- 958 RB. Mallet—Temperature attainable by Rock-crushing. 
the American Journal of Science, vol. vii, June, 1874,* has, in 
terms as clear as they are courteous, pointed out the /acune in 
the author’s original paper in the following passage :— 
inal memoir, viz: the preéminence given by Mallet to the 
crushing of sold rock as the means of producing heat and 
instantaneously, or under such circumstances that the heat 
cannot be conducted away, and, further, that the resistance of 
the rock has not been materially diminished by the downward 
increase of hypogeal temperature. At the most moderate 
depths at which volcanic phenomena can be supposed to 
originate the last-mentioned factor must exert a very consider- 
able influence, reducing materially the available heat-increment. 
Hence the numerical results of Mallet’s laborious experiments 
on rock-crushing, however interesting and useful as affording a 
definite measure of the thermal effects producible by this 
means, yet fail to carry conviction as to the efficacy of this 
particular modus operandi in reducing large masses of solid 
rock to fusion, unless essentially supplemented by friction, not 
-so much of rock walls against each other, but more probably 
by the heat produced within more or less | caninnied detrital 
 * Phil. Mag., July, 1874, p. 41. 
