VARIOUS VIEWS OF CONTACT AND CHEMICAL EXCITEMENT. 
63 
have this property, yet the degree in which they possess it is unworthy of considera- 
tion in comparison with the degree to which it rises amongst the metals*. The present 
views of the Italian and German contact philosophers are, I believe, generally the 
same, except that occasionally more importance is attached to the contact of the im- 
perfect conductors with the metals. Thus Zamboni (in 1837) considers the metallic 
contact as the most powerful source of electricity, and not that of the metals with 
the fluids 'f' ; but Karsten, holding the contact theory, transfers the electromotive 
force to the contact of the fluids with the solid conductors;};. Marianini holds the 
same view of the principle of contact, with this addition, that actual contact is not 
required to the exertion of the exciting force, but that the two approximated dissi- 
milar conductors may affect each other’s state, when separated by sensible intervals of 
the T ^a- W dth of a line and more, air intervening §. 
1801 . De la Rive, on the contrary, contends for simple and strict chemical action, 
and, as far as I am aware, admits of no current in the voltaic pile that is not conjoined 
with and dependent upon a complete chemical effect. That admirable electrician 
Becquerel, though expressing himself with great caution, seems to admit the possi- 
bility of chemical attractions being able to produce electrical currents when they are 
not strong enough to overcome the force of cohesion, and so terminate in combina- 
tion ||. Schienbein states that a current may be produced by a tendency to chemical 
action, i. e. that substances which have a tendency to unite chemically may produce 
a current, though that tendency is not followed up by the actual combination of the 
substances^. In these cases the assigned force becomes the same as the contact of 
Volta, inasmuch as the acting matters are not altered whilst producing the current. 
Davy’s opinion was, that contact like that of Volta excited the current or was the 
cause of it, but that chemical changes supplied the current. For myself I am at pre- 
sent of the opinion which De la Rive holds, and do not think that, in the voltaic 
pile, mere contact does anything in the excitation of the current, except as it is pre- 
paratory to, and ends in, complete chemical action (1741. 1745.). 
1802. Thus the views of contact vary, and it may be said that they pass gradually 
from one to another, even to the extent of including chemical action : but the two 
extremes appear to me irreconcilable in principle under any shape ; they are as fol- 
lows. The contact theory assumes, that when two different bodies being conductors 
of electricity are in contact, there is a force at the point of contact by which one of 
the bodies gives a part of its natural portion of electricity to the other body, which 
the latter takes in addition to its own natural portion ; that, though the touching 
points have thus respectively given and taken electricity, they cannot retain the 
charge which their contact has caused, but discharge their electricities to the masses 
* Annales de Chimie, 1802, xl. p. 225. f Bibliothbque Universelle, 1836, v. 387 ; 1837, viii. 189. 
+ L Institute, No. 150. § Mem. della Soc. Ital. in Modena, 1837, xxi. 232—237. 
|| Annales de Chimie, 1835, lx. 171 ; and Traite de l’Electricite, i. pp. 253, 258. 
H Philosophical Magazine, 1838, xii. 227, 311, 314; also Bibliotheque Universelle, 1838, xiv. 155, 395. 
