ELECTRICAL INVENTIONS 247 



In wiring a house for electric lighting, it is customary to 

 connect the lamps in parallel rather than in series as the latter 

 method would offer more resistance, since all the current must 

 then go through each fine filament (Fig. 109). When the lights 

 are connected in parallel, the current flows through all the fila- 

 ments simultaneously, which is equivalent to being carried in 

 one wire as many times as large as one filament as there are 

 lamps. 



The current goes to the several lamps through wires that 

 connect with a fuse in a fuse box. The fuse is merely a strip 

 of some easily melted alloy inclosed in a tube or porcelain box. 

 If through the accidental crossing of wires an unduly strong 

 current should be sent into the light circuit, this strip or fuse 

 would become hot, melt, and so sever the connections before 

 enough heat could be generated in the wiring of the house to 

 start fires in the woodwork along which the wires might be laid. 



In the arc light the current is made to flow through two carbon 

 pencils whose tips are opposed at a slight distance from each 

 other. As the current jumps this space it carries with it nu- 

 merous highly incandescent particles from the positive to the 

 negative carbon and so produces the arc. The tip of the positive 

 carbon is, therefore, always hollowed while the negative is 

 always pointed. 



The temperature of the glowing tip of the positive carbon is 

 about 6,000 F. Such temperature makes the electric furnace 

 possible. A crucible of heat-resistant substance is fitted about 

 the ends of a pair of large carbons adjusted like those of the arc 

 light. A heavy current sent through the carbons melts exceed- 

 ingly refractory substances placed in the crucible. Carbon so 

 melted under high pressure forms artificial diamonds. 



In electric heat devices of various sorts, e.g., the heater, 

 the toaster, the percolator, the curling-iron heater, the bed 

 pad, the flatiron, etc. (Fig. no), the current is sent through 

 coils of wire or metallic plates that become more or less heated 

 according to their resistance and the strength of the current. 



