HERO OF ALEXANDRIA AND HIS PNEUMATIC MACHINES
Air as source of energy in the Treatise on Pneumatics of Heron of Alexandria
André J. Fabre Octobre 2012
Texts from Antiquity often refer, at least on a theoretical basis, to the use of air as source of energy : thus, the pneumatic machines of Heron of Alexandria (IId century AD), celebrated in his time for his works on geometry and geodesy.
Heron of Alexandria
Heron (or Hero) was a Greek engineer (c. 20-62 A.D.) living in Alexandria (in Roman Egypt), main center of all hellenistic sciences of Antiquity. He became famous from his works on geometry and geodesy among which Metrica, giving descriptions of how to calculate surfaces and volumes of objects.
Heron's original texts were altered many times with the passing centuries and some commentators have raised the question of their authenticity. However, Heron's works give evidence of the major role given to the great School of Alexandria during the whole Ptolemean dynasty, with a constellation of physicians (Erasistratus, Ascklepiades, Galen of Pergam), astronomers (Ptolemy), mathematicians (Pappus) and beside Heron, many other engineers as Archimedes (287-212 before J.C.), Ctesibius (285-222 before J.C.) and Philo of Alexandria (280-220 before J.C.), the probable inventor of pneumatic energy : his Treatise of Pneumatic Macines has been partly preserved in a latin translation (De ingeniis spiritualibus) of an Arab version
Heron's Treatise on Pneumatics
Ten projects from the Treatise refer specifically to "steam engines":·
.1. Automatic door opening system
A fluid (water or, better, quick-silver), contained in a vessel, is brought to boiling point by a furnace. The steam thus obtained starts an automatic opening of the doors through a pulley (#37). Thereafter, closure of the doors is automatically obtained when fire gets extinct
.2. Other system of automatic door opening.
An air-tight leather bag is attached to a tube inserted in the altar (#38) with a small weight hanging from a chain attached across a pulley. When the bag is folded empty, the weight will close the doors. When hot air is blown from a fire placed on the altar, the bag will rise up, starting aperture of the doors.
.3. Ball lifted up by a steam jet
A fire is lighted under a cauldron (#45) containing water. At the top a tube going through a lid to an hollow hemisphere. The steam coming out from the cauldron lifts up the ball which appears to be suspended in the air.
.4. Solar fountain
If the sun falls on a globe (#47), the air inside is heated and brings out the liquid in a siphon through a funnel into a tank placed in a pedestal. When the globe is placed in the shade, the air gets out from the globe bringing the tube to suck up the liquid in order to fill the void. All that can take place as often as there is sun falling upon the globe
.5. Aeolipile ("Ball of Aeolus")
A fire is lighted under a cauldron metal sphere (#50) revolving on an axis. Two bent tubes get out from the sphere in opposite direction. By heating a fluid contained in the sphere a steam jets keeps turning the sphere.
.6. Dancing automates
Figures of dancers are animated by a fire lit on an altar (#70). A tube is let down turning on a pivot at the base of the altar with smaller tubes lying at right angles in opposite directions. A platform on which dancing figures stand, surrounded with transparent walls of glass or horn, is fastened to the pivot. Hot air will pass into the tubes and get the dancing figures to revolve.
.7. and .8. Boiler projecting a jet of steam
A statuette of animal activates combustion by blowing on the fire (#74). Main singularity : hot water flows on by adding cold water. Another construction of the same kind can blow a trumpet or make a blackbird sing.
.9. and .10. Altar Libations from a fire
Two figures holding libation bowls stand on an air-tight pedestal filled with fluid (# 11). Inside the figures, tubes are connected to the pedestal:
when a fire is lit, steam pressure in the pedestal pours libations from the bowls. Libations last as long as fire is ignited
Other devices inventied by Hero
Besides "steam engines", 67 other projects for pneumatic machines are present in the Treatise, mainly siphons and pressure pumps, all based on the physical principles of barodynamics. Among them, three projects deserve some comments : ·
.1. Sacrificial vase
flowing only when a five drachmas coin is introduced through a slit in the lid : a distant ancestor to our modern "slot machines" ? (#21) ·
.2. Fire pump
with piston-machinery moved by a rocker-arm pivoting from a center post, thus, the tube leading out of the pump can be moved in all directions : a precursor of modern firemen water-pumps ? (#27)
.3. Pipe organ
activated by a wind mill (#77). This project marks an important milestone in History of mechanics : Watermills were certainly common in Antiquity but very few documents can attest of the presence of windmills in Occident before Medieval times. Many sorts of pipe organs have been devised during Antiquity converting dynamic energy of water into air pressure. An early model, the so-called hydraulis is attributed to an Alexandrian engineer already mentioned, Ctesibius, living in the 3rd century BC. Air supply was usually brought into the pipes, as shown in the famed Mariamine mosaic, by bellow pumps. Heron was quite certainly a precursor when he proposed air-mil as source of air pressure.
Air, breath and “pneuma” during Antiquity
Air, in Ancient Greek, is the wind, the mist or, on a more general level, the atmosphere. It has to be stressed that many medical terms of our times originate from the word "aer", thus, "arteria", "aorta" and "aura". In fact, air is, in Ancient Greek an emanation, a sparkle, a radiance, with a same meaning as our "Grand air", symbol of splendour…
Air, as fire, water and earth, was one of the four traditional elements of Greek mythology, symbolizing the cosmos where all things are and from which all things came. Since the earliest times, mythology often referred to the air :
. Aether, son of Erebus ("Darkness") and of Nyx ("Night"), brother of Hemera ("Day"), was the pure, upper air that gods breathe, as opposed to "aer", which simple mortals breath. Thus, the name given to the “land of sunburned faces”, “Aithiopia”, might suggest some form of celestial fire…
. Aeolus (or Eolus), ("Wind") was a triple divinity : legendary ancestor of the Aeolians, son of Poseidon and descendant of Hippotes who was, according to Homer's Odyssey, "Keeper of the winds".
The concept of "breath" with the meaning of "respiration" holds a great role in Antique medicine : according to Galen, the air, after inspiration, passes through the lungs “to refresh cardiac fire” then goes partly in arteries in form of “pneuma” while another part is rejected in form of hot air.
"Pneuma" meant in early times "blast of air", thus impersonating the function of life with the idea of a subjacent energy, hence the concept of “vital breath”. A clear reference to that meaning is demonstrated in modern medical language with words as "apnea", "hyperpnea" and "dyspnea". The concept of “pneuma”, the "spirit", led to complicated philosophical developments: thus, the rise of a sect, the so-called “pneumatism” regarding "pneuma" as the cause of life and, consequently, of all diseases.
Pneumatic machines in Antiquity
The air as source of energy :a concept from Greek Antiquity but Its use during Antiquity remained limited
. Sailing boats
. Wind machineries : Pneumatic organs, mills
. A wide array of bellows, pumps and engines of all kinds
Slavery left no place in Antiquity for labour-saving machines but pneumatic machines were promised too a bright future as shown, many centuries after, by Arabic and Renaissance construction of fountains, clocks, and all sorts of automated figures. Paradoxical as it may seem, Heron can be seen, instead of Thomas Savery (1650-1715) or Denis Papin (1647-1712), as a precursor of modern steam-machines : Cugnot, steam boats and…jet turbines…
In conclusion, this presentation was mainly intended to give tribute, after many others, to the Knowledge of the Ancients, which, according to Paul Valéry, has been the true "incubator" of our modern times.
“The pneumatics of Heron of Alexandria, from the Greek, translated for and edited by Bennet Woodcroft professor of machinery in University College, London, Taylor Walton and Maberly 1851".
. "Les pneumatiques de Heron d'Alexandrie et de Philonn de Byzance ou L'art des thaumaturges dans l'Antiquité, par Albert de Rochas, ancien membre du Conseil d'instruction de l'Ecole polytechnique, Paris, G. Masson éditeur 1882"
. "Spiritale di Herone Alessandrino ridotti in lingua vulgar da Alessandro Giorgi da Urbino, Printed by brothers Bartholomeo & Simone Ragusi, Urbino, 1592"
. Le livre des appareils pneumatiques et des machine hydrauliques par Philon de Byzance édité d'après les versions arabes d'Oxford et de Constantinople et traduit en français par le baron Carra de Vaux, membre du conseil de la Societé asiatique de Paris. Tire des notices et extraits des manuscrits de la Bibliothèque nationale et autres bibliothèques Tome XXXVIII. Paris Imprimerie nationale . Librairie C. Klincksieck, 11 rue de Lillle Paris 1902
 Ήρων ο Αλεξανδρεύς πνε umαtikωn. “The pneumatics of Heron of Alexandria, from the Greek, translated for and edited by Bennet Woodcroft professor of machinery in University College, London, Taylor Walton and Maberly 1851".
Date de dernière mise à jour : 29/07/2013