SCIOPTICON MANUAL. 27 



the incident rays a b c. Some advocate a larger reflec- 

 tor, a parabolic reflector, or reflectors at the sides; but 

 unless the reflected light coincides with a b c, or nearly 

 so, it is not transmitted by the objective lens. 



"With proper adjustments, the light J, with that from 

 the reflector, is focused at the objective tube, of a com- 

 parative size proportionate to its relative distance from 

 the condenser; and the picture p is focused upon the 

 screen at i of a comparative size proportionate to its 

 relative distance from the objective. As represented in 

 Fig. 14, the smallest diameter of the cone of light in the 

 objective A B would be twice that of the point of light 

 I, and the height of the image i would be twice that of 

 the picture^. 



To project a picture to a great distance without too 

 much enlargement, the objective must be of low power 

 and carried forward; and the light should be from a 

 point (as in the calcium light) to avoid loss, and should 

 bo carefully adjusted to secure even illumination. 



The longitudinal ridge of light E (Fig. 15), with a 

 medium objective gives uniformly good results without 

 perplexing experimental adjustments. 



VARIOUS MODES OF LANTERN ILLUMINATION. 



The Hydro-Oxy-Calcium light, or lime made incan- 

 descent by a jet of hydrogen and oxygen in flame upon 

 it, is the most brilliant available light. Its concentrated 

 form adds greatly to its value for the lantern. The Oxy- 

 Calcium light produced by a jet of oxygen on to lime, 

 through an alcohol flame, is much inferior to what is 

 produced by the mixed gases. It is much used, because 

 ono gas is easier to manage than two, and it is counted 



