MICROSCOPE LAMPS 



159 



FIG. 91. 



Microscope Lamp; Bausch & Lomb. 

 Arc Type. 



ing a current of more than 4 or 6 amperes, but for ultramicro- 

 scopic investigations an arc of 1 5 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. In Fig. 51 an inexpensive 

 but very convenient type of more powerful arc lamp l is 

 shown in partial section. 



Arc lamps for -microscopic 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, 111. 



FIG. 92, 



Microscope Lamp; Spencer Lens Co. 

 Arc Type. 



