This pattern combines within itself the firing and testing apparatus,—that is, the firing-key is permanently connected to the machine and the binding-screws of the C machine occupy a position analogous to that of the binding-screws T, T, of the firing-key. =To Test the Machine.=—Ship the crank and turn it rapidly with the sun; if it turn somewhat hard the short-circuit is complete; press the key T; the crank should turn with ease; connect the binding-screws by a short wire; turn the crank as before and press the key T; if the crank turn easier and a small bell be heard to strike inside, the test-circuit is complete. Continue turning the crank, press the key F and then the key T; if it continue to turn somewhat hard, and the bell does not sound, the firing-circuit is complete. The difference of force necessary to turn the crank during the several tests is not so apparent as with the larger machine. If any of the tests fail the machine should be taken from its case and the fault treated as with the larger machines. WIRES. =Insulation.=—Insulation is for the purpose of confining the electric current to the path we wish it to take and should be carefully looked after at all points not covered by the rubber or other permanent insulating matter. Faults in the insulation of the wires leading from the testing or firing apparatus to the torpedo may be so situated as to cause, in the former case, false tests and, in the latter, a sufficient weakening of the current through the detonator to prevent its firing; or, they may be so situated as to cause accidental explosion of the torpedo. The insulation of the wires, as well as that of the testing or firing apparatus, must therefore be carefully preserved. In order to preserve good insulation, all binding-screws should be kept clean and dry. Rain water has little effect, but salt water is bad. Wires which make short angles should be protected from chafe and all splices should be very carefully insulated by rubber tubing. Particular care must be taken to prevent metallic contact of the two legs of the detonator. Any such contact at that point would not be detected by testing and would be fatal to success. =Splicing Wires.=—Remove the jute braiding and rubber tape from the two ends to be spliced for such a distance as to be clear of the rubber tubing used to insulate the splices and whip the braiding. Bare the conductors of the two wires for about an inch and a half, lay them up and brighten them. Slip the piece of rubber tubing over the end of one of the wires. Unite the wires by a square-knot or sheet-bend, soldering the splice if it is to be permanent. Slip the rubber tubing over the splice so that its ends will overlap the rubber insulation of the wires and pass a snug seizing around each end of it.