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

596 SUBTERRANEAN TELEGRAPHS.
To protect the rod still further, chiefly from mechanical
injury, it was finally laid in a row of thin roofing tiles, of semicylindrical form (the koprile, of Bengal). These were half
filled with a melted mixture of three parts dry sand and one
part rosin by weight, and when laid, the whole was filled up
with the same melted mixture. When cold, the mass is as
hard as brick or sandstone, and perfectly impermeable to water
when well prepared.
The sand used for this purpose must be sifted to free it from
particles of straw, leaves and sticks; next thoroughly washed,
to remove clay and saline matter; thirdly, dried perfectly over
a furnace of iron plates, heated by a strong fire. When quite
dry and cool it is stored in barrels for use.
The rosin and sand, weighed in separate bags of 10 pounds
rosin and 30 pounds sand, are sent on the road and melted in
iron bowls (kuroys), on temporary fireplaces by the roadside.
the mixture is thoroughly incorporated during the melting of
the rosin, and poured on the tiles from iron ladles with long
handles."
MODE OF TESTING SUBTERRANEAN TELEGRAPHS.
Having now explained the different modes of laying a wire
underground and insulating it for telegraphic service, I will add
a few explanations in regard to the mending of the gutta-percha
insulated wires, and the testing of the line to discover faults in
Fig. 9. the conductors. Fig. 9 represents a test-'- E Kbox, made of iron plates, resembling when
screwed together a mile post. The small
RJI! door is fastened with a lock. The line
wires, at given distances, for example,
every mile, more or less, are brought into
these test-boxes, where they can be ex-.l_ -- amined and the place of difficulty ascer|gj a Ad tarneA, whneter to Mee YignidOnt o Sine o1Ao.
L-E-~.~-~.~ "q~'Fig. 10 represents the wire, insulated with'~'~2 " -^'~ —~~TM gutta-percha, separated ready to be tested.
The flat pieces above are brass, and fastened below to the
copper wire, covered by the gutta-percha. Fig. 11 represents
the two wires fastened together by the double screw at the
top of the figure. The projecting nipples seen in fig. 10,
fit in the holes seen in the respective pieces, which, together
with the double screw in fig. 11, unite the wires tightly. In
order to prevent the brass pieces from oxydating, or from
causing an earth circuit, a gutta-percha cap is fitted on as seen
in fig. 12. All the wires brought into the test-box are thus