408 T. A. Jag gar Jr. — Microsclerometer, for 



allows only the one line to be in sharp focus at a time. L is 

 locked, and the rotation started with the clockwork at a uni- 

 form speed. L is released, and the diamond begins to bore. 

 The uniformity of the rate is indicated by the movement of 

 the index hand, i : care must be taken to note the initial posi- 

 tion of e, and to keep record of the number of times it makes 

 a complete revolution. The micrometer focus is watched care- 

 fully in the microscope and when the upper line appears sharp 

 the lock is closed and the clockwork then checked. In this 

 way the diamond is moving at a uniform rate when it begins 

 to bore and when checked, i and i 1 now give the hardness in 

 terms of rotations of the diamond. 



The accessory parts of the apparatus are a levelling table of 

 seasoned mahogany for the microscope with a sunk spirit level 

 and three levelling screws, and the clockwork, which is attached 

 to the levelling table by an adjustable slide for regulating the 

 belt tension. 



The adjustments necessary prior to experiment are : 



Levelling 



table, 



Adjusting 



tension of belts, 





" pivots, 

 lock, 



(i 



foot-screws, 



a 

 it 



counterpoises, 



inclination of micrometer, 



Centering 



diamond. 



The diamond is centered by inverting the apparatus and hold- 

 ing it in a vise so that the diamond is turned upward in the 

 field of the microscope. "With a jeweler's screw-driver the 

 three radial screws of the chuck may be so adjusted that the 

 extreme tip of the diamond rotates on the cross-hairs of the 

 ocular without eccentricity : or, if it is desirable that the dia- 

 mond move iu a circular path, and so describe a ring shaped 

 scratch, it may be so adjusted. 



Calibration and Measurement. 



The instrument is calibrated by testing the constancy of 

 each element, viz : depth, rate, the diamond point and weight. 

 Tests with various weights show that the action of the diamond 

 is slow, and moreover, there is a very rapid increment of resist- 

 ance with increased depth. A weight of 10 gm , rate 10 revolu- 

 tions per second, gave the value for an ordinary cover-glass of 

 about three thousand revolutions for a depth of *01 mm . Thus 

 the test occupied about five minutes. The increment of resist- 

 ance implies increment of surface of abrasion. The constancy 



