1833.] Attraction and Repulsion. 463 
atoms must be compressed with great force, and must exert an equal 
repulsion. If the compressing force is suddenly increased, so also must 
the repulsion, the iron being somewhat condensed. But, when these 
forces become superior to the affinity, which detains the heat in the 
iron, it is manifest that part of the heat must leave the iron, and this 
will take place until the affinity for the remaining heat becoming very 
great, little or none can be evolved, and the density cannot be increas- 
ed.—This explanation is verified by the experiment. Less and less 
heat is evolved, at every succeeding blow, until at last little or none 
can be driven out, and here condensation ceases. 
2. That much heat is made sensible by the friction and attrition of 
many bodies. 
Since the particles of heat attract so powerfully, the atoms of all other 
bodies, as to enter even the densest, much more then will they be ac- 
cumulated on the surface of bodies, and endow them with a repulsive 
force. Hence the fact that two plates of glass cannot be brought into con- 
tact, as Newton has shewn*. But if two bodies, rubbing againste ach 
other, have this superficial heat compressed, with a force superior to that 
which detains the most distant particles of it (which from their distance 
must be weakly attracted), it must happen, that part of the heat will 
be separated, while the friction lasts, and will be renewed as soon as 
it ceases. This explanation, which I have given of the fact, appears 
to render it perfectly conformable with the material doctrine of heat. 
As, in attrition, both the forces of friction and percussion on compres- 
sion operate, there will be a double cause for heat becoming sensible, 
which has been just explained under the two former heads. The ex- 
periment of Rumrorp, in which much heat was evolved, in the boring 
of metal, and yet the parts torn off appeared to possess their former 
capacity, has been sufficiently explained by Mr. Daron in these words: 
** The fact is, the whole mass of metal is more or less condensed, by 
the violence used in boring, and a rise of temperature of 70° or 100° is 
too small to produce a diminution in its capacity for heat. Does Count 
Rumrorp suppose, that if in this case the quantity of metal operated on 
had been 1\b. and the dust produced the same as above, that the whole 
quantity of heat evolved would have been the samet?” 
3. The fact, that heat is evolved, in the sudden change of gunpow- 
der, by explosion from the solid to the aérial state, has been consider= 
ed as an objection to this doctrine of heat; for this appears contrary to 
_* Treatise on Optics, Query 31, 
+ New System of Chemical Philosophy, page 98. 
