“Was it not, think you, owing to the pressure of the atmosphere upon the surface of the water? When you raised the piston, the air above it was also raised, and ultimately driven out by the force of the ascending piston; and since the air could not find any entrance from below as long as the point was under the water, the interior of the squirt would necessarily have remained quite empty, or have been a vacuum, had it not been for the weight of the atmosphere, which, not having any counteracting pressure, drove the water into the tube, and thus filled it; and which, by pressing down the piston, you again expelled with considerable force.”
“Your explanation,” cried Louisa, “is so clear and intelligible, that I feel quite confident I could now explain any machine that owes its action to the exhaustion of the air, and the pressure of the atmosphere.”
“If that be your belief,” said Mr. Seymour, “I will not lose a moment in putting your knowledge to the test.--Tom, do you run into the house, and fetch hither the kitchen bellows.”
The bellows were produced, and Louisa having been desired by her father to explain the manner in which they received and expelled the air, proceeded as follows: “Upon raising the upper from the under board, the interior space of the bellows is necessarily increased, and immediately supplied with an additional quantity of air, which is driven into it by the pressure of the atmosphere; when, by pressing down the upper board, it is again expelled through the iron tube or nosle.”
“To be sure,” said Tom, “in the same manner that the water was expelled from my squirt, when I pushed down the handle.”
“So far you are quite correct,” said Mr. Seymour; “but you have not yet told us the use of the hole in the under-board, and which is covered, as you perceive, with a movable flap of leather: it is termed a valve, or ‘wind-clap.’”
“That,” replied Tom, “is for the purpose of admitting the air, when we raise up the board.”
“Exactly so; and also to prevent the air from passing out again, when you press it down. I wish to direct your attention particularly to this contrivance, because, simple as it may appear, its action will teach you the general nature of a valve. Without it, the operation of filling the bellows with air would have been so tedious as to have destroyed the utility of the instrument; for the air could, in that case, have only found admission through the nosle, and that, again, would have been attended with the additional disadvantage of drawing smoke and other matter into its cavity; when, however, you raise up the board, the air, by its external pressure, opens the wind-clap inwards, and thus finds an easy entrance for itself; and when you press the board downwards, the air, thus condensed, completely shuts the valve, and its return through that avenue being prevented, it rushes out through the tube.”
The children were much pleased with the simplicity of this invention, and Tom enquired of the vicar who first thought of it.
“We are informed by Strabo,” replied Mr. Twaddleton, “that Anacharsis, the Scythian philosopher, who lived in the time of Solon, about six hundred years before Christ, invented the bellows, as well as the anchor, and potter’s wheel; but,” he added, “there is some reason to doubt the truth of this statement. The bellows, however, were certainly known to the Greeks; and the great poet Virgil alludes to them in his fourth Georgic:[[40]]