ASTRO-PHYSICS 273 



interest, and their importance with regard to 

 terrestrial meteorology became manifest. It 

 has long been held that sun-spots were the seat 

 of movements of gases on a gigantic scale in 

 the solar atmosphere, and direct evidence of 

 such storms is supplied by the spectroscope. 

 Professor Hale gives a drawing of the spectrum 

 of a sun-spot in the neighbourhood of the C line. 

 This drawing is reproduced in Fig. '^'j. The 

 slit of the spectroscope was directed to the sun's 

 disc so as to include the area covered by the 

 spot. The figure shows a small part of the 

 spectrum, which extends from left to right across 

 the paper. The faint horizontal dark line shows 

 the effect of the sun-spot, from which much less 

 light proceeds than from the rest of the sun's 

 surface. Several faint Fraunhofer's lines cross 

 the diagram vertically, and it will be seen that 

 these lines are still dark lines in the sun-spot 

 region. The sun-spot itself, then, must be the 

 source of continuous radiation, from which 

 definite rays are abstracted by cooler gases in 

 higher regions, the process being identical with 

 that going on in other parts of the sun. The 

 heavy dark line crossing the figure from top to 

 bottom is the C line to which reference has been 

 made. It is much stronger and darker than 

 any of the other lines shown. In the neighbour- 

 hood of the sun-spot, like the fainter lines, it still 

 shows dark, but in its centre is a bright patch 

 or reversal of the line. This intense luminosity 

 indicates that, superposed on the layer of gas 

 which absorbs the light, is a mass so hot that 

 its radiation is even greater than the normal 

 radiation from the sun's surface. The curious 



