4.96 Intelligence and Miscellaneous Articles. 



The object of this paper is to show that all the tin -ore found 

 in these clays is derived from rocks now in situ in the Kinta 

 district; that it is not necessary to bring in glacial action to 

 explain any of the features which led to the adoption of the theory 

 of their glacial origin ; to point out that these deposits cannot be 

 correlated with the Talchirs of India ; and to show that a simple 

 interpretation may be given to the geology of the Kinta district. 



The sources of the tin-ore here are : (1) the stanniferous 

 granite of the Main Eange and of the Kledang Range ; (2) other 

 granite outcrops known to carry cassiterite ; (3) the granitic 

 intrusions in the phyllites and schists, notably near the granite- 

 junction ; and (4) the granitic intrusions traversing the limestone, 

 and forming an important source of ore. 



The angularity of the boulders and of the tin -ore in some 

 of these clays is due (1) to weathering in situ of the phyllites and 

 schists, which then sink on the dissolving limestone underneath ; 

 (2) to soil-creep effecting the same result ; (3) to the breaking-up 

 of the much- weathered cassiterite-bearing boulders and pebbles in 

 the alluvium. 



Over 90 per cent, of the ore worked in the whole of the Kinta 

 district is obtained from mines situated at less than a mile from 

 granite or from granitic intrusions. 



LIX. Intelligence and Miscellaneous Articles. 



ON MUTUAL- AND SELF-INDUCTANCE SERIES. 

 To the Editors of the Philosojihical Magazine. 



GrENTLEMEN, — 



IN my paper on " Mutual- and Self-Inductance Series " which 

 appeared in the Philosophical Magazine for April, I stated 

 that the formulae for the mutual induction between coaxial circles 

 had only been completely determined in the case of circles far 

 apart. Since the publication of the paper my attention has been 

 drawn to two papers published by Dr. T. J. I'a. Bromwich 

 (Quarterly Journal of Pare and Applied Mathematics, No. 176, 

 pp. 363, 381, 1913), in which a number of the formulas given by 

 me for circles close together are obtained by a method which is 

 substantially the same as the one I used. 



I wish to take this opportunity of apologizing to Dr. Bromwich 

 for trespassing on ground already covered by him, and to assure 

 him that I was totally unacquainted with his work in this direction 

 until a few clays ago. 



Tours faithfully, 

 School of Technology, S. Butter worth. 



Manchester. 



April 7th, 1916. 



