Note 86 — Chapter VIII · Watt’s Connexion with Dr. Roebuck—Watt acts as Surveyor and Engineer.

He anticipated the use of high-pressure steam, as afterwards employed in the locomotive by Trevithick, in the following passage:—“I intend,” he said, “in many cases to employ the expansive force of steam to press on the piston, or whatever is used instead of one, in the same manner as the weight of the atmosphere is now employed in common fire-engines. In some cases I intend to use both the condenser and this force of steam, so that the powers of these engines will as much exceed those pressed only by the air, as the expansive power of the steam is greater than the weight of the atmosphere. In other cases, when plenty of cold water cannot be had, I intend to work the engines by the force of steam only, and to discharge it into the air by proper outlets after it has done its office.”—Watt to Small, March, 1769. Boulton MSS.