344 



Mr. W. Grant on the Curves of 



extend in space to an infinite distance. The negative surfaces 

 turn outwards and close up in a plane containing the axes of 

 x and z ; they are hollow circular rings which enclose one 

 another, and which have their common centre at the origin of 

 coordinates. 



In the series of measurements for the determination of the 

 second set of curves, the axis of the coil D was perpendicular 

 to that of C, but otherwise every thing was arranged as in the 

 diagram. The same values were given to M for these curves 

 as for the others, by setting the coil B in the same positions 

 on the scale E F which it had occupied during the previous 

 experiments. These curves are numbered in accordance with 

 Table Y. 



Table V. 



Number of curve. 



X. 



M. 



1 



316 



24-0 



18-7 

 14-45 

 1105 

 815 



0125 



0-25 



0-5 



10 



2-0 



40 



2 



3 



4 



5 



6 





The zero- curve of this set coincides with the axes of coor- 

 dinates; and, in general, when two similar coils with their axes 

 perpendicular are employed, one as primary and the other as 

 secondary, their mutual induction is zero when the axis of the 

 one lies in the mean plane of the other. This shows that any 

 curve of the second set for which the value of M is small must 

 make a near approach to the axes of coordinates in the neigh- 

 bourhood of the origin, and that a part of each curve in that 

 region cannot be traced experimentally with the coils em- 

 ployed. The coordinates of these curves, as far as it was 

 found possible to determine them experimentally, are given in 

 Table VI. ; but there is with this set a larger space near the 

 origin within which the dimensions of the coils made it im- 

 possible to get measurements than was the case with the first 

 set of curves. In the figures, the curves are continued con- 

 jecturally within this space by dotted lines. The second set 

 of curves are given in fig. 5, PI. X. 



