PBOCEEDINGS 



OF 



THE ROYAL SOCIETY. 



The Bakerian Lecture. — " On the Forms of Equipotential 

 Curves and Surfaces and on Lines of Flow." By W. G. 

 Adams, M.A., F.R.S., Professor of Natural Philosophy and 

 Astronomy in King's College, London. Received February 

 18,1875*. 



[Plates 1 & 2.] 



When any portion of a conducting-wire which joins the two poles of 

 a voltaic battery is increased in size, the resistance of the circuit is 

 diminished and a greater current flows through the wire ; and as any 

 increase in the cross section of any portion of the wire causes a corre- 

 sponding increase in the current, it is clear that there is no part of the 

 conducting-wire through which some portion of the current does not 

 flow from the one pole to the other ; and the outer boundary of such a 

 wire will be a line of flow. 



A line of flow is a line drawn in a conductor which indicates at every 

 point of it the direction of the current at that point. A portion of the 

 conductor completely enclosed by lines of flow may be termed a tube 

 of flow. 



If a portion of the wire be beaten out into a flat disk, or if a sheet of 

 metal or tinfoil be employed, it will still be true that there is no part of 

 it to which the lines of flow do not extend, although the amount of 

 current will be weak at points of the disk which are far removed from 

 the shortest line of flow. 



If instead of a variable wire or disk the circuit consist in part of a 

 conducting liquid whose cross section is greater than the surface of the 

 electrodes in the liquid, the lines of flow extend throughout the liquid ; 

 and an increase in the cross section of the liquid diminishes to some 

 extent the resistance of the circuit. 



* Bead February 25, 1875. See vol. xxiii. p. 280. 

 VOL. XXI Y. B 



