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Your discussion of the photoelectric effect as an possible "amplifier" for radiation emitted by depleted uranium (DU) lodged in human tissue is thought-provoking and timely (6 September, p 8) . What was missing was a quick review of some of the other well-known problems associated with the use of DU in munitions. First, the extreme …

In 1997 I was walking in the Bulgarian mountains with David George, an Oxford physicist who worked with Joe Farman in the Antarctic. It was David George who actually operated the Dobsonmeter that produced the seminal ultraviolet measurements (20 September, p 46) . He told me Joe realised the significance of the measurements but needed …

Your interesting article "Graphical search engine will cheer sports fans" (20 September, p 24) overlooks one of the most interesting uses of the technology. Many people who are blind or have low vision are able to read research papers in electronic formats using speech synthesis. However, the lack of simple alternative presentations such as data …

You ask whether we should trust the modellers in the banking system who already claim they know where the gaps in their knowledge are ( 27 September, p 5 and p 8 ). The answer must be no. In general, the great economist John Maynard Keynes noted over half a century ago that " markets …

There may be good reasons for keeping brain scans out of courts (4 October, p 5) , but doubt about their ability to "read minds" is not the best of them. Whenever someone says of brain scanning "it'll never be able to do that", it goes and does it. Yet A. C. Grayling, for instance, …

Phyllida Brown discusses possible interactions between persistent organic pollutants (POPs), human body fat and diabetes (13 September, p 36) . I learned of the connection in 1987. The Victorian Department of Agriculture here in Australia had recommended the POP dieldrin to control wireworm in potato fields – and then found it in the meat of …

Hunter-gatherers in the Congo basin will be happy to hear that international conservation organisations are finally realising how important they are to the conservation of tropical wildlife (20 September, p 6) . Baka Pygmy communities were hunting sustainably in forests recently overlapped by the Boumba Bek and Nki national parks in south-east Cameroon long before …

While electric cars are promising, your graph greatly overstates their greenhouse gas emissions advantage (20 September, p 26) . I estimate that it shows the tailpipe emissions of a conventional vehicle as about 210 grams of carbon dioxide per kilometre, and of a hybrid vehicle as 140 grams per kilometre. But The Economist magazine (6 …

Rob Jameson describes William Perraudin saying that developing a model to cope with feedback in economies is "fiendishly difficult" (27 September, p 8) . No, it isn't. It is impossible. Economies are monumentally chaotic, representing the financial antics of millions of us, and thus susceptible to our well-known tendency to make decisions for the strangest …

Marcus Chown writes about possible sources of the anomalies in spacecraft's fly-by velocities (20 September, p 38) . Surprisingly, he does not mention that calculating the interaction of the Earth, moon and spacecraft is a three-body problem, doable only by iterative approximation, and tends to chaos. Could the anomalies arise from errors in the approximations?

Walter Mischel's experiment to determine whether 4-year-olds could resist marshmallows was interesting, but his conclusions were wide of the mark (13 September, p 40) . The children who had two marshmallows did better in life than the children who had one. So marshmallows are essential for a child's development, and two are better than one. …

Perhaps the answer to bats exploding in low-pressure vortices at the tips of wind-turbine blades (30 August, p 4) is to fit the blades with winglets . As I understand it, the winglets attached to the ends of aircraft wings increase efficiency by reducing vortex formation. So perhaps winglets would not only help to reduce …

• The paper by Mile Gu and colleagues on emergent properties of Ising lattices is at www.arxiv.org/abs/0809.0151 (4 October, p 12) . • We said ambiguously that "a molecule released by bacteria called lipopolysaccharide seems to initiate tolerance" to bacteria (27 September, p 16) . To clarify: lipopolysaccharides are a class of molecules. • We …