Note 111 — Chapter IV

In the rare Notes that he has left, James Watt writes that one afternoon he had gone out for a stroll on the Green at Glasgow, and his thoughts were absorbed with the experiments in which he was busied, trying to prevent the cooling of the cylinder. The thought then came to him that steam, being an elastic fluid, should expand and be precipitated in a space formerly void; and having made a vacuum in a separate vessel and opened communication between the steam of the cylinder and the vacant space, we see what should follow. Thus, having imagined the masterpiece of his discovery, he enumerates the processes that, employed in turn, allowed him to perfect it.