Here we present selected parts from the very interesting corresponding paper by K. P. Valavanis, G. J. Vachtsevanos, P. J. Antsaklis.
The School of Alexandria
During the golden era of the School of Alexandria, Greek thought evolved towards what Newton called Natural Philosophy. This turn of Greek thought culminates in the search for observation, measurements, design and construction. The School of Alexandria is directly linked with three Greek engineers of the Hellenistic world: Ktesibius, Philon of Byzantine and Heron of Alexandria who lived in the second century B.C. through the first century A.D. Their contributions influenced western science and technology and their writings were reprinted until the 16th century A.D.
Ktesibius (circa 270 B.C.) was a Greek physicist and inventor, the first great figure of the ancient engineering tradition of the School of Alexandria. The discovery of the elasticity of air is attributed to him, as is the invention of several devices using compressed air, including force pumps and an air powered catapult. His most famous invention, however, was an improvement of the clepsydra (in Greek κλεψύδρα), or water clock, in which water dripping at a constant rate raised a float that held a pointer to mark time (the passage of hours). Another notable invention was a ‘hydraulis’, or water organ, in which air was forced through the organ pipes by the weight of water rather than by falling lead weights. Unfortunately, Ktesibius’ writings have not survived, and his
inventions are known only from references by Vitruvius and Heron of Alexandria. The pictures below illustrate inventions made by Ktesibius.
Ktesibius’ water clock incorporated a feedback mechanism that used a floating device as both a sensor and actuator that kept the water level approximately constant and ensured constant flow of water and so accurate time keeping. This device was so successful that it was still used in Baghdad in 1200 A.D. when the Mongols conquered the city!
Philon of Byzantium (circa 230 B.C.) authored several books (most of which have survived) on levers, water clocks, pneumatic mechanisms and military machines, among others. His major contribution relates to the subject of spur gears (in Greek οδοντοτοί τροχοί). The transfer of mechanical power and the multiplying or dividing effect of circular motion machines are based on such gears. Philon’s treatise Pneumatica is addressing key physical properties of liquids and gases supported by a plethora of
experiments. He also had advanced knowledge of metallurgy. Philon explained thoroughly Ktesibius’ contention regarding the replacement of animal fibers with thermally treated metal leaves. In essence, Philon advanced further the Alexandrian School’s developments in automatic mechanisms started by Ktesibius. The Arabic translation of Philon’s Pneumatica is a thesaurus of such automatic devices based on properties of air, liquids, fire, floaters and gears. They offer a rich foundation for a new
technology, automation. Although he did not complete his work, he laid the groundwork for the European technological developments for the next 1500 years.
Eight hundred years of tradition in ancient Greek science and technology culminated with the enormous work of Heron who was a scientist of great breadth. Heron of Alexandria (circa 60 A.D.) taught at the museum of Alexandria and presented in his books About Pneumatica and About Automation (in Greek Αυτοματοποιητική) the up until then known knowledge of automation technologies. Among his surviving writings, his book on automation according to historians, lays the foundation of modern automatic
control and it is the oldest known document that describes mechanical automatic systems capable of performing programmed movements. Αυτοματοποιητική refers to automatic machines that operate and move without human intervention by capitalizing on properties of steam, liquid and gaseous matter, and involve complex mechanical systems and ingenious programming of movements. Every mechanical device was broken down to its constituent components which, in turn, refer to levers with a basic
geometric interpretation. Therefore, a methodology was pursued although the ultimate objective of Heron’s books was applications.
Heron’s two books, About Pneumatica, introduced steam as a major driving force. He did not invent Watt’s steam engine, but he presented basic notions such as the lifting and driving force of steam as well as its properties under compression and expansion. These two books are the oldest preserved in their original Greek manuscripts that describe applications of pneumatic and hydraulic control systems; they comprise a systematic collection of machines dating before and during his lifetime. These machines moved
with water, air or steam pressure, produced sounds and were intended to decorate public places and to amaze or serve the practical needs of the spectators.
Although in his books he describes a menagerie of mechanical devices, or ‘toys’ like singing birds, puppets, coin operated machines, a fire engine, and a water organ, his most famous invention is the first steam powered engine, of special significance to the
science of automation because he presented automatic means necessary to control steam supply. The device consists of a sphere mounted on a boiler and supported by an axial shaft with two canted nozzles that produce a rotary motion as steam escapes (Greek word ατμοστρόβιλος); it constitutes a revolutionary entry into the field of today’s automatic control.
Among Heron’s inventions are the ‘automatic theaters’, capable of conducting an entire theatrical performance with automatic portals, changing automatically the stage props, and moving puppets that performed a myth. For these mechanical automata, Heron wrote “A prop is placed on a pylon depicting a theatrical scene with portals that open and
close automatically. Therefore, it allows several scenes of a play to be enacted in sequence and the puppets are able to move, act, and speak or produce sounds like live characters. In addition, fires are lit automatically and new puppets appear on the stage
until the end of the story”.
Heron’s book The Belopoeica (Engines of War) purports to be based on a work by Ktesibius. His three books on Mechanics (in Greek Μηχανική) survived in a somewhat altered Arabic translation. Mechanics is closely based on the work of Archimedes, presenting a wide range of engineering principles, including a theory of motion, a theory of balance, methods of lifting and transporting heavy objects with mechanical devices,
and how to calculate the center of gravity for various simple shapes. Both books include Heron’s solution to the problem of two mean proportionals, two quantities, x and y that satisfy a/x = x/y = y/b, with a, b known. This may be used to solve the problem of constructing a cube with double the volume of a given one.
A catalogue of 60 mechanical devices is attributed to Heron, not mythical but historical and indeed functional, as proven by their modern reproductions. The function of his devices was based on scientific observations of nature. But unlike pure science that involves theoretical understanding of the environment but often lacks immediate implementation, his observations were applied science brought to use. Heron himself, however, explained that some of these devices were not meant to cover any practical use but they were created only for aesthetic pleasure. Heron’s devices were explored and reproduced by Romans, Arabs and Byzantines* and served as the link that united the Ancient Greek and the European technologies of the Renaissance that marks the beginning of the technological advances of Western Civilization. Pictures below illustrate the oil press and a hoisting machine, two of Heron’s creations.
On the picture below figure a shows the agiasterion that which supplied an amount of holy water by throwing a coin figure b the water mechanism for the automatic opening of the gate of a temple, figure c the dioptra, mechanism useful in geodesics, and figure d the armonio, musical instrument operated by air pressure.
Picture below depicts Heron’s steam boiler
and picture below the odometer, along with modern reproductions.
Mechanical achievements during those centuries were very significant. The world had one of the greatest geniuses, Archimedes, who devised remarkable weapons to protect his native Syracuse from the Roman invasion and applied his powerful mind to such basic mechanical devices as the screw, the pulley, and the lever. Alexandrian engineers, such as Ktesibius and Heron, invented a wealth of ingenious mechanical contrivances including pumps, wind and hydraulic organs, compressed air engines, and screw cutting machines. They also devised toys and automata that may be regarded as the first successful steam turbine.
Little practical use was found for these inventions, but the Alexandrian school marks an important transition from very simple mechanisms to the more complex devices that properly deserve to be considered machines. In a sense, the School of Alexandria provided a starting point for modern mechanical practice.
(End of Part 2)
*(NovoScriptorium: There were no ‘Byzantines’ ever nor such a state; only Christian Romans and Christian Roman Empire (we could add ‘of the East’). This is the appropriate description)
Research: Anastasius Philoponus