The basic element of the mandala is the circle. The mandala in Figure 1 expresses the motif of intersecting circles, in which the circumference of one circle passes through the centre of another at a paradoxical point where the circumference is at the same time the centre.3
Figure 1 shows the circumference of an inner circle intersecting the centres of four outer circles, while the circumferences of the four outer circles intersect the centre of the inner circle, the creative midpoint of the mandala where opposites meet. The centre is therefore polar and ambivalent, representing a tension of opposites from which energy flows. As a dynamic structure the mandala symbolises the transformation of the year through the four seasons, represented by the four circles, and the solar cycle of equinox and solstice, the centre and circumference of the circle. Beneath the heavenly sphere this solar cycle is mirrored in the lunar cycle of wax and wane and tidal ebb and flood. These two form the celestial opposites Sol et Luna, the alchemical equivalent to the Taoist concept of yang and yin.
§
The motif of intersecting circles or cycles illustrates a dynamic relationship between the opposites. Figure 2 shows a repeating sequence of four conjunctions of Sun (Sol) and Tide
(Luna), demarking the four cardinal events which divide the seasons of the year. By way of amplification, the four events can be related to the cardinal
arrangement of Chinese trigrams in the I Ching or
Book of Changes.4
1. Sunrise at Low tide. Sol at the centre rises upon the vernal equinox above the black void of Luna's eastern circumference. This is the trigram Chên, THE AROUSING, 
Thunder, which stands in the east and signifies the spring. "God comes forth in the sign of the Arousing."
2. Half tide at Midday. Sol has ascended to his summer solstice realization at the circumference and Luna has gained the centre. This is the trigram Li, THE CLINGING, 
Fire, which "stands in the south and represents the summer sun, which illumines all earthly things."
3. Sunset at High tide. Sol regains the centre and sets upon the autumn equinox beneath the fullness of Luna's western circumference. This is the trigram Tui, THE JOYOUS, 
the Smiling Lake, which stands in the west "and leads the year toward its fruition and joy."
4. Half tide at Midnight. In darkness Sol has sunk to his winter nadir at the circumference as Luna regains the centre. This is the trigram K'an, THE ABYSMAL, 
Water, which stands in the north and signifies winter. "He toils in the sign of the Abysmal."
These two cycles are balanced or harmonized so that when one is at the centre the other is at the circumference, thus the solstice of one is the equinox of the other. The result is a marriage of opposites in which the equalisation of one partner polarises the other in an endless oscillation that always seeks to restore the balance, by which what is too full is emptied and that which is empty is filled. Thus the real opposition is between equality in one partner and polarity in the other, as summarized below :-
Circumference Solstice = the polarity of Sol or Luna. The solstice is associated with conception at the nadir and realization at the zenith, the polarities of light and dark (Sol) and fullness and void (Luna) contained within the circumference.
Centre Equinox = the equality or parity of Sol or Luna. The equinox is associated with death and rebirth at the centre, that mysterious place where all things begin and end, the unextended seed-point which contains the whole in potentia.
In this way the two alternate between what might be termed an instability phase in one partner and a stable phase in the other, the one providing for the other continuity through change and unity within polarity, a condition in which rest and recuperation is merely an intermediate or latent state of movement and in essence the whole a devotion to movement.
§
Sol is associated with the trigram Ch'ien, THE CREATIVE, 
and Luna with K'un, THE
RECEPTIVE 
. These two trigrams represent heaven and earth. The I Ching says: "There is heaven, the upper world of light, which, though incorporeal, firmly regulates and determines
everything that happens, and over against heaven there is the earth, the lower, dark world,
corporeal, and dependent in its movements upon the phenomena of heaven."
5 What Sol begets as the Father, Luna brings forth as the Mother in the form of the new son. This generative process is expressed in the following relations of the two partners:
1. Following the vernal equinox the new sun ascends to its maximum moment upon the summer solstice, and behind it the Luna tide rises midway, thereafter passing into the upper vessel of day, which however initiates Sol's decline.
2. After the zenith of the summer solstice the declining sun reaches the western horizon upon the autumn equinox, the tide having continued to rise to at last capture the splendour of the dying sun upon the maximum moment of high tide. The sun sinking below the horizon and passing into the lower vessel of night marks the reversal of tide, which regresses back out to sea.
3. Following the coniunctio of the autumn equinox the dead sun-god, like the dismembered Osiris, plummets to the midnight nadir at the very bottom of the lower vessel of night, undergoing the 'night sea journey' of the hero to fulfil the mystery of rejuvenation (or initiation) in a mythical underworld,6 carried into the darkness by the tide that ebbs rapidly away, passing into the lower vessel of night upon the winter solstice. Luna's descent however into the lower vessel signifies Sol's nascent progression, in the silent conception of the new sun.7
4. And after the nadir of the winter solstice the new sun secretly climbs towards the eastern
horizon while the tide ebbs further and further out to final emptiness, whereupon Sol's nascent
progression is suddenly announced at the vernal equinox, when he appears so resplendently above
the distant waves and enters the upper vessel of day, which heralds the turn of tide, the reversal of
regression to forward flow. As the 'remembrance' or recollection of the dismembered Osiris,
8 the sunrise fulfils the meaning of the regression of tide; the renewal and regeneration of the forward
flowing life-force of the sun-god.
This eternal cycle of renewal is aptly symbolised by what is probably the
oldest alchemical symbol, the Uroboros, the dragon that bites its own
tail.9 The Uroboros is a symbol of the opus, 'which proceeds from the one and leads back to the one'. But the opus represents the individuation
process, which likewise is not a linear process that leaves things behind,
but turns back on itself as a cyclic integration of all that lies buried in the
unconscious. For the unconscious contains not only the undigested
problems of the past but also the dormant seeds of the future, all that
languishes undeveloped and unrealized, all that longs (in a feminine way)
for the light of day. In the unconscious sleeps the image of the Self, the
completion of the whole rather than the perfection of the isolated part.
From the great image of sunrise at low tide we can recall the ageless idea or archetype of rebirth; from the regression of energy, the death of the old ruling principle or conscious attitude in its negative aspect and worn out ways, comes forth the redeeming new symbol of renewal. This cycle of events is primarily a matter of feeling, the mute grief over death, the regression of tide bearing away the dead king, and the great joy of rebirth, the saviour sun born of the darkness and void; the fullness and prosperity of life, and the barren emptiness of longing. No intellectual concept can replace the actual experience that this entails; the inescapable process of death and renewal of the life-force that the opus represents. The symbol belongs to the realm of the Eternal Feminine, sacred matters of the Mother.
Hollow is the Uroboros
The first and last
She who was at the beginning
Appears again at the end
To reinstate the ring, rota and rhyme
For she is all measure, metre and time
She is the eternal One and All