Note 122 — Chapter X · Boulton and the Steam Engine—Correspondence with Watt.

Small informed Watt that it was intended to make an engine for the purpose of drawing canal boats. “What Mr. Boulton and I,” he wrote, “are very desirous of is, to move canal boats by this engine; so we have made this model of a size sufficient for that purpose. We propose first to operate without any condenser, because coals are here exceedingly cheap, and because you can, more commodiously than we, make experiments on condensers, having several already by you. Above 150 boats are now employed on these new waveless canals, so if we can succeed, the field is not narrow.” This suggestion of working canal boats by steam immediately elicited a reply from Watt on the subject. Invention was so habitual to him that a new method of employing power was no sooner hinted than his active mind at once set to work to solve the problem. “Have you ever,” he wrote Small, “considered a spiral oar for that purpose, or are you for two wheels?” And to make his meaning clear, he sketched out a rough but graphic outline of a screw propeller. Small’s reply was unfavourable: he replied, “I have tried models of spiral oars, and have found them all inferior to oars of either of the other forms; I believe because a cylinder of water immersed in water can be easily turned round its own axis. We propose to try gun-lock springs with the fixed part longer than the moving. If we cannot succeed, we will have recourse to what you have so obligingly and clearly described.” Finally Watt writes a fortnight later, “concerning spirals, I do not continue fond of them.”