116 Jiutoricai Sketch of Eleciro-mugueiism. [Fsi. 



which had guided him so saf<?ly to swch novej and important 

 results. 



The traversing of the curve hy the magnetism of the earth 

 added 4uioth«r argument to those in support of M. Ampere'^ 

 Uieory. If the experiment had not succeeded, the distinction 

 between the curve and the needle would have been fairly urged 

 gainst the theory ; as it succeeded, it admits of being adduced 

 as another proof that currents in cyrv.es such as those M. Am- 

 pere assumes to exist in the magnet, arc sufficient to account for 

 the phenomena presented by it. But the' important conclusion 

 M. Ampere arrives at from it is, that the magnetism of the earth 

 i^ itself caused by currents of electricity, which, moving from the 

 east towards the west round the globe are at right angles to the 

 magnetic meridian. These currents, if they exist, are compared 

 io those which would be found in a voltaic battery if its two 

 extremities were made to meet. There is nothing probably in 

 the globe which can be compared to the continuous conductor 

 formed by the metallic wire, but M. Ampere has shown that the 

 battery itself is magnetic ; and he supposes it probable that the 

 ^rangement of the materials of the globe may be such as to 

 constitute a battery existing like a girdle round the earth, which, 

 though composed of <iom|>aratively weak elements, is suffi- 

 .ciently extensive to produce the effects of terrestrial magnetism. 

 Its irregularity in that ease wQUld account for the distorted forms 

 uf lines of similar variation, and the changes that take place in 

 it would explain the change of th^ direction of the needle- 

 -Some general action, however, ifi; supposed to exist which aid^ 

 Hi producing the cijirreutis of,;ftl^((?tricity, and in a direction 

 approaching parallelism with the equator; and the variation i§ 

 supposed to depend on thc/pyogress of oxidation in the conti- 

 jaental regions of the e*rth».i .' ' 



The diurnal variation is considered as dependent on the diurn9l 

 change of temperature, in the superficial electro-motors of tlie 

 globe. The varioys strata of magnetic materials are considered 

 a,s so mar4y voltaic piles. 



Snppoi?mg that electric currents actually exist in the masses 

 pf matter which form the planetary and stellar globes, M. Am- 

 |)ere suggests the possibility that they may sometimes be sp 

 |)Owerful as to make the heat which is necessarily excited ris^ 

 to ignition. In this case, a permanent incandescence with a 

 tolliant hght would be produced without either combustion Qr 

 loss of substance. " May we not suppose,*' says M. Ampere, 

 *^ tliat the opaque globes are so only because of the small degree 

 ©f energy in the electric currents established in them, and find 

 in the more active currents the cause of the heat and light of 

 those globes that shine by tliemselves." 



Such, Sir, is the sketch I must bog you to accept of M, Am- 

 pere's theory. I need not again u}K>logize for its imperfections, 

 but refer^ a» to an easy remedy, to the philosopher's own papers 



