82 EXPERIMENTS IN AERODYNAMICS. 



out of its gearings by the means shown in plate 11, and with full current from 

 the dynamo the little propeller blades proved capable of rotating the great turn- 

 table, though slowly, for manifestly the work to be done in moving this great 

 mass Avas quite incommensurate with the capacity of a small propeller of 15 or 20 

 inches radius. Some special means must therefore be devised for utilizing the 

 advantages given by the attainable speed, steadiness, and size of so large a 

 whirling-table, without encountering the disadvantages of friction, resistance of 

 the air to the exposed surface, and similar sources of difficulty. To place the 

 propeller wheels, either actually driving inclined planes or models, or otherwise, 

 so, far as possible under the conditions they would have in actual free flight, and 

 to measure the power put out in actuating them, the resistance experienced, etc., 

 under these conditions, is evidently an object to be sought, but it is equally 

 evident that it is difficult of attainment in practice. Much study and much 

 experiment were given to this part of the problem, with the result of the inven- 

 tion, or rather the gradual evolution through successive forms, of the auxiliary 

 instrument described in the last chapter as the Component Pressure Recorder. 

 This conception of a method by which the I)i/namometer could be effectively 

 used was reached in Februaiy, 1889. and. together with its tinal mechanical 

 embodiment, was the outcome of much more thought than the invention of the 

 Dynamometer itself. 



As already stated, one of the objects of the Dynamometer is to determine the 

 power necessary to be expended in mechanical flight ; but manifestly this must be 

 done indirectly, for we have to experiment with a model or an inclined plane so 

 small as to be incapable of soaring while supporting the relatively great weight of 

 the Dynamometer-Chronograph, even if it had an internal source of power capable 

 of giving independent flight (wiiich the simple inclined plane has not). If such 

 a working model were placed upon the end of the turn-table arm, with the 

 Dynamometer supported on this arm behind or beneath it, and if the arm of the 

 turn-table were without inertia and offered no resistance to the air, the whole 

 might be driven forward by the reaction of the propeller of the model, actuated 

 by a motor, until the latter actually soars, and the Dynamometer supported on 

 such an imaginary arm might note the work done when the soaring takes place. 

 This conception is, of course, impossible of realization, but it suggests a method 

 by which the actual massive turn-table can be used so as to accomplish the same 

 result. Suppose the model with attached propeller and Dynamometer to be placed 

 on the end of the whirling arm, and the latter rotated by its engine. Further, 

 suppose the model aerodrome be also independently driven forward by its pro- 

 peller, actuated by an independent motor, at the same speed as that of the table ; 

 then, if both speeds are gradually increased until actual soai-ing takes place, it is 



