R, MALLET ON HIS THEORY OE VOLCANIC ENERGY. 517 



deformation and detrusion by forcing forward, through highly irre- 

 gular or constricted rock- channels, the now heated and viscous 

 mass. 



There do not exist at present sufficient data by which to calculate 

 the amount of work necessary to a given amount of deformation in 

 viscous masses ; and hence we cannot calculate the amount of heat 

 that in nature might arise from it. Hirn, however, has shown that, 

 in the case of plastic bodies such as lead, the heat developed is pro- 

 portional to the work done in deformation ; so that if we knew the 

 pressure per unit of surface necessary to produce a certain deforma- 

 tion in an already healed mass of given viscosity, we could calculate 

 how much its temperature would be exalted by the work of the 

 assigned deformation. 



The action of the machine employed in the arsenal at Woolwich 

 for making lead rods to be afterwards pressed into bullets affords a 

 striking example. In this machine a cylindrical block of lead 

 maintained at a temperature of 400° R, is by a steady pressure 

 upon the end, which is 8*5" in diameter, of 16,700 lb. per square 

 inch of its surface, forced through an aperture at the other extre- 

 mity into a rod of 0*525 inch diameter, at such a rate that 5 

 inches in length of the cylindrical block becomes a rod about 100 

 feet in length, of the above diameter, per minute. We have thus 

 393,906 foot pounds of work done upon the lead per minute, 

 dividing which by J we have 510*2 British units of heat developed 

 per minute from the transformed work. In the actual machine the 

 whole of this is ultimately dissipated and lost; but if none of it were 

 dissipated, as the cylindrical block of lead of 8-5" diam. by 0*416 foot 

 in length weighs 116*3 lb., and the specific heat of lead is =0*029 

 (or perhaps a little more at 400° F.), it follows that the heat 

 developed by its deformation from the short cylindrical block of 5 

 inches length to a rod of about 100 feet is enough to raise the 

 temperature of the lead through 151° P., or, were no heat lost, to 

 raise its temperature from 400° to 551° ¥., or thereabouts — that is, 

 to within about 50° of its melting-point. If, therefore, the velocity 

 of deformation were greater by one fourth, the lead would be melted, 

 assuming the latent heat of liquefaction to be small. Or if we 

 could by a reverse process squeeze the 100-feet rod back into the 

 original block of 8*5" x 5", we should find the lead in the latter not 

 only liquid but considerably above its temperature of fusion. It is 

 obvious therefore that any viscous or plastic body, such as lava, 

 continually forced through apertures varying in area and form and 

 suffering continual deformation, as when forced through a volcanic 

 tube or vent, must have its temperature continually exalted so long 

 as it continues thus to be urged forcibly forward, assuming, as is 

 very nearly the truth in nature, that an extremely small proportion 

 of the heat developed in the process can be dissipated by conduction 

 to the walls of the tube. 



The writer has thus shown that crushing alone of rocky masses 

 beneath our earth's crust may be sufficient to produce fusion. He 

 has also shown that the heat developed by crushing alone cannot be 



