A recent work proposed that the double spiral motif found at Newgrange (ca. 3200 BC) is a calendrical representation. Looking south the northern peoples observed that the arc traced by the sun widens steadily from winter solstice to midsummer. A natural supposition is that what is actually observed is just a part of a spiral, its lower half being hidden below the horizon. This seems to be strikingly original in contrast with our habit to think about circles. The author mentions just two refs from the 1980's (M.Brennan 1983, N.L. Thomas, 1988), where this interpretation has been made. Besides vague generalisations, such as "solar motif", are there earlier mentions of the idea as explained along the lines given here?
New is well forgotten old, it seems. In a couple of papers from 1916 Marcel Baudouin discusses as matter of fact the linking of spiral and the Sun's path:
The spiral represents the Sun's path in the sky between a solsticial rising and setting, that is between two solsticial points corresponding to Summer and Winter, as far as what we know about this symbol during the Age of metals.(1)
The same is repeated in a second paper (2).
Ref1. Baudouin M., ''La préhistoire des étoiles: Les Pléiades au Néolithique''. In: Bulletins et Mémoires de la Société d'anthropologie de Paris, VI° Série. Tome 7 fascicule 1, 1916. pp. 25-103; Ref2. ''La préhistoire des étoiles au paléolithique. Les pléiades à l'époque aurignacienne et le culte stello-solaire typique au solutréen''. In: Bull. et Mémoires de la Soc. d'anthropologie de Paris, VI° Série. Tome 7 fasc. 5-6, 1916. pp. 274-317