DEVELOPMENTS IN ILLUMINATION—MILLAR. 613 
filament lamp for free renewal to customers by the larger central 
stations of the country, and was lost in 1912 as a result of the influence 
of lamp manufacturers in promoting the sale of the metallized fila- 
ment rather than the sale of the carbon filament lamp. The substi- 
tution of the metallized carbon filament lamp for the earlier form of 
carbon filament lamp resulted in an increase of the standard of 
illumination throughout the country, for it consumed the same 
energy and produced about 20 per cent more light than did the earlier 
carbon filament lamp. 
In 1905 the various forms of carbon filament lamps were supple- 
mented by the tantalum lamp, an importation from Europe. This 
lamp never entered largely into American practice, its largest sale 
in the country probably never exceeding 3 per cent of the total 
sales of incandescent lamps. Its inferiority when operated upon 
alternating current and the announcement of the invention of the 
tungsten lamp shortly after its appearance prevented its attaining 
a position of importance in our practice. 
The tungsten filament lamp, first made available commercially in 
1907, was a marked improvement over other lamps then available, 
although its fragility and relatively high price led to restriction of 
its use in the earlier years of its history. Through the splendid de- 
velopment work of American lamp manufacturers this lamp has been 
rendered much more effective in all respects than it was a few years 
ago. The substitution of the drawn wire mounted as a continuous 
filament placed the lamp in a class with the carbon filament lamp 
in respect to ruggedness. The development of bulb-blackening pre- 
ventives has permitted its operation at, somewhat higher efficiencies. 
These improvements, with notable price reductions, have led to the 
large use of the tungsten, now known chiefly as the Mazda lamp, 
so that in 1913 sales of the Mazda lamp exceeded sales of all other 
types of incandescent electric lamps, notwithstanding’ the fact that 
the life standard which it sets is twice that which obtained pre- 
viously. 
During the past year a new form of tungsten filament lamp has 
been announced, in which the bulb contains an inert gas which re- 
duces the rate of evaporation of the filament and permits operation 
of the lamp at a higher efficiency. This gas-filled Mazda lamp is 
chiefly of importance in the larger sizes, and in effect creates a new 
lamp of characteristics similar to the incandescent lamp but of 
power equivalent to the arc lamp. In its smaller sizes it is included 
on the diagram, marking the highest efficiency attainment in the 
- production of light by small incandescent lamps. 
The Nernst lamp was brought to its highest development in 1908 
in the Westinghouse Nernst. Its active exploitation practically 
ceased in 1912, due to the superior qualities of the tungsten filament 
lamps. 
