the hand; and this observation led to an invention of some account in
the subsequent applications of electricity, known, from the place of its
conception, as the Leyden jar. This is a glass jar, the inside of which
is coated with tinfoil, and the outside as far as the neck, and into
which, so as to touch the inside coating, a brass rod with a knob at
the top is inserted through a cork, which closes its mouth. By means of
this, in consequence of the isolation of the coatings by the glass,
electricity can, in a dry atmosphere, be condensed, and stored up and
husbanded till wanted.

A series of eggs, arranged in contact and in line, give occasion to a
pretty experiment. In consequence of the shells being non-conductors,
and the inside conducting, it happens that a current of electricity,
applied to the first of the series, will pass from one to another in a
succession of crackling sparks, in this way forcing itself through the
obstructing walls. This effect of electricity in making its way through
non-conducting obstructions accounts for the explosion which ensues when
a current of it comes in contact with a quantity of gunpowder; as it
also does for the fatal consequences which result when, on its way from
the atmosphere to the earth, it rushes athwart any resisting organic or
inorganic body.

_Magnetism_.--Unlike electricity, which acts with a shock and then
expires, magnetism is a constant quantity, and constant in its action;
and it has this singular property, that it can impart itself as a
permanent force to bodies previously without it. Thus, there being
natural magnets and artificial, we can, by passing a piece of steel over
a magnet, turn it into a strong magnet itself; although we can also,
when it is in the form of a horse-shoe, by a half turn round and then
rubbing it on the magnet, take away what it has acquired, and bring it