“Simple?” Frederick said. “Amazing! But did the Greeks really know such wonders?”
“These and others, and they were known also to the Egyptian priests, who used this device to command, by speaking, the opening of the doors of a temple, while the faithul cried miracle,” Ardzrouni said. Then he invited the emperor to cross the threshold. They entered a room in whose center rose another extraordinary instrument. It was a leather sphere fixed to a circular surface by what seemed to be handles bent at right angles, and the surface held a kind of metallic basin beneath which there was another pile of wood.
From the sphere, above and below, ran two little pipes, which ended with two taps facing in opposite directions. On closer observation, you could see that the two handles holding the sphere to the round level were also pipes, which below were fixed to the basin, and above penetrated the interior of the sphere.
“The basin is filled with water. Now we’ll heat this water,” Ardzrouni said, and again he started a great fire. They had to wait a few minutes before the water came to a boil, then a hissing was heard, faint at first, then louder, and the sphere began to revolve around its supports, while from the taps came puffs of steam. The sphere turned for a little while, then its impetus seemed to weaken, and Ardzrouni hastened to seal the little faucets with a kind of soft clay. He said: “Here again the principle is simple. The water boiling in the basin is transformed into steam. The steam rises in the sphere, but, emerging violently from opposite directions, it imposes on it a rotary motion.”
“And what miracle does it pretend to be?” Baudolino asked.
“It doesn’t pretend anything, but it demonstrates a great truth: namely, it allows us to see the existence of the vacuum.”
Just imagine Boron then. Hearing the vacuum mentioned, he became suspicious at once and asked how this hydraulic toy proved that the vacuum exists. “It’s simple,” Ardzrouni said. “The water in the basin becomes steam and fills the sphere, the steam escapes the sphere making it rotate; when the sphere looks as if it will stop, it’s a sign that it has no more steam, so you close the taps. And then what remains in the basin and in the sphere?
Nothing: that is to say, the vacuum.” “I’d really like to see it,” Boron said.
“To see it, you’d have to open the sphere, and then air would immediately enter. However, there is a place where you can stand and sense the presence of the vacuum. But you are aware of it only briefly, because, for lack of air, you will die of suffocation.”
“And where is this place?”
“It’s a room above us. Now I’ll show you how I can create a vacuum in that room.” He held up the torch and showed us another machine that till then had remained in the shadows. It was far more complex than the two previous ones, because it had, so to speak, its viscera exposed. There was an enormous alabaster cylinder, which showed in its interior the dark shadow of another cylindrical body that occupied half of it, while half protruded, its upper part bolted to a kind of enormous handle that could be operated by a man’s two hands, as if it were a lever.
Ardzrouni operated that lever, and the inner cylinder was seen to move first up, then down, until it completely occupied the exterior cylinder. To the upper part of the alabaster cylinder a great tube was attached, made of pieces of animal bladders, carefully sewn together. This tube was finally swallowed by the ceiling. On the lower part,
at the base of the cylinder, a hole opened.
“Now then,” Ardzrouni explained, “here we have no water. Only air.
When the inner cylinder is lowered, it compresses the air contained in the alabaster cylinder, expelling it through the hole at the base. When the lever raises it, the cylinder operates a lid that blocks the hole on the inside, so that air that has left the alabaster cylinder cannot reenter. When the inner cylinder is raised completely, it operates another lid that allows air to enter through the tube you can see; it comes from the room I have told you about.
When the inner cylinder is lowered again, it expels that air also. Little by little the machine draws all the air from that room and expels it here, so in that room the vacuum is created.”
“And no air enters that room from anywhere else?” Baudolino asked. “No. As soon as the machine is set in motion, through the ropes to which the lever is attached, every hole or fissure that might allow air in the room is sealed.”
“But with this machine you could kill a man if he were in that room,” Frederick said.
“I could, but I have never done so. I did put a chicken there. After the experiment I went up to the room and the chicken was dead.”
Boron shook his head and murmured into Baudolino’s ear: “Don’t trust him. He’s lying. If the chicken was dead, it would mean that the vacuum exists. But since it does not exist, the chicken is still alive and kicking. Or if it’s dead, it died of overwork.” Then he said, raising his voice, to Ardzrouni: “Have you ever heard of animals dying also at the bottom of a well, where candles go out?
Some have drawn the conclusion that there is no air down there; there is no air and hence there is a vacuum. On the contrary, at the bottom of wells fine air is lacking but the thick and mephitic air remains, and it suffocates both men and a candle’s flame. You breathe the fine air, but the thick remains, which doesn’t allow us to inhale it, and that’s enough to kill your chicken.”
“Enough,” Frederick said. “All these devices are charming, but, except for the mirrors up above, none could be used in a siege or in a battle. So what use are they then? Let’s go, I’m hungry. Ardzrouni, you promised me a good supper. It seems to me the time for it has come.”
Ardzrouni bowed and led Frederick and his men into the banquet hall, which, truth to tell, seemed splendid, at least to people who for weeks had eaten the scant provender of the camp. Ardzrouni offered the best of Armenian and Turkish cuisine, including some very sweet cakes that gave his guests the sensation of drowning in honey. As all had agreed, Baudolino and his friends tasted every dish before it was offered to the emperor. Contrary to court protocol (but in war protocol always suffers numerous exceptions) they all sat at the same table, and Frederick drank and ate merrily, as if he were one of them, listening with curiosity to a debate that had begun between Boron and Ardzrouni.
Boron was saying: “You insist on talking about the vacuum, as if it were a space lacking any other body, even aerial. But a space lacking all bodies cannot exist, because space is a relation among bodies. Further, the vacuum cannot exist because Nature holds it in horror, as all the great philosophers tell us. If you suck air through a reed immersed in water, the water rises because it cannot leave a space empty of air. Furthermore, listen: objects fall towards the earth, and an iron statue falls more rapidly than a piece of cloth. Birds fly because by moving their wings they stir up much air, which supports them in spite of their weight.
They are supported by the air just as fish are supported by the water. If the air weren’t there, the birds would fall, but—mind you—at the same speed as any other body. Hence, if in the sky there were the vacuum, the stars would have an infinite velocity, because they would not be restrained in their fall, or in their circling, by the air, which resists their immense weight.” Ardzrouni rebutted: “Who ever told you that the speed of a body is in proportion to its weight? As John Philoponus said, it depends on the movement that is impressed on it. And anyway, tell me this: if there were no vacuum, how would things move? They would bump against the air, which wouldn’t allow them to pass.”
“Oh no! When a body moves, the air from the space the body then occupies shifts and fills the space that the body has left! Like two people going in opposite directions along a narrow street: they suck in their bellies, each pressing against the wall, as one gradually slips in one direction, the other slips in the opposite, and finally one man has taken the other’s place.” “Yes, because each of the two, thanks to his own will, impresses a movement on his own body.
But it isn’t the same with air, which has no will. It moves because of the impetus imposed on it by
