Absolute Zero and the Conquest of Cold (6 page)

T
HE CAPSULE VERSION OF SCIENCE HISTORY
holds that in a stroke of genius, Galileo invented the thermometer in 1592. The real story is more complicated. In northern Italy just then, people were touting the wonders of a J-shaped tube, closed at one end and filled with water that rose and fell during the day like the tides of the sea, the movement supposedly influenced by the moon. A
scherzo,
a trick, Galileo fumed, and set out to show what actually moved the water—rising and falling temperature. Half-filling a narrow-necked glass flask with colored water, he suspended it upside down in a bowl of more colored water; when the temperature went up or down, the air contained in the bulb expanded or contracted, moving the column of water in the neck down or up.

Galileo's device was not a thermometer—it was a thermoscope, which records the presence of heat but lacks a scale to measure relative heat. Moreover, he may not have designed the thermoscope on his own but instead appropriated a device from Santorio, a colleague and professor of medicine at Padua. Both men may have been attempting to reproduce a demonstration made by Hero of Alexandria in the first century
A.D.,
itself modeled on work by Philo of Byzantium in the third century
B.C.
Documents show that Galileo had read a 1589 Italian translation of Hero's
Pneumatics.

A great deal more about heat and cold awaited discovery, and as Bacon wrote, "It would be the height of folly—and self-defeating—to think that things never heretofore done can be accomplished without means never heretofore tried." In this history the artificer has had his day; and the natural philosopher; and the dogged experimentalist. Now it was time for the instrument maker to provide the "means never heretofore tried," equipment to enable would-be explorers of the far extremes of temperature to travel further, learn more, and accomplish "things never heretofore done."

Seventeenth-century natural philosophers had mathematical dreams. Those who yearned to better understand the heat and cold wanted to subject them to mathematical analysis. What was the relationship between the temperatures of melting ice and of boiling water? Precisely how much colder was ice than snow? How hot did dry wood have to become before it burst into flame?

Thermoscopes could not answer these questions, but an attached mathematical scale might give some answers, depending on the reliability of the power moving an indicator up and down the scale. Friends touted to Galileo the 1598
perpetuum mobile
of Cornelis Drebbel, believed to rely for its motion on the expansion and contraction of air. Galileo's first true thermometer, made in the first decade of the seventeenth century, used heated air to move the indicator, a fact that made some later writers ascribe the invention of the thermometer to Drebbel. There is not much to that claim, since other contemporary thermometers also used heated air. A stronger attribution for the invention of the thermometer can be made for Santorio. He published an important commentary that reproduced the attempt by the Greek physician Galen in the second century
A.D.
to measure heat and cold along a scale, and he provided his own design for a thermometer to the instrument maker Sagredo, who constructed several of them and then wrote excitedly to his teacher Galileo about using them to discover "marvelous things, as, for example, that in winter the air may be colder than ice or snow; that the water just now appears colder than the air; that small bodies of water are colder than large ones."

Sagredo's note to Galileo confirms that the near borders of the country of the cold had never before been accurately mapped, because prior to this moment, no one could prove that winter air was physically colder than ice or snow.

Although these first thermometers did have a scale, to glean more useful information scientists required a better scale, one whose divisions denoted intervals that had meaning and that showed the temperature in relation to one or more fixed reference points. What intervals should be used? What points could be designated as fixed? If there was a zero, where in the scale should it be put? And what would that zero signify? Would thermometer A in location B always give readings comparable to those obtained from thermometer C in location D?

Those questions had to wait for answers until the solution of the motive-power problem. In the 1640s, when Otto von Guericke in Germany, Boyle in England, and Evangelista Torricelli in Italy proved that air pressure varies with a location's height above sea level and with changing weather conditions, the use of air as a motive power in an open thermometer had to be abandoned. Grand Duke Ferdinand II and his Accademia del Cimento in Florence took up the problem of what motive power to substitute for open air in a thermometer.

Like the Royal Society in London and the Académie des Sciences in Paris, the Accademia del Cimento was founded by distinguished experimenters and had highborn patronage. The Accademia lasted a mere ten years, though, and perhaps because of its short life it has not been invested with the same reverence by later generations—but it was crucial to the history of thermometers. It was an institution devoted to experimentation, as evidenced by its name, translated as the "academy of the concrete" or the "academy of experiments," and by its motto,
Provando e Riprovando,
"proving and proving again." The father of Ferdinand II and of Leopold Medici had been a student of Galileo's, and the sons were fascinated by the work of Torricelli; those ideals translated into their installing facilities for the use of ten scientists in the Pitti Palace in Florence in the late 1650s. The Medicis' Accademia flourished at a moment when the imprimatur of a scientific institution could have the greatest influence on the exploration of the cold, by influencing the acceptance of its critical tools over those produced by other groups.

In contrast to the English and French patrons of science, the Medicis were actively involved in the institution's experimental work. Ferdinand was a corpulent man with a bulbous nose and a black mustache whose ends rose up toward his eyes. "The grand duke is affable with all men, easily moved to laughter and ready with a jest," a contemporary account stated. One of his heartaches was his inability to interest his son in scientific work; the "melancholy" teenager exhibited "the symptoms of a singular piety" that dismissed experimentation as incompatible with religious faith. Ferdinand's brother Leopold was quite devout, but that did not prevent him from being a serious scientist. He spent four hours a day reading books on literature, geography, science, architecture, and general curiosities; it was said that, like a little boy with a piece of bread, Leopold always kept "a book in his pocket to chew on whenever he [had] a moment to spare."

The Accademia shared with the Royal Society the goal of discrediting the pseudoscience of Aristotle's followers. The Medicis corresponded with the Royal Society, and they employed a secretary to carefully note the Accademia's experiments on the incompressibility of water, the gravity of bodies, and the electrical properties of metals and liquids. But mostly the men in the Pitti Palace addressed the task of making more capable and subtler measuring implements of every sort then in use—barometers, hygrometers, telescopes (Ferdinand ground his own lenses), astrolabes, quadrants, calorimeters, microscopes, magnetic devices, and thermometers. One visitor reported seeing "weather glasses" (barometers or thermometers) even in the grand duke's bedchamber, and another marveled at thermometers displayed as works of art rather than as implements of science. There were thermometers to measure the air temperature, thermometers to measure heat and cold in liquids, thermometers for baths. During the winter,
strumentini,
little temperature-measuring thermometric instruments, hung in every room of the palace.

Several members of Ferdinand II's court were, in the words of a food historian, "ice-mad," among them the secretary, who reverently called snow "the fifth element" and wrote novels in which characters begged one another for ice-based treats. Other courtiers were known to delight in the ice goblets and fruit bowls, the ice pyramids, and the table-sized ice-capped mountains of the Medici celebratory feasts.

It was Ferdinand who invented the sealed-glass thermometer. When the Medici workshop devised one with a scale that marked off into fifty segments the bulb in which the measuring fluid was held, Sagredo accepted that innovation and used it as a base from which to further divide his new thermometers. On these, he marked off 360 divisions, like the gradation of the circle; after that, all scientists started calling the divisions "degrees."

Most of the Florentine sealed-glass thermometers used "spirit of wine," distilled alcohol. Small glass bubbles filled with air at varying pressures hovered within the liquid, changing position as the temperature rose or fell. Later the Accademia flirted with the use of mercury, but its scientists soon—and for reasons that to this day remain obscure—abandoned this choice and went back to spirit of wine. Spirit thermometers did not work well at the low and high ends of the scale, because alcohol boils at a lower temperature than water, and it freezes lower, too; moreover, because the density of the distillate varied from batch to batch, spirit thermometers were often incompatible with one another. Counterbalancing such inadequacies was the high quality of the thermometers produced by the Accademia del Cimento, which was why those that bore its good name came to be requested and used throughout Europe.

Just when the Accademia had built up enough expertise to be well on the way to solving the remaining technical problems with thermometers, quarreling among the members reached an absurd height. In 1657 one member had written that "only disorder is to be found" at the Accademia. By 1666 some members could only be induced to speak at meetings if certain others were absent. The institution decayed. Louis the Sun King lured Christiaan Huygens to become the director of his Académie Royale and enlisted one of the key members of the Accademia del Cimento with a promise of a pension and the right to publish his experimental results under his own name; two others defected elsewhere, ostensibly to seek better climates for their health.

Leopold was discouraged by the infighting, which was going on at the same time the Catholic Church was requesting that one of the Medicis become a cardinal. A former Accademia member's memoir suggests that shutting down the Accademia was made a condition for awarding Leopold the red hat of a cardinal, though other contemporary accounts dispute this notion. In any event, there was an abrupt end to the diary of the Accademia's experiments at the time Leopold was summoned to Rome. He sent a passing-the-baton letter to Constantijn Huygens, entreating him "to look over the great book of nature by means of experiments, and find new things never heard of before, and to purge books of those experimental errors that have been too easily believed, even by the most esteemed authors." In March 1668 Leopold journeyed from Florence to Rome to become a prince of the church; in the coach, as though in defiance of leaving science behind, he took along one of the Accademia's last
strumentini
and whiled away the hours of his journey recording its changing observations.

Boyle obtained a Florentine thermometer, as did other English experimenters; Hooke tried to improve Boyle's in several ways, not the least of which was to substitute mercury as the liquid within the glass tubing; once again, however, for some unknown reason, mercury was soon rejected in favor of spirit of wine. Hooke adapted Florentines for himself and for his friend Christopher Wren. There was even an attempt to put the Royal Society's imprimatur on a thermometer adapted from a Florentine model with Hooke's modifications. Political considerations quashed that, but Hooke's own thermometric innovations advanced the field.

By the 1660s this son of a parish curate, though still in his twenties, had matured from his stint as Boyle's assistant to become one of the most inventive and mechanically able of the Royal Society Fellows, having done significant work in microscopy, astronomy, geology, combustion, and meteorology. He also helped Wren rebuild London after the Great Fire of 1666. When the diarist Samuel Pepys became a member of the Royal Society, its president told him that Hooke did the most, and promised the least, of any of the Fellows. Bent almost completely askew, Hooke was described as "meanly ugly, very pale and lean"; John Aubrey agreed with that description but balanced the picture by adding that Hooke was "of great suavity and goodness." In later life, Hooke would run afoul first of Isaac Newton, then of Henry Oldenburg, secretary of the Royal Society; their combined opposition would succeed in downplaying his accomplishments and undercutting the acceptance of his work by the wider world.

Those accomplishments were considerable, especially in regard to the scientific history of the cold. Hooke was the first person to minutely grade a thermometric scale with marks representing a precise volumetric quantity, each equal to one-thousandth of the expanding volume of spirit in the bulb. He was also among the first to assert that thermal expansion might be a general attribute of matter. "This property of Expansion with Heat, and Contraction with Cold, is not peculiar to Liquors only, but to all kinds of solid Bodies also, especially Metals," he wrote, and italicized his conclusion: "
Heat is a property of a body arising from the motion or agitation
of its parts.
" Two hundred years would elapse before James Joule would prove this same conclusion experimentally and deduce from it the idea—central to the further exploitation of the cold—that heat is a form of energy related to the motion of atomic particles. Hooke was also among the first to propose establishing a permanent flagpost in the country of the cold, one that could be used for navigation by all later explorers: he sought to make the freezing point of water a fixed point of reference on a thermometer.

Today the need for a thermometer to have such a fixed point may seem obvious, but near the end of the seventeenth century, fixed points were a matter of controversy. Some people thought the freezing point of water varied with the time of day, the latitude, or the season. Following the tenets of Hobbes—the old notion that atmospheric conditions changed as one approached the planet's poles—even such usually astute men as the English astronomer Edmund Halley contended that the freezing point of water would not be the same in London as in Paris. Not until the 1730s was that notion finally disproved.
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