Meeting of March 31, 1898. 205 



i 



72 /dx dM.x/dx = 727 (M 2 M^.* 



*i 



As special cases, we have equation (11) reducing the calculation of 

 the force between a circular cylindrical uniform current sheet and a 

 coaxial helical current to the calculation of the coefficients of mutual 

 induction of the helix and the circular ends of the sheet ; and the 

 simpler case of the force between a circular cylindrical uniform 

 current sheet and a circular current, which is obtained from the 

 calculations of the coefficients of mutual induction of the circle and 

 the circular ends of the sheet. 



I hope that equation (11) may be of service in the accurate calcu- 

 lation of the constants of current weighing apparatus. My attention 

 was drawn to the matter from this point of view in consequence of 

 the Report of the Electrical Standards Committee of the British 

 Association made at Toronto, in which mention is made of the 

 importance of re-determining the ampere. 



March 31, 1898. 

 The LORD LISTER, F.R.C.S., D.C.L., President, in the Chair. 



Preliminary communications upon the results of the recent Solar 

 Eclipse were made by the following members of the expeditions : 



The Astronomer Royal, Sir J. Norman Lockyer, K.C.B., Professor 

 H. H. Turner, Dr. R. Copeland, and Captain E. H. Hills, R.E., and 

 Mr. H. P. Newall. 



The Society adjourned over the Easter Recess to Thursday, 

 April 28. 



* Professor A. Q-ray has pointed out to me that this result may be deduced from 

 the consideration that the removal of an element from one end of the sheet to the 

 other is equivalent to a small motion of the sheet parallel to its generating lines. 

 J. V. J., April 21, 1893. 



VOL. LX1II. 



