“Come,” said Mr. Seymour, “I will perform this experiment myself, and endeavour to satisfy the doubts of our young sceptic; but I must first take the opportunity to observe, that I am never better pleased than when you attempt to raise difficulties in my way, and I hope you will always express them without reserve.”
“Here, then, is a penny piece; and here,” said Tom, “is a piece of paper.”
“Which,” continued Mr. Seymour, “we will cut into a corresponding shape and size.” This having been accomplished, he held the coin in one hand, and the paper disc in the other, and dropped them at the same instant.
“There! there!” cried Louisa, with an air of triumph; “the coin reached the ground long before the paper.”
“I allow,” said Mr. Seymour, “that there was a distinct interval in favour of the penny piece;” and he proceeded to explain the cause of it. He stated that the result was not contrary to the law of gravitation, since it arose from the interference of a foreign body, the air, to the resistance of which it was to be attributed; and he desired them to consider the particles of a falling body as being under the influence of two opposing forces,--gravity, and the air’s resistance. Louisa argued, that the air could only act on the surface of a body, and as this was equal in both cases (the size of the paper being exactly the same as that of the penny piece), she could not see why the resistance of the air should not also be equal in both cases.
“I admit,” said Mr. Seymour, “that the air can only act upon the surface of a falling body, and this is the very reason of the paper meeting with more resistance than the coin; for the latter, from its greater density, must contain many more particles than the paper, and upon which the air cannot possibly exert any action; whereas almost every particle of the paper may be said to be exposed to its resistance, the fall of the latter must therefore be more retarded than that of the former body.”
At this explanation Louisa’s doubts began to clear off, and they were ultimately dispelled on Mr. Seymour performing a modification of the above experiment in the following manner. He placed the disc of paper in close contact with the upper part of the coin, and, in this position, dropped them from his hand. They both reached the ground at the same instant.
“Are you now satisfied, my dear Louisa?” asked her father. “You perceive that, by placing the paper in contact with the coin, I skreened it from the action of the air, and the result is surely conclusive.”
“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.”