IX GREEK SCIENCE OF THE ALEXANDRIAN OR HELLENISTIC PERIOD A History of Science: in Five Volumes. Volume I: The Beginnings of Science | ||
CTESIBIUS AND HERO: MAGICIANS OF ALEXANDRIA
Just about the time when Hipparchus was working out at Rhodes his puzzles of celestial mechanics, there was a man in Alexandria who was exercising a strangely inventive genius over mechanical problems of another sort; a man who, following the example set by Archimedes
Unfortunately, the pupil of Ctesibius, whatever his
The man who would coolly appropriate some discoveries of others under cloak of a mere prefatorial reference was perhaps an expounder rather than an innovator, and had, it is shrewdly suspected, not much of his own to offer. Meanwhile, it is tolerably certain that Ctesibius was the discoverer of the principle of the siphon, of the forcing-pump, and of a pneumatic organ. An examination of Hero's book will show that these are really the chief principles involved in most of the various interesting mechanisms which he describes. We are constrained, then, to believe that the inventive genius who was really responsible for the mechanisms
The main purpose of Hero in his preliminary thesis has to do with the nature of matter, and recalls, therefore, the studies of Anaxagoras and Democritus. Hero, however, approaches his subject from a purely material or practical stand-point. He is an explicit champion of what we nowadays call the molecular theory of matter. "Every body,'' he tells us, "is composed of minute particles, between which are empty spaces less than these particles of the body. It is, therefore, erroneous to say that there is no vacuum except by the application of force, and that every space is full either of air or water or some other substance. But in proportion as any one of these particles recedes, some other follows it and fills the vacant space; therefore there is no continuous vacuum, except by the application of some force [like suction]—that is to say, an absolute vacuum is never found, except as it is produced artificially.'' Hero brings forward some thoroughly convincing proofs of the thesis he is maintaining. "If there were no void places between the particles of water,'' he says, "the rays of light could not penetrate the water; moreover, another liquid, such as wine, could not spread itself through the water, as it is
Here, clearly enough, was the idea of the "atomic'' nature of matter accepted as a fundamental notion. The argumentative attitude assumed by Hero shows that the doctrine could not be expected to go unchallenged. But, on the other hand, there is nothing in his phrasing to suggest an intention to claim originality for any phase of the doctrine. We may infer that in the three hundred years that had elapsed since
DEVICE FOR CAUSING THE DOORS OF THE TEMPLE TO OPEN
WHEN THE FIRE ON THE ALTAR IS LIGHTED
(Air heated in the altar F drives water from the closed receptacle
H through the tube KL into the bucket M, which descends through
gravity, thus opening the doors. When the altar cools, the air
contracts, the water is sucked from the bucket, and the weight
and pulley close the doors. See p. 248.)
[Description:
(Air heated in the altar F drives water from the closed receptacle
H through the tube KL into the bucket M, which descends through
gravity, thus opening the doors. When the altar cools, the air
contracts, the water is sucked from the bucket, and the weight
and pulley close the doors. See p. 248.)
]
Again, we know that Empedocles studied the pressure of the air in the fifth century B.C., and discovered that it would support a column of water in a closed tube, so this phase of the subject is not new. But there is no hint anywhere before this work of Hero of a clear understanding that the expansive properties of the air when compressed, or when heated, may be made available as a motor power. Hero, however, has the clearest notions on the subject and puts them to the practical test of experiment. Thus he constructs numerous mechanisms in which the expansive power of air under pressure is made to do work, and others in which the same end is accomplished through the expansive power of heated air. For example, the doors of a temple are made to swing open automatically when a fire is lighted on a distant altar, closing again when the fire dies out—effects which must have filled the minds of the pious observers with bewilderment and wonder,
Other mechanisms utilized a somewhat different combination of weights, pulleys, and siphons, operated by the expansive power of air, unheated but under pressure, such pressure being applied with a force-pump, or by the weight of water running into a closed receptacle. One such mechanism gives us a constant jet of water or perpetual fountain. Another curious application of the principle furnishes us with an elaborate toy, consisting of a group of birds which alternately whistle or are silent, while an owl seated on a neighboring perch turns towards the birds when their song begins and away from them when it ends. The "singing'' of the birds, it must be explained, is
THE STEAM-ENGINE OF HERO
(The steam generated in the receptacle AB passes through the tube EF into the
globe, and escapes through the bent tubes H and K, causing the globe to
rotate on the axis LG. See p. 250.)
[Description:
(The steam generated in the receptacle AB passes through the tube EF into the
globe, and escapes through the bent tubes H and K, causing the globe to
rotate on the axis LG. See p. 250.)
]
The utilization of the properties of compressed air was not confined, however, exclusively to mere toys, or to produce miraculous effects. The same principle was applied to a practical fire-engine, worked by levers and force-pumps; an apparatus, in short, altogether similar to that still in use in rural districts. A slightly different application of the motive power of expanding air is furnished in a very curious toy called "the
In recent times there has been a tendency to give to this steam-engine of Hero something more than
THE SLOT-MACHINE OF HERO
(The coin introduced at A falls on the lever R, and by its weight opens the
valve S, permitting the liquid to escape through the invisible tube LM. As
the lever tips, the coin slides off and the valve closes. The liquid in tank
must of course be kept above F. See p. 251.)
[Description:
(The coin introduced at A falls on the lever R, and by its weight opens the
valve S, permitting the liquid to escape through the invisible tube LM. As
the lever tips, the coin slides off and the valve closes. The liquid in tank
must of course be kept above F. See p. 251.)
]
The particular function which the mechanism of Hero was destined to fulfil was the distribution of a jet of water, presumably used for sacramental purposes, which was given out automatically when a five-drachma coin was dropped into the slot at the top of the machine. The internal mechanism of the machine was simple enough, consisting merely of a lever operating a valve which was opened by the weight of the coin dropping on the little shelf at the end of the lever, and which closed again when the coin slid off the shelf. The illustration will show how simple this mechanism was. Yet to the worshippers, who probably had entered the temple through doors miraculously opened,
IX GREEK SCIENCE OF THE ALEXANDRIAN OR HELLENISTIC PERIOD A History of Science: in Five Volumes. Volume I: The Beginnings of Science | ||