Owing to information received after the table on p. 14 was printed it is neces- 

 sary to replace that table bv one containing the latest information. In this revised 

 table tube-length b-d of the diagram greatly preponderates, and the great majority 

 of unadjustable objectives are corrected for a thickness of cover-glass falling be- 

 tween fifteen and twenty one hundredths of a millimeter (0.15-0.20 mm.). 



Length in Millimeters and Parts included tn the "Tube-Length" by 

 , Various Opticians. 



Pts. included 

 in '"Tube- 

 length." 



See Diagram. 



"Tube-Length" in 

 Millimeters. 



[Chas. Baker, London, England ._. 



The Bausch & Lomb Optical Co., 



Rochester, N. Y. . _ 



R. & J. Beck, London, England .. 



Bezu, Hausser & Cie, Paris, France 



Klonne und Miiller, Berlin, Germany. _. 

 Queen & Co., Incorporated, Phila., Pa. _ 



Ross, Ltd , London, England 



W. und H. Seibert, Wetzlar, Germany.. 



Swift & Son, London, England 



Watson & Sons, London, England 



R. Winkel, Goettingen, Germany 



Carl Zeiss, Jena, Germany 



a-d 



f Ernst Leitz, Wetzlar, Germany 



J Nachet et Fils, Paris, France 



j Powell & Lealand, London, England 



j C. Reichert, Vienna, Austria 



I Spencer Lens Company, Buffalo, N. Y 



I W. Wales, New York' 



The Gundlach Opt. Co., Rochester, N. Y. 

 E. Hartnack, Potsdam, Germany.. 



Dollond & Co., London, England 

 Verick (Stiassnie) Paris, France. _._ 

 P. Waechter, Berlin-Friedenau, Germany 

 J. Zentmayer, Philadelphia, Pa. 



150 or 250 mm. 



160 or 216 mm. 

 .160 or 220 mm. 



180 mm. 



160 or 250 mm. 

 b-d [ Queen & Co., Incorporated, Phila., Pa 170 mm. 



160 or 254 mm. 

 .170 mm. 



160 or 228 mm. 



160 or 250 mm. 

 . 192 mm. 

 .160 or 250 mm. 



170 mm. 



160 mm. 



254 mm. 



1 60- 1 80 mm . 

 .160 mm. 

 .254 mm. 



254 mm. 



160 mm. 



165, 240 mm. 

 .160-200 mm. 

 .160 mm. 



160 or 235 mm. 



Thickness of Cover-Glass for Which Non- Adjustable Objectives are Corrected by 



Various Opticians 



f The Bausch & Lomb Optical Co., Rochester, N. Y. 



] Klonne und Miiller, Berlin, Germany. 



I Queen & Co., Incorporated, Philadelphia, Pa. 



I The Spencer Lens Co., Buffalo, N. Y. 



( Ernst Leitz, Wetzlar, Germany. 



-] P. Wachter, Berlin-Friedenau, Germany. 



( R. Winkel, Goettingen, Germany. 



f Chas. Baker, London, England. 



] R. .&. J. Beck, Ltd., London, England. 



J Gundlach Optical Co. , Rochester, N. Y. 



I W. und H. Seibert, Wetzlar, Germany. 



J E. Hartnack, Potsdam, Germany. 



t C. Reichert, Vienna, Austria. 



(Ross, Ltd., London, England. 



X Verick (Stiassnie), Paris, France. 



I Carl Zeiss, Jena, Germany. 

 J. Zentmayer, Philadelphia, Pa. 



I Dollond & Co., London, England. 



1 Nachet et Fils, Paris, France. 

 Bezu Hausser & Cie, Paris, France. 



j Powell & Lealand, London, England. 



I. Swift & Son, London, England. 

 0.20 mm. Watson & Sons, London, England. 



0.25 mm. W. Wales, New York. 



0.18 mm. 



0.17 mm. 



o. 15 mm. 



0.15-0. 18 mm. 



0.15-0.20 mm. 



o. 12-0. 17 mm. 

 0.10-0. 15 mm. 

 o. 10-0. 12 mm. 

 o. 10 mm. 



