THE CONQUEST OF NATURE 



gether without any special arrangement, like wool fibres 

 in felting. In passing through such a substance, there- 

 fore, the current cannot travel along a continuous fibre, 

 but must jump from fibre to fibre, "like a man crossing 

 a brook on stepping-stones." Each piece of fibre 

 constitutes a lamp or miniature voltaic arc, so that the 

 current is no longer a continuous one; and the little 

 interior sparks thus generated quickly destroy the fila- 

 ment. This discovery made it apparent that such an 

 artificial, feltlike substance as paper could not be made 

 to answer the purpose, and Edison set about searching 

 for some natural substance having fibres sufficiently 

 long to give the necessary homogeneity for the passage 

 of the current. 



For this purpose specimens of all the woods and fibre- 

 substances of all countries were examined. Special 

 agents were sent to India, China, Japan, South America, 

 in quest of peculiar fibrous substances. The various 

 woods thus secured were despatched to the Edison 

 plant at Menlo Park and there carefully examined and 

 tested. Without dwelling on the endless details of this 

 tedious task, it may be said at once that only three sub- 

 stances out of all the mass withstood the tests reasonably 

 well. Of these, a species of Japanese bamboo was 

 found to answer the purpose best. Thus the practical 

 incandescent lamp, which had cost so much time, in- 

 genuity, and money, came into existence, fulfilling the 

 expectation of the most sanguine dream of its inventor. 



In using these bamboo carbon filaments the original 

 spiral form of filament was abandoned, the now familiar 

 elongated horseshoe being adopted, as the carbon 



[232] 



