ELECTRIC LIGHTS. 



'63 



to the inch of filament. By increasing the current the 

 light increases very rapidly, so that by doubling it the 

 light may be made equal 

 to 100 candles or more, that 

 is, sixteen candles or more, 

 to the inch of filament. 

 When filaments are made 

 tubular, like Bernstein's, 

 they may be made much 

 shorter. Such an one, hav- 

 ing a length of three inches, 

 bent into a U form may give 

 a light equal to 300 candles, 



100 candles to the inch, 



and this answers for 

 projections where the de- 

 tails of the picture are not 

 too minute. It will not 

 answer well for micro- 

 scopic projections, but for 

 common transparencies 

 works well enough. 



When such a lamp is 

 placed in the lantern and 

 moved towards the con- 

 denser, the light upon the 

 screen will increase to a 

 maximum, when the en- 

 larged image of the fila- 

 ment will appear, and the 

 disc will not be uniformly 



lighted. The lamp should therefore be drawn back 

 a little to secure a uniform field. This will be at 

 the sacrifice of some of the light, but the brightness 



BERNSTEIN'S ELECTRIC LAMP. 



