Continued … Good fit loyally follows the body's outline, and flow determines the way fabric travels away from it. Ideally, it travels along imaginary "flow lines" that jut into the space around the body's silhouette. Classic couturiers thought of little else as they tugged at their toiles. Continues here.

The invisible line, for example, that slopes at about a 45-degree angle from a woman's hipbones to the ground, is a flow line. Ditto the soft spear of space jutting out and down from her shoulders. Often, the fabric of a skirt fits the hip line, then follows the hip's flow line, continuing away from the body in a smooth and logical stream.

It looks "right" for reasons we might not immediately fathom.

It just does.

Ditto the shoulder line; sleeves that are puffed, leg o' mutton, trumpeted or simply belled, and which have a silky relationship with the body's silhouette, look more "right" than designs that may be more inspired, but have a less intimate relationship with the body's natural silhouette.

Which is all a convoluted way of saying that some of the nicest spring hats are designed by clever milliners who keep the shape of a woman's head in mind. Some of spring's worst hats are simply ostentatious decorations and, invariably, need a spectacularly good-looking wearer to offset their oddity.

Somewhere around the middle of last century, the phenomenon of fashion's flow lines was convincingly proved by a generation of gifted milliners who crafted fashionable hats that appeared to belong on each wearer's head. Wearing a hat was as natural as carrying a handbag.

The best hats are still crafted by milliners mindful of those fundamental principles.

The best picture hats have softened brims that echo a woman's shoulderline and don't bulge too high above her natural crown. The most beautiful cocktail hats and fascinators are carefully proportioned and shaped along the flow lines that curve away from a woman's face.

The cloche, the beret, bowler and trilby styles that are pecking along fashion's fringe at the moment (most European catwalks show some manner of hat for spring/summer 2007) reflect the neo-reverence for ergonomic principles and any milliners not well acquainted best get cracking to learn them.