140 Electromagnetic Experiments of Faraday and Pliicker. 
it would seem desirable that any diverse views on a tolerably 
fundamental question of electromagnetism should cease, or a 
satisfactory general agreement be arrived at; which may be 
facilitated by an unbiassed discussion of the subject in the 
interests of truth. 
Subsequent Addendum.—Besides the practical aspect of this 
question as relating to the revolving earth (as a magnet), and 
to the identity in fundamental qualities between the magnet 
and the helix (involving the validity of Ampere’s theory), 
there is another practical application of the matter. 
It seems, namely, extremely difficult (if not impossible) on 
Faraday’s view of “a singular independence of the magnetism 
and the bar in which it resides,” to explain how a bar-magnet 
is caused to rotate on its axis when one terminal of a galvanic 
element is connected with one pole of the magnet, and the other 
terminal with the equatorial part of the magnet (the magnet 
being suspended freely, and the terminals of the galvanic cell 
maintained in sliding contact with its equator and pole). Thus, 
suppose the galvanometer, g, of fig. 3 to be removed, and a 
battery or galvanic element substituted for it. Then the 
magnet is observed to revolve (as is well known). But how 
is the magnet to be made to revolve by the action of the cur- 
rent on its lines of force if the lines of force are independent 
of (the rotary motion) of the magnet? The lines of force 
may be made to revolve no doubt (by the current) ; but how 
are they to drag the magnet round with them when they are 
independent of it?—indeed so independent (as Faraday sup- 
poses) that the magnet can be actually made to rotate through 
ats own lines (or field of force). If the rotation of the magnet 
cannot cause the field of force to rotate, how can (con- 
versely) the rotation of the field of force cause the magnet 
to rotate ; in other words, how is the rotation of the magnet 
by the action of a current to be accounted for on Faraday’s 
hypothesis? It appears that, on the opposite hypothesis, the 
explanation is simple; viz. the rotation of the magnet is then 
easily referable to the reaction of the current in the external 
portion of the circuit upon the external lines of force of the 
magnet (whereby these external lines of force are caused to 
revolve), and, being dependent on the magnet, the magnet is 
caused to revolve with them. 
Heatherfield, Bournemouth, Dec. 1883, and 
Paris, February 1885. 
