370 Miscellanies. 



rents, successively produced hy ivfluence was easily observed; tlie 

 needle of the instrument sufFerino- a deviation which caused it to pass 

 throuo-h nearly an entire circumference. Two pieces of platina wire 

 inserted into a vessel of acidulated water and placed in the route of 

 these currents, produced no trace of chemical decomposition. A 

 substitution of iron wire, however, gave rise to bubbles of hydrogen, 

 resulting from the oxydation of the wire. But on putting the bars in 

 motion, so as to cause the currents developed by influence to pass 

 through the liquid, the evolution of gas was much more abundant, 

 and increased with the acceleration of the rotation. 



By a peculiar arrangement of his apparatus, M. Botto succeeded 

 in obtaining separately the two contrary currents, and according to 

 the one passed through the liquid, caused a development of gas at 

 the one or the other pole. The same effects were obtained when a 

 platina wire was substituted for one of the pieces of iron wire, ex- 

 cept that the quantity of evolved gas was more or less considerable 

 according as the current by influence coincided with that proceeding 

 from the small voltaic battery of iron and platinum. When silver 

 wire was used, with a solution of sulphate of copper, metallic copper 

 was deposited on the negative wire. / 



After studying the effects which result from the opposition of the 

 electro-magnetic currents, to those produced by the voltaic elements, 

 our author paid particular attention to a fact, observed by Mananini 

 in regard to the latter, but studied by him with respect to the for- 

 mer. The fact is, that if the copper arc which unites the two li- 

 quids terminates at one extremity in a point and at the other m a 

 broad plate, the transmission of the electro-magnetic current is the 

 most free when the current passes from the liquid through the plate, 

 and consequently from the point into the hquid. 

 . The reverse is the result when a non-oxydable metal, as platmum, 

 is used. 



M. De la Rive explains this phenomenon by supposing that the 

 oxydation which takes place at the positive point of the metallic arc, 

 facilitates the communication and compensates for the less extent ol 

 surface in contact with the liquid ; a compensation which does not 

 happen when the current passes in the contrary direction, as oxyda- 

 tion then takes place on that portion of the surface, which because 

 of its greater dimensions gives the easiest passage to the current. 

 Marianini finding that platinum produces sometimes similar phenom- 

 ena with an oxydable metal, and sometimes the contrary, does not 



