49 
was employed, no line was seen which was not also obtained 
in a tube of the same dimensions containing carbonic 
oxide. 
Captain Abney, E-.E., F.E.S., exhibited his photographs 
of the ultra-red portions of the Solar Spectrum, and first of 
all showed that the light transmitted by ordinary bromide 
of silver was of an orange tint, showing absorption in the 
lowest end of the spectrum. He then went on to explain 
how he had tried to load the molecules comprising this 
bromide of silver by means of gum resins, and that 
he had thus been enabled to photograph slightly beyond 
the lowest limit of the visible spectrum. Further re- 
searches proved that bromide of silver could be prepared 
in two molecular states, one that already shown, and the 
other in which absorption takes place in the red as well as 
in the blue. This was found sensitive to every radiation. 
He pointed out that the blue form of the silver bromide 
could be converted into the red form by simple friction, and 
that after friction it was insensitive to the ultra red radiation. 
Prof. Eoscoe here exhibited the different preparations 
of gold in minute division made by Faraday himself, 
some of which transmitted blue light and others red, 
showing that at all events two cases of molecular condition 
exist in the case of metallic gold. 
Captain Abney then threw upon the screen photographs 
of the prismatic spectrum, in one of which the lowest limit 
of the prismatic spectrum was reached. He demonstrated 
this on the black board, by setting up as ordinates the 
wave lengths of the various portions of the photographs as 
obtained from the photographs of the diffraction spectrum. 
He then exhibited various photographs of the ultra-red 
portion of the diffraction spectrum, extending from 7,600 
