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new internationalist
issue 238 - December 1992

...that have always intrigued you about the world will appear in this,
your section, and be answered by other readers. Please address
your answers and questions to ‘Curiosities’.

Are broad-leafed trees better than conifers in terms of soaking up
excess carbon dioxide - and so helping to reduce global warming?

. Yes, in principle, because they are 30 per cent more dense than coniferous trees. But it may make more sense, in the short term, to plant fast-growing conifers such as spruce or radiata pine. These can grow to a large size relatively quickly - around 20 to 25 years. It would take an oak tree 80 to 100 years to reach the same size. The oak would soak up 10 to 30 per cent more carbon but the time-scale required might make planting it less ecologically appropriate.

WS Taylor Milton
Keynes, UK

Is unleaded petrol more polluting than leaded petrol?

. Rosemary Thompson's answer in the September issue (NI 235 Curiosities) is wrong. Benzene is not - as she asserts - a fuel additive like tetra-ethyl lead. It is a fuel, which is burnt in the engine to produce power. And it does not pass through unchanged, as she claims.

The whole subject of engine efficiency is enormously complicated. Currently I believe that it is true to say that the best efficiency and the lowest emission is achieved by the modern diesel engine. Next best efficiency coupled with good emissions performance is achieved by a lean burn engine running on high octane unleaded fuel. The very worst efficiency (greatest fuel wastage) is achieved by a petrol engine using a catalytic converter. It is also the dirtiest engine in the first miles of travel before the converter warms up. The increase in fuel consumption caused by running on low octane unleaded fuel is usually less than that caused by using a catalytic converter.

Martin Bacon
Frame, UK

Can anyone recommend a book about trepanning or tell me anything
about the benefits of having a hole bored in the skull?

. The ancient practice of trepanning still exists today, though under a different name. Originally it was thought to release 'bad humours' from the skull. This possibly worked by letting out collections of pus or blood which would otherwise press dangerously on the brain. Some sufferers from migraine say they think their headache would feel better if somebody drilled a hole to let the pressure off, so this may have contributed to its original use. Today it is used for extradural haemorrhage - where a bruise forms just under the solid skull, pressing on the soft brain. Now it is called a burr-hole, and is performed with a surgical drill. I do not know of any book on trepanning, but any text book on neurosurgery or emergency surgery would have instructions on performing burr-holes. I am very curious to know why Dafydd Saer wants to know the technique. Does he suffer from bad headaches?

Mog Bremner
Mollymook, Australia

Awaiting your answers...

Is it true that the menstrual cycles of women living together in women-only
communities (convents, for example) synchronize? And if so, why?

Zoe Simpson Green
Oxford, UK

How did the wretched term (economic) 'basket case' originate?
Who used it first and in reference to which country?

Stephen Langford
Paddington, Australia

If you have any questions or answers please send them to Curiosities,
New Internationalist, 55 Rectory Road, Oxford OX4 1BW, UK,
or to your local NI office (click here for addresses).

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Big Bad World by PJ POLYP [image, unknown]
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New Internationalist issue 238 magazine cover This article is from the December 1992 issue of New Internationalist.
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