1. In thirteenth-century England an improved form of gunpowder was introduced by Roger Bacon. Active- In thirteenth-century England, Roger Bacon introduced an improved form of gunpowder. 2. In the early eighteenth century a twenty-pound rocket that traveled almost two miles was constructed by William Congreve, an English artillery expert. Active- In the early eighteenth century William Congreve, an English artillery expert, constructed a twenty-pound rocket that traveled almost two miles.
3. By the late nineteenth century thought was given to supersonic speeds by the physicist Ernst Mach. The sonic boom was predicted by him. Active- By the late nineteenth century, the physicist Ernst Mach gave thought to supersonic speeds. He predicted the sonic boom.
4. The first liquid-fuel rocket was launched by the American Robert Goddard in 1926. A pamphlet written by him anticipated almost all future rocket developments. Active- The American Robert Goddard launched the first liquid-fuel rocket in 1926. A pamphlet he wrote anticipated almost all future rocket developments.
5. Rockets were fired by soldiers at enemy armies and usually caused panic. Active- Soldiers fired rockets at enemy armies and usually caused panic.