MAKING AND LA YING SUBMARINE CABLES. 14 7 
substance. In consequence of this greater conductivity, mes¬ 
sages can be sent better through a copper than through an iron 
wire of the same dimensions. The conducting quality of the 
wire is always carefully tested by the electricians, to see 
whether it answers the conditions stipulated in the contracts. 
In the earlier cables, the spaces between the thin wires in 
the strand were not filled, and the water always reached the 
Fig. 90. —Sir Daniel Gfoocli, Chairman of the Telegraph Construction and 
Maintenance Company. 
copper through the pores of the gutta-percha, and then found 
a passage along the spaces between the wires. The wires have 
thus been found oxidised in nearly all the early cables. This 
risk has since been obviated by the use of Chatterton’s com¬ 
position for filling up the strand. The composition is a mix¬ 
ture of 3 parts by weight of gutta-percha, 1 part of resin, 
and 1 part of Stockholm tar, and it has the advantage of 
filling all the interstices in the strand, and of making the 
insulating layer adhere more strongly to it. 
The manufacture of the copper strand is extremely simple. 
The bobbins on which is wound the wire for the strand, are 
