Scientific Instruments

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SCIENTIFIC INSTRUMENTS

SCIENTIFIC INSTRUMENTS. The early modern period saw the use of devices both to advance scientific research (such as the telescope and the microscope) and those of a more practical nature that embodied scientific knowledge (such as the astrolabe and the thermometer). Because scientific instruments are typically made by specialized craftsmen who produce improvements in design and effectiveness through technical means, their production may also be considered as a discrete technology.

Although in the Middle Ages there had been specialized craftsmen who made astrolabes and, later, clocks, the emergence of a specialized craft for the production of a line of scientific instruments with distinct functions first emerged (in England, at least) in the 1540s, in response to the need for more accurate measurement in navigation, surveying, and astronomy. In England, the multiple forces of population growth, agricultural expansion, and, later, the draining of The Fens, stimulated the development of professional surveying, which required instruments for making angular measurements. The age of discovery, moreover, expanded the market for navigational instruments at a time when the "lunar distance" method (involving difficult observations of the distance between the Moon and a designated star, the use of tables, and calculation) was the predominant method of navigation. At the same time, in the course of the sixteenth century, practical mathematics was developed and then diffused in printed manuals. The primary measurements involved in describing the use of such instruments themselves required instrumentation, as did the mathematical manipulation of observations made by using such manuals. The emergence of a scientific-instrument craft in the 1540s was the result of the interaction of all of these factors.

THE TELESCOPE

Once eyeglasses came into common usage toward the end of the thirteenth century, it was just a matter of time until two such lenses were combined to produce either a telescope or a microscope. That insight, however, took quite a long time to realize. The telescope is first documented in Holland in the fall of 1608, when at least three different craftsmen, including a maker of spectacles, were manufacturing them. Because the principles involved were widely known, the telescope is a good example of invention appearing simultaneously in different places. Galileo Galilei heard of the Dutch instruments by the summer of 1609 and made his own version, with a diverging eye lens and a converging (convex) object lens. These early examples had magnifications of two or three, but within a year Galileo, who ground his own lenses, achieved magnifications of twenty and thirty and objectives with increasingly long focal lengths. The Englishman Thomas Harriot heard of the Dutch instruments in the same period and was drawing maps of the Moon in August 1609, before Galileo's most significant research had begun. Galileo published his first telescopic results in March 1610 in his famous Sidereus nuncius (Starry messenger) and by the end of the year Johannes Kepler had published two little books on the results of telescopic research, without having done any yet himself. (Kepler's contribution was a telescope with both eyepiece and objective converging, which made it possible to create a real, though inverted, image and project it onto a screen beyond the ocular, which became the normal way of observing the Sun.) As is frequently the case with recognizably important inventions (the automobile, the airplane), the invention and innovation of the telescope caused a quickening of communication among scientists and stimulated simultaneous excitement in countries widely removed from one another.

Galileo's earliest telescope observations—of the lunar landscape, the satellites of Jupiter, and the Milky Way—caused a sensation. The satellites of Jupiter, moreover, revealed that Earth was not the only planetary center of rotation, which worked against Aristotelian cosmology and in favor of that of Nicolaus Copernicus, as did Galileo's subsequent description of the phases of Venus. The discovery of sunspots also contradicted the Aristotelian axiom of the unchangeable nature of celestial bodies. In the hands of Galileo alone, the telescope changed the nature of planetary astronomy, both how it was conceptualized and how it was observed.

One of the problems of early telescopes was that the objective caused the images to appear with extraneous colors. The solution was the achromatic lens, developed in England in the 1730s. To avoid such coloring and other distortions, seventeenth-century telescopes had very small apertures and long focal lengths. The eventual solution was a two-component objective, with two lenses of different density in contact with one another, worked out by Parisian craftsmen in 1763, and then by John Dolland in England. This was the most popular telescope until William Herschel (1738–1822), toward the end of the century, invented a reflecting telescope with a large mirror that made possible the gathering of enough light to be able to examine much fainter celestial objects.

The telescope's impact was sudden, immense, and rippled across the length and breadth of cultures, affecting scientific theory and method, of course, but also theology, philosophy, literature, and art. In particular, Galileo's depiction of a jagged, rough, and crater-pocked lunar surface threatened a whole range of entrenched cultural conventions, including the Aristotelian perfection of heavenly bodies and the pure, diaphanous quality of the Moon, which was theologically associated with the purity of the Immaculate Virgin. Galileo himself had had training in art and interacted with artists, many of whom had observed the Moon telescopically with reference to specific paintings. Ever since Plutarch wrote his essay on the face that seemingly appeared on the Moon's surface, it had been common to refer to the lunar facade as similar to the surface of a painting, and in the seventeenth century writers conventionally likened the dark and light sides of the Moon to painted pigments. The Virgin was, for theological reasons, conventionally painted in the presence of a crystalline moon. In his Inmaculada of 1619, Diego Velázquez depicted the Virgin standing on a textured moon, the image he had almost certainly seen for himself through a telescope in Seville.

THE MICROSCOPE

The success of the telescope and consequent diffusion of its optical principles led quickly to the appearance of the first compound microscopes between 1612 and 1618. Galileo himself had one, but until the second half of the seventeenth century they seem to have been more a curiosity than an active research tool. The main technical problems of microscopes were to illuminate the substance under observation effectively and to produce a small lens that could provide a sharp image. Large magnifications tended to yield blurry images. Microscopy really got under way with the publication of Robert Hooke's Micrographia (1665) and Jan Swammerdam's general history of insects in 1669. In the early 1670s they were joined by contributions from Marcello Malpighi (1628–1694) and Antoni van Leeuwenhoek (1632–1723).

The earliest microscopes looked like telescopes: the lenses were set in wooden rings mounted on the ends of cardboard tubes, the one that held the ocular fitting inside the tube with the objective. Hooke used a compound microscope with a double-convex lens objective and a complicated three-lens eyepiece. By this time, however, improvements in grinding techniques had produced simple microscopes with much higher powers of magnification, the kind used by Leeuwenhoek. Sold in large numbers at the end of the seventeenth century, this was the instrument that popularized microscopy.

NAVIGATIONAL, SURVEYING, AND PRACTICAL INSTRUMENTS

In the late Middle Ages and early modern times, the so-called mariner's astrolabe was used for telling time: by lining up the site with the Sun the user could read the time of day directly from a dial on the instrument. But the device had no use in practical navigation. The most common nautical instruments were the cross-staff, the back-staff, and the quadrant, reasonably simple handheld devices for measuring the altitude of stars but which could not easily be used to measure the angle between two stars from a moving boat. These instruments were all abandoned in the 1770s, replaced by John Hadley's reflecting quadrant, or octant, which eventually gave rise to the sextant, still in use today. With it, the navigator could bring the Moon's reflection down to the horizon, where the image would remain immovable, no matter how violently the ship was rolling.

Folding rules could be used by surveyors, gunners, or carpenters for small-scale plotting of terrain, or to estimate heights and depths, and were engraved with useful information like timber and board measures. A sector was a jointed rule with two radial arms engraved with a graduated scale. With the invention of logarithms (1614), the sector gave rise to the slide rule. Such ruled instruments were only as accurate as their graduations. Various methods of graduation, constantly improved, such as subdividing a scale by transverse lines that could be read to the one-hundredth part of quite small units, depending on the quality of the engraving, allowed the direct reading of angles, to an accuracy of five or ten seconds. Such graduation schemes became increasingly geometrical in the course of the eighteenth century and finally machines were devised for engraving linear scales.

There were also instruments of a practical nature designed to be carried by ordinary citizens. One such was the compendium, a pocket-sized brass gadget made for personal use that typically included an equinoctial sundial, religious calendars, a table of latitudes, a magnetic compass, a nocturnal (to determine time at night), a tide computer, and a table for establishing ports.

PHYSICAL INSTRUMENTS

Thermometers based on a variety of principles and materials were built as curiosities in the seventeenth century. It was not until the German physicist Daniel Gabriel Fahrenheit began to use mercury systematically in the 1720s that the thermometer design stabilized, even though competing models used other kinds of liquid. Most used alcohol, which was cheaper, but the reading of the scale varied with the concentration of alcohol. The Fahrenheit thermometer (with two fixed points, the freezing [32°] and boiling [212°] points of water, respectively) was adopted in England, Germany, and the Netherlands; France used René-Antoine Ferchaulte de Réaumur's scale, where 0° was the freezing point of water.

Robert Hooke devised a barometer to measure atmospheric pressure based on the variation of a column of mercury; Christiaan Huygens made a similar model but, following an idea of René Descartes, it used two liquids, mercury and water. The only barometer widely used around 1700 was that of Evangelista Torricelli, a tube plunged into a container of mercury. At issue was how to achieve consistent variations in the height of the mercury column, how best to contain the mercury, and what kind of scale could be devised (in the end, a metal casing placed around the glass tube bore the graduation marks). The hygrometer, to measure humidity, presented similar difficulties. The problem was to find an appropriate substance that was sturdy yet suitably sensitive to humidity. Finally, around 1783, Horace-Bénédict de Saussure perfected a model in which a hair held by a clamp at one end was attached at the other to a silver thread which, as it wound around a horizontal axis, caused a pointer to move across a 360° graduated dial. In the case of all three of these instruments, there was a century-long process whereby scientists devised workable instruments through the trial-and-error methods of empirical craftsmen.

ELECTRICAL MACHINES

Benjamin Franklin's discoveries made electrical machines and demonstrations fashionable after 1750. A variety of machines featuring the production of electrical current with a hand crank were made in the first half of the eighteenth century; but they were not generally produced until the English instrument maker Jesse Ramsden's plate machine of 1766, which was equipped with an electrometer to measure the charge produced. Subsequently, all such machines had electrometers because they were useful in measuring the shock applied to patients undergoing electric-shock therapy. Such machines could be connected to Leyden jars serving as batteries.

SPECIALIZED WORKSHOPS

Specialized workshops making and selling scientific instruments proliferated in England and in France in the eighteenth century. Some of the earlier ones specialized either in navigational or surveying instruments, on the one hand, or physical instruments, especially barometers, on the other. The first large instrumentation workshop in England was that of George Adams founded in 1735, identified by a sign of Tycho Brahe's head in Fleet Street, London. Brahe (1546–1601), of course, was a pre-telescopic astronomer famous for his design and use of huge, finely calibrated observational instruments using the unaided eye alone, and thus became an apt symbol for the craft of instrumentation. Microscopes were Adams's specialty, as well as mathematical instruments of all types. John and Peter Dolland, father and son, opened an optical shop in London in 1752. The Dollands made quadrants, telescopes, and other observational instruments in large numbers. Of all the English instrument makers of the period, Jesse Ramsdem (1735–1800) was said to be the best mechanician and optician. He was famous for large-scale astronomical and geodesic instruments, built telescopes for European observatories, and was elected a fellow of the Royal Society. In Holland, Jan van Musschenbroek, himself an important popularizer of Newtonian physics, had a famous workshop (in which he made instruments for his brother Pieter), as did Fahrenheit, a German born in Danzig who lived and worked in Amsterdam. Fahrenheit specialized in glass instruments, particularly the thermometer whose scale he established, and the barometer.

In France, the great instrument makers of the late eighteenth century tended to work for institutions. The Mégniés (probably two brothers) were associated with the Academy of Sciences, where they built chemical apparatuses for Antoine-Laurent Lavoisier (1743–1794), as well as telescopes and other optical instruments. Étienne Lenoir (1822–1900) worked mainly for the Weights and Measures Commission, where he built the apparatus that French expeditionaries used to measure the meridian.

INSTRUMENTS AND IMPERIAL RIVALRIES

As the expeditions sent out by European powers to the Pacific came increasingly to focus on scientific matters, they began to take on the guise of floating laboratories, equipped with instrument collections that increased in size with each succeeding expedition. In the last quarter of the eighteenth century, numerous expeditions tested the marine chronometer devised by John Harrison (1693–1776) for the determination of longitude at sea. The instrument was a matched set of clocks, one set to the prime meridian, the other to local time. The difference in hours multiplied by fifteen yields the degree of longitude. On his 1772–1775 voyage, Captain James Cook tested four English chronometers, one by Harrison and three by John Arnold. He quickly determined that with accurate chronometers longitude could be determined within 1.5 degrees of accuracy, and more importantly, he let it be known publicly that he was abandoning the complex and tedious "lunar distance" method for determining longitude in favor of chronometers.

The role that scientific instrumentation played in imperial rivalries of the late eighteenth century can be appreciated in the provisioning of the expedition that the Italian captain Alessandro Malaspina led for the Spanish crown between 1782 and 1794. For the procuring of scientific instruments, the Spanish navy had an agent in London and another in Paris. The instrument makers were anxious to place their wares on spectacular expeditions such as the one being planned, because the performance of the instruments was highly publicized after the voyage in the string of memoirs by officers and naturalists sure to follow. Malaspina carried seven sets of chronometers, four made by Arnold and three by Ferdinand Berthoud. Alexander Dalrymple, who supplied Malaspina with English instruments, had close connections with Arnold's shop, as a result of which Malaspina offered to provide Arnold with systematic comparisons of the longitude results given by Arnold's instruments and those obtained simultaneously by astronomical methods. In this way, detailed field results were fed back to the manufacturer, who could then make the necessary corrections in future models. Malaspina's judgment was that an Arnold chronometer was the best of the six, a Berthoud almost as good; the others ran too fast. The rest of Malaspina's apparatus was heavily English: an astronomical pendulum invented by George Graham, two Dolland achromatic telescopes with triple objectives, and thermometers from the houses of Nairne and Blunt, respectively.

INSTRUMENT COLLECTIONS

As a result of the scientific revolution, collections of scientific instruments emerged in all of the centers of the Western world. Some collections were formed at universities and other teaching institutions for didactic purposes; others fulfilled the whims of wealthy scientific amateurs. Popularizers of Isaac Newton, who diffused the results of the scientific revolution in public lectures in the early eighteenth century, required a large number of instruments with which to conduct experiments or illustrate scientific principles during their presentations. The prototypes of much of this Newtonian demonstration apparatus were built by Pieter van Musschenbroek at the request of Willem J. s'Gravesande. The entire collection, including pulleys, weights, pendulums, pumps, and machines for illustrating specific concepts of physics is still preserved in Holland. In the second half of the eighteenth century, electrical apparatus was added to the repertory of demonstration equipment. The reputation of lecturers on physics depended in great part on the quality of their apparatus. Instrumentation became so expensive that private institutions like the Royal Society were dependent on patrons to supply them with instruments. The collection of the German counts of Hesse in the early eighteenth century had 57 telescopes and 32 microscopes. To own such instruments was a mark of culture. The collection of the kings of France at Versailles contained 245 instruments, including 52 pieces of electric apparatus, at the time of its confiscation during the French Revolution. In Madrid, the Spanish crown established in 1791 a Royal Machine Museum (Real Gabinete de Máquinas), a collection of 270 models of different kinds of machines. Private collectors of the same period, whose collections we know through inventories included in their wills, inevitably owned electrical machines and air pumps. Franklin's experiments had made the former a symbol of scientific progress, and air pumps, as a kind of prototypical machine, though of a size manageable for demonstrations, were a convenient symbol of the incipient industrial revolution and could be used to run a multiplicity of experiments.

See also Astronomy ; Barometer ; Biology ; Brahe, Tycho ; Chronometer ; Copernicus, Nicolaus ; Galileo Galilei ; Hooke, Robert ; Huygens Family ; Lavoisier, Antoine ; Malpighi, Marcello ; Optics ; Scientific Revolution ; Shipbuilding and Navigation ; Surveying .

BIBLIOGRAPHY

Bradbury, S. The Evolution of the Microscope. Oxford and New York, 1967.

Daumas, Maurice. Scientific Instruments of the Seventeenth and Eighteenth Centuries and Their Makers. Translated and edited by Mary Holbrook. London, 1989.

Glick, Thomas F. "Imperio y dependencia científica en el XVIII español e inglés: La provisión de los instrumentos científicos." In Ciencia, vida y espacio en Iberoamerica, edited by José L. Peset, vol. 3, pp. 49–63. Madrid, 1989.