, each about the thickness of a small pin. Six of
these wires were wound spirally round the seventh. This was in order to
prevent what is termed a "breach of continuity," for it will be at once
perceived that while a single wire of the core might easily break in the
process of laying the cable, and thereby prevent the flow of
electricity, the probability of the seven small wires all breaking at
the same spot was so remote as to be almost impossible, and if even one
wire out of the seven held, the continuity would remain. Nay, even all
the seven might break, but, so long as they did not all break at the
same place, continuity would not be lost, because copper would still
continue to touch copper all throughout the cable's length.

In the process of construction, the central wire of the copper core was
first covered with a semi-liquid coating of gutta-percha, mixed with
tar--known as "Chatterton's Compound." This was laid on so thick that
when the other wires were wound round it all air was excluded. Then a
coating of the same compound was laid over the finished conductor, and
thus the core was solidified. Next, the core was surrounded with a
coating of the purest gutta-percha--a splendid non-conductor, impervious
to water--which, when pressed to it, while in a plastic state, formed
the first insulator or tube to the core. Over this tube was laid a thin
coat of Chatterton's Compound for the purpose of closing up any small
flaws or minute holes that might have escaped detection. Then came a
second coating of gutta-percha, followed by another coating of compound,
and so on alternately until four coats of compound and four of
gutta-percha had been laid on.

This core, when completed, was wound in lengths on large reels, and was
then submerged in water and subjected to a variety of severe electrical
tests, so as to bring it as near as possible to a state of perfection,
after which every inch of it was examined by hand while being unwound
from the reels and re-wound on the large drums, on which it was to be
forwarded to the covering works at East Greenwich, there to receive its
external protecting sheath.

All this, and much more besides, did Robin Wright carefully note down,
and that same evening went home and delivered a long and luminous
lecture, over which his mother wondered, Madge rejoiced, his father
gloried, and uncle Rik fell asleep.

Next day he hastened to the covering works, and, presenting his
credenti