332 EPOCHS IN THE HISTORY OF THE CONTEMPLATION OF 



very of "rotation-magnetism" by.Ar<igo (1825), it has been 

 practically proved that all kinds of matter are susceptible of 

 magnetism; and Paraday's latest researches on diamagnetic 

 substances have, under particular conditions of " axial or 

 equatorial direction/' and of solid, fluid, or gaseous in- 

 active conditions of the bodies, confirmed this important 

 result. Gilbert had so clear an idea of the imparting of 

 the telluric magnetic force, that he already ascribed the 

 magnetic state of iron bars in the crosses on old church 

 towers or steeples to this circumstance. ( 512 ) 



In the 17th century, by the increasing activity of navi- 

 gation to the higher latitudes, and by the improvement of 

 magnetic instruments, to which, since 1576, the clipping 

 needle or inclinatorium, constructed by Robert Norman of 

 Hatcliffe, had been added, a general knowledge of the pro- 

 gressive motion of a part of the magnetic curves i. e. of 

 the lines of no variation was first obtained. The position 

 of the magnetic equator (or line of no inclination), which 

 was long believed to be identical with the geographical 

 equator, was not examined. Observations of inclination 

 were made only in a few of the principal cities of western 

 and southern Europe : the intensity of the earth's magnetic 

 force, which varies both with place and with time, was indeed 

 .attempted to be measured by Graham in London, in 17 23, 

 by the oscillations of a magnetic needle ; but after the failure 

 of Borda's endeavour on his last voyage to the Canaries in 

 1776, it was Lamanon who, in 1785, in the expedition of 

 La Perouse, first succeeded in comparing the intensity in 

 different regions of the earth. 



Edmund Halley, availing himself of a great mass of ex- 

 isting observations of declination, of very unequal value (by 



