THE RECORD
What changed
Newcomen's atmospheric engine worked by 1712; Watt's separate condenser improved efficiency and rotary mechanisms widened use.
EVIDENCE
What remains
Patents, drawings, surviving engines and fuel records document incremental improvement and adoption.
WHY IT MATTERS
Why it matters
It shifted power from rivers and muscle toward coal, enlarging both industrial output and carbon emissions.
OPEN QUESTION
Where interpretation begins
Watt did not invent the steam engine alone; coal, mines, craftspeople and labour systems were all necessary.