Complex sentence: In 1690 Polhem was appointed to improve upon the current mining operations of Sweden, his contribution was a construction for lifting and transporting ore from mines, a process that was rather risky and inefficiant at the time.
Split into simpler sentences: In 1690 Polhem was appointed to improve upon the current mining operations of Sweden. His contribution was a construction for lifting and transporting ore from mines, a process that was rather risky and inefficient at the time.