44 PORT ECONOMICS
Middle grounds, or the bifurcation of channels, are
marked by Spherical Buoys with domed tops.
Pillar Buoys, having a tall central structure on a broad
base, indicate special positions.
As regards colour, starboard hand buoys are always
painted one colour only; port hand buoys are painted
another characteristic colour, either single or parti-colour.
CHANNEL LIGHTSHIP AT ENTRANCE TO RIVER MERSEY
(PorT OF LIVERPOOL)
Spherical buoys are distinguished by white horizontal
stripes. Buoys used for marking the position of wrecks
are coloured green with the word wreck” in white
letters.
For night signals, Luminous Buoys are employed, and
these are lighted either by oil or gas—the former petroleum,
the latter, oil gas or acetylene. Acetylene is commonly
used in the dissolved form, the solvent being acetone.
Buoys burning acetylene gas can be arranged to give
flashing or occulting lights automatically, and they can be
left unattended for long periods.
Lightships afford a more powerful light than buoys,

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