54 THE SCIENTIFIC PAPERS OF 



sound nor heat would be produced at the point of concussion. 

 If a piece of copper were suddenly introduced between anvil and 

 hammer, the latter would not rebound, but would make the copper 

 the recipient of the expended force. If the hammer were now 

 lifted again and again by an engine, and the piece of copper were 

 turned about on the anvil, so that at the end of the operation it 

 had precisely the same form as at the commencement, then no 

 outward effect would be produced by the force expended, but the 

 piece of copper would be heated perhaps to redness ; and if the 

 engine employed to lift the hammer were perfect, then the heat 

 produced within the copper should be sufficient to sustain its 

 motion. 



A familiar instrument for converting force into heat was the 

 fire-syringe. The force expended in compressing the air imparted 

 a sufficient temperature (about 600 Fahr.) to the same to ignite 

 a piece of German tinder. When the plunger of the syringe was 

 drawn back, it might be observed that the temperature of the 

 enclosed air was again reduced to its original degree, because the 

 heat developed in compression of the air had been spent again in 

 its expansion behind the piston. If the expansion of the heated 

 and compressed air had been without resistance, no reduction of its 

 temperature could have taken place, because no force would be 

 obtained ; a fact which had been recently proved by Eegnault, and 

 which was perhaps the strongest point in favour of the dynamic 

 theory of heat that could be brought forward. If the heated and 

 compressed air in the fire-syringe could be produced by some ex- 

 ternal cause and be introduced behind the plunger after it had 

 descended freely to the bottom, then the force imparted to the 

 plunger in the expansion might be turned to some useful purpose, 

 and a dynamically perfect engine might be obtained. But although 

 the elevated temperature might be readily supplied by means of a 

 fire, it would not be possible to give a sufficient density to the air, 

 except by an expenditure of force in its compression. If, how- 

 ever, heat were applied to a drop of water confined below the 

 plunger till its temperature was raised sufficiently to effect its 

 conversion into steam of the density of the water itself (Gaignard 

 de la Tour's state of vapours), and then allowed to expand below 

 the plunger till its temperature was reduced to zero, a dynamically 

 perfect engine would be obtained. The impracticable nature of 



