applied to Magnetic Phenomena. 175 
so that within the conductor 
C C 
a= —2 py; B=2p02, cee RE yh 0 een 5) 
Beyond the conductor, in the space round it, 
$=2Ctan-1%, . cele ae eR green ae et 
eae y __o¢__# OP 5 
If p=/x? + y? is the perpendicular distance of any point from 
the axis of the conductor, a unit north pole will experience a 
2C : 
force = ——, tending to move it round the conductor in the 
direction of the hands of a watch, if the observer view it in the 
direction of the current. 
Let us now consider a current running parallel to the axis of 
z in the plane of xz at a distance p. Let the quantity of the 
current be c’, and let the length of the part considered be /, and 
its section s, so that = is its strength per unit of section. Put- 
ting this quantity for p in equations (12, 18, 14), we find 
F 
X= —pp F 
per unit of volume; and multiplying by Js, the volume of the 
conductor considered, we find 
X= —pBell 
— —2u—, Whee ial h gy ate as ° > (26) 
showing that the second conductor will be attracted towards the 
first with a force inversely as the distance. 
We find in this case also that the amount of attraction depends 
on the value of w, but that it varies directly instead of inversely 
as 2; so that the attraction between two conducting wires will be 
greater in oxygen than in air, and greater in air than in water. 
We shall next consider the nature of electric currents and 
electromotive forces in connexion with the theory of molecular 
vortices. 
