Torpedo:--33 lbs. of granulated gun-cotton, saturated with water; total weight of charge being about 41 lbs. It was enclosed in a 1/4" iron case, 12-1/2" × 12" × 12-1/2", the primer being 2-1/2 lbs. of slab gun-cotton, included in the 33 lbs. It was placed at 4' actual distance from the target, measuring from the centre of the case, and opposite No. 30-1/2 solid frame on the starboard side; 9-1/4' below the surface of the water. Effect of explosion:--Outer bottom blown in from upper edge of the lower longitudinal to the lower edge of the upper longitudinal between Nos. 28 and 32 frames; an area of 18 × 11 feet. The butts of the flat keel were started and the plating broken across No. 30-1/2 frame from the flat keel plate to the upper deck. Shelf plate at Nos. 30-1/2 and 32-1/2 frames was broken. Nos. 29, 30, and 31 frames were blown in from first to third longitudinal; lower longitudinal from No. 28 to 31 also blown in. Two holes were blown through the inner bottom, measuring respectively 6 × 1·5' and 5' × ·25', making the total area of inner bottom destroyed 10 square feet. A steam launch with steam up and outrigger torpedo gear in place, one pole being rigged out, was placed with the stem of the boat 22' horizontally from the torpedo. She was uninjured and shipped very little water. 4TH EXPERIMENT. Torpedo:--31 lbs. 14 oz. of gun-cotton in slabs, saturated with water, total weight about 40 lbs. It was enclosed in a 1/4" iron case 12-1/2" × 12-1/2" × 6"; primer being 20 oz. of gun-cotton, included in the 31 lbs. 14 oz. It was placed at 4' actual distance from the target measuring from the centre of the case, and opposite No. 30-1/2 solid frame on the port side; 9-1/4' below the surface of the water. Effect of explosion:--Outer bottom and frames injured in a similar manner to that described in the third experiment. Outer angle irons of the 1st, 2nd, and 3rd longitudinals were started in the wake of the broken place. A hole was blown through the inner bottom, measuring 9·5' × 1', or about 10 square feet in area. The bolts of the outer bottom plate of stern post much open, and at Nos. 16 and 17 on the port side the upper two strakes were buckled and the shelf plate started. A steam launch, arranged in the same manner as in the fourth experiment, was uninjured, and shipped but little water. _Experiments with Countermine._--The following experiments have been carried out in England and other countries to ascertain some reliable data for countermining operations. 1ST EXPERIMENT. _Experiments in the Medway, England, 1870._--Countermine:--432 lbs. of compressed gun-cotton, enclosed in a 3/16" iron case. It was moored at a depth of 37' below the surface of the water. Submarine mines:--A series of similar cases containing coal dust, &c., were moored at distances of 50' to 100' from the countermine, and 37 feet below the surface.