[Illustration: Fig. 79.--Two dynagraphs, one for making a diagram of the lifting effect off the main axle-tree, and the other for making a diagram of the lift off the front axle-tree. By this arrangement, I was able to ascertain the exact lifting effect at all speeds, and to arrange my aeroplanes in such a manner that the center of lifting effect was directly over the center of gravity. The paper-covered cylinders made one rotation in 2,000 feet.] When fully equipped, my large machine had five long and narrow aeroplanes projecting from each side. Those that are attached to the sides of the main aeroplanes are 27 feet long, thus bringing the total width of the machine up to 104 feet. The machine is also provided with a fore and an aft rudder made on the same general plan as the main aeroplane. When all the aeroplanes are in position, the total lifting surface is brought up to about 6,000 square feet. I have, however, never run the machine with all the planes in position. My late experiments were conducted with the main aeroplane, the fore and aft rudders, and the top and bottom side planes in position, the total area then being 4,000 square feet. With the machine thus equipped, with 600 lbs. of water in the tank and boiler and with the naphtha and three men on board, the total weight was a little less than 8,000 lbs. The first run under these conditions was made with a steam pressure of 150 lbs. to the square inch, in a dead calm, and all four of the lower wheels remained constantly on the rails, none of the wheels on the outriggers touching the upper track. The second run was made with 240 lbs. steam pressure to the square inch. On this occasion, the machine seemed to vibrate between the upper and lower tracks. About three of the top wheels were engaged at the same time, the weight on the lower steel rails being practically nil. Preparations were then made for a third run with nearly the full power of the engines. The machine was tied up to a dynamometer (Fig. 78), and the engines were started with a pressure of about 200 lbs. to the square inch. The gas supply was then gradually turned on with the throttle valves wide open; the pressure soon increased, and when 310 lbs. was reached, the dynamometer showed a screw thrust of 2,100 lbs.,[9] but to this must be added the incline of the track which amounts to about 64 lbs. The actual thrust was therefore 2,164 lbs. In order to keep the thrust of the screws as nearly constant as possible, I had placed a small safety valve--3/4-inch--in the steam pipe leading to one of the engines. This valve was adjusted in such a manner that it gave a slight puff of steam at each stroke of the engine with a pressure of 310 lbs. to the square inch, and a steady blast at 320 lbs. to the square inch. As the valves and steam passages of these engines were made very large, and as the piston speed was not excessive, I believed if the steam pressure was kept constant that the screw thrust