1879.J 



of Magnetic Lines of Force. 



105 



This obliquity of the magnetic equator of the bar is demonstrated by 

 the coup cVceil of the curves traced out magnetically, as shown in 

 fig. 1. 



The magnetic lines are the outcome of some thousand observations.* 



The oblique convergency of the magnetic lines towards the north 

 and south poles is strongly pronounced, and a neutral zone was disco- 

 vered, which is indicated in fig. 1 by crosses + + • 



The region of this neutral zone was explored by examining all 

 those points where the suspended magnetic particle of steel exhibited 

 indifference, either of its poles being observed to be equally attracted. 



This interesting experiment can be far better appreciated by actual 

 observation than by description, and is best shown perhaps by carry- 

 ing the l-4th inch test-magnet from the north towards the south pole 

 across the equator. When over the north side of the equator the 

 south pole dips ; if it be then allowed to fall upon the bar, and is 

 raised again, the south pole will leave the bar last. When it has been 

 carried south across the equator the north pole dips, but if it be again 

 allowed to fall upon the bar, and is once more raised, the south pole 

 will leave the bar last, just as it did on the north side of the equator. 



But this novel feature of an oblique zone is more beautifully dis- 

 played by examining small curves, traced out in the way indicated, by 

 the smallest test-magnets near the geometrical centre of the bar, for 

 lines equidistant from its axis. 



The obliquity (measured as close as possible to the bar by means of 

 curves traced out so as to enter the two sides of the bar) has a very 

 equable value, varying according to the nature of the magnet, as 

 regards the intensity of the magnetism, the quality of the material, 

 and its temper, from 7° to 10° ; and this result is confirmed by the 

 investigation of the internal curves of many thousand observations 

 on magnets from 7 J to 18 inches long. Indeed, it was the invari- 

 able inclination of the surface lines which suggested the equatorial 

 obliquity. 



* The principle of squares was adopted in the enlargement : a lens being em- 

 ployed on the original chart. 



