Miss Tumble told the class that the era in which steam engines were developed and used extensively was known as the Steam Age. According to Miss Tumble, before the Steam Age mankind had to make do with human or animal muscle power or the power of the wind or of water to operate machines or do heavy work. Newcomen’s steam engine marked the start of a new era. Thomas Newcomen and other engineers quickly found ways of improving the design of steam engines so that they worked better and were less expensive to make.

The rocking motion of Newcomen’s steam engine was suitable for operating pumps, but, for many applications rotary motion was required: so said Miss Tumble. Other steam engines were developed in which the to-an-fro movement of a piston was converted to a rotary motion of a wheel or shaft. Miss Tumble drew a diagram to show what she meant.

Many more innovations followed in the development of steam engines. One major improvement that was made to early steam engines was the introduction of a separate condenser. Miss Tumble said the condenser made good use of the condensation effect that occurred on the mirror in Angela’s bathroom. The condenser contained a large amount of cold surface on which the steam condensed. Once this improvement was introduced, the cylinders of the steam engines didn’t have to be heated up and cooled down for every cycle. This allowed steam engines to be built that operated at higher speeds and needed less fuel for the same work output. James Watt was the inventor of the separate condenser and he introduced many other improvements as well.

Another major improvement, which was made by a man called Richard Trevithick, was the use of high-pressure steam in steam engines. Miss Tumble explained that by enclosing water in a boiler and heating it steam could easily be produced at high pressure, but the boiler would have to be strong enough to withstand the pressure of the water and steam inside it. In the early days of steam engines this was a real problem and accidents occurred when steam boilers exploded. High pressure steam was able to push much harder on the pistons of steam engines. For a given size of engine, running at a given speed, more work could be produced if high pressure steam was used. High pressure engines were more efficient than low pressure engines.

Miss Tumble said that Richard Trevithick also invented the first self-propelled vehicle. In order to do this he had to discard Watt’s invention of the condenser, as it would have been too big and heavy to carry around in a vehicle. He decided to let the steam go up the chimney instead, mixing with the smoke from the fire. The escaping steam had the effect of pushing the smoke out and drawing more air through the fire. The fuel burned more easily as a result. Trevithick’s engines were called ‘Puffers’ because the mixture of smoke and steam came out in puffs from the chimney. Of course, stationary engines that had condensers were more efficient than Trevithick’s engines for vehicles that didn’t. Miss Tumble said that Trevithick’s idea of leaving out the condenser was a very good example of a compromise. He had settled for lower efficiency in order to make self-propelled vehicles practical. Miss Tumble wrote COMPROMISE on the blackboard. Rose volunteered to explain what compromise meant. She said it was a best choice in between two other choices that were not satisfactory. One day she had wanted to play skipping in the school yard and Eve had wanted to play chasing. They had compromised by playing chasing for half their break time and skipping for the other half.

Miss Tumble thanked Rose for that example. She said that being able to compromise was a very important skill to have. New inventions often involved compromise, as in the case of Trevithick’s vehicle.

Steam engines were built in great numbers and in many sizes. They were used to pump water out of mines so that coal could be extracted from deep below the Earth’s surface. They were used instead of animals to draw coal wagons to bring the coal to the surface. Steam engines were used in farming for threshing wheat. They were used in factories to power machines that made all kinds of products: from linen cloth to nails to wooden furniture. Steam engines provided power for trains and ships. Steam engines allowed roads to be built more quickly and economically. Geraldine asked Miss Tumble why people didn’t use steam engines anymore. Miss Tumble said that other types of engines had been invented since the first steam engines. Some of these, such as the petrol or diesel engines used in cars and the diesel engines used in railway locomotives, were found to be better than steam engines because they took up less space, were cleaner, were quieter or used less fuel. Miss Tumble told Geraldine her question was a very good one and said that she herself still wondered why there didn’t seem to be any modern steam engines around.

Miss Tumble was not the type of person to leave a question incompletely answered for long. She soon resolved the question of modern steam engines. She spoke to her sister-in-law, Ida Donut, who was a mechanical engineer, and found out that modern steam engines did exist after all. The modern form of the steam engine was the steam power plant. These were mostly used for generating electricity in power stations. In effect a steam power plant, such as the Moneypoint power plant in County Clare, was a huge steam engine. Instead of pistons that moved up and down or back and forth, as in the early steam engines, turbines were used. These rotated very smoothly at a steady speed of 3,000 revolutions per minute to drive electric generators that produced the electricity. The most common form of modern steam turbine was invented by the Irishman Charles Parsons.

In a modern steam power plant there was a boiler to produce high pressure steam, a turbine to provide the power output and a condenser to change the low pressure steam that came out of the turbine back into liquid water. There was also a pump to pump the condensed water back into the boiler. Freddie asked if that meant that the same water went around and around inside the steam power plant, changing from water to steam in the boiler and condensing again in the condenser. Miss Tumble said that was correct.

Eve then had a brilliant idea: she said it would be better to let the steam that came out of the turbine go straight back into the boiler. Then there would be no need for the condenser or the pump. Miss Tumble agreed that that sounded like a very good and sensible idea, but she didn’t know why it was not done that way. She promised to make some enquiries to find an explanation.

Professor Leo Nest of the University of Linnduv kindly gave Miss Tumble an explanation over the phone as to why the condenser and the pump were used. It was rather technical, but Miss Tumble was able to explain it to the children more simply. Any given amount of the low-pressure steam coming out of the turbine took up a great deal of space. It would have required a very big pump to push all of this back into the boiler against the high pressure of the steam and water that were already inside. It would also have taken so much work that nearly all of the work produced by the turbine would have to have been used for this alone, leaving very little for the production of electricity. However, when the low-pressure steam was condensed, it became liquid water, which took up very little space. A very small pump could then be used to pump it back into the boiler. This pump only required a small amount of work to drive it. Therefore nearly all of the work output of the turbine could be used to produce electricity. Freddie was relieved to learn that condensation was such an important part of steam power plants after all.

Professor Nest also gave Miss Tumble his opinion as to why steam engines were not in common use in such applications as cars, lawnmowers or aeroplanes. In the case of aeroplanes he considered that it was a question of weight. He said the heavier an aeroplane was, the more difficult it was to make it fly. In comparison to the jet engines or gas turbine engines that were usually used in aircraft, steam engines were very heavy. The water, the boiler and the condenser of a steam power plant would all add considerably to the weight of the aircraft. He said that the same reason applied, though to a lesser extent, for cars or lawnmowers. He told Miss Tumble that modern steam engines had been built that were capable of powering cars or even lawnmowers. However, in terms of cost of manufacture, compactness and fuel consumption, petrol and diesel engines had been found to be more suitable. He said he would not like to rule out the possibility that some form of steam power plant might be used in these applications in the future. Perhaps, he said, the Steam Age had not ended yet!