“Assuredly not: have you so soon forgotten that the air presses equally in all directions, and would therefore tend to straighten, as much as to give a curved direction to the string? But, as you now appear to have let out the whole of your string, suppose you allow the kite to enjoy its airing, while we proceed to consider the philosophy of its ascent, and the nature and direction of those forces by which it is effected.” “The kite pulls so amazingly hard,” cried Tom, “that unless I fix the string securely around the tree, we shall run the chance of losing it.” “I am well aware of the force it exerts,” replied his father. “Dr. Franklin has said, that, with a good kite, a man unable to swim might be sustained in the water, so as to pass from Dover to Calais; but I agree with him in thinking, that a packet would be a much safer, as well as a pleasanter mode of conveyance.” “Now, then, for your explanation of the kite’s ascent. Unless I am mistaken, you will find the subject much more complicated than you imagine,” said the vicar. “Not at all; Tom, who, I trust, has a perfect acquaintance with the composition and resolution of forces, will very readily understand the explanation I propose to offer. I admit, however, that there are some few points in the enquiry, which cannot be successfully treated without a knowledge of the higher branches of the mathematics; but I shall, of course, avoid all such difficulties.[42] Can you tell me, Tom, what advantage is gained by your running with the kite?” asked Mr. Seymour. “I suppose that you thus obtain more force from the wind.” “Certainly: action and reaction are equal. By running, therefore, with your kite against the wind, you strike the air, and thus produce a reaction, which is equal to the force of the blow given to it. When the wind is high, and its action is not intercepted by surrounding objects, there cannot exist any necessity for such an expedient.” “The principle is the same as that which enables the bird to rise into the air by flapping its wings,” observed the vicar. “Unquestionably,” replied Mr. Seymour. “Does the kite, then, rise in the air, from the same causes that enable a bird to fly?” asked Tom. “We are not, at present, considering the ascent of the kite, but the advantage which is obtained by running with it: this latter, as the vicar has properly observed, undoubtedly depends upon the same principle as that which enables the bird to rise, by the motion of its wings, and which constitutes the third law of motion,[43] viz. that _action and reaction are equal_; that is to say, whenever one body exerts a force upon another, the second body opposes the first, with equal force, in an opposite direction. If, then, the bird strikes the air below it with a force which is equal to its weight, then must there be a reaction of the air, upwards, exactly equal to it; and the bird, being acted upon by two equal forces, in opposite directions, will, necessarily, rest between them.”