April 29, 1769

James Watt

James Watt enrolls the specification for his steam-engine patent

The patent was already nearly four months old on the date usually credited as its grant — and the specification enrolled that day contained no drawings at all.

29 April 1769: enrollment, not grant

On 29 April 1769 Watt caused the technical specification for his already-granted patent to be enrolled in the High Court of Chancery. The letters patent themselves — number 913 — bear the date 5 January 1769; British grant and later enrollment of the specification were distinct legal steps.

The grant had required Watt to enroll a particular description of his invention within four calendar months. He prepared it with advice from associates including Matthew Boulton and William Small, and filed with days to spare.

Principles, deliberately undrawn

The specification described a method for reducing steam and fuel consumption, opening with what amounted to thermal discipline: the working cylinder should remain as hot as the steam entering it. It specified condensing steam in vessels separate from the working cylinder, keeping those vessels cold, and drawing off air and uncondensed vapor with pumps or equivalent means.

It contained no drawings — a deliberate effort to claim governing principles rather than tie the patent to one detailed machine layout. Patent 913 accordingly covered several fuel-saving principles, not solely a detachable component.

A record that mattered later

Nothing commercial began that day: no Boulton & Watt production enterprise, no mature engine. What Watt achieved was satisfying the disclosure condition before his deadline, putting on record the principles whose legal scope would later sit at the center of licensing and infringement litigation.

The original monopoly ran fourteen years; under the 1775 Act, protection was extended to June 1800.

Sources

Researched 23 Aug 2026 6 sources 3 audit passes

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

What the sources leave uncertain

The date is secure, but the listed action is mislabeled: 29 April was enrollment of the specification, not the grant of the letters patent. The grant bears the date 5 January 1769.
Accounts traditionally date Watt's separate-condenser insight to a Sunday walk on Glasgow Green in May 1765, but the exact reconstructed day and details derive from later recollection.