ERRATA. 



p. 31, third line below fig. 6. 



For = - eR cos 6 . 00'= - eR (OP l - O'Pi) read =eR cos . 00' = eR (OPi - O'Pi). 



p. 49, fourteenth line from top. For 45 read 30. 



41 41 



p. 52, second line from bottom. For nl = ^; read =- - == . 



jrA JrJi t: A. xL> 



p. 65, last symbol on page. For )&. read )i. 



p. 220, last two formulae, and first formula on p. 221. For 4?r read 



