QUARTER CENTURY OF ELECTRIC LIGHTING i6i 



thing that it was ten years ago, save that improvements in 

 manufacture have rendered the product somewhat more 

 uniform. Chief among these we must reckon the almost 

 universal use of the squirted cellulose filament and the intro- 

 duction of the chemical method of final exhaustion. Various 

 efforts have been made to introduce incandescent lamps of 

 about double the usual voltage. The difficulties of construc- 

 tion of such lamps, their relatively low efficiency and the use 

 with which an alternating distribution at the usual voltages 

 is effected constitute ample reasons for the small use of these 

 high voltage lamps; while the vigorous objections of the fire 

 underwriters have discouraged any extensive exploitation 

 of them. 



The greatest change of recent years in general lighting 

 has been the introduction of the enclosed arc lamp, which has 

 worked a revolution in indoor lighting at constant potential 

 as well as in street lighting. It has on the whole stimulated 

 incandescent lighting, however, by raising the common 

 standard of brilliancy, and by aiding in the unification of 

 service. Considerably more than half the arc lights in use are 

 enclosed, the bulk of the open ones being used for street 

 lighting by companies not yet quite ready to undertake 

 re-equipment. Of the alternating arcs more than nine tenths 

 are of the enclosed type, a result due almost to necessity. 

 The introduction in recent years of series alternating arcs fed 

 from constant current transformers is responsible for most of 

 the use of alternating current arcs, and practically all such 

 are enclosed. 



Through all these years of progress the incandescent lamp 

 has held its own and has grown in relative popularity. The 

 same virtues that gave it its start in life have kept its fortunes 

 in the ascendant. With all its failings in points of efficiency 

 it is to-day, as it was in the beginning, the best available 

 illuminant in point of quality and general usefulness. Within 

 very recent years determined efforts have been made to obtain 

 other electric lamps of equally good qualities and of higher 

 efficiency, but up to the present these efforts have not been 

 crowned with success. The Nernst lamp, most admirable in 

 some respects, is at its best in competition with the arc rather 



Vol. 7—11 



