CIRCULAR MAZE WITH CAMERA LUCIDA ATTACHMENT 59 



to an iron collar which slides freely up and down the rod CR. 

 This gives a very easy means of adjusting the size of the image, 

 focusing, etc. Below this first disc will be found a second disc 

 similar in character and controlled in the same way. A pad of 

 circular paper is laid upon this disc. 3 A reduced image (IM) of 

 the maze appears upon this paper. Extraneous light is excluded 

 by means of a soft black flannel curtain attached to the disc 

 which supports the lens (L). As may readily be seen from the 

 figure, the maze must be illuminated quite highly in order to 

 produce a clear image. The illumination is obtained by means 

 of six lights placed symmetrically around the maze and by one 

 light in the center of the maze. The six lights on the periphery 

 are supplied with opaque half shades, the light in the center of 

 the maze with a similar opaque circular shade. These shades 

 are of aluminium, blackened on the upper surface. The floor of 

 the maze is covered with imported white linoleum. This serves 

 to reflect the light upward to M,, thence to M. Passing through 

 the lens the rays are brought to a focus at IM. The ratio 

 between the maze and the image is 6.4 to 1. The image appearing 

 at IM is extremely clear when proper precautions are used to 

 sensitize the eye. Even the smallest mouse can be seen quite 

 clearly. 



The movements of the animal are traced upon white paper 

 with a soft pencil. In the early stages of learning several sheets 

 of paper are used on each animal at any given trial in order to 

 avoid a too complicated tracing. Each sheet is marked with 

 the number of the animal, the number of the trial and the serial 

 number of the tracing. The length of the lines so traced is meas- 

 ured by means of a chartometer furnished by Eugene Dietzgen 

 and Co. Keuffel and Esser furnish a similar and somewhat 

 better instrument. This instrument is surprisingly accurate 

 even in measuring lines which are tortuous in their course. The 

 error in measuring the length of the charted lines is about one 

 per cent. Fig. 2 shows the chartometer actually employed. 



3 It is convenient to cut out several sheets upon a disc cutter and to stamp a 

 hole 13 mm. in diameter in the center of each for the reception of a stud 13 mm. 

 in diameter and 1 cm. height placed in the center of the board IM. 



