ERRATA. 



Page 47, lines 6 and 5 from bottom, for The roots of (40) are real ; and 

 therefore aplanaticism is possible if read The roots of (40) are 

 real, and therefore aplanaticism is possible, if 



— 193, art. 5, line 12, after frame insert from 



— 196, art 11, line 3, for 319 read 313 



— „ „ line 9, move all the figures one place to the left. 



— 197, line 2, after that insert after the first stage, and for collecting 



read unaccented 



— 271, line 37 for U*"n read Ujt ra N 



— 271, — 38, for Vkn is not read TJjfcnN is not 



— 271, — 41, for U;fcn=45 read U*»n=45 



— 272, — 7, for observations read vibrations 



— 282, — 31, for curve read error. 



— 349, penultimate line, for M read 2E?. 



— 351, art. 37, column 5, for 2 read 2 2 . 



„ „ columns 4, 5, and 6, for 1 read 2. 



