Rainmaker, a weather modification startup backed by the venture capitalist Peter Thiel, among others, flew an aeroplane over south-central Texas in early July, depositing 70 grams of silver iodide within two clouds. The technique, known as cloud-seeding, aims to coax more water from the heavens than the clouds would yield on their own. This is done by aeroplanes; Rainmaker wants to do it more cheaply, and, therefore perhaps more frequently, using drones.