144 Analyses of Books. [Feb. 



dent, after some prefatory remarks, " is known to increase in a 

 much higher ratio than the arithmetical one of the temperature ; 

 but the exact law is not yet, determined ; and the result is 

 a complicated one, and depends upon circumstances which 

 require to be ascertained by experiment. Thus the ratio of the 

 elastic force, dependent upon pressure, is to be combined with 

 that of the expansive force dependent upon temperature ; and 

 the greater loss of radiant heat at high temperatures, and the 

 developement of latent heat in compression, and the necessity 

 for its reabsorption in expansion (as the rationale of the subject 

 is at present understood) must awaken some doubts as to the 

 economical results to be obtained by employing the steam of 

 water under very great pressures, and at very elevated temper- 

 atures. 



" No such doubts, however, can arise with respect to the use 

 of such liquids, as require for their existence even a compression 

 equal to that of the weight of 30 or 40 atmospheres : and where 

 common temperatures, or slight elevations of them, are sufficient 

 to produce an immense elastic force ; and when the principal 

 question to be discussed is whether the effect of mechanical 

 motion is to be most easily produced by an increase or diminu- 

 tion of heat by artificial means. 



" With the assistance of Mr. Faraday I have made some 

 experiments on this subject, and the results have answered my 

 most sanguine expectations. Sulphuretted hydrogen, which 

 condenses readily at 3° Fahr. under a pressure equal to that 

 which balances the elastic force of an atmosphere compressed 

 to T ' T , had its elastic force increased so as to equal that of an 

 atmosphere compressed to T ' T by an increase of 47° of temper- 

 ature. Liquid muriatic acid at 3° exerted an elastic force equi- 

 valent to that of an atmosphere compressed to -^ ; by an 

 increase of 22°, it gained an elastic force equivalent to that of 

 an atmosphere compressed to ? ' T ; and by a further addition 

 of 26°, an elastic force equivalent to that of air condensed to 

 ■^t, of its primitive volume. These experiments were made in 

 thick glass tubes hermetically sealed. The degree of pressure 

 was estimated by the change of volume of air confined by mer- 

 cury in a small graduated gage, and placed in a part of the tube 

 exposed to the atmosphere, and the temperatures were dimi- 

 nished from the degree at which the gage was introduced, i. e. 

 the atmospheric temperature by freezing mixtures ; so that the 

 temperature of the air within the gage could not be considerably 

 altered ; and as the elastic fluid surrounding the gage must have 

 had a higher temperature than the condensed fluid, the diminu- 

 tion of the elastic force of the vapour from the fluids cannot be 

 considered as overrated. 



" From the immense differences between the increase of elastic 

 force in gases under high and low pressures, by similar incre- 



