512 Mr. R. E. Baynes on the Steam and 



increased. Now this may take place by the vibration-period 

 diminishing while the amplitudes remain unaltered or even 

 become smaller than before. When the last-mentioned takes 

 place, the action of the attraction-force which tends to carry 

 the electric molecules from N to M becomes feebler at the 

 higher than at the lower temperature ; and hence there results 

 in the thermoelectric ring a current running in the contrary 

 direction to that current which is produced by a smaller tem- 

 perature-difference between the two junctions. Herein is to 

 be seen the cause of the known alteration of the current- 

 direction shown by several metallic combinations with great 

 difference of temperature between the junctions *. 



If, therefore, it be admitted that the electric fluid consists 

 of the luminiferous sether, it may be regarded as proved that 

 contact electromotive force must vary with the temperature — 

 a relation which, besides, has been, in my opinion, practically 

 demonstrated by Le Eoux f. 



Stockholm, June 3, 1876. 



LXVIII. Note on the Steam and Hoar-frost Lines of Water- 

 Substance. By Robert E. Baynes, M.A., Senior Student 

 of Christ Church, Oxford, and Lee\ Reader in Physics%. 



IN the ' Report of the British Association ' (1872), ii. p. 24, 

 and the i Proceedings ' of the Royal Society (1873), xxii. 

 p. 27, Prof. James Thomson shows that the steam and hoar- 

 frost .lines of water-substance (to use Prof. Maxwell's terms for 

 the curves p=f(t), p f =f'(f), which represent the maximum 

 tension of steam in contact with water and ice respectively) 

 are not continuous, as M. Regnault thought, but intersect at 

 an angle which is re-entrant downwards. Two proofs of this 

 are given: — one, that in any other case the perpetual motion 



dry dr) 

 might subsist ; the other, that the values of -~, ~ at 0° C. 



are theoretically in the ratio of 1 to 1*13, while M. Regnault's 

 empirical formulas give the ratio 1 to 1-10. 



* In consequence of Prof. Clausius maintaining* that thermoelectric 

 force cannot arise from the contact-electromotive force changing with 

 the temperature, F. Kohlrausch has (Pogg. Ann. yol. clvi.) set up the 

 hypothesis that these forces are not in any way connected with one ano- 

 ther, but that it is much more probable that the thermoeiectromotive 

 force is caused by the heat-current from the hotter to the cooler contact, 

 and is proportional to this heat-current. M. Kohlrausch, however, has not 

 shown the physical necessity or the possibility of such a connexion between 

 these phenomena. 



t Annates de Chimie et de Physique, (4) t. x. 



\ Communicated by the Author. 



