276 Proceedings of the Royal Society. 



the possibility of such an application, if at any time, such know- 

 ledge and command of the decomposition of oil or coal by heat 

 should be obtained, as would enable us to furnish the substance 

 in abundance. 



An Account of the Repetition of M. Arago's Experiments on 



the Magnetism developed during the Act of Rotation^ by Chas. Bab- 

 bage, Esq., F.R.S., and J. F.Herschell, Esq., Sec. R.S., was read. 

 The experiments of M. Arago having excited much interest, the 

 authors of this communication were induced to erect an apparatus 

 for their verification ; and after a few trials, they succeeded in caus- 

 ing a compass to deviate from the magnetic meridian, by setting 

 in rotation under it plates of copper, zinc, lead, ^-c. 



To obtain more visible and regular effects, however, they found 

 it necessary to reverse the experiment, by setting in rotation a 

 powerful horse-shoe magnet, and suspending over it the various 

 metals, and other substances to be examined, which were found to 

 follow with various degrees of readiness the motion of the magnet. 

 The substances in which they succeeded in developing signs of 

 magnetism were, copper, zinc, silver, tin, lead, antimony, mercury, 

 gold, bismuth, and carbon in that peculiar metalloidal state in 

 which it is precipitated from carbonated hydrogen in gas works. 

 In the case of mercury, the rigorous absence of iron was secured. 

 In other bodies, such as sulphuric acid, rosin, glass, and other 

 non-conductors, or imperfect conductors of electricity, no positive 

 evidence of magnetism was obtained. 



The comparative intensities of action of these bodies were next 

 numerically determined, by two different methods, viz.^ by observ- 

 ing the deviation of the compass over revolving plates of great 

 size cast to one pattern, and by the times of rotation of a neu- 

 tralized system of magnets suspended over them, and it is curious 

 that the two methods, though they assigned the same order to 

 the remaining bodies, uniformly gave opposite results in the cases 

 of zinc and copper, placing them constantly above or below each 

 other according to the mode of observation employed. 



Our authors next investigated the effect of solution of continuity 



