THE PLANE-DEOPPEK. 27 



poiieiit of pressure derived from the wind of advance ; but, so far as I am now 

 aware, this problem of the velocity of fall of a horizontal plane moving hori- 

 zontally in the air has never been worked out theoretically or determined experi- 

 mentally, and I believe that the experimental investigation whose results I am 

 now to present is new. 



With all the considerations above noted in view, I have devised a piece of 

 aj^paratus which, for distinction, I will here call the Plane- Dropper, intended, in 

 the first place, to show that a horizontal plane in lateral motion requires an 

 increased time for its descent ; second, to make actual measurement of the time 

 of fall of Vt\riously shaped planes and to give at least the first approach to the 

 procuring of the quantitative data ; third, to connect these experiments with those 

 immediately allied to them, where the plane has an inclination to the horizon ; 

 and, fourth, to make experiments to show the depth of the air strata disturbed by 

 the moving plane during the time of its passage. 



Drawings of the Plane-Dropper are given in plate VI. F is a vertical iron 

 fi-ame with a wooden back WW, which is shown fastened b}^ bolts B to the 

 end of the arm of the turn-table. The fourth side of the rectangle is a planed 

 brass frame on which an aluminum falling-piece runs up and down on friction 

 rollers. The plate contains enlarged front and side views of the falling-piece, 

 and a section of the brass frame and falling-piece, showing the arrangement of 

 the ebonite friction rollers. By means of the clamps CC' the falling-piece carries 

 two wooden planes, which may be set by the clamps DD' horizontal, or at any 

 angle with the horizon up to 45°. Gruy lines extend from the top and bottom of 

 the falling-piece to the outer edges of the planes and keep them from bending. 

 A detent at the top of the frame holds the falling-piece until released at any 

 desired instant by the action of an electro-magnet, M. A spring cushion, S, at 

 the bottom of the frame, breaks the force of the fall. 



Provision is made for setting the brass frame vertical, and hy means of the 

 handle H the frame can be revolved 180° about its vertical axis, so as to present 

 successively one side or the other side to the wind of advance, and thus to eliminate 

 any defect in setting the wings absolutely horizontal, or any inequality in the 

 instrument not otherwise suspected. 



The total fall is four feet, and the total time of fall is registered electrically 

 by means of contact-pieces a and e, near the top and bottom of the frame. As 

 soon as released, the aluminum falling-piece presses the contact-piece a against 

 the frame and completes the circuit. Wliile falling, the circuit is open, and at 

 the distance of four feet the contact-piece e is pressed against the frame and the 

 circuit is again closed. In November, 1890, three additional contact-pieces, 

 J, c, d, were added, so as to measure the time of fall through each successive foot. 

 The registration is made on the stationary chronograph, together with that of 



