ROYAL MICROSCOPICAL SOCIETY STANDARDS 

 FOR EYE-PIECES. 



During the year 1915 the Council of the Society deposited with the 

 Director of the National Physical Laboratory their Standard Eye-pieces 

 and Sub-stage Gauges.* These gauges were made for the Society in 1900, 

 and were good examples of the Plug and Ring gauges of that date.f They 

 have recently been carefully checked at the Natural Physical Laboratory, 

 and are found to be not sufficiently accurate for use as standards. Further- 

 more, the Committee on Standardization of the Elements of Optical 

 Instruments of the Department of Scientific and Industrial Research 

 recommend that as the standards were for the eye-piece tube only, and 

 the fit of the eye-piece was left to the maker's own judgment, it would 

 be in accordance with advanced practice if suitable tolerances were 

 defined and approved by the Society. This has accordingly been done, 

 and the dimensions are shown in the followins: table : — 



The obsolete gauges have been returned from the National Physical 

 Laboratory, and are now deposited in the Society's collection of instru- 

 ments. It is worth while, however, recording the variation from the 

 true nominal diameters of these old gauges. The N.P.L.'s report on 

 them is follows : — 



" The gauges have been measured at the Laboratory at 62° F., and 

 the following table gives the dimensions : — 



* Trans, of the Royal Microscopical Society, 1915, p. 558. 

 t Ibid., 1900, pp. 141, 147. 



