io6 ROYAL MICROSCOPICAL SOCIETY STANDARDS [Cn. Ill 



" Core Diameter of Thread (D) at bottom of thread not to exceed 

 0.7626 in. (=19.3699 mm.), or to be less than 0.7596 in. ( = 19.2937 

 mm.)." 



176. Royal Microscopical Society standards for eye-pieces and 

 substage. The standards adopted in 1899 were four in number, 

 but in actual practice only two are used: 



Small or Continental size, 0.917 in. = 23.300 mm. 



Large size, 1.27 in. = 32.258 mm. 



The size here given is the internal diameter of the draw-tube, the 

 tightness of the fit being left to the manufacturer. 



Standard size for substage fitting, 1.527 in. = 38.786 mm. 



The gauges for the above sizes have been deposited at the National 

 Physical Laboratory, and maker's gauges may be compared with 

 the standards on payment of a small fee. 



For Collateral Reading, see the list at the end of Chs. I and II. 

 and: 



\ELSON. E. M. On the Origin of the Society Screw. Jour. Roy. Micr. Soc., 1910 



P- 443- 



BROCHER, F. Jour. Roy. Micr. Soc., 1912, p. 244. In this discussion it is shown 

 that the weariness in using the microscope is due to the effort to make the 

 image sharp by eye accommodation instead of by the fine adjustment. 



