And the same eflfect will be produced upon the electricity

QuBETiOM 686. In case a dischRrge actually takes place upon a building, how doefl
Ihe conductor protect It 1 Why are buildings provided with water-conductors, extend-
ing from the eaves downward, often injured only in the roof? Do lightning<conductor8,
in all probability, often convey the electricity of the clouds silently to the earth, aoa
thus prevent a disruptive discharge 1 What will be the etteet if a person standing near
an electrical machine, as it is turned, presents the point of ills pen-knila in tilt Tieinitj
•f the prime conductor %



KLBGTRICITT. 875

of the clouds by pointed conductors presented toward
them.
586. When the atmofiphere is highly charged with
electricity the points of bodies projecting into the air
often appear luminous in the dark. This was probably
the cause of the fire seen upon the points of the spears
of a division of the Roman army, in ancient times, men-
tioned in history ; and it is here, too, we are to look for
an explanation of meteors often seen, during storms, upon
the extremities of the masts and spars of shipping, called,
by sailors. Castor and Pollux, or fire of St. Elmo. The
points of electrical conductors attached to buildings have
been known to present the same appearance when highly
electrified clouds have been passing over them ; and^
there can be no doubt the cause in each case is the
same.
587. That conductors attached to buildings do really
protect them from injurv from lightning has been abun-
dantly proved by actual experiment a thousand times.
