There could be there causes for the non-explosion of the boiler: 1st, a leak in the boiler; 2nd, a rupture of the cable; 3rd, a defect in the construction of the fuse.

In a few days I expect to overhaul the boiler and decide on the subject. The cable has been already overrun and tested and found perfectly sound. The only remark I made at the time was, that in order to produce the spark at the end of the line (within a few feet from the torpedo) I had to reduced to about one thirty-second of an inch the distance between the poles, which remark induced me to believe that the distance of the poles in the fuse was too great for the length of the cable.

The cable has since been taken off and laid for telegraph purposes between Forts Sumter and Johnson, in lieu and place of the air line running over the Middle Ground. The 5th of April last General Ripley ordered Mr. Waldron to prepare and have ready the other boiler, to be laid in the channel between Sumter and Moultrie, with special instructions to have it ready to leave the wharf on the 7th, in the morning. The works was pushed ahead, as directed, under the supervision of Captain Ferguson, appointed there by General Ripley; but having not frame ready to receive the boiler, a portion of an old raft found near the wharf was planked and turned into a sort of flat, on which the torpedo was secured and chained, land the sinking weight attached. During the afternoon of the 7th Mr. Waldron was directed to sink the same in the Poor Man Hole opposite White Point Battery, which was done accordingly. When the fight was over Mr. Waldron sent mr. Kate with the light-ship to haul up the boiler and take it back to the dock. During the operation the frame broke, and the bailer, case lose, was carried away by the tide; being about dark at the time they soon loss light of it. Several times since attempts have been made to find the stray boiler, but we always failed in our search.

Allow me, general, before ending the above statement, to suggest the sinking of a certain number of submarine batteries in the channel between Sumter and Moultrie, ad located in certain positions, as may be determined by the engineer department; each one having its own independent cable, and containing from 1,000 to 1,500 pounds of powder. Old boilers 10 feet long can be used for that purpose. The different cables will runt ot he same battery on Sullivan's Island. An arrangement of sights and buoys can be easily combined so as to signal to the operator the passage of any Yankee gunboat on or near by, and afford him time to exploded the one nearest to it. Such plan is very simple, and avoids the complications and difficulties of Dr. Cheves' cable. Besides the set between Sumter and Moultrie a similar one could be arranged in the Ship Channel opposite Fort Wagner, or near by the next subsequent attack on the harbor.

Very respectfully, general, your most devoted and obedient servant,

CH. G. DE LISLE,

Assistant Engineer.

P. S.-We have here all the necessary material and submarine cable to complete ten big torpedoes.