About four-posters​….

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Hob H
Hob Jan 23, 2007 20:04:26
Replying to tiompan

tiompan wrote:
some of the Irish four posters didn't have stones on the perimeter and were more asymmetric .
That's partly feeding the thing that perplexes me. It's a bit like the thing about how many points you need to describe a linear alignment, in that any two points can form either a straight line or a curve. If you've got four points in any kind of square/parallelogram/trapezium, they're going to be points on some theoretical circle or other, just as any two points are on some theoretical line or other. But it doesn't really imply that the things were actually set out as four points on a circle. Maybe they cardinal points were important as part of a cross?

The fact that some of the Irish ones are asymmetric implies some are not, now those I'd accept as being part of a circle, as five points would describe a circular perimeter. But that there are five posters that aren't symmetrical just confuses me even more.

Which is of course why the ancients did all this stuff. Just to confuse those of us who live in their future.

T tiompan
tiompan Jan 23, 2007 20:25:09
Replying to Hob

Hob wrote:
[quote="tiompan"] some of the Irish four posters didn't have stones on the perimeter and were more asymmetric .
That's partly feeding the thing that perplexes me. It's a bit like the thing about how many points you need to describe a linear alignment, in that any two points can form either a straight line or a curve. If you've got four points in any kind of square/parallelogram/trapezium, they're going to be points on some theoretical circle or other .

What if you have three of them on the perimeter then one askew then do another one for luck .

F FourWinds
FourWinds Jan 23, 2007 20:30:37
Replying to Hob

Hob wrote:
square/parallelogram/trapezium, they're going to be points on some theoretical circle or other,
The vertices of a parallelogram will never all be on the perimiter of the same circle unless it's actually square or rectangular.

As for trying to work out where a fourth, missing stone was from the three remaining stones by fitting a circle to them doesn't work. There are loads of circle that will pass through the three stones, because you don't know which point to choose on each stone. Should the circle pass through the outermost point? The point directly below the centre of gravity? The inner edges? You will get a good idea of roughly where it could be, as gjrk says on this drawing - http://www.themodernantiquarian.com/post/55001, but it could have been a parallelogram. If it was then the fourth stone would have been off the circle somewhere between the top stone and the compass.

If you use the innermost edges of the three stones at Lettergorman then you get a totally dfferent circle to the one shown in the above mentioned drawing. Do that would make the plan trapezoidal.

Interesting stuff!

S StoneLifter
StoneLifter Jan 23, 2007 21:31:26
Replying to Hob

It helps to play with the shape, by altering pebbles on a windowsill, for instance. Aren't the four stones often arranged as two pairs of stones - two large ones and two little ones. By moving little stones about one finds that it's fairly easy to produce balanced and pleasing arrangements.