that (as the story goes) he saw an apple fall, and called the force that caused it to fall, gravity, but this law was known from the beginning of time. There was not a living man, in any age, who was not conscious that if he stumbled, he would fall to the earth. There was not a monkey or a climbing beast of the old animal life that did not know that if he failed to retain his footing or his hold, he would fall to the earth beneath him. The birds of the air knew that if they ceased to keep their wings in motion they would fall. So, it is evident that this fact which we call the earth's attraction for bodies was known although not named before Newton was thought of. Still, he was undoubtedly a great man, and reduced this force to a measurable quantity for the use of science. Well, this attraction of the earth is one of the great powers that we use. To explain this, I take this globe, and I take this piece of elastic, I attach one end of the elastic to the globe, and another to this little model vessel. You see
