158 Transactions of the American- Institute. 



its excellence. Let us again muse over our work and see if we can- 

 not gain further mastery over these actions. You remember that the 

 red or lower end of the bar is of north magnetism. Suppose, how- 

 ever, I place this end up and the white end down. Will this white- 

 end then have a north magnetism ? Let us try. No, it is evidently 

 weaker in its action on the needle, but is yet of south magnetism — 

 but weaker. This weakening evidently comes from the action of 

 the earth on the reversed bar. Therefore suppose, while holding the 

 bar in this position, I strike it again with the hammer ; what will 

 happen % Will merely a blow be sufficient to take the south magnet- 

 ism out of that end of the bar, and to leave the bar neutral, or, will 

 it do even more and replace the south by north magnetism ? In other 

 words, will it reverse the magnetism of the bar ? I will test it. Look 

 steadily at the needle and observe its fixed position, while the end 

 of the bar is near it, and keep your eye on the needle, and when 

 you hear the blow of the hammer and ring of the bar, observe what 

 takes place. I have struck the bar, and look, how the needle swings, 

 and now its spear-end is away from the bar, thus showing that its 

 magnetism has indeed been reversed. Thus can we cause the magnet- 

 ism of the ends to change places as often as we wish ; but can we 

 not do something else ? Can we not, by a properly regulated blow, 

 shake (allowing such a crude expression) the magnetism entirely out 

 of the bar ? I think we can. You know that the lower or white end 

 is of north polarity. I now reverse the position of the bar and the 

 white end is up. I strike a blow. I now test the bar, but you see 

 that I struck it with too much force, for the magnetism of the white 

 end is now south; but feebly so, for the needle is only slightly 

 deflected. Now I will show you a pretty experiment. I again 

 reverse the bar, and the white or south magnetic end is down, and I 

 strike the upper end with the palm of my hand. I place the bar in 

 a horizontal position and I test it ; it has evidently been weakened. 

 I again bring my hand down on it. Its magnetism has, you see, 

 almost disappeared. I again bring the bar into the upright position 

 and tap it with my fingers. See, it is entirely freed of magnetism. 

 I stated, when I began working on these bars, that they had all been 

 demagnetized by a process which you would soon appreciate. I hope 

 you now appreciate it. 



How satisfactory is such work ; we here repose on the decision of 

 an upright judge. We bring our doubts and differences to the bar 

 of nature, and the verdict is convincing to all. It is truth, which is 

 the soul of science. 



