Prof. Volpicelli on Fridional Electricity. 29 



by the hand at the other, it will change the nature of its polarity. 

 Hei'e, however, it is important to observe that, contrary to the 

 deportment of resin and glass, energetic friction tends to deve- 

 lope jjositive, gentle friction negative electricity. 



Although it would be premature at present to attempt to 

 explain the alternate phsenomena above described, one or two 

 hypotheses may be safely advanced. The change of temj)erature 

 consequent upon more or less energetic friction can at most have 

 but an indirect influence on the effects. To be convinced of this, 

 it will be suflicient to recall the following facts : — 



First. The contrary electricities may be made to succeed each 

 other as rapidly as may be desired, each by a single stroke dif- 

 fering very little in energy from the preceding one, and hence 

 producing no sensible variation in temperature, especially after 

 the alternations have been continued for some time. 



Secondly. A rod of glass or resin may be made to manifest 

 both kinds of electricity at one and the same time, its tempera- 

 ture remaining sensibly the same throughout its whole length. 



Thirdly. Negative electricity may be changed to positive by 

 passing the rubber alongside the rod without contact. 



Fourthly. At the commencement, positive electricity may be 

 developed on glass or resin by means of very gentle friction, 

 which will be accompanied by a small elevation of temperature ; 

 afterwards more energetic friction may increase the temperature 

 greatly, and still not change the nature of the electricity. 



These and many other facts would lead us to believe that 

 change of temperature cannot be regarded as a direct cause of 

 the phsenomena under consideration ; indirectly, however, by 

 facilitating more or less the vibration of the superficial molecules 

 of the body, temperature is no doubt influential. The cause of 

 the alternate effects must, in fact, be sought in the different 

 kinds of vibration imparted to the molecules of the body; the 

 experiments described appear to indicate that a mere difference 

 in the amplitude of these vibrations may be sufficient to alter the 

 electric state, — a greater amplitude (at least in resin and glass) 

 corresponding to negative, a less to positive electricity, greater 

 and less having reference to a certain mean amplitude which 

 corresponds to a neutral electric state. 



The electric state of a body depending so essentially upon the 

 quantitij of motion impressed upon its superficial molecules, it 

 can no longer surprise that one and the same body entering into 

 different chemical combinations should act at one time as the 

 electro-positive, and at another as the electro-negative element. 

 The distinction between vitreous and resinous electricity is at 

 once seen to be untenable; and the electricMJ classification of 

 bodies given in most physical works, and founded upon the 



