nd to have no
communication with each other.

1054. Another helix was constructed upon a similar pasteboard tube, two
lengths of the same copper wire being used, each forty-six feet long. These
were united into one consistent helix of ninety-two feet, which therefore
was nearly equal in value to either of the former helices, but was not in
close inductive association with them. It may be distinguished by the
number iii.

1055. A fourth helix was constructed of very thick copper wire, being
one-fifth of an inch in diameter; the length of wire used was seventy-nine
feet, independent of the straight terminal portions.

1056. The principal _electro-magnet_ employed consisted of a cylindrical
bar of soft iron twenty-five inches long, and one inch and three quarters
in diameter, bent into a ring, so that the ends nearly touched, and
surrounded by three coils of thick copper wire, the similar ends of which
were fastened together; each of these terminations was soldered to a copper
rod, serving as a conducting continuation of the wire. Hence any electric
current sent through the rods was divided in the helices surrounding the
ring, into three parts, all of which, however, moved in the same direction.
The three wires may therefore be considered as representing one wire, of
thrice the thickness of the wire really used.

1057. Other electro-magnets could be made at pleasure by introducing a soft
iron rod into any of the helices described (1053, &c.).

1058. The _galvanometer_ which I had occasion to use was rough in its
construction, having but one magnetic needle, and not at all delicate in
its indications.

1059. The effects to be considered _depend on the conductor_ employed to
complete the communication between the zinc and copper plates of the
electromotor; and I shall have to consider this conductor under four
different forms: as the helix of an electro-magnet (1056); as an ordinary
helix (1053, &c.); as a _long_ extended wire, having its course such that
the parts can exert little or no mutual influence; and as a _short_ wire.
In all cases the conductor was of copper.

1060. The peculiar effects are best shown by the _electro-magnet_ (1056.).
When it was used to complete the communication at the electromotor, there
was no sensible spark on _making_ contact, but on _breaking_ contact there
was a very large and bright spark, with considerable combustion of the
mercury. Then, again, with respect to the shock: if the han