1 14 TERRESTRIAL ADAPTATIONS. 



nism, that they may be said to be almost different 

 aspects of the same agent. All the phenomena 

 which we can produce with magnets, we can 

 imitate with coils of galvanic wire. That gal- 

 vanism exists in the earth, we need no proof. 

 Electricity, which appears to differ from galvanic 

 currents, much in the same manner in which a 

 fluid at rest differs from a fluid in motion, ap- 

 pears to be only galvanism in equilibrium, is there 

 in abundance ; and recently, Mr. Fox* has shown 

 by experiment that metalliferous veins, as they 

 lie in the earth, exercise a galvanic influence on 

 each other. Something of this kind might have 

 been anticipated ; for masses of metal in contact, 

 if they differ in temperature or other circum- 

 stances, are known to produce a galvanic current. 

 Hence we have undoubtedly streams of galvanic 

 influence moving along in the earth. Whether 

 or not such causes as these produce the directive 

 power of the magnetic needle, we cannot here 

 pretend to decide ; they can hardly fail to affect 

 it. The Aurora Borealis too, probably an elec- 

 trical phenomenon, is said, under particular cir- 

 cumstances, to agitate the magnetic needle. It 

 is not surprising, therefore, that, if electricity have 

 an important office in the atmosphere, magnetism 

 should exist in the earth. It seems likely, that 

 the magnetic properties of the earth may be 



* Phil. Trans. 1831. 



