378 



C. B. Thwing — Photographic Method of 



Figure 8 is a representation of the field of a disc magnet, 

 made by magnetizing a small circular slotting-saw of 2£ 

 inches diameter and -g-th of an inch thickness. The lines of 



Fig. 6. Horseshoe Magnet. 



force bear a striking resemblance to some drawings of the 

 solar corona, and may suggest the correct explanation of that 

 but little understood phenomenon. 



Fig. 7. Alternate Poles. 



The remaining figures illustrate sections of fields of various 

 forms of electro-magnets. 



Figure 9 is a section of the field of a small motor of the 

 closed field type, and resembles quite closely the field of the 



