140 
PROCEEDINGS OF SOCIETIES. 
irregular pieces of sandstone rock might be fixed, as they were useful 
as shelter to the live stock, and by increasing the superficial area of 
the bottom adding considerably to the aerating capacity of the vege- 
tation which will ultimately clothe it. If the observer constructs an 
aquarium for himself, great care must be taken that the rockwork and 
cement are thoroughly soaked for a fortnight or even longer, that all 
the soluble salts may be eliminated from them, the water being 
frequently changed : sea sand (or in default of that silver sand), re- 
peatedly washed till the water is clear when stirred up, is to be placed 
in the tank. The sea water may now be added ; this may be either 
natural or artificial, the preference being given to the former, but in 
localities where it is not easily procurable that made from Mr. Gosse's 
formula may be used : 
This may be dissolved in a little less than four quarts of fresh water, 
and a specific gravity bubble of 1026 ought to sink slowly in this 
fluid if it is of the right density. The tank being filled with this, 
some handfuls of freshly-gathered seaweeds, especially TJlva latissima, 
may be washed in it, but not left permanently in, and the tank 
exposed to the .sunlight for about a fortnight, when it will be found 
teeming with the germs of vegetable life and in a suitable condition 
for the support of its animal occupants. The use of the specific gravity 
bubble in regulating the density of the water was shown, and a new 
method of aerating the water devised by the author described, by 
which the use of syringes advocated by writers on Aquaria was super- 
seded. The utility of the aquarium to the microscopist was then ad- 
verted to, and its advantages pointed out in the facilities it afforded 
for the observation of the conjugation and multiplication of Dia- 
tomaceaB, the development of the Foraminifera, the growth of the 
germs of marine Algae, and the various transitional stages in the life 
history of the Polyzoa. The paper concluded with some practical 
suggestions relative to the selection of suitable occupants for the 
tank, and upon those which would be likely to interest the practical 
microscopist. 
Mr. Ingpen described a portable microscope, designed and made 
by Mr. Moginie especially for use with low powers. The eye-piece 
was very large, and gave a fine field of view. Its lenses were made 
to slide instead of screwing, so that they could be very readily cleaned. 
The general pattern of the instrument was somewhat similar to the 
portable microscope of the same maker, but the stage was moved by 
rackwork instead of the body, which was fixed to the stand, thus 
adding greatly to the steadiness of the whole. The rackwork was 
sufficiently delicate for use with a ^ or even \ inch power. Not- 
withstanding its large size, the instrument was exceedingly portable, 
and its wide range and great steadiness rendered it very serviceable 
for many purposes, particularly in botanical and aquarium work. 
Common salt, 3 J ounces 
Epsom salts, \ ounce 
Chloride of magnesium, 200 grains 
Chloride of potassium, 40 „ 
avoirdupois. 
