Complex sentence: Fraser is said to have displayed great skill in watercolours, and several of his drawings have been engraved; and the astronomical observations which he took during some of his journeys did considerable service to the cartography of Asia.
Split into simpler sentences: Fraser is said to have displayed great skill in watercolours, and several of his drawings have been engraved. The astronomical observations which he took during some of his journeys did considerable service to the cartography of Asia.