ELEMENTARY ELECTRICITY AND MAGNETISM. 7 



field at that point. Such lines are called lines of force. Where 

 the lines of force are crowded together the intensity of the field 

 is great, and where the lines of force are spread apart the intensity 

 of the field is small. When the lines of force are parallel straight 

 lines the intensity of the magnetic field is everywhere the same in 

 value and in direction, and the field is said to be homogeneous or 

 uniform. 



Magnetic figures. The trend of the lines of force in the 

 neighborhood of a magnet is beautifully shown by placing a pane 

 of glass over the magnet and dusting iron filings upon it. The 

 filings, becoming magnetized, tend to arrange themselves in fila- 



Fig. 2. 



ments along the lines of force. Slight tapping of the glass 

 facilitates this arrangement of the filings. Figs. I, 2, 4, 5, 6 and 

 7 are photographic reproductions of magnetic figures obtained 

 in this way. Fig. I shows the trend of the lines of force in the 

 neighborhood of two unlike poles and Fig. 2 shows the trend of 

 the lines of force in the neighborhood of two like poles. 



