106 ROYAL MICROSCOPICAL SOCIETY STANDARDS [Ch. 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 1S99 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. 



