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

556 TELEGRAPH INSULATION.
without further explanation. Fig. 62 represents the top view
and the curvature that fits to the post. The nail or screw holes
Fig. 64. are marked by the dotted lines. Besides this form of insulator, another is
employed for holding the wire taut
upon the poles. Fig. 63 represents
the contrivance, commonly known as
a Spankoff, or tightening apparatus.
The figs. 61 and 62 are the same in form
and make, excepting the wire support D of fig. 63 has the klemmbacken,
B B. The wire is drawn taut, and
then B B holds it tight and does not
permit it to slip through or become
loose or sagging. If the wire is cut
between two of these insulators, it can
only be slack for that particular section,
and it does not extend to the sections beyond the spankoffs.
They are usually placed on the line, one for each half mile, and
sometimes at a less distance.
I have seen these insulators on the German and Russian lines,
and wherever they have been employed the telegraph worked
with the most complete success so far as pertained to the insulation. The glass P. securely insulates the iron supporter D,
from the cast-iron bell G, and the flange mouths of G and P
prevent the collection of water whether in times of rain or of.fog.
Fig. 64 represents the top view and the curvature that fits
to the post. The nail or screw holes are al-o shown.
This insulator has proved to be the most perfect as to insulation and permanency used on the continental telegraph lines.
It cannot be broken from the post, and it is capable of sustaining a far greater weight than the wire which it suspends.
It is used on the Russian lines, and comports fully with the
otherwise substantial structure of those northern telegraphs.
THE HINDOSTAN INSULATOR.
On the Hindostan lines, Dr. O'Shaughnessy, Surgeon of the
Royal Bengal army, adopted a novel process of insulation,
peculiarly applicable to the lines of that country.
The post is tapered so as to be two and a half inches in
diameter at the small end, and three inches in diameter at
seven inches from the top. The wood is to be roughened with
a chisel so as to hold the cement by which the cap is to be
attached.