334 MAGNETISM OF SUN AND PLANETS. SECT. XXXV. 



binations probably exist, which have never yet been no- 

 ticed. 



According to the observations of MM. Biot and Gay- 

 Lussac, during their aerostatic expedition, the magnetic 

 action is not confined to the surface of the earth, but 

 extends into space. The moon has become highly 

 magnetic by induction, in consequence of her proximity 

 to the earth, and because her greatest diameter always 

 points toward it. Her influence on terrestrial magnetism 

 is now ascertained : the magnetism of the hemisphere 

 that is turned toward the earth attracts the pole of our 

 needles that is turned toward the south, and increases 

 the magnetism of our hemisphere ; and as the magnetic, 

 like the gravitating force, extends through space, the 

 induction of the sun, moon, and planets must occasion 

 perpetual variations in the intensity of terrestrial mag- 

 netism, by the continual changes in their relative posi- 

 tions. 



Jn the brief sketch that has been given of the five 

 kinds of electricity, those points of resemblance have 

 been pointed out which are characteristic of one indi- 

 vidual power. But as many anomalies have been lately 

 removed, and the identity of the different kinds placed 

 beyond a doubt by Dr. Faraday, it may be satisfactory 

 to take a summary view of the various coincidences in 

 their modes of action on which their identity has been so 

 ably and completely established by that great electrician. 



The points of comparison are attraction and repulsion 

 at sensible distances, discharge from points through air, 

 the heating power, magnetic influence, chemical decom- 

 position, action on the human frame, and lastly, the spark. 



Ordinary electricity is readily discharged from points 

 through air, but Dr. Faraday found that no sensible ef- 

 fect takes place from a Voltaic battery consisting of 140 

 double plates, either through air or in the exhausted 

 receiver of an air-pump, the tests of the discharge being 

 the electrometer and chemical action, a circumstance 

 owing to the small degree of tension, for an enormous 

 quantity of electricity is required to make these effects 

 sensible, and for that reason they cannot be expected 

 from the other kinds, which are much inferior in de- 

 gree. Common electricity passes easily through rare- 



