Embrace the Christmas science cult and avoid unnecessary snowmen

This year's Melvyn Bragg Christmas Science Lecture is to be given by Professor Gene Jones at the Royal Broadcasting Institute next Wednesday. For those of you who cannot get to London or who aim to start their Christmas shopping that evening, I am pleased to be able to bring you the entire abridged text today and tomorrow.

"Good evening and welcome. As you know, the idea of the Melvyn Bragg Christmas Science Lecture is to popularise science by any means possible, including that of making it topical and interesting, and that is why on this day every year we look at all aspects of science which are peculiarly applicable to Christmas time and see what lessons we can draw from it.

"People are often amazed by the idea that there are connections between science and Christmas time, but in fact any science you care to name could be quoted for the purpose. Astronomy? Astronomy can explain the wise men's star. Chemistry? Chemistry can explain the affinity that brandy seems to have with butter, creating brandy butter, something which is only eaten at Christmas time. Mathematics ...?

"Ah, now, mathematics! Maths is very involved with Christmas. For instance, it is the only time of the year that we find ourselves counting backwards, because - anybody? That's right! We count backwards for Advent! Yes, I know we count backwards for darts matches as well, but I'm just thinking of Christmas things today. Any more mathematical examples at Christmas time? Yes, there are the twelve days of Christmas. There is the whole question of when Christ was born, and you may have read in a paper this week that an Italian expert now reckons that Christ as born in 12BC, which means that we celebrated the Millennium without knowing it in AD 1988 ...

"But let's take a simpler Christmas maths problem, that of providing everyone with their fair share of roast potatoes at the Christmas dinner. We all know that mother divides the potatoes to give enough to every guest present. We also know that there is never enough to go round, and that someone goes short. How can maths help us here?

"Well, as a trained mathematician or at least statistician, I have observed that some people take more than others. I have also observed that the people who take more potatoes also take the larger potatoes. The solution is obvious. Along with the roast potatoes, also roast a quantity of large chunks of parsnip. The greedy people, going for the bigger bits, will be filling themselves up with parsnip, thus leaving ample potatoes for the less greedy.

"Anthropology, do I hear someone cry? Has anthropology got any lessons for us at Christmas time? Well, yes, it has. When last week's snow came, I went out in the field with my boy to roll a big snowball. Now, one thing we noticed as we rolled our snowball along and it got bigger and bigger, was that if you roll a big snowball, you roll more than just snow: you roll grass, and sheep's droppings, and twigs, and stones, all bundled up inside that big, three-foot-high snowball.

"From a distance your snowball looks big and white, but you know better; you know that the snowball is a bran tub of other things. If you took all the snow away, there would still be a lot of non-snow material left - and this is precisely what happens when the snow melts! And this week, sure enough, the snow had all melted, even my big snowball, and what was left behind was an otherwise inexplicable little pyramid of grass, sheep droppings, stones and glass.

"Imagine if, as an anthropologist, you came across such a cache of objects. Aha! you might say to yourself, here is a tribe that worships glass, stone, sheep droppings and twigs! Similarly, if you came across a pile of three pieces of coal, a carrot, four twigs and an old scarf, you might, as a scientist, be baffled. But as a Christmas scientist, you would know immediately that - anyone? Very good! It was the remnants of a snowman! You see, we Christmas scientists can explain things in terms of someone in the past having fun, a thing that anthropologists never let themselves do!"

Tomorrow: why there is always one dud bulb in the Christmas lights, plus scientific musings on wet gum boots, the effect of medieval candles on the medieval ozone layer, how evaporation can help keep the Brussels sprouts warm, and why the human mind is incapable of drawing Christmas trees accurately. Don't miss part 2 of the Melvyn Bragg Christmas Lecture!