Mr. R. H. M. Bosanquet on Electromagnets. 347 



experimentally, for any condition of the machine. We vary 

 the speed slightly, and measure the two speeds and the two 

 currents. Then we have x from the equation 



x (log n— logft )=log C— log C . ... (9) 



A rough determination of the values of x for my Gramme 

 machine, by this method, is given at Phil. Mag. [5] xv. 

 p. 285. It is as follows * :— 



Current Amperes. x. y. 



5 .... 3 f 



10 .... 2 i 



20}' ' - ' ™ i 



x = l, 7 = 0, correspond to the condition of saturation, accor- 

 ding to the theoretical assumption of a saturation limit, which 

 we know is not quite justified in practice. 



I have now to show how the assumption (6) can be fitted 

 to a law of magnetization when the law is given by a series 

 of numbers representing the magnetic resistances or conduc- 

 tivities of the magnets of the machine, for the different induc- 

 tions used. 



Rearrange (6) as follows : — 



23=K/ (magnetizing force)?; .... (7) 

 then 



U l ~y( % Y=Ki, (8) 



\magn. force/ ; v ' 



or 



W~y (conductivity)* = &! ; (9) 



or, if B, cy\ U ? <%/o are pairs of values differing but little, 



W-y{cy)y=Wr(cyoy, (10) 



and 



1-7 



. * _ rm¥~' 



whence 



a _ 1= Iog«-lo g 8o . . _ ( 



logcyo-logcy 



* These numbers are so far justified by my later determinations that 

 it is not worth while to amend them at present. The conditions and 

 limitations to which they are subject will be touched upon in the discus- 

 sion of my dynamo. 



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