Lecture I

Now suppose someone came along and said: “I don't altogether believe what you tell me about the force of gravity, nor do I believe in the obstructing force. Is the mountain the cause of the stream taking a particular path? I don't believe it.” “Well, what do you believe?” one might ask. He replies: “I believe that part of the water is down there, above it is more water, above that more water again, and so on. I believe the lower water is pushed down by the water above it, and this water by the water above it. Each part of the water drives down the water below it.” Here is a noteworthy distinction. The first man declares: “Gravity pulls the water down.” The second man says: “Masses of water are perpetually pushing down the water below them: that is how the water comes down from above.”