Science: Technoquest

Q: I saw a rainbow very high in the sky near cirrus clouds, with no curve. It was on a damp evening. What was this?

What you saw was no rainbow - although it was very similar. Rainbows are caused by sunlight being reflected and split inside raindrops. This other effect is called parhelia, or sundogs. Instead of water, ice crystals (hexagonal in shape) refract light and refocus some of it towards you, giving a ring of light around the Sun.

It is rare to see the whole ring, but arc-sections are common. At the four compass points of this ring you often see brighter patches of "rainbow- like" light, several degrees in extent.

Q: How does a fish know what species it is? It can't look in a mirror to see what it looks like and then find others that look similar. I guess this applies to all animals - how can a baby elephant recognise an adult elephant, without seeing itself in a mirror?

A deceptively simple question. Fish recognise their own species by, eg: luminous organs, in lantern fish; colour spots, in John Dory; smell, in chemicals released by an injured minnow.

We do not know whether, or how, they can recognise individuals of their own species. The recognition-response to these signals is usually genetic, ie they do not need to learn it from parents. They don't have to see themselves, only respond to a particular smell or colour that indicates another member of the species. It seems that fish, and presumably other animals, know what patterns and colours to look for by some genetic coding - it's just natural! However, it's clear that some animals don't recognise, or feel comfortable with, others of their own species if they're older and bigger. I foster an elephant that was recently introduced to a new family in Kenya. It had no memory of adult elephants, as its mother was killed when it was young. It took a couple of hours to feel comfortable with the adult elephants.

Q: How did Pascal measure atmospheric pressure with a 40-ft glass tube full of wine?

Barometers can be made using any liquid. Imagine a long tube almost filled with water. Turn the tube upside down and put the open end in a bucket of water. The weight of the atmosphere on the water in the bucket pushes against the water in the tube and stops it coming out. The lower the atmospheric pressure, the more water will flow out of the tube, causing the level of water in it to drop. Conversely, high pressure will force the level up. Barometers are usually made of mercury because it is so dense - 76cm of mercury in a thin tube can typically be supported by an average atmospheric pressure. Pascal showed that the same atmospheric pressure, which most people were unaware of until then, could support 40ft of wine in a tube.

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