Proceedings of the British Association. 217 



tulated the history of this part of electrical science, and resumed 

 by saying, that between the two extremes of electric omnipotence 

 and of electric nullity, which have been attributed to the friction of 

 conductors, he endeavoured to find out the mean course of truth. 

 The first step he reached in this career by a great variety of experi- 

 ments, (on different groups of metals, their primitive temperature 

 being equal to that of the surrounding space, or lower or higher than 

 it,) was, that the effect of such friction is always like that of an 

 addition of heat to the point of contact. This was shown, among 

 other methods, by the fact that groups of metals which, by difference 

 of temperature, give rise to an electric current of an anomalous weak^ 

 ness or direction, act similarly when rubbed. This applies to galena, 

 sulphuret of molybdena, and some others. In allusion to this in- 

 termediate office of heat, our author calls the dynamical electricity 

 produced by the friction of conductors, the tribo-thermic electricity. 

 But now the wonders and paradoxes which happen where things are 

 in the status nascendi present themselves once more in this case; 

 but when exerting its tribo-thermic effect, it is neither like conducted 

 heat nor like radiant heat. Indeed, its production when friction 

 commences, and its disappearance when friction ceases, prove entirely 

 independent of the mass of the rubbing bodies ; and almost inde- 

 pendent, also, of the duration of the process which produces it. 

 M. Erman points out, that these remarkable facts seem to be highly 

 favourable to the supposition of a peculiar kind of molecular vibra- 

 tion, excited exclusively in the rubbed points, and spreading through 

 the conducting medium as instantaneously as electricity does. Con- 

 nected with this fact is a circumstance which M. Erman thinks will 

 be used for the measurement of tribo-thermic effects, almost in the 

 same way as the two fixed points of our thermometers are used 

 for temperature ; viz. — there exists, for any group of thermo-electric 

 metals, a given positive and a given negative difference, between 

 their temperature and that of the surrounding space, which, when 

 previously existing at the point of contact, continued friction will 

 have no further influence on the electric current. In another part 

 of this valuable paper, M. Erman reports some facts connected with 

 the brilliant discovery of Peltier, that, according to the direction in 



