72 PROCEEDINGS OF SOCIETIES. 
glassy surface of the water, the greater part of them are 
reflected, and those which permeate are refracted and twisted 
in various directions by the currents of the water; and where 
the depth is considerable, it would be few rays which would 
penetrate to the bottom: but let the surface become ruffled 
by the passing wind, and it is little light that can be trans- 
mitted; and when this same disturbing cause lashes into 
waves and foam, not a ray can pass, and all below must be 
dark as night. Too much light should therefore be avoided ; 
and the direct action of the sun prevented by means of blinds, 
stipling, or the like. It is a great desideratum to preserve the 
growth of the lovely red alge in all their natural beauty, and 
prevent their becoming covered with a parasitic growth of 
green or brown coloured plants; this can be effected by 
modifying the light which illuminates the aquarium by the 
intervention of a blue medium, either of stained glass, of 
tinted varnish, coloured blinds, &c. The tint should be that 
of the deep sea, a blue free from pink, and having a tendency 
rather to a green hue. This modified light affects also the 
health of those creatures which are confined to shallow waters, 
so that a selection of the inhabitants must be made. 
Heat.—The proper control of this agent is also most 
material to the well-being of these tanks, for experience has 
proved that an increase or diminution of temperature beyond 
certain limits acts most fatally on many of the creatures 
usually kept. These limits appear to be from 45° to 75° 
Fahrenheit. The mean temperature of the ocean is estimated 
to be about 56°; and this does not vary more than 12° through- 
out the varying seasons of the year, showing the extreme 
limits to be from 44° to 68°. Great care should therefore be 
taken to afford as much protection as possible, by the arrange- 
ment of the rockwork, both from the sun’s rays by day, and 
the effects of radiation at night, as from the small volume of 
water contained in the aquarium these effects are rapidly 
produced. 
Food.—As many persons, to whom those interested in 
these matters have naturally looked for instruction, have 
decried the idea of feeding, it will be necessary to offer a few 
remarks on that point. How creatures so voracious as most 
of the denizens of the water are, both fresh and marine, are 
to thrive without food, is a question it would be difficult to 
solve; common sense would say they must gradually decrease 
in size, and ultimately die from starvation. The food em- 
ployed should be in accordance with the habits of the fish, 
xe. For the vegetable and mud feeders, vermicelli, crushed 
small, with now and then a little animal food, as worms, 
