But if the ground has to be dug
deeply in order to sink the conductor, the form of the electrode must
be more condensed, and selected in such a way that the necessary
action may be obtained with a minimum output of copper and labor. For
great depths, and when the ground will permit of boring, an elongated
and narrow cylinder will be used. Such a system, however, can only be
employed when the cylinder is surrounded by spring water, since,
without that, an intimate contact with earth that is only moist,
cannot be obtained with certainty. In earth that is only moist and for
moderate depths, preference may be given to an electrode laid down
flat. The digging necessary in this case is onerous, it is true, but
it permits of very accurately determining the state of the earth
beneath and of obtaining a very perfect adherence of the electrode
therewith. Two forms, the annular ribbon or the flat ring and the
network, present themselves, according to calculations, as a
substitute for copper plates, which are so expensive; and these forms
are satisfactory on condition that the labor of digging be not notably
increased. These forms should always have a diameter a little greater
than that of the plate. The flat ring and the network, however, offer
one weak point, which they possess in common with the plate, and that
is, their dimensions cannot be easily adapted to the nature of the
ground met with without a notable increase in the expense.
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