JF Ptak Science Books Post 1762
The ouroboros--and in this particular case, the double, over-and-under ouroboros--is an interesting and ancient symbol. In my experience, the single unit is to be expected, but the double seems uncommon. The symbol ("oura" or tail and "boros", eating, in Greek, one who eats one's tail) stretches back into the dim and dusty past, at least to the Egyptian Book of the Dead, and is Plato's first living thing--its is the primordial unity, the rebirth of forever, death/life/birth/rebirth, continuing into infinity, the great world soul...a kind of Western equivalent of the Taoist Yin Yang.
There's much more to be said about this symbol, especially by such people as Erich Neumann and Carl Jung, but I'll resist, mainly because it is just too complicated for me to make an intelligent statement. (I've tried to read the Great Mother as well as The Origins of the History of Consciousness by Neumann, but only made my way around the edges of the first, and picked through the interesting bits of the later. Jung is someone I've never had much luck with.)
The first symbol, and a gorgeous one it is, comes from the Theatrum chemicum (1659-1661, and published in six volumes by Lazarus Zetzner in Strasbourg), and shows the combination of what was supposed to be an alchemical highpoint: the spiritual coming together of sulfur and mercury, elements of what the practioners believed were the basic constituents of all metals and minerals. And of such stuff miracles were understood to be made, except that of course, they weren't--the fact that this stuff never worked to produce something more substantial than mercuric sulfide wasn't due to the theory or practice or thought but to the "fact" that the mercury and sulfur used in the process weren't "pure" enough. That said, the Theatrum was a very important work, the largest collection of alchemical works ever gathered and published together--it was also evidently much appreciated by Isaac Newton, who was said to consult it often and who owned the set in his library.
A more classical appearance of the ouroboros (De Lapide PhilosophicoTriga Chemicum (Prague 1599) compiled by Nicolas Barnaud), depicting a dragon seizing the polarities of its soul, ultimately uniting them:
And in the discussion of the ouroboros and philosophical aspects of infinity it should be mentioned that there is some connection between it and the mathematical symbol for infinity, which seems to arise from (the remarkable and original) John Wallis' De Sectionibus Conicibus, which was published in 1655. Wallis employed the old Roman symbol for 1,000 to use for the mathematical infinity, which of course is the ouroboros on its side. (Wallis it should be noticed was also among the earliest people to put into print the symbol for pi, as well.)