In the Great Exhibition there were two other Centrifugal Pumps shown in action, one by Mr. Bessemer, and one by Mr. Gwynne, from America; but neither of them exhibited such striking effects as Mr. Appold's, which was so arranged as to throw out a continuous cascade of water from an aperture six feet wide, at a height of twenty-six feet. The Jury of Class V., who made numerous experiments to determine the practical efficiency of Centrifugal Pumps, and the relative merits of the three exhibited, reported very favourably of that of Mr. Appold, to whom a Council Medal was awarded. When rotating at the rate of 788 revolutions in a minute, and lifting the water 19·4 feet, the greatest practical effect, compared with the power employed, was attained. The discharge of water per minute at that height, with the pump rotating with a velocity of 788 revolutions, was 1,236 gallons; and with a lift of 8 feet, 2,100 gallons per minute were discharged, when the rotating velocity was 828 revolutions per minute. In Mr. Gwynne's and Mr. Bessemer's pumps, which had straight vanes, the ratio of power to the effect did not exceed 0·19. One of Mr. Appold's pumps, only one inch in diameter (the exact size of the small diagram), will discharge ten gallons per minute. The greatest height to which water has been raised by the pumps that are one foot in diameter is 67·7 feet, with a velocity of 4,153 feet per minute. The velocity with which the pump should revolve depends upon the height to which the water is to be raised. Beyond a certain height, the required velocity is practically unattainable, but long before that limit is reached the waste of power becomes so great, that the pump is of no value, for the pressure on the circumference counteracts the force with which the water is expelled. It is, therefore, only at comparatively low levels that the Centrifugal Pump is a useful engine. The absence of all valves renders it very suitable for draining marshes, and for other similar purposes, as the muddy water and suspended matters will not obstruct its action.