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XLIV. On the Distribution and Retentiofi of Magnetic Polarity 

 in Metallic Bodies. By W. Sturgeon, Lecturer 07i Expe- 

 rimental Philosophy at the Honourable East India Company's 

 Military Academy, Addiscombe. 



[Concluded from page 279.] 



TT EARING that Messrs. Hei'schel and Babbage had ob- 

 *- -*■ tained some curious results by cutting the revolving disc 

 in several of its radii, I also made some experiments with a 

 disc of copper similarly cut. Fig. 10# (Plate III.) will repre- 

 sent the manner in which the disc was cut. An experiment 

 was first made whilst the disc was whole, and the means of 

 six trials were as below : 



Experiment 10. — Without the magnet, 150 vibrations. 

 With the magnet, 45 vibi'ations. 



The disc was now cut with a pair of scissors, as at No. 1. 

 fig. 10, and an experiment made; next at No. 2, and another 

 experiment made ; and so on till nine slits were cut in the disc : 

 and in every case the vibrations were performed between the 

 poles of a horse-shoe magnet, as shown in fig. 9. 



Vibrations. 



rWith 1 slit 

 With 2 slits 

 With 3 slits 

 With 4- slits 

 Experiment ll.<^ With 5 slits 



48 



54 



55 



59 



65 } 



67 



70 



70 



70 



The slit side of the 

 disc vibrating be- 

 tween the mag- 

 netic poles. 



With 6 slits 

 With 7 slits 

 With 8 slits 

 With 9 slits 



I also tried an annular disc of copper, the inner diameter of 

 which was six inches, and the external diameter eight inches. 

 This rim was cemented to a disc of pasteboard, and vibrated 

 between the poles of a horse-shoe magnet. 



Experiment 12. — Without the magnet, 178 vibrations. 

 With the magnet, 140 vibrations. 

 The results of this experiment show that the central parts 

 of copper discs are very much concerned, either in receiving 

 or in transmitting the magnetic impressions ; for those im- 

 pressions, in whatever way they may operate, were much less 

 efficient in this annular rim than in any of the former modi- 

 fications of the disc. 



Experiment 1 3. — A disc of zinc was vibrated in this experi- 

 ment ; and the horse-shoe magnet, when employed, was laid 



on 



