From around 1933 to 1977, Professor of Engineering at Oxford Alexander Thom spent most of his weekends and holidays surveying megalithic sites in Britain. Later, he would mention that “in all, some 450 sites have been visited and about 300 surveyed”. Even on long-distance walks, Thom had his theodolite with him. In his “Megalithic Sites in Britain”, Dr. Thom analyzed the geometry of the stone circles and classified them into Type A, Type B, Type B modified, and Type D flattened circles, Type 1 and Type 2 eggs, ovals, and true circles. “The builders of the circles, rings, alignments, etc., had a remarkable knowledge of practical geometry, – wrote Thom, – They were intensely interested in measurements and attained a proficiency which is only equaled today by a trained surveyor. They concentrated on geometrical figures which had as many dimensions as possible arranged to be integral multiples of their units of length.” In his opinion, “the tremendous organizing effort” was necessary to transport and erect numbers of stones some weighing up to 30 tons. and “a civilization which could carry a unit of length from one end of Britain to the other, and perhaps much further afield, with an accuracy of 0.1 per cent and could call for the erection of 5000 to 10,000 megaliths must have made demands on its engineers”.
Of special interest is what Dr. Thom had to say about the way the builders of the Megalith sites in Britain built eclipses:
“The earliest known study of the properties of the sections of a cone, of which the ellipse is one, seems to have been made by Menaechmus in the middle of the fourth century before Christ but the ellipse may have been known to earlier Greeks. Our forefathers early in the second millennium B.C. were laying out ellipses but their approach was much simpler. Almost certainly their ellipses were set out either with a loop of rope round two stakes or with a rope tied to two stakes. In either method, a third stake round which the rope could slide would be used to scribe the curve on the ground.”
And we recall that some scholars see the poles in the dots in the Yin-Yang symbol. See also the title image of this text. It is taken from “Taiji Variations: Yin and Yang in multiple dimensions” by Cameron Browne. Interestingly, we see two circles in one circle in the famous Avebury.
Dr. Alexander Thom: “The greatest and most remarkable circle in Britain, if not in the world, is at Avebury. Its greatness does not lie in its size alone but in the remarkable manner in which its arcs are built up from a basic Pythagorean triangle so that each retains an integral character, and in the exceedingly high precision of the setting out, a precision only surpassed today in high-class surveying. Avebury provides the final proof of the exact size of the Megalithic yard and demonstrates the use of the larger linear units, 21 and 10 yds.”