Richard Trevithick
	Trevithick, Richard, (1771-1833), English engineer and inventor. He is known as the father of locomotive power because of his invention (1800) of the high-pressure steam engine. He built a steam carriage that on Christmas Eve, 1801, in London, carried the first passengers transported by steam power. In 1804 a steam locomotive he constructed was used in Wales on a railway, the first vehicle to be so operated. Trevithick also developed steam engines for use in mines and invented a steam threshing machine. Reproduced with permission from The Columbia Electronic Encyclopedia. Copyright (c) 2000 Columbia University Press. All Rights Reserved.

Boulton & Watt's engine design was, subject to the economic caveats already discussed, specifically designed to satisfy the demands of the small-scale industry most prevalent up until 1800. From then on, two parallel paths of development presented themselves. First, the size of individual factories began to slowly increase. There were finite limits as to how far these could be satisfactorily served by the Watt engine, yet the development of new practises, like the use of high-pressure steam, were subject to considerable delay. Secondly, in the small- to medium-scale market, engine designs were emerging which challenged Boulton & Watt's supremacy in their chosen field.

Despite fierce opposition, the separate condenser patent was extended in 1775 to 1800. Thereafter, Boulton & Watt kept a close eye on developments elsewhere, intervening if necessary against those who infringed their patent. Two court cases against Jabez Hornblower (1796) and Edward Bull (1799) upheld the patent's validity, and henceforth concerns using their engine designs were forced to pay the premium to Boulton & Watt.

The circumspection with which others now sought to develop new types of steam engine helped reinforce Boulton & Watt's position, giving them a commanding role in industry even when the patent ended in 1800. In 1827 John Farey, an engineer, wrote:

Men of superior intellect, who might have been induced to investigate the subject, have been led to suppose that nothing further remains to be perfected…

How, then, did industry drive its machinery? By 1838, 3,053 steam engines and 2,230 waterwheels were employed in textiles manufacture, with water providing only 27 percent of all power used. Water was of declining relative importance in industry, although Scotland, Ireland, and parts of the north-west of England saw its use rising right up to the 1860s. William Fairbairn commented on this in 1864, stating that '…the time has not yet arrived when it [water] can be disposed with … in our own country'.

Science Museum, London/ Science & Society Picture Library

High-pressure engine built by Richard Trevithick in 1811. This compact engine was built for thrashing and chaff cutting duties in agriculture--not all steam engines were destined for heavy industrial and manufacturing use.

But if steam had, by 1838, grown to become industry's main power source, we must ask whether this growth was sustainable. Watt's continued reliance on low steam pressures limited the steam engine's growth potential. Watt was partly concerned that the available 'wagon' boilers couldn't safely work at higher pressures. However, he may also have feared that high-pressure engines like those pioneered by Richard Trevithick from 1800, being more efficient, could have operated without the separate condenser. Whatever the reasons for it, Watt's authoritative advocacy of low pressure helped to, in the words of historian TS Ashton, '…clog engineering enterprise for more than a generation.'

Extracting more power from low-pressure steam required increasingly complicated arrangements. One arrangement quite widely used was to install a double-beam engine with two low-pressure cylinders driving a common flywheel. However, this was a costly and bulky solution, whereas high-pressure operation would have allowed engines to be reduced in size for comparable power output, or made larger and even more powerful.

So, while water did continue to play its part, steam gained the upper hand after 1820, albeit through continued use of low pressures which precluded steam 'compounding'. This was a system where an engine was equipped with two or more cylinders of increasing volume, the steam passing through them in sequence and exerting pressure as it expanded, the pressure declining at each stage but the power produced in each cylinder being more or less the same. This 'recycling' of the steam theoretically made compound engines more economical to run.

Science Museum, London/ Science & Society Picture Library

Hornblower's compound engine, 1781. The first example was built in 1782. However, having two cylinders it was more expensive to build than a Watt engine, and the low pressures used meant it was no more economic. But, in the longer term, it laid the way for successful adoption of more efficient compound engines designed by Arthur Woolf and William McNaught.

Jonathan Hornblower built a compound engine in 1781 but it proved a failure, being no more economical than a Watt engine. Arthur Woolf revived the idea in 1804, but he based his design on an incorrect theory of the law of the expansion of steam, and the highest-pressure cylinder was much too small for it to work properly. Thereafter, even in 1845 most large mills were still driven by low-pressure engines of the type championed by Boulton and Watt, despite this consuming 50 percent more fuel than the newest Woolf compound type. These engines were not built sufficiently strongly to withstand the stresses imposed by higher steam pressures, and many millowners were put off from rebuilding them by the sheer cost of such a project.

As with their steam engines, millowners appear to have been equally conservative in their choice of boiler. During the 1830s, average steam pressures rose from approximately four pounds per square inch to more than twelve, and this increase seems to have been sustained thereafter. But in 1840, 75 percent of boilers in the Manchester area were still of the old and weak wagon type, and it was only after that date that the Cornish boiler developed by Trevithick began to be widely used.

If the development of larger steam installations seems to have stalled somewhat, elsewhere much progress was being made. Around 1800, there arose a requirement for a small, self-contained and low-power engine more suitable for driving small workshops and mills than the Watt beam engine, which required a sizeable engine house and boiler installation to support it. In 1799, William Murdoch built his first bellcrank engine. This was the first 'independent' (i.e., self-supporting) engine, of just 2-3 horsepower, to be made available commercially. It was followed by Freemantle's 'Grasshopper' engine in 1803 and Henry Maudslay's table engine in 1807, and these thereafter provided the power for many small workshops and mills.

Conclusion
The picture that emerges of motive power in the early nineteenth century is a varied one. There was, by no means, a straight transfer from using water power to steam: In 1820, water remained quite widely used, and would prove a resilient power source in many places for the rest of the century. Elsewhere, low pressures inhibited development of larger steam engines although, at the same time, much fruitful development work concerned with small, self-contained installations took place.

Looking to the future, methods of constructing high-pressure compound steam engines continued to be refined. Although it would be after 1850 before they came into general employment, the foundation was laid for steam to drive the very largest establishments.