and the Laws regarding the Nature of Heat. 17 



entertained on this subject ; I believe_, however, that no experi- 

 ment can be found which contradicts it. On the contrary, it 

 harmonizes with the observations of Pambour better than the 

 common notion. Pambour found* that the steam issuing from 

 a locomotive after a journey always possesses the temperature 

 for which the tension observed at the same time is a maximum. 

 From this it follows that h is either 0, as was then supposed, 

 because this agreed with the law of Watt, which was considered 

 correct at the time, or that h is negative. If h were positive, then 

 the temperature of the issuing steam must have been too high 

 in comparison with its tension, and this could not have escaped 

 Pambour. If, on the contraiy, in agreement with the above, h be 

 negative, too low a temperature cannot occur, but a portion of the 

 vapour wdll be converted into water so as to preserve the remainder 

 at its proper temperature. This portion is not necessarily large, 

 as a small quantity of vapour imparts a comparatively large 

 quantity of heat by its precipitation ; the water thus formed is 

 probably carried forward mechanically by the steam, and might 

 remain unregarded ; the more so, as, even if observed, it might 

 have been imagined to proceed from the boiler. 



So far the consequences have been deduced from the above 

 maxim alone, without any new assumption whatever being made. 

 Nevertheless, by availing ourselves of a very natural incidental 

 assumption, the equation for permanent gases (II«.) may be ren- 

 dered considerably more productive. Gases exhibit in their de- 

 portment, particularly as regards the relations of volume, tem- 

 perature and pressure, expressed by the laws of M. and G., so 

 much regularity as to lead us to the notion that the mutual 

 attraction of the particles which takes place in solid and fluid 

 bodies is in their case annulled ; so that while with solids and 

 fluids the heat necessary to efi*ect an expansion has to contend 

 with both an inner and an outer resistance, the latter only is 

 effective in the case of gases. If this be the case, then, by the 

 expansion of a gas, only so much heat can be rendered latent as 

 is necessary to exterior work. Further, there is no reason to 

 suppose that a gas, after it has expanded at a constant tempera- 

 ture, contains more sensible heat "than before. If this also be 

 admitted, we obtain the proposition, when a permanent gas ex- 

 pands at a constant temperature, it absorbs only as much heat as is 

 necessary to the exterior work produced by the expansion ; a pro- 

 position which is probably true for all gases in the same degree 

 as the law of M. and G. 



From this immediately follows 



■«\-A.Ki±i, (9.) 



o- 



* Traite des locomotives, 2nd edit., and Theorie des machines a vapeur, 

 2nd edit. 



Phil, Mag, S. 4. Vol. 2, No. 8. July 1851. C 



