in Maynetism and Electricity. 83 



4. The force of a permanent magnet is usually estimated by 

 the weight which is required to separate the armature or sub- 

 magnet from its poles ; and if the question were asked, for the 

 first time, what relation existed between the sustaining-power 

 of an electromagnet excited by means of a magneto-electric 

 machine, and the sustaining-power of the permanent magnet 

 from which the electricity was derived, it would probably be 

 answered, that since the permanent magnet was the primary 

 cause of the phenomena, the electromagnet would possess, at 

 the most, no greater sustaining-power than the permanent mag- 

 net. This, however, is not the case ; for I have found that an 

 indefinitely small amount of magnetism, or of dynamic elec- 

 tricity, is capable of inducing an indefinitely large amount of 

 magnetism, and, again, that an indefinitely small amount of 

 dynamic electricity, or of magnetism, is capable of evolving an 

 indefinitely large amount of dynamic electricity. 



5. That Faraday himself stood on the threshhold of this dis- 

 covery will be obvious from the following observations made 

 by him in a paper " On the Physical Character of the Lines of 

 Magnetic Force "*, in which, when speaking of the magnet as 

 a source of electricity, he says, "Its analogy with the helix 

 is wonderful ; nevertheless there is, as yet, a striking experi- 

 mental distinction between them ; for whereas an unchangeable 

 magnet can never raise up a piece of soft iron to a state more 

 than equal to its own, as measured by the moving wire (3219), 

 a helix carrying a current can develope in an iron core magnetic 

 force of a hundred or more times as much power as that pos- 

 sessed by itself, when measured by the same means. In every 

 point of view, therefore, the magnet deserves the utmost exer- 

 tions of the philosopher for the development of its nature, both 

 as a magnet and also as a source of electricity, that we may 

 become acquainted with the great law under which the apparent 

 anomaly may disappear, and by which all these various phe- 

 nomena presented to us shall become one." 



6. As the investigations which led to the paradoxical conclu- 

 sions enunciated above (4) were not originally intended for 

 publication, but were undertaken for my own instruction, I find 

 that it will be much more convenient to describe the experimental 

 results in a more methodical manner than that in which they 

 were obtained. 



7. The numerical determinations, derived from the experi- 

 ments to be described, will be given with sufficient exactitude 

 to allow of a comparison being made between them and those of 

 other experimentalists. Other quantitative determinations will, 

 for the present purpose, be sufficiently expressed by the terms 



* Philosoohical Magazine, June 1852, pav. 3273 

 G2 



