for the non-spinning gyroscope, were carefully noted. These po
sitions did not differ by more than 1.5 divisions of the auxiliary
amplitude scale, with each other, nor by more than 2.5 divisions
relative to the zero-line on the same scale. No correlation was
detected between the non-spinning gyroscope tape torque-free
positions and gyro-indicated north, consequently any minor
effects resulting from these phenomena were ignored. The results
summarised in the following section therefore discount any differen
tial torque effects resulting from secular changes in the suspension
tape.
The unquestionable simplicity of the transit method coupled to
its accuracy parity with the tracking procedure makes it a generally
more attractive field technique although the requirement of a stop
watch with trailing second hand places some restriction on its use.
In contrast, reversal point observation is a straightforward pro
cedure which although tiring over protracted oscillations, does not
require any ancillary equipment.
A Sierra portable tape recorder (see Figure 2) proved to be a
useful accessory when no booker was available for recording
observations. Admittedly when using the transit method, the ob
server has sufficient time available in which to make the observation,
record it, and carry out the necessary reductions during oscillation,
but the reversal point requirement of smooth tracking does not
allow the observer time for very much more than reading the circle,
let alone booking comments on gyro-behaviour, weather conditions,
etc. not unless the amplitude is very small.
Tests and Results
Formulating a suitable test model for any experiment always
requires a critical analysis of the task and its aims and objects.
Determining azimuth along a single known line, nine kilometres in
length, in preference to a figural test was the logical outcome after
deciding to study the pendulous gyroscope's behavioral character
istics during protracted oscillation. Observing at more than two
stations for this purpose gives little or no added weight to the results
and comparative accuracies of different observing procedures can
be derived as convincingly from a forward/reverse single line azimuth
determination as from a figural test in which a number of lines
have been observed. The total number of observations are not
dissipated over a large number of stations but rather confined to
the two terminals of the test line. Furthermore, the choice of a
relatively long line in preference to the customary short line found
in mining applications eliminated the effects of critical non-cen
tering of the theodolite.
The accurately known positions of the test lines' terminals
enable the meridian convergences at these, relative to the appro
priate projection central meridian, to be calculated accurately.
The difference between these results is the amount of convergence,
276
