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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



coil, and this current was rapidly interrupted by a vibrator on the 

 principle of an electric bell. This induced an alternating current of 

 high voltage in the secondary coil as this coil had a great many more 

 turns than the primary coil had. Scientists found that about 70 per 

 cent of the electrical energy put into the Geissler tube was converted 

 into the actual energy in the light given out. 



In 1891 Mr. D. McFarlan Moore, an American, impressed with the 

 fact that only one-half of one per cent of the electrical energy put 

 into the carbon-incandescent lamp came out in the form of light, de- 

 cided to investigate the possibilities of the vacuum tube. After 

 several years of experiments and the making of many trial lamps, 



T,UBE DISTRIBUTED IN 



ANY FORM DESIRED 



TO LENGTHS OF 200 FT. 



Diagram of Feeder Valve of Moore Tube. 



As the carbon terminals inside the tube absorbed the very slight 

 amount of gas in the tube, a feeder valve allowed gas to flow in the 

 tube, regulating the pressure to within one ten thousandth part of an 

 atmosphere above and below the normal extremely slight pressure 

 required. 



he finally, in 1904, made a lamp that was commercially used in con- 

 siderable numbers. 



The first installation of this form of lamp was in a hardware store 

 in Newark, N. J. It consisted of a glass tube if inches in diameter 

 and 180 feet long. Air, at a pressure of about one-thousand part of 

 an atmosphere, was in the tube, from which was obtained a pale pink 

 color. High voltage (about 16,000 volts) alternating current was 

 supplied by a transformer to two carbon electrodes inside the ends 

 of the tube. The air had to be maintained within one ten-thousandth 

 part of atmospheric pressure above and below the normal of one- 

 thousandth, and as the rarefied air in the tube combined chemically 

 with the carbon electrodes, means had to be devised to maintain the 



