168 



OPTICAL PROJECTION 



fig. 90. The reflector is here simply set in a wooden cubical 

 box, with the side which is turned towards the lantern con- 

 densers left open. A rod at the side carries a plain lens in one 

 of the sliding fittings presently figured, and another sliding 

 socket carries the reflector. 



The illumination is not even and good with such attach- 

 ments, unless pains are 

 taken to accurately adjust 

 the first reflector as re- 

 gards the parallel (or 

 slightly diverging) rays 

 from the lantern con- 

 densers. To ensure this 

 the lantern itself is often 

 fitted up by Hawkridge, 

 and other American opti- 

 cians, as in fig. 91 . Here 

 the two first lenses of 

 a triple condenser are 

 mounted in the body of 

 the lantern, which is sup- 

 ported on pillars ; while 

 the third or converging 

 lens is fitted in a plate 

 hinged to the top of the 

 lantern front. This plate 

 has at one side a pillar 

 or standard, which carries 



the focussing power and second reflector. For vertical work, 

 the lantern is arranged as in the diagram, the front plate and 

 lens being supported in a horizontal position by a movable 

 triangular box, to whose hypotenuse side is fixed the reflector ; 

 but when ordinary work is required, this box is removed, when 

 the plate drops down to a vertical position, with the focussing 

 power out in front as usual. The second small reflector is 



FIG. 91 



