Complex sentence: It was while Galileo was under house arrest that he wrote one of his finest works, "Two New Sciences", in which he summarised the work he had done some forty years earlier, on the two sciences now called kinematics and strength of materials.
Split into simpler sentences: It was while Galileo was under house arrest that he wrote one of his finest works, "Two New Sciences". Here he summarised the work he had done some forty years earlier, on the two sciences now called kinematics and strength of materials.