NOTES AND APPENDICES. j 1 3 



but the moment this pressure begins to diminish or increase, 

 either on account of nodosities in the carbon, or from other 

 causes, the brake is loosened or tightened, and thus the 

 carbon is allowed to advance more easily or less easily. 



This arrangement of the end contact at the extremity of a 

 jointed lever enabled the lamp to be automatically re-lighted 

 in case it went out. For this purpose it was sufficient to 

 place a contact below the jointed lever. When the latter is 

 no longer kept up by the movable carbon, it falls upon the 

 contact spring, and sends the current into the supplementary 

 lamp. 



NOTE E. 



The new metal discovered by Edison, mentioned on page 

 215, is simply platinum freed from the bubbles of gas enclosed in 

 its pores by being several times heated in a vacuum for pro- 

 longed periods. Under these conditions the metal becomes 

 much harder than in its ordinary state, and less fusible. 



Edison states that he has succeeded in obtaining a wire of 

 this kind, giving with a radiating surface of -fa of an inch, a 

 light of 8 candles, which would, with the ordinary wires of 

 commerce, have been only i candle. " I can therefore," he 

 says, " by increasing the calorific capacity of platinum, use 

 wires of very small radiating surface, and considerably reduce 

 the electric energy necessary for the production of a light of 

 i candle. / have, in fact, succeeded in obtaining in this way 

 8 luminous centres, each giving a perfectly fixed light of 18 

 candles, and yielding a total light 0^ 138 candles, using for the 

 purpose only 36,000 foot-lbs., that is to say, less than i horse- 

 power of steam" 



