Hot line to less troubled waters

HERE'S a great way to amuse yourself at the expense of your work- mates, for less than the price of a gin and tonic. First, go to a fishing tackle shop and ask for a 25-metre spool of the lightest monofilament line on sale. It won't be very strong; in fact, it will probably break at a pull of 1lb or less. That doesn't matter. The secret is its diameter, which could be as fine as 0.05 millimetre. Unless you have exceedingly sharp eyes, you won't be able to see it at all from a few feet away - and nor will your victim.

Next, tie something to the end of the line. A pen is ideal, but if you're feeling exceptionally mischievous, use quick-drying glue to attach a £l coin, or even a fiver. Put it on the floor, close to where your mark will walk. Run the line round a table or chair-leg, so the prank can't be immediately associated with you. The secret is to be close enough to manipulate the line, but not so far away that you can't see exactly what's happening. At this stage, you may want to tip off others so they can enjoy the fun too.

You can guess the rest. The victim walks along, sees a pen or a coin on the floor and bends to pick it up. The pen moves just out of reach, seemingly by itself. If you manipulate the line correctly, you can nudge the object enough for them to miss when they try to grasp it, but not enough to realise they're being hoodwinked. It is, you might say, a fine line between success and failure. With practice, you can manoeuvre a particularly gullible person right across a room in a series of Quasimodo-like lurches, as if their hand is glued to their ankle. It's very childish. But on quiet days, it can be "a source of innocent merriment" (did WS Gilbert ever play Liners?).

Wonderful stuff, line. Window dressers use it for displaying their wares in those famously contorted positions. Tailors use it for invisible mending. Surgeons have used it for stitching the wounded. It makes a brilliant amateur burglar alarm (an idea for Blue Peter here). It's far less intrusive than string for displaying Christmas cards. I'm assured it is far superior to cotton when you're restringing pearls. And soon, you will be able to buy a line that is environmentally friendly too.

You might think that a line which dissolves in water isn't going to be a whole lot of use to anglers. Though such a product would appeal to fishermen who don't want to get their hands covered in slime, or go to the bother of continually winding in, it would be hopeless for fishing on a rainy day.

However, a unique monofilament designed by Daiwa, a Japanese company with a large factory at Wishaw, Strathclyde, seems to have overcome all the obvious problems. For a start, the line doesn't start to melt like a sunbathing jellyfish as soon as it comes into contact with water. Their marketing director, John Middleton, says that it only starts to decline in strength after about a month in water or soil, and it takes up to two years to vanish.

Furthermore, the line will not deteriorate on a reel, as long as you don't store your tackle underwater or in a very damp place. The bacteria that destroys it does not breed easily in air. "It can be kept just like conventional monofilaments when rinsed in fresh water and stored in a dry place," Middleton says. "Anglers will not even have to worry about the line breaking when they have a big fish on the end. It will be as good as anything else on the market - but it's environmentally friendly."

Daiwa, which has about 200 scientists beavering away in Japan to develop tomorrow's tackle, has developed it to answer criticisms about the dangers of lost line. If monofilament gets caught in a tree, or snagged on a river bottom, it will last for decades, its strength relatively unimpaired. This makes it a danger to birds, fish and even animals like otters. Fixed nets made from monofilament are banned in many countries (not the UK, alas) because they often break free of their moorings and drift the ocean, swathing a path of destruction and trapping fish, dolphins and seals, which die a lingering death.

I can't quite see the trawling industry switching to Daiwa's product. They still think conservation means talking to each other. But the new line has won praise from the Royal Society for the Protection of Birds, and it would overcome a serious environmental problem for anglers. The colour, no doubt, will be green - just right, in fact, for an outdoor version of Liners.