400 T. A. Jaggar, Jr. — Microsclerometer, for 



Drawing point over mineral: 



(a) H. = weight to draw point (inversely) — (Franz). 



(b) H. = weight on point — (Turner*). 



Grooving with a standard edge: 

 H. = depth of groove — (Pfafff). 



Boring with a standard point : 

 H. = number of rotations — (PfafFJ). 



Grinding toith a standard powder : 



(a) H. = period required for polish (inversely) — (Behrens§). 



(b) H. = loss of volume (inversely) — (Rosiwalfl). 



(c) H. = comparative loss of four substances (inversely) 



(Jannettaz and Goldberg^"). 



Static pressure-tests. 

 Compressing lens on plate of substance : 



(a) H. = limit pressure per unit of surface — (Hertz**). 



(b) H. = " " " " multiplied by the cube 

 root of the radius of ei ure — (Auerbachff). 



nto a surface : 

 - 



a ^andard depth — (Calvert and 

 JohnsonJJ, Bottone§§). 



(b) H. = volume of indentation (inversely) — (U. S. Ordnance 



TestslHI). 



Reference to the foregoing table shows a wide diversity of 

 method, all designed to measure the resistance which a sub- 

 stance opposes to permanent deformation ; all come within the 

 scope of four processes utilized as the measure of such deforma- 

 tion, viz : 



(1) Abrasion, (2) Penetration, (3) Friction, (4) Fracture. 



Of the eighteen authors mentioned, thirteen used abrasion 

 (76 per cent) ; friction was used as an alternative (and found 

 inadequate) by two of these. All were mineralogists except 

 Turner, who was a practical metallurgist. The five authors 

 who used static pressure as a test of hardness (penetration and 

 fracture) were physicists and metallurgists, and in all five cases 



*Proc. Phil. Soc, Birmingham, v, 1886. f Sitz. k. k. Bayer. Akad., 1883. 



JSitz. k. k. Bayer Akad., 1884. 



§ Anleitung zur Mikrochemische Analyse. 1895. 



j Verhandl. k. k. Geol. Reichsanstalt, 1896. xvii, 475. 



% Asso§. Prang, p. l'Avanc. d. Sc., 9 Ang., 1895. 



** Verhandl. Berlin Phys. Gesells, 1882. +f Wied. Ann., 1891, 1892, 1896. 



\X Phil. Mag., xvii, 114. §§ Chem. News, 1873, xxvii. 



II Report of experiments on metal for cannon, U. S. Ordnance Dep't. 1856. 



