Hero of Alexandria

Egyptian scientist and inventor

• Born: Before 62
• Birthplace: Alexandria, Egypt
• Died: c. 100
• Place of death: Alexandria, Egypt

Hero wrote about mechanical devices and is the most important ancient authority on them. Some of these were his own inventions, including a rudimentary steam engine and windmill. He also investigated mathematics, where his most noted contribution was a method for approximating square roots.

Early Life

Virtually nothing is known about the personal life of Hero (HEE-roh), also known as Heron, of Alexandria, other than the fact that an eclipse of the moon visible from Alexandria and mentioned in one of his books occurred in 62 c.e. Under the Roman Empire, Alexandria flourished somewhat less than it had under the Ptolemies, but the famous museum was still a center of research and learning where scientists and philosophers were active. Technology also continued to make amazing strides, so that Hero found an atmosphere conducive to his own theories and inventions. His writings show that he was an educated man, familiar with Greek, Latin, Egyptian, and even Mesopotamian sources, and reveal a wide-ranging mind unusual for his time. There is no indication that he worked for either a Roman patron or the Roman government.

Life’s Work

Hero’s greatest renown results from the fact that many of his writings on mechanics and mathematics are extant. The mechanical works include the two-volume Pneumatica (The Pneumatics of Hero of Alexandria, 1851), on devices operated by compressed air, steam, and water; Peri automatopoietikes (Automata, 1971), on contrivances to produce miraculous appearances in temples; the three-volume Mechanica, surviving in Arabic, on weight-moving machines; Dioptra (partial English translation, 1963), on instruments for sighting and other purposes; Catoptrica (surviving in Latin), on mirrors; and two artillery manuals, Belopoeïca (English translation, 1971) and Cheiroballistra (English translation, 1971), on different types of catapults. Missing are other works on weight-lifting machines (Baroulkos, which might be a name for part of Mechanica), water clocks, astrolabes, balances, and the construction of vaults.

Of his mathematical treatises, there exist the three-volume Metrica, on the measurement and division of surfaces and bodies, and Definitiones, on geometrical terms. There are other works, more or less heavily edited by later redactors, such as Geometrica, Stereometrica, and Peri metron (also known as Mensurae), all treatises on measurement, as well as Geodaesia and Geoponica or Liber geeponicus, on the measurement of land. A commentary on Euclid is represented by extensive quotations in the Arabic work of an-Nairīzī.

The contents of Hero’s mechanical works reveal the state of technological knowledge during the early Roman Empire, reflecting the heritage of the Hellenistic period and Ptolemaic Alexandria in particular. Later writers referred to him as “the mechanic” (ho mechanikos). In most cases, he gives the best or most complete description extant of ancient machines. In Mechanica, he gives attention to the simple machines—lever, pulley, wheel and axle, inclined plane, screw, and wedge—but he goes on to present others, there and in his other books, that are more complex.

Devices described by Hero include a machine for cutting screw threads on a wooden cylinder; a syringe; an apparatus for throwing water on a fire by hydraulic pressure, which is produced by a two-cylinder force pump (designed by the earlier Alexandrian mechanic, Ctesibius); and the odometer, for measuring distances by a wheeled vehicle. Of value to scholars, there was a pantograph for enlarging drawings and an automatic wick-trimmer for lamps. Hero provides a careful account of the diopter, a sighting instrument used in surveying and astronomy that contains sophisticated gears.

The automata mentioned by Hero are of fascinating variety, including singing birds, drinking animals, hissing serpents, dancing bacchants, and gods such as Dionysus and Hercules performing various actions. Some of these were activated by lighting a fire on an altar or pouring libations into a container, and their effect on worshipers when seen in temples can be imagined. Hero also described coin-operated machines to dispense holy water, a sacred wand that whistled when dipped into water, and a device powered by heated air that would open temple doors without any visible human effort. In order to invent such a device, Hero had to recognize that a vessel containing air was not empty but contained a substance that could exert force, a fact that he clearly explained in The Pneumatics. His demonstration depends on the observation that water will not enter a vessel filled with air unless the air is allowed to escape. He also was aware that air is compressible, which he said was the result of its being made up of particles separated by space.

The nonproductive character of some of the inventions just mentioned has led some modern critics to call Hero’s technology impractical, but he also described demonstrably useful machines. Cranes, which could be used to lower actors portraying gods into theaters (the famous deus ex machina), also were available to help in heavy construction. There were other weight-lifting machines utilizing gears. Cogs and gears were highly developed even before Hero’s day, as archaeological evidence such as the Antikythera Machine, a calendrical, mechanical analogue computer retrieved from the Aegean Sea, demonstrates. Hero also described a twin screw press. He knew the use of compound pulleys, winches, and cogwheels interacting with screws. Not merely theoretical, his catapults were effective in war, particularly in siege operations. There was also the gastraphetes, or “belly shooter,” a kind of crossbow.

Hero’s most famous invention was a prototype steam engine called the aeolipile. A free-spinning, hollow sphere was mounted on a pipe and bracket on the lid of a boiling vessel. Steam from the vessel came up through the pipe and escaped through open, bent pipes on the sphere’s surface, causing the sphere to rotate. Less often remarked upon but also significant is his windmill, used to work the water pump of a musical organ. Both of these show that Hero recommended harnessing sources of power that were not actually exploited until centuries later. In the form in which he presented them, to be sure, these engines were extremely inefficient, and the industrial processes of the first century might not have allowed improvement to the point where they could have been widely used.

In mathematics, Hero emphasized pragmatic applications rather than pure theory. For example, he showed methods of approximating the values of square and cube roots. In his writings on geometry, he followed Euclid closely, making only minor original comments or improvements. The first book of Peri metron deals with the mensuration of plane and solid figures, and the second explains the ways to calculate the volumes of various solids. The third explains problems of the division of plane and solid figures.

Significance

Hero of Alexandria looms large in the history of ancient technology because a considerable portion of his writings on mechanics still exists, while little else on the subject survives from the Greek and Roman world. He preserved much information that came to him from earlier writers whose works have been lost, and his own contribution has been downgraded by some modern scholars because it is unclear how much he owes to previous writers, including Archimedes, Strato of Lampsacus, Philon of Byzantium, and especially Ctesibius of Alexandria. This tendency is probably unfair, however, as his work reflects a systematic mind and tireless research. Moreover, some of his ideas, such as the harnessing of steam and wind power, were clearly ahead of their time.

Although he was interested in the principles of mechanics, Hero was not primarily a theoretician. His mechanics and his mathematics are presented in a way that would have made them useful to the practical engineer of his day. For example, in Stereometrica, he shows how to calculate the number of spectators a theater would hold and the number of wine jars that could be stacked in the hold of a ship of a certain size. Both are approximations intended for utilitarian needs.

Hero’s writings were prized by later authors. Both Pappus of Alexandria (fourth century c.e.) and Proclus (fifth century) quoted from his works. Some of his works were translated and preserved by learned Arabs, and an-Nairīzī commented extensively on Hero’s critique of Euclid. Four of Hero’s shorter books on mechanics were published in Paris in 1693, and interest in Hero accelerated with the Industrial Revolution. In the twentieth century, he continued to receive attention, in histories of mechanics and mathematics.

Bibliography

Drachmann, Aage Gerhardt. The Mechanical Technology of Greek and Roman Antiquity: A Study of the Literary Sources. Madison: University of Wisconsin Press, 1963. Contains translations of Hero’s mechanical writings, with useful running commentary. Also including sections from Vitruvius and Oreibasios, this book gives a clear idea of the written evidence for ancient mechanical technology.

Heath, Thomas. A History of Greek Mathematics. 2 vols. New York: Dover, 1981. Volume 2 includes an excellent, detailed chapter on Hero’s mathematical achievements.

Landels, John G. Engineering in the Ancient World. Berkeley: University of California Press, 2000. Hero is discussed in the context of the development of technology, and Landels provides a useful brief treatment of Hero and his major writings in the final chapter.

Marsden, E. W. Greek and Roman Artillery: Technical Treatises. Oxford, England: Clarendon Press, 1971. This book includes the texts and translation of Hero’s two works on war machines, Belopoïeca and Cheiroballistra, with illuminating diagrams and helpful notes and commentary.

Singer, Charles Joseph, ed. From the Renaissance to the Industrial Revolution, c. 1500-c. 1750. Vol. 3 in A History of Technology. Oxford, England: Clarendon Press, 1954-1984. Despite its title, volume 3 contains an informative section on Hero’s diopter.