Effect of explosion:--Several plates in the outer bottom were cracked, and outer bottom made to leak in several places, owing to the fractures in the plates, rivets being started, and seams being opened. Considerably more damage was effected than in previous experiment, but inner bottom still remained uninjured. 7TH EXPERIMENT. Torpedo:--As in the 5th experiment. It was placed on the ground, immediately under the edge of the outer bottom, 39-3/4' from the target, and opposite No. 18 frame, 70' from the stern; 50' below the surface of the water. Effect of explosion:--Outer and inner bottom broken entirely asunder at No. 19 frame on the starboard side, and between Nos. 16 and 17 on the portside. A fracture was caused in the outer bottom extending from the shelf plate to upper edge of strake next the keel on the starboard side, and from the shelf plate to upper edge of flat keel plate on the port side. A fracture was also caused in the inner skin extending from the topside to the outer edge of the garboard strake on the starboard side, and from the topside to upper edge of garboard strake on the port side; this including a fracture of the keel at No. 17. The vertical keel, the longitudinals, as well as numerous bracket plates and angle irons, were broken, and about 2000 rivets in the outer bottom were rendered defective. The outer bottom was indented over a considerable length, the indentation being greatest between the frames, and the maximum being 8 inches. The inner bottom was not indented or damaged, with the exception of the fractures before mentioned. _Experiments at Pola, Austria, 1875._--These experiments were carried out to determine the effect of very heavy charges of dynamite on an iron pontoon fitted with a double bottom, similar to that of H.M.S. _Hercules_. Target:--An iron pontoon 60' long and 40' beam, with circular ends and fitted with a double bottom, also a condenser and two Kingston valves. 1ST EXPERIMENT. Torpedo:--617 lbs. of dynamite. It was 62' horizontally from the keel, 53' actual distance from the side, and opposite amidships, 40·5' below the surface of the water, and 20' from the ground. Pontoon:--Draught of water 19', and moored in 62' of water. Effect of explosion:--The pontoon moved away bodily a distance of 13 feet; a few rivets in the outer bottom were started, and the outer skin was slightly indented between the frames; the maximum indentation being 1·5". No other damage was sustained by the hull. Several of the screws securing the flanges of the Kingston valves were slightly loosened. 2ND EXPERIMENT. Torpedo:--585 lbs. of dynamite. It was placed 60' horizontally from the keel, 48' actual distance from the side, and opposite amidships; 36' below the surface of the water, and 42' from the ground. Pontoon:--Draught of water 19·5', and moored in 74' of water.