THE CONQUEST OF NATURE 



tested, fitted with the familiar brass collars, and are 

 ready for use. 



The combined discoveries of all experimenters had 

 made it evident that certain conditions were necessary 

 to success, regardless of the structure of the carbon 

 filament. It was essential that the vessel containing 

 the filament should be entirely of glass; that the current 

 should be conveyed in and out this by means of platinum 

 wires hermetically sealed through the glass; and that 

 the glass globe must be as thoroughly exhausted as 

 possible. This last requirement proved a difficult 

 one for a time, but by improved methods it finally be- 

 came possible to produce almost a perfect vacuum in 

 the bulbs, with a corresponding increase in the efficiency 

 of the lamps. 



THE TUNGSTEN LAMP 



For twenty years the carbon-filament lamp stood 

 without a rival. But meanwhile the science of chem- 

 istry was making rapid strides and putting at the 

 disposal of practical inventors many substances 

 hitherto unknown, or not available in commercial 

 quantities. Among these were three metals, osmium, 

 tantalum, and tungsten, and these metals soon menaced 

 the apparently secure position of the highly satisfac- 

 tory, although expensive, Edison lamp. 



It will be recalled that the early experimenters had 

 used two metals, platinum and iridium, for lamp 

 filaments; and that these two, although unsatisfac- 

 tory, were the only ones that had given even a promise 



[234] 



