20 THE BOOK OF THE LANTERN. 



mount be square or cushion-shaped, such a small condenser 

 would infallibly cut off the corners of the projected image, 

 and for such pictures, therefore, a 4-inch condenser is 

 necessary. But the smaller condenser transmits more 

 light, for the reason that being of shorter focus, the lime 

 cylinder is brought nearer to it. Some well-known 

 exhibitors, seeing the great importance of getting all the 

 light upon the screen that they possibly can, use nothing 

 but 3J-inch condensers, but this obliges them to confine 

 themselves to round pictures. On the whole, I prefer 

 myself the 4-inch condenser, for although I lose some 

 light, I can make use of any shaped pictures or diagrams 

 which may be required. (If the lantern be used for 

 photographic enlarging purposes, then a large-sized con- 

 denser is the great thing needful, at least, we must have 

 one of a size large enough to cover the negative which 

 has to be enlarged ; a quarter-plate size necessitating a v 

 5 -inch condenser and so on. But in that case brilliancy 

 of image is quite a secondary matter, and is compensated 

 for by extension of time occupied in the operation.) It 

 must also be borne in mind that, quite apart from the 

 question of focal length of the condensing lens, there is a 

 limit to the near approach of the incandescent lime 

 cylinder towards it, for the intense light is naturally ac- 

 companied by a fervent heat, which will surely crack 

 a lens if it be too near to ifc. In the chapter on the 

 working of the lime-light, precautions against this accident 

 are fully dealt with. 



There are two forms of condensers, either of which 

 may be commonly found in commercial lanterns. One 



