In order to
render such a disentanglement possible, it is indispensable to mark by
hand, at least once every twenty-four hours, upon each curve, the date
of the day corresponding to it. It is equally useful to verify the
exactness of the indications given by the apparatus by making readings
several times a day on a scale of tides placed alongside of the float.
Nine times out of ten the rise of the waves renders such readings very
difficult and the control absolutely illusory.
All these conditions united, as well as others that we neglect in this
brief discussion, necessitate a surveillance at every instant. The
result is that these marigraphs must be installed in a special
structure, very near the bank, so as to be reachable at all times, and
that the indications that they give are always vitiated by error,
since the operation is performed upon a level at which are exerted
disturbing influences that are not found at a kilometer at sea. It
were to be desired that the float could be isolated by placing it a
certain distance from the shore, and transmit its indications, by
meant of a play of currents, to a registering apparatus situated upon
_terra firma_.
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