ELECTRICITY. 107 



action of the battery will be proportioned to the facility with 

 which the heat is circulated or radiated by these media, and 

 we thus establish an alternating reciprocity of action between 

 these two forces : a similar reciprocity may be established 

 between electricity and motion, magnetism and motion, and 

 so of other forces. If it cannot be realised with all, it is 

 probably because we have not yet eliminated interfering ac- 

 tions. If we carefully think over the matter, we shall, unless 

 I am much mistaken, arrive at the conclusion that it cannot 

 be otherwise, unless it be supposed that a force can arise from 

 nothing can exist without antecedent force. 



In the phenomenon of the voltaic arc, the electric spark, 

 &c., to which I have already adverted, electricity directly 

 produces Ught of the greatest known intensity. It directly 

 produces magnetism, as shown by Oersted, who first distinctly 

 proved the connection between electricity and magnetism. 

 These two forces act upon each other, not in straight lines, 

 as all other known forces do, but in a rectangular direction ; 

 that is, bodies affected by dynamic electricity, or the conduits 

 of an electric current, tend to place magnets at right angles 

 to them ; and, conversely, magnets tend to place bodies con- 

 ducting electricity at right angles to them. Thus an electric 

 current appears to have a magnetic action, in a direction 

 cutting its own at right angles ; or, supposing its section to 

 be a circle, tangential to it : if, then, we reverse the position, 

 and make the electric current form a series of tangents to an 

 imaginary cylinder, this cylinder should be a magnet. This 

 is effected in practice by coiling a wire as a helix or spiral, 

 and this, when conducting an electrical current, is to all in- 

 tents and purposes a magnet. A soft iron core placed within 

 such a helix has the property of concentrating its power, and 

 then we can, by connection or disconnection with the source 

 of electricity, instantly make or unmake a most powerful 

 magnet. 



We may figure to the mind electrified and magnetised 



