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1 Galilei, Galileo
SUBJECT AREA: Photography, film and optics[br]b. 15 February 1564 Pisa, Italyd. 8 January 1642 Arcetri, near Florence, Italy[br]Italian mathematician, astronomer and physicist who established the principle of the pendulum and was first to exploit the telescope.[br]Galileo began studying medicine at the University of Pisa but soon turned to his real interests, mathematics, mechanics and astronomy. He became Professor of Mathematics at Pisa at the age of 25 and three years later moved to Padua. In 1610 he transferred to Florence. While still a student he discovered the isochronous property of the pendulum, probably by timing with his pulse the swings of a hanging lamp during a religious ceremony in Pisa Cathedral. He later designed a pendulum-controlled clock, but it was not constructed until after his death, and then not successfully; the first successful pendulum clock was made by the Dutch scientist Christiaan Huygens in 1656. Around 1590 Galileo established the laws of motion of falling bodies, by timing rolling balls down inclined planes and not, as was once widely believed, by dropping different weights from the Leaning Tower of Pisa. These and other observations received definitive treatment in his Discorsi e dimostrazioni matematiche intorno a due nuove scienzi attenenti alla, meccanica (Dialogues Concerning Two New Sciences…) which was completed in 1634 and first printed in 1638. This work also included Galileo's proof that the path of a projectile was a parabola and, most importantly, the development of the concept of inertia.In astronomy Galileo adopted the Copernican heliocentric theory of the universe while still in his twenties, but he lacked the evidence to promote it publicly. That evidence came with the invention of the telescope by the Dutch brothers Lippershey. Galileo heard of its invention in 1609 and had his own instrument constructed, with a convex object lens and concave eyepiece, a form which came to be known as the Galilean telescope. Galileo was the first to exploit the telescope successfully with a series of striking astronomical discoveries. He was also the first to publish the results of observations with the telescope, in his Sidereus nuncius (Starry Messenger) of 1610. All the discoveries told against the traditional view of the universe inherited from the ancient Greeks, and one in particular, that of the four satellites in orbit around Jupiter, supported the Copernican theory in that it showed that there could be another centre of motion in the universe besides the Earth: if Jupiter, why not the Sun? Galileo now felt confident enough to advocate the theory, but the advance of new ideas was opposed, not for the first or last time, by established opinion, personified in Galileo's time by the ecclesiastical authorities in Rome. Eventually he was forced to renounce the Copernican theory, at least in public, and turn to less contentious subjects such as the "two new sciences" of his last and most important work.[br]Bibliography1610, Sidereus nuncius (Starry Messenger); translation by A.Van Helden, 1989, Sidereus Nuncius, or the Sidereal Messenger; Chicago: University of Chicago Press.1623, Il Saggiatore (The Assayer).1632, Dialogo sopre i due massimi sistemi del mondo, tolemaico e copernicano (Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican); translation, 1967, Berkeley: University of California Press.1638, Discorsi e dimostrazioni matematiche intorno a due nuove scienzi attenenti allameccanica (Dialogues Concerning Two New Sciences…); translation, 1991, Buffalo, New York: Prometheus Books (reprint).Further ReadingG.de Santillana, 1955, The Crime of Galileo, Chicago: University of Chicago Press; also 1958, London: Heinemann.H.Stillman Drake, 1980, Galileo, Oxford: Oxford Paperbacks. M.Sharratt, 1994, Galileo: Decisive Innovator, Oxford: Blackwell.J.Reston, 1994, Galileo: A Life, New York: HarperCollins; also 1994, London: Cassell.A.Fantoli, 1994, Galileo: For Copemicanism and for the Church, trans. G.V.Coyne, South Bend, Indiana: University of Notre Dame Press.LRD -
2 Photography, film and optics
See also: INDEX BY SUBJECT AREA[br]Ding HuanGabor, DennisKlic, KarolLippershey, HansMarton, LadislausTournachon, Gaspard FélixBiographical history of technology > Photography, film and optics
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3 Torricelli, Evangelista
SUBJECT AREA: Photography, film and optics[br]b. 15 October 1608 Faenza, Italyd. 25 October 1647 Florence, Italy[br]Italian physicist, inventor of the mercury barometer and discoverer of atmospheric pressure.[br]Torricelli was the eldest child of a textile artisan. Between 1625 and 1626 he attended the Jesuit school at Faenza, where he showed such outstanding aptitude in mathematics and philosophy that his uncle was persuaded to send him to Rome to a school run by Benedetto Castelli, a mathematician and engineer and a former pupil of Galileo Galilei. Between 1630 and 1641, Torricelli was possibly Secretary to Giovanni Ciampoli, Galileo's friend and protector. In 1641 Torricelli wrote a treatise, De motugravium, amplifying Galileo's doctrine on the motion of projectiles, and Galileo accepted him as a pupil. On Galileo's death in 1642, he was appointed as mathematician and philosopher to the court of Grand Duke Ferdinando II of Tuscany. He remained in Florence until his early death in 1647, possibly from typhoid fever. He wrote a great number of mathematical papers on conic sections, the cycloid, the logarithmic curve and other subjects, which made him well known.By 1642 Torricelli was producing good lenses for telescopes; he subsequently improved them, and attained near optical perfection. He also constructed a simple microscope with a small glass sphere as a lens. Galileo had looked at problems of raising water with suction pumps, and also with a siphon in 1630. Torricelli brought up the subject again in 1640 and later produced his most important invention, the barometer. He used mercury to fill a glass tube that was sealed at one end and inverted it. He found that the height of mercury in the tube adjusted itself to a well-defined level of about 76 cm (30 in.), higher than the free surface outside. He realized that this must be due to the pressure of the air on the outside surface and predicted that it would fall with increasing altitude. He thus demonstrated the pressure of the atmosphere and the existence of a vacuum on top of the mercury, publishing his findings in 1644. He later noticed that changes in the height of the mercury were related to changes in the weather.[br]Bibliography1641, De motu gravium.Further ReadingT.I.Williams (ed.), 1969, A Biographical Dictionary of Scientists, London: A. \& C.Black.Chambers Concise Dictionary of Scientists, 1989, Cambridge.A Dictionary of Scientific Biography, 1976, Vol. XIII, New York: C.Scribner's Sons.A.Stowers, 1961–2, "Thomas Newcomen's first steam engine 250 years ago and the initial development of steam power", Transactions of the Newcomen Society 34 (provides an account of his mercury barometer).W.E.Knowles Middleton, 1964, The History of the Barometer, Baltimore.RLHBiographical history of technology > Torricelli, Evangelista
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4 Huygens, Christiaan
SUBJECT AREA: Horology[br]b. 14 April 1629 The Hague, the Netherlandsd. 8 June 1695 The Hague, the Netherlands[br]Dutch scientist who was responsible for two of the greatest advances in horology: the successful application of both the pendulum to the clock and the balance spring to the watch.[br]Huygens was born into a cultured and privileged class. His father, Constantijn, was a poet and statesman who had wide interests. Constantijn exerted a strong influence on his son, who was educated at home until he reached the age of 16. Christiaan studied law and mathematics at Ley den University from 1645 to 1647, and continued his studies at the Collegium Arausiacum in Breda until 1649. He then lived at The Hague, where he had the means to devote his time entirely to study. In 1666 he became a Member of the Académie des Sciences in Paris and settled there until his return to The Hague in 1681. He also had a close relationship with the Royal Society and visited London on three occasions, meeting Newton on his last visit in 1689. Huygens had a wide range of interests and made significant contributions in mathematics, astronomy, optics and mechanics. He also made technical advances in optical instruments and horology.Despite the efforts of Burgi there had been no significant improvement in the performance of ordinary clocks and watches from their inception to Huygens's time, as they were controlled by foliots or balances which had no natural period of oscillation. The pendulum appeared to offer a means of improvement as it had a natural period of oscillation that was almost independent of amplitude. Galileo Galilei had already pioneered the use of a freely suspended pendulum for timing events, but it was by no means obvious how it could be kept swinging and used to control a clock. Towards the end of his life Galileo described such a. mechanism to his son Vincenzio, who constructed a model after his father's death, although it was not completed when he himself died in 1642. This model appears to have been copied in Italy, but it had little influence on horology, partly because of the circumstances in which it was produced and possibly also because it differed radically from clocks of that period. The crucial event occurred on Christmas Day 1656 when Huygens, quite independently, succeeded in adapting an existing spring-driven table clock so that it was not only controlled by a pendulum but also kept it swinging. In the following year he was granted a privilege or patent for this clock, and several were made by the clockmaker Salomon Coster of The Hague. The use of the pendulum produced a dramatic improvement in timekeeping, reducing the daily error from minutes to seconds, but Huygens was aware that the pendulum was not truly isochronous. This error was magnified by the use of the existing verge escapement, which made the pendulum swing through a large arc. He overcame this defect very elegantly by fitting cheeks at the pendulum suspension point, progressively reducing the effective length of the pendulum as the amplitude increased. Initially the cheeks were shaped empirically, but he was later able to show that they should have a cycloidal shape. The cheeks were not adopted universally because they introduced other defects, and the problem was eventually solved more prosaically by way of new escapements which reduced the swing of the pendulum. Huygens's clocks had another innovatory feature: maintaining power, which kept the clock going while it was being wound.Pendulums could not be used for portable timepieces, which continued to use balances despite their deficiencies. Robert Hooke was probably the first to apply a spring to the balance, but his efforts were not successful. From his work on the pendulum Huygens was well aware of the conditions necessary for isochronism in a vibrating system, and in January 1675, with a flash of inspiration, he realized that this could be achieved by controlling the oscillations of the balance with a spiral spring, an arrangement that is still used in mechanical watches. The first model was made for Huygens in Paris by the clockmaker Isaac Thuret, who attempted to appropriate the invention and patent it himself. Huygens had for many years been trying unsuccessfully to adapt the pendulum clock for use at sea (in order to determine longitude), and he hoped that a balance-spring timekeeper might be better suited for this purpose. However, he was disillusioned as its timekeeping proved to be much more susceptible to changes in temperature than that of the pendulum clock.[br]Principal Honours and DistinctionsFRS 1663. Member of the Académie Royale des Sciences 1666.BibliographyFor his complete works, see Oeuvres complètes de Christian Huygens, 1888–1950, 22 vols, The Hague.1658, Horologium, The Hague; repub., 1970, trans. E.L.Edwardes, AntiquarianHorology 7:35–55 (describes the pendulum clock).1673, Horologium Oscillatorium, Paris; repub., 1986, The Pendulum Clock or Demonstrations Concerning the Motion ofPendula as Applied to Clocks, trans.R.J.Blackwell, Ames.The balance spring watch was first described in Journal des Sçavans 25 February 1675, and translated in Philosophical Transactions of the Royal Society (1675) 4:272–3.Further ReadingH.J.M.Bos, 1972, Dictionary of Scientific Biography, ed. C.C.Gillispie, Vol. 6, New York, pp. 597–613 (for a fuller account of his life and scientific work, but note the incorrect date of his death).R.Plomp, 1979, Spring-Driven Dutch Pendulum Clocks, 1657–1710, Schiedam (describes Huygens's application of the pendulum to the clock).S.A.Bedini, 1991, The Pulse of Time, Florence (describes Galileo's contribution of the pendulum to the clock).J.H.Leopold, 1982, "L"Invention par Christiaan Huygens du ressort spiral réglant pour les montres', Huygens et la France, Paris, pp. 154–7 (describes the application of the balance spring to the watch).A.R.Hall, 1978, "Horology and criticism", Studia Copernica 16:261–81 (discusses Hooke's contribution).DV -
5 Neri, Antonio Ludovico
[br]b. 29 February 1576 Florence, Italyd. 1614 Florence, Italy[br]Italian glassmaker.[br]Neri entered the Church and by 1601 was a priest in the household of Alamanno Bertolini in Florence. There he met the Portuguese Sir Emanuel Ximenes, with whom he shared an interest in chemistry. The two later corresponded and the twenty-seven letters extant from Ximenes, who was living in Antwerp, are the main source of information about Neri's life. At the same time, Neri was working as a craftsman in the Medici glasshouse in Florence and then in their works at Pisa. These glasshouses had been flourishing since the fifteenth century with the help of Muranese glassmakers imported from Venice. Ximenes persuaded Neri to spend some time with the glassmakers in Antwerp, probably from 1603/4, for the correspondence breaks off at that point. A final letter in March 1611 refers to Neri's recent return to Florence. In the following year, Neri published the work by which he is known, the L'arte vetraria, the first general treatise on glassmaking. Neri's plan for a further book describing his chemical and medical experiments was thwarted by his early death. L'arte belongs to the medieval tradition of manuscript recipe books. It is divided into seven books, the first being the most interesting, dealing with the materials of glassmaking and their mixing and melting to form crystal and other colourless glasses. Other sections deal with coloured glasses and the making of enamels for goldsmiths' use. Although it was noted by Galileo Galilei (1564–1642), the book made little impression for half a century, the second edition not appearing until 1661. The first Venice edition came out two years later, with a second in 1678. Due to a decline in scientific activity in Italy at this time, L'arte had more influence elsewhere in Europe, especially England, Holland and France. It began to make a real impact with the appearance in 1662 of the English translation by Christopher Merrett (1614–95), physician, naturalist and founder member of the Royal Society. This edition included Merrett's annotations, descriptions of the tools used by English glassmakers and a translation of Agricola's short account of glassmaking in his De re metallica of 1556. Later translations were based on the Merrett translation rather than the Italian original. Ravenscroft probably used Neri's account of lead glass as a starting point for his own researches in the 1670s.[br]Bibliography1612, L'arte vetraria, 7 vols; reprinted 1980, ed. R.Barovier, Milan: Edizioni Polifilo (the introd., in Italian, England and French, contains the most detailed account of Neri's life and work).LRD
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