sufficiently to exert their pull on the spring scales without being affected by the supply and exhaust of water. [Illustration: PL. 82 DYNAMOMETER TESTS OF LARGE ENGINE] [Illustration: PL. 83 DYNAMOMETER TESTS OF LARGE ENGINE] [Illustration: PL. 84 DYNAMOMETER TESTS OF LARGE ENGINE] The water for cooling the cylinders is led from the bottom of the tank ‹E› to the circulating pump ‹F›, supported in a discarded lower pyramid of the aerodrome frame, the pump being driven by the small vertical shaft, as already described. The water, after passing through the pump and the engine cylinders, is led back to the upper part of the tank. By suitable connections to the water mains and sewer, the water in the tank is kept at any desired temperature. The gasoline supply tank is seen on the left-hand side of the testing frame, as viewed in Plate 82, the carburetor being placed below it and the gas supply pipe from the carburetor passing through the gasoline tank. Instead of jacketing the carburetor, a grid formed of thin copper tubes is supported just above the multitude of small air pipes leading into the carburetor, and some of [p249] the hot water from the engine is by-passed through this grid and thus warms the air as it passes into the carburetor. The small pipe that by-passes this water through the grid is seen connected to the outlet water pipe just above the cylinders, a small butterfly valve in the outlet pipe enabling the amount of heated water passing through the grid to be controlled. The return from the grid is by means of the small pipe leading to the top of the large water tank. The tachometer, which gives instantaneous readings of the speed of the engine, is seen at ‹G›, where it is at all times in full view of the operator. These dynamometers proved to be excellently suited for the testing work, and far ahead of anything else the writer has ever found for engine testing. Since the power required to rotate the rotor plates, with a uniform amount of water in the drums, varies as the cube of the speed, it is readily seen that it is impossible for the engine to race or injure itself by running away, as frequently happens where there is no engine governor and Prony brakes are used to measure the power.