20 ROBERT M. YERKES AND JOHN B. WATSON 



track made by soldering, or screwing, a 3-16 inch diameter 

 coppered iron rod to the broader side of a ^xf inch coppered 

 iron bar. The weight of this track is sufficient to hokl it in 

 position, but it may advantageously be lightly secured to the 

 floor of the box at two points. If the rod be screwed, instead 

 of soldered, to the bar, it is well to insert a strip of -^ inch felt 

 between them, throughout their length, to diminish the noise 

 of the moving carriage. 



Against the experiment box end of each compartment of the 

 light box is placed a water cell (R, fig. i) to serve as an adia- 

 thermal screen. The cooling cells used by Bausch and Lomb 

 in their projection lanterns prove satisfactory. They are circular 

 metal cells of at least 11 cm. diameter with a water space of 4.8 

 XI 2.5 cm. 



The stimulus adapter is a device by means of which the ex- 

 perimenter is able to regulate the size, form and position of 

 the visual stimuli. It appears as the front (end) of the light 

 box when the experiment box, fig. 4, is removed. In fig. i it is 

 shown as a unit and in fig. 3 construction drawings are provided. 



A steel casting | inch thick, carefully planed, and firmly 

 bolted to the light box is shown at z, fig. i. This sheet of steel 

 contains two circular apertures, 10 cm. in diameter, through 

 which the light passes from the light box to the experiment 

 box. 



To the metal plate z, the stimulus adapter is attached by 

 four bolts, one of which is labelled as h in fig. i. 



The essential parts of the stimulus adapter are: (i) a metal 

 frame composed of the straps d and d', fig. i, and the two vertical 

 •straps, e, fig. 3. The inner edges of the horizontal straps are 

 rabbeted and into them is fitted (2) the aluminum plate y, 

 which slides smoothly on a pair of tracks, k, fig. 3, which are 

 screwed to d and d'. Y moves on six rollers, m, n, o, fig. 3. 

 It contains three windows, each 12 cm. square, located 27 cm. 

 apart (center to center). These windows receive the standard 

 stimulus plates described below. (3) Back of each window 

 is attached by four small screws a square frame of 1-16 inch 

 sheet brass, p, fig. i, 9.3 cm. on its inner edges and 13.3 cm. 

 on its outer edges. A flange is thus created which serves to 

 hold; in each window, (4) a brass plate, s, fig. i, 12x12 cm. and 

 I -1 6 inch thick. This plate contains an accurately cut opening.. 



