148 
THE TELEGRAPH. 
placed on a revolving table, which turns round the central 
wire. Brakes suitably check the motion of each bobbin, and 
allow it to be so adjusted that an equal tension may be felt in 
each wire. Each of the wires in the strand is unwound with 
a constant and uniform tension; otherwise the wire would be 
liable to kineh and knot while it was being covered with the 
insulating materia], through which it would force its way. 
Each length of wire is soldered to the next, so that no free ends 
shall penetrate the gutta-percha. When it is necessary to join 
one strand to another, the ends are made stiff by solder, and 
are filed to a bevel so that the two parts shall fit perfectly. A 
small vice, arranged for the purpose, keeps the parts together 
while they are being soldered. This first soldering is covered 
with fine wires, and again soldered so as to give the joint the 
strength of a solid wire. 
The gutta-percha is applied warm and in a plastic state, in 
successive layers, while the strand is passing through a series 
of moulds progressively increasing in size. Between each 
layer of gutta-percha a coat of Chatterton’s composition is 
interposed, and this not only increases the insulation but per¬ 
fectly combines the layers of the insulating matter together 
(figs. 91 and 92). 
As fast as it is produced the wire is laid in long troughs filled 
with w 7 ater kept very cold. The covering quickly becomes 
solid and the wire is automatically wound on the drums. 
When it has been finished, the wire is left for some time in 
w^ater to become seasoned. There are two cylinders to each 
machine, so arranged that there may be no stoppage; for while 
one is being charged with the composition the other is being 
emptied through the mould. It will be easily understood that 
in making telegraph wires it is essential to keep the wire 
exactly in the centre of the gutta-percha. This is done by 
means of guides and by the special arrangement that has 
already been referred to and is shown in the figure. 
The joinings of the wire are done by hand, by applying to 
the ends, properly softened and connected together, one or two 
layers of plastic gutta-percha in sheets cemented together by 
means of the Chatterton composition (fig. 93). This operation 
requires great care and extreme cleanliness; but the workmen 
in the shops whose duty it is to make the connections soon 
