14 ANIMAL MECIIAXLSM. 



calorie is the quantity of heat necessary to raise a kilogramme 

 of water from zero to one degree centigrade. 



Unit of work. Mechanical force has been accurately de- 

 fined only since the notion of work has been introduced into 

 science. The unit of mechanical work admitted iu France 

 is the kilogrammetre ; that is to say, the force necessary to 

 raise the unit of weight the kilogramme to the uuit of 

 height, the metre. 



Electric force is measured by one of its effects, the decom- 

 position of water, for it is demonstrated that to decompose 

 the same volume of water the same quantity of electricity will 

 always be requisite. 



These measures of forces in action furnish, in their turn, 

 the means of estimating the quantity of potential force con- 

 tained in a body. Thus, it will be demonstrated that in a 

 kilogramme of coal, and in the quantity of oxygen necessary 

 to transform that coal into carbonic acid, there were in tension 

 7000 units of heat, since by combining all the heat disen- 

 gaged by combustion, a mass of water of 7000 kilogrammes 

 shall have been heated. 



But a substance which burns is not alwaj'S completely 

 oxidized ; hence, it does not put in action the totality of the 

 force which it contained iu tension. A kilogramme of carbon, 

 for example, may undergo only a first degree of oxidation, and 

 thus becoming oxide of carbon it yields only 5000 units of 

 heat. This oxide of carbon burning in its turn, and becoming 

 carbonic acid, will then yield only the remaining 2000 units 

 of heat. 



Transformation of physical forces takes place, as we have 

 said, without any loss of the transformed force. To demon- 

 strate this, it must be proved that a certain number of units 

 of heat transformed into work, will furnish a constant number 

 of kilogrammetres, and inversely, that this work in becoming 

 heat again, will restore the primitive number of units of heat. 



The science which explains the relations between heat and 

 mechanical work, and fixes the value of the mechanical cqitirnlent 

 (>f licut is called thermo-dynamics. This conception, which is 

 the complement of the theory of the transformation of forces, 

 and which proves that in their transformation they lose 



