THE UNIVERSE. DISCOVERIES IN THE CELESTIAL SPACES. 331 



The most ingenious and important work on electric aircl 

 magnetic forces, William Gilbert's Physiologia nova de Mag- 

 nete, of which I have already several times had occasion to 

 speak, ( 509 ) was published in 1600. Gilbert, whose saga- 

 cious mind was so highly admired by Galileo,, ( 51 ) antici- 

 pated by his conjectures much of our present knowledge. 

 He regarded magnetism and electricity as two emanations of 

 one fundamental force pervading all matter, and there- 

 fore treated of both at once. Such obscure anticipations, 

 founded on analogies of tho attracting power of the Heraclean 

 magnetic stone on iron, and of amber (when animated, as 

 Pliny says, with a soul by warmth and friction) on dry straws, 

 have been common k all periods, and even to the most dif- 

 ferent races ; for they were shared by the followers of the 

 Ionic philosophy of nature, and by Chinese physicists. ( 5U ) 

 William Gilbert regarded the earth itself as a magnet, and 

 the lines of equal declination and inclination as having their 

 inflections determined by distribution of mass, or by the 

 form of continents and the extent of the deep intervening 

 oceanic basins. It is difficult to reconcile the periodic 

 variation which characterises the three elementary forms of 

 the magnetic phsenomena (the isoclinal, isogonic, and iso- 

 dynamic lines) with this rigid system of distribution of force 

 and mass, unless we imagine the attractive force of the ma- 

 terial particles modified by similarly periodical variations m 

 the interior of the globe. 



In Gilbert's theory, as in gravitation, the quantity of 

 material particles only is estimated, without regard to the 

 specific heterogeneity of substances. This circumstance 

 gave to his work, in the period of Galileo and Kepler, a 



character of cosmical grandeur. By the unexpected disco- 

 VOL. n. z 



