There are more ways than one to get things done.

If one wants to detect an enemy plane in time of war, one can stand on a high hill and simply watch.

Or, as at one of my favourite haunts in Dungeness, Kent, one can station great concrete ear trumpets on the beach, to listen for the hum of the enemy.

Built between 1928 and 1930, these incongruous structures are acoustic mirrors which were built as an experimental early warning system. They are there because it is one of the quietest places in Britain. If not there, then where?

But a third way superseded these great white elephants very soon after their creation. Because in the heart of the darkest days of the second world war, radar was born.

Radar was a name which first lived, in 1940, in capitals. It stood for Radio Detection and Ranging. It works by sending out radio waves in a straight line from a radar station. They meet a plane coming the other way and bounce back.

And what they can do is little short of miraculous.

They can determine not only that these things are there: but how fast they are going, which direction they are travelling in, and even their altitude.

What a wonderful invention. Even pilots could fly in the dark with knowledge of who else was about, long before they could see company.

Apocryphal tales are told of the propagandists making up a story to put the enemy off the scent of these miraculous powers the British pilots had acquired. It was put about that the pilots were being fed a diet rich in carrots, because carrots help one to see in the dark.

Radar was not, however, foolproof. Because while radar signals travel in straight lines, the earth’s surface is curved.

Which means that until we can invent intelligent radio waves which defy nature and make like a banana, the radar will start out fitting the earth’s surface snugly, and gradually move in a straight line away from the curve of the planet. Thus leaving a space underneath the radar for planes to remain invisible.

It has, these days, become a figure of speech: a way of talking about something which has characteristics which render it undetectable.

Today I have a headache, which forces one to take things a little more carefully than usual. I am living life with a little less gung-ho bravado, and a little more softly-softly caution. Life is grey: but I find I am noticing things which would usually be undetectable to me.

The rain, it raineth every day. Outside, the colours are muted.

This morning I walked across the iron age fort on the hill behind our house. The dog holds me personally responsible for the rain, and every now and then, as the wet seeps ever closer to the base of his tough wiry coat, he throws me a look of infinite reproach. Make it stop, he grumbles non-verbally. This is not acceptable.

But as I walked, I happened to glance towards a set of wiry birch trees with not a leaf to their frames. And there, a study in intricate oriental detail, nature had sketched a community of small birds silhouetted against the grey.

They were dynamic and ever-changing: someone was always moving from one branch to another, or flitting down for a puddle-bath. There must have been thirty tiny creatures, and I couldn’t see their colour in the gloom, only their shape.

A study in line and form, no-one said anything. The scene was set to the music of heavy ponderous raindrops, and it held an incredible, silent, charge.

My customary radar veers off before it picks up this kind of event, usually. Today, I was looking with different eyes, in a different place.

I came home and went out cybervisiting, paying my respects to friends and reading the stories of their daily preoccupations, just as once Jane Austen’s society paid less virtual respects to those in their sphere.

There is a new house I have been visiting, every day.

Its archivist is Barbara, and the one I visit – called simply ‘It’s About Time’ – posts works of art to contemplate, at least once a day. It is an art gallery from the comfort of one’s armchair: and it has a gifted director who makes a personal choice of art for you.

Today I stumbled upon work after work by a Danish man called Vilhelm Hammershoi. From the moment I set eyes on them, these paintings arrested my attention, there, in my muted world. For they, too, would have slipped beneath the radar on a normal day.

Hammershoi lived an existence which was far from being spectacular. He was born in the old quarter of the gracious city of Copenhagen. he stayed there and worked there all his life. His father was a rich merchant and so there was no garret struggle for financial security. His mother recognised his talent and fostered it from the age of eight. By the time he was in his mid teens he was studying in Copenhagen’s Royal Academy of Art.

His perfect, spare style captivated many who saw his work, and right from his first portrait out of art school he attracted acclaim. Famous artists flocked to meet him. He was shy and retiring.

He led a life rooted in one place, a muted existence. And as he lived, so he painted: with consummate taste, and perfect style and proportion. Not for Hammershoi brash primary colours: rather, muted scenes of moving depth, strong in form, minimalist before minimalism was a twinkle in the eye of the art world, often with a single figure turned away from the artist.

For 43 years this man and these startling paintings have slipped under my radar, because I love the brash and the bold. I wouldn’t have glanced in the direction of this spellbinding work.

It took a rainy day and a headache to slow me down enough to wonder at an artist’s muted style: and at the startling beauty of a tiny flock of birds.

When the headache is gone and the rain has ceased, I must remember this place, beneath the radar.