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

 sary to replace that table by 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 in the "Tube- Length" by 

 Various Opticians. 



Pts. included 

 in "Tube- 

 length." 



See Diagram. 



"Tube-Length" 

 Millimeters. 



I 



150 or 250 mm. 



1 60 or 2 1 6 mm . 

 .160 or 220 mm. 

 . 1S0 mm. 

 . 160 or 250 mm. 



170 mm. 



160 or 254 mm. 

 .170 mm. 



160 or 22S mm. 



160 or 250 mm. 

 _ 192 mm. 

 . 160 or 250 mm. 



170 mm. 



Fig. 24. 



o 20 mm 

 0.25 mm 



| 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 



I Carl Zeiss, Jena, Germany 



I Ernst Leitz, Wetzlar, Germany 



Nachet et Fils, Paris, France 160 mm. 



j Powell & Lealand, London, England 254 mm. 



I C. Reichert, Vienna, Austria 160-180 mm. 



I Spencer Lens Company, Buffalo, N. Y 160 mm. 



I W. Wales, New York 254 mm. 



The Gundlach Opt. Co., Rochester, N. Y. 254 mm. 



E. Hartnack, Potsdam, Germany 160 mm. 



Dollond & Co., London, England __. 165, 240 mm. 



Verick (Stiassnie) Paris, France 160- 200 mm. 



P. Waechter, Berlin-Friedenau, Germany, 160 mm. 



J. Zentmayer, Philadelphia, Pa. 160 or 235 mm. 



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

 Various Opticians 

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

 ] Klonne und Miiller, Berlin, Germany. 

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

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

 j Ernst Leitz, Wetzlar, Germany. 

 ■ P. Wachter, Berlin-Friedenau, German}'. 

 I R. Winkel, Goettingen, Germany, 

 f Chas. Baker, London, England. 

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

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

 ( W. und H. Seibert, Wetzlar, German}'. 

 1 E. Hartnack, Potsdam, Germany. 

 I C. Reichert, Vienna, Austria. 

 ( Ross, Ltd., London, England. 

 - Vdrick (Stiassnie), Paris, France. 

 I Carl Zeiss, Jena, Germany. 



J. Zentmayer, Philadelphia, Pa. 

 1 Dollond & Co., London, England. 

 I Nachet et Fils, Paris, France. 



Bezu Hausser & Cie, Paris, France. 

 ( Powell & Lealand, London, England. 

 I Swift & Son, London, England. 



Watson & Sons, London, England. 



W. Wales, New York. 



Tin 



o. 18 mm. 



o. 17 mm 



o. 15 mm. 



o. 15-0. 18 mm. 



0.15-0.20 mm. 



o. 12-0. 17 mm. 

 o. 10-0. 15 mm. 

 o. 10-0. 12 mm. 

 o. 10 mm. 



