[ [121] Watt to Small, 20th September, 1769.
[ [122] 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.”
[ [123] Roebuck to Boulton, February 12, 1770.
[ [124] Small to Watt, 17th September, 1770. Boulton MSS.
[ [125] Watt to Small, 20th October, 1770. Boulton MSS.
[ [126] He then held an eighth share in the pottery, which brought him in about 70l. a year clear.
[ [127] Watt to Small, 30th August, 1772. Boulton MSS.
[ [128] Small to Watt, 16th November, 1772. Boulton MSS.
[ [129] About this time, in order to bring himself and his engine into notice, Watt contemplated writing a treatise on steam and its applications. “I have some thoughts,” he wrote to Small, “of writing a book on the elements of the theory of steam-engines, in which, however, I shall only give the enunciation of the perfect engine. This book might do me and the scheme good. It would still leave the world in the dark as to the true construction of the engine. Something of this kind is necessary, as Smeaton is labouring hard at the subject, and if I can make no profit, at least I ought not to lose the honour of my experiments.”—Watt to Small, 17th August, 1773. Boulton MSS. To this letter Small replied, “The more I consider the propriety of your publishing about steam, the more I wish you to publish. Smeaton has only trifled hitherto, though he may perhaps discover something. He told Boulton some time ago that the circular engine would not do. He said he had considered it, and was sure of this. As B. does not much respect his genius, this had no effect.” Watt’s treatise was, however, never written; his attention being shortly after fully occupied by other and more engrossing subjects.
[ [130] Boulton to Watt, 29th March, 1773. Boulton MSS.