300 Intelligence and Miscellaneous Articles. 



"b 



upon the zinc surface of the condenser, and consequently produces 

 (whatever M. Pfaffmay say) an electrical effect, the nature of which 

 always corresponds with what ought to occur, according to the che- 

 mical theory. I have not confined myself to negative experiments, 

 although their number and agreement gave me the utmost confidence 

 in them ; but 1 have endeavoured also to discover such as would yield 

 positive results. In this way I have obtained signs of electricity, 

 under circumstances in which according to the theory of contact I 

 ought not to have procured the slightest trace. 1 will give an example 

 of this : In each end of a cylinder of wood from ten to twelve centi- 

 metres long, and from one to two in diameter, I inserted a plate of 

 zinc terminated externally by a brass end, which was soldered to it ; 

 holding in my hand the brass end of one of these plates, I touched the 

 condenser (also of brass) with the brass end of the other. According 

 to the theory of contact, I ought not to have obtained any sign of 

 electricity, the two plates of zinc with brass being opposed and united 

 by an insulated piece of wood, serving as a conductor from one to the 

 other. Nevertheless, one of the ends of the wooden cylinder being a 

 little more damp than the other, I obtained signs of electricity, the na- 

 ture of which always agreed with the slight chemical action arising 

 from the contact of the well cleaned zinc with the damp wood. These 

 signs were positive, if I held the brass end of the plate inserted in 

 the least damp end of the wood. In order to succeed in the experi- 

 ment, the wood must be slightly moistened ; the humidity which it 

 acquires in moist air is quite sufficient ; care must be taken to keep 

 one of the ends drier than the other. It appears to me impossible, as 

 I have endeavoured to show in my memoir, to reconcile this fact, when 

 carefully examined in all its details, with the theory of contact." 



M. Delarive, while he denies that the contact of two heterogeneous 

 substances can be the cause of developing electricity, admits that it 

 may often be a necessary condition. As to the real cause, it is always 

 either 



Physical, as heat. M. Becquerel has given, he observes, a complete 

 and satisfactory analysis of this cause in his last memoir upon thermo- 

 electrical currents; — or 



Chemical. M. Delarive has already shown in his preceding memoirs, 

 how he regards this kind of action ; — or 



Mechanical. There still remains, the author observes, much to be 

 done, in arranging according to general principles the mechanical 

 processes for exciting electricity, such as friction and pressure. He 

 has already had occasion to make a considerable number of observa- 

 tions relating to friction. When rubbing, he says, a very dry finger, 

 a cork, or a piece of wood, upon a piece of metal, of a cubic form, for 

 example, placed upon a condenser, electrical appearances of astonish- 

 ing intensity are developed, which are sometimes negative and some- 

 times positive. The nature of the electricity depends upon the kind 

 of metal, its figure, temperature, the manner in which it is rubbed, 

 whether upon an edge or a face ; the nature of the rubbing body, 

 which should always be an imperfect conductor, has but little influ- 

 ence. M. Delarive states, that in all his experiments he carefully 



avoided 



