464 Mr. W. T. A. Eintage on the Velocities of 



Summary of Principal Conclusions. 



In calculating the theoretical electromotive force of voltaic 

 cells from thermochemical data the chemical attraction of a 

 haloid cation for the positive plate (measured by its combining 

 heat with this) does not, so far as these experiments tend to 

 show, enter into the calculation. The cation behaves as if 

 inert, like hydrogen or metals in the commoner forms of cell 

 (§§ 23 to 27) ; 



The attraction of the haloid cation for the negative plate, 

 when the latter is a metal (or so-called electropositive element) 

 does also not enter into the calculation, but its attraction for 

 a so-called electronegative element (e. g. oxygen) may in 

 certain conditions influence the result (§§ 23 to 27). 



The chlorides of iodine and of bromine in aqueous solutions 

 are decomposed by small electromotive forces, corresponding 

 to their small heats of combination, and the secondary electro- 

 motive force in these solutions is of the same order (§§ 11, 12). 



The electromotive force of cells with iodine- or bromine- 

 chloride solutions as electrolytes is not decreased after tem- 

 porary short-circuiting. They do not " polarize " like cells 

 containing hydrogen chloride. 



Dry iodine chloride is a good conductor and electrolyte 

 (§§8,9). 



Dry bromine chloride, a chemically similar body, does not 

 conduct at all (§§ 18,19). 



The chlorides of phosphorus and sulphur and several of 

 their double salts are not electrolytes (§ 22). 



LVIII. On a Method of Determining the Velocities of Propa- 

 gation of Disturbances in Elastic Media. By W. T. A. 

 Emtage*. 



WHEN a disturbance of any sort is travelling through 

 an elastic medium so that all parts of the medium, 

 after the disturbance has passed them, are left at rest, and in 

 the same relative positions as they had before the disturbance 

 reached them, we may investigate the velocity of propagation 

 of the disturbance in a simple manner as follows. 



First, consider the momentum generated in any portion of 

 the medium by the entrance of the disturbance into it. This 

 will be proportional to the velocity of propagation. Next, 

 consider the time integral of the forces producing this mo- 

 mentum ; that is, find the mean resulting force acting on the 



* Communicated by the Author. 



