Flat Earth Experiments You Can Do
Zetetic Astronomy:
Earth Not a Globe
On several occasions
the six miles of water in the old Bedford Canal have been surveyed by
the so-called "forward" process of levelling, which
consisted in simply taking a sight of, say 20 chains, or 440 yards,
noting the point observed, moving the instrument forward to that
point, and taking a second observation; again moving the instrument
forward, again observing 20 chains in advance, and so on throughout
the whole distance. By this process, without making allowance for
convexity, the surface of the water was found to be perfectly
horizontal. But when the result was made known to several surveyors,
it was contended "that when the theodolite is levelled, it is
placed at right angles to the earth's radius--the line of sight from
it being a tangent; and that when it is removed 20 chains forward,
and again 'levelled,' it becomes a second and different tangent; and
that indeed every new position is really a fresh tangent--as shown in
the diagram, fig. 9, T 1, T 2, and T 3, representing
FIG. 9.
the theodolite levelled
at three different positions, and therefore square to the radii 1, 2,
3. Hence, levelling forward in this way, although making no allowance
for rotundity, the rotundity or allowance for it is involved in the
process." This is a very ingenious and plausible argument, by
which the visible contradiction between the theory of rotundity and
the results of practical levelling is explained; and many excellent
mathematicians and geodesists have been deceived by it. Logically,
however, it will be seen that it is not a proof of rotundity; it is
only an explanation or reconciliation of results with the supposition
of rotundity, but does not prove it to exist. The following
modification was therefore adopted by the author, in order that
convexity, if it existed, might be demonstrated. A theodolite
FIG. 10.
was placed at the point
A, in fig. 10, and levelled; it was then directed over the flag-staff
B to the cross-staff C--the instrument A, the flag-staff B, and the
cross-staff C, having exactly the same altitude. The theodolite was
then advanced to B, the flag-staff to C, and the cross-staff to D,
which was thus secured .as a continuation of one and the same line of
sight A, B, C, prolonged to D, the altitude of D being the same as
that of A, B, and C. The theodolite was again moved forward to the
position C, the flag-staff to D, and the cross-staff to the point
E--the line of sight to which was thus again secured as a
prolongation of A, B, C, D, to E. The process was repeated to F, and
onwards by 20 chain lengths to the end of six miles of the canal,
.and parallel with it. By thus having an object between the
theodolite and the cross-staff, which object in its turn becomes a
test or guide by which the same line of sight is continued throughout
the whole length surveyed, the argument or explanation which is
dependent upon the supposition of rotundity, and that each position
of the theodolite is a different tangent, is completely destroyed.
The result of this peculiar or modified survey, which has been
several times repeated, was that the line of sight and the surface of
the water ran parallel to each other; and as the. line of sight was,
in this instance, a right line, the surface of the water for six
miles was demonstrably horizontal.
This mode of forward
levelling is so very exact and satisfactory, that the following
further illustration may be given with
FIG. 11
advantage. In fig. 11,
let A, B, C, represent the first position, respectively of the
theodolite, flag-staff, and cross-staff; B, C, D, the second
position; C, D, E, the third position; and D, E, F, the fourth;
similarly repeated throughout the whole distance surveyed.
The remarks thus made
in reference to simple "forward" levelling, apply with
equal force to what is called by surveyors the "back-and-fore-sight"
process, which consists in reading backwards a distance equal to the
distance read forwards. This plan is adopted to obviate the necessity
for calculating, or allowing for the earth's supposed convexity. It
applies, however, just the same in practice, whether the base or
datum line is horizontal or convex; but as it has been proved to be
the former, it is evident that "back-and-fore-sight"
levelling is a waste of time and skill, and altogether unnecessary.
Forward levelling over intervening test or guide staves, as explained
by the diagram, fig. 11, is far superior to any of the ordinary
methods, and has the great advantage of being purely practical§ and
not involving any theoretical considerations. Its adoption along the
banks of any canal, or lake, or standing water of any kind, or even
along the shore of any open sea, will demonstrate to the fullest
satisfaction of any practical surveyor that the surface of all water
is horizontal.
