290 The Mickoscope. 



"tube-length." From nearly all, precise and satisfactory answers 

 were received, and I wish to express here my appreciation of their 

 courtesy. The answers received are given below, and indicated on 

 the accompanying diagram: 



Table giving length in millimeters, and showing parts included 

 in " tube-length " by various opticians. 



Pts included 

 in "Tube- 

 lengths." 



See Diagram 



'lengtite^'' " Tube-length " in Millimeters. 



b-d. 



iGrunow, New York 203 mm. 

 Nachet et Fils, Paris 146 or 200 mm. 

 Powell and Leland, London 254 mm. 

 C. Reichert, Vienna 160 to 180 mm. 

 W. Wales, New York 254 mm. 



/Bausch &Lomb Opt. Co., Rochester, 216 mm. 



\Bezu, Hausser et Cie., Paris * 220 mm. 



jKlonne und Mliller, Berlin 160-180 or 254 mm. 



)W. & H. Siebert, Wetzlar 190 mm. 



'Swift & Son, London 228| mm. 



IC. Zeiss, Jena 160 or 250 mm. 



a-g Gundlach Optical Co., Rochester. . . . 254 mm. 



c-d Ross & Co., London 254 mm. 



c-e R. & J. Beck, London 254 mm. 



c-g H. R. Spencer & Co., Geneva, N. Y., 254 mm. 



c-f J. Green, Brooklyn f 254 mm. 



c'-e E. Leitz, Wetzlar 125-180 mm. 



Oil immersions 160 mm. 



Fig. 1. Diagram showing the parts of the microscope included 

 in "tube-length " by the various opticians of the world. (See table 

 above. ) 



A crlance at the table and diagram is sufficient to show that 

 there is about as great diversity as possible in the parts included in 

 " tube-length," and that 'the length in millimeters, including these 

 parts, is likewise very diverse. This has, doubtless, come about sim- 

 ply because there was no general standard, and each optician selected 

 for himself a standard. For the sake of those who iise the micro- 

 scope, it is hoped that a uniform standard may be chosen, or that, at 

 most, but two standards should be decided on by all opticians. 

 These two lengths in millimeters would probably best be 254 mm. 



* Successors to Hartnack. 

 + Successor to Tolles. 



