ON THE ABSOLUTE MEASUREMENT OF HARDNESS. 21th 
cations are introduced by the motional phenomena, the lateral sheer 
which accompanies scratching, and in short by conditions which have 
nothing to do with hardness at all. It is easy to imagine how the 
method originated, for the tests must primarily have been made to find 
out whether the point was capable of puncturing the surfaee; but 
inasmuch as a puncture is not easily recognized, the passage was made 
from the point to the scratched line. The statie method is, in fact, much 
older than the dynamic method of rating hardness. If therefore the 
static method is sufficient (and this will be shown below) to define hard- 
ness as a characteristic, independent, and clearly intelligible property 
of bodies, it is worse than superfluous to introduce processes by which 
the result can only be complicated. 1 do not mean to imply, of course, 
that the method of scratching has been fruitless. It has conquered its 
own ground. Thus, for instance, the gradual change of hardness at 
points within a given surface of a crystal is among the striking accoin- 
plishments within the reach of the method; but we can only arrive at 
a clear knowledge of the meaning of such observations after having 
solved the statie problem of hardness and then noting the additional 
circumstances introduced, when we pass from the dent to the scratch. 
Regarded as practical method of quiet interpolation, scratching must 
retain a value which can only be enhanced by giving clear interpreta- 
tions to the nature of the process, and the discrepancies which I have 
pointed out * need not then be apprehended. 
Under the circumstances I am inclined to regard it as a step in the 
right direction, that the static method (static because motion is 
excluded) has recently again been taken up by a number of observers. 
Among these Crace-Calvert and Johnson, Hugueny,t Bottone,t and also 
Pfaff§ may be mentioned. In this class of apparatus a hard point is 
pressed or struck or drilled into the body to be measured, and the hard- 
ness is variously measured relative to given depths of penetration. 
This may be done by noting the weight necessary to sink the stylus or 
by the number of rotations of a definitely weighted needle (Pfaff’s me- 
so-sklerometer). Again, the depth to which the stylus sinks fora given 
weight or even the time necessary to produce a given depth of impres- 
sion have been used for registry. Here however it is clear at once 
that these methods are intrinsically different, and that far-fetched 
assumptions must be made relatively to the proportionality of hardness 
with the divers data obtained,—assumptions which need not even be 
approximately true. Furthermore, the body to which these different 
tests are applied is necessarily acted on in a state of strain, if not ac- 
* Hugueny (see below), to whom similar considerations are due, takes account of 
three kinds of hardness, one ‘* tangential” and the other two ‘‘ normal.” 
t Hugueny: Rech. Lap. sur la dureté des corps, Paris, 1865. Cf. Ber. de Strasb., Ges., 
1865. 
{ Bottone: Sill. Journ., 1873, p.457; Pogg. Ann., 1873, vol. 150, p. 644, 
§ Pfaff: , Miinch. Ber., 1884, p. 255, 
