IX 



ERRATUM : VOL. XXVIII, ME. GORDON'S PAPER, Pp. 156, 157. 



The refractive indices given for hard crown and for light flint must be inter- 

 changed, as it has been found that the polisher to whom the prisms were 

 entrusted has interchanged the H. C. and L. F. labels. 



ERRATA IN VOL. XXIX. 



Captain Creak's Paper, vol. xxix, in the Table, page 35, for 1875 read 1876. 

 Vol. xxix, page 140, line 12 from top, for 3| read 5f. 



