GENERAL SUMMARY. 231 



this to the same degree from the induction of a single cell, 

 as from any number of similar cells. Wires of different metals 

 are unequally heated, according to the resistance which they 

 offer to induction. The following numbers express the heat 

 evolved by the same circulation in different metals, as observed 

 by Mr. Snow Harris. 



Heat evolved. Resistance. 



Silver . .6 . 1 



Copper 6 1 



Gold . .9 . ij 



Zinc . .18 . 3 



Platinum . .30 . 5 



Iron . .30 . 5 



Tin . . 36 . 6 



Lead . -72 .12 



Brass . .10 . 3 



The conducting powers of the metals are inversely as these 

 numbers ; silver being a better conductor than platinum in 

 the proportion of 5 to 1 . The conducting power of all of them 

 is found to be diminished by heat. 



11. As a portion of the voltaic circle, the conducting wire 

 acquires extraordinary powers of another kind, which can only 

 be very shortly stated here, belonging as they properly do to 

 physics. 



(1) Another wire placed near, and parallel to the conducting 

 wire has the polar condition of its molecules disturbed, and an 

 induction propagated through it in an opposite direction to 

 that in the conducting wire. 



(2) If the conducting wire be twisted in the manner of a 

 cork-screw so as to form a hollow spiral or helix, it will be 

 found in that form to represent a magnet, one end of the helix 

 being a north, and the other a south pole ; and, if moveable, 

 will arrange itself in the magnetic meridian, under the influence 

 of the earth's magnetism. Its poles are attracted by the unlike 

 poles of an ordinary magnet, and it imparts magnetism to 

 soft iron or steel by induction. Two such helices attract and 

 repel each other by their different poles, like two magnets. 

 Indeed an ordinary magnet may be viewed as a body having 

 a helical chain of its molecules in a state of permanent che- 

 mico-polarity. 



