112 K Mr. J. Gill on the Dynamical Theory of Heat. 



pressure steam, — but not as heat or molecular vis viva ; for the 

 steam contains only the vis viva of its heat of conversion, or 

 change of state. 



Imagine a mass often cubic feet of atmospheric-pressure steam 

 to be compressed by exterior force into the space of one cubic 

 foot, supposing no heat to be lost or applied in the process, and 

 excluding the idea of friction ; it will be allowed that the result- 

 ing cubic foot of steam will be identical with a cubic foot of 

 steam formed directly by the agency of fire under a pressure of 

 ten atmospheres. A radical mistake in the doctrine of thermo- 

 dynamics is the assumption that compression, apart from the idea 

 of friction, is a source of heat. In elastic fluids it is evidently 

 only a cause of concentration of heat, or increase of temperature 

 resulting from a change of latent heat into sensible, as it would 

 be commonly expressed. This all-important difficulty must be 

 fairly met, and this corner stone in the foundation of the theory 

 must be satisfactorily placed before the superstructure can be of 

 permanent value. It is obvious that a very large amount of 

 energy exists in high-pressure steam (and in compressed gases) 

 which is not molecular motion, or heat as described by the dyna- 

 mical theory, but quiet, statical energy, or force wound up, 

 ready to give out equivalent work when the fluid is allowed to 

 expand against moderated resistance, or to be converted into 

 interior heat, or molecular motion of its own mass when allowed 

 to increase its volume by free tumultuous expansion. 



This packed up energy must be repulsion in some shape ; but 

 it cannot be the centrifugal repulsion of molecular vortices, 

 because that must be a result of existing motion ; and it is seen 

 that no corresponding motion exists in the compressed fluids. 

 Physical phenomena present numerous instances of the action of 

 statical repulsion quite distinct from the idea of centrifugal force ; 

 and it was said above, that when motion or vis viva disappears, 

 it is replaced by equivalent energy under the form of attraction 

 or repulsion in a statical condition of disturbed equilibrium. 

 The heat of conversion of water into steam passes from the fire 

 to the fluid as molecular motion, whether of vibration or rotation 

 is a question of minor importance, if we allow that the work- 

 producing power is not dynamical centrifugal force. Something 

 equivalent to the work-producing power must also be supposed 

 to pass from the fire to the steam. If it is energy existing in the 

 fire as molecular vis viva or dynamical force, it must be supposed 

 to disappear as such in the act of transfer to the steam, and to 

 assume, for the time, the equivalent form or condition of molecular 

 repulsion in the state of statical force, under the influence of some 

 opposing statical resistance. And, conversely, when the opposing 

 statical resistance is removed, vis viva or motion reappears either as 



