MICROSCOPE LAMPS 
159 
Fig. 91. 
Microscope Lamp; 
Arc Type. 
Bausch & Lomb. 
In Fig. 51 an inexpensive 
more powerful arc lamp ^ is 
ing a current of more than 4 or 6 amperes, but for ultramicro- 
scopic investigations an arc of 15 to 30 amperes is desirable and 
in many instances abso¬ 
lutely essential. Many 
styles of construction are 
found on the market. 
Several typical lamps are 
here illustrated. Fig. 91 
shows the 4 ampere hand- 
feed arc lamp of the 
Bausch & Lomb Optical 
Company; Fig. 92 that 
of the Spencer Lens Com¬ 
pany; and Fig. 93, the 
automatic 4 to 5 ampere 
lamp as manufactured by E. Leitz. 
but very convenient type of 
shown in partial section. 
Arc lamps for Tnicroscopic illumination should always have 
their carbons -at right 
angles, or approxi¬ 
mately so. Direct cur¬ 
rent arcs are far better 
than alternating cur¬ 
rent. The horizontal 
carbon should be the 
positive pole and the 
carbons should be .soft 
cored. By this means 
the crater is main¬ 
tained at a fixed point, 
and the condensing 
lenses of lamps or of 
special stands will pro¬ 
ject an image of the crater upon the microscope mirror or into 
the vertical illuminator without getting seriously out of align- 
1 Sold by Wm. Gaertner & Co., Chicago, Ill. 
Fig. 92. 
Microscope Lamp; Spencer Lens Co. 
Arc Type. 
