Having described this instrument in a way which I hope will be understood, I may be permitted to put the following question to my readers, which is, knowing that the explosion of one hundred pounds of powder, or more if required, under the bottom of a ship of the line, would destroy her, and seeing, that if a ship in sailing should strike the lever of an anchored torpedo, she would be blown up, would he have the courage, or, shall I say, temerity, to sail into a channel where one or more hundred of such engines were anchored? I rely on each gentleman's sense of prudence and self-preservation, to answer this question to my satisfaction. Should the apprehension of danger become as strong on the minds of those who investigate this subject as it is on mine, we may reasonably conclude that the same regard to self-preservation, will make an enemy cautious in approaching waters where such engines are placed; for, however brave sailors may be, there is no danger so distressing to the mind of a seaman, or so calculated to destroy his confidence, as that which is invisible and instantaneous destruction. The consideration which will now present itself, is, that the enemy might send out boats to sweep for and destroy the Torpedoes. It is therefore proper to examine the nature of such an operation, and its chance of success. Suppose two hundred Torpedoes to be placed in three miles of channel, the enemy's boats, in attempting to sweep for them, would be exposed to the fire of our land batteries, or necessitated to fight our boats, for whenever they leave their ships and take to boats, we can be as well armed and active at boat fighting as they; and thus opposed by batteries and boats, they would have three or more square miles of channel to sweep, which, even if successful, would be a work of time, and were they to get up some of the Torpedoes, they could not ascertain if all were destroyed, for they could not know whether five or five hundred had been put down; nor could they prevent our boats throwing in additional numbers each day and night. It therefore amounts to an impossibility for an enemy to clear a channel of Torpedoes, provided it were reasonably guarded by land batteries and row boats. Added to the opposition which might be made to the enemy, there is a great difficulty in clearing a channel of Torpedoes with any kind of sweep or drag, so as to establish full confidence in sailing through it. It is only they who put them down and know the number, that could tell when all were taken up. To facilitate the taking of them up, I have, since Plate II was engraved, thought of a very useful and simple piece of mechanism which, being screwed to the box C, will hold the Torpedo under water at any given depth, and for any number of days. They may be set to stay under water a day, week, month, or year, and on the day which shall be previously determined, they will rise to the surface; at the same instant