*582 



SCIENCE. 



Science, was repeated this summer, (1825) by Mr. Babbage 

 Curiosities an j jyj r Herschel, who obtained many new and in- 



_^^ teresting results. They mounted a powerful compound 



horse-shoe magnet, capable of lifting 20 Ibs. so as 

 to receive a rapid rotation round its axis of symmetry 

 placed vertically, the lines joining the poles being placed 

 horizontal, and the poles upwards. A circular disc of 

 copper, 6 inches in diameter, and one-twentieth of an 

 inch thick, was suspended centrally over it by a silk 

 fibre, without torsion, just capable of supporting it. A 

 sheet of paper, properly stretched, was interposed, and 

 no sooner was the magnet set in rotation, than the 

 copper disc began to revolve in the same direction, 

 slowly at first, but with a velocity gradually and stea- 

 dily increasing. When the motion of the magnet 

 was reversed, the velocity of the copper was gradually 

 destroyed. It rested for an instant, and immediately 

 began to revolve in the opposite direction, and so on 

 alternately, as often as was wished. When discs of 

 wood, antimony, zinc, bismuth, copper, lead, tin, and 

 glass were interposed between the magnet and the 

 copper disc, they did not intercept the magnetic vir- 

 tue, a revolution being performed nearly in the same 

 time as before ; when iron was interposed, the effect 

 was very different, the magnetic influence being great- 

 ly diminished by one, and almost annihilated by two 

 thicknesses of common tinned iron plate. When the 

 plates and the revolving magnets were connected by a 

 piece of soft iron, the rotation of the copper disc was 

 in like manner almost annihilated. 



Mr. Babbage and Mr. Herschel now caused to re- 

 volve on their axes plates of copper, &c. ten inches in 

 diameter, and half an inch thick, with a velocity of 

 seven turns in a second. Above these plates was 

 placed an azimuth compass, and the deviations which 

 were produced in it by different metals, were ob- 

 served as follows : 



Ratio of the Force 

 to that of Copper. 



1.00 

 0.93 

 0.46 

 0.25 

 0.09 

 0-02 



Copper 



Zinc, 



Tin, 



Lead, 



Antimony, 



Bismuth, 



Among the other metals tried, silver held a high rank ; 

 and fluid mercury ranked between antimony and bis- 

 muth. 



Mr. Babbage and Mr. Herschel are of opinion, that 

 in all the phenomena of rotation, the magnetic virtue 

 is induced by the action of the magnetic bar, compass 

 needle, &c. ; and that in Mr. Barlow's experiments, 

 the earth is the inducing magnet ; the rationale of the 

 phenomena, therefore, they consider to depend on the 

 principle, that in the induction of magnetism, time enters 

 as an essential element, and that no finite degree of 

 magnetic polarity can be communicated to, or taken from 

 any body whatever, susceptible of magnetism, in an in- 

 stant. By the application of this principle, and with- 

 out calling in the aid of any additional hypothesis or 

 new doctrine in magnetism, they have given a most 

 plausible and ingenious explanation of most, if not all, 

 the phenomena produced by rotation. 



In a set of experiments made subsequently to the 

 preceding, Mr. Christie confirmed the results obtained 

 by Mr. Babbage and Mr. Herschel. When a thick cop- 

 per plate revolved beneath a small magnet, he found 

 that the force which caused the needle to deviate, 

 yaried directly as the velocity, and inversely as the 



fourth power of the distance ; a law which would arise Science, 

 from the magnetism in the needle developing the mag- Curiosities 

 netism in the particles of copper, so that its intensity 

 should vary inversely as the square of the distance, and 

 this magnetism again acting on the poles of the needles 

 with a force varying as the square of the distance. 



From this result, and from some others obtained by 

 Mr. Christie, the opinion of Mr. Babbage and Mr. 

 Herschel seems to be placed beyond a doubt, that the 

 magnetism is induced on the copper from the needle 

 itself. See the Philosophical Transactions for 1825, 

 for the original memoirs in which the preceding dis- 

 coveries are published. Abstracts of all the papers will 

 be found in Dr. Brewster's Journal of Science, No. IV. 

 V. VI. and VII. 



4. On the formation of Magnets by Percussion. 



The formation of magnets by percussion we owe to On the for- 

 the ingenuity of Captain Scoresby. In the interesting mation of 

 experiments which he has published on this subject, magnet* by 

 he found that in soft iron, percussion generated a percussiop. 

 strong, bt*t evanescent magnetism ; whereas, in soft 

 steel, the greatest degree of magnetic energy could be 

 developed by percussion. In order to produce this ef- 

 fect, he hammered a bar of soft steel six and a half inches 

 by one quarter of an inch in diameter, and weighing 

 S92 grains, held in a vertical position, with its lower 

 end resting on any metal, or even on stone, and after 

 1 7 blows, it lifted six and a half grains. The magnetic 

 effect was amazingly increased when the lower end of the 

 steel bar rested on the upper end of a large rod of iron or 

 soft steel ; the preceding bar, which lifted only 6^ grains 

 by the first process, now lifting eighty-eight grains after 

 twenty-two blows. When the poker, or a large rod of 

 iron, had been itself previously hammered in a vertical 

 position, a single blow gave a lifting power of twenty 

 grains, and in one instance ten blows produced a lift- 

 ing power of 188 grains, which was nearly one-third 

 of its own weight. Mr. Scoresby has subsequently im- 

 proved this process, by hammering the steel bars be- 

 tween two bars of iron. In this case the steel bar 

 which lifted 186 grains by the first process, now lifted 

 826 grains ; and when the new process was employed 

 with an iron bar eight feet long, the same wire lifted 

 669 grains, or four times its own weight. When mag- 

 netised iron and steel are hammered in the magnetic 

 equator, or nearly in a horizontal position, their mag- 

 netism is destroyed by a few blows. 



Mr. Scoresby's theory of this process is, that percus- 

 sion on magnetiseable substances in mutual contact dis- 

 poses them to assume an equality of condition, in the 

 same manner as bodies of different temperatures assume 

 the same temperature by juxta-position. As the two 

 large iron bars are magnetical by position, the bar of 

 steel, hammered between them, will, when thus thrown 

 into a state of vibration, receive a share of their mag- 

 netism. For particular details respecting Captain 

 Scoresby's experiments, see the Edinburgh Transac- 

 tions, vol. ix. p. 243, 353, and Philosophical Transac- 

 tions, vol. xxii. p. 241. 



For an account of Mr. Barlow's Correcting Plate, 

 see the article VARIATION of the Needle. 



MECHANICS. 



1. Kempelen's Chess Automaton. 

 Among the curiosities of mechanical science we may, Kempelen's 



without hesitation, rank the chess automaton of Kern- chess auto ~ 



maton. 



