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 What would you think, then, of water in which there are from fifteen to twenty quarts of salt and other minerals in every hundred quarts of water? The water of our Great Salt Lake and of the Dead Sea is four or five times as salt as the ocean. Like the ocean, they have no outlets in rivers. So they keep all the minerals that come into them. After ages and ages they will lose all their water, dry up and leave great salt beds behind. Do you think that could ever happen to the big oceans?

When James Watt invented the stationary steam engine, one of the difficulties he had was to be certain how large an engine was needed to do a given amount of work. He would get an order something like this: "An engine is wanted to pump water from a mine. It must do the work that is now done by twenty-four horses." The thing he had to find out was just how much work one horse can do. He tested many horses until he found that the average force of the working horses then used, was just enough to raise thirty-three thousand pounds one foot high in one minute of time. Allowance also had to be made for friction, or rubbing of the parts of the machinery, and other things. For this reason the term "nominal horse power," which was formerly employed to indicate the theoretical capacity of an engine based on the size of its cylinder is no longer used in the best practice, since it does not tell the real working force.

That depends. On the weight of it? No, indeed. You remember how Galileo, the great astronomer, dropped a one-pound and a ten pound cannon ball together from the leaning tower of Pisa? They struck the ground the same instant. The speed with which things drop depends upon the height from which they fall. If you fall from the limb of an apple tree sixteen feet from the ground, you strike the ground in just one second. But if you fall from a church steeple three times as high, or forty-eight feet, you strike the ground in two seconds. Every second a falling body gains thirty-two feet on the distance covered in the preceding second. You fall sixteen feet in the first second, forty-eight feet in the second, eighty feet in the third, one hundred and twelve in the fourth and one hundred and forty-four in the fifth, or four hundred feet in less than a twentieth of a minute. This increase in speed, according to the height, is what