42 Notices respecting New Books. 



those who, like M. Regiiault, follow a route necessarily leading to 

 the end and leaving nothing to chance. The latter improve, rectify, 

 what the others have discovered ; they often complete it ; sometimes 

 they diminish its importance; in all cases they co-ordinate the dif- 

 ferent parts of it, in a manner to render evident the true capacity and 

 just proportions of the new elements with which science is enriched. 

 Without the first, no science ; without the second, no true science. 

 But we shall not further attempt to compare that which, in reality, is 

 not susceptible of it, since the elements of the comparison are so 

 different. Let us confine ourselves to a summary of our idea, in 

 declaring that, if Regnault is the type of one of the schools, Faraday 

 is the glory of the other ; this is to state in two words all that science 

 owes to them, and the services she still expects from them. 



Returning to our subject. The question is the theoretical calcu- 

 lation of the work done by steam-engines, which requires, according 

 to M. Regnault, a knowledge of the following laws and data : — 



1. The law which connects the temperatures and the ela^^tic forces 

 of aqueous vapour in a state of saturation. 



2. I'he quantities of heat which 1 kilogramme of liquid water at 

 0° Cent, must absorb, to be reduced to vapour in a state of satu- 

 ration under different pressures. 



3. The quantities of heat which 1 kilogramme of liquid water at 

 0° Cent, must absorb to elevate its temperature to that at which it 

 becomes vaporized under different pressures. 



4. The specific heat of steam in different states of density and at 

 different temperatures. 



5. The law according to which the density of the steam in a state 

 of saturation varies under different pressures. 



6. The coefficients of the dilatation of steam acquired in its dif- 

 ferent states of density. 



But before entering upon the investigation of these laws, M. 

 Regnault was compelled to undertake long preliminary researches, in 

 order to determine a great number of auxiliary data, which ap- 

 peared fixed with certainty by the earlier labours of other phy- 

 sicists, which however they were not, as experience has shown. 

 These researches are in particular relative to the laws of dilatation 

 and compressibility of elastic fluids, and to the measurement of 

 temperatures. The first seven memoirs contained in the volume 

 before us, are essentially devoted to these. It is only in the three 

 last, the eighth, ninth and tenth, thatM. Regnault begins to attack 

 the very questions, the solution of which was the primitive intention 

 of his great task, in treating the three first points denoted above. 



We reserve the analysis of these last three memoirs for another 

 article. At present we shall confine ourselves to the examination 

 of the preliminary researches. We do not pretend at all, be it un- 

 derstood, to give a complete account of them. Of seven memoirs 

 which are devoted to them, there are three which we shall be con- 

 tent merely to mention, namely, that which relates to the determi- 

 nation of the weight of the litre of air and of the density of mercury, 



