NICHOLS. — THE VISIBLE RADIATION FROM CARBON. 



83 



ure 4 c), in which the two cylindrical jets of gas in the process of combus- 

 tion unite to form a single flat vein or envelope which constitutes the 

 luminous portion of the flame. When this third stage is readied, there 

 is oreat stability of form and position. Such a flame responds with a 

 sharp lateral motion to air waves such as are produced by the slamming 

 of a door, but is comparatively unaffected by slight drafts. Even in a 

 room not essentially free from air currents the lateral motions of the 

 flame, which may be accurately observed by throwing an enlarged 

 ima^e of it, viewed edgewise, upon a screen, rarely amount to more 

 than .1 mm., and in an especially protected place, these lateral move- 

 ments become entirely imperceptible. The temperature gradient in the 

 layer of air bordering upon the luminous envelope of such a flame is 

 very steep, but it is capable of definite deter- 

 mination by exploration with suitable thermo- 

 elements, and so long as the flame remains 

 undisturbed by lateral drafts its stability is 



surprising. 



The burner used is of a well-known form 

 (Figure 5), and is made from a single block of 

 steatite. It is mounted upon a horizontal bar 

 of steel (Figure G), along which it may be Figure 5. 



moved by means of a micrometer screw. 



The bar is set up in an inner room without windows, being opposite a 

 circular opening in the wall through which the flame may be observed 

 from without. In this opening is placed the lens of a micro-camera, 



«C~J 



Figure G. 



upon the ground-glass screen of which instrument, at a distance of abut 

 two meters, an enlarged image of the flame is focussed. The platinum 

 and platinum-rhodium wires to be tested are drawn down to a 



