The wars of the seventeenth century were horribly destructive of lives and property, as we have seen, and the burden laid on people over whom armies trampled, seeking food and lodging, horses, wagons, recruits – and likewise women to rape and valuables to steal – was immense. It has been said that the German-speaking parts of Europe suffered as much devastation as the Third Reich in the Second World War. The figure attached to those who, in the Holy Roman Empire, died in direct and indirect ways attributable to the Thirty Years War, is, again as mentioned, one out of every three people. As a measure of the wreckage to lives, land and material welfare in central Europe, that is a tragic number.
Yet, alas, times of disruption and destruction are also times of opportunity for some; the bleak saying ‘it is an ill wind that blows no one any good’ reminds one that bad times are good for those who can profit from them. Yet it is not just a matter of who might profit: there are also genuine opportunities – for new ideas, for the breaking down of barriers that had prevented exchanges of ideas beforehand, and the fresh inspirations that such exchanges bring. This happened in the unsettled condition of Europe in the seventeenth century, aided by the happy accident that the means of communication – chiefly: the sending and receiving of letters – was not harmed but in fact enabled by the greater uncertainty of the time.
To make sense of this aspect of the seventeenth century requires lifting its floorboards to peer beneath. Somewhat unexpected aspects come to light, such as the role of a French Minim monk, a Polish-German war-refugee, and the story of postal services. These latter play a significant part in what made the intellectual debate of the seventeenth century flourish. Without them the role of ‘intelligencers’ such as Mersenne, Hartlib and others, collecting and resending correspondence at the hubs of postal networks of enquirers, could not have existed.
The significance of Mersenne to the intellectual history of the seventeenth century has not been properly acknowledged.1 Histories of mathematics remember him for his contributions to geometry and the study of prime numbers, histories of musical theory remember him for his work on oscillating strings, and studies of Descartes cite him as the correspondent who kept the philosopher in touch with friends and rivals during his most creative years. Those years were lived by Descartes in privacy (actually, for much of the time, in secrecy) in the Netherlands; his correspondence with Mersenne was a necessity for him. But Mersenne’s significance is greater than that. To employ a wholly anachronistic metaphor which nevertheless does not stretch matters, he – as with others of the intelligencers who played a similar role – can be described as the seventeenth century’s closest thing to an internet server, in a way to be demonstrated below.
Mersenne was born in 1588 at Oizé in the north-western region of France then called Maine (divided during the French Revolution into the now existing departments of Sarthe and Mayenne). His family were poor peasants, but the intellectual gifts he manifested early in life gave him the chance of an education. He studied locally at first, then at the nearby newly established Jesuit college of La Flèche, then the best school in France.
After completing his education in Paris at the Collège Royal de France and the Sorbonne, Mersenne entered the Order of Minims, founded in 1436 by St Francis of Paola. The order still exists today in rump, but in the early seventeenth century it was flourishing. It is a mendicant order of friars, contemplative nuns and lay persons who attempt to live its discipline of simplicity, poverty and veganism. The name ‘Minim’ derives from Italian minimo meaning ‘least’ or ‘smallest’, St Francis of Paola having described himself as il minimo dei minimi, the ‘least of the least’ as a poor hermit and devotee of St Francis of Assisi. In addition to the usual three monastic vows of chastity, poverty and obedience, the Minims adopt a ‘Lenten’ diet excluding all meat and dairy products except in case of illness, and they dedicate themselves to contemplation and study.
The Minims’ simplicity of life and devotion to scholarship is what attracted Mersenne. He entered the order in July 1611 and was ordained to the priesthood in 1612. After three years teaching philosophy and theology at a monastery in Nevers he returned to Paris, remaining at the Place Royale monastery with only a few forays abroad until his death in 1648.
Although his interests lay principally in mathematics and musical theory, Mersenne’s first published works were attacks on scepticism and atheism: L’Usage de la raison and L’Analyse de la vie spirituelle. His first major work was Quaestiones Celeberrimae in Genesim, published in 1623. Ostensibly a commentary on the Bible’s Book of Genesis, it is in major part a sustained attack on magic, cabalism, astrology and other like ‘arts’, and forms part of the important moment in the history of ideas when the transition from thought’s obeisance to the demands of religious orthodoxy passed through a period of inflated hopes for mystical or magical short-cuts to the universe’s secrets (and therefore of the means to transmute base metals into gold, to secure immortality or at least longevity and eternal youth, and the like) – and thence to the triumph of the more accurate methods of mathematics and empirical enquiry which have given rise to today’s sciences. Mersenne’s attack on magic, Cabala and the rest was of a piece with the efforts by Bacon and Descartes to distinguish, each in his own way, science from those magical forms of thinking, by describing and enjoining methodologies better destined to arrive at knowledge. Of this important matter, and Mersenne’s part in it, more in the next chapter.
It’s a telling fact about Mersenne’s character that he began as a staunch defender of the Aristotelianism attacked by Descartes and other leaders of the seventeenth-century intellectual revolution, but very soon joined the ranks of Aristotelianism’s critics when he had learned more about their reasons. Likewise in the early 1620s he was a severe critic of Galileo, whose views he said should be condemned; within a decade he was one of Galileo’s chief supporters, conveying news of the scientist’s work to other savants in Europe.
Perhaps Mersenne’s chief technical contributions to science are those included in his Traité de l’harmonie universelle, published in 1637. In this book, apart from introducing major improvements to the design of mirrors for use in reflecting telescopes, he stated what are known as ‘Mersenne’s Laws’ describing the oscillation frequency of a taut string. The ancients knew that the frequency of a taut string is inversely proportional to its length, but Mersenne noted further that the frequency is inversely proportional also to the square root of the stretching force, and to the square root of the mass per unit length. The practical application of these insights relates to the construction and operation of stringed instruments such as violins, harps and pianos. They all require that the tension force of the component strings has to be maintained at the right level to yield the correct pitch, and Mersenne’s Laws explain the science of why lower-pitched strings are thicker and require less tension, while higher-pitched strings are thinner, require more tension, and can be shorter.
He also made empirical tests of Galileo’s law of motion for falling bodies, and enquired into the principles of the barometer, in the course of which he discovered that the density of air is about one-nineteenth that of water. It is quite likely Mersenne who suggested to Pascal, Roberval, Périer and others the experiment soon afterwards carried out on the Puy de Dôme volcano to see whether the height of the mercury column in a barometer is determined solely by air pressure.
Mersenne is remembered by mathematicians for his work on the curved line known as the cycloid – an example is the figure traced by a point on a rolling wheel as it moves along – and especially on prime numbers and a related application of them now made to computing and cryptography.
Prime numbers – numbers that are divisible without remainder only by themselves and one (all other numbers are called ‘composite’) – have always been a mystery and a fascination to those interested in numbers as such. The innocuous description of prime numbers just given disguises their extraordinary significance in the number universe and indeed the physical universe (for a striking example of this latter: cicadas of the genus Magicicada only emerge from their grub stage, lived underground, every seven, thirteen or seventeen years, each of these numbers being prime; entomologists surmise that this is to protect them from predators which would co-evolve to feed on them if they emerged from underground at more regular intervals). Mersenne wished to find a formula for generating all primes, and although he did not find a wholly general device for doing this, the formula he proposed yields a sequence with interesting and still puzzling properties, and their role in number theory (and latterly in cryptography) makes them a target of much study, not least by the Great Internet Mersenne Prime Search or GIMPS conducted by ‘distributed computing’ – linking millions of personal computers – to hunt for them. To date fewer than fifty have been found, and the first sequence claimed by Mersenne himself contained errors; but in the search for ever greater cryptographic security a Mersenne prime whose period is known as the ‘Mersenne twister’ has become a standard random number generator.
This interest in number theory was occasioned by Mersenne’s editorial work on the mathematical treatises of the ancients, among them Euclid, Apollonius and Archimedes. His wide range of interests, his intellectual gifts, his generosity and encouragement to others, his dedication to the cause of science, and his evident personal charm which attracted and kept together a large and disparate group of sometimes prickly clever people make him a key figure in the seventeenth-century story.
The role Mersenne played was described above as a kind of one-man human internet server. The simile is apt. He was the recipient of letters from almost all the great savants of the day, which he then multiply copied and disseminated to spread news, opinions, discoveries and conjectures around Europe. Copies of his correspondence were available in his lodgings for any visitor to read, and as Paris was a major intellectual centre, many came to him as to a library to get news of the latest scientific ideas. The reputations of some of the century’s leading minds – Hobbes, Descartes, Gassendi – were created by Mersenne in this way. Thomas Hobbes became famous long before he published a book as a result of the esteem in which he was held by Parisian intellectuals who read his letters in Mersenne’s lodgings. The same was true of Descartes; Mersenne had in effect made him famous through their correspondence well before the appearance of the philosopher’s first publication, the Discourse on Method. Likewise Descartes would not have remained so closely in touch with the course of debate in the period between the late 1620s and the end of Mersenne’s life (in 1648) without this invaluable relationship, because – for reasons one can speculate about2 – he lived in near-exilic private circumstances in the Netherlands for almost the whole period between 1628 and 1649, the year before his death.
It is pertinent and of interest to know the background to letter-writing and the post in Mersenne’s time, and how it came to be so. The story is not an obvious one; in our age of instant electronic social media, letters are a very diminished form of communication. In the pre-email age, and despite the advent of the telephone, they were still the principal way to be in touch with those at a distance. Before the telephone this was even more emphatically the case; Victorians wrote several or more letters a day – and had them delivered that same day if they lived in a city.
In the seventeenth century the mails were not quite so frequent or convenient as in Victorian times, but letter-writing had long been re-established as a common means of communication – ‘re-established’ because of course it had been common enough among educated Romans, but was lost with the near-total destruction of intellectual culture in the ‘Dark Ages’.3 A common practice of letter-writing requires a literate class, pens, ink, parchment or paper, and a postal service; it was only in late medieval times that this congeries of means started to be available once again, though in partial and stuttering fashion at first. Even so, as illustrated by the administrative affairs of Henry I of England (1068–1135), royal messengers carried an average of 4,500 official letters a year – meaning that an average of a dozen letters were being written and sent every day by the King and his ministers alone.
By the beginning of the fourteenth century a number of factors had come together to make letters a principal means of connecting the European world with itself. The needs of banking and commerce involved not just direct communication about orders, invoices, financial transactions, instructions on credit lines, and the like, but information; and letters about these things were typically written in vernacular tongues. The classical languages remained the resource of humanists and scholars as they communicated the fruits of their studies of antiquity and the recovery of texts, and debated matters of philosophy and theology. Politics and diplomacy, centralised military structures, tax raising, judicial functions and administration necessitated a professional class of notaries and secretaries and a reliable postal network for the sending and receiving of every kind of document.
By the end of the sixteenth century all the elements were copiously in place for a flourishing culture of letter-writing, abetted by two developments: the availability of inexpensive paper made from pulp – water-powered pulp mills were invented in Italy as early as the fourteenth century – and the widespread availability of printed books among which letter-writing manuals and compilations of models of classical and rhetoric-based epistolary styles abounded.4 Cicero was taken as the outstanding example of a letter-writer, and schoolboys were coached in his manner. Europe was criss-crossed by a variety of postal services from imperial and royal to local and private, the messengers of the official royal mails supplementing their incomes by taking personal letters for a fee on the side.
In the seventeenth century, accordingly, there existed a fully formed overlapping network of postal services, and it sustained an unofficial and informal respublica litterarum – a Republic of Letters largely based upon exchanges of letters – itself constituting an elaborate network of communication which was as important a way for savants to spread their ideas and secure their reputations as publishing them in book form. ‘There were two ways in which the ideas of a philosopher could come to be known in this invisible republic,’ writes Daniel Garber, using ‘philosopher’ in the then general sense of enquirer, thinker, scientist; ‘one was of course the appearance in print of his ideas, but the other was through the remarkable network of letters which writers across the continent exchanged with one another. European scholars had always been busy letter-writers; Erasmus complained that he had to write more than ten a day’ – and that was a century before the period under consideration.5
The seventeenth-century republic of letters was an ‘international, unstructured’ association for which the letter post was the practical bond. ‘The posts across the continent were surprisingly efficient; it is very rare to find any seventeenth-century scholar complaining that a letter had been lost in the post, and the post between major cities was fairly quick (Paris to The Hague in a week or ten days, and Paris to London the same).’6 The idea of there being an efficient, reliable and regular postal service in the seventeenth century seems an unlikely one perhaps, but its existence and character are fundamentals of the story. How this came to be the case is well illustrated by the history of the Taxis family.
In the early fourteenth century the couriers in the service of the Signoria of Venice were largely drawn from members of a single extended family which hailed from the Bergamo valley in the Italian Alps.7 They derived their name, the Tassi, from their habit of fastening the pelt of a badger (tasso) to their horses’ heads as a means of protection against the whip of tree branches and the risk of falling stones in the Alpine passes. The Tassi extended their expertise as messengers and postmen from Venice to Milan and Rome over the course of the next two centuries, at length appearing in the records of the Holy Roman Emperor Maximilian I at the end of the fifteenth century, in Innsbruck where Maximilian kept his court. There were three Tassi family members in Maximilian’s service – they were there known by the German version of their name, Taxis – and one of them in particular, Baptista, was already rich and influential, having graduated from Chief Postmaster of the city to Imperial Court Postmaster. The phrase ‘rich and influential’ scarcely does him justice; he was in a position to make loans to the Emperor, who in gratitude ennobled him. Thenceforth the family were no less than (and in time much more than merely) ‘von Taxis’.
There were soon von Taxis in a number of imperial cities, including Vienna. Although they were officially carriers of imperial mail, they also took private commissions, and their wealth steadily increased. Another of the von Taxis at Innsbruck was Francesco or Franz, who served as private courier to Maximilian’s son Philip, who on his father’s behalf ruled over part of Spain, the Netherlands and Burgundy. Philip required a line of communications both swift and sure between his Spanish and Dutch dominions, and gave Franz von Taxis the task of establishing it. Franz offered to set up a full-blown postal service with Philip as his main customer, and Philip agreed. The resulting network linked Flanders, Paris, Castile, Vienna and Rome, and was based on a relay system in which horses and their riders were changed at each post. The mail pouches were sealed and the postmen carried a book known as a Standenpass or ‘hour book’ to record the time at which a mail pouch was handed over. The swiftness of the system is attested by the fact that it took a mere ten and a half days for the mail to get from Brussels to Rome in summer; in winter it took twelve days.
Franz von Taxis’ service carried private mail also, and the logbooks show how voluminous that traffic was, and how quickly it grew. The mail routes were also the principal travel and commercial routes, and as the population of Europe doubled from 30 million to 60 million between the years 1500 and 1600, with growing literacy and trade alongside, the volume of mail rose steeply. It was expensive to send letters; a Taxis postman earned 8 gulden a month, out of which he had to keep his horse too, whereas it cost anything between 25 and 80 gulden to send a letter by the Taxis post, depending on distance.8 The von Taxis accordingly became even richer as demand for their services burgeoned. And burgeon it did; in the Exchequer archives of England’s Henry VIII are records of substantial payments to ‘Master of the Posts Francis de Taxis’ for mail services to France and Italy.9 It is no surprise therefore that Henry VIII’s celebrated portraitist, Hans Holbein, also painted Franz von Taxis’ portrait.
Franz built himself a palace in Brussels, and when he died in 1517 he was buried in the city’s church of Notre Dame de Sablon to which he had donated four magnificent tapestries, each worth 6,000 gulden, into one of which was woven his own portrait three times over.
So far had Franz enhanced the patrimony of his name and its trade that through the succeeding centuries the family went (mainly by purchase for large sums from indigent monarchs) from barons to counts to marquises to dukes and eventually to princes – different branches of the family, depending on the country they lived in, varying the name from von Taxis to de Tassi to di Tasso, and intermarrying with other great aristocratic families to yield combinations such as von Thurn und Taxis, de la Tour et Tassis, della Torre e Tassi, and magnificently resounding strings such as Prince Vicenz von Zapata und Taxis, Duke of Saponara, and Don Iñigo Vélez Ladrón de Guevara y Taxis. The basis of the family’s vast wealth remained postal services, and the family itself evolved into something like a sovereign state with which actual states or their rulers entered into treaties; in 1844 France entered such a treaty with the Taxis, the signatory parties being respectively described as ‘His Majesty the King of the French and His Most Serene Highness the Prince de la Tour and Taxis.’10
Bit by bit, as the Holy Roman Empire decayed through the wars of the seventeenth and eighteenth centuries and was given its death-blow by Napoleon at the beginning of the nineteenth, so the extent and power of the Taxis postal services declined. The last post for the Taxis was played when the Prussian state purchased the one remaining Taxis franchise for 3 million thaler in 1867 (perhaps about 8 million US dollars today). But by then the Taxis dynasty was well beyond mourning its commercial beginnings in the smell of leather and horse sweat; they were in different spheres altogether. In 1912 a German history of postal services was dedicated to ‘His Highness Albert Maria Joseph Maximilian Lamoral, Ruling Prince of the House of Thurn and Taxis, Duke of Wörth and Donaustauf, Prince of Buchau, Prince of Krotoscyn, Princely Count of Friedberg-Scheu, Count of Valsassina and of Marchthal and Neunheim . . .’ and so on ‘for thirteen more lines of print’.11
It was not just the demand for postal services that underlay the aristocracy-engendering commercial success of the Taxis post in the period to the seventeenth century, but also the fact that the Holy Roman Emperors granted and renewed near-monopoly status for its operations in all their parts of Europe, and in 1615 made it a fief so that it was heritable by succeeding generations just as if it were land. It had of course functionally been a fief for a long time by then, and making the fact official was merely a recognition that the Taxis network was the blood and sinews of continental communications. In 1628 that network reached its apogee; more than 20,000 postmen in the Taxis blue and silver livery galloped between its relay stations from the Mediterranean to the North Sea, from the Atlantic coast to the Holy Roman Empire’s precarious border with the Ottoman Empire.
One drawback of the Taxis post’s close connection with the Empire was that as spying on the mails increased with the increasingly tense state of European affairs in the sixteenth and seventeenth centuries, so concerns about the security of the mails grew. Many of the Taxis relay stations had ‘lodges’ in them, staffed by Imperial agents tasked with scrutinising the mail pouches and opening any letters they regarded as suspicious.
By the seventeenth century, then, the Taxis system was extremely well established and flourishing, with an associated network of co-operative local services to carry mail into provincial nooks and corners. At the same time it had stimulated rivals, smaller services regarded as less accessible to spying, which made arrangements among themselves to carry each other’s mails onward. Postal companies were also often passenger coach companies, the post sometimes coming first and sometimes the passenger service. The commercial viability of all these operations depended on reliability, which explains why there were so few complaints of lost letters.
Almost certainly, the savants of the seventeenth century used these smaller mail services for the bulk of their correspondence. They included town services, university messengers, private carriers, guilds, merchant groups, rich nobles with their own messengers who would deliver letters for savants living on their patronage, and the like. The Taxis network was not allowed to gain dominance in France because of French suspicion of the Habsburgs, so it was in France that one of the earliest state postal systems developed. That however was not until later in the seventeenth century, so the spider’s-web of correspondence which had Mersenne at its centre chiefly consisted of the numerous smaller rivals to the Taxis post. In France the Holy Roman Emperor’s grant of monopoly facilities to the Taxis did not apply, so whereas in Habsburg dominions no other postal service was allowed to operate by relay, in France there had long been such services. Louis XI (1461–83) is credited with having established a relay post in France, and there is an evocative entry dated 1480 in the town archives of Tours for a payment for torches ‘to light the watch gathered every night at the drawbridge to admit the couriers called posts’.
It is against this background that we can understand the ease with which Mersenne became the centre of a republic of letters in both the figurative and literal senses of ‘letters’. By being a poste restante and human internet server, he drew about him a group of some of the most distinguished minds of the century. He corresponded with – and in many cases personally knew and collaborated with – Descartes, Pascal, Pierre Petit, Gassendi, Beeckman, van Helmont, Roberval, de Peiresc, Hobbes, Giovanni Doni, Torricelli, Constantijn Huygens, Galileo and many others. It was indeed Mersenne who made Galileo’s work more widely known outside Italy, just as he had made Descartes known across Europe. In 1635 he gave his circle of acquaintance a semi-formal institutionalisation as the Academia Parisiensis (Académie Parisienne; friends sometimes called it the Académie Mersenne) which had nearly 150 corresponding members, among them all the leading mathematicians, astronomers and philosophers of the day. It was in effect the embryo of the Académie des Sciences which Jean-Baptiste Colbert set up in 1666, and arguably also part of the inspiration for the Royal Society of London founded in 1660.
An example of Mersenne’s role as a focal point for the republic of letters is afforded by Descartes’ visit to Paris from his exile in the Netherlands in 1647. He stayed only for four months, but that was long enough for him to meet Pierre Gassendi, proponent of a version of an atomic theory of matter, Thomas Hobbes, author of the Leviathan published four years later, and Blaise Pascal, the mathematical prodigy. Pascal was close to Roberval and Fermat, with both of whom Descartes had clashed bitterly, so neither of the two expected to become friends, and this proved right. Descartes was curious about Pascal, though, because he had heard much about his mental powers, and had been struck by the genius of an essay that Pascal had written on conic sections at the age of sixteen. For at least that reason he welcomed the encounter.
Descartes met Hobbes and Gassendi at a dinner especially arranged by Mersenne to effect a rapprochement between the three, because the two men had been severely critical of ideas in the Meditations, their criticisms appearing in the ‘Objections’ which Descartes had openly invited, through Mersenne’s good offices, from anyone interested enough to comment. Always sensitive to criticism, Descartes had been very annoyed by their objections, and he had formed the view, as he told Mersenne tartly, that Hobbes was profiting from the opportunity to criticise his Meditations as a way of promoting his own reputation. When the day of the dinner arrived Hobbes and Claude Clerselier were present along with Mersenne, but Gassendi was unable to attend because he was ill. When the dinner was over, therefore, the four men went to Gassendi’s home to wish him well.
Mersenne was also instrumental in putting Descartes together with Blaise Pascal. At the time of Descartes’ visit Pascal was aged twenty-one. Descartes had two meetings with him, during the first of which the young man was feverish and confined to bed. Roberval was there too, which irritated Descartes, who wished to talk with Pascal alone. Nevertheless Pascal showed Descartes the calculating machine he had constructed – not perhaps the first ever computer, for the Chinese abacus might count as such – but cleverly based on knitting-machine technology. When Descartes left to keep a luncheon appointment Roberval accompanied him; they both climbed into the coach Descartes had hired, and argued vigorously with each other as they crossed Paris.
This first meeting between Descartes and Pascal was recorded by the latter’s sister Jacqueline, who commented dryly on the way it ended: ‘Monsieur Descartes took [Roberval] away with him in a grand coach, where the two of them were all alone, insulting each other, but somewhat louder than here.’12
The next morning Descartes and Pascal met again, tête-à-tête, and were therefore able to talk uninterruptedly. Descartes urged his view of the plenum on Pascal, suggesting an experiment to settle the conflict between his theory and that of Torricelli, which invoked the concept of a vacuum to explain atmospheric pressure. This was the same debate to which Mersenne contributed, and which resulted in the Puy de Dôme experiment to resolve the question.
Mersenne was not of course alone in facilitating the intellectual intercourse of the continent. Another of the intelligencers was Samuel Hartlib (1600–62).13 Like Mersenne he was the centre of a voluminous correspondence among European savants, and was the first to have the sobriquet ‘intelligencer’ applied to him, in fact by the compatriots of his adoptive land, England. He had been born at Elbing on the Baltic coast of the German-speaking part of Poland, and was educated at the Albertus University of Königsberg (the ‘Albertina’). He was in effect a refugee from the Thirty Years War, for in 1628, when Imperial armies took up positions in the west of Poland and the threat of invasion from Sweden was growing, he chose to leave. He settled in England, perhaps drawn there because he had an English grandmother (who had once been the head of an English trading post at Elbing), studying briefly at Cambridge then unsuccessfully attempting to establish a school at Chichester in Sussex.
Despite the failure of this project he maintained an active and enduring interest in education and educational reform, under the influence of both Bacon and Comenius. John Milton dedicated his own tract On Education to Hartlib in 1644, having been encouraged by him to write it. Hartlib’s most ambitious educational endeavour was the effort to set up an institute of advanced study on the model of Bacon’s ‘Solomon’s House’ as outlined in The New Atlantis. So large a project required public funding, which Hartlib failed to get. Nevertheless his campaigning on education was instrumental in persuading Cromwell to increase the number of elementary schools in England, and it also played a significant role in the founding of the short-lived New College at Durham, which was staffed largely by Hartlibians.
A number of distinguished men gathered round Hartlib in his efforts at educational reform – Milton and Kenelm Digby included – forming the nucleus of the ‘Hartlib Circle’ or ‘Invisible College’ which was a primary source of the Royal Society. He encouraged a group of gifted young men, Robert Boyle and William Petty among them, who were influenced by his belief that if knowledge is to be truly valuable it must have useful applications.
Hartlib’s association with the Parliamentary cause in the Civil War led to his exclusion from the Royal Society when it was founded in 1660, because of course the Society was under the patronage of Charles II who had no time for rebel sympathisers. The pension Cromwell had given Hartlib was also therefore discontinued – altogether a poor reward for the contribution Hartlib had made to the development of the century’s mind.
He also made significant contributions to social welfare thinking. With his close friend the Calvinist divine John Dury he set up the ‘Office of Public Address’, a semi-charitable project aimed in part at being a labour exchange and putting poor people (whether intellectuals or labourers) into contact with possible benefactors. It was also intended to be a clearing house for news of all kinds including scientific and philosophical developments, a point of contact for merchants from all over Europe, and a place at which new inventions, technologies and schemes could be demonstrated and discussed. Above all it aimed to promote education and entrepreneurship of all kinds, applying Hartlib’s educational ideal of combining the practical and theoretical.
Hartlib was a polymath like Mersenne, but had even broader interests than the latter, among them agriculture (extolling crop rotation and the use of nitrogenous vegetables for increased soil fertility), fruit-farming and bee-keeping. His proposal for a glass beehive (the designs for it were provided by Christopher Wren) was one of the highlights of his book The Reformed Commonwealth of Bees. He took an active part in the political debates of the Civil War, urging religious toleration and publishing proposals to achieve it. So wide was the range of his interests that the diarist John Evelyn dubbed him ‘Master of innumerable curiosities’,14 and it is unsurprising to find him discussing by letter with Henry Oldenburg clocks, perpetual-motion devices, lanterns, medical prescriptions, chemical formulae, agricultural machinery, and much besides.
A major contrast with Mersenne was Hartlib’s interest in ideas drawn from alchemy – he read the alchemical literature with interest – and sympathetic medicine. He was indeed receptive to ideas from anywhere, including speculative and fanciful sources, though he was not an uncritical thinker and was always prepared to experiment. It is likely that he hastened his death by drinking sulphuric acid to see if it would dissolve the kidney stones that plagued him.
Like Mersenne, Hartlib occasionally travelled in pursuit of his intellectual interests, and in the course of a visit to the Netherlands in 1634 met Descartes at the house of Princess Elizabeth Stuart, the daughter of James I and ‘Winter Queen’ to the hapless Frederick of the Palatine.15 As this shows, the circuit of letters and their writers was a constantly overlapping one.
When Hartlib died he left over 25,000 folios of correspondence and notes, including 4,250 letters from 400 different correspondents mainly but not exclusively in England, the Netherlands and France. The collection is now housed in the Sheffield University library, which has made it digitally available.16 He accordingly furnishes another example of the way that the seventeenth-century revolution in thought was carried out: by a level of communication and an open exchange of ideas unprecedented since the Edict of Thessalonica – the Cunctos Populos – in 380 C.E. ordered all subjects of the Roman Empire to profess the faith of the bishops of Rome and Alexandria, thus making Christianity the Empire’s sole official religion.
Over a thousand letters sent and received by Mersenne are extant, but these are almost certainly only a part of his correspondence. He was known to contemporaries as ‘the Mailbox of Europe’, which implies something about the volume of letters he handled, even if not as many as another of his fellow intelligencers whose full collection of letters survives: this was Nicolas-Claude de Peiresc (1580–1637), whose extant correspondence numbers close to 14,000 items.
Peiresc’s sobriquet was ‘the Prince of Erudition’, high praise for anyone in the seventeenth century. He was an astronomer, collector and archaeologist; among his chief contributions to science were his telescopic identification of the Orion nebula, and his measurement of differences in the longitude of locations across Europe and around the Mediterranean Sea. By the precision with which he collated observations of the lunar eclipse of 28 August 1635 he was able to determine that the Mediterranean is a thousand kilometres shorter than had hitherto been thought. Among the extensive and varied collections kept at his home in Aix-en-Provence were a number of cultural treasures, including the Barberini ivory, now in the Louvre, and a copy of the Codex Luxemburgensis, itself a copy of an illuminated manuscript made in 354 CE known as the Calendar of Filocalus.
But his greatest contribution was the correspondence network he created. He is said once to have written forty-two letters in a single day. He had nearly 500 correspondents across Europe, among them Mersenne, Galileo, Tommaso Campanella and Pierre Gassendi.
Another of the scientific revolution’s intelligencers was the mathematician and astronomer Ismaël Boulliau (1605–94), who left a collection of 5,000 letters dating from the period between the years 1632 and 1693. Born into a Calvinist family, Boulliau converted to Catholicism as a young man, and was ordained to the priesthood. With the brothers Jacques and Pierre Dupuy he helped to build the collections of the Royal Library in Paris. In 1667 he was elected a foreign associate of the Royal Society of London on the strength of his work on planetary motion, involving the ‘conical hypothesis’ relating to the planets’ orbits, and his discovery of the inverse square law which states that an effect’s intensity (e.g. the effect of the gravitational force, or of illumination) changes proportionally to the square of the distance between a given point and a source. This law, as applied to gravitation, is chiefly associated with Newton, for which reason Boulliau is described as the law’s ‘finder but not keeper’.
The Royal Society’s first Secretary, Henry Oldenburg (1619–77), was also a copious correspondent, even before his official duties as Secretary required it of him. He earned the sobriquet ‘the Clearinghouse of Science’ in consequence. His correspondence fills thirteen volumes, and the geographical spread of his correspondents was even greater than that of his fellow intelligencers – it ranged across Europe, the Levant and North America. As editor of the Society’s Philosophical Transactions, for which he invented the practice of referring submitted manuscripts for peer review, he is a key figure in the transition between the first and second halves of the seventeenth century in the way that science was communicated and debated. In the first half of the century this was done by private correspondence between individuals, whose networks were informal and dispersed; in the second half of the century it was done by groups of scientists in state-sponsored institutions publishing their findings in printed journals.
Mention of the Winter Queen – Princess Elizabeth Stuart, daughter of James I of England – brings to mind a particular example of an intellectual exchange of letters; that between René Descartes and the daughter of the Winter Queen, namely Princess Elisabeth of Bohemia (note the mother’s ‘z’ in Elizabeth and the daughter’s ‘s’ in Elisabeth).
When Hartlib met Descartes at a soirée held by the Winter Queen, Princess Elisabeth was only sixteen. She was however at that point being sought in marriage by King Władisław IV of Poland, an offer she rejected on the grounds of the difference in their religions – he was Catholic, she Calvinist – for unlike Henri IV of France, she did not think conversion a price worth paying for a crown.
Elisabeth and her mother and siblings were living in the Netherlands because, as a previous chapter relates, that is where her father, Elector Frederick V of the Palatinate and briefly King of Bohemia, had chosen to go into exile. His wife the Winter Queen was cousin of the Prince of Orange, who honoured the family tie by giving the exiles two substantial houses and a pension. Frederick died of the plague in 1632, leaving his family wholly to the Prince of Orange’s charity – and his political acumen: while the Electorate of the Palatine had a legitimate Protestant claimant, Habsburg control of it was incomplete, and that served the Netherlands well.
The Winter Queen had eight children, four of each. That was quite a burden for an impoverished exile, but although her brother was Charles I of England and she could have claimed refuge with him, she decided to stay where she was. For one thing Charles I was preoccupied with his own troubles, but for a more important thing she calculated – in line with the views of her cousin of Orange – that her eldest son’s Palatinate claims were best served by staying geographically close to them in the Netherlands.
Such were the conditions in which Princess Elisabeth of Bohemia was raised.17 She was a highly intelligent and gifted individual who loved to study. She made very good use of her otherwise unpropitious circumstances to acquire six languages, among them Latin, and mathematics, at which she excelled. She read Descartes’ Meditations and the Discourse and wished to talk to him about the ideas they contained. She asked Alphonse de Pollot, a Piedmontese member of the Prince of Orange’s staff, to find out if Descartes would be willing to meet her. Descartes was always ready to meet royals, and was flattered to be noticed. Moreover he had heard of her intellectual reputation and was interested.
They met in 1642, in the autumn. Descartes travelled from his home in Endegeest to her home in The Hague along a canal which passed through beautiful countryside and wealthy suburbs, a circumstance he particularly remembered because, he said, of the importance to him of the relationship that began that day.18 He visited her again in the following spring, and a lively and increasingly warm exchange of letters began. The probing questions Elisabeth asked in her letters eventually obliged Descartes to write a book he would not otherwise have written, The Passions of the Soul.
This short treatise arose directly from Elisabeth’s dissatisfaction with Descartes’ inability to solve the mind–body problem. She was puzzled as to how substances defined as essentially different – mind was ‘thinking stuff’ and body ‘spatial stuff’ according to Descartes’ Meditations – could mutually interact. She therefore asked him to explain ‘the manner of [the soul’s] actions and passions on the body’. She wrote on 6 April 1643,
Given that the soul of a human being is only a thinking substance, how can it affect the bodily spirits, in order to bring about voluntary actions? The question arises because it seems that how a thing moves depends solely on how much it is pushed, the manner in which it is pushed, or the surface-texture and shape of the thing that pushes it. The first two of these require contact between the two things, and the third requires that the causally active thing be extended. Your notion of the soul entirely excludes extension, and it appears to me that an immaterial thing can’t possibly touch anything else. So I ask you for a definition of the soul that homes in on its nature more thoroughly than does the one you give in your Meditations – that is, I want a definition that characterizes what it is as distinct from what it does.19
In replying on 21 May Descartes acknowledged the acuity of her question, and provided a lengthy response offering a somewhat fudging attempt at a solution, which is that the notion of a physical thing x moving a physical thing y is different from the notion of a mental event x moving a physical thing y: there are, Descartes claimed, two different senses of ‘move’ in play. Of course the second sense of ‘move’ requires an explanation, and Descartes attempted a partial one, saying that if in accounting for how a rock moves, for example by falling, we single out the weight of the rock as the significant factor, we do not imagine that weight is a thing like the rock of which it is a property. ‘How do we think that the weight of a rock moves the rock downwards?’ he asks; ‘We don’t think that this happens through a real contact of one surface against another as though the weight was a hand pushing the rock downwards! But we have no difficulty in conceiving how it moves the body, nor how the weight and the rock are connected, because we find from our own inner experience that we already have a notion that provides just such a connection . . . I believe that this notion was given to us for conceiving how the soul moves the body.’
This was not an explanation calculated to satisfy a sharp mind. Elisabeth replied on 10 June, ‘I don’t see how the idea that you used about weight can guide us to the idea we need in order to judge how the (non-extended and immaterial) soul can move the body. To put some flesh on the bones of my difficulty: I don’t see why we should be persuaded that a body can be pushed by some immaterial thing . . .’ She went on to say that she found it easier to attribute extension to the soul than to conceive of an immaterial thing acting materially on a material thing. As we know, Descartes in the end was obliged to confess that he did not know the answer either.
Elisabeth’s interest was practical as well as theoretical, for she noted her emotions’ effect on her health, writing on 24 May 1645, ‘My body is awash with many of the weaknesses of my sex; it is affected very easily by the troubles of the soul and doesn’t have the power to restore itself when the soul is restored . . . It doesn’t take long for sadness to obstruct the spleen and infect the rest of the body by its vapours. I imagine that this is the source of my low-grade fever and dry throat . . .’
She had raised the problem of mind–body interaction at their very first meeting in 1642. At last, in a letter of September 1645, she demanded that he provide her with ‘a definition of the passions’. From this came Descartes’ little treatise dealing with that subject.
In an account of their relationship Léon Petit suggests that Descartes and Elisabeth were in love with one another.20 Others, including Geneviève Rodis-Lewis, agree, though in Rodis-Lewis’ opinion it was not a sexual relationship. It did not really have time or opportunity to be such before Elisabeth was sent by her mother to live with other relatives, the family of the Elector of Brandenburg in Berlin. Elisabeth left the Netherlands in August 1646 soon after she and Descartes had their last ever meeting together. But their correspondence continued, sometimes on intellectual matters and sometimes on less recondite topics such as Elisabeth’s rashes, headaches and even bowel movements.
In dedicating his Principles of Philosophy to Elisabeth – he regarded it as his magnum opus, the definitive statement of his scientific views – Descartes wrote,
when I consider that such a varied and complete knowledge of all things is to be found not in some aged pedant who has spent many years in contemplation, but in a young princess whose beauty and youth call to mind one of the Graces rather than grey-eyed Minerva or any of the Muses, then I cannot but be lost in admiration . . . together with your royal dignity you show an extraordinary kindness and gentleness which, though continually buffeted by the blows of fortune, has never become embittered or broken. I am so overwhelmed by this that I consider that this statement of my philosophy should be offered and dedicated to the wisdom which I so admire in you – for philosophy is nothing else but the study of wisdom. And indeed my desire to be known as a philosopher is no greater than my desire to be known as your Serene Highness’s most devoted servant, Descartes.21
That was in 1644. In 1648 he said of The Passions of the Soul that he had written it ‘only to be read by a princess whose mental powers are so extraordinary that she can easily understand matters that seem very difficult to our learned doctors’.22 Elisabeth’s sister, Princess Sophie, wrote, ‘My sister, who is called Madame Elisabeth . . . loves to study, but all her philosophy cannot keep her from chagrin when the circulation of her blood causes her nose to turn red . . . She knows all the languages and all the sciences, and has a regular commerce with Monsieur Descartes, but this thinker renders her a bit distracted, which often makes us laugh.’23 Reference to the ‘circulation of the blood’ shows how alert these young women were to up-to-date currents in science; William Harvey’s book on the subject, completely overturning what had been thought about blood and the heart and proving by experiment that blood is conserved and circulates, had been published in 1628.24
Elisabeth lived with her boring cousins at the Court in Berlin for twenty-one years. In 1667 she entered a Protestant convent at Herford in Westphalia, and after a time became its abbess – a job suitable for one who might have been a queen, considering that the convent employed 7,000 people in its factories, farms, mills and vineyards. It is notable that while Elisabeth was abbess the convent became a refuge from religious persecution for people from any religious background. She died in 1680, at the age of sixty-four.
It was mentioned a few pages ago that Mersenne was a significant contributor to that important moment in the history of thought when, at first in supplementation of, and then gradually freeing itself from, obedience to religious orthodoxy, thought passed through a phase of hope in magical and Cabalistic short-cuts to a knowledge of the universe’s secrets, before settling to the disciplined scientific and philosophical approaches which have marked its best endeavours since, giving us via technological applications computing, space flight, television, modern medicine and so much besides, as well as astounding advances in understanding of nature and the universe. This passage in the history of method – for that is what it really is – and the role in it of Bacon, Descartes and Mersenne himself, merits mention; which the next chapter offers.