Effect of explosion:--(_a_) mine, at 146' distance, split in two; (_b_) mine, 34' distance, destroyed; at 49' distance, fractured; at 68' distance, indented but not fractured; (_c_) mine, 58' distance, case much bulged, and leaky; (_d_) mine, at 244' distance, rivets started, case half full of water; at 195' distance, sunk, several rivets started; (_e_) mine, at 195' distance, bolt loosened; (_f_) mine, at 68' distance, not injured. 3RD EXPERIMENT. Countermine:--453 lbs. of dynamite, enclosed in a case, 24-1/2" × 28-1/4" × 1/8". It was moored 9-3/4' below the surface; depth of water as before. Submarine mines:--As before. Effect of explosion:--(_b_) mine, at 49' distance, sunk and not recovered; at 58' distance, very much indented; (_c_) mine, at 58' distance, case much indented and leaky; (_f_) mine, at 48-1/2' distance, uninjured. 4TH EXPERIMENT. Countermine:--As before, but moored 29-1/4' below the surface. Effect of explosion:--(_a_) mine, at 195' distance, completely stove in; (_c_) mine, at 58' distance, case indented but charge dry; (_e_) mine, at 175' distance, slightly leaky; (_f_) mine, at 48-1/2' distance, upper half indented in three places. It was also discovered during the above experiments that submarine mines charged with dynamite can be caused to explode by the detonation of a charge of the same explosive, at distances from it considerably beyond those at which the cases themselves are damaged by a similar charge. To prevent the foregoing, it is necessary to pack the dynamite very carefully, using at the same time special precautions. CHAPTER X. THE ELECTRIC LIGHT--TORPEDO GUNS--DIVING. ELECTRIC lights combined with fast steam launches as guard boats and specially constructed torpedo guns, such as the Nordenfelt and Hotchkiss machine guns, are at the present time the only _truly practicable_ means afforded to a man-of-war of defending herself against the attack of torpedo boats, whether these latter are armed with the spar, fish, or towing torpedo; the torpedo gun sinking the boats after the electric light and guard boats have detected their approach and position. As has been before stated, nets, shields, booms, &c., placed around a vessel of war, must, however slightly constructed, affect to a considerable degree her efficiency, by decreasing her power of moving quickly in any desired direction, which is essential to the utility of such a vessel in time of war; and thus on electric lights, guard boats, and torpedo guns must the safety of ships in future wars really depend, when attacked by torpedo boats. _The Electric Light._--The phenomenon of the _Voltaic arc_ was first discovered by Sir Humphry, then Mr., Davy at the beginning of the present century. The following is an account of the matter as given by him in his "Elements of Chemical Philosophy":--