r; since the moment we leave in the smallest degree
perfection at either extremity, we involve the element of perfection at the
opposite end? Especially too, as we have not in nature the case of
perfection either at one extremity or the other, either of insulation or
conduction.

1331. Again, to return to this beautiful experiment in the various forms
which may be given to it: the forces are not all in the wire (after they
have left the Leyden jar) during the whole time (1328.) occupied by the
discharge; they are disposed in part through the surrounding dielectric
under the well-known form of induction; and if that dielectric be air,
induction takes place from the wire through the air to surrounding
conductors, until the ends of the wire are electrically related through its
length, and discharge has occurred, i.e. for the _time_ during which the
middle spark is retarded beyond the others. This is well shown by the old
experiment, in which a long wire is so bent that two parts (Plate VIII.
fig. 115.), _a, b_, near its extremities shall approach within a short
distance, as a quarter of an inch, of each other in the air. If the
discharge of a Leyden jar, charged to a sufficient degree, be sent through
such a wire, by far the largest portion of the electricity will pass as a
spark across the air at the interval, and not by the metal. Does not the
middle part of the wire, therefore, act here as an insulating medium,
though it be of metal? and is not the spark through the air an indication
of the tension (simultaneous with _induction_) of the electricity in the
ends of this single wire? Why should not the wire and the air both be
regarded as dielectrics; and the action at its commencement, and whilst
there is tension, as an inductive action? If it acts through the contorted
lines of the wire, so it also does in curved and contorted lines through
air (1219, 1224, 1231.), and other insulating dielectrics (1228); and we
can apparently go so far in the analogy, whilst limiting the case to the
inductive action only, as to show that amongst insulating dielectrics some
lead away the lines of force from others (1229.), as the wire will do from
worse conductors, though in it the principal effect is no doubt due to the
ready discharge between the particles whilst in a low state of tension. The
retardation is for the time insulation; and it seems to me we may just as
fairly compare the air at the interval _a, b_ (fig. 115.) and the wire i