MOTIVE POWER OF HEAT. 129 



through the medium of certain simple operations, 

 may be clearly appreciated. Thus it is that 

 Carnot, in accordance with the strictest principles 

 of philosophy, enters upon the investigation of the 

 theory of the motive power of heat. 



2. The sole effect to be contemplated in inves- 

 tigating the motive power of heat is resistance 

 overcome, or, as it is frequently called, " work per- 

 formed" or " mechanical effect" The questions to 

 be resolved by a complete theory of the subject are 

 the following: 



(1) What is the precise nature of the thermal 

 agency by means of which mechanical effect is to 

 be produced, without effects of any other kind? 



(2) How may the amount of this thermal 

 agency necessary for performing a given quantity 

 of work be estimated? 



3. In the following paper I shall commence by 

 giving a short abstract of the reasoning by which 

 Carnot is led to an answer to the first of these 

 questions ; I shall then explain the investigation 

 by which, in accordance with his theory, the ex- 

 perimental elements necessary for answering the 

 second question are indicated ; and, in conclusion, 

 I shall state the data supplied by Regnault's recent 

 observations on steam, and apply them to obtain, 

 as approximately as the present state of experi- 



