51 



a 



b 



c 



- -g 



Pts. included Tube-length 

 in Tube-length. in 



See Diagram. Millimeters. 



Grunow, 203 



E. Leitz, 170 



Nachet et Fils, 146 or 200 



a-d{ Powell and Lealand, 254 



j C. Reichert, 160 to 180 



j Spencer Lens Co., 235 or 160 



IW. Wales, 2o4 



f Bausch & Lomb Opt. Co., 216 or 160 



d-d 



Bezu, Hausser et Cie., 

 Klonne und Muller, 

 W. & H. Seibert, 

 Swift & Son, 

 C. Zeiss, 



Gundlach Optical Co., 

 ' ( R. Winkel, 

 d c-d Ross & Co., 

 e c-e R. & J. Beck, 

 c-f J. Green, 

 Hartnack, 

 Verick, 

 Watson & Sons, 



220 



160 -180 or 254 



190 



165 to 228| 



160 or 250 



254 



254 

 254 

 254 



160-180 

 160-200 

 160-25(1 



Fig. 21. 



