to about 11,000. He stated that the photographs from 
which he was making his final map were taken on double 
the scale, with twice the amount of dispersion. 
He then showed various prismatic spectra, exhibiting 
difierent states of atmospheric absorption, in one of which 
Piazzi Smyth’s rain band was markedly visible. 
After a short discussion. Captain Abney exhibited some 
photographs of the spectrum in natural colours. 
