The section of a disconnector is shown at Fig. 46. It consists of an iron cover, or dome _a_, which is provided with a screw fitting on to another screw on the ebonite body _b_ of the apparatus. When the dome _a_ is screwed tightly down on the washer _i_, the whole is made perfectly watertight. _c_, _c_ are insulated terminals for connecting the cores of the branch and main cables after their armouring has been removed, as shown at Fig. 44. _d_, _d_ are two copper conducting wires (No. 16 B. W. G.) passing through the centre of the ebonite body _b_, and projecting into the interior of the apparatus. These wires are held in position and insulated by means of a composition formed of a mixture of pitch, tallow, beeswax and gutta percha. This composition is put on whilst hot and allowed to cool gradually, when it becomes hard and durable. Great care is necessary to ensure the cavity within the ebonite body _b_ being completely filled, as otherwise a leakage might occur, owing to the great pressure of water at depths where the disconnection would be generally used. _f_ is a boxwood cover which is slipped on, and fits fairly tight to the ebonite body _b_; _g_ is a piece of thin platinum wire, weighing 1·6 grains to the yard, and being 4/10 inch in length; _h_ is an ebonite pin, which passes through two small holes in the boxwood cover _f_, into which it fits tightly, and in such a position as to be directly beneath the platinum wire bridge _g_, when the boxwood cover _f_ is fixed on. The pin _h_ is pushed through the holes in the cover _f_ from the outside, so as to pass beneath the bridge _g_ after the priming has been inserted, and the cover has been placed on. When prepared for use, the platinum wire bridge _g_ is surrounded by some loose gun-cotton priming, sufficient in quantity to blow off the boxwood cover _f_, without destroying the dome _a_; the cover _f_ being blown off, carries the ebonite pin _h_ with it, and through the platinum wire bridge _g_, thereby rupturing it, and breaking the continuity of the circuit. The object of so doing is to cut off the connection of an exploded mine, so that the full amount of the firing current is available for the other mines, and not suffered to be wasted by passing through the exposed wire of the broken circuit, which, were the disconnector not employed, would be the case. When any particular mine of a system is struck, the current passes through the main cable _b_, the disconnector _a_ (which is in connection with that mine), and branch cable _b'_ to the fuze, and so explodes the mine, and destroys the platinum wire bridge _g_ of the disconnector at practically the same instant. The effect of the latter operation would be to cut off and insulate the branch cable of the exploded mine, and so prevent any loss of the electrical current, when another mine of that system is required to be fired.