Academy of Sciences in Paris. 369 



Thus, either the peroxide of manganese, silver, or sulphate of iron, 

 filed into very small particles and thrown on to a plate of zinc, tin, or 

 gold in motion, assumes a negative electricity. Filings of zinc when 

 thrown upon a plate of the same metal in motion exhibit no electri- 

 city, but become electric when the plate is in repose. Hence 

 it appears that the swiftness of rotation augments the negative 

 tendency of the zinc plate, probably by producing a concussion of 

 all the molecules on the surface. There is great reason to suppose 

 that the electric effects of decomposition and recomposition, operated 

 during the concussion of the molecules, may furnish a clue to the 

 cause of the magnetic phenomena observed by M. Arago in metallic 

 plates when in motion. The general result of all M. Becquerers 

 experiments establishes that, when friction is produced between any 

 two metals whatever, either in repose or in motion, that metal the 

 parts of whose surface are most displaced becomes affected with ne- 

 gative electricity. 



M. Becquerel also examines the effect of friction in bodies which 

 are bad conductors of electricity ; and although the variation of these 

 effects, according to the state of the surfaces, renders the solution of 

 the problem more difficult than when metals are employed, the rela- 

 tion between the phenomena in the two classes is plainly to be per- 

 ceived. Thus fibrous substances are more strongly susceptible of 

 electric affection than other bodies, because their particles are more 

 easily displaced ; for the same reason, heat augments the negative 

 tendency of bodies. From these experiments M. Becquerel was 

 easily led to consider the phenomenon of phosphorescence, and a 

 great number of experiments have convinced him that electricity is 

 disengaged whenever a change of equilibrium is operated in the 

 molecules of bodies. This phenomenon he considers to consist in 

 the separation of the two electricities, the composition of which pro- 

 duces, according to its greater or less rapidity, light, heat, chemical 

 or magnetic effects. 



Phosphorescence is produced by heat, light, percussion, the electric 

 shock, certain chemical actions, and sometimes by the exposure to 

 a high temperature, which occasions the body to lose its faculty of 

 entering into combination with others. M. Becquerel proves that all 

 these causes may disturb the equilibrium of the electric forces with- 

 out occasioning free electricity to be disengaged. He has also 

 proved that, when two bodies combine, that which acts the part of 

 acid assumes, with respect to the other, a positive electricity, and that 

 which acts the part of alkali assumes a negative electricity. In 

 many cases these two electricities instantly recombine ; but when 

 the action is slow and the bodies are bad conductors, recomposition 

 does not take place until the two electricities have both acquired a 

 tension sufficient to enable them to overcome the obstacle opposed 

 to their reunion by the want of conductibility. This is probably the 

 cause of the phosphorescence produced in some slow chemical ac- 

 tions which take place spontaneously in the air, as in the earthy 



