ERRATA IN VOL. XXVI. 



Page 168, line 4 from bottom, for e, the thickness of the lens at its 

 centre, read ne, the thickness of the lens at its centre. 



— 451, line 8 from bottom, for Figs. 7 to 14 (Pis. IV., V.) read 



Figs. 1 to 6 (PL IV.). 



— 453, line 9 from bottom, for Figs. 8 to 14, PL V., read Figs. 8 



and 9, PL V. 



— 453, line 2 from bottom, after the present insert (PL V. fig. 10). 



— 454, line 7 from above, omit the word following, and at the end 



of the sentence insert (PL V. fig. 12). 



