The first well-formulated scheme for lighter-than-air transport was put forward by Francesco de Lana-Terzi in a scientific treatise in 1670. He visualised a craft made lighter than air by evacuating the air from within it, and conducted the first accurate experiments to determine the density of air, which he found to be 1/640th that of water. It comes to most of us today as surprisingly relevant to recall why he did not carry his idea into practice: he was a Jesuit priest and wrote, in the words of Robert Hooke's translation, “God would not suffer such an invention to take effect, by reason of the disturbance it would cause to the civil government of men. For who sees not that no city can be secure against attack …“.