H 



THE BOOK OF THE LANTERN. 



which proceeds from the lower lantern and carries away 

 the hot air, so that it cannot influence the lamp above. 



f^n 



FIG. 8. 



In the triple lantern (fig. 9) we have three optical 

 systems, and of course three lime-lights. This is the 

 exhibition instrument par excellence , and is commonly 

 used by those exhibitors who may be described rather as 

 entertainers than lecturers. . The third lantern is in reality 

 not often used. It is kept in reserve for producing occa- 

 sional effects while the other two lanterns are at work. 



In some respects the optical lantern resembles the king of 

 musical instruments, for the effects which can be produced 

 by it are dependent upon and limited by the number of its 

 parts. If an organ has but one row of keys, the instrument 

 can do little beyond furnishing an accompaniment. With 



