THE BANISHMENT OF NIGHT 



he was perhaps in a more receptive state of mind than 

 if hampered by false or prejudicial conceptions. Be 

 this as it may, he began experimenting with mercury 

 confined in a glass tube from which the air had been 

 exhausted, the mercury being vaporized either by 

 heating, or by a current of electricity. No results of any 

 importance came of his numerous experiments for a 

 time, but at last he made the all-important discovery 

 that once the high resistance of the cold mercury was 

 overcome, a comparatively weak current would then 

 be conducted, producing a brilliant light from the glow 

 of the mercury vapor. Here, then, was the secret of the 

 use of mercury vapor for lighting a powerful current 

 of electricity for a fraction of a second passed through 

 the vapor to overcome the initial resistance, and then 

 the passage of an ordinary current to produce the light. 



In practice this apparent difficulty in overcoming the 

 initial resistance with a strong current is easily over- 

 come by the use of a "boosting coil," which supplies the 

 strong current for an instant, and is then shut off auto- 

 matically, the ordinary current continuing for producing 

 the light. The mechanism is hardly more complex than 

 that of the ordinary incandescent light, but the current of 

 ordinary strength produces an illumination about eight 

 times as intense as the ordinary incandescent bulb of 

 equal candle-power. 



The form of lamp used is that of a long, horizontal 

 tube suspended overhead in the room, a brilliant light 

 being diffused, which, lacking the red rays of ordinary 

 lights, gives a bluish-green tone to objects, and a par- 

 ticularly ghastly and unpleasant appearance to faces and 



[239! 



