M. E. Edluiid on the Nature of Electricity* 185 



As what is uuder the sign of integration is independent of R, 



if ~ remain constant^ the induction-current will be proportional 



to R, in accordance with Felicias experiments. 



In this way we obtain^ instead of formula (18), the following 

 expression of the induction between two elements : — 



-{_ ^ cos 6^ cos ^' ds ds (20) 



In order to ascertain if the results obtained by formula (19), 

 after the determination of the function r(r) in the way above 

 indicated, agree with experiment, Dr. Sundell, iVggregate Pro- 

 fessor at the University of Helsingfors, devoted himself to a 

 great number of experiments at the physical laboratory of the 

 Stockholm Royal Academy of Sciences. Such an inquiry was 

 necessary to enable us rigorously to control the results obtained 

 by theory ; for previously we had only a very limited number of 

 experiments applicable to the object we are here pursuing. We 

 take the liberty of communicating one series of those experi- 

 ments, referring the reader to Dr. SundelFs memoir itself for 

 further details*. 



The radius R of the induction-coil w^as equal to 21*7 centims. ; 

 the radius R^ of the induced coil was 7'\ centims. The 

 distance between the planes of the two circles is indicated in 

 centims. under the letter z. 



Deflections of the Magnetometer. 



z 



Observed. 



Calculated. 



Difference, 



1-5 . 



. . 176-0 . 



. . 176-7 . 



. . +0-7 



10 



. . 127-4 . 



. . 128-3 , 



. . +0-9 



15 



. . 93-3 . 



. . 93-4 . 



. . +0-1 



20 



. . 66-1 . 



. . 66-0 . 



. . -01 



25 



. . 46-8 . 



. . 46-6 . 



. . -0-2 



30 



. . 33-8 . 



. • . 33-8 . 



. . -0-5 



40 



. . 17-9 . 



. . 18-1 . 



. . 4-0-3 



The agreement between the calculations, on the one hand, 

 and Dr. Sundell's experiments, on the other, is fully satisfactory 

 in every respect. 



If the inducing circle is in the plane of xy with the centre at 

 the origin, and the induced circle in the plane of yz, but has its 

 centre neither on the axis of z nor on the axis of ?/, integration 

 causes the term of the induction-formula (17) containing cos ^ 

 to vanish, while the other term, which contains cos 6^'^, alone 

 remains. Such an arrangement of the induction-circuits is 

 consequently suitable for investigating whether that term has or 

 has not an appreciable inductive force. By means of this pro- 

 * (Efversigt af Vef.-Akad, Fork. February 1872. 



