TEANSACTIONS OF SECTION A. 6! "I 



the ends of which are connacted with the ends of the standard resistance, and 

 observing whether any deflection is obtained by*closing this circuit. 



STANDAifB»-fi£SlS.Z^AICE 



'v'X^v ^ ysy^ ^ \ .'V v^.A^N/\ 'V'^^'^'JAA Ayv\/Vl_ 



pRQUADT ELECT} 



Suppose, for example, the standard resistance to be 10 ohms, and the current 

 as indicated by the balance, 0-108 amperes ; when no deflection is obtained on the 

 mirror galvanometer by closing its circuit, the potential of the cell is 10 x -108, or 

 1-08 volts. Proper precautions must of course be taken to eliminate thermo- 

 electric or other disturbances in the circuit. 



The quadrant electrometer may be used with advantage in the derived circuit 

 when it is important that no current should flow through the cell, but the miiTor 

 galvanometer has the advantage of much greater sensibility. 



9. On Induction between Wires and Wires. By W. H. Peeece, F.R.S. 

 A continuation of a subject brought before the Association last year, when it 

 was shown that electro-magnetic disturbances extended to distances much greater 

 than was imagined, and that effects were observed across many miles of country. 

 Experiments were made on the banks of the Severn and Mersey, on the Portcawl 

 Sands of South Wales, in the fields in the neighbourhood of Cardiff", on the roads 

 and railways in Oxfordshire, Worcestershire, and Shropshire, in the air and under 

 water, in the corridor of the General Post Office in London, and the law was 

 formulated that the distance depended directly on the strength of the currents 

 inducing the disturbance, and on the length of the wires opposed to each other, 

 and inversely on the square of the distance separating them, and on the electrical 

 resistance of the disturbed wire. 



The influence of one mile of wire carrying one ampere of current can apparently 

 extend to a distance of I'D miles. The law is given by the following formula: — 



B B 2 





