e
of metallic rods, without necessitating a greater output of material.
These facts, however, have not as yet been put to profit in practice
for the reason, perhaps, that the considerations, which have remained
general, have not at once permitted of obtaining forms what could be
employed with perfect knowledge of the results. This is what led Mr.
Ulbricht, of Dresden, to make calculations for a few forms of
conductors, and to test their approximate values. The results of these
researches are printed in the _Elektrotechnischen Zeitschrift_ for
1883 (p. 18).

[Illustration]

The equations found show, in the first place, that there exist three
means of obtaining a considerable effect, as regards the ground
conductor, with a slight expenditure of material: The cylindrical
electrode may be drawn out into the form of a bar or wire; the plate
may be rendered narrow, and elongated in the form of a ribbon; and,
besides, the annular plate may be enlarged in lessening the metallic
surface.

Finally, a short, open cylinder with a vertical axis may be formed by
curving a narrow plate or ribbon. It is not necessary to see the
formula to recognize the fact that this cylinder must behave like a
ribbon and a flat ring. The radius increasing, and the surface
remaining constant, the resistance of the earth here likewise
approaches zero.

As the resistance of the earth is inversely proportional to the
diameter of the plates, the zero resistance can also be reached by
dividing a plate _ad infinitum_. As the parts of the plate may be
brought quite close to each other without perceptibly interfering with
the action, a _network_ has finally been reached by a division carried
very far, yet limited, and by connecting the parts with one another by
conducting cylinders.

If we seek to determine what forms of ground conductors are efficient
and economical under given conditions, we shall have to begin by
informing ourselves as to the choice of material to be used for the
electrode, and shall then have to ascertain whether putting it in the
ground will or will not necessitate much outlay. The most suitable
material is copper, which may be used with advantage, in that it lasts
pretty well underground, and that the facility which it may be worked
permits of easily giving it more appropriate forms than those that can
be obtained with cast iron, which is of itself less costly.

If the burying in the ground requires little or no labor, as when