216 



CHEMISTRY OF THE SUN. 



[CHAP. 



By the use of the shutter, four or more spectra showing posi- 

 tions and thicknesses (but not lengths) of the lines could readily 



S-S 



I- 8 



CO fc( 



o> 

 bO - 



<u 



"^ rt fl 



Ml 



152 

 I? 



be obtained on one plate; and one of these might be the 

 solar spectrum to serve as guide and scale. Subsequently a 

 system of five slides outside the slit was used. 



