10 THE ART OF PROJECTING. 



* 



vention. All who have seen its performance speak in 

 high terms of praise of it. At present there is but one 

 of them in the United States ; that one belongs to the 

 University of Pennsylvania, at Philadelphia. Its cost 

 was about $1,000. It needs but one or two horse-power 

 to run it eight hundred revolutions a minute, when it 

 gives a light equal to 1,600 candles. The latest pattern, 

 made especially for produciug the electric light, weighs 

 400 pounds, is run by one-horse power, and gives a light 

 equal to 2,000 wax candles. It would seem as though 

 this was the thing we have so long waited for. It is 

 now being used for lighting up large manufactories, only 

 four lamps being needed in a room three hundred feet 

 long, which is so well lighted as to leave no shadows. 



MAGNESIUM LIGHT. 



Wire made of the metal magnesium can be lighted 

 like a piece of pine wood, and continues to burn 

 with a most brilliant and dazzling light. In order to 

 regulate the burning of the wire or narrow ribbon, 

 which is generally employed, a lamp with a feed run by 

 clock-work is used. Sometimes two ribbons are burned 

 at the same time. This light is not constant, and is 

 even more liable to go out than the electric light, and 

 furthermore a special arrangement of cloth tubing is 

 used for carrying away the product of the combustion, 

 magnesium oxide, a bulky white powder, which accu- 

 mulates very rapidly. 



The cost of a lamp is about fifty dollars, and the 

 cost of the magnesium is about two dollars an hour. 

 It has the great advantage of being very compact, re- 

 quiring but a few minutes to prepare at any time, and 

 giving then a light which is amply sufficient for ary ex- 



