APPARATUS FOR SCIENTIFIC DEMONSTRATION 155 



portability. The rails and legs are here dispensed with ; the 

 lantern body is a mere frame hinged together, with a metal 

 top, and covered round when in use with thick black cloth ; and 

 the whole is placed on a table. The jet is also modified for 

 compactness, the usual long metal tubes being dispensed with. 

 Otherwise the lantern is essentially the same as the German 

 model. 



Lanterns of this type, either mounted on rails, or for 



FIG. 82. American Lantern 



simply placing on a table, with little unimportant variations 

 in detail, are now supplied by all the leading opticians. 



For optical experiments chiefly, and incidentally for other 

 physical demonstrations, the most popular pattern in public 

 institutions till lately has been the well-known Duboscq lantern 

 (fig. 83), fitted usually with the electric light. The square 

 body is of sheet brass, and is mounted upon four brass pillars. 

 There is a flange-nozzle fixed to the body ; and the special 

 feature of the arrangements is, that the condensers are fitted 

 in the back end of a large tube which slides freely backwards 

 and forwards in this nozzle, the character of the beam being 



