186 APPENDIX. 



IV. TRANSMISSION FROM THE BOILER TO THE CYLINDER. 



M. Pambour professes to determine the velocities on considerations of a novel nature, which 

 may be briefly explained, thus : If the evaporating power of the boiler be capable of supplying 

 a greater quantity of steam, at the required pressure, than is consumed at the successive 

 strokes of the piston, it is evident that the pressure of the steam in the boiler will gradually 

 increase, provided no portion is supposed to escape through the safety valve or otherwise. 

 This increasing pressure will gradually accelerate the velocity ; and finally, when the engine 

 attains her permanent speed, the quantity of steam consumed in the cylinder and supplied 

 through the steam pipe, must evidently correspond with the quantity evaporated by the 

 boiler. Thus he pretends to introduce a new element into the calculation, viz., the evapo- 

 rating power of the boiler, which again is to be estimated by the quantity of fire surface ; and, 

 the density of steam at a given temperature being, according to the law of Boyle and Mariotte, 

 proportional to the pressure and inversely as the volume, as in the case of gases, the evapo- 

 rating power is measured by the volume of steam, generated in a given time, multiplied into 

 its pressure. We submit, however, that M. Pambour is mistaken if he supposes such a mode 

 of proceeding to involve any new doctrine, or any principle that had not already been laid 

 down by Mr. Tredgold in the first edition of this work. In support of this statement we 

 need only refer to the equations (F), (G), which are founded on Tredgold's well-known rule for 

 calculating the power of an engine, and from which it will appear that he measures the power 

 by the quantity of steam effectively consumed in the cylinder per minute, multiplied into its 

 pressure. Indeed, the preceding equations (A), (B), (C), (D), (E), (F), (G), which are strictly 

 in accordance with the principles laid down by Tredgold, constitute the whole of our scientific 

 information on the power of the steam engine that has hitherto been established on theoretical 

 principles. No scientific theorist or experimentalist has yet satisfactorily ascertained the laws 

 which regulate the transmission of the steam from the boiler to the cylinder, 1 and we cannot, 

 therefore, be surprised that Tredgold has treated this part of the subject in a very slight and 

 imperfect manner. We here allude to Art. 396, which has especially been objected to by the 

 Chev. de Pambour, in a Memoir on the Steam Engine, just published in the form of a 

 pamphlet by Mr. Weale. With this we may include Articles 402, 408, 416, and 426 ; and we 



1 It is impossible that this difficulty can ever he properly surmounted until we first determine either the specific heat of 

 steam, or the whole quantity of heat contained in a given volume of steam at a given temperature and pressure. A decisive 

 step towards the solution of this most important problem has been effected by E. Clapeyron, in a Memoir inserted in the 

 ' Journal de 1'Ecole Royale Fob/technique,' vol. xiv. page 153. The investigation is conducted on a principle which to all 

 appearance is deserving of credit, viz., that no power can possibly be created or generated without the transmission of a 

 portion of heat, and that the amount of power must be wholly independent of the nature of the medium of transmission. 

 The latter condition depends on the former ; for if the power developed varied with the nature of the medium, a quantity of 

 heat being transmitted by one medium and returned by another, a portion of power might be so gained or lost without any 

 resulting or effective transmission. In this principle it is of course assumed that no loss of power or vis viva is occasioned by 

 contact of bodies of different temperatures. The application of it is very ingenious, and leads to the following expression for 

 the whole quantity (Q) of heat contained in a volume (B) of steam at the pressure (p), viz., 



Q =/0> ) - F (p . ) hyp. log. JB, 



in whichy (p . ), F (/).) denote functions of the product (p . ) of the pressure and volume, the nature of which functions 

 still remain to be determined before the solution can be considered to be complete. It is found by experiments, that the latter 

 function increases gradually with the temperature. 



