144 THE NORTHERN MICROSCOPIST. 

III. Lamps. 
The micrographer can utilise all kinds of lamps, nevertheless. 
the voltaic arc regulators are not often convenient save in some 



























































Fig. 9. 
experiments of photo-micrography. The incandescent are the 
lamps that will supersede all others. 
We may name two kinds of them,—incandescent lamps in free 
air and those in vacuo or rarefied gases. 
Incandescent lamps in free air, of which there are numerous 
examples, were invented by E. Reynier, of Paris. 
These lamps consist essentially of a carbon of the thickness of 
I, 2, Or 3 millimetres which touches against a copper or carbon 
point of contact of relatively large size. This contact is produced 
either by a weight or by the pressure of a column of mercury into 
which the pencil is plunged. The incandescence of the carbon 
pencil is limited by a lateral contact to one or a half centimetre. 
The light produced thus is at once vivid and soft, and we get the 
equivalent of several carcel burners with a small number of cells or 

