Popular Science Monthli/ 



771 



lens-board in or out. Remove the slide 

 and adjust the arc-hini[) to remove the 

 bluish spots that will most likely be seen 

 in the field of light. By moving the 

 lamp up or down, to the right or left, or 



A #- 



Fig. 12. Dimensions of the upright 

 which serves to carry the light-shield 



back and forth upon the tubes, the field 

 will gradually be made perfectly clear. 

 When the light is uniformly white, the 

 slide may be replaced and a sharp focus 

 obtained by turning the milled, adjusting 

 knob on the lens-barrel. All lenses 



should be ke()t scrupulously clean, since 

 the slightest trace of dust will diminish 

 the brilliancy of the illumination to an 

 astonishing degree. 



Lantern-slide plates may be oblainerl 

 from any dealer in photographic ma- 

 terials. The standard size is t,}4 in. by 

 4 in. in the United States, and all slide- 

 carriers made for use in this country 

 take that size. The lantern slide emul- 

 sion or coating is so sensitive that the 

 slides must be han- 

 dled under ruby or 

 deep orange light 

 only, in order to 

 avoid fogging. 

 With this one ex- 

 ception, they ma>- 

 be handled precise- 

 ly as one would use 

 the popular devel- 

 oping-out papers. 



To make the 

 slide, the plate is 

 placed in a print- 

 ing-frame, with its 

 emulsion (dull) 

 surface next to that 



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Fig. 13. The light 

 shield which is sol- 

 dered to the upright 



of the film or 

 plate from which the print is to be made. 

 The frame is then held at a distance of 

 about 6 ft. from a 25-watt tungsten 

 lamp, and the latter turned on for two 

 seconds. This exposure is correct for 

 the average negative and is cited merely 



Scnsivs muit^ 

 not touch "^R^ 



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=i^ 



.r 



CJeorance i*-!0 

 a 



^fVnf ^fie^^i brass 'strip z fie^ ^ b'°^ ^^"P 

 ^onwitfi solder 1- 



n 



Rear v/etf 



o/lar 



Sheet iron hood 

 riveted on over 

 large opening 



Oisc of thin gtais 



w^ 4- ^ .^1 



i/iec}. fibre 



Jma/t flowerpot 

 fined with fire day 



efleq brass tube 

 sour cuts 



\^r~ 



^Rea. brass tube 



Clomps irirea on 

 Rear vietv 



■^ 2 Peg fibre 

 I Reg brass 



Fig. 14. Details of the arc-lamp which is adapted for use on comparatively small currents. 

 The carbons are fed by merely twisting and pushing the knobs fitted to their ends 



