SOUECES OF ILLUMINATION 83 



at which the best light is to be got is just short of this condition 

 in which the hissing occurs, so that it is best to let the gases be 



FIG. 23. Lime-light Jets, (a) Mixed, (6) Blow-through. 



somewhat in excess and then turn them both down slightly 

 until little or no sound be heard. 



The distance of the lime from the orifice of the jet is of great 

 importance, and it should be carefully moved away from the 

 jet until no black spot on the lime can be seen. This is perhaps 



G2 



