A while ago, frustrated by the sullen unresponsiveness of my readers, I put here a list of subjects, asking people to send it back with ticks against things they might like me to write about. So far just two people have responded, one of whom sent the marked list back, (I’ve told her privately what the plural of ‘Clitoris’ is), while the other suggested other things I might write about, among them ‘How X-Rays Work’. (It is pleasing to find I am not the only person with total, unquestioning confidence in my ability to explain anything and everything.) Here goes:
I described in my text ‘The Anatomy of Wireless’ (You can have the whole 37 pages in pdf — just ask) the way in which electrons can be ‘boiled off’ a hot wire inside an evacuated glass envelope, and how they can then be attracted across the empty — really, literally empty — space to a positively charged metal plate. (Electrons have a negative charge, you see — homophobes will be pleased to hear that they are never attracted to each other).
The electrons travel faster than a ferret up a trouser-leg, and many overshoot the positive plate, or anode, and hit the glass, and some of them in some sense get through it. What do you mean ‘In some sense’? Either they get through or they don’t. Well, yes and no. Oh, stop it. No, really: if we think about electrons at all, we probably think of them as tiny little tennis-balls. Most of the time that makes sense, but they are so really, really invisibly tiny they sometimes behave not as ‘things’ at all, but as waves. (If you think about it, a wave, unlike the water or whatever in which it occurs, is not really an actual physical ‘thing’.) Scientists for a while used the word ‘Wavicle’ for electrons and such-like. The electrons that get through the glass are wearing their wave hat rather than their tennis-ball hat.
You can’t see these waves of course, but researchers (that is to say, people fooling about with hot wires in evacuated glass envelopes) noticed that unexposed glass photographic plates, still in their light-proof wrappings, left nearby (all sorts of odd things tend to lie about in researcher’s laboratories, often with unexpected consequences) proved to be ‘fogged’ when they came to be used, as if light had got through the wrapping. It occurred to someone — I think it was one of the Curies — to put his or her hand on top of a still-wrapped plate and hold it near the electron-producing device. On development, there was the outline of her hand — and not just the outline; you could see right through and make out all the bones. Lo and behold, X-Rays. They called them X-Rays because X, or rather lower-case x, is the usual mathematical sign for ‘Unknown Quantity’; you may remember it from school maths lessons. No-one really knew what these mysterious rays were. I may say more about that in a future post, but I hope what I’ve said so far gives readers some ideas about the things. Or rather not-things.