CH. V] MAGIC LANTERN WITH ACETYLENE LAMP 127 



ends to their connections by tying a string tightly around 

 them, if rubber tubes are used. If the supply is at a con- 

 siderable distance there should be a stop-cock at the lamp to 

 regulate the amount of gas, and to turn it off completely if desired. 

 At the end of the exhibition the gas must be turned off at the source 

 of supply. 



207. The management of the exhibition is simple, and should 

 follow th3 general lines laid down in Chapter I ( 21-41). It is 

 not wise to try to use a screen more than two to three meters square 

 (6-9 ft.), and one must keep in mind the requirements for feeble 

 lights ( 193). 



THE MAGIC LANTERN WITH AN ACETYLENE LAMP 



208. Source of acetylene. This may be from a house supply, 

 a special generator, or from a tank or cylinder of acetylene dis- 

 solved in acetone under pressure (prestolite tank). 



209. Acetylene lamp. The burners now used are in pairs. 

 Two jets set at an angle give a fused, flat flame. For the magic 

 lantern the lamp has from one to four of these twin burners in 

 a line. Behind the burner is a concave reflector returning the 

 backward reflected light to the burner and from thence on to the 

 condenser, so that as much of the light as possible is utilized for the 



screen image (fig. 70). 



210. Position of the concave mir- 

 ror. If a concave mirror is used to save 

 the light extending away from the screen, 

 its center of curvature should coincide 

 with the flame of a single burner, or its 

 center should be at the middle flame, if 

 there are several burners in a row. 

 FIG. 70. DOUBLE-JET The acetylene flame is very transpar- 

 R^Ko R L To' R "HE it, so that a mirror behind the burner 

 MAGIC LANTERN. will increase the light nearly the theo- 



retical amount (75%)- while with nearly 



