Photograph: David Remes (2003)

A rough sketch from 1779 can be understood as a rocket motor powered by compressed hydrogen and oxygen (inflammable air and dephlogisticated air in Darwin’s terminology) as propellants. The gases are stored in separate containers and fed into a cylindrical chamber with an exit nozzle at one end. The volume of hydrogen is correctly shown as being greater than of oxygen. Darwin’s idea appears to be very advanced for his time, as the invention of hydrogen-oxygen rocket has been usually associated with Konstantine Tsiolkovskii (1857-1935). It came into use for space launches from the late 1960s.