343 



E. L. XICHOLS. 



niMM..m""l" 



place, thèse latéral movements become entirely iini)erce])til)le. Tlie 

 température gradient iu the lajer of air borderiiig u])oii tlie luminous 

 euvelope of sucli a flame is very steep but it is capable of delînite déter- 

 mination by exploration with suitable thermo-elements; and so long as 

 the flame remains uudisturbed by latéral drafts its stability is surprising. 

 Fig. 2 shows the range of température near the flat face of an acétylène 

 flame determined by a method already described iu tlie paper to whicli 

 référence has just been made '). In this diagram abscissae are distances 

 in millimeters, measured from the médian ])lane 

 of the flame, and ordinates are températures cen- 

 trigade. The vertical dotted line indicates the 

 ])osition of the luminous mantle of the flame; 

 tlie horizontal dotted line shows the meltiug])oint 

 of the platinum. 



The line along whicli thèse measurements were 



Fig. 3. made passes through the flame at right angles 



to the médian plane; cutting tlie luminous mantle in tlie région of 



maximum brightness. This région is indicated a])proximately by the X 



in Fig. 3. 



Desoiuption of the apparatus. 



The burner used in the method to be described is of a well known 

 form, (Fig. 4), and is made from a single block of steatite. It is mounted 

 upon a horizontal bar of steel (Fig. 5) along 

 whicli it may be inoved l)y means of a micro- 

 meter screw. "J'he bar is set u]) in an inner 

 room without windovvs; being opposite a cir- 

 cular opening in the wall througli wliich the 

 flame may be observed from without. Jn this 

 o])ening is placed the lens of a micro-camera, 

 upon the ground glass screeu of which instrument, at a distance of 

 about two meters, an enlarged image of the flame is focussed. The pla- 

 tinum and platinum-rhodium or platinum-iridium wires to be tested are 



') NicnOLs; 1. c. 



