4 A MARINE AQUARIUM. 
—_—— 
3.—The Waste-pipe. A vulcanite pipe leaves the right side of the 
Tank near the front, and carries away the spare water to the Reservoir, 
passing down alongside of the Pump-supply-pipe. The position of its 
exit, about 2in. from the margin, of course determines the level at which 
the water always stands in the Tank. It was at first proposed that this 
should be a simple pipe, screwed into a hole in the side; but this would 
have carried off only the surface-water. To make the circulation com- 
plete, I chose to take it from a point very near the bottom. To ayoid 
the uncouth appearance of a pipe, however, Mr. Lloyd deyised the 
following contrivance. A slab of slate, 24in. wide, lin. thick, and as 
high as the Tank, has a semi-cylindrical groove gouged out of one 
face, but not reaching quite so far as either end. Its upper end meets 
the hole in the side of the Tank at the surface, while its lower end meets 
a similar hole bored through the slab itself. The slab being firmly 
cemented in place, the water in the Tank, entering through the 
horizontal hole, rises in the hidden groove (now become a tube) till it 
reaches the exit-hole in the Tank, when it begins, and continues, to 
trickle out through the waste-pipe. Thus the Tank can never overflow, 
unless the inflow be more copious than the bore of the waste-pipe can 
carry off, or this pipe become choked. To meet the latter peril, a 
strainer was cemented around the interior orifice, in this form: suppose a 
shallow box of vulcanite, to which there is no cover; the bottom drilled 
with a number of holes tin. wide. This is set up on one of its sides, on 
the Tank-bottom, with its lidless top in contact with the lower part of 
the slab, the perforated bottom (now become the side) facing the interior 
of the Tank. It is not cemented, but merely kept in position by a heavy 
piece of the rock-work ; because I need sometimes to remove it, in order 
to cleanse the straining-holes. By this contrivance (while the water can 
freely percolate and escape), since nothing larger than the pin-holes can 
pass, the waste-pipe, which is of lin. bore, clear, can never become 
choked. 
4.—The Siphon. It was judged desirable to have the power of 
lowering the surface in the Tank, and even of emptying it of water, at 
pleasure, without dipping. For this object the waste-pipe was cleverly 
turned into a Siphon, in this wise. The waste-pipe, after leaving the 
Tank, runs horizontally for a foot, before it reaches the pump-plank, and 
turns to the perpendicular. In the midst of this space a stop-cock of 
vulcanite is inserted, which ordinarily is left open, and serves as an air- 
vent. But, if I wish to draw off the water from the Tank, I take the 
tip of the stop-cock into my mouth, and suck strongly, till the salt water 
comes rushing up. This should be sufficient; but in practice I find it 
needful to suck such a mouthful thrice at least, before the up-current of 
water is strong enough to pour continuously, which is manifest to the \ 
ear, as it roars down the perpendicular waste-pipe. I have carefully to 
close the stop-cock with my fingers at each suck, before I withdraw my 
mouth; or the vacuum, in part formed, would be again destroyed. The 
water sucked into my mouth I instantly discharge into the Tank at 
each effort. When the current is set up, the surface in the Tank is seen 
rapidly to descend, until it is as low asI wish; when, the opening of 
