ON THE LINES OF MAGNETIC FORCE. 
29 
the transmission of the force is after the manner of a vibration or current, or simply 
action at a distance; and the many other questions that arise in the minds of those 
who are pursuing this branch of knowledge. 
3084. I will proceed to take the case of a simple bar magnet, employing it in 
illustration of what has been said respecting the lines of force and the moving con- 
ductor, and also for the purpose of ascertaining how these lines of force are disposed, 
both without and within the magnet itself, upon which they are dependent or to 
which they belong. For this purpose the following Fig. i. 
apparatus was employed. Let fig. 1 represent a 
wooden stand, of which the base is a board 17'5 
inches in length, and 6 inches in breadth, and 0’8 of 
an inch in thickness : these dimensions will serve as 
a scale for the other parts. A B are two wooden 
uprights ; D is an axis of wood having two long 
depressions cut into it, for the purpose of carrying 
the two bar magnets F and G. The wood is not cut away quite across the axis, 
but is left in the middle, so that the magnets are about ^^th of an inch apart. 
From O towards the supports A, it is removed, however, as low down as the axis 
of revolution, so as to form a notch between the two magnets when they are in 
their places ; and by further removal of the wood, this notch is continued on to the 
end of the axis at P. This notch, or opening, is intended to receive a wire, which 
can be carried down the axis of rotation, and then passing out between the two 
magnets, anywhere between O and N, can be returned towards the end P on the 
outside. The magnets are so placed, that the central line of their compound system 
coincides with the axis of rotation ; E being a handle by which rotation, when 
required, is given. H and I are two copper rings, slipping tightly on to the axis, by 
which communication is to be made between a wire adjusted so as to revolve with 
the magnets, and the fixed ends of wires proceeding from a galvanometer. Thus, let 
L represent a covered wire ; which being led along the bottom of the notch in the 
axis of the apparatus, and passing out at the equatorial parts of the magnets, returns 
into the notch again near N, and terminates at P. When the form of the wire loop 
is determined and given to it, then a little piece of soft wood is placed between the 
wires in the notch at K, of such thickness, that when the ring I is put into its place, 
it shall press upon the upper wire, the piece of wood, and the lower wire, and keep 
all tightly fixed together, and at the same time leave the two wires effectually sepa- 
rated. The second ring, H, is then put into its place on the axis, and the introduc- 
tion of a small wedge of wood, at the end of the axis, serves to press the end P into 
close and perfect contact with the ring H, and keep all in order. So the wire is free 
to revolve with the magnets, and the rings H and I are its virtual terminations. 
