54 ROBERT M. YERKES AND JOHN B. WATSON 



front of the stimulus carriage, H, is placed the bench G, upon 

 which the experimenter sits. 



Between wall D and the stimulus carriage, H, is shown the 

 apparatus for the control of intensity, mounted upon the trestle- 

 work E. A heavy maple block, 46, 2" x 12" x 18", is mounted 

 upon four ball-bearing rollers, 47, so as ^to slide on track 48 

 parallel to and synchronously with the carriage H. A small 

 metal spur, 49, is fastened to block 46. By means of this metal 

 spur and the gut cord system 50, which is attached to the metal 

 framework of the reversing mechanism 36, block 46 is made 

 to operate the device for reversing the colors. The gut cord 

 50 passes around pulley 51, over and down 52, under 53 and 

 under another one not shown in the cut, up and over 54, thence 

 to 55 and back to the opposite side of the framework of the 

 reversing mechanism. Two stops, 56 and 57, are attached 

 to the cord in such a position that the spur 49 can throw^ the 

 mechanism 36 to the right or left, depending upon the extreme 

 right or left position of block 46. Since it has already been 

 pointed out that this block moves synchronously with the 

 stimulus carriage H it follows that a movement of H to the 

 extreme right or left position serves to reverse the right-left 

 relation of the two beams. 



The block 46 is made to move synchronously with the stimulus 

 carriage H by means of a heavy gut cord, 60, which passes 

 over a pulley 61 , connects with a small 3-32" iron rod, 62, through 

 turn-buckle, 63, with gut cord, 64, which runs over a fixed pulley 

 (not shown) fastened to the framework supporting the track 

 upon which carriage H runs, and is attached to the right-hand 

 side of the carriage. With this single cord system in operation 

 it will be seen that when carriage H is moved to the left block 

 46 is moved an equal distance to the left also. To the opposite 

 end of the block 46 is fastened a similar heavy gut cord, 66, 

 running over a fixed pulley not shown, but similar to pulley 

 61 on the opposite side, and connecting with the iron rod 67, 

 through tufn-buckle 68, with gut cord 69, over fixed pulley 70 

 to carriage H. It will be seen that this latter link system will not 

 be operative when the carriage moves from the left to the right 

 position, but that it does operate when the carriage is moved 

 from the right to the left. 



