536 JAMES CLERK MAXWELL. 



wire, and to pressure in planes passing through the wire, 

 reminding us of the cylinders of an Armstrong gun. 



If the wire be bent the same will be true in kind, but 

 the lines will no longer be accurately circles. All the 

 magnetic lines of force pass through a closed circuit in the 

 direction in which a right-handed screw would advance if 

 rotating in the direction of the current. Fig. 11, taken from 

 the paper in the Philosophical Magazine, shows the relations 

 between the current, the lines of magnetic force, and the 

 direction of motion of the vortices, the arrows E E' represent- 

 ing the current, S 1ST indicating the direction of the magnetic 

 force, while the arrows V V 7 show the direction of rotation 

 of the vortices. 



Now suppose a wire conveying a current to be placed in 

 a magnetic field at right angles to the lines of force. Let 

 S N" (Fig. 12) represent the lines of force, A the section of 



Fig. 12. 



the conductor, and let the current be travelling from the 

 reader through the paper. In the space immediately above 

 the wire, the molecular vortices due to the magnetic force 

 originally in the field will be rotating in the direction in 

 which the current in A urges them, while in the space 

 below the conductor the reverse will be the case. Hence 

 the velocity of the vortices above the wire will be increased 

 by the current, while that of the vortices below the wire 

 is diminished. The pressure of the medium at right angles 

 to the lines of force will therefore be greater above the wire 

 than below it, and the wire will be urged downwards at 

 right angles to the lines of force and to its own direction. 



