THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. XIV. NOVEMBER, 1893, No. 11. 



The American One-Seventy-Fifth Inch Objective. 



By E. cutter, M.D. 



NEW YORK. 



[Read at the College of Physicians and Surgeons in Boston, October 31, 1893.] 



On July 1st, 1873, Robert B. Tolles delivered this objective to 

 Dr. G. B. Harriman, who had ordered it for the purpose of 

 working up his demonstrations in dental histology. The price 

 paid was $400. 



No mention was made of the one-seventy-fifth at the Tercen- 

 tennial of the microscope lately celebrated at Antwerp. Only a 

 few months ago, the very distinguished Professor J. D. Dana of 

 Yale, whose academic and scientific titles number 25 in the Har- 

 vard quinquennial of 1890 and whose gold, silver and bronze 

 medals of American, European and Australian honors, number 

 twelve or more, said when this objective was shown to him that 

 he had not before known that there was a seventy-fitth objective. 

 It is therefore time the one-seventy-fifth was better known. 

 America has produced the highest power objectives for telescopes 

 arid microscopes and America should enjoy this credit with no 

 disparagement to others. 



DESCRIPTION. 



American. Tolles. Wet or dry. Three systems. 170° angu- 

 lar aperture. Working distance l-250th inch. Magnifies at ten 

 inches from its face, as much as a biconvex lens of l-75th -inch . 

 focus, to- wit. 750 diameters — with a two inch ocular 3750 diame- 

 ters — with a one inch ocular 7500 diameters — with a ? inch ocu- 

 lar 15,000 diameters. 



Screw collar moves 45.° Facial aperture of lens l-64th inch. 

 The mathematical formulas of this objective cover two pages of 



