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Megalithic Mensuration 1.

3.1.1   In 'Megalithic Sites in Britain' Thom states that, if it were not that two features of megalithic construction were assiduously adhered to he could not have unravelled the subtleties of the circle and ring geometries. The first was the insistence of coherent integer rules governing as many of the construction lengths as possible. See     Megalithic Mathematics. The other was the very high grade of survey apparent in the laying out of the designs. Thom found that this standard did not fluctuate appreciably throughout the length of Britain suggesting that an accurate standard unit of length, available to all communities, must have been employed. Thom believed, from mathematical analysis of his large collection of personal, high-class surveys that he could identify this unit which he termed the Megalithic Yard, (MY). He further claimed to be able to identify this basic length to a resolution of some hundreds of a foot leading him to think that the unit of measurement used had to be recorded, copied and dispersed from a single place of manufacture. If this measurement had been passed on by copying from tribe to tribe throughout the length of Britain, there would surely have been detectable discrepancies in highly coherent ring geometries dispersed over large geographic distances. The dimension identified is 1 MY = 2.720 feet or 0.829 metres.

A.Thom,'Megalithic Sites in Britain' p.43 1 MY = 2.720 +/- 0.003 ft. A further conclusion is that this unit was in use from one end of Britain to the other. It is evident from Table 5.5 that it is not possible to detect by statistical examination any difference between the values determined from the English and Scottish circles. There must have been a headquarters from which standard rods were sent out but whether this was in these islands or on the Continent the present investigation cannot determine. The length of the rods in Scotland cannot have differed from that in England by more than 0.03 ins or the difference would have shown up in Table 5.5. If each small community had obtained the length by copying the rod of its neighbour to the south the accumulated error would have been much greater than this.

This unit of measurement may be seen to have been consistent for at least the 400 year span of the construction period of high-resolving observatories, (2000 to 1600 BC). To appreciate the achievements of the British megalith builders in this skill a brief resume of the attempts over nearly a millenium to establish an accurate standard of measurement in historic Britain might be instructive. Even by 1885 AD a reliable, non- perishable standard had not been achieved.

The British Imperial Standard Yard.

Precise, agreed, standards of measuring length and quantity which can be deployed across communities have been a vital issue in the development of all societies since the evolution of agrarianism and larger scale communities and economies. The quantification of land, goods and building materials and a system of recording the figures is mandatory for activities such as trade, construction, agriculture and ownership. Further demands for accuracy in measurement have been made, perhaps, since even earlier times by the proto-science of ancient astronomy. 3.1.2  Anthropomorphic mensuration is generally believed to be the basis of most historical measures. In the middle of the 10th century the Saxon king Edgar secured 'The Yardstick' at Winchester as the official standard of measurement for southern Saxon lands. How Edgar came by his stick is not known but, in the early 12th century Henry I decreed that the yard be-

"....the distance from the tip of the King's nose to the end of his outstretched thumb."

It would appear that Henry had lost Edgar's 'Yardstick', or, more likely it had perished. At the Assize of Measures in 1196, in Richard the Lionheart's reign, the first documentation of a standardised unit of measurement was made-

"Throughout the realm there shall be the same yard of the same size and it should be of iron".

In Edward I's reign (1272-1307) the yard (or Ulna) and its sub- and aggregated divisions were defined. Barleycorns and the Rod.

"It is remembered that the Iron Ulna of our Lord the King contains three feet and no more; and the foot must contain twelve inches, measured by the correct measure of this kind of ulna; that is to say, one thirty-sixth part [of] the said ulna makes one inch, neither more nor less.... It is ordained that three grains of barley, dry and round make an inch, twelve inches make a foot; three feet make an ulna; five and a half ulna makes a perch (rod); and forty perches in length and four perches in breadth make an acre."

Whilst copies made from Edward's Iron Ulna may have sufficed for land measurement a builder or astronomer would be hard put to it, when requiring parts of an inch, to have to resort to handfuls of barley seeds. The perch or rod, as it was also known, was a traditional Saxon land measure and survives in the twentieth century. It had originally been defined as;

"....the total length of the left feet of the first sixteen men to leave church on Sunday morning."

By the late 15th century Henry VII refreshed 'The Yardstick' of Edgar I which is thought to have beeen a direct copy of the 350 year old Saxon standard. In 1588 Elizabeth I established yet another new standard which remained the legal British yard for over 300 years. But in 16th century Scotland the people had to do with James V's pronouncement;

"Tak' the meesure of a sma' maun's nose to his finger-tip. Tak' the same from a reeg'lar maun, and a meikle maun. Combine all and divide by three. Yon is yi'r Yaird."

In 1824, under George IV, an Act of Parliament attempted to introduce systems of measures more widely into British society and remove inaccuracies associated with measurement. This 'new' yard became the first imperial standard but had actually been commissioned by the Royal Society in 1742, which in it's turn had been based on an earlier Elizabethan standard. In 1834 this yard perished in a fire that burned down both Houses of Parliament. It had lived for only 9 years and 198 days. In 1855, eventually, a new standard was legitimised. This was based on copies of unofficial standards that had been compared to the Imperial Yard before it was damaged. This yard was refreshed as the Imperial Standard Yard of 1855, which was, however, made of base metal and shrank at the rate of one part per million in about 20 years. The Metre des Archives. In 1889 the International Bureau of Weights and Measures (BIPM) presented Great Britain with a platinum-iridium alloy bar which was an exact copy of the International Prototype Metre. This alloy proved to be exceptionally stable and the Imperial Yard was also committed to it. The Polar Quadrant Survey. For the first time in history a standard measurement was derived from a natural constant. BIPM decided that a metre should be the 10 millionth part of a quarter circumference of the Earth, measured through the Poles. Provided the necessary high-quality survey methods, (and equipment), were available this standard could always be re-assessed and re-established. With the committment of the metre, 'Mètre des Archives', to an iridium/platinum alloy bar universal agreement on a unit of length to the requirements of 19th century science and technology was achieved.

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