128 



MAGIC LANTERN WITH ACETYLENE LAMP 



[CH. V 



opaque sources, such as the incandescent mantle light or the 

 petroleum flame, a mirror placed behind the light does not in- 

 crease the brilliancy so much. 



211. Position of the acetylene lamp. This should be so that 

 the middle point of the flame is on the axis (fig. 64) and it should 

 be at a distance from the condenser of about the principal focal 

 length of the first element of the condenser and the middle flame 

 of the burner. For the best position in practice one must experi- 

 ment while looking at the screen image or disc of light, and arrange 

 the lamp to give the best effect ( 17, 55). 



B 



FIG. 71. UPPER AND LOWER ENDS OF A PRESTOLITE TANK USED \VITH 



THE MAGIC LANTERN. 

 FIG. 7iA. UPPER END OF THE PRESTOLITE TANK. 



V Outlet valve. It is opened and closed by a special wrench. 



Connector The metal connector for joining the gas supply and the acetylene 

 burner. 



Rt Rubber or flexible metal tube extending from the connector to the 

 burner. 



N Nut for holding the conical part of the connector in gas-tight union with 

 the hollow cone of the tank-valve. This valve must be set gas-tight before 

 opening the outlet valve (V). 



FIG. 71 B. LOWER END OF THE PRESTOLITE TANK SHOWING THE 



PRESSURE GAUGE. 



P G Pressure gauge indicating the pressure of the gas within the tank. 

 The pressure is given in atmospheres or in pounds per square inch or in both. 



