Page:The American Cyclopædia (1879) Volume XI.djvu/13

 THE AMERICAN CYCLOPAEDIA MAGNETISM MAGNETISM, the name given to the phenomena displayed by magnets. If a bar of slightly tempered steel be held vertically and struck several blows with a wooden mallet, it will acquire the property of attracting iron filings at its two extremities. The same property may be communicated from one bar of steel to any number of similar bars, by rubbing one half of the length of each of the latter with the end of the former which was toward the earth in the experiment above mentioned, and the remaining half with the other end of the same bar. In this process a remarkable fact becomes evident, namely, that the bar which is employed to impart the magnetic property loses none of its own power; on the contrary, if the process is properly performed, it will become stronger; and hence we deduce the conclusion, that in magnetization there is no transfer of any substance from one body to another, but the development of a latent principle. If a magnetized bar be suspended by a fibre of untwisted silk, in such a manner as to have perfect freedom of motion, it will assume a N. and S. direction; that is, it will exhibit the phenomena called polarity. If to either end of a magnetized bar thus suspended a piece of soft iron be approached, attraction will be exhibited between them; when a similar bar is rolled in iron filings, the latter will be found to adhere in thick clusters at the two ends or poles, while none will attach themselves to the middle of the bar. If, instead of presenting to the suspended magnet pieces of soft iron, we bring near to its two ends in succession the two poles of another magnetized bar, repulsion as well as attraction will be exhibited; and by an attentive study of the phenomena we shall find that similarly magnetized ends repel, and dissimilarly magnetized ends attract each other. These forces act at great distances, through all interposed bodies, and like gravitation diminish in intensity with the square of the distance from each pole. If a number of bars of soft iron be placed near each other in the same straight line, and the N. end, for example, of a strongly magnetized steel bar be brought near one end of the series, each piece of iron will become magnetic and exhibit polarity. The near end of the first magnet will be a S. pole, the far end a N. pole, and so on throughout the series, as follows: 8. N. S. N. S. N. S. N. S. N. N. S. N. When the magnet is removed, the polarity of the iron bars ceases; and when the pole of the developing magnet is reversed, the polarity of the whole series is also reversed. The development of magnetism in this way is called induction, and by it we are enabled to explain many facts which would be otherwise perplexing. In accordance with this principle, we can assert that a magnet does not attract soft iron in its natural state, but that it first renders the metal magnetic, and then the attraction takes place between the dissimilar poles of two magnets. Again, when we sprinkle iron filings on a paper placed over a magnetic bar, they arrange themselves in beautiful curves radiating from each pole and joining near the equator of the bar. These lines result from the fact that each particle of iron becomes by induction a separate magnet, and attracts the adjacent filings, their arrangement in this case being the same as that of a series of small needles when under the influence of the two poles of a magnetic bar. The induction takes place readily in soft iron, and disappears as soon as the inducing magnet is removed, but not so with hardened steel; though the effect is less powerful in this, the polarity is permanent--The method of making steel magnets of great power, which we have found from long experience the sim-