626 Original Articles. [ Oct., 
not found to interfere seriously with the working. The conducting 
power of copper wire was taken to be directly as the area ; there were, 
however, no precise data for determining a priori the size of wire 
requisite for any given length of circuit and speed of transmission. 
The wire was joined by being carefully lapped and soldered at the 
joint, and wrapped with smaller binding-wire, which was also soldered 
with silver solder. In spite of the utmost care in the construction of 
these joints, some were always imperfect, owing to their liability to 
fracture, and a break at any single joint destroyed the value of the 
whole cable. Moreover, the defects in the copper, owing to want of 
homogeneity, and the presence of foreign matter, frequently rendered 
the wire so weak that it ultimately parted after being covered, break- 
ing the circuit, or stretched out and reduced the diameter to an incon- 
venient extent. It was also found that, if the covered wire was 
excessively stretched, and then allowed to contract, the copper wire, 
being incapable of regaining its original dimensions, knuckled through 
the elastic coating. 
To remedy these defects, instead of a single copper wire bundles 
of smaller ones, of similar area, were adopted, the joints being so 
distributed that the fracture, or defect, of a single wire, does not 
destroy the whole cable. One serious objection to this form of con- 
ductor is that, if a single wire breaks, the sharp end is liable to 
penetrate through the gutta-percha, and establish a communication 
with the outer conductor. Such a defect is not easily detected, and it 
can only be guarded against by close examination of the strand itself, 
and by the constant testing of the coating during the manufacture. In 
the form of a strand the bulk of the conductor is also greater, and 
more gutta-percha will therefore be required to cover it. It will, 
moreover, not be perfectly solid, but will allow water, if it happen to 
penetrate to any part of the wire, to passalong as inatube. This latter 
objection the Gutta-percha Company propose to remove by coating the 
central wire of the strand with Chatterton’s Compound, and then 
bedding the six centre wires in it in the process of twisting. The 
compound squeezed out between the wires unites firmly with the 
insulating material, and the whole becomes so solid that a few inches 
of this cable will prevent the percolation of water at a pressure of 600 
pounds per square inch. Mr. Daft proposes to obtain the same object 
by bedding copper wires coated with brass in vulcanized india-rubber. 
Mr. Clark obtains solidity by making the conductor in the shape of a 
solid wire, divided into three or four sections longitudinally, fitting 
closely to each other. Mr. Newall unites the several wires of a strand 
with solder. 
Dr. Matthiesson, Professor Thompson, and other experimentalists, 
have shown that the quality of the copper exercises a material influence 
on the conducting power of the wire, and it is very important that 
copper, as pure as can be obtained in commerce, should be used. 
The following table, extracted from the commissioners’ report, 
shows the relative value, or conducting powers, of certain commercial 
coppers :— 
