i;:i 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Mr. Turrill in England ; (2) tlio two screw stage-micrometers acting 

 at riglit angles, so that measurements can be made in both directions, 

 and (3) the variable diaphragm beneath the stage, consisting of two 

 rectangular plates, each having a large; Y-shaped aperture, and so 



arranged that a pinion at the side causes them to move together but 

 in opposite directions, thus varying the size of the square aperture of 

 the diaphragm from the full opening (1^ in.) to a minute hole. 



The fine adjustment is by a direct-acting screw behind the body- 

 tube, raising or lowering a stud to which is attached the support of 

 the body-tube. 



The stage has spring clips connected by a rod, to grip glass cells 

 of special design. 



The question of duly balancing the instrument on its inclining 



