ERRATA. 
Page 257 : 
t, 10 8 27r 2 E 2 e 2 Mm _ , 27r 2 E 2 e 2 Mm 
0/ ch? (M+m) )ea ch z (M+m.) 
Page 258 : 
t i 16 (M + m) 7 16 (M + m) 
r or —A--+ read , A-A • 
4 (M + m) (4M + m) 
For 
read 
