Phenomena of Ordinary Electricity, 167 



nerally, progressive forces. By arrangement, I understand a 

 local adjustment of particles, or fluids, or forces, not progres- 

 sive. Many other reasons might be urged in support of the 

 view of a current rather than an arrangement, but I am 

 anxious to avoid dilating unnecessarily upon what can be 

 supplied by others at the moment. 



II. Ordinary Electricity, 



284-. By ordinary electricity I understand that which can 

 be obtained from the common machine, or from the atmo- 

 sphere, or by pressure, or cleavage of crystals, or by a mul- 

 titude of other operations ; its distinctive character being that 

 of great intensity, and the exertion of attractive and repulsive 

 powers, not merely at sensible but at considerable distances. 



285. Tension. The attractions and repulsions at sensible 

 distances, caused by ordinary electricity, are well known to 

 be so powerful in certain cases, as to surpass, almost infinitely, 

 the similar phasnomena produced by electricity, considered as 

 of other kinds. But still those attractions and repulsions are 

 exactly of the same nature as those already referred to under 

 the head Tension, Voltaic electricity (268.); and the difference 

 in degree between them is not greater than often occurs be- 

 tween cases of ordinary electricity only. I think it will be 

 unnecessary to enter minutely into the proofs of the identity 

 of this character in the two instances. They are abundant; 

 are generally admitted as good ; and lie upon the surface of 

 the subject : and whenever in other parts of the comparison 

 I am about to draw, a similar case occurs, I shall content my- 

 self with a mere announcement of the similarity, expanding 

 only upon those parts where the great question of distinction 

 or identity is still controverted. 



286. The discharge of common electricity through heated 

 air is a well-known fact. The parallel case of voltaic electri- 

 city has already been described (272, &c). 



287. In motion, i. Evolution of Heat. The heating power 

 of common electricity when passed through wires or other 

 substances, is perfectly well known. The accordance between 

 it and voltaic electricity is in this respect complete. Mr. 

 Harris has constructed and described* a very beautiful and 

 sensible instrument on this principle, in which the heat pro- 

 duced in a wire by the discharge of a mere spark of common 

 electricity is readily shown, and to which I shall have occa- 



* Philosophical Transactions, 1827, p. 18. Edinburgh Transactions,1831. 

 Harris on a New Electrometer, &c. &c. 



