The method of taking the observations with two theodolites, as
adopted by the writer, can best be explained by a reference to
Fig. 9, which represents an indented piece of the coast. The
end of the proposed sea outfall sewer, from which point the
observations would naturally start, is marked 1, the numerals
2, 3, 4, etc., indicating the positions of the float as
observed from time to time. Many intermediate observations
would be taken, but in order to render the diagram more clear,
these have not been shown. The lines of sight are marked 1A,
1B, etc. The points marked A1, A2, etc., indicate the first,
second, etc., and subsequent positions of observer A; the
points B1, B2, etc., referring to observer B. The dot-and-dash
line shows the course taken by the float, which is ascertained
after plotting the various observations recorded.

It is very desirable to have a horse and trap in waiting to
move the observers and their instruments from place to place as
required, and each observer should be provided with small flags
about 2 ft square, one white and one blue, for signalling
purposes.

The instruments are first set up at A1 and B1 respectively, and
adjusted to read on to the predetermined point 1 where the
float is to be put in Then as soon as the boatmen have reached
the vicinity of this point, the observers can, by means of the
flags, direct them which way to row so as to bring the boat to
the exact position required, and when this is done the anchor is
dropped until it is time to start, which is signalled by the observers
holding the flags straight above their heads. This is also the