James Watt. James Watt (1736-1819), Scottish engineer and inventor. Watt made numerous practical improvements to the steam engine of his day. By 1790 the superior Watt steam engine had completely replaced the older Newcomen variety. His inventions included the double acting engine where the piston is made to both push & pull (1782); the centrifugal governor, a device that controlled a process by means of variations in the process itself (1788); & the pressure gauge (1790). Watt also coined the term horsepower" to describe a unit of energy. Watt's innovations, coupled with the business acumen of his partner Matthew Boulton, made him financially successful."