Note 151 — Chapter XII · Boulton and Watt begin the Manufacture of Steam-engines.

Boulton to Watt (without date), 1776. Boulton MSS. In this letter, Boulton throws out a suggestion for Watt’s consideration—“When,” he says, “we have got our two-foot pumps up, I think it would be right to try our Soho engine with a steam strong enough to work the pumps with the axis in the centre of the beam, which will be almost 19 lb. upon the inch.”