In constructing my apparatus, which is shown in the photographs, and also in a side elevation (Fig. 32), I aimed at making the apparatus very light and strong, avoiding as far as possible atmospheric resistance. In the drawing, _a_, is a thick seamless steel pipe 6 inches diameter; _b_, is a cast-iron pedestal firmly bolted to _d_, and connected to a large cast-iron spider embedded in hydraulic cement; by this means great rigidity and stiffness were obtained. _n_, _n_ was formed of strong Georgia pine planks 2 inches thick, and strongly bolted together. The two members of the long radial arm _h_, _h_, were made of Honduras mahogany, an extremely strong wood, and had their edges tapered off as shown at _y_, _y_. The power was transmitted from a small steam engine provided with a sensitive governor through the shaft _f_, _f_. In the base _c_, of the casting _b_, was placed a pair of tempered steel bevel gears, giving to the vertical shaft a high velocity. From a pulley on the top of this shaft, the belt _i_, was run through the arms _h_, _h_, as shown in section _y_, _y_. This gave a rapid rotation to the screw shaft in a very simple manner. The operation of the machine was as follows:--the aeroplane _g_, to be tested was secured to a sort of weighing apparatus which is shown in detail (Fig. 36), and the screw attached to the shaft. Upon starting the engine, a very rapid rotation was given to the screw which caused the radial arm to travel at a high velocity, the whole weight resting on a ball bearing at _w_. The radial arms and all of their attachments were balanced by a cigar-shaped lead weight _s_, which was secured to a sliding bar so as to make it easily adjustable. The thrust of the screw caused the screw shaft to travel longitudinally, and this was opposed by a spring connected by a very thin and light wire to the pointer of the index _o_. As the apparatus rotated rather slowly on account of its great diameter, it was quite possible to observe the lift while the machine was running at its highest speed. The aeroplanes were mounted after the manner of the tray of a grocer’s scales (see Fig. 36), and the lift of the aeroplane was determined by what it would lift at _r_--that is, while the machine was running at a given speed, iron or lead weights were placed in the pail _r_, until the lift of the aeroplane was exactly balanced, and then, in order to ascertain exactly what the lift was, the aeroplane was placed under what might be called a small crane, and a cord, running over a pulley, attached. The amount of weight necessary to lift the plane into the same position that it occupied while running was taken as its true lift. In order to facilitate experiments the gauge _p_, was provided. This gauge consisted of a large glass tube and the index _p_, with a quantity of red water at _q_. The centrifugal force of rotation caused the red water to rise in the tube. This was easily seen, so that if