Trevor Leggett was head of the Japanese Department of the BBC and this  is a part of one of his broadcasts

ZUBARI 19. 04. 1982

Hullo listeners!

Last week I asked you whether you could remember seeing a conjuring trick for the first time

Something which cannot happen is happening there before one’s eyes. Do you remember the feeling of bewilderment? It is quite interesting, to look at small children when they are seeing these tricks for the first time – often the jaw drops and the mouth opens nearly as wide as the eyes.

Well, gradually we get to know that there is an explanation for all these apparent mysteries; there is an explanation in terms of the laws of physics. When we analyse the trick carefully, we find that however mysterious it seems, it is in accordance with the laws of physics.

Then one has a comfortable feeling.

But …, supposing the laws of physics begin to show effects as incredible as a conjuring trick?   I don’t mean something on the infinitely small in the remote world of the atom and nucleus, but something happening before our eyes like a conjuring trick.

Recently, something has happened at a famous science centre in London called the Royal Institution; here, for the past nearly 200 years, there have been held each year a series of lectures to demonstrate and explain new scientific advances to the public. Some of the greatest scientists of Britain have been lecturers there.

Recently – goes the report in the science magazine called New Scientist – there was a demonstration of various possibilities of a laser beam. One unexpected one was to detect the minute movements of window glass caused by the pressure of sound waves from a conversation inside a room, and reconvert those movements back into the original conversation. That is already like a conjuring trick, isn’t it? Still, we can see that it is possible: it does not contradict any laws of physics.

After this lecture, the apparatus was being dismantled. The laser beam was switched on momentarily, and after almost immediately switched off again. NOW …. at the moment of switching off, the laser beam appeared to turn black. The experimenter noticed this, but he thought it was the visual effect called ‘after-image’. When we look at a brilliant light, and then that light is turned off, for a short time we see a black image where the light was. But this soon fades, and this black beam did not fade.

He called the attention of colleagues to it. They switched on the laser beam again and then again switched it off. Nothing unusual happened – no black beam. But they kept on switching it on and off, and about every ten times, the black beam appeared – Something like the lead of a pencil.

Altogether they switched it on and off a hundred times, and nine times the beam went black. They placed objects in the path of the black beam, and black spots were visible.

The only explanation that occurred to them was that, in some unknown way, the laser had reversed, as if it were sucking light out, but maintaining its coherence, in other words maintaining its beam form.

The effect is still a mystery,, concluded the report, but it is now being studied in at least three laboratories in the UK, one a government laboratory, and the other two -universities.

The magazine included a large photograph of the effect; it shows the jet-black beam coming out from the apparatus.

Well, like a conjuring trick, isn’t it? How could a switched-off laser apparatus suck up light? Well, if any listeners have access to a laser apparatus, try switching it on and off a hundred times, and see whether the effect appears in Japan.

In honesty, I must add that the report appeared on April 1, which as you know, is April’ Fool’s Day. But the rest of the magazine was perfectly serious, and it would have been quite expensive to fake the photograph.

© Trevor Leggett