26 HAROLD C. BINGHAM 



hinged at the outside, and is equipped with a 2 c.p. frosted 

 electric lamp, a watch glass for water, and sand or litter in which 

 food may be scattered. It is also provided on the outer side 

 with hidden holes for ventilation. 



Between W and iV is a vertically sliding door, E closed and 

 E' open, 3 mm. thick which fills an opening 8 by 10. Suspended 

 from an upright frame, F, is a coiled spring, S, which passes 

 through the walls of the experiment box to the top of E. When 

 E is closed, 5 is extended and in a state of torsion, hence when 

 E is released 6* tends to return to a state of rest and the doorway 

 is opened. 



The method of closing the exits is best illustrated in figure 3. 

 A silk line, e, passing up through a wire loop directly under E, 

 is attached to the lower part of the door. By pulling on e, 

 the experimenter can close E which automatically locks when 

 it is closed. By stepping on or striking T, the chick can release 

 the lock. The experimenter, however, by catching e on the 

 hook, h, can prevent the exit from opening when the lock has 

 been released. This automatic release was devised by Professor 

 F. S. Breed. 



The construction of this mechanical device for locking and 

 opening E appears in figure 5 where T is the trip that was seen 

 in the other figures and t is a short piece of No. 30 black thread 

 attached to T a.t a. Passing down through the floor, F, of the 

 electric box, t runs over a pulley, P, and is fastened to the spring 

 lock, L, at b. B is a. block through which L passes and against 

 which one end of the spring, C, presses. Z) is a stop attached 

 to L supporting the opposite end of C. This spring tends to 

 force L in the direction of X and to keep T in the position as 

 illustrated. But when sufficient pressure is applied to T at any 

 point above R, L is forced back in spite of the pressure of C, 

 E is released at X, and the recoil of 5 raises £. When E is 

 drawn down, L, by reason of the slanting end surface at X, is 

 forced toward P until the notch of E has passed below the lower 

 side of L when the constant pressure of C toward X forces L 

 into the notch of E and the door is again locked. 



In several respects, figure 5 is a poor representation of this 

 tripping device. L is shown as constructed solidly in B, when, 

 in reality, it slides freely through B. Moreover, L is shown in 

 the figure as wide as the floor of the experiment box, but it is 



