CH. 112 DARK-GROUND ILLUMINATION WITH HIGH POWERS ;6a 



lamps requiring a 6-volt current. This six-volt current may be 

 direct or alternating. In America alternating current is more 

 commonly found in lighting systems than direct, but it is at a volt- 

 age of no or 220. In order to employ the alternating current, then, a 



FIG. 5oc. DIAGRAM OF A LAMP FOR DARK-FIELD MICROSCOPY. 

 (About one eighth natural size.) 



Axis The axial ray from the lamp. The parallelizing lens is centered to it and 

 the lamp filament is in the focus of the lens. 



bb Baffle plates to prevent the escape of light around the bottom of the lamp- 

 house. 



DG Plate of daylight glass to which is cemented the colorless parallelizing 

 lens (L). 



es Metal plate over the lens to shade the eyes. 



Lamp The 6-volt, headlight lamp with very concentrated filament. 



Lamp House. The metal container for the headlight lamp. 



ms Mogul socket for the 6-volt lamp. 



5 Thumb screw for holding the lamp at the right height. 

 si Slide for focusing the lamp with the parallelizing lens. 



ot, it The outer and inner tubes for centering the lamp vertically. 



Lamp wires The large conducting wires between the secondary of the trans- 

 former and the mogul socket. 



me Mistakeless connection for the lamp wires and the transformer. It is 

 unlike any connection for the no-volt circuit ( 675). 



6 Volts The voltage of the secondary (S) side of the transformer. 



j/o Volts. The voltage of the supply to the primary (P) side of the transformer. 

 Transf. Transformer to step down from no to 6 volts. 

 PS P the primary and S the secondary side of the transformer. 

 Supply wires. The wires from the electric supply. The voltage in them is 

 no, while that in the lamp wires is 6. 



