26 NOMOS. 



leave in the smallest degree perfection at either ex- 

 tremity, we involve the element of perfection at the 

 other end ? especially, too, as we have not in 

 nature the case of perfection, either at one extremity 

 or the other, either of insulation or conduction." * 



Conduction, moreover, is intimately connected 

 with the spark, and not with this mode of discharge 

 only; but we will only now speak of the spark. 

 This luminous phenomenon, then, is not confined 

 to the air ; on the contrary, it may be obtained in 

 oil of turpentine, in olive oil, in resin, in glass. A 

 metal wire will also ignite when it is not large 

 enough to transmit the electric current; and what 

 is to separate this luminous condition from the ordi- 

 nary electric spark ? Is it not directly allied to the 

 spark by the luminous discharges which occur in 

 glass, in resin, in oil, and in turpentine? And if 

 so, where does the process of conduction end? 

 There is, indeed, no end ; and we may say indiffe- 

 rently that the luminosity of the wire is owing to 

 discharge between the several component molecules, 

 or that the ordinary spark is the consequence of 

 conduction between the aerial particles. Discharge 

 and conduction, indeed, go hand in hand in a beau- 

 tiful experiment by Sir T. Snow Harris. A fine 

 platinum wire is stretched across a glass globe con- 

 taining highly rarified air, and a current of electricity 

 is passed through the wire, when the wire and the 

 rarified air surrounding it both become luminous. 

 The wire is not sufficient to carry the current, and 

 part of the duty devolves upon the air; the one 



* Op. cit. p. 421. 



