336 



Mr. W. Grant on the Curves of 



Table I. 



Distance between 



Relative value of 



Distance between 



Relative value of 



centres of coils 



induction- 



centres of coils 



induction- 



=#. 



coefficient =z. 



=x. 



coefficient =zZ. 



centim. 





centiin. 





1-6 



39-567 



15-0 



0-9 



1-7 



37-731 



160 



0-758 



1-8 



35-936 



17-0 



0-631 



1-9 



34-016 



18-0 



0-557 



20 



32-251 



190 



0-48 



2-2 



29-551 



20-0 



0423 



25 



25-593 



21-0 



0364 



30 



21-194 



22-0 



0-321 



35 



17341 



23-0 



0-284 



4-0 



14-468 



240 



0-25 



50 



10-227 



25-0 



0-224 



60 



7-449 



300 



0131 



7-0 



5-504 



35-0 



0-083 



8-0 



4-163 



40-0 



0056 



90 



3-158 



45 



040 



10-0 



2528 



50-0 



0029 



110 



2-021 



550 



0-022 



120 



1-641 



600 



0-017 



130 



1-338 



65-0 



0013 



140 



1093 



70-0 



0-011 



primary coil, x being measured parallel to the axis of the 

 coil, y perpendicular to it, and z being taken equal to M, 

 the coefficient of mutual induction between the primary coil 

 and the secondary coil placed with its centre at the point x, y y 

 o. Then, the curve just described may be viewed as a section 

 of this surface in a plane containing the axes of x and z, the 

 curves of constant induction may be looked upon as contour- 

 lines of the surface, or as sections of it in planes parallel to 

 the plane of x and y, and the curve whose coefficient of mutual 

 induction is equal in value to z will pass through the point in 

 question. 



The values of M, whether positive or negative, are synony- 

 mous with those of z : hence in the figures the curves of 

 variable induction, which are situated in vertical planes, are 

 to be taken as positive if they are above the plane of x and y, 

 and negative if they are below it. Where the values of the 

 coordinates of any curve are represented in the Tables by x and 

 y, the curve is situated in a horizontal plane ; where they are 

 represented by x and z, the curve is situated in a vertical 

 plane. On examining the numbers in this Table, it appears 

 that the values of z or M are approximately inversely 

 proportional to the cube of the distance from the centre 



