Oy 



48 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



diameter of the circular dent. The milled screw-head S provides for 

 the vertical adjustment of the tube ; S' and S" govern the backwards- 

 and-forwards movement in the direction of its length ; 8'" controls the 



Anszug- 



Fig. 42. 



horizontal motion perpendicular to the last and moves the whole of the 

 over-stage parts. In taking the measurements, the tube is first got 

 upright, and the vernier by means of the screw S' brought to the zero ; 



the dent to be examined is then applied to the object-stage, and the tube, 

 by means of S", moved so that one cross-thread is tangentially over the 

 edge of the dent, thus o The tube is now moved sideways until the 

 other thread (perpendicular to last) passes through the centre of the 



