CH. II] 



LIGHTING AND FOCUSING 



79 



ring, size 0.7596 in. diameter, and no die will be allowed to be stamped with 

 the Society's stamp unless it will pass easily over the 0.7596 in. plug and will 

 not pass over the 0.7626 in. plug." 



" These taps and dies will be for sale almost immediately, at cost price, 

 il. 15^. for each pair of tap and dies, and it is earnestly requested that every 

 maker of Microscopes will possess himself of a pair of these sizing gauges." 



" The Council believe that at such time as these sizing taps and dies have 

 come into universal use the standard screw-thread will have been put upon a 

 permanent basis, and complete interchangeability of all object-glasses will 

 have been established." 



h 137. 

 Screw. 



New Specification of the Royal Microscopical Society Standard 



Fig. 69 



"Thread. — Whitworth screw, i. e.,a. V-shaped thread, sides of thread 

 inclined at an angle of 55 to each other, one-sixth of the V depth being 

 rounded off at the top and the bottom of the thread. 



Pitch. — 36 to the inch. 



Length of Thread on Object-Glass o. 125 in. 



