188 
The Secretary laid on the table sixty specimens of sound- 
ings, which had been freed from the tallow “ arming” in 
two evenings after business hours, at Mr. Dale’s laboratory, 
by Mr. Dale, Mr. Dancer, and himself, assisted by Mr- 
Richard Dale. The system adopted is that described in Mr. 
Mosley’s Paper, read to this Section on 21st January, 1861, 
published in the Quarterly Journal of Microscopical Science, 
vol. 1st, new series, p. 143, and is found to answer better than 
any other method yet made known. 
Professor Williamson presented fourteen specimens of 
dredgings, supposed to be from the mouths of the Ganges. 
A communication from Mr. A. G. Latham was read, upon 
the subject named for the evening’s discussion, “ On the 
cause of the metallic lustre on the tvings of the Lepidoptera, 
both diurnal and nocturnal. 
Mr. Latham believes that the metallic lustre may be 
simply referred to the presence of a pigment in the substance 
of the wing, in some cases light-absorbing, and in others light- 
reflecting ; all the scales seem equally adapted for reflecting 
the prismatic colours, consisting of three distinct membranous 
films, covered with minute irregularities. Mr. Latham sent 
to be exhibited a number of slides for illustration. 
A communication was read from Mr. Dancer, in which he 
referred to a paper, read by Sir D. Brewster at the last 
meeting of the British Association, containing the following 
remarks by Professor Dove : — 
“ In every case where a surface appeared lustrous there was 
“ always a transparent, or transparent reflecting stratum of 
“much intensity, through which we see another body; it is 
“ therefore externally reflected light in combination with 
“ internally reflected or dispersed light, whose combined action 
“produced the idea of lustre. * * This effect we see 
“ produced when many watch glasses are placed in a heap, or 
