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From the above mentioned letter it appears that while at Havre he carried the same crew as at Rouen, he now had a lighted candle. On his early experiment he plunged in darkness fearful that a light might seriously vitiate the air. He now remained submerged in one test six hours without inconvenience, during which time he obtained some air through a tube with the open end supported by a surface float that could not be seen at a distance of 200 fathoms. While trying relative speeds produced by two men rowing as against two men working the screw, the former made the boat cover 60 fathoms in 7 minutes, while the latter propelled it the same distance in 4 minutes. He reported that the Archimedes screw and the horizontal rudder for depth control did not satisfy him in point of efficiency. The Bushnell screw was literally a full screw with several turns as proposed by Archimedes twenty centuries earlier to raise water. When Fulton found that a full screw was not efficient, he proposed to replace it with separate blades set at an angle similar to the sails of a windmill. To this arrangement he gave the name of “Flier.” The error of trying to use a full screw in propeller design persisted for more than forty years after Fulton had appreciated the lack of efficiency. Other engineers for nearly two generations ignored Fulton’s experience and decision.