16 ART. 15 H. nAGAOKA: note ON THE POTENTIAL. 



/V^- JlXz) r-^'^^H ; = 1.2.3 (2 m + lXa;^ + ^')-'"-^^P2.+i ( , f. , ), 







where Pam+i denotes zonal harmonies of 2m + lth order, we arrive 

 at the ordinary expression for the solid angle in terms of spherical 

 harmonics. M can be similarly expressed by using (B'). 



It is needless to remark that such expansions converge very 

 slowly. What I wish to show in the present paper is that we may 

 sometimes arrive at a convenient and practical result by using a 

 ^-series, instead of falling into the grooves of spherical harmonics. 



