Archaeoastronomy in the British Isles - The Stones and the Stars: Building Scotland's Newest Megalith - page 91

F IG . 4.27 (Continued)
and a standard fraction, the megalithic inch (40 meg. in. = l MY),
used in laying out the spiral carvings. He maintained that the non-
circular rings are elegant geometrical constructions of ellipses,
“egg-shaped rings,” “flattened circles,” etc., which were attempts
by the builders to make the perimeters of the rings and the radii
of the arcs used into whole-number multiple of megalithic rods
and yards, respectively (Fig. 4.28 ). His histogram of measured
diameters (Fig. 4.29 ) shows that half-yards were sometimes used
(quarter-yards in the radii). The ground plan often appears to be
based on two right-angled triangles, back to back. At Clava, to
take a single example, there is a ring that gives perimeter arc radii
of 15, 19 and 25 megalithic yards relative to two internal triangles
of sides 6, 8 and 10 MY. Referring to these analyses, immediately
before the paragraph quoted above, Daniel wrote: “Thom's sur-
veys had already led him to argue for the existence of a megalithic
“yard” measuring 2.72 ft and to suggest that the builders of stone
rings had a knowledge of Pythagorean geometry 2,000 years before
the Greeks. These are extravagant and unconvincing claims: what
the builders had was a practical knowledge of laying out right-
angled triangles [ 15 ].”