552 KEPORT— 1881. 



4. On Volta-Elecfric Inversion. Bi/ Professor Silvanus P. Thompson, 



b.aI, D.Sc. 



The author gives the name of volta-electric invergion to a phenomenon which is,, 

 for voltaic currents, the precise analogue of the thermo-electric inversion discovered 

 by Gumming- in the case of thermo-electric currents. 



It is known that when voltaic cells are heated both their resistance and their 

 E.M.F. are afiected. The latter sometimes increases, sometimes diminishes. The 

 latter phenomenon led the author to suspect the existence of a volta-electric inver— 

 sion. This he discovered as occurring in a cell containing sulphuric acid of density 

 1"753, into whicli dipped electrodes of iron and copper. At 25° C. this cell gave 

 a current which flowed through the liquid from iron to copper, the iron dissolving 

 in the acid, with evolution of hydrogen at the copper pole. On heating the cell the 

 current fell oft^ and became null between 140° and 150°, when it recommenced 

 powerfidly in the inverse direction, bubbles believed to be SO.j coming oft" from the 

 iron pole, the copper pole dissolving m the acid. The currents in question were 

 true voltaic currents, being of much greater E.M.F. than the thermo-currentsof an 

 iron-copper pair, and being moreover accompanied by strong cliemical action in 

 the cell. The author cited as explanatory of this eftect some experiments of War- 

 burg on the electrolysis of strong sulphuric acid, whicli when electrolysed below 

 80° C. yielded only and H gases ; between 80° and 90° gave O at anode and at 

 kathode II and S ; Init above 90° gave O at anode, S only at kathode. It was 

 fiu'ther pointed out that this discovery rendered possible a battery of two metals 

 and one liquid, from which a constant current could be obtained without contact 

 of dissimilar metals, alternate cells in the series being heated ; and the copper of 

 one cell should be joined to the copper of the next, and the iron of this to the iron- 

 of the next. 



6. On the Eotational Coefficient in Variotis Metals. By E. H. Hall. 



This communication treated of the recently discovered fact that when a con- 

 ductor bearing an electric current is acted upon by a magnetic force at right angles 

 to the ciurent, an electro-motive force is set up in the conductor, the direction of 

 this force being perpendicidar to the plane of the electric current and the magnetic 

 force. 



Several articles upon the subject have already been published, but the present 

 communication made known a few new facts not yet in print which had been 

 ascertained quite recently during the author's short stay in the laboratory of Prof. 

 Helmholtz in Berlin. 



The numerical -n alues given in the table below are in any case only tentative,, 

 and those which are marked thus (?) are particularly uncertain, being liable to 

 errors of perhaps 100 per cent, or more. It is believed, however, that in every 

 case the sign fixed to any number is correct. 



Arranging the metals thus far examined in the order of magnitude of the trans- 

 vei-se effect in them, we obtain the following table. 



The numbers given are intended to be p}-0]}ort.ional only to the magnitude of the- 

 transverse effect, and not to have any absolute significance. 



Iron 



Cobalt 



Zinc 



Lead 



Tin 



Brass ....... 



Platinum ...... 



Gold 



Silver 



Copper 



Aluminium ...... 



Magnesium 



Nickel -120 



