PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 



561 



Fig. 303. 



Here only a narrow pencil of rays falls through the slit in the screen. These rays continue their 

 course round the terrella, undulating above and below the plane of the magnetic equator. There are 

 distinct nodes and loops visible in the light-figures upon the terrella, which resemble vibrating strings. 

 These figures become fainter according to their number, exactly like those in the preceding photographs; 

 and by magnetising the terrella more highly, they disappear from the equatorial regions, a circum- 

 stance which is in accordance with what we found with regard to the light-figures in fig. 68. The 

 reason of this must be that the corresponding rays, on higher magnetisation, go farther out from the 

 terrella, while those that were nearer turn right round, some of them striking against the terrella. 



