162 E. H. Hall—New Action of Magnetism 
along the radii of the disk, but if a strong magnetic force were 
made to act perpendicularly to the face of the disk a new 
electromotive force would be set up, which would be always 
perpendicular to the direction of the magnetic force and to the 
In fig. 1, which is about one-half the actual size of an ordi- 
nary plate, g g g g represents the plate of glass upon which 
the metal strip m m mm is mounted. Contact with this strip 
is made at the ends by the two thick blocks of brass b, b, which 
are held firmly in place by the four brass clamps worked by 
means of the screws S, 8, 8, S. The main current of electricity 
