James Watt's patent for 'a new method of lessening the consumption of steam and fuel in fire engines' was granted on January 5th 1769. The patent embodied not only Watt's revolutionary use of a separate condenser but covered the entirety of his work on the development of the atmospheric engine into a machine which used steam as the actual driving force.

 

The wording of the specification for the patent was, however, to prove contentious. Watt had been advised by a close colleague to simply file a description of the principles involved in the working of the new engine and not, as would normally be the case, a design for an engine including a set of drawings. Although the set of principles as listed in the patent clearly covered Watt's revolutionary innovations, taken together they amounted to a virtual monopoly on the harnessing of steam pressure for useful work, regardless of the design of engine it was to be used to drive.

 

The original patent was granted for a period of fourteen years, but was later extended to expire in 1800, giving a total of 31 years. Watt joined forces with Mathew Boulton, the entrepreneurial Birmingham manufacturer, to build the new engines and by 1776 the first commercial engines had been constructed. This was to be the start of a highly successful business as industrialists realised the potential savings to be made in fuel costs by use of the new engine. In fact, Boulton and Watt's income from construction of engines was largely generated from patent royalties which were calculated initially as one third the cost of the coal saved by using a Watt engine instead of a comparable Newcomen engine.

 

As a result of the high cost of coal in Cornwall, which has no indigenous supplies of its own, Cornish mine owners were quick to employ the new engines to replace the inefficient and outdated Newcomen engines for draining their mines. However, it was not long before these same mine owners began to resent the royalties they had to pay Boulton and Watt and began to look for ways in which they could avoid paying.

 

From 1790 onwards, Edward Bull (1759-1798), assisted by the young Trevithick, had introduced a design of engine in Cornwall in which the cylinder was inverted over the mine shaft, thus dispensing with the massive beam and engine house of a conventional Watt engine. It has been suggested that from 1792, ten other examples of this type of engine were constructed, thus underlining the Cornish desire to support competitive engine suppliers. However, the principles involved in the operation of the Bull engine were more or less identical to that of the Watt engine. Watt had built what was described as a 'Topsy Turvy' engine in 1777 for J Wilkinson the iron founder, and the operating cycle with constant condenser vacuum reacting the piston was that of Watt's interim design of 1780.