On completing the _Argonaut_ in 1897 we amplified these experiments, five men remaining hermetically sealed in the _Argonaut_ for a period of five hours without admitting any air from our air storage tanks, and later on in the _Protector_ eight men remained submerged for twenty-four hours, no fresh air being admitted during the first twenty hours. As the volume of air space in the _Protector_ was about three thousand cubic feet, this averaged about eighteen cubic feet per man per hour. Without the definite knowledge of my previous box experiment it is very doubtful if the crew would have consented to remain submerged so long without renewing the air supply, so great is the effect of imagination. In our first test to determine a practical time of submergence in 1897 we had been submerged for nearly two hours when I noticed some members of the crew showing signs of distress. After a time they got together in the after part of the boat and appointed a spokesman, who came to me and asked if I had not noticed that breathing had become very difficult. They urged that we should go up immediately. By this time two of the men were breathing with evident exertion, and beads of perspiration were on their faces. I told them they were suffering from imagination, and explained my experiment with the box. I then took a candle and proved to them that it burned freely in all parts of the boat. We measured the height of the candle flame at the floor of the boat and found it one and five-eighths inches high. In the twenty-four hours' test on the _Protector_ the men became frightened in the same way, but after an explanation had been made and the candle demonstration had been shown them they lost their fear and in a few minutes all were breathing as normally as ever. I have always had some little sympathy for the sensations or fears which those without a knowledge of natural physics might experience on going down into the water; but I have had little sympathy for those who by their education should know and understand the principles of submarine navigation, when operating with a properly designed boat with an experienced crew. Now, one of the features which the _Argonaut_ possessed, which was new in its application to submarine boats at that time, was the use of a diving compartment and air-lock connected with the main hull of the vessel, which would permit divers to leave the vessel when submerged by opening a door in the bottom of this diving compartment after first filling the compartment with compressed air corresponding to the pressure of the water outside of the vessel, which varies in accordance with the depth of submergence.