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no leaning tower, but the roof of this building is pretty high: we have no Galileo, but some one has kindly offered to represent him, and he will drop these two balls, a wooden one and a leaden one, from the roof overhead into this box of sand, so that we may see for ourselves whether they fall together or not. There! you see they fall together just as they did 300 years ago from Pisa's leaning tower. Perhaps you may think that Galileo's representative did not drop them quite fairly together? That is quite possible, though I feel sure he tried to do so; but to make quite sure of being fair we have arranged a kind of trap for the balls up aloft which can be worked from below by means of this long string, which perhaps one of the audience will pull for me.

There again! they have fallen, you see, quite together; and do you see that the wooden one is lying on the top of the sand while the leaden one has quite disappeared? It is buried so deep in the sand that it is quite difficult to find it. This fact does not concern us very much at the moment, though it is interesting as showing the different weights of the two balls; but when we come to speak of meteorites in the next lecture, we shall find it useful to remember how a body striking the Earth may bury itself deeply. A very great man, Charles Darwin, used to say that we ought to learn all we can from an experiment, whether it is of immediate importance or not: and this tendency of heavy falling bodies to bury themselves in the earth is just such an extra consequence as he would have delighted to note.