NERNST LAMPS 



91 



Incandescent Filament Lamps. Ordinary filament 

 lamps are not at all suitable for photomicrography, as 

 the filament is so thin that it is practically impossible to 

 obtain a sufficiently broad image of it to fill the field of 

 the objective. They may sometimes be used, in ground- 



Fig. 26 



ZEISS 5 NERNST LAMP 



glass globes, for low-power work, but they are never very 

 satisfactory, as their intensity is low. 



Nernst Lamps. The Nernst lamp is a very convenient 

 illuminant in certain of its forms. The usual 1 -ampere 

 type has a single straight filament broad enough to fill 

 the field of an objective with even illumination when a 

 suitable condenser is used, and of sufficient intensity to 

 use with high powers. There are other types with more 



