82 LIFE AND DEATH. 



action. In the steam engine, for instance, the work 

 that is received arises from the combustion of carbon 

 by the oxygen of the air. This gives rise to the heat 

 which vaporizes the water, produces the tension of the 

 steam, and ultimately produces the displacement of 

 the piston. The theory of the steam engine might be 

 reduced to these two propositions: chemical activity 

 gives rise to heat, and heat gives rise to motion ; or to 

 use the language to which the reader by now will be 

 accustomed, chemical energy is transformed into 

 thermal energy, and that into mechanical energy. It 

 is a series of phases and of instantaneous changes, and 

 the exchange is always affected according to a fixed 

 rate. 



TJie Measurement of Chemical Energy. Our know- 

 ledge of chemical energy is less advanced than that of 

 the energies of heat and sensible motion. We have 

 not yet reached the stage of numerical verifications. 

 We can only therefore affirm the equivalence of 

 chemical and thermal energies without the aid of 

 numerical constants, because we do not yet, in the 

 present state of science, know how to measure 

 chemical energy directly. Other known energies are 

 always the product of two factors: the mechanical 

 energy of position, or work, is measured by the 

 product of the force f, and the displacements; work 

 =/?; the mechanical energy of motion, U = ^mv 2 , is 

 measured by the product of the mass into half the 

 square of the velocity. Thermal energy is measured 

 by the product of the temperature and the specific 

 heat; electric energy by the product of the quantity 

 of electricity (in coulombs) and of the electromotive 

 force (in volts). As for chemical energy, we guess 

 that it may be valued directly according to Berthollet's 



