that I can pull this little vessel away to the extent of the elastic limit of the elastic, but when I suddenly release my hold, the little model flies towards the globe with considerable force.
"Now, you must clearly understand that this illustration is not a correct one, and is simply given to you to fix your ideas as to the principle or law of the earth's attraction. Remember that the model should (if uninfluenced by the elastic), like what you called a balloon, float in the atmosphere, and that in falling towards the globe the power of the elastic should increase instead of becoming exhausted.
"Well, here I have four globes of different sizes: one is supposed to represent the earth at its surface, that is at the tops of its highest mountains, which are only, when compared with the globe itself, but slight roughnesses like those on an orange. You will notice that this globe is wound round with red silk threads from north to south diagonally. These represent the north and south lines of force. Then you will
