grooved wooden bars, and may be moved by the screw E. 
the frame may be raised or lowered, and the slit kept constantly 
ing 2 
a distance of 50 or 60 feet from a curtain or white wall, the i 
prism “ 
: 1e electric | 
- point of contact of the carbon poles is in the axis of the lenses 
and about two inches behind the slit, and the galvanic circuit 
having been closed so. ‘yi focal 
distance of the lenses is so adjusted as to form a distinct image 
of the slit on the screen. We then turn the lantern on the re- 
" The stands used by photographers are well adapted for the purpose. 
