Science of Discworld III

motion to all sorts of mill works, by the important force of fire, which will be of great use in draining mines, serving towns with water, and for the working of all sorts of mills, when they have not the benefit of water nor constant winds; to hold for 14 years; with usual clauses.
    Steam engine time was close at hand. What clinched it was that Savery was a born businessman. He didn’t wait for the world to beat a path to his door: he advertised . He gave lectures at the Royal Society, some of which were published in its journals. He circulated a prospectus among mine-owners and managers. And the selling point, naturally, was profit. If you can open up deeper levels of your mine, you can extract more minerals and make more money out of the same mine and the same bit of land.
    Two more major steps were needed before what Thurston calls the ‘modern’ steam engine – that of 125 years ago – became firmly established. The first was to move from specialised, single-purpose machines, to multi-purpose ones. The second was to improve the engine’s efficiency.
    The move to multi-purpose steam engines was made by Thomas Newcomen, a blacksmith by trade, who introduced a radical new kind of engine, the ‘atmospheric steam engine’. Previous engines had effectively combined a steam-driven piston and a pump in the same apparatus. Newcomen separated the components, and threw in a separate boiler and a condenser to boot. The piston moves up and down like a ‘nodding donkey’, driving a rod, which can be attached to … anything you like. Another engineer who must be mentioned here was John Smeaton, who scaled Newcomen’s design up to much larger size.
    Now, finally, we come to James Watt. Whatever credit he deserves, it is clear that he stood on the shoulders of a number of giants. Even if he had been capable of inventing the steam engine on his own,the plain fact is that he didn’t. His grandfather was a mathematician – there seem to be a lot of mathematicians in the history of the steam engine – and Watt inherited his abilities. He carried out lots of experiments, and he made quantitative measurements, a relatively new idea. He worked out how heat travelled through the materials of the engine, and how much coal it took to boil a given amount of water. And he realised that the key to an efficient steam engine was to control unnecessary heat loss. The worst loss occurred in the cylinder that powered the piston, which kept changing temperature. Watt realised that the cylinder should always be kept at the same temperature as the steam that entered it – but how could that be done? The answer, when he finally chanced upon it, was simple and elegant:
    I had gone to take a walk on a fine Sabbath afternoon. I had entered the Green by the gate at the foot of Charlotte Street, and had passed the old washing-house. I was thinking upon the engine at the time, and had gone as far as the herd’s house, when the idea came into my mind that, as steam was an elastic body, it would rush into a vacuum, and, if a communication were made between the cylinder and an exhausted vessel, it would rush into it, and might be condensed there without cooling the cylinder … I had not walked farther than the Golf-house, when the whole thing was arranged in my mind.
    Such an easy thing to come up with – don’t cool the steam in the cylinder, cool it somewhere else . Yet it improved the machine’s efficiency so much that within a few years the only steam engines that anyone even thought of installing were those of Watt and his financial partner Boulton. Boulton-and-Watt engines cornered the market. No really significant improvements were subsequently made to their design. Or, to be more accurate, later ‘improvements’ supplanted the steam engine with engines of a very different design, driven by coal and oil. The steam engine had evolved to the pinnacle of itsexistence, and what displaced it was, in effect, a new species of engine altogether.
    In retrospect, steam engine time arrived around the period of Savery, when the ability to make practical machines coincided with a genuine need for them in an industry that could afford to pay for them and would make more profits as a result. Add to that a sound business mind, to notice the situation and exploit it, and a sense for publicity to raise money from investors and get the idea off the ground, and the steam engine went like a … train.
    Ironically, before most people realised that