300 Prof. Minchin on the Coefficient of Self -Induction 



Table VII. (continued). 

 New solution Sodium Acetate ; sp. gr. = l"13. 



Temperature 23° 27° 



Current -70 '80 



New partition. 



Temperature 23° 28° 



Current -80 10 



New partition. 



Temperature 24° 30° 35° 38° 



Current '95 1'05 1-20 1'29 



New partition. 



Temperature 14° 19° 24° 29° 34° 39° 44° 



Current -57 '67 -78 "85 -93 -98 1-05 



New partition. 



Temperature 30° 36° 41° 46° 



Current -87 *91 '99 11 



New partition. 



Temperature 25° 30° 35° 40° 



Current '71 '76 -86 '94 



Same partition. 



Temperature 25° 30° 35° 40° 45° 



Current '60 -65 '69 -74 '82 



New specimen. 



Temperature 25° 30° 35° 40° 45° 



Current '72 -85 -92 -98 105 



Same gold-leaf, repeated. 



Temperature 25° 30° 35° 40° 45° 



Current -72 -85 -92 -98 1-05 



The means of all the above results plotted give almost a 

 straight line (Plate IV. fig. 3). 



XXV. Calculation of the Coefficient of Self-induction of a 

 Circular Current of given Aperture and Cross-Section. By 

 Professor G. M. Minchin, M.A.* 



LET ACB (fig. 1) represent a circular wire in which a 

 current of strength i is circulating ; let be its centre 

 and OV its axis (perpendicular to its plane) ; let P be any 

 point in space and through P describe a circle, PQ, parallel 

 to the plane of the current, its centre being V on the axis. 

 It is required to calculate the normal flux of magnetic force 

 passing through the circle PQ. If VP = #, and the vector 

 potential of the current at P is G (this latter being, of course, 



* Communicated by the Physical Society : read December 8, 1893. 



