In the course of one of his lectures published in the December number
(1883) of the _Elektrotechnische Zeitschrift_, Mr. Von Hefner-Alteneck
tells us that such a desideratum has been supplied by the firm of
Siemens & Halske. This marigraph, constructed on an order of the
German Admiralty, gives the level of the sea every ten minutes with an
approximation of 0.12 per cent., and that too for a difference of 8
meters between the highest and lowest sea. The apparatus consists, as
we said above, of a float and registering device, connected with each
other by means of a cable. This latter is formed of three ordinary
conductors covered with gutta percha and surrounded with a leaden
sheath, which latter is itself protected against accident by means of
a strong covering of iron wire and hemp. The return is effected
through the earth. We shall enter into details concerning each of
these two apparatus in-succession, by beginning with the float, of
which Fig. 1 gives a general view, and Fig. 2 a diagrammatic sketch.
The float moves in a cast iron cylinder, having at its lower part a
large number of apertures of small diameter, so that the motion of the
waves does not perceptibly influence the level of the water in the
interior of the cylinder.
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