214 



ELEMENTS OF GENERAL SCIENCE 



TERMINAL 



STEEL 



street lighting (fig. 105), for locomotive and street-car head- 

 lights, for projectors for lighting buildings and monuments? 

 and for stereopticons. A lamp is now on the market which 

 operates successfully at 6 volts (24 watts) from a storage bat- 

 tery. Tungsten lamps requiring 20 amperes at 30 volts are 



used in motion-picture ma- 

 chines. Special lamps with 

 a blue bulb are made for 

 photographic purposes. 



The ordinary spark plug 

 used in the gas engine 

 (fig. 106) is of interest, 

 since it is said that there 

 are now nearly 

 5,000,000 auto- 

 mobiles in use 

 in America an 

 average of about 

 one motor car for 

 each twenty per- 

 sons. This spark 

 device consists of 

 a break in a cir- 

 cuit caused by 

 separating two 

 wires. An elec- 

 tric spark similar 

 to that which 

 can often be obtained by opening a knife switch is caused to 

 jump between the metallic tips. The gas mixture is exploded 

 when this spark occurs. 



224. The . motion-picture machine. The invention of the 

 motion-picture machine (fig. 107) is generally credited to 

 Eadweard Muy bridge, who was born in England. Muybridge 

 came to America, and in 1872, while at work in California 



PORCELAIN 



ELECTRIC SPARK 

 FIG. 106. An automobile spark plug 



