94 The Dancing Mouse 



wire netting of \ cm. mesh, hinged at the top so that a mouse 

 could readily open them, in one direction, by pushing with 

 its nose at any point along the bottom. On the floor of 

 each of the electric-boxes, W, was an oak board i cm. in 

 thickness, which carried electric wires by means of which 

 the mouse could be shocked in W when the tests demanded 

 it. The interrupted circuit constituted by the wires in the 

 two electric- boxes, in connection with the induction appa- 

 ratus, 7C, the dry battery, C, and the hand key, K, was 

 made by taking two pieces of No. 20 American standard 

 gauge copper wire and winding them around the oak board 

 which was to be placed on the floor of each electric- box. 

 The wires, which ran parallel with one another, J cm. apart, 

 fitted into shallow grooves in the edges of the board, and 

 thus, as well as by being drawn taut, they were held firmly 

 in position. The coils of the two pieces of wire alternated, 

 forming an interrupted circuit which, when the key K was 

 closed, was completed if the feet of a mouse rested on points 

 of both pieces of wire. Since copper wire stretches easily and 

 becomes loose on the wooden base, it is better to use phosphor 

 bronze wire of about the same size, if the surface covered by 

 the interrupted circuit is more than three or four inches in 

 width. The phosphor bronze wire is more difficult to wind 

 satisfactorily, for it is harder to bend than the copper wire, 

 and it has the further disadvantage of being more brittle. 

 But when once placed properly, it forms a far more lasting 

 and satisfactory interrupted circuit for such experiments as 

 those to be described than does copper wire. In the case of 

 the electric-boxes under consideration, the oak boards which 

 carried the interrupted circuits were separate, and the two 

 circuits were joined by the union of the wires between the 

 boxes. The free ends of the two pieces of wire which con- 

 stituted the interrupted circuit were connected with the 



