248 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



ratus is clearly shown in Plates 82, 83 and 84. The engine ran in a clockwise 

 direction, as viewed in Plate 82. A A are the fly wheels; BB the balance weights; 

 CC the dynamometer shafts, on which are fastened the rotor plates which re- 

 volve inside of the dynamometer drums, DD, between stator plates fastened 

 therein. The drums have a hub on either side, by which they are supported, 

 these hubs being journaled on ball-bearings in the pedestals resting on the 

 wooden framework. The rotor plates do not touch the stator plates in the dyn- 

 amometers, but drag on the water with which the drums are partially filled, 

 and thus tend to cause the drums to revolve around with them. The torque on 

 each drum is measured by means of a rope, not shown, fastened into the hook 

 at the top of the drum, the rope being given a partial coil around the drum and 

 passing off tangent thereto at the horizontal diameter is fastened to a pair of 

 spring scales hung from the ceiling vertically above the point of tangency. The 

 scales and ropes were unfortunately not in position when these photographs 

 were taken, but the arrangement of them should be readily understood. As the 

 friction of the rotor plates on the water heats it in exact proportion to the 

 amount of power absorbed, the small amount of water in the drums would be 

 soon converted into steam unless continually renewed or cooled. When the rotor 

 plates are revolving the centrifugal force keeps the water pressed toward the 

 circumference of the drum, and the friction at any speed is dependent on the 

 area of the rotor plates in contact with the water. The horse-power required 

 lo revolve the plates at any definite speed can therefore be controlled by hav- 

 ing an outlet for the water at the proper radial distance from the shaft. The 

 water from the water mains is led through the upper vertical pipe and allowed 

 to How into the funnel, and thence into the drum near the center where the cen- 

 trifugal force throws it to the circumference of the drum. The lower vertical 

 pipe is connected to the drum at a suitable radial distance from the center, and 

 the heated water thus passes through this pipe and into the lower funnel con- 

 nected to the sewer. By the use of the funnels the drums are allowed to rock 

 sufficiently to exert their pull on the spring scales without being affected by the 

 supply and exhaust of water. 



The water for cooling the cylinders is led from the bottom of the tank E 

 to the circulating pump /•', supported in a discarded lower pyramid of the aero- 

 drome frame, the pump being driven by the small vertical shaft, as already 

 described. The water, after passing through the pump and the engine cylin- 

 der-, is led hack 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 tempera- 

 ture. 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 passim.; through the gasoline tank. Instead of 

 jacketing the carburetor, a mid formed of thin copper tubes is supported just 

 above the multitude of small ail- pipes leading into the carburetor, and some of 



