What foundational industrial concept did the Newcomen engine successfully demonstrate?

The conversion of heat into continuous mechanical motion on an industrial scale.

The historical significance of the Newcomen engine transcends its technical flaws. It achieved something entirely unprecedented: it proved, on a large, sustained industrial scale, the fundamental concept that thermal energy could be reliably converted into kinetic, mechanical motion usable for industry. While inefficient, this success demonstrated the potential inherent in steam power. By establishing the basic mechanical architecture—the cylinder, piston, and beam linkage—it laid the essential groundwork and created the undeniable need for subsequent inventors, like Thomas Watt, to focus on improving thermal efficiency to fully realize the implications of large-scale mechanical power.