1 86 PROJECTION OF IMAGES OF OPAQUE OBJECTS [Cn. VII 



290. Precaution for heavy currents. The lamps for heavy 

 currents are mostly of the hand-feed type and burn large carbons. 

 When starting the lamp it is much safer to make sure that the car- 

 bons are separated before closing the knife switch. Then one can 

 use the feeding screws and bring the carbons together to strike the 

 arc, and separate them a short distance immediately. If the 



FIG. 103. DIAGRAM OF THE PARTS AND COURSE OF THE RAYS IN THE 



UNIVERSAL PROJECTOSCOPE FOR OPAQUE AND LANTERN-SLIDE 



PROJECTION. 



(Cut loaned by the C. II. Sloelting Company). 



The instrument is here arranged for the projection of opaque objects. The 

 mirror, Af,, reflects the parallel beam from the first element of the condenser 

 (C), down on the horizontally placed object. The large aperture projection 

 objective directly above, and the 45 mirror beyond, project the image upon 

 the screen. 



Ordinary lantern-slide projection is shown by the broken lines, (for a de- 

 tailed description of all the parts see fig. 16). 



