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VALUE OF THE BRITISH ASSOCIATION UNIT OF RESISTANCE. 
In Lorentz’s method the effect of a short circuit in the induction coil is in the same 
direction. M, and therefore R and x, will be over-estimated by l/n. 
If we examine the formulae applicable to determinations by other methods, we shall 
see that a similar conclusion holds good, so that in every case leakage leads to an over¬ 
valuation of x, at least whenever the result is calculated from the number of turns of 
wire in a coil.* Even without such an examination, it is pretty evident from considera¬ 
tion of the magnitudes involved that the large factor 10 9 in the denominator of the 
formula corresponding to (1) can only be compensated by one or more large factors 
expressive of the number of windings in a coil or coils. An over-valuation of these 
factors, due to leakage, will therefore lead to an over-valuation of x. 
In carefully constructed coils serious leakage is, perhaps, not likely to occur, but its 
presence in a smaller degree is more probable, and is usually difficult of detection. So 
far as this argument applies, we may say that the smaller values of the number 
expressive of the B.A. unit, or of the mercury unit, in absolute measure are to be 
preferred to the larger. 
* The case is different when the constants of a coil of many turns are determined by electrical com¬ 
parison, as for instance in Kohlrausch’s recent correction of the constant of his earth-inductor. 
