Dv. Tyndall on the Laws of Magnetism: 2^1 



tion of a sphere placed at a small distance^- will Le expressed by 

 the product' ilol oili ril > .t' .o^ /,i j^'juupi Jj^iH ^■^"-•" •!-- - ^^^ 



It has been already proved, that to hold a cei-tain v/eight in 

 equilibi'iiim, the ball No. 2, when in contact, requires 2'4 times 

 the magnetic power that No. 1 requires. But I found this to 

 vary a little when small intervals existed between the ball and 

 magnet. When a film of mica jn'o yf^^b of an inch in thickness 

 was placed upon the pole, the above factor reduced itself to 2"3 ; 

 at a leaf thickness, or y J^ydth of an inch distant, it was 2"25 ; 

 at ^jijth of an inch distant it was 2'22 ; while at ;j\jth of an 

 inch distance it was nearly the same as in contact. For our 

 present purpose, the number 2'25 is nearest the truth. At any 

 given moment let iiiq be the magnetism of the magnet, and (Jq 

 and i(j the magnetic components of the ball No. 1 ; then, as 

 before observed, the attraction of the ball will be 



Let »<„ (J I and /j represent the corresponding quantities for the 

 ball No. 2, its attraction wiH be • ^ 



But each of these attractions is measured by the weight which it 

 can hold in equilibrium ; and if the same weight be used in both 

 cases, we shall have , 



'«i?i''i = »«oWo- • • . . "'•' • (1.) 

 But for the same weight, as above remarked, we have 



?«o=2-25wi; 

 and as the intensity is assumed proportional to the magnetism 

 of the magnet, we have also •' ' 



Substituting these values in equation (1.), w^e obtain 



*"o'/o'o= 2'35?«iry,2-^52p 

 or »?jo«7o?o = 5w/i(7i7'„ 



or %=5qv 



As the quantity dej)ends solely upon size, the relative quan- 

 tities of two l)alls may be supposed to rt'main constant, whatever 

 be the power of the magnet. 'When, therefore, the same mag- 

 netic power is applied to both Ijulls, the difference between the 

 forces exerted upon them will depend solely on the factors q^ 

 and q^ ; for in this ease we shouldhave inQ = m^ and?,j = «\. But 

 it has been proved that q^^=~)q^ ; hence, v.ith the same magnetic 

 power, the attraction of tlie large ball ought to hcfice timesi\y>\t 

 of the small one. A remarkable coincidence with this deduction 

 is exhibited in Table VT. At the top of the columns the mag- 

 netic forces applied to both balls liappen to be nearly alike, and 



'' 'I'lic iin])ovtaiicc of lliis condition will appcnv fiirtlicr on. 

 VInl. Mnij. S. 4. \'..l. I , Xo. I. . /;//■;/ 1 H.") 1 . 1) 



