NO. 2 HISTORY OF ELECTRIC LIGHT SCHROEDER 65 



THE ENCLOSED ARC LAMP 



Up to 1893 the carbons of an arc lamp operated in the open air, 

 so that they were rapidly consumed, lasting from eight to sixteen 

 hours depending on their length and thickness. Louis B. Marks, an 

 American, found that by placing a tight fitting globe about the arc, 

 the life of the carbons was increased ten to twelve times. This was 

 due to the restricted amount of oxygen of the air in the presence of 

 the hot carbon tips and thus retarded their consumption. The amount 

 of light was somewhat decreased, but this was more than offset by 



'f 



Enclosed Arc Lamp, 1893. 



Enclosing the arc lengthened the life of the carbons, thereby greatly 

 reducing the cost of maintenance. 



the lesser expense of trimming which also justified the use of more 

 expensive better quality carbons. Satisfactory operation required 

 that the arc voltage be increased to about 80 volts. 



This lamp rapidly displaced the series open arc. An enclosed arc 

 lamp for use on i lo-volt constant potential circuits was also developed. 

 A resistance was put in series with the arc for use on iio-volt direct 

 current circuits, to act as a ballast in order to prevent the arc from 

 taking too much current and also to use up the difference between the 



