Complex sentence: In 1766, Admiralty engaged Cook to command a scientific voyage to the Pacific Ocean to observe and record the transit of Venus across the Sun for the benefit of Royal Society inquiries into a means of determining longitude.
Split into simpler sentences: In 1766, Admiralty engaged Cook to command a scientific voyage to the Pacific Ocean. The purpose of the voyage was to observe and record the transit of Venus across the Sun for the benefit of Royal Society inquiry into a means of determining longitude.