You have perhaps seen in the papers a French account of a little blow-up which took place at Boulogne on the first of this month; it was an experiment on a small scale to try the effect of four of my submarine bombs or torpedoes. They were carried in by two small boats which the French have magnified to many fire-ships with a formidable attack of boats, etc., which shows that they were much frightened or that the public must be amused with a long story; however, the torpedoes did not produce the desired effect and I saw a great prejudice arise in the minds of the officers against them: but sure of their effects and convinced that they had only been badly applied, I the next day purchased a strong Danish brig of 250 tons, determined to blow her up and at the same time give the officers a lesson how to act: the brig was soon put in order, ballast and water casks were laid in, and sails bent as if intended for a voyage; she was then surveyed and acknowledged on all sides to be as strong as any of the craft at Boulogne: Everything being ready she was on Monday morning sent to Walmar road and anchored opposite Walmar Castle, about half a mile at sea. The public curiosity was soon excited, who expected the experiment to be made about 4 o’clock; but that evening and the next morning passed in practicing my men. About 3 yesterday I came on there and walked down the beach where I made the signal of attack: instantly one of my long galleys rushed forward and grappled the torpedo line in the cable of the tug. The force of the tide then pressed the torpedo, which was set to fifteen minutes, under her bottom, and in fifteen minutes the awful explosion took place: it lifted the whole body of the vessel almost out of water and broke her completely in two in the middle; the mainmast and pumps were blown out of her and in one minute nothing of her was to be seen but floating fragments. The torpedo contained 170 pounds of powder. The experiment was the most complete that could be desired but most tremendous and frightful and carries with it one reflection which gives me some pain, that in vessels thus attacked it will be impossible to save the men, and many a worthy character must perish. All doubts are now removed on the power and simplicity of this invention. The defects which have attended it was bad management which is now corrected. Yours truly, ROBT. FULTON.