120 Lord Rayleigh and Dr. A. Schuster. [May 5, 



Maxwell as most in harmony with the original experiments. The 

 process adopted by Rowland is evidently equivalent to determining the 

 coefficient of self-induction from the deflections themselves, and his 

 result, rather than that given by the Committee, must be regarded as 

 the one supported by the evidence of the original experiments. 



Rowland's own determination, by a wholly distinct method, gives — 



lohm=-9911 oarthqna f ant ; 



second 



and according to our experiments the ohm is even smaller — 



1 ohrn-'9893 eart]l q^ adrant 

 second 



The question, therefore, arises whether any further explanation can 

 be given of the different result obtained by the Committee. The 

 value of GK employed in calculating the experiments according to 

 (4) was — 



GK=299,775 metres. 



For the principal term in GK, as given by (7), we require the values 

 of n, a, and a. From p. 115 of the Reprint we find a— •158194 metre, 

 ?i=313. The angle a must be recalculated, as the value of log sin 3 a 

 (1*9624955) is evidently incorrect. Fix>m 2b' = "03851 metre by means 

 of sin «=a/ v/(a 2 + &' 2 ) we find log sin 3 a=l'99043. From these data 

 the final value is — 



GK=299,290 metres, 



differing appreciably from that used by the Committee. The further, 

 discussion of the question is a matter of difficulty at this distance of 

 time. There may have been some reason for the value adopted, which it 

 is now impossible to trace, so that I desire to be understood as merely 

 throwing out a suggestion with all reserve. But I think it right to 

 point out a possible explanation, depending upon the interchange of 

 the axial and radial dimensions in the paper on the electro-magnetic 

 field. The data there given are the mean radius, the two dimensions 

 of the sections, arid the distance between the coils ('02010). This 

 distance is correct, being equal to 2b' — b, that is, to "03851 — '01841. 

 The distance between the mean planes of the coils is not given, but 

 could, of course, be calculated by addition of '02010 and '01841. If, 

 however, the radial dimension '01608 were substituted for the axial 

 dimension '01841, an erroneous value would be obtained for 2b', that 

 is, '03618 instead of '03851. Using '03618 to calculate a, I find— 



GK = 299,860 metres, 



agreeing much more nearly with the value used in the reductions. 

 If it be thought probable that the value of GK was really 299,290, 



