530 On the Production of very intense Sodium Flame. 



the central one upon the slit of a spectroscope capable of 

 clearly resolving the D lines. 



If the optic axis is not vertical some parts of the slit will 

 be illuminated with D l5 others with D 2 , and others with both 

 Dj and D 2 , as shown bv the photograph reproduced orr 

 PL VII. fig. 2. 



The completeness of the extinction is seen from the very 

 faint trace of D x seen at the regions where D 2 only was 

 transmitted. A very fine slit was used, and the plate over- 

 exposed. 



The block must be tilted forwards or back until the same 

 condition obtains all along the slit. The block is now rotated 

 slightly until either D, or D 2 is completely quenched. We 

 can now be sure that the image is made up entirely of 

 monochromatic light, as shown in fig. 3, in which the upper 

 portion of the slit is illuminated by D 2 light, and the lower 

 by the light of the sodium flame. 



For work with the spectroscope alone, in which cones of 

 light of large aperture are not needed, a quartz echelon) 

 answers every purpose, so that this instrument, recently 

 placed on the market by the Hilger Co., may be utilized in 

 a new way. 



The experiments outlined in the present paper were carried 

 on at the Sorbonne, in the laboratory of Monsieur Bouty,. 

 who placed every facility at my disposal. 



LXI. Note on the Production of a very intense Sodium 

 Flame. By R. W, Wood *. 



IN the course of the experiments described in the preceding- 

 paper, it was found desirable to have an exceedingly 

 intense sodium flame available for the adjustment of the 

 quartz block for the complete extinction of one of the 

 I) lines. 



As a flame of this description is often desirable in many 

 branches of optical work, it has seemed worth while to add 

 a separate note on the subject. 



The intensity of a soda flame depends chiefly upon the 

 rate at which the sodium molecules are delivered into 

 the flame, that is the rate at which the chloride of sodium is 

 volatilized. If a small fragment of the mantle of a Welsbach 

 light is laid upon the grill of a Meker burner, and two or 

 three small fragments of fused sodium chloride are placed on 



* Communicated by the Author. 



