124 PRACTICAL MICROSCOPY. 



An immense amount of discussion took place in reference 

 to these lenses in England, nearly all the opponents to the 

 system averring that by the use of an immersion fluid the 

 aperture was cut down ; that, in fact, rays which were 

 equivalent to more than 180 in air were of no practical 

 utility, even if they could be made to enter an object-glass 

 and form an image. The editors of the 'Journal of the 

 Royal Microscopical Society,' on page 305 of the ' Journal/ * 

 write : " The * aperture question ' will ever hold a most 

 prominent place in the history of the microscope, represent- 

 ing as extraordinary a series of mistakes as were ever com- 

 mitted in any branch of science, and in which (down to 

 comparatively recent times) both the leaders and the rank 

 and file were equally involved. * Aperture ' may be said to 

 have been the haschische of the microscopist ; when that has 

 formed the subject of consideration, the simplest and oldest 

 established optical principles have not been disregarded 

 merely, but their very converse tacitly assumed, as if the 

 great optical physicists of this and the previous century had 

 never lived or had written nothing that was worthy of con- 

 sideration ! " 



Since penning the foregoing remarks, the author has 

 been informed by Mr. J. B. Dancer, of Manchester, that 

 for some years he has practically effected the reduction of 

 aperture in somewhat a similar manner to that indicated 

 on page 107. Instead, however, of screwing in a diaphragm 

 of definite aperture behind the back lens of the objective, 

 he uses an ingeniously constructed graduating diaphragm, 

 screwing into the lower end of the microscope body as an 

 adapter, into the lower end of which the objective is made 

 to fit. 



Mr. Dancer constructed this, some years ago, to give 

 penetration to wide angle lenses, and has sent the author 



* Series ii. vol. i. part 2. 



