This is a science show about hair, which Amanda Jopling and I dreamt up while we were working at Glasgow Science Centre.
In the show, the presenter (or a volunteer) has their head shaved in front of an infra-red camera. By shaving only half of the head at first, we see how effectively your hair keeps your head warm. The show introduces other snippets of hair-related science, too.
Naturally, this is not a show that gets done very often. Here are some pictures from April 2005, when we did two shows as part of Glasgow Science Centre's Stand-up Science season of science shows. I am one of the victims, and the other is my son, Matt, aged 10 at the time. He provided the best spectacle, because his hair had been flourishing unchecked for at least 12 months.
I hold forth while Amanda gets to work with the electric clippers.
Matt half-way through the process.
We glue a piece of aluminium foil to the shaved head, to show (on the thermal camera) how badly shiny metallic surfaces radiate heat. Our volunteer from the audience can't believe that she's being allowed to glue something onto somebody's head.
Seen in the thermal camera, Matt's head seems to have a hole in it where the foil has been glued on. The foil is very nearly as warm as the rest of his scalp, but because it is so shiny it emits very little of the infra-red radiation that the thermal camera detects. Shiny surfaces are used to retain heat in thermos flasks and survival blankets.
In the last part of the show a volunteer from the audience annotates the victim's head to produce a map of brain function.
Matt was delighted with his new hairdo (and also with the £20 note).
More hair than I ever had before.
A few things you might not know about your head and your hair
There are about 100,000 hairs on your head. That's if you have black or brown hair. Blondes can have up to 150,000, carrot-tops as few as 80,000.
In any town of 150,000 people or more, you can guarantee that at least two people will have exactly the same number of hairs on their heads as each other. Why? There are only about 150,000 options for the number of hairs on your head, so if there are more than 150,000 people, someone has to share.
Your head is potentially a major source of heat loss from your body. Although the brain is only one-fiftieth of your body mass, it receives about one-fifth of the blood pumped by the heart. What's more, when you are cold, your body withdraws the circulation from your extremities, but not from your head. In cold weather, wearing a hat is a very effective way to keep warm.
Each of your hairs grows about 0.3mm every 24 hours. It doesn't sound like much, but if you've got 100,000 hairs, it adds up to over 30 metres of new hair on your head every day.