The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

AMERICAN INSULATORS. 539
course the lower end of the glass will not be dry, but there
will be less liability for a watery connection with the earth
from the wire than when the drip is at the lower end of
the glass. I have seen this philosophy illustrated at the
Niagara Falls. The immense volume of water passes over
the shelf or point of drip, and beneath the mass of water
is a passage-way for travellers, precisely as represented by fig.
26. If the reader desires to see this idea illustrated, he can
do so by setting a teacup upon an upright pin, then fill
the cup with water until it overflows. The water will fall
over the rim, and the smaller end of the cup will be dry.
Fig 21 represents the glass adjusted to the wire when on a
right line; fig. 22 when the wire is oblique, as upon the side
of a hill, and fig. 23 when the wire is perpendicular with the
post. In order to prevent the glass from pulling off from the
iron arm, the screw combination represented by fig. 24 was
adopted. The iron arm 3, is cut so that the teeth will serve
as a male screw. The glass is made with a female screw as
seen by numeral 2. Fig. 25 represents the glass on the arm,
with the line wire fastened to it at an angle pulling the glass
upward, the teeth of the iron arm fitted into the grooves of the
screw prevents the glass from being separated from the iron
arm.
The above figures are engraved with so much variety that
further explanation is unnecessary. They have been gotten
up with care, and they are replete with demonstrative philosophy.
Fig. 19 represents the application of these insulators to the
poles. The cross beam at the top of the pole has upon it two
insulators, set upon iron pins. Some lines have several of these
cross beams on the poles for the Fig. 27.
use of other wires; others have
the insulators fastened to iron
arms driven into the sides of the
poles, as seen below the beam
in fig. 19. This iron arm is
shaped as seen in fig. 18. An
auger hole is bored into the
post, and into it is driven the
iron arm as seen by the figure.
An advantage is realized in the
use of this class of insulaters, in the fact that there is not
much surface for the wind to act upon. Many lines are leveled
to the earth by the heavy storms.
Among the improvements historic in telegraphing is the one