52 



Tables of the values of these quantities, for different ranges, ob- 

 tained by using the values of ^ shown in Table I. of the author's 

 Account of Carnot's Theory, are given. An application to the case of 

 the Fowey-Consols engine which, according to the data quoted in the 

 Appendix to that paper, appears to have worked at 76 per cent, of 

 the true duty for its range of temperature (which was assumed to be 

 from 30° to 140° cent.), instead of only 67 per cent, of the duty 

 according to Carnot's Theory ; and to have emitted into the con- 

 denser only 82 per cent, of the heat taken in at the boiler, the re- 

 maining 18 per cent, having been converted into mechanical effect. 



It is shown that the advantage originally pointed out by Carnot 

 may be still anticipated from the use of air instead of steam, as the 

 effective range of temperature of the air-engine can be made much 

 greater than is practicable in the case of the steam-engine. As an 

 example of the economy attainable by using a large range, it is 

 shown that, with a range of from 0°to 600° cent., about three-fourths 

 of the full equivalent is attainable by a perfect engine, while with 

 the range from 30° to 140°, which is about the greatest that is 

 practicable with steam-engines, even a perfect engine could not ob- 

 tain more than 27, or about one-fourth of the full equivalent of the 

 heat used. 



The third part of the paper contains investigations of some for- 

 mulae with reference to the specific heats of substances of any kind, 

 derived from the equations which express the two fundamental pro- 

 positions. It contains also an application of these equations to the 

 case of a medium consisting of two parts, of the same substance, at 

 the same temperature, in different states. The results are appli- 

 cable both to the effects of pressure on the melting points of solids, 

 and to the conditions of saturated vapours. One of the conclusions 

 pointed out is, the very remarkable property of saturated steam, that 

 its *' specific heat is negative," which was discovered independently 

 by Rankine and Clausius. 



The following Donations to the Library were announced : — 



Philosophical Transactions of the Eoyal Society of London, for the 

 year 1850. Part 2, 4to. — From the Society. 



Observations on Days of unusual Magnetic Disturbance, made at 

 the British Colonial Magnetic Observatories, undei' the depart- 



