In the Report of the Jury the influence of the curved shape of the radial arms is considered very important in producing the effects. "If the vanes be straight," the Report observes, "it is evident, that whatever may be the velocity of the water in the direction of a radius, when it leaves the wheel its velocity in the direction of a tangent will be that of the circumference of the wheel, so that the greater the velocity of the wheel the greater will be the amount of _vis viva_ remaining in the water when discharged, and the greater the amount of power uselessly expended to create that _vis viva_. If, however, the vanes be curved backwards as regards the motion of the wheel, so as to have nearly the direction of a tangent to the circumference of the wheel at the points where they intersect it, the velocity due to the centrifugal force of the water carrying over the surface of the vane in the opposite direction to that in which the wheel is moving, and nearly in the direction of a tangent to the circumference, will--if this velocity of the water over the vane in the one direction be equal to that in which the vane is itself moving in the other--produce a state of absolute rest in the water, and entire exhaustion of _vis viva_." It is an interesting fact in the history of the invention, that the curved form was formerly adopted in some of the American pumps, and afterwards abandoned. There are competing claims to the invention of Centrifugal Pumps in the form now adopted. This kind of pump is stated to have been used in America in 1830. M. Charles Combe took out a patent in France for a similar pump in 1838; but though Mr. Appold was later in the field with his more perfect machine, he appears to have proceeded independently of previous inventors. TUBULAR BRIDGES.