Royal Institution. 311 



its pole. A given hard magnet placed in an invariable position, 

 being thus estimated, was found to have a force equivalent to 16°" 3 

 of deflection. Another magnet, having a power of 25 0, 74, was then 

 placed close to the first in different positions, with like or unlike 

 poles near together, so as to tend sometimes to exalt its power and 

 at other times to depress it ; and the results observed. In the ex- 

 tremest favourable case, namely, when the two were conjoined as a 

 horseshoe magnet, the force of the first magnet was only raised 

 2°'45, which fell directly the dominant magnet was removed ; in the 

 corresponding adverse case the depression was only 1°. A very 

 hard magnet, made by Dr. Scoresby, of 6 0- S8 power, when under the 

 influence of another of double its power, was not sensibly affected 

 either way. When under the influence of one of six times its force, 

 it could be affected to the extent of nearly 1°. Ordinary magnets 

 can be affected to the extent of one half of their power or more ; and 

 indeed in extreme cases can be altogether overruled and inverted. 



From these results the author concludes, that, with perfect un- 

 changeable magnets, the lines of force (as before denned) of different 

 magnets in favourable positions, coalesce : that there is no increase 

 of the total force by this coalescence ; the sections between the 

 associated poles giving the same sum of power as the sections of 

 the lines of either magnet alone : that as the external amount of 

 force of the magnet is not varied, neither is the internal amount at 

 all changed : that the increase of power upon a magnetic needle, 

 or a piece of soft iron, placed between two opposite favourable poles, 

 is caused by concentration of the lines which before were diffused, 

 and not by the addition of the power represented by the lines of 

 force of one pole to that of the lines of force of the other. There is 

 no more power represented by all the lines of force than before, and 

 a line of force is not in itself more powerful because it coalesces with 

 a line of force of another magnet. In this and in other respects, the 

 analogy of the magnet with the voltaic pile is perfect. 



The paper concludes with some practical remarks upon the deli- 

 neation of the forms of the lines of force by iron filings, and by a 

 description of the inflection of the lines by hemispheres of hot and 

 cold nickel ; which the author considers as the corresponding case 

 to the action of warm and cold oxygen in the atmosphere, as applied 

 by him in the explication of some of the phenomena of atmospberic 

 magnetism, and especially of the annual and daily variation. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



Friday, February 13. — On the Heating Effects of Electricity aud 

 Magnetism. By W. it. Cove, Esq., M.A., F.R.S. 



In the ear! | by when any unusual phenomenon 



attracted the i ttention of thinking men it was frequently referred to 

 a preternatural or spiritual cause ; thus with regard to the subject 

 about to be discussed, win n the attraction of light substances by 

 rubbed amber was first observed, Tbalea referred it to a soul or 

 spiritual power potMMl d by the amber. 



Passing to the period antecedent to the time of more strict indue- 



