LIGHT, CALORIC, ELECTRICITY AND MAGNETISM 201 



repel, and dissimilarly attract each other. Both are developed by fric- 

 tion, and by the inductive influence of bodies already excited. And in 

 reference to both it may be said that their peculiar efl'ects are more easily 

 manifested in some bodies than in oiliers. Vitreous and resinous sub- 

 stances and a few others, are, for example, easily put into the state of 

 excitement called statical electricity, and remain in that condition with 

 some degree of permanency; but the excitement in all others is tran- 

 sient, except when they are insulated by the interposition of one of the 

 former. So iron, nickel, and cobalt are the only substances which have 

 been known to exhibit that permanent excitement called magnetism, and 

 have therefore been rejifarded as constituting the whole class of magne- 

 tics. But Faraday has recently shown that seven others belong to this 

 class, being capable of exhibiting the magnetic condition in a limited de- 

 gree. As this subject is yet new and approached from only one direc- 

 tion, may we not suppose that farther research will yet prove that, as in 

 electricity, all bodies, without exception, under proper conditions will 

 be found capable of magnetization. 



But their close connection is more fully shown by their reciprocal 

 action. 



Electricity produces magnetism. If an electric current be made to 

 pass at right angles to a short rod of soft iron or steel, magnetism will 

 be developed, in the former case temporarily, in the latter permanently. 

 If the current be made to flow through an insulated wire, wound so as 

 to form a helix or hollow cylinder, into which the rod can be introdu- 

 ced, the magnetic effect is increased in proportion to the number of turns 

 of the wire, which thus makes the one current equivalent to as many 

 currents as there are turns. Magnetism far transcending in power any 

 that was known previously to the discovery of this arrangement for its 

 production, is produced in this manner. The magnet thus formed is 

 called an electro-magnet, and the interesting branch of physical science 

 to which it has given rise, has been denominated Electro-magnetism. It 

 is the electro-magnet, it may be remarked, which furnishes the moving 

 power in the writing apparatus of the great American Telegraph. 



Magnetism produces electricity. When a permanent steel magnet is 

 thrust into the helix or hollow cylinder of wire above alluded to, an 

 electric current at the same time flows through the wire. The same ef- 

 fect is produced when a permanent magnet is made to approach either 

 end of a bar of soft iron previously introduced into the helix. Upon 

 this principle is founded the construction of the Magneto-electrical ma- 

 chine, and the department to which this class of eflfects is referred is 

 called Magneto-electricity. 

 25 



