Newcomen’s engine was a great help to the coal mines of England and Scotland, but it was very expensive to run, a large engine consuming no less than twenty-eight pounds of coal per hour per horse-power. Then it happened that in 1764 a small Newcomen engine that belonged to the University of Glasgow was given to James Watt, an instrument-maker at the university, to be repaired. To do this properly he made a study of all that had been discovered in regard to engines, and then set about to construct one for himself. There are many stories told of the boyhood of James Watt. He lived at Greenock on the River Clyde in Scotland, and was of a quiet, almost shy disposition, and delicate in health. He was fond of drawing and of studying mechanical problems, but rarely had much to say about his studies. The story goes that as he sat one evening at the tea-table with his aunt, Mrs. Muirhead, she said reprovingly to him, “James Watt, I never saw such an idle boy: take a book or employ yourself usefully; for the last hour you haven’t spoken a word, but taken off the lid of that kettle and put it on again, holding a cup or a silver spoon over the steam, watching it rise from the spout, and catching the drops it falls into. Aren’t you ashamed of spending your time in this way?” And history goes on to presume that as the boy watched the bubbling kettle he was studying the laws of steam and making ready to put them to good use some day. [Illustration: WATT FIRST TESTS THE POWER OF STEAM] He picked out the trade of a maker of mathematical instruments, and went to London to fit himself for it. He was apprenticed to a good master and made rapid progress, but the climate of London was bad for his health, and as soon as his term of instruction was finished he went back to Scotland. There he found it difficult to get employment, but at last he obtained permission to open a small shop in the grounds of the University of Glasgow, and to call himself “Mathematical-instrument-maker to the University.” When the Newcomen engine was given to Watt to repair he studied it closely, and soon reached an important conclusion. A great amount of heat was lost whenever the cold water was let into the cylinder to condense the steam, and this loss vastly increased the expense of running the engine, and cut down its power. He saw that to prevent this loss the cylinder must be kept as hot as the steam that entered it. This led him to study the nature of steam, and he had soon made some remarkable discoveries in regard to it. He found that water had a high capacity for storing up heat, without a corresponding effect on the thermometer. This hidden heat became known as latent heat.