OIL IMMERSION OBJECT-GLASSES. 309 



OIL IMMERSION OBJECT-GLASSES. 



Since the introduction of the duplex objectives 

 another form of four-system, wide apertured glass, 

 constructed by Carl Zeiss, of Jena, Denmark, has made 

 its appearance in this country. 



With the advent of these glasses came also the an- 

 nouncement that their balsam apertures excelled those 

 of the American duplex. A novel feature in the 

 mounting of the oil immersions was that they were not 

 provided with adjustment collar ; it being asserted that 

 the only requirements necessary to secure the perfect 

 action of the object-glass were to use the same with a 

 tube of exactly ten inches length, and to employ cedar 

 oil as the immersion medium. 



It was further stated that when these simple require- 

 ments were alone attended to, that no further adjust- 

 ment of the objective would be required, and that the 

 performance ot the object-glass would be found un- 

 equaled. 



As might be supposed, the above claims on behalf of 

 the oil immersions were destined to receive attention 

 at the hands of American microscopists. 



A fact well known to experts concerning wide aper- 

 tured objectives is this, viz: An object-glass exactly 

 corrected to the eye of A may not be in exact correc- 

 tion to the eye of B without suitable change of the 

 collar adjustment. 



During a sitting with Mr. Chas. A. Spencer at 

 Buffalo last fall, the above fact became immediately 



