Letters archive

Reading Helen Thomson's interesting and amusing article on hypnosis, I wondered if hypnotists aren't taken seriously because, historically, they claimed to be using only their minds to do it ( 9 November, p 34 ). As Thomson reports, anaesthetist Aurore Marcou uses local anaesthetics and mild sedation in modern, medical-based hypnosis, making the hypnotist one …

With Clare Wilson's article on the neglected nutrient choline, you present a diagram showing beef liver as an important source of it ( 26 October, p 20 ). As Wilson reports, some research suggests that women should have more choline when they are pregnant. But pregnant women are advised to avoid liver of any kind, …

You mention the camera obscura as an example of unconventional imaging ( 9 November, p 42 ). I saw a camera obscura after moving into a house with high ceilings, tall windows and a short front garden. On a bright first morning, I saw tiny figures moving on the ceiling. The folds at the top …

As Adam Vaughan says, gas boilers are a UK election battleground, with three of the main parties wanting to phase them out, each at a different rate ( 9 November, p 18 ). But methane is a great biofuel that is relatively easy to make, store and transport. Sensibly, three times more UK domestic energy …

Matthew Allan proposes that we retrofit homes with integrated heat-handling equipment ( Letters , 26 October ). This is a great idea. We already have a sealed house. Its controlled ventilation incorporates a heat exchanger working at 92 per cent efficiency. The only heat we waste is water from washing machines and showers. These use …

You report the pollution and possible health risks of plastic particles from teabags ( 5 October, p 16 ). There is a simple way to avoid these: stop using teabags. For the price of a box of teabags that makes 25 cups, I buy loose tea to make 250 cups.

You ask us to imagine an international research institution dedicated to climate change, bringing together "the best minds from climate science, energy technology, economics, social science and beyond" (Leader, 23 November ). The European Centre for Medium-Range Weather Forecasts , based in Reading, UK, is an international institution supported by 34 states. It employs around …

Your article on ways of removing carbon dioxide from the atmosphere was fascinating ( 10 August, p 18 ). Options included bioenergy, carbon capture and storage and sequestration of carbon in the soil. The only one on your list that ordinary people can do is to plant trees. But how effective is this? An average …

David Burns's idea for a "helical engine" with no propellant is ingenious ( 19 October, p 15 ). He imagines a movable ring, whose mass is much greater when it slides in one direction than the other. But transferring energy to the ring to increase its velocity and hence, by the rules of relativity, its …

It looks hard to find any fault with Burns's design for propulsion without a propellant , but centuries of experience tell us that, in all attempts to get around the conservation of energy, an increase in energy somewhere is always balanced by an exactly equal decrease somewhere else. My guess is that this proposal will …