A. L. Parsons — New Sclerometer. 



165 



xs"ow by means of the transport screw (4) and the accom- 

 panying spring (5) the crystal is moved in the direction indi- 

 cated by the arrow points so that as the surface acts as a wedge 

 the test point (EL) is raised and the spring (F) is bent from 

 position F, to position F 2 . By this movement a position is 

 reached where the test point makes a scratch on the surface to 

 be tested which is indicated in the figure as b. By the move- 

 ment of the test object from position I to position II this 

 point b has been brought to the position V and the point b has 

 also been raised the distance a V = d. After the scratch has 

 been made a reading is made on the micrometer screw E. 

 The crystal is then lowered by means of the micrometer screw 



Fig. 2. 



until the test point just touches the crystal or other substance 

 at the point b\ in other words at the beginning of the scratch, 

 and a second reading is made on the micrometer screw which 

 gives the distance db' in divisions on the micrometer screw. 

 This distance gives a measure of the bending of the spring or 

 of the pressure necessary to make a scratch on the crystal, 

 that is, it is a measure of the hardness. 



In practice the lowering of the crystal by means of the 

 micrometer screw gives a forward motion of the crystal in the 

 direction of the arrow points in the figure and the beginning 

 of the scratch must be brought under the test point by the 

 transport screw (4). It is also found better in practice to 

 lower the crystal or other test object so that the test point 

 does not touch the surface, and then raise the test object again 

 until the point just touches. 



Calibration. 



In this instrument the force that is necessary to make a 

 scratch is measured by the strain on the spring (F) and the 



