectives and a smaller focal 

 distance with greater angular aperture, and in this opticians have 

 arrived at a rare degree of perfection. Objectives of -J^ in. are made, 

 and the greatest angular aperture, so far as I know, is in the .jV ob- 

 jective by Spencer, with 1 75° angular aperture. But even here further 



