Miss Tumble brought the kettle from the teachers’ room into class and boiled water so that the children could all look at steam coming out of the spout. Everybody stayed at their places because boiling water and steam were very dangerous.

Marjorie said that she had a kettle at home that could whistle. This special whistling kettle had a whistle attached to the spout. Marjorie’s mum or dad had to take off the whistle in order to fill the kettle from the tap. They placed the whistle back on the spout and put the kettle on the gas cooker to boil. When the water boiled, steam came out of the spout and through the whistle. The kettle whistled loudly until Marjorie’s mum or dad turned off the gas. Marjorie said it was great because everyone in the house could hear when the kettle had boiled. Her mum or dad didn’t have to stand watching it to know when the water would be ready to make tea.

The kettle from the teachers’ room didn’t have a whistle. Miss Tumble said it contained a sensor that turned off the electricity automatically once the water had boiled and steam started to form. Otherwise the kettle could have continued to boil until all the water had been turned into steam by evaporation. If that had happened, the classroom would have been turned into a sauna. Everybody laughed at the thought of the classroom becoming a sauna, especially Tom. Freddie didn’t laugh so much because he preferred condensation to evaporation.

For thousands of years before electricity had been discovered, people boiled water by heating it in pots or kettles. They needed the hot water to cook food, or perhaps to make tea (the Chinese did this). They weren’t very interested in the steam that was produced, but once the steam appeared they knew that the water was as hot as it could become. Occasionally people may have noticed that the steam from boiling water could lift the lid of a pot, but did not think too much about it. If they tried heavier lids that fitted tightly, the steam lifted them too. The solution to the lifting lid problem was to ensure that the steam was not restricted too much from escaping. Putting a hole in the lid or making sure it was not a close fit prevented the lid from lifting. Maybe lots of different people thought of using the effect of the steam pushing on a lid to do useful work. If so, the idea did not catch on for a long time – not until the early part of the eighteenth century, in fact.

A man called Hero, who lived in Alexandria more than two thousand years ago, invented a toy that was good fun and worked on steam. He made a hollow metal ball that could rotate about an axle. To this he attached two bent tubes that pointed in opposite directions, rather like the ends of the letter Z. He let steam flow into the ball from a vessel like a kettle that was heated over a fire. The steam entered the ball through the axle, which was hollow. It left the ball through the bent tubes and caused it to spin around quite fast. This was quite a novelty and was great to watch. It is a pity that Hero did not think of using the motion for something useful, like driving a children’s merry-go-round.

In fact Hero had invented a baby steam turbine. Eventually it ‘grew up’ and became the powerful turbines that are used today for making electricity or powering aircraft.

The children had all studied shapes like circles, rectangles, squares, triangles, spheres and cubes. Miss Tumble did not have to remind them that the metal ball of Hero’s machine was a sphere. As a test, Miss Tumble asked the class what was the name for a half sphere.  Eve, Freddie, Benjamin and Tom all put up their hands. She asked Tom first and he said it was a semi-sphere. Miss Tumble said that was a good answer, but stated that another term was generally used; so she asked Eve next. Eve said a half sphere was known as a hemisphere. Yes, that was the usual name for a half sphere, according to Miss Tumble. She thanked Eve and wrote HEMISPHERE on the blackboard. Tom whispered to Coleman that hemisphere had only ten letters in it.

According to Miss Tumble, the technical name for the kettle-like vessel that produced the steam was a boiler. The name for the part that spun around was a turbine. Much of the electricity produced in Ireland and in the world was produced by steam turbines. Robert, Benjamin’s twin brother, wanted to know how the rest of the electricity was produced. Miss Tumble wasn’t sure about that. She said she thought some of the electricity was produced by water turbines like the ones on the River Shannon at Ardnacrusha, or on the River Liffey at Leixlip. Later Benjamin won a prize of a spider plant for copying a picture of Hero’s turbine from the blackboard and colouring it in. He showed the steam as blue. Miss Tumble said that was OK because white would not have shown up against the paper of his copybook.