EXPLANATION OF TERMS USED } 
at all, in that they are not closed by gates or in any way 
cut off from the river Clyde. The author considers that 
it would be a great advantage if the use of the word Dock 
could be confined to docks properly so-called, namely, 
those which are completely encloseable by gates or other- 
wise, and not continuously in free and open communication 
with an outer waterway. There is scope for both terms 
and a rational field for each. 
Dealing with the subdivisions of the word Dock, a Wet 
Dock is a dock in which water is retained for the purpose 
of receiving and berthing vessels alongside its walls or 
quays, and so keeping them continuously afloat at all stages 
of the tide. This means that at ports round the British 
Isles, where the rise and fall of the tidal level is generally 
considerable, ranging up to as much as 50 ft. between 
high and low water, gates have to be provided to impound 
the water between successive periods of high water. 
Where the tidal range is small or moderate, say not 
exceeding 12 to 15 ft., gates are not found to be absolutely 
essential, and an open basin may serve the same purpose 
as a dock, provided it be dredged deep enough to afford 
the necessary draught at extreme low water. 
This impounding of the water to maintain the level 
naturally involves the separation of the dock from the 
outer waterway for long periods—that is at all times 
except when the two levels, the outer and the inner, 
approximately coincide; in other words, at and about 
high water. Such isolation, however, could hardly be 
submitted to in any important commercial port, and -the 
difficulty is overcome by a system known as Locking. 
A Lock is a small antechamber to a dock with dimensions 
sufficient to accommodate the largest single ship likely to 
make use of it. It has essentially two pairs of gates, 
one at each end, communicating respectively at the outer 
end with the waterway and at the inner end with the 
dock. One pair of gates being closed for impounding 
purposes and so maintained, a vessel is able to enter from 
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