A bar of wood similar in shape to _d_ (Fig. 25), but being 9 inches wide instead of 12 inches, was mounted in a wind blast of 41 miles an hour, with the front edge 3·31 inches above the rear edge, and this showed a lift of 7·08 lbs. and a drift of 3·23 lbs. When the angle was reduced to 2·31 inches, it gave a lift of 4·53 lbs. with a drift of 0·78 lb., and with the angle reduced to 1·31 inches, the lift was 3·37 lbs. and the drift 0·5 lb. It will, therefore, be seen that even objects rounded on both sides give a very fair lift, and in designing the framework of machines advantage should be taken of this knowledge. The bar of wood _c_ (Fig. 25) was next experimented with. With the sharp edge to the wind, and with the front edge 2 inches higher than the rear edge, the lift was 2·54 lbs. and the drift 0·76 lb. By turning it about so that the wind struck the thick edge, the lift was 4·45 lbs. and the drift 0·47 lb. This seemed rather remarkable, but, as it actually occurred, I mention it for other people to speculate upon. It, however, indicates that we should take advantage of all these peculiarities of the air in constructing the framework of a machine, which in itself is extremely important, as I find that a very large percentage of the energy derived from the engines is consumed in forcing the framework through the air. It is quite true that a certain amount of this energy may be recovered by the screw, provided that the screw runs in the path occupied by the framework. Still, it is much better that the framework should be so constructed as to offer the least possible resistance to the air, and, as far as possible, all should be made to give a lifting effect. [Illustration: Fig. 30.--Cross-section of condenser tube, made in the form of Philipps’ sustainers, in which _c_ is the steam passage.] [Illustration: Fig. 31.--The grouping of condenser tubes, made in the form of Philipps’ sustainers. This arrangement is very effective, condenses the steam or cools the water, and gives a lifting effect at the same time. The shape and arrangement of tubes shown at _b_, _b_, although effective as a condenser, produce no lifting effect, but a rather heavy drift.]