Mathieson's Joint.—This somewhat complicated, though very effective mode of jointing, which is adopted in the English torpedo service, is shown at [Fig. 37], in elevation and section. It consists of two ebonite cylinders a, a, through which the cables to be connected are passed. Within these cylinders an ebonite tube b, b is placed, the ends of which are wedge-shaped, and which press against two vulcanite rings c, c; in the interior of this tube b, b is the metallic joint d of the two cables. The centre of the tube b, b is of square section, and fits into a hollow of similar form in the cylinders a, a, the object of this being to prevent any twisting of the wires during the process of screwing up, which would be liable to injure the metallic joint d.
The manner of making this joint will be easily understood from the figure. With this, as with all other temporary joints, it is advisable to form a half-crown in the cable, including the joint.
Beardslee's Joint.—This form of temporary joint when used with strand conductors, which are composed of a number of small wires, has been found to be exceedingly useful and effective, the only defect of such a joint being the liability of straightening the wires of the conductors should a direct strain be brought upon the wire extremities. [Fig. 38] represents a section of this joint; it consists of an ebonite cylinder a, one end of which is solid, and the other open and fitted with a screw thread, into which is screwed a plug b; through both the plug b, and the solid end of the cylinder a, perforations are made just large enough to admit the insulated wires c, c; about half an inch of the extremities of these wires are bared and cleaned, and then passed, the one through the plug b, a disc of vulcanised india rubber d, and a metal disc e, and the end of the strand conductor turned back on the face of this metal disc, the other through the perforation in the solid end of the cylinder a, then through similar discs d and e, and the end of the strand conductor treated in the same manner as the former one; then by means of the screw plug b, the two metallic discs b, b, and consequently the bare extremities of the strand conductors are brought into close metallic contact.
McEvoy's Joint for Iron Wire covered Cable.—This form of joint is shown in section at [Fig. 39]. Two brass caps a, a are slipped over the ends of the cables required to be joined, then the iron wire and other coverings of the cables down to the insulating substance are removed, the former being bent back close against the bottom of the caps a, a, as shown in [Fig. 39] at b, b; the cores of the cables are then joined by an india rubber temporary joint c, which has been described at [page 45]: the whole is then placed in the body of the joint, and the brass caps a, a screwed up, jamming the bent back iron wires against a solid piece of brass d, d, by which means a firm and perfect joint is made in the cables.
PERMANENT JOINTS FOR ELECTRIC CABLES.
[Fig. 40] represents a section of a McEvoy temporary joint for single cored unarmoured cables, which seems to fulfil all the conditions necessary to a perfect joint of that description. This joint is, with the exception of there being two screw plugs instead of one, very similar to Beardslee's joint described at [page 46]; this alteration is a great improvement, remedying as it does the one defect of Beardslee's joint, viz., the liability of the cables to be drawn apart due to any great tension being brought on them.
A permanent joint in electrical submarine cables, which from its nature requires to be an exceptionally good one, is a somewhat difficult and troublesome operation, and also requires a considerable time to form a thoroughly reliable one.
Siemens's Methods of Jointing.—The following methods, and instructions for forming such joints, are those adopted by Messrs. Siemens Brothers in connection with their telegraph cables, and which will be found generally applicable to all insulated cables.