approximately the Self-induction of a Coil. 



225 



a, b, and c, it is enough if one of these remain constant. Mr. 

 C. E. Holland has worked out for me the following values of 



-7 — g in C.G.S. units, keeping c = l centimetre, from the series 



published as Appendix III., page 321, vol. ii. of the second 

 edition of Maxwell s ' Electricity and Magnetism/ Unfortu- 



c b 

 natelv, unless the ratios of -and - are small, this series does 

 J9 a a ' 



not enable L to be calculated. I propose later to amend the 



formula when I have, either by calculation or experiment, 



c b 



found L for values of - and - greater than \ ; and I regret 



that the difficulty of obtaining values of L in these cases is so 



L 



great as it is. Calling Mr. Holland's calculated 



kirn 1 



by the 



letter /, the following Table shows the results of his calcula- 

 tions : — 



a. 



b. 



c. 



I. 



4 



1 



1 



9-060 



4 



2 



1 



7-303 



4 



3 



1 



5-993 



2 



1 



1 



3094 



2 



2 



1 



1-985 



2 



3 



1 



1-034 



4 



1 



2 



7-460 



3 



1 



1 



5-914 



3 



2 



1 



4-510 



3 



3 



1 



3-420 



6 



1 



1 



16-0436 



6 



2 



1 



13-527 



6 



3 



1 



11-704 



10 



1 



1 



31-8655 



10 



2 



1 



27-763 



10 



3 



1 



24-834 



Now it is evident that if of any coil the dimensions are a, 

 6, and c, then L for this coil is c times the L for a coil 



whose dimensions are — , — , 1. Hence Mr. Holland's num- 



00 c b 



bers enable us to study the general case, so long as - and - 



are less than J. I find that with more than enough accuracy 



