_a_, _a_ battery terminals. _b_ ” tester. _c_ fuze-bridge in tester. [Illustration: PLATE XIV.] =PLATE XV.= FIG. 1, HAND-FIRING KEY.—PATTERN B. _a_, _a_ hickory pieces. _c_, _c_ contact studs. _L_, _L_ leading-wires. _d_ rubber cot. _e_ safety-pin with hole for laniard. _f_ eye-bolt for laniard. FIG. 2, DIAGRAM SHOWING HAND-FIRING KEY IN CIRCUIT. _B_ battery. _H_ hand-firing key. _w_, _w_ leading-wires. [Illustration: PLATE XV.] =PLATE XVI.= FIG. 1, “A” MACHINE AND FIRING-KEY CONNECTED. _A_ “A” machine. _C_ firing-key. _B_, _B_ terminals of firing-key. _T_, _T_ ” ” ” Key “T” test key. ” “F” firing-key. _O_ machine-connecting wires. _w_, _w_ wires to torpedo. FIG. 2, “C” MACHINE CONNECTED. _D_ “C” machine. _C_ firing-key (in the machine). Key “T” test key. ” “F” firing-key. _w_, _w_ wires to torpedo. [Illustration: PLATE XVI.] =PLATE XVII.= FIG. 1, firing-key, short-circuit. ” 2, ” testing circuit. ” 3, ” firing-circuit. _O_, _O_ machine-connecting wires. _w_, _w_ wires to torpedo. _B_, _B_ terminals of firing-key. _T_, _T_ ” ” ” Key “T” test key. Key “F” firing-key. [Illustration: PLATE XVII. _Fig. 1._] [Illustration: _Fig. 2._] [Illustration: _Fig. 3._] =PLATE XVIII.= STEAM-DRIER. [Illustration: PLATE XVIII. _Fig. 1._] [Illustration: _Fig. 2._]