_Third Experiment_:—On August 25th I tried to manœuvre the _Nautilus_ by means of wings 4 feet diameter like the sails of a wind-mill; to this end at first I placed on the bridge two men with oars; they took 7 minutes to row about 192 yards, the length of the basin; then I ordered the same 2 men to set the sails and in 4 minutes the _Nautilus_ covered the distance to the starting place;—I proved by this that the speed of sails to that of oars is about 2 to 1 and that these sails are very suitable to manœuvre a boat under water. The success of this experiment has given me several new ideas which I hope will facilitate much the use of carcasses [iron cases] of powder or torpedoes. _Fourth Experiment_:—On the 26th of August I tried balancing the _Nautilus_ under water in such a way as to prevent it rising towards the surface or descending to the bottom, meanwhile advancing. This is executed by means of a pair of wings placed horizontally on the front of the _Nautilus_ and which communicates with the interior. By turning these wings from left to right the _Nautilus_ is made to descend below the water, in turning them from right to left, it is raised to the surface. My first trial was unfortunate, in not having placed the boat in the necessary trim in order that the wings could act. The next day I had a decided success and I kept my _Nautilus_ below water at a depth of about 5 feet whilst it covered a distance of 192 yards, about from one end of the basin to the other. This day I made several movements under water and I observed that the Compass acts as well under water as at the surface. The three people who have been my companions during these experiments are so familiarized with the _Nautilus_ and have so much confidence at present in the movements of this machine that they undertake without the least concern these aquatic excursions.