i: 



JOHN LTNCK TTLRTCH 



lever. Electric contacts were placed on the longer arm of the 

 lever and on the base of the plane. These points were con- 

 nected in circuit with a solenoid coil, the armature of which 

 held the door closed. The coil was operated by a house current 

 of 110 volts with a rheostat in circuit to obtain the exact current 

 needed. The plane was placed 12 cm. back of the problem 



FIG. 3. INCLINED PLANE 



box in direct line with the center of the door and the entrance 

 to the wire hood which covered the problem. 



The principle of the plane is that of a lever, the fulcrum 

 being at one end of the base. The existence of another lever 

 underneath the upper arm of the first makes the entire apparatus 

 a double lever. With such an arrangement, slight pressure on 

 the upper surface of the plane brought about a better electrical 

 contact when the plane was plunged, and the movement of the 

 plane downward could be accomplished through a greater dis- 



