CH. VII] PROJECTION OF IMAGES OF OPAQUE OBJECTS 187 



carbons are in contact after striking the arc, so much current flows 

 that there is danger of blowing the fuses or burning out some con- 

 nection. Be sure that the fuses and wiring are adapted to the 

 current (fig. 3, 691). 



291 . Illuminating the entire opaque object. For illuminating 

 opaque objects, Zeiss uses the principle of the search-light. That 

 is, the tw r o carbons are horizontal, the positive one has its crater 

 facing the concave mirror (fig. 95, 96). This mirror then reflects 

 the light toward the object. Depending upon its position, it can 



FIG. 104. NEW MODEL CONVERTIBLE BALOPTICON IN POSITION FOR 



OPAQUE PROJECTION. 

 (Cut loaned by the Bausch & Lomb Optical Co.). 



In the new (1913) models of projectors by the Bausch & Lomb Optical Com- 

 pany provision is made in each case to place the object in a horizontal position 

 and then to illuminate it either by a mirror (fig. iO5a) or preferably by tilting 

 the radiant and first element of the condenser (fig. 105), so that the light from 

 the lamp is projected directly upon the object. From the object a part of the 

 light extends out through the vertically placed projection objective to the 

 mirror and from the mirror to the screen. The mirror gives correct images on 

 the screen. 



