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THREE ELECTRICAL ACHIEVEMENTS 189 



per cent efficiency of the incandescent lamp compares very 

 unfavorably, indeed, with the forty per cent efficiency of the 

 gasoline engine, the twenty two per cent efficiency of the 

 marine engine, and the ninety per cent efficiency of the 

 dynamo. 



Mr. Hewitt first stated his problem very accurately. The 

 waste of power in the incandescent lamp is known to be due 

 largely to the conversion of a considerable part of the electricity 

 used into useless heat. An electric lamp bulb feels hot to the 

 hand. It was therefore necessary to produce a cool light; 

 that is, a hght in which the energy was converted wholly or 

 largely into light rays and not into heat rays. This, indeed, 

 has long been one of the chief goals of ambition among in- 

 ventors. Mr. Hewitt turned his attention to the gases. Why 

 could not some incandescent gas be made to yield the much 

 desired light without heat? 



This was the germ of the idea. Comparatively little was 

 known of the action of electricity in passing through the 

 various gases, though the problem involved had long been the 

 subject of experiment, and Mr. Hewitt found himself at once 

 in a maze of unsolved problems and difficulties. 



''I tried many different gases," he said, ''and found that 

 some of them gave good results — nitrogen, for instance — but 

 many of them produced too much heat and presented other 

 difficulties." 



Finally, he took up experiments with mercury confined 

 in a tube from which the air had been exhausted. The mer- 

 cury arc, as it is called, had been experimented with years 

 before, had even been used as a hght, although at the time 

 he began his investigations Mr. Hewitt knew nothing of these 

 earher investigations. He used ordinary glass vacuum tubes 

 with a httle mercury in the bottom which he vaporized under 

 the influence of heat or by a strong current of electricity. He 

 found it a rocky experimental road; he has called invention 

 systematic guessing. 



''I had an equation with a large number of unknown 

 quantities," he said. ''About the only thing known for a 

 certainty was the amount of current passing into the recep- 

 tacle containing the gas and its pressure. I had to assume 



