A Garden of Marvels

by Ruth Kassinger

  fifteen

  A Momentous Mint

  According to ancient Greek myth, Apollo, pierced by one of Eros’s golden, passion-inducing arrows, became enamored of the woodland nymph Daphne. Sworn to virginity, she rejected the god’s advances, but he chased after her, pursuing her relentlessly across the countryside. As he gained on her and she neared exhaustion, she called out to her father, the river god Peneus, to save her from impending rape. Just as Apollo’s hands reached to grab his prize, her skin turned into bark, her slender arms became branches, and her flowing hair morphed into leaves. She had metamorphosed into the beautiful bay laurel tree (and made Apollo the original tree-hugger). And that’s about all the ancient Greeks had to say about foliage. It was an adornment, like hair. Only Aristotle imagined that leaves had any purpose at all, writing in The Physics that they exist to hide fruit from marauding birds and beasts.

  Fifteen hundred years later, a medieval farmer, if asked what leaves are for, might have answered, in teleological fashion, that God created them to feed cattle, sheep, and goats: Otherwise what would they eat? Paracelsus, the Swiss physician and mystic who wrote and preached in the sixteenth century, believed God created leaves and other plant parts to heal man’s illnesses, and left prescriptions in their shapes. Heart-shaped leaves were good for the heart; the liverwort’s triangular leaves announced its ability to cure diseases of the liver.

  In the 1640s, Belgian physician and alchemist Jan van Helmont ran an experiment he hoped would reveal the secret of what plants are made of. He potted a sapling willow tree in a tub filled with two hundred pounds of soil, and for five years added only water. At the end of the fifth year, he discovered the tree had gained 164 pounds while the soil lost an insignificant two ounces, and concluded that trees “arose out of water only.” Van Helmont’s experiment is one of the most famous in the history of science, not, obviously, for its conclusion, but because Van Helmont was the first to use quantitative methods to understand a living organism. What interests me, however, is that while Van Helmont was exacting enough to design a cover for the pot that kept “air-borne dust from mixing with the earth” while also allowing evaporation from the soil, he didn’t bother to weigh each year’s fallen leaves. He didn’t say why he omitted them from his calculations. I suspect he thought that leaves, doffed like clothes before a bath, were not an integral part of a tree.

  Malpighi and Grew were well aware that leaves were generated from a plant’s substance and assumed they had some function. In 1686, Malpighi cut off leaves from living plants, and found they grew less and produced fewer fruits. Leaves, he posited, serve “to allow the nutritive juice flowing from the fibers of the wood to be cooked . . . allowing growth of new parts.” Their stomata allowed “excremental liquids” to escape. Grew didn’t buy the poop hypothesis, but he couldn’t decide whether the stomata were for evaporation “of superfluous sap, or the admission of air” for breathing. Fifty years later, Stephen Hales looked into the question, stripped plants of all their foliage, and discovered that denuded plants inevitably died. Like Malpighi, however, he concluded that leaves must be the plant’s main “excretory ducts.”

  Enter, whistling, the polymathic genius Joseph Priestley.

  Priestley was born in 1733 near Leeds, in the heart of northern England’s wool manufacturing district. His father was a cloth-dresser, an artisan who singed, trimmed, and ironed rough woven cloth to transform it into finished fabric. When Joseph was six, his mother died giving birth to her sixth child. The boy had already spent much of his life at his grandfather’s house in order to lessen the burden on his prolific parents, and now was virtually adopted by his father’s childless aunt Sarah and her well-to-do husband. The adoption proved a mixed blessing. His aunt and uncle recognized his intelligence and saw to it that he was educated in a way his father could not have afforded. On the other hand, they were adherents of the strictest Calvinism. Joseph grew up believing that Adam’s sin destined most of mankind, most likely himself included, for the roaring, stinking fires of hell. Only a few predestined “elect”—recognizable by their unwavering faith and sinless lives—would escape the eternal wrath of a merciless God. Joseph was terrified, especially because such horrors seemed no distant prospect. He was a sickly child with a disease, probably pulmonary tuberculosis, that often left him feverish and struggling for breath. He had watched his mother and a sister die, likely of the same disease, and so damnation must have felt not only real but imminent.

  His illness came to a crisis when he was sixteen, as did his terror. He later wrote of this period that he was sure God had forsaken him, and experienced “such distress of mind as is not in my power to describe.” He survived, however, and somehow in surviving, his belief in such an unforgiving deity vanished with his fever. He began to question not only the reality of original sin and other fundamental tenets of his family’s religion, but even Christ’s divinity. Decades later, this reevaluation would lead him to help found the English branch of the Unitarian Church and get him hounded out of England. At nineteen, although he was a long way from constructing his mature set of beliefs, he already found it impossible to either swear to his sect’s ten articles of faith or affirm that he had experienced the requisite visitation from God and conversion experience.

  His intransigence had important practical consequences. Like Grew, as a Nonconformist he was barred from attending Oxford or Cambridge. (This was in fact no great loss. By the mid-1700s, the universities’ standards and enrollment had fallen sharply. For the most part, their diplomas were the equivalent of a passport issued to the sons of the Anglican gentry into careers as landholders, politicians, and curates. As one Cambridge historian writes, although it was possible for a prospective clergyman to get a decent, albeit circumscribed, education, it was equally possible to get a B.A. “and precious little else except advanced skills in drinking and driving a coach and pair.”) Instead, thanks to the Act of Toleration of 1689, he could attend one of the excellent Nonconformist institutions, which at the university level were known as academies. Joseph, however, was in a bind. Because of his nonconforming Nonconformist views, he was unwelcome at most of the Calvinist academies his aunt and uncle had in mind for him. Luckily, Daventry Academy, an institution run by orthodox Calvinists who, most unusually, did not require a conversion experience and enrolled qualified men of a range of Protestant stripes, accepted him. It may have been the only institution that his aunt and uncle would pay for that their nephew could in good conscience attend.

  The young man who arrived at Daventry was a tallish, thin, darting sort of fellow with an asymmetrical face, a kind heart, and a disconcerting stutter. He was academically advanced, at least in the course work he needed to become a minister, and was already proficient in Latin, Greek, Hebrew, French, and German and had started studying Arabic and the ancient Middle Eastern languages of Chaldee and Syriac. He had also learned enough logic, history, and philosophy—much on his own—to be excused from the first two of the five years of study. As for natural philosophy, he rejected the Calvinist idea that trying to unravel the secrets of the natural world was sinful pride, and considered it an honorable endeavor to appreciate God’s creations. So, he plunged into courses on anatomy, mechanics, acoustics, and astronomy, struggled with mathematics (it would never be his strong suit), and independently read Boerhaave’s Elements of Chemistry and Newton’s Opticks. Fizzing with intellectual curiosity, he got up early, worked late, and learned shorthand so he could work with maximum efficiency.

  Socially, the young man was in heaven. For a nineteen-year-old whose single childhood memory of fun was reading Robinson Crusoe, Daventry was a fairground of recreations. Emancipated from guilt and fear, he attended clubs and parties and even tried to woo the “cuddliest creature,” a certain Miss Carrott. By the time he graduated, the anguished teenager who had once snatched a book of chivalric stories from his younger brother’s hands and trembled with revulsion at the sound of an oath was transformed.

  It was un
lucky, therefore, that his first professional position or “calling” was as an assistant minister to an orthodox congregation of a hundred souls in the impoverished village of Needham Market in Suffolk, far from his native Yorkshire. He attempted a series of lectures on religious theory, but his parishioners quickly recognized his heterodoxy. With his Yorkshire dialect and his stutter, his preaching was an ordeal for all. His congregation diminished rapidly, and because Nonconformist clergy were paid by their congregants, so did his already meager salary. Then his brother (the one with the immoral book) told his aunt what a “furious freethinker” her favorite nephew had become, and she cut off his allowance. Priestley thought he might supplement his income by starting a school, but not a single pupil showed up. Only charity funds available to impoverished clergy allowed him to survive.

  One resource he was rich in was friends, who were drawn to the openhearted young man. After three years in Suffolk, a sympathetic acquaintance rescued him, securing him a temporary appointment to a congregation in the town of Nantwich. Nantwich was in the tidewater salt-manufacturing region of Cheshire, both culturally and physically close to his hometown. His new congregants were more tolerant of his unorthodox religious views and could understand his accent. Without the pressure of a hostile audience and with perseverance, he improved his performance in the pulpit. Finally, he had escaped the gloom of orthodoxy, and his natural joy in the world seemed to bubble out of him. He couldn’t keep himself from whistling in public or leaping over the counter at the greengrocer’s, habits that amused rather than offended his new parishioners.

  Best of all, when he started a small grammar school for the children of his congregants, he discovered a more congenial métier. A natural teacher, he was able to share his own delight in a subject, and there seemed to be no subject that did not delight him. At a time when grammar schools taught primarily Latin and Greek, he added math, history, and English. His scientific education was sketchy, but he spent long evenings talking with and learning from a Cambridge-educated vicar who lived nearby and kept up with the latest developments in the experimental sciences. With his small earnings, Priestley bought himself scientific equipment, including a microscope, a machine that generated static electricity, and an air pump, and shared the devices with his young pupils.

  Priestley’s success in the classroom led to a position as tutor at the Warrington Academy in Lincolnshire in 1761. Here he came into his own, taking on responsibilities at the school for hiring a chemistry teacher, preaching sermons at a local chapel (to highlight their unsanctioned nature, non-Anglican churches had to be called chapels or assemblies), and becoming a member of the board of governors of the town library. In June the following year, he married Mary Wilkinson, a well-read, assertive, chess-playing young woman who was the sister of one of his students. Mary, whom Priestley described in his memoirs as a woman “of excellent understanding, much improved by reading, of great fortitude and strength of mind, and of a temperament in the highest degree affectionate and generous,” created a happy and busy social life for her still somewhat awkward husband. After a year of marriage their first child, Sally—named after his aunt, who was not appeased by this honor—was born.

  Priestly had been pondering the educational needs of young men, particularly Nonconformists barred from government careers and comfortable Church of England livings, who needed to prepare for a world increasingly dominated by commerce and manufacture. He wrote a book on English usage, not for men writing speeches or sermons but for those who needed a guide to clear, everyday communication. Young men employed in “the useful arts,” he believed, should be well grounded in modern history, mathematics, physics, and chemistry. While these insights were hardly his alone, he articulated them coherently in books, essays, and, notably, with detailed course syllabi.

  Priestley also convinced a local surgeon to teach a course on “practical,” that is, lab-based, chemistry at Warrington, and volunteered to act as his lab assistant. Yellow and blue flames, red fumes, acids that devoured metals, explosions, they all entranced him as they had generations of alchemists pursuing gold or the philosopher’s stone. But he was also interested in the commercial side of chemical transformations, the processes by which clay turned into pottery, sand and lime into glass, and coal into coke.

  In 1765, the University of Edinburgh granted Priestley an honorary degree for his work in education. That year, he embarked on a completely novel literary endeavor: writing a history of the experimental sciences. He decided to start with the new science of electricity, a subject that fascinated the public at the time. His position at Warrington had given him entrée into the intellectual community of nearby Liverpool, and one of his new friends helped introduce him to the “electricians,” men like Benjamin Franklin, famous for his experiments with lightning and storing static electricity in Leyden jars; Englishmen John Canton, who verified Franklin’s discoveries; and William Watson, who had passed an electric current along a wire across the Thames River. The scientists invited him to their periodic meetings in London coffeehouses and agreed to help him by explaining their work and lending him their papers. Even better, both for his book and science, they encouraged him to make his own explorations. Now thirty-three, Priestley threw himself into experimentation, melting wire with an electrical current and repeating Franklin’s kite experiment (which kite he was wise enough to ground with a chain). He reported his progress in a flood of letters to his new friends, and barely a year later finished the seven-hundred-page The History and Present State of Electricity, with Original Experiments. The book won him election to the Royal Society.

  He then turned his attention to another experimental science, “pneumatic chemistry” or the chemistry of air. Robert Boyle and his seventeenth-century contemporaries had considered air to be a single, homogeneous substance, one of the four “elements” of which the world was made. Any differences among particular samples of air—say, a human breath or the “mephitic” air that rises from certain springs or the bottom of swamps—was a difference in its condition. Just as meat could be good or “off,” air could be good or bad. Of course, no matter what their current condition, meat was meat and air was air.

  In 1757, a young Scottish physician named Joseph Black had sent a major tremor through the bedrock of that belief. While investigating a cure for bladder stones, he heated a sample of magnesium carbonate, and found it emitted an air that seemed distinct from ordinary air. This “fixed air”—“fixed” because it had been affixed to or stuck in the magnesium—is what we know as carbon dioxide, or CO2. Black further realized that this air was the same one given off by burning wood, the exhalations of animals, and fermentation. Fixed air killed birds and small animals imprisoned in glass jars and snuffed out candle flames. When he burned crushed limestone (what we know as calcium carbonate), fixed air emerged and left behind quicklime (or calcium oxide). When he exposed the quicklime to common air, it turned back into limestone. Fixed air was both a distinct substance and a part of common air. This meant received wisdom was wrong: Air was not an element. Ten years later, English chemist Henry Cavendish produced another air, what he called “flammable air” (and we know as hydrogen).

  What made these airs different from one another and how they related to common air, no one knew. But fixed air particularly interested Priestley, and he repeated Black’s experiments for himself. After their daughter’s birth, Mary convinced him to leave Warrington, where she feared the river air was undermining her own and Sally’s health. Joseph found a position as a minister at Mill-Hill Chapel in Leeds, only seven miles from his birthplace. Because the minister’s house was undergoing renovation, he temporarily took a house that happened to be next to a brewery. He knew the vats of fermenting grain produced an endless supply of this fixed air and, to his delight, the brewers let him experiment with it.

  Priestley soon discovered that water could absorb the fixed air of fermentation, and that it then became bubbly and tasted slightly sour. By pouring water from one bowl to
another in the flow coming off a vat (carbon dioxide is heavier than air, so it cascaded invisibly over the vat’s edges), he “carbonated” it, creating an artificial Perrier or soda water. Priestley didn’t try to capitalize on his invention, although he did propose it as a cure for scurvy and other illnesses. (It was Jacob Schweppe who patented bottled soda water in 1787 and, later, other carbonated drinks. Lest you think this unfair, although Priestley put the bubbles in the water, it was Schweppe who figured out how to keep them there. He put the soda water in an egg-shaped bottle that couldn’t stand upright. As it leaned, the soda water contacted the cork, keeping it damp so it didn’t shrink and allow the carbon dioxide to escape.) But if soda water was of little interest to Priestley, it did inspire him to consider an interesting scientific question. If fermentations, animals’ respirations, swamp bubbles, and volcanic explosions all poisoned the air, how had God arranged for it to be “rendered fit for breathing again”? He understood there had to be some mechanism; otherwise, our air would have become hopelessly corrupted.