ce it consists of two teeth
only. The electro-magnets are arranged at an angle of 120 deg., and for a
change of current the wheel, r, describes an angle of 60 deg., that is
to say, a sixth of a circumference. The motion of r is transmitted, by
means of the pinion, d, and the wheel, e, to the wheel, T. For a
one-meter variation in level the wheel, T, makes one complete
revolution. It is divided into 100 equal parts, and each arc therefore
corresponds to a difference of one centimeter in the level, and
carries, engraved in projection, the corresponding number. As a
consequence, there is upon the entire circumference a series of
numbers from to 99. The axle upon which the wheel, T, is keyed is
prolonged, on the side opposite e, by a threaded part, a, which
actuates a stylet, g. This latter is held above by a rod, I, which
is connected with a fork movable around a vertical axis, shown in Fig.
6. The rectilinear motion of g is 5 mm. for a variation of one meter
in level. Its total travel is consequently 40 mm. The sheet of paper
upon which the indications are taken, and which is shown of actual
size in Fig. 7, winds around the drum, P, and receives its motion from
the cylinder, W. This sheet is covered throughout its length with fine
prepared paper that permits of taking the imprints by impression.

[Illustration: FIG. 5]

[Illustration: FIG. 6--RECEIVER OF SIEMENS AND HALSKE'S MARIGRAPH.]

[Illustration: FIG. 7]

This stated, the play of the apparatus may be easily understood. Every
ten minutes a regulating clock closes the circuit of the local pile,
B2, and establishes a contact at C. The electro-magnet, E4,
attracts its armature, and thus acts upon the lever, h, which
presses the sheet of paper against the stylet in front that serves to
mark the level of the lowest waters, and against the stylet, g, and
the wheels, T and Z. In falling back, the lever, h, causes the
advance, by one notch, of the ratchet wheel that is mounted at the
extremity of the cylinder W, and thus displaces the sheet of paper a
distance of 5 mm. The wheel, Z, carries engraved in projection upon
its circumference the hours in Roman figures, and moves forward one
division every 60 minutes. The motion of this wheel is likewise
controlled by the cylinder, W.

It will be seen upon referring to Fig. 7, that there is obtained a
very sharp curve marked by points. We have a general view on
considering the curve itself, and the height in meters is read
d