The exposition continues beyond the simplest cases of interferences - the horizontal and vertical or rotational around a single point - into more complex patterns which arise when the interferences between two slightly displaced centres create an actual and illusory throbbing. These can be on the material itself - moiré silks where one sees within the silk the pattern oscillating slightly against another and printing the result or (as here) where the result is computer generated by slightly displacing the centres. This can also be seen in more ordinary material than silk, which does not have this innate interference within its weave, by printing one pattern then slightly moving it and printing another. All these arise out of the phase shifts, the redoubled impressions.
Using a computer, the interference patterns
of moirés are demonstrated and their changing structures as their centres approach and
recede. One can experience the extraordinary vibrations which would change subtly and
systematically with a migraine - inducing, hallucinatory regularity where one centre of
convergence moved gradually accross another or turned in relation to it.
'Using the printing press demonstrate that the double impression of any one uniform texture will give a moiré (due to the interference between a ratio of 1:1 and a ratio of 1:2). Using sheets with ruled straight parallels, divergent straight lines and sheets covered with consistent curved systems as concentric circle, repeated curves from stencils, superimposed against light, observe the interference of patterns in motion. For this to be completely successful the thickness of the lines should have a relation to the intervals between them not greater than 1:2. Where more open structures are used the moirés produced can only be demonstrated by filling in the intervals.'
Even though the computer has been used instead of the printing press, the same patterns emerge. Moiré: two patterns (of material) slightly displaced which yield complex interference patterns.
.D. Convergent axis
Drawing executed with the computer. Although there are no interferences here, this figure possesses strong optical phenomena in the form of radiations - but not those of the expected circular nature - but tending out and beyond a centrally indented square.
Fig.132. Concentric circles slightly
displaced executed by hand move in a moiré pattern, in three lightish rays and three
darkish rays approaching the centre
These displaced circles oscillate in a migraine - producing way. The relatively coarse weave of moiré silk allows such interference in a concrete material when the centres are displaced slightly and flickeringly create radian oscillating patterns; or in slightly moving a printed pattern; or in slightly moving the centres of radiating coordinate systems.
.E. Helical axis computer drawn
Although this does not display interference, it curves inward and outward violently and makes illusory hopping after-images scintillating in elliptical forms.
.F. The superimposition of two almost
coinciding helical axes generates a number of curiously shaped white curved lines arising
from the after-image of two black lines intersecting
It resembles a magnetic force field.
.G. The superimposition of two slightly
disjoined helical axes generates a number of white curved lines arising from the
after-image of two black lines intersecting
It too resembles a magnetic field of force.
.H. The superimposition of two rectilinear
much disjoined convergent axes generates white ellipses narrow and ever widening in the
diagonal direction and deep concavities between them slowly inverting to convex fields in
Why does it function so? Perhaps perceptions in the eye because of too much precision, emphasizing the contrast overact.
.XVII. ASCENDING LIGHT, S. W. Hayter
1966, acrylic on canvas. Collection of Julian Hayter, Paris.
Number of simple curves complexly interfere resulting in emergent wave patterns. 'ASCENDING LIGHT' is remarkable because it pictures light in its physical nature as waves, embodying all of the conditions of interference in a pure but physical way: thus it enlarges the idea of what can vibrate and have interferences.