

THE MICROSCOPE. 



Vol. V. ANN ARBOR, APRIL, 1885. No. 4. 



ORIGINAL COMMUNICATIONS. 



HOMOGENEOUS IMMERSION OBJECTIVES. 



PROF. A. Y. MOORE. 



CONSIDERABLE has been written in regard to the con- 

 struction of homogeneous immersion objectives with and 

 without the collar adjustment; but I think the views recently 

 expressed by Dr. W. B. Carpenter are about correct. That, in 

 the hands of those familiar with the optical conditions govern- 

 ing the use of the collar adjustment, in objectives so constructed, 

 this adjustment permits of far more correct results than can 

 conveniently be otherwise attained by the use of the same 

 lenses when placed in fixed mountings, there is no doubt in the 

 minds of those who have understandingly used both kinds. It 

 does not happen, however, that all practical workers with ob- 

 jectives constructed upon the principle of homogeneous immer- 

 sion, are capable of using the collar properly; and it is for this 

 reason that Dr. Carpenter thinks it may well be questioned 

 whether this class of workers had not better accept the correc- 

 tion given the non-adjustable lenses of this kind, by their 

 makers, as indicating the point of their best performance. Un- 

 doubtedly, with this class of observers this is correct ; for, while 

 the best performance in their hands, owing, perhaps, to con- 

 ditions differing from those under which it was originally 

 corrected — such as differing tube length or density of the im- 

 mersion medium — may not reach its maximum performance 

 when used under the proper conditions, still, its average work 

 may be far more nearly perfect than would be the case were ad- 

 justable objectives used without paying proper attention to the 

 collar. 



On account of the change in the chromatic corrections of 



