U MAGIC LANTERN WITH DIRECT CURRENT [Cn. I 



13. Lamp-house. This is a metal box in which the arc lamp 

 is enclosed. It should be of good size, and be well ventilated by 

 means of openings at the bottom, and a flue at the top. There 

 should be one or more large doors, so that the lamp can be reached 

 for changing the carbons and making any necessary adjustments. 

 Opposite the crater at the end of the positive carbon there should 

 be a window about 2 to 3 cm. (2 in.) square so that the ends of the 

 carbons can be observed when the lamp is burning without opening 

 the door. This window should be provided with a combination of 

 red and green, or red and blue glass, or with smoky mica or with 

 deeply tinted glass so that the eyes will not be injured when look- 

 ing at the crater (fig. 133, 147). 



14. Incandescent lamp. If experiments are to be made it is 

 desirable to have an incandescent lamp with wire guard to use in 

 connection with the lantern. It should have a flexible cord of 

 sufficient length so that it can be carried to any desired position. 

 This lamp must be connected with the supply wires before the 

 rheostat is inserted ; then it will burn brightly while the arc lamp 

 is going. By consulting fig. 2, it will be seen that the two wires for 

 this lamp are connected one with each of the supply wires. That 

 is the incandescent lamp is not connected with one wire like the 

 rheostat and the ammeter but with both wires. 



15. Electric flash-light. An electric flash-light is a great 

 convenience about a lantern; and is almost a necessity when an 

 incandescent light (fig. 1,2) is absent. It should lock, so that it 

 will burn continuously ; then carbons may be changed by its light 

 and other corrections made. It is an absolutely safe light also. 



16. Incandescent lamp to burn when the arc lamp is turned 

 off. To avoid the great darkness in the room when the arc lamp is 

 turned out, it is advantageous to have an incandescent lamp con- 

 nected with the line, as indicated in fig. 4. 



17. Condenser. --This collects the light from the arc lamp 

 and directs it through the objective. In passing from the con- 

 denser to the objective it passes through the lantern slide or other 

 object whose image is to be projected (fig. 1,2 4). 



