SOUND 



271 



the ceiling or an overhead screen. But a better and more 

 complete apparatus is one which Mr. C. Darker arranged for 

 me, as shown in fig. 142. The figure almost speaks for itself. 

 The plates, with apertures of various shapes which carry the 

 films, and which before use are blackened, heated, and then 

 coated thinly with solid paraffin, are laid upon the mouth of 

 a funnel, whose 

 narrow end has 

 an elbow over 

 which is strained 

 the speaking- tube, 

 the whole being 

 arranged in a sim- 

 ple frame which 

 can be inserted in, 

 or removed from, 

 a sort of box open 

 at one side. The 

 edge of the funnel 

 is pierced with 

 apertures to allow 

 air to escape from 

 under the film. 

 By slots in a board 

 at the back,two'in- 

 clined plane mir- 

 rors are adjust- 

 able in position, 



and can also be turned on axes. The nearly parallel beam 

 from the condensers, falling on the first mirror, is reflected 

 down upon the film ; from this it is reflected again to the 

 second mirror, and thence reflected out in a horizontal direc- 

 tion, where is adjusted the focussing lens, which focusses the 

 film upon the screen. Thus the whole works direct towards the 

 ordinary screen, and can all be adjusted before a lecture, which 



FI3L 142. Lantern Phoneidoscope 



