258 Rev. Mr Scoresby on some of the Laws 



tion of an active magnet. For though the natural quantity of 

 inherent magnetism cannot be altered, yet an active and con- 

 stant influence may be, and is, externally exerted, without in 

 the smallest degree diminishing the original power of the ac- 

 tuating magnet. That this is the case, a well known fact suffi- 

 ciently proves, — that a magnet may elicit the magnetic condi- 

 tion in ten thousand bars of steel, and yet retain its original 

 strength perfectly unimpaired. And that the magnetisms re- 

 side inalienably in their own particles of the metal, is equally 

 evident from another familiar fact, — that if a bar in a magnetic 

 condition be broken in the centre, so as to separate apparently 

 the northern and southern polarities, each portion, instead of 

 comprising one quality only, will be found to be a distinct mag- 

 net, exhibiting, like the original mass, the two different polari- 

 ties at the extremities. 



These general principles being premised, we are prepared for 

 the consideration of the particular objects of this Essay. 



Chap. I. — Exposition of some of the Laws and Phenomena 

 OF Magnetic Induction. 



Induction is that well known property of magnets, of pro- 

 ducing in contiguous ferruginous substances the magnetic con- 

 dition. It is not, however, strictly speaking, the communica- 

 tion of any thing pi-eviously foreign to the ferruginous bodies, 

 as nothing (as we have shewn) is abstracted from the inducing 

 magnet, and nothing in reality infused into the iron thus mag- 

 netized. Induced magnetism, therefore, may be defined, — the 

 development of the latent magnetism in iron or steel, hy the 

 juxtapositimi of any substance in a magnetic condition. For 

 this property is elicited not only by actual magnets, but by all 

 electro-magnetic or thermo-magnetic arrangements. And the 

 inductive effect is produced upon all substances capable of a 

 magnetic condition, according to their respective susceptibility. 

 The degrees of capacity of different ferruginous bodies for mag- 

 netism by induction may be ranged, beginning with the least sus- 

 ceptible, in the following order ; iron-ores, hard cast iron, hard 

 cast steel, hard blistered steel, soft steel, common malleable iron, 

 best Swedish iron, — the most susceptible of all being the softest 

 and most ductile iron. Hence it is probable, that the measure of 



