ERRATA. 



Vol. XV. page 469, Hne 6 from bottom, the expression in brackets -[ ]■ should be 

 raised to the nth. power. 



Vol. XV. p. 486, in equation (1) for ^ read ^. 



dy dx 



The equation which occurs at the foot of page 488 is limited to the case where 

 a=a?-f-a const. 



Vol. XV. page 497, line 3.2 from bottom, /o/- -f-0'00631 read + •000631. 



