236 ELEMENTS OF GENERAL SCIENCE 



There is almost no limit to the industrial uses of motors. 

 Electric vehicles, printing presses, lathes, cranes, dental 

 appliances, air compressors, coal cutters, band saws, shoe- 

 making machinery, tool grinders, and automobile and farm 

 machinery may be named as illustrations. 



242. Electric bells in a modern city residence. If a resi- 

 dence is supplied with alternating current both day and 

 night, the electric bells can be operated with a small device 



FIG. 120. Demonstration materials lor studying the transformer 



At the left, a bell-ringing transformer for an alternating current circuit ; in the 



middle, the parts of two transformers; at the right, an ordinary commercial 



transformer used outside of houses for reducing electric currents for house use 



called a bell-ringing transformer. This, when once installed, 

 will last many years, requires no repairs, and costs practi- 

 cally nothing for operation. How does this appliance work ? 

 Two wires are brought from the alternating-current circuit 

 (110 volts) to the terminals on the left (fig. 120) of the 

 transformer. The bell circuit is attached to the binding 

 posts on the right side of the transformer. The bell rings 

 vigorously. However, the full current from the 110-volt 

 circuit does not enter the magnets of the bell. 



It is a peculiar fact that in this case a current is obtained 

 from a coil which has no direct connection with a source of 



