56 Prof. Jones on the Calculation of the Coefficient of 



and 



Isobiityl iodide, v-l =4749, 



Ref. eqniv. Isobutyl cMoride, —j- E = 4163'9. 

 Table II. — Bromine. 



Spec. grav. 



Ma. 



Assumed upper limit. 



/Xd. 



p-r. 



flG. 



3-085 



1-6260 



give 10-9 13-1 13-7 

 corresponding refraction-equivalents. 



Note on these Tables. — They can only be accepted as ap- 

 proximate, but the calculations have been carried quite as far 

 as the uncertainty of the original data warrant. Under these 

 circumstances the coincidences noticed between sulphur and 

 selenium are of no great value, except perhaps as pointing out 

 a likely direction in which the search for these empirical 

 relations amongst the refractive indices should be pursued. 



VI. On the Calculation of the Coefficient of Mtitual Induction 

 of a Circle and a Coaxal Helix. By Prof. J. V. Jones, 

 M.A., Princij^al of the Uiiiversity College, Cardiff*. 



IF M is the coefficient of mutual induction of any two 

 curves, we have 



M 



'^i 



cos e 



ds ds' ; 



where r = the distance between two elements ds and ds', and 

 e = the angle between them. 



Let us take for the equations of the circle and helix : — 



y = acos 6 

 z =a sin 0. 

 y'=Acos6', 



} 



■y =.a- cos (7 , -\ 

 /=Asin6'', K . . 

 x'^^hd'. 3 



(i.) 

 (ii.) 



* Communicated by the Physical Society : read November 10, 1888. 



