162 



SCIENCE. 



[N. S. Voi . XXIV. No. 606. 



quite large if the supposition is to be given 

 any serious consideration. 



The object of this paper is to present a 

 view of the origin of volcanic heat which 

 may possess some elements of novelty and, 

 it is hoped, of rationality. According to 

 this view, much of the heat manifested is 

 due to mechanical work converted into 

 heat, a theory based upon dynamical prin- 

 ciples to be later pointed out. Primarily 

 it will be admitted that any substance, gas, 

 liquid or solid, upon which work is done 

 acquires heat in proportion to the energy 

 expended upon it, which heat, if prevented 

 from escaping, at once results in an in- 

 <j9".ease of temperature of the substance. If 

 tthe mechanical energy so converted be of 

 iknown amount, we may calculate from the 

 mass and specific heat of the substance or 

 •body upon which such energy is expended 

 the rise in temperature. Even if air at 

 ordinary temperature under high pressure 

 escapes through a tortuous or frictional 

 passage surrounded by a good heat non- 

 V. conductor, it emerges hot. The higher the 

 '^iRessfsare and the greater the friction met 

 in the passage the greater the increase. 

 The heating is directly related to the work 

 done upon the mass. 



If a liquid be substituted for the air the 

 general result is the same, and the liquid 

 may be made to boil upon its escape. If 

 a somewhat plastic solid like hard pitch be 

 subjected to the process, the energy re- 

 quired will be greatly increased, or the 

 pressure required to force it through the 

 tortuous passage of some length will be 

 great. It may emerge hot and melted if 

 the conditions be properly selected. 



If now it be assumed that any solid be 

 subjected to a pressure such as to cause it 

 to flow in a tortuous or restricted channel, 

 it will, in so moving, rise in temperature, 

 and -continue so to rise until it has reached 

 a degree of fluiditv such as to lessen or 



practically stop the absorption of energy 

 in moving the mass ; or until it escapes from 

 the passage through which it is being im- 

 pelled. The pressure is but one factor of 

 the energy, the other being the distance 

 through which the pressure acts. The 

 pressure required depends upon the resist- 

 ance to motion, which in turn is greater 

 with more rigid bodies and greater with in- 

 crease of distance through which friction 

 is met and overcome. The pressure or 

 force required will be at a maximum when 

 the solid mass starts cold or nearly so and 

 will diminish as the temperature is raised 

 and consequent plasticity or fluidity 

 brought about. A rock mass forced to 

 move under great pressure over distances 

 of thousands of feet must soon become 

 melted in the process. It is not necessary 

 to assume that the mass so heated starts 

 cold. It may start at any temperature 

 at which it possesses sufficient rigidity or 

 viscosity to require the exertion of great 

 force to move it in the assumed restricted 

 or tortuous passage or channel. Great 

 velocity of movement in such passage 

 means of course great energy expenditure 

 and rapid heating. The idea thus out- 

 lined may now be applied as an explana- 

 tion of volcanic phenomena. For example, 

 a hot-water spring may be the result of the 

 water having been forced by high pressure 

 to traverse somewhat porous rock, or to 

 pass through narrow but long fissures in 

 which it is churned for a long time before 

 escaping. In like manner any rock mass 

 which, subjected to very high pressure, 

 begins to flow must become heated. If its 

 distance of traverse be great enough in a 

 restricted flssure or channel, it must melt, 

 or even become so heated as to partially 

 vaporize when the pressure is relieved, as 

 when it finally escapes. Let it be admitted 

 that the flexures taking place in the earth 's 

 crust or in the outer portions of its mass 



