LIGHT. 89 



focus just within their outer and narrower end^ and at 

 the same time be so inclined that the light falls upon 

 the surfaces of the glasses from the broader end, as 

 shown above. Everything now depends upon the ad- 

 justment of the light to these reflectors. 



When properly placed, there will appear, high upon 

 the screen, the sectors of the polygon equally illumi- 

 nated : six of them, if the reflectors are sixty degrees 

 apart, and eight, if they are forty-five degrees. No 

 direct light should fall upon the screen, and will not, if 

 the end of the reflectors be kept high enough to cover 

 the focus of the condenser. A few minutes' work with 

 this will enable one to find the proper position for the 

 best effect. 



When the sectors appear equally illuminated, the 

 objects to be projected may be placed between the 

 condenser and the reflectors, — the fingers moved 

 about, a pencil, a key, a comb, or a strip of paper 

 with pins in it, or a leaf of a plant, perforated paper, 

 or the common glass trinkets which are usually put in 

 kaleidoscopes. If the objective lens be put close to 

 the outer end of the reflectors, the objects shown will 

 have a much sharper outline. For the best chromatic 

 effects flat pieces of colored glass will be found better 

 than round ones, as they transmit much more light, 

 but an assortment of the two will make a fine ap- 

 pearance. 



The common kaleidoscopes, which are so abundant 

 in the market, can be used for this work by removing 

 the ground glass in front of them and substituting a 

 piece of plain glass. These are generally provided 

 with a small lens, which will answer for an objective, 

 but at the end for the eye there is seldom quite room 

 enough to permit light to pass in sufficient quantity for 



