68 



Mr. J. Stuart on Galvanomagnetic Attraction. [Dec. 5, 



cos 



— — — ( - 27 cos 6 + 105 cos 3 0) % 

 + _L(525 cos 0—3150 cos 3 + 3465 cos 5 Q) — 



128 



(2) 



Each of these expressions consists of a series of terms in ascending powers 

 of — which will be converging. 



"We shall now seek to find X and Y for a galvanic current traversing a 

 wire coiled into the form of a hollow cylinder, of which the internal 

 radius is b, the external radius b-\- c, and of which the length is 2f. We 

 shall suppose the individual turns of the wire to lie so close as that each 

 may be regarded as an exact circle. 



Let A B be the axis of the coil, so that A and B are the centres of its 

 two faces ; then A B = 2f. Let be the middle point of A B. Let P be 

 the attracted point, PM its perpendicular distance p from AB. Let 

 PAM= a , PBM=/3. 



Let C be the centre of any turn of the wire regarded as a circle of 

 radius a, CP=r, PCM=0, 6 C—oo ; then it is readily seen that for the 

 whole cylindrical bobbin the forces X, T are given by 



