Re Gustav Eiffel (NCE 17 June): much less well known are Eiffel's fundamental studies, made during the 20 years or so after the age of 70, as an aerodynamicist.
Initially, an aerodynamics laboratory was established on the 'second floor' of his Paris tower and, from there, novel tests (including those on wires to ground level) were successfully undertaken to determine the drag-coefficients of bodies of differing shapes.
Later, a larger wind-tunnel laboratory was built in Paris, and other tests were made to determine the effects of wind-pressure distributions on factory buildings, airship hangers, airships and early aircraft designed both for France and Britain.
Comparisons between Eiffel's (large scale) and others' (small scale) test results for the drag-coefficients of spheres eventually gave rise to the modern practice of, for example, making golf balls rough.
Who says engineers (and others) are unemployable after the youthful age of 70?
Maurice J Kenn (F), 38 Corkscrew Hill, West Wickham, Kent BR4 9BB