NEW OIL IMMERSION OBJECTIVES, ETC. 317 



doubtless contract with either Tolles or Spencer for 

 objectives on the model of the Zeiss, and fully equal to 

 the latter in performance, and at figures considerably 

 below those quoted in the Danish catalogue. 



Our experience with the Zeiss oil immersions has 

 neither weakened our appreciation of the screw-collar 

 adjustment, nor our high estimation of wide apertured 

 objectives of American manufacture. 



