where yL is the distance from the closest stake (the rightmost stake in this example) to the place where the maximum declination would have been seen if it occurred at the moment of setting or rising.

A similar procedure was used, arguably, to find the maximum date from observations at several lunations (Thom 1971/1973/1978, pp. 89-90). The same equations are still applicable, but the time interval is a lunar month instead of a lunar day, and the specific values of the variables, such as G will be different.

In Thom's view, the relating of the position of stakes to the location of the Moon requires only empirical ideas based on observation. Whether these ideas were in fact carried out is moot; if they were not, however, some alternative explanation for the sectored stone rows is required. This has not yet been provided.

Again, in Thom's view, the value of the site at Mid-Clyth was that it provided a grid for interpolation, from which the foresight direction at the peak of the Moon's extreme declination could be determined. The stones are arranged in grids of convergent sectors. The base and height of the main sector are 132 ft or 17L, where L = 20/7 MY, the grid element at Mid Clyth. Although Thom asserts that this is exactly equal to G (Thom 1971/1973/1978, p. 89), the calculated value of G is actually equal to 126ft [38.36m from (6.15)], within 5% of the correct value, if one uses the closest of the foresights discussed by Thom. More problematic is the quantity 4G, which should be the radius of the sector, if Thom's proposed extrapolation scheme was used. The radius of the main sector is 360 ft and that of the SW sector, 413 ft, far from the calculated value, ~503 ft (Thom 1971/1973/1978, p. 104).

The evidence for alignments at the site is also provided by Thom (1971/1973/1978, pp. 93-95). There is a small notch only 1.8 miles (2.9 km) distant in an otherwise featureless western horizon to which a line of stones at the top of the hill seems to point. According to Thom, the directions to the notch from various backsight positions along the "Hill o' Stanes" ridge mark the direction of rise of the Moon in a full range of variables: perhaps e + i - s, e + i - s + A, e + i, e + i + s - A, e + i + s, and e + i + s + A in the direction toward A ~ 24°, and -(e + i) with similar variations, to the southeast. However, the distance to the southeastern foresight is ~50 miles (~80kms) and a value of G calculated for such a foresight greatly exceeds the scale of the known grid.

Three similar sites of stone sectors are found within 20 km of Mid Clyth: at Camster, Dirlot, and Loch of Yarrows (Wood 1978, p. 124). At Dirlot, a similar sectored grid of 70 to 80 stones is found, and as at the Hill o' Stanes, the narrow end of the sector is uphill. Thom asserts that the radius of the base is 145 MY and that the grid elements are 3 MY apart. Here, there is evidence for alignment to the minor standstill moonrise but not with a distant, natural foresight. There is also evidence for the quantity 4G, here computed to be 398 ft, compared with the radius of the sector, 394 ft. The base of the sector, however, is 147ft, not a calculated G = 100 ft. The azimuth of a direction of three menhirs of which only one is standing currently is 52.°3, corresponding to a declination of +19°11', the extreme northern limit of a minor standstill moonrise (8 = e - i + s + A). There is also an

(as yet) unexplained precisely laid-out zigzag of stones with bearings 59°28' ± 2', 337°59' ± 1', and 61°33' ± 1'.

The Loch of Yarrows is 8 km south of Wick and has a nonorthogonal grid. Several distant menhirs and a cairn could have provided artificial foresights, and Thom (1971/1973/1978, p. 99) suggests that a very small break in the contours of Tannoch Hill, about 1 km away, now filled with peat, could have been greater in the past. Alignments to 8 = -(e + i - s - A) for the artificial foresights and to 8 = (e + i) for the natural one are proposed. The measured length of the radii of the rows is 800 ft, compared with computed values of 756, 765, and 826 ft. Thom (1971/1973/1978, p. 98) indicates the lozenge-shaped grid element size to be 2.5 x 2.75 MY.

At Camster, there are two cairns north of a series of stone rows. Here, only about 33 stones are currently known in place, about half of those at the Loch of Yarrows. An alignment is noted to 8 = -(e + i - s - A), but Thom (1971/ 1973/1978, p. 100) indicates that excavations are needed to establish the radii of the sparsely filled grid rows with greater precision. From what is extrapolated, it appears that the radius is ~544ft, against 4G = 606 ft sufficient, Thom felt.

Finally, we discuss the situation at Kintraw. From the platform above the gorge, the midwinter Sun's upper limb may briefly twinkle when it is seen at a coll between Beinn Shiantaidh (43.7 km distance) and Beinn a' Chaolais (46.5 km). Thom (1971/1973/1978, p. 38) suggested that a green flash might have been visible at this instant in what he regarded as the clearer skies of the Megalithic. For the Sun, (6.12) is still valid:

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