280 Dr. Tyndall on the Laws of Magnetism. 



strong as that required by JXo. 1, and that No. 3 requires a cur- 

 rent 2'4 times that required by No. 2. In the following table 

 this multiplication by the factor 2"4' is carried out for the two 

 first balls. The first three figures of the tangents have been 

 taken; and as we hare simply to do with ratios, and not with 

 absolute values/ these three iiguv^ are treated as tfhole li'iii!nbers'.' 



•'■ 300 141 ... 338 346 



X 325 152 ... 365 371 ' 



350 160 ... 384 391 'T "'J'''"^ 



375 171 ... 410 / , ^09 '^ '" 



400 181 ... 420-^'^*''' "'' W'"'^*' 



425 193 ... 463 459 



450 203 ... 487 481 



475 209 ... 501 501 



500 218 ... 523 525 



525 229 ... 549,„,,,,j,^ , 546 ,, j^a 



550 23S ... 571 , ,,.j 573 { nr. 



575 247 ... 593 588 



600 254 ... 609 614 



,.-, \;, .>^- • ■• ve- 

 il i.iilVU'UodlG ?.B Jd^siavr snrsB 9flj lo't Jiifl 



23. Magnetic attraction, like the attraction of gra\dtation,is the 

 result of a reciprocated force. The atti'action of a sphere of soft 

 iron depends, not only upon the magnetism of the magnet, but 

 also upon that of the excited ball. The attraction is equal to the 

 product of both. In operating with balls of different diameters, 

 two things are to be taken into accoimt, which, in default of 

 better terms, may for the present be called quantity and intensity ; 

 the former depending upon the volume of the ball, though not 

 proportional to it; the latter on the power of the magnet, to 

 which it is proportional. According to this view, the intensity 

 of magnetism in a 1)all of a certain diameter, placed at a certain , 

 distance from the magnet, is the same as that of a ball of twice 

 or half the diameter placed at the same distance ; but the quan- , 

 titles of magnetism are veiy different. Tlie attraction of the 

 ball depends upon both quantity and intensity. Tluis the force 

 with which the sphere reciprocates that of the magnet may be 

 regarded as being made up of the tw^o components q and i, the 

 former of which stands for the quantity, the latter for the inten- 

 sity. Let m be the magnetism of. the magnet, then the attrac- 



. ■•■■, .,,;i't, 



