THE RADIANT 41 



in lecture halls and institutions all over the country such 

 electric lanterns are now to be found. A fuller description 

 of these lamps and their management will be found in the 

 appendix at the end of the book. 



The Incandescent Filament Lamp. This has for some 

 years been applied to the ordinary slide lantern, and where 

 the electric current is laid on is a very convenient and handy 

 radiant. The ordinary loop filament diffuses the radiating 

 part too much, and is also too feebly luminous, but the 

 Edison and Swan Company have brought out a lamp in 

 which the carbon is bent into a close grating, covering a 

 space of about half an inch square, which is perfectly suitable 

 for the purpose. This lamp is supplied complete with 

 reflector, etc., with a fitting to clamp on to any limelight 

 tray, for about forty- two shillings, and has been consider- 

 ably used where current heavy enough for an arc lamp is 

 not available. The current required is from three to six 

 amperes, and a light of 50 to 100 candle-power is obtainable. 

 Of late years, however, these lamps have been practically 

 superseded by 



The Nernst Lamp. This is really also an incandescent 

 lamp the filament taking the form of one, two, or three 

 straight rods and the vacuum bulbs being entirely dispensed 

 with. 



The light does not compare with the electric arc as the 

 size of the radiant is too large for really critical definition, 

 but these lamps do mark a very great improvement on the 

 above-mentioned incandescent lamps; and as they can be 

 connected to any ordinary lamp socket in connection 

 with the ordinary house -lighting mains, and can be used 

 with alternating or continuous current indifferently, they 

 are being extensively employed for ordinary lantern 

 demonstrations. 1 



1 For fuller details of Nernst lamps the reader is referred to the 

 Appendix. B. S. W. 



