"Now," continued Johnny, "you know that your grandmother's spinning-wheel twists only one thread; but at the factory there are hundreds and thousands of threads all twisting at once." "What a number of people there must be to twist so many threads!" "Oh no," said Johnny, "it is the spindles that twist the threads." "But, then, who turns the spindles? I suppose men must do that?" "No such thing; all the spindles are all turned by one single thing." Willy stared with surprise; but Johnny went on: "Yes, not only all the spindles, but everything that turns in the factory, is made to turn by one great wheel, which is as big as a house." "But what is it turns this great wheel? it cannot be a man nor a horse, for they would not be strong enough. Oh! I dare say it is a steam-engine, for that is the strongest thing I ever heard of." "Well, it is true," returned Johnny, "that the great wheel is turned by a steam-engine in most factories, but in that I saw it was something else, which cost less, and did as well." "What can that be?" said Willy. "Why, it is a stream of water, which is higher than the great wheel, and so it falls down upon it, and pushes it round." "That is just like the wheel at the miller's, which grinds corn," said Willy; "it is called a water-wheel, because the water turns it; but," added he, laughing, "when the great wheel of a factory is turned by a steam-engine, it is turned by water too." "How do you make that out?" "Why, steam is made of hot water, and the stream of cold water; so it's only the difference between hot and cold." "I never thought of that," said Johnny, "but it's true enough; the power that moves the wheel is in the water, whether it be hot or cold." "Well, I think between grandmamma's spinning-wheel and the corn-mill you will understand something of a factory at last." "Indeed," said Willy, "I think a spinning-wheel must be very like a factory in little, for it does just the same thing, only grandmamma's foot, which turns the wheel, is not a bit like a steam-engine or a stream of water." Betsey could not help laughing at such a ridiculous comparison. Then Johnny said, "Well, if it is not like, it does the same thing; her foot is the power that turns the wheel; it don't signify what the power is, so that it be strong enough to do the work." "But then," observed Willy, "if the great wheel and the spindles do all the work, what is there left for the men and women and children to do?" "Oh, there's plenty of work for everybody," returned Johnny, "a deal more than I can explain to you. When the threads that are spinning break, they stop the twisting and fasten them together, and even the children can do that." "To be sure, if it's only tying the broken thread together in a knot, that is easy enough." "But it's not tying a knot," said Betsey. "When your grandmother breaks the thread she is spinning, does she tie it together in a knot?"