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You say that a hygroelectric generator based on graphene produces 1.5 volts and that this is equivalent to an AA or AAA battery ( 1 December 2018, p 20 ). But I want to know what current it delivers, and so its power in watts. The editor writes: • The experimental device produced of the …

James Mitchell Crow gives a short description of some synthetic engineered life forms, currently being developed by Nina Pollak in Australia, that will look like juvenile jellyfish ( 8 December 2018, p 40 ). You called them "pseudo-creatures" . They will be real creatures, in the original, historical sense of the word, as they will …

Graham Lawton says beavers at a site in Devon, UK, have a huge impact on flood management there by building dams that can store and slow the release of water ( 22/29 December 2018, p 10 ). But Richard Brazier, a lead scientist behind the reintroduction project that Lawton visited, says that this potential is …

Rob Cannell reiterates doubts about the ecological benefits of electric vehicles (EV) because of the proportion of electricity from burning fossil fuels that currently powers them (Letters, 8 December 2018 ). But anyone who has driven an EV will regard a car powered by an internal combustion engine as positively agricultural, whether fuelled by petrol, …

Cannell mentions the benefits of running vehicles on liquid petroleum gas (LPG). It does produce less nitrous oxide and other pollutants and is less carbon intensive than petrol/gasoline. But this gain is more than countered by the low efficiency of a small internal combustion engine (20 per cent) compared with burning fuel for electricity generation …

Emma Young's article on human navigation prompted me to reflect on my own ability ( 15 December 2018, p 38 ). After living for 35 years south of the equator and easily navigating around unfamiliar locations in New Zealand and Australia, I was perplexed at discovering it nearly impossible to find my way around London, …

While my wife Roslyn and I rarely become lost in New South Wales, a trip to Hawaii demonstrated that we use different means to navigate. I consistently turned north when I meant to turn south and swore blind that I was going in the right direction while my wife indicated the opposite direction, and was …

Karen Hinchley asks whether Elon Musk will retrieve and recycle obsolete satellites in his plan to provide internet access from orbit (Letters, 1 December 2018 ). These satellites would be in low Earth orbits and would eventually burn up. On the same page, Robert Hill notes that keeping 4425 working satellites in orbit may require …

Chris Baraniuk reports UK police plans to use machine learning to predict criminal behaviour and offer interventions ( 1 December 2018, p 6 ). It seems that the system was trained on databases including information unrelated to court findings of guilt, such as police stops, searches and crime reports. I expect it will lead to …

Eric Kvaalen notes the sun's contribution to tides on Earth (Letters, 15 December 2018 ), in response to my letter on the importance of lunar tides to life moving from the oceans to land ( 3 November 2018 ). With respect, I didn't suggest that there would be no tides on Earth without our large …