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Mr. Froude. Naval Architects, he represented the method of investigation mainly as a comparison between two contrasted conditions of experiment. I n one of those conditions the screw was working in undisturbed water, and the speed of advance, the speed of rotation, the revolutions per minute, the thrust yielded, and the force of rotation-in other words, the HP.-were all measured by dynamometric apparatus.I n fact, that condition of experiment precisely corresponded to the condition of experiment from which the data given in the Tables were obtained. I n the other condition of experiment, the only difference consisted in this, that the screw, instead of working in undisturbed water, was working behind the hull of the model, placed just as would be the screw of a ship ; and the effect of the presence of the model in front of the screw was of course to produce important differences in the condition of its working. He only wished to refer to two of those differences. One of them was that in order that the screw working behind the model should give the same thrust with the same number of revolutions as it gave in undisturbed water, the whole systemmodel, screw, and all-must be advancing a t a speed greater than the speed in undisturbed water, by the mean amount of the forward Downloaded by [] on [11/09/16].