168 Prof. J. Perry on the 



electrolytes increase in mean amount of their specific gravities 

 during mixture or dilution ; these statements agree with the 

 usual views entertained on the subject. 



By comparison of these results with those in Table L, and 

 those of Table 1. with one another, it appears, 1st, that increase 

 of mean specific gravity of the two liquids during dilution or 

 mixing occurs not only in cases in which heat is evolved and 

 lost, but also in those in which heat is absorbed and becomes 

 latent ; 2nd, that increase of mean electromotive force of the 

 two liquids also occurs not only in those cases in which heat 

 is absorbed and becomes latent, but also in those in which it 

 is set free. And 3rd, that in 17 cases out of 20 an increase 

 of mean specific gravity of the two liquids was attended by 

 an increase of the mean amount of their electromotive force. 

 We may therefore conclude that in cases of mere physical 

 mixture , the changes of mean specific gravity and of mean elec- 

 tromotive force of electrolytes are probably related to each other 

 as concomitant effects of the same cause, change of molecular 

 motion. From the known general relation of increase of specific 

 gravity to decrease of specific heat, it further suggests the in- 

 ference that in cases of simple dilution the mean electromotive 

 force of electrolytes is related to their mean specific heat. 



As in all such cases, each phenomenon, whether it be physical 

 mixture, dilution, specific gravity, specific heat, latent heat, 

 or electromotive force, involves the mutual action of two sub- 

 stances, it is essentially necessary in every case to ascertain the 

 mean amount of change occurring in the two substances. 



In a separate and more extensive research, not yet pub- 

 lished, I have measured the losses and gains of electromotive 

 force by means of different positive metals in different classes 

 of mixtures of electrolytes, including cases of chemical union 

 as well as of mere physical mixture. 



XXY. The Study of Transformers. 

 By Prof. John Perry, F.R.S., D.Sc* 



[The following paper was written in February last, at a time when I 

 had been compelled to listen to many discussions on the Transformer. 

 It has been nearly forgotten till now ; but I see that it ought to be 

 published now, so that it may precede my paper read four days ago 

 before the Physical Society on ' Mr. Blakesley's method of Measuring 

 Power in Transformers."— 26th May, 1891.] 



I HAVE been engaged on quite other matters during 

 the last few years, and thought a few weeks ago that I 

 must be hopelessly in arrear concerning the subject of 

 * Communicated by the Author, 



