64
currents; it is composed of two end-pieces of copper connected together by a strip of alloy composed of a number of metals so combined as to cause it to be readily acted upon by a very low degree of heat; that is, to be melted by a current far below what would have an injurious effect upon the wires or other portions of the electrical apparatus in circuit with it. The copper end-pieces are provided with slots for the purpose of passing about the shanks and under the heads of the screws by which they are secured to the switch. A space is left between the parts of the switch to which it is secured, so that the safety-catch forms a bridge from one portion of the switch to the other. Should the current become too great for its carrying capacity, the alloy would melt and fall down upon the non-conducting base upon which the several portions of the switch are mounted, thus breaking the circuit and cutting off the current until suitable provision be made for its control, when another safety-catch is substi-
