Letters archive

I think more is going on with new definitions of the "base" units in modern metrology than Stephen Battersby describes ( 3 October, p 38 ). Defining the metre in terms of the speed of light tells us that the metre per second, rather than the metre, is now the base unit. The proposal he …

Battersby shows an interesting, nearly tautological connection between units that depend on fundamental constants and constants that depend on those measured units. It would be good, though, to see more light cast on the candela, the unit of luminous intensity. Why is it tied to a monochromatic frequency? Real candles are polychromatic. Hertford, UK

• The candela is fundamentally tied to our ability to perceive light, and is defined with reference to the single frequency at which a standard eye is most sensitive.

Doubtless there are some therapists guilty of instilling false memories ( 10 October, p 8 ). But it would be tragic if this occasional bad practice makes us doubt the value of psychological work and the need to listen to victims. The experience of church abuse shows that the pendulum of belief is firmly stuck …

Most of this article relates directly to the 1990s. It cites old studies by Elizabeth Loftus about the creation of false memories. What does her contrived laboratory research tell us about somebody who has suffered years of abuse? You promote a myth about hordes of therapists using "recovered memory therapy" after giving patients "strong tranquillisers" …

• Our concern for real cases should not make us credulous about all past claims – especially those triggered by dangerous and outdated psychotherapy methods. The National Health Service records of Carol Felstead, whose death in the UK we discussed, show that she was at times "heavily sedated" on diazepam during psychotherapy sessions. And Elizabeth …

But... this technique is practiced by medics with nothing more than a gloved finger Deborah Buffalin comments on a machine to estimate due dates ( 31 October, p 16 ), ending: "But, yay, technology."

Manfred Spitzer claims that information technology is of little or no use in education ( 17 October, p 28 ). I suggest that he checks out the subject in more detail with actual examples. As a secondary school teacher 25 years ago I had a physics class of not-very-interested 15-year-olds who would have their bags …

Your article on having kids does not take into account one crucial factor contributing to happiness: fitting in with your peers ( 5 September, p 40 ). My grandmother, talking about the war, used to say: we were poor but it didn't matter, because everybody was. My aunt once stated that she eventually decided to …

Pedro Ferreira says that the first "proof" of general relativity was Arthur Eddington's observation of gravitational lensing in the 29 May 1919 eclipse ( 10 October, p 33 ). But in November 1915 Einstein calculated the anomaly in the precession of the orbit of Mercury, which had never been explained by conventional gravitational theory. When …

While Tim Flannery's "Here comes Plan C" ( 10 October, p 24 ) inspires optimism that more new ideas and possibilities for combating climate change are continually being advanced, there is also pessimism at the realisation of how our national and world leaders will receive the notion. Will his proposals not vindicate their assertions that …

As a petroleum geologist engaged in the search for oil and gas, I was encouraged by David Deutsch's words that "the awful secret at the heart of probability theory is that physical events either happen or they don't: there's no such thing in nature as probably happening" ( 3 October, p 30 ). When we …

Oh dear, oh dear, Gregory Laughlin: you must have caused great consternation among the purveyors of fresh fruit and vegetables. You said that squeezing an object is a handy way to learn about its insides, likening this to testing a melon for ripeness ( 19 September, p 37 ). The right thing to do is …

David Boswell shifts focus from machine to rider when describing how to stay upright on a bicycle (Letters, 26 September ). Years ago, an infection substantially affected my inner ear function. Later, improved yet still impaired, I cautiously attempted to ride my bicycle. As if by magic, all sense of impairment vanished. I realised then …

• Too chilled out: we meant to refer to "frozen carbon monoxide" on the surface of Pluto ( 17 October, p 6 ). • Some figures we gave for global production of lithium were for the gross weight of compounds in which lithium is contained: the true weight of lithium extracted in 2013 was 31,300 …