547. If we again refer to the bodies which were used
ill performing the expeiiments with the pith-balls, it will
be seen they are all non-conductors ; and but for this
property the fluid, as it was excited, would have been
conveyed away to the earth, and failed to make itself
manifest in the manner we have seen. Hence it is tha
only non-conductors usually become electrical by fric-
tion ; but conductors may also be excited by friction^
provided they are first insulated. Thus, if a piece of

•oce to their condacting power 1 What are some of the best conductors 1 What ar«
■ome of the principal non-conductors 1 646. When is a body said to be insulated *
How is this usually accomplished 1 Why do electrical experiments succeed oxi^ witL
difficultT in a moist atmosphere 1 547. Why do non-conducting substances onljf
usually become excited by friction 1 How may a piece of iron, which is a cox»ductor
bfi excited 1




Electrical Light,



ELECTRICITY. 341

iron, which is a conductor, be supported on glass pillars,
in a dry atmosphere, and struck several times with a cat's
skin, it will be found to be feebly excited.
548. Electrical Light — When an excited body is held
in a dark place— or, Tbtetter, when a body, as a glass tube,
is excited in a dark room — :faint flashes of light will be
seen upon its surface, accompanied by a crackling noise.
