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Alice Klein discusses the prevalence and prevention of domestic violence and the treatment of victims and perpetrators ( 19 October, p 20 ). Another aspect worth mentioning is the effect of post-traumatic stress disorder (PTSD) on behaviour. As Joshua Goldstein writes in War and Gender , PTSD typically leads to emotional numbing, recurrent nightmares, substance …

Leah Crane argues that 214 moons is too many for a solar system because some are just rocks ( 26 October, p 23 ). She suggests we only include satellites that are large enough to be roughly spherical: 400 to 600 kilometres in diameter. This limit would remove Phobos and Deimos, at 22 km and …

Things are getting out of hand with the number of moons in our solar system, says Crane. Perhaps she could go one step further than redefining moons and consider the well-established example of binary stars as a model. Why not binary planets? The moons Ganymede and Titan are bigger than Mercury. If they occupied independent …

According to David Werdegar, "a composer may internally hear a melody, hum the tune and have a second person hum it too (Letters, 26 October ). But developing it for an instrument or an entire orchestra requires much thought, and that thought requires language." That contrasts with my own experience composing Sweet and Sour Harmony …

• Carbon dioxide emissions from human activities are estimated at about 35 billion tonnes of carbon per year ( 5 October, p 34 ). • One song of the white bellbird ( Procnias albus ) measures 116 dB(a) at a distance of 1 metre ( 26 October, p 9 ).

Chris Simms reviews Ahab's Rolling Sea: A natural history of Moby-Dick ( 19 October, p 28 ). The sinking of the Nantucket whaler Essex by a large whale in the Pacific in 1820 is generally regarded as inspiration for Moby-Dick . Its author, Herman Melville, was friendly with the first mate, Owen Chace, and knew …

Derek Bolton mentions Daniel Milo's assertion that giraffes' long necks have no significant advantages (Letters, 14 September, p 27 ). On the contrary, the length of their necks allows them to drink water on the ground, but only just. Giraffes have to splay their front legs to get their mouth low enough to drink, which …

I have been following for some time the progress of Alan Handley's Varialift project, reported by Donna Lu ( 12 October, p 15 ). The Varialift is an aerial bathyscaphe, able to perform highly accurate and maintainable altitudes. I believe the most important use for it will be in disaster relief. Delivering basic supplies in …

Lu mentions exploiting the buoyancy of an airship to propel it by storing compressed air and using it for thrust. Your columnist Daedalus ( David E. H. Jones, 1938-2017 ) had a more elegant solution with his thermal "glidoon" ( 17 February 1972, p 400 ). He proposed effecting buoyancy change through the condensation of …

Like your letter writers Andrea Needham and Marcus Swann , my first reaction to the series of adverts by BP in Â鶹´«Ã½ was "they shouldn't be publishing these" (Letters, 2 November ). On reflection, if Â鶹´«Ã½ doesn't get funded from advertising, we will all be the poorer as it will cease to exist. …