The old mill was infested with rats. My wife laid down to the boys the principle that good housekeepers were never troubled with vermin of any kind. The rats' sole occupation is to search for food. If you don't feed them they will not stay with you. But the boys said that they were glad of a chance to try an experiment on the rats. So one day when I went down to the mill I found them discussing the possibility of killing the rats by electricity. Harold said that he had read that it took much less electricity to kill any animal than to kill a man, and he would like to try, for instance, whether the shock which they had received from a bell would kill a rat. "Well, who's going to sit by," said Erg, "to close the primary circuit when the rat happens to get himself into the secondary circuit?" "Make him close it himself by some device," said Ernest. "They have a regular thoroughfare, a beaten highway, along by the wall, under the mill and up through a hole in the floor of my bedroom," said Dyne. [Illustration: Fig. 154] [Illustration: Fig. 155] "Well," said Harold, "I propose an electric trap which shall have two compartments. We will keep cheese in the inner compartment, the walls of which shall be of wires so that the rats may see the cheese. The floor of the outer apartment shall be covered with wire, as shown in Fig. 154. The wires of the secondary circuit from the bell (Fig. 156) shall be fastened to the binding posts _b_ and _c_ (Fig. 154). The partition _d_ shall be a swing door into the apartment _A_ where the cheese is. This is shown in profile in Fig. 155. _d_ must act as a switch to close the primary circuit through the bell _P_ (Fig. 156). We will have three dry cells in the primary circuit. Now this is the way it will work: A rat comes up from under the mill with wet and slimy feet--just suited for making contact for the electric current to enter his body. The smell of the cheese attracts him. He circles around the trap several times, watching the cheese in apartment _A_ through the wire screen. He sees a narrow opening into this apartment under the door _d_. He puts himself in position upon the floor of the outer apartment _B_, his feet bridging the gaps between the two systems of wires belonging to the secondary circuit. When he thrusts his head under the door and pushes it, it swings in a little, bringing one metal strip against another, which belongs to the primary circuit. This closes that circuit. He will never hear the bell ring, for the electric current which will shock him to death travels 186,000 miles per second, while his sensations travel only sixty miles an hour. If the involuntary recoil of his muscles does not make him jump back, so that the door will shut and stop the bell from ringing, Dyne will be awakened and he will close the door, since we will put the trap at that hole where the rats enter his bedroom." [Illustration: Fig. 156] The next night three rats were electrocuted by this device.