In some cases we may protect the plungers from the pressure of ooze, etc., by guards fitted to the stem of the grapnel, but in practice we have not found these to be necessary.
The water is allowed free access around and about each separate part, in order that its pressure shall be equal on all sides. This arrangement renders the grapnel as effectual in the deepest as in the shallowest water.
By making the plungers in two pieces, with a rubber washer or its equivalent between them, we prevent mud or ooze from getting behind and interfering with their working. As the hole in the rubber surrounding the contact-plate, by caused the passage of the pin through it, closes up as soon as the pressure is removed, leaving in the rubber a fault of exceedingly high resistance, the rubber does not require renewing.
In the rubber in which we embedded the contact-plate, we place a layer or more of tinfoil or other easily pierced conducting surface, through which the pin passes on its way to the contact-plate proper. This method we have adopted in order to make the assurance of contact doubly sure.

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