All About Engines

Power and Its Measurement 309 or lever which would have to be used would not be without friction, and some work would be required to overcome that. Similarly, if you put work into a wheel by setting it in motion, the wheel will do work after the force has been removed, until it comes to rest. But it will not give out the work that has been put into it, because of the friction of the axle, and the resistance of the air. Stored up work is called energy, and energy due to position, as in the case of the Weight, is called potential energy, while energy due to motion, as in the case of the grind- stone, is called kinetic energy. In Watt’s days, though something was known about energy from the discoveries of Sir Isaac New- ton, very little was known about heat—in fact, a good deal of what was thought to be known was erroneous. And while it is evident that Watt realised the connection, he never stated it in such a way as to carry conviction. A clear demonstration was given by Benjamin Thomson, an American, who held the Austrian title of Count Rumford and who, in 1799, noticed the great amount of heat produced by boring- cannon. Surrounding the portion which was being bored with a vessel of water, he showed that very shortly the water began to boil. From this it fol- lowed that mechanical energy was being converted into heat. Whenever friction occurs a very small part of the energy required to overcome it is used in removing a small quantity of material, and the main part is converted into heat. Soon after Count Rumford’s experiments Sir Humphry Davy caused