CH. I] MAGIC LANTERN WITH DIRECT CURRENT 21 



In testing the lantern the following points should be especially 

 looked to : 



(A) That there is voltage in the supply line. This is easily 

 determined by turning on the incandescent lamp (fig. 2), or by 

 trying to light the arc lamp. 



(B) That the arc lamp is in working order and has carbons long 

 enough to last during the exhibition. By closing the switch and 

 bringing the carbons in contact and slightly separating them the 

 arc light should be established almost instantly (see also 30). 

 It takes a certain amount of experience to tell whether the carbons 

 are long enough to last during the exhibition. If there is any 

 doubt, put a new pair in position. 



From the high temperature of the carbons, and the lamp gener- 

 ally, after the current has been on some time, it is not easy to put 

 in new carbons in the midst of a demonstration. It also makes an 

 embarrassing break in the exercises (see 27). 



27. Gloves with asbestos patches. In spite of all precau- 

 tions it is sometimes necessary to work about the arc lamp after it 

 has been running, and is therefore very hot. By the use of suitable 

 pliers or tongs one can usually manage to do the things necessary ; 

 but for certainty and rapidity one always needs to be able to use 

 the hands directly. This is rendered possible by the use of gloves 

 with asbestos patches in the places which come in direct contact 

 with the hot metal or carbons. The gauntlet form of gloves is best 

 for then the wrists also are protected. 



The asbestos patches may be of asbestos cloth, or preferably of 

 quilted asbestos paper. The asbestos cloth is very thick and 

 clumsy. The asbestos paper of about half a millimeter thickness 

 (Vso in.) quilted between thin cotton or linen cloth answers well. 

 The quilting stitches should be long and extend obliquely in two 

 directions (fig. 5). The object of the quilting is to overcome the 

 weakness and easy tearing of the asbestos paper. 



For most work a patch on the thumb and index finger is sufficient 

 but as it is often convenient to grasp a hot carbon between the 

 index and middle finger, it is well to have a patch on the middle 

 finger also (fig. 5). 



