is here called to them so that the description immediately following may be more easily understood. Although this method of launching the aerodrome seemed to Mr. Langley, both theoretically and from the experience with the models, to be a satisfactory and feasible plan, there were two very important respects in which it seemed from the very first open to objection. In the first place, it was necessary that the aerodrome should be launched as nearly at its soaring speed as possible, because either an excess or deficiency of speed interfered to some extent with the equilibrium of the machine. So many factors were involved in the determination of what this final velocity should be that it seemed almost impossible to be sure of the results until at least one test of the aerodrome had been made. In the second place it was not known whether the rapid acceleration of the car would seriously interfere with the equilibrium of the aviator. In reference to the first question it was, of course, known that a freely falling body acquires a speed of 32 feet per second at the end of the first second after having fallen a distance of 16 feet. It was proposed to launch the aerodrome at approximately 35 feet per second; and, since the distance over which the car would pass in acquiring this speed was approximately 60 feet, the rate of acceleration would, of course, be less than that for a freely falling body. The conditions in the two cases, however, are quite different. In the case of the freely falling body there is the constant force of gravity which causes the acceleration. In the case of the aerodrome the car is initially standing still but ready to be acted upon by the combined force of the thrust of the propellers and the tension of the springs. The propeller thrust is approximately 450 pounds at the moment of releasing the car, while the spring tension adds approximately 400 pounds more pull, giving a total pull of 850 pounds acting on the car at the start. The weight of the aerodrome including the aeronaut being approximately 850 pounds, and the weight of the car being approximately 450 pounds, the total weight to be accelerated is 1300 pounds. The resistance of the car and the aerodrome is zero at the moment the car is released, and increases approximately as the square of the velocity until it reaches approximately 300 pounds at the soaring speed of the aerodrome; while on the other hand the spring tension decreases uniformly from 400 pounds at the start to approximately 76 pounds at the end of the track, and the thrust due to the propellers decreases from 450 pounds at the start to approximately 250 pounds at the moment of launching. Consequently, it is in a general way clear that the rate of acceleration of the aerodrome and car decrease, probably in a geometric ratio, the rate of acceleration [p162] at the moment of launching the aerodrome being much less than that of a freely falling body.