PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 739 
157 . Exp. 3. Attempt to discover the effect of transverse magnetization on the longitu- 
dinal conductivity of a slip of sheet iron, — Two brass cores like those described above, 
and of the same length (10 inches), but of larger inner and outer diameters, were pre- 
pared, and a quantity of covered copper wire rolled on one of them in four strands, or 
in all 570 turns. Two slips of sheet iron, each 7 feet long and ^ inch broad, were wound 
upon single brass tubes coated with paper, and the successive spires of each were kept 
from contact by a piece of twine wound on between them. A length of 9 inches of 
each brass tube had 84 inches of the slip iron laid upon it, and therefore the inclination 
of the helix to a plane perpendicular to its axis was about 6°, being the angle whose sine 
is Each of these iron spirals was protected outside with a coating of paper, and 
pushed into the interior of one of the brass cores. A copper arc, C, was soldered to 
each of them so as to connect their extremities on one side, and powerful copper 
electrodes, A and B, were soldered to their other extremities. Then, a stream of water 
being kept constantly flowing through each of the inner tubes and through the spaces 
between the concentric brass tubes outside, a current from a large cell of Daniell’s 
63) (exposing 2'5 square feet of zinc to 4‘4 square feet of copper) was sent through 
the irQn spirals, and a testing conductor (the same one as before) was put in com- 
Fig. 42. 
munication with their electrodes, A and B. One electrode of the galvanometer being, 
as before, soldered to the middle of the copper arc connecting the iron spirals, the 
other was applied to the scale of the testing conductor. The galvanometer being 
brought to zero by the insertion of adjustment wires at one end or other of the test- 
ing conductor, it was found to be rather steadier than in the former experiments, 
probably because of the diminution of thermal effects by the stream of water through 
the cores, and the greater surface of iron exposed outside and inside to refrigeration. 
When a current was sent and maintained through the magnetizing helix, a very 
decided permanent deffection was occasioned in the galvanometer; and this the 
same with each direction of the magnetizing current. If the galvanometer circuit was 
kept complete, its needle experienced a powerful impulse, sending it through a great 
many degrees in one direction or the other at the instant of starting, or of reversing, 
or of stopping the magnetizing current, but quickly in each case showed the nature 
of the permanent deflection by oscillating about one position, when the current was 
steadily maintained, in either direction. These impulsive deflections were of course 
due to induced currents, and were entirely prevented by keeping the galvanometer 
MDCCCLVI. 5 E 
