Di'. Tynctall on the Laws of Magnetism. 289 



wnat"nTll iake place if it be removed from the ninth plane to the 

 first plane_, withoxd altering the trebled jjower of the magnet. The 

 law established in section 6 replies, that at one plane distant it 

 will be attracted nine times as strongly as at nine planes distant. 

 But at nine planes distant it is attracted with the same force by 

 the treble power as at one plane distant by the single power. 

 Hence upon the same plane three times the magnetic power will 

 cause nine times the attraction ; or, expressed generally, the 

 mutual attraction of the magnet and the sphere of soft iron, when 

 both are separated by a fixed distance, is directly proportional to 

 the square of the strength of the magnet. ' ' ' 



We have thus arrived, by direct deduction 'fr'oiii' feistablisbed 

 principles, at the well-known law of Lenz and Jacobi, which, 

 exjn-essed in their own words, runs as follows : — 



T7ie attraction between two electro-magnets, or betiveen an electro- 

 magnet a7\d a mass of soft iron, is proportional to the square of the 

 strength of the magnetizing stream. 



^Ve shall now ])ring the deduction to the test of experiment. 

 At the moment the ball gives way, the magnetic power, or, 

 what is the same, the strength of the magnetizing stream, is 

 expressed by tan/3. The weight upon the scale-pan is the mea- 

 sure of the force with which the ball i^ attracted at the same 

 moment. According to 'tlier above layl th^iJefOre, the quotient 



— :irp — niust be a constant quantity, and hence also 



tan/3 



.,,, = const. 

 V W 



For the sake of convenience in the calculation, the quotient is 

 introduced in the latter fonn in the following table. The angles, 

 as in the former cases, are each the mean of four observations; •. 



Table VIII. 



Distance between balls and magnet ^ ju*^ ^^ '■^^^ mch. 



Ball mi'ti-'-'''-^\\ '^uu.. ■ >\ AN^Ball No. 2. 



V' '"MV »^tdn'j8 V>'A-.. >■■ ■\\\ '.... ,. rtan/3 



Wj\m\, \>m-^ ^^ y,A V',VWV^''- - - ^'^^ »\"'A'^v ^yVj \\o?.'\y'W * 

 gruK-'Jlni -jttiit,) (irui.Jii ■<il; w,,i!i; gi-wi, iJi '«-,„,f,,,_ .',;,''i'; 



!w, 75.,,',, ,9;55,, ,!■' ,2-0,!,,„,., '^0 11 10 



IpO , U 30 , i?Oi ^, 13 30 



150 13 35 ,.;>:pii,„,| Jb ' 15 40 



200 16 ,Q, ,.;,,M|,„„,iW 17 25 



250 17 50 ,,,,,a'0 ,, 66 19 



300 19 19 ,;.'i-0;, ;,,,,7Q',:: 2025 



350 20 40 2-0 80 21 38 



4.^0 22 58 -• "5.8" "'-''^^""■••>"f^''^. '•<■.-.. ■■li.l^.v,. 



