DEMONSTRATIONS OF APPARATUS 



219 



fig. 106. We push in the radiant n so that the rays diverge 

 considerably from the condenser c (removing the large lantern- 

 nozzle, if there is one, as such a tube would cut off the 

 diverging rays), and adjust the large lens L so that it collects 

 them all, and converges them upon the focussing lens F, which 

 projects an image upon the screen beyond s. The effect of this, 

 of course, is to convert the double condenser into a triple one, 

 with a much larger front to cover the object o. For many 

 purposes this method of work is very convenient. 



If the ordinary condenser is so deep that it will not bear 

 the radiant close enough for this arrangement, it may be 



Fiu. 1U6. Enlarging the Condenser 



better to remove the front lens of the lantern condenser, and 

 especially if the large lens L be itself pretty deep in curve. 

 It must of course be deep enough to converge the diverging 

 rays from c through F when the latter is focussed, and if it 

 is mounted with a shade round it to stop scattered light, the 

 effect will be all the better. With large projections like this, 

 the focussing lens F should be pretty long in focus say 12 to 

 18 inches and itself of a good size and with a marginal shade. 

 A vast number of projections illustrating mechanical and 

 molecular physics, resolve themselves simply into projections 



inch lens, or even six-inch, will however immensely increase the range of ap- 

 paratus brought within the field. 



