Letter: In Brief

Sir: Oh dear, there still exists strong evidence of C P Snow's "two cultures". Weight and mass can never become the same, virtually the same or anything like the same (letter, I March). Whilst the state of weightlessness is now regularly seen in images from orbiting spacecraft, those astronauts are not massless - they still contain all the molecules they left Earth with. Mass is a measure of how much stuff there is, whereas weight is a force, which only exists when there is at least one other mass around to create this attractive force.

Dr ANTHONY EGAN

Surbiton, Surrey