167 



If a gas in a compressed state be allowed to expand by rushing 

 through small apertures, so that the expansive power developed shall 

 all bo converted, first, into tangible motion, and then by friction into 

 heat, while the gas gives out no mechanical power to other bodies, 

 and neither receives nor gives out heat, its condition is expressed by 

 the following equation : — 



O^A^f^A . fQ+/(Q)f /q^_A CvdvX 



-x[a/— c?V-itN (A.- + Ahyp.logr j | 



The cooling effect of a given expansion in atmospheric air, — Ar, 

 has been the subject of experiment. The term 



which represents the heat expended in overcoming molecular attrac- 

 tion, is calculated by means of formulae deduced by the author from 

 M. Regnault's experiments, with the aid of the hypothesis, as well 

 as^ the function by which x is multiplied. Thus each series of ex- 

 periments supplies data for computing an approximate value of x, 

 the absolute temperature of total privation of heat. The values of x 

 thus calculated from ten series of experiments, range from 1°"08 to 

 2''-345 centigrade. The greatest discrepancy is therefore l°-265 

 centigrade, which would cause a maximum error of only one three- 

 hundredth part in calculating the power of any expansive engine. 

 The values of x are both largest, and agree best together, for 

 those experiments in which the quantity of air used was greatest, 

 and therefore the risk of error least. The author considers that the 

 experiments prove the formulae deduced from the Hypothesis of Mo- 

 lecular Vortices to be at least sufficiently correct for practical pur- 

 poses ; that they afford a strong probability of the theoretical sound- 

 ness of the hypothesis ; and that the position of the absolute zero of 

 heat is neai'ly as follows : — 



Centigrade. Fahren. 

 Above absolute zero of a perfect gas thermometer, . 2°'l 3°'78 



Below the temperature of melting ice, . . . 272°-5 490''-6 



The paper concludes with formula} for future use in reducing ex- 

 periments on Carbonic Acid Gas. 



