signal used to indicate to the men that the day's work is
finished, and they can pick up the float and start for home.

[Illustration: FIG. 9.--PLAN OF INDENTED COAST-LINE LLUSTRATING
METHOD OF TAKING CURRENT OBSERVATIONS WITH TWO THEODOLITES.]

Directly the float is put in the water, and at every even
quarter of an hour afterwards, each observer takes a reading of
its exact position, and notes the time. As soon as the readings
are taken to the float in position 2, the observer A should
take up his instrument and drive to A2, where he must set up
ready to take reading 3 a quarter of an hour after reading 2.
It will be noticed that he might possibly have been able to
take the reading 3 from the position A1, but the angle made by
the lines of sight from the two instruments would have been too
acute for accurate work, and very probably the float would have
been hidden by the headland, so that he could not take the
reading at all. In order to be on the headland A4 at the proper
time, A must be working towards it by getting to position A3 by
the time reading 4 is due. Although the remainder of the course
of the float can be followed from B1 and A4, the instruments
would be reading too much in the same line, so that B must move
to B2 and then after reading 5 and 6 he should move to B3. As
the float returns towards the starting point, A can remain in
the position A4 while B goes to B4 and then moves back along
the shore as the float progresses.

The foregoing description is sufficient to indicate the general
method of working, but the details will of course vary
according to the configuration of the shore and the course