i88o.] 
Notes . 
J 43 
shown, and the other in which absorption takes place in the red 
as well as in the blue. This was found sensitive to every radia- 
tion. 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. 
Roscoe 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. Capt. 
Abney then threw upon the screen photographs of the prismatic 
spectrum, in one of which the lowest limit of the prismatic 
spectrum was reached. Various photographs of the ultra-red 
portion of the diffraction spectrum, extending from 7600 to about 
11,000, were exhibited. Those from which Capt. Abney has 
made his final map were taken on double the scale, with twice 
the amount of dispersion. Capt. Abney showed various prisma- 
tic spectra, exhibiting different states of atmospheric absorption, 
in one of which Piazzi Smyth’s rain-band was markedly visible. 
Some photographs of the spectrum in natural colours were also 
exhibited. 
In many public aquaria, as at the Crystal Palace and West- 
minster, and also at that recently opened at the Aston Lower 
Grounds, near Birmingham, unchanged sea-water is employed; 
and such water has been found by experience to be fit for an 
almost indefinite period for maintaining marine animals in 
health. The principle adopted is to keep the bulk of the water 
in underground reservoirs, and to constantly pump from them a 
fresh supply into the show tanks, the delivery of the water 
being made through a series of fine jets. The great object of a 
constant supply, delivered in such a manner, is to force air along 
with fresh cool water into the tanks containing the animals. By 
that means the water is maintained of an almost constant tem- 
perature, and even if temporarily rendered cloudy by the presence 
of decaying fragments of food, &c., the rapid oxidation resulting 
from the air forced in along with the fresh water from the jets, 
soon renders the water quite clear. At Brighton and some 
other places the sea-water is intended to be used for a limited 
time only, a fresh supply being pumped in from the sea as often 
as required. Since it would be impracticable for inland aquaria 
to be supplied even at distant intervals with fresh sea-water, on 
account of the great cost incurred in collecting and for carriage, 
the system of unchanged water has of necessity to be adopted. 
Mr. H. Williams Jones examined a sample of water which, 
after being used for eight years in a large public aquarium, was 
quite bright, and appeared to answer perfectly the requirements 
of the animals. The results obtained we take from the “ Chemical 
News,” vol. xl., p. 282. It was inferred that a very large 
amount of nitric nitrogen would be present as a result of the 
