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SUMMARY OF CURRENT RESEARCHES RELATING TO 



into the vertical if desired for spectrum observations. In this latter 

 case, the iron cover, fastened with two milled heads, and carrying the 

 chimney -like protuberance, has to be placed in such a way that the b T oad 

 opening behind the lamp is covered up. The advantage of settir j the 

 carbon obliquely is that the light from the more brilliantly glowiug pole 

 (the positive) is thrown out almost horizontally, whereas in a vertical 

 setting the light is thrown downwards. On each side of the box is a 

 door for inserting the carbons ; the door contains a dark glass window. 



Fig. 89. 



The two large screws S t' and S t" are for centering the light. S t" 

 regulates the height, and S t', which terminates each end of a horizontal 

 axle, adjusts the light sideways. The lamps require a tension of 45 to 

 50 volts. The lamps are also fitted with mechanism for automatically 

 approximating the carbons so as to keep the incandescent crater in 

 the same spot. In one form of lamp this is done by hand movement. 

 In the selection of a lamp regard should be paid to the purpose in 

 view. For micro-projection a current of 20 amperes is sufficient ; for 



