146 



THE CHEMISTRY OF THE SUN. 



CHAP. 



line? of sodium on a screen to a large audience. The arrange- 

 ment is rather a delicate one, but the point is that we have not, 

 as in the case of the electric lamp as ordinarily used, vertical 



FIG. 64. Another arrangement of apparatus for projecting the long and short 

 lines on a screen, using a horizontal slit in the lamp close to the poles. 



poles, but horizontal ones, and we have a vertical slit close to the 

 poles in the very middle of the lamp, so that if the experiment is 

 carried far enough we can then prove the accuracy of the state- 

 ment that the line is an image of the slit, because the slit 



