726 PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 
was broken by its own commutator, and a current was sent through the magnetizing 
helix. The galvanometer circuit was completed again, and immediately a strong 
indication of a current through it was manifested. The galvanometer circuit was 
broken, the magnetizing current reversed, and the galvanometer circuit again com- 
pleted ; again the same current as before was observed. The steam and cold water 
were interchanged in the spiral pipes, and the galvanometer current soon set in the 
reverse direction, with about the same force as before. The magnetizing current was 
stopped (the galvanometer circuit being broken for the time and closed again), and 
only slight traces of the current that had been so powerfully indicated could now be 
observed. 
139. In this experiment the action of the electro-dynamic helix caused the double 
slip of iron to receive magnetization in lines nearly parallel to the axis of the cylin- 
der (only a little disturbed in consequence of the gaps between the adjacent edges), 
that is to say, magnetization as nearly as may be in directions at an angle of 45° to 
its length. The sources of heat and cold applied along the two spirals, gave either 
heat along each of the outer edges of the double slip, and cold along the inner edges 
between the two branches, or cold along the outer edges and heat along the inner 
edges. When the ends were connected with the electrodes of the galvanometer, in 
the case illustrated in the diagram, the current was in the direction indicated by the 
arrow-heads ; and it was always in such Fig. 36. 
a direction, that if a zigzag line be traced 
through the two slips from side to side of 
each, on the whole in the same direction 
as the current, the changes of direction at 
the sides of the slips are from transversely to longitudmally magnetized through hot, 
and from longitudinally to transversely magnetized through cold; which is the con- 
clusion that was anticipated. 
140. I also experimented on the thermo-electric effects of retained magnetism 
in steel after the magnetizing force is removed, and obtained very decided results, 
showing that at least in the case of magnetization along the lines of current, the 
effect is of the same quality as in soft iron or in the steel itself while under a mag- 
netic force which induces such a state of magnetization. 
141. In one of these experiments, thirty-nine pieces of steel wire, each about i\th 
of an inch diameter and 2 inches long, soft tempered, were connected by thirty-eight 
pieces of copper wire, each an inch long, placed between each two of the pieces of 
steel, and hard soldered to their ends. Pieces of copper wire of the same length were 
soldered to the outer ends of the first and last pieces of steel, and several feet of steel 
wire to the ends of each of these. A little electro-dynamic helix was made, 2 inches 
long and wide enough internally to slide freely over this compound steel and copper 
conductor; and by means of it every second piece of the 2-inch steel wires, com- 
mencing with the first and ending with the thirty-ninth, were magnetized alternately 
