II.] 



PIONEERING DIFFICULTIES. 



'21 



FIG. 14. Spectroscope attached to a large refractor which throws an image of' 

 the sun on the slit plate. 



In the first method of work adopted in the laboratory the spectro- 

 scope was directed to the light source, so that the spectrum was built 

 up of the light coming from all parts of it without distinction. 



FIG. 15. The first method of work with the slit of the spectroscope close to the light 

 source. In the experiment illustrated the light source is an electric spark produced 

 by an induction coil with Leyden jar in circuit. The slit end of the spectroscope 

 is shown to the right. 



