“Many thanks to you, dear papa; I am perfectly satisfied, and shall feel less confident for the future.” Tom was delighted; for, as he said, he could now understand why John’s paper _parachute_ descended so deliberately to the ground; he could also explain why feathers, and other light bodies, floated in the air. “Well then,” said Mr. Seymour, “having settled this knotty point, let us proceed to the other question, viz. ‘that a body will fall with the same velocity, during a given number of feet, from the ball of St. Paul’s as from the top of a house.’ You maintain, I believe, that, since the attraction of the earth for a body diminishes as its distance from it increases,[7] a substance at a great height ought to fall more slowly than one which is dropped from a less altitude.” Neither Tom nor Louisa could think otherwise. Mr. Seymour told them that, _in theory_, they were perfectly correct, but that, since attraction acted from the centre, and not from the surface of the earth, the difference of its force could not be discovered at the small elevations to which they could have access: “for what,” said he, “can a few hundred feet be in comparison with four thousand miles, which is the distance from the centre to the surface of our globe?--You must therefore perceive that, in all ordinary calculations respecting the velocity of falling bodies, we may safely exclude such a consideration.” “But suppose,” said Tom, “it were possible to make the experiment a thousand miles above the earth, would not the diminished effect of gravity be discovered in that case?” “Undoubtedly,” replied his father, “indeed it would be sensible at a much less distance: for instance, if a lump of lead, weighing a thousand pounds, were carried up only four miles, it would be found to have lost two pounds of its weight.” (2) “This discussion,” observed Mr. Twaddleton, “reminds me of a problem that was once proposed at Cambridge, to find the elevation to which the Tower of Babel could have been raised, before the stones would have entirely lost their gravity.” “Its solution,” said Mr. Seymour, “would require a consideration which Tom could not possibly understand at present, viz. the influence of the _centrifugal force_.” “I am fully aware of it,” replied the vicar, “and in order to appreciate that influence, it would, of course, be necessary to take into account the latitude of the place; but, if my memory serves me, I think that under the latitude of 30°, which I believe is nearly that of the plains of Mesopotamia, the height would be somewhere about twenty-four thousand miles.” Mr. Seymour now desired Tom to inform him, since all bodies fall with the _same_ velocity, what that velocity might be. “Sixteen feet in a second, papa;--I have just remembered that I had a dispute with a school-fellow upon that subject, and in which, thanks to Mrs. Marcet, I came off victorious, and won twelve marbles.”