326 Dr. Tyndall on the Progress of the Physical Sciences : 



had been permitted to remain in action for some time was suddenly 

 broken, and the ends of the wires were brought into connexion 

 with the plates of the condenser. The plates were then sepa- 

 rated; one of them was immediately brought into connexion 

 with the electrometer, and the strength of the charge was mea- 

 sured. The results derived from this process are contained in 

 the following table : — 



This table establishes the important result, that the electromo- 

 tive force is proportio?ial to the electric tension at the ends of the 

 newly-broken circuit. 



The following experiments were instituted to ascertain the 

 electroscopic properties of the active simple circuit. The author 

 considers it practically impossible at present to construct an 

 electrometer which shall directly declare the almost infinitesimal 

 tension which obtains at the various points of the simple circuit, 

 and hence the necessity of calling in the aid of the condenser : 

 the manner in which the instrument was charged is as follows : — 



From the lower condensing plate a wire of the same metal as 

 the plate itself proceeded, and was buried in the earth. A 

 branch was earned from this wire to a point a of the closed 

 circuit. When another point, b, of the circuit was brought into 

 metallic connexion with the upper plate of the condenser, it be- 

 came charged to an amount which depends upon the tension 

 existing at b, and on the condensing power of the plates. If 

 several such points, b, be examined, the charges imparted to the 

 condenser will be proportional to the electroscopic tension at the 

 different points. Instead of connecting the lower plate with the 

 earth, we might connect it and the point a directly, and bring 

 the upper plate, as before, into connexion withi; experiment 

 proves that the result obtained from this procedure is exactly 

 the same as that obtained bv the former method. The mode of 



