THE HELICOIDAL OR WIRE STONE SAW.


The sides of solid bodies, whatever be the degree of hardness, and
however fine the texture, possess surfaces formed of a succession of
projections and depressions. When two bodies are in contact, these
projections and indentations fit into one another, and the adherence that
results is proportional to the degree of roughness of the surfaces. If,
by a more or less energetic mechanical action, we move one of the bodies
with respect to the other, we shall produce, according as the action
overcomes cohesion, more or less disintegration of the bodies. The
resulting wear in each of them will evidently be inversely proportional
to its hardness and the nature of its surface; and it will vary, besides,
with the pressure exerted between the surfaces and the velocity of the
mechanical action. We may say, then, that the wear resulting from rubbing
two bodies against each other is a function of their degree of hardness,
of the extent and state of their surface, of the pressure, of the
velocity, and of the time.

[Illustration: FIGS. 1, 2 and 3.--APPARATUS FOR SAWING STONE.]

According as these factors are varied in a sense favorable or unfavorable
to their proper action, we obtain variations in the final erosion. Thus,
in rubbing together two bodies of different hardness and nature of
surface, we obtain a wear inversely proportional to the hardness and
state of polish of their surfaces. Through the interposition of a
pulverized hard body we can still further accelerate such wear, as a
consequence of the rapid renewal of the disintegrating element.