The dioptra became the standard surveying instrument of the Greeks and, although no actual example has yet been found (or at least identified), we can discover a surprising amount about its design and employment by tapping sources hitherto almost untouched. Apart from Hero's well-known manual, three treatises or fragments of treatises on the dioptra survive under the names of Julius Africanus, the Anonymus Byzantinus and al-Karaji, along with many passing mentions in other literature. To ease the diffculties of understanding these sources, it may help at this early stage to paint a brief preliminary picture of this very flexible device. Contrary to widespread belief, Hero's complex dioptra was not the only version. It was, rather, a oneoff and probably fruitless attempt at improving on the earlier and much simpler dioptra, which already existed in a number of varieties that differed only in detail.

This simple type was a disc, engraved with two diameters at right angles and carrying an alidade or comparable sighting bar pivoted at its centre (Figs. 3.1–2). It could be mounted in two different ways. If it was suspended on edge by a ring from a suitable stand it acted as its own plumb, and hung vertically. A horizontal sighting line for levelling was obtained by aligning the alidade with the horizontal diameter.

THE U-TUBE LEVEL

This simple builder's level of recent times works on the principle of the U-tube in which water finds its own level. A long flexible tube of rubber or polythene is laid along the ground. One end is held vertical against the mark from which the level is to be taken, the other end is also held vertical, but initially rather higher, at the point to which the level is to be transferred. The tube is then filled until the water reaches the brim at the starting end, and the other end is slowly lowered until it coincides with the water surface. Because no sighting is involved, the result is extremely accurate. The question of whether the method was used in the ancient world has in the past been asked, but rejected on the grounds that making a U-tube of sufficient length would have been difficult.

Flexible pipes, however, were not unknown. A leather pipe at least 50 cubits long, no doubt sewn and greased, was used to raise fresh water to the surface from a spring on the sea bed off the Phoenician coast, and others for carrying steam were installed in a fiendish early Byzantine device. A better material, because less prone to leakage and easier to make, would be animal intestine.

GRIDS

The groma was an extremely simple instrument, possibly of Greek origin, which became almost the trademark of the Roman land surveyor. Because its function was limited to sighting and setting out straight lines and right angles, its use was restricted to surveying roads and the like and to establishing the rectangular grids of towns, military forts and, above all, land divisions. Since roads form the subject of Chapter II, we may here confine ourselves to a brief outline of the history of surveyed grids.

An irregular street pattern was normal to early Greek cities; but in later times a regular rectangular grid became more widespread. Its introduction was generally attributed to Hippodamus of Miletus who rebuilt a number of cities in this way in the first half of the fifth century BC, and certainly it was a commonplace by 414 BC when Aristophanes lampooned the astronomer Meton as a town planner laying out Cloudcuckooland. But while Hippodamus may have popularised the grid, he did not introduce it, for there are many Greek instances from earlier centuries, and even Egyptian and Mesopotamian antecedents. It was most commonly applied to Greek colonies overseas, which often had the advantage of being built on virgin sites.

CATEGORIES

Surveying and driving tunnels must count among the most difficult of engineering projects. Not only are conditions of work underground unpleasant and dangerous, but to establish and maintain the required gradient and the required alignment through solid rock demand skills of a high order.

Tunnels could be of two basic kinds. One was the single-ended tunnel with only one mouth opening to the surface, the other end being underground in an aquifer as in the Persian qanat or in orebearing rock as in a mine adit. The other was the through tunnel for conducting water (or occasionally a road) through an obstruction such as a mountain ridge. This variety could be driven by two different methods.

The first, but certainly the second best, was the two-ended tunnel, where the depth of rock above was too great to sink shafts, except perhaps near each end for the purposes of alignment. The best known example is that built about 530 BC for the tyrant Polycrates by Eupalinus of Megara to bring water to the town of Samos. Its length was 1036 m, but it was not the longest of its kind.

BASIC PRINCIPLES

Much the best-known feature of Roman roads is their straightness. Over long distances this is not, of course, by any means invariable. In hilly terrain the route necessarily meanders in search of reasonably gentle gradients, and although in such cases the engineer evidently used instruments to achieve a succession of short straight alignments he must have relied overall, as he did in setting out aqueducts, on his eye for the country. Nor, very probably, did early Roman roads follow such straight courses as did later ones. It seems likely that the first routes out of Rome, built in the wake of conquest and traditionally beginning with the Via Appia of 312 BC, were quite basic in alignment and structure and were merely improvements of existing trackways. In just the same way, when Vespasian's army advanced into Galilee in AD 67, ‘road-makers straighten bends on the highway, level the rough places and cut down woods that are in the way, so as to spare the troops the fatigue of laborious marching’. The origin of straight alignment and solid structure is often ascribed on the basis of Plutarch's biography to C. Gracchus and his laws of 123 BC.

Zealotry and the well-ordered state

In the late 1580s, Bacon began to be concerned about what he saw as ill-considered criticisms of traditional learning, and the attempt by radical Puritans to set themselves up as arbiters of knowledge. His hostility to this movement is explicit, and there are two strands in his criticisms of it. First, there is an unyielding commitment to the authority of the sovereign. Bacon tells us approvingly in An Advertisement touching the Controversies of the Church of England of 1589 that ‘it is a precept of Salomon, that the rulers be not reproached; no, not in thought: but that we draw our very conceit into a modest interpretation of their doings.’ This is very much in line with traditional Tudor thinking, which was quite sensitive to potentially disruptive forces in society and aimed to contain the various forces in society by subordinating them to the absolute authority of the sovereign. Although there has been a tendency to stress this ingredient in Bacon's criticisms, as if it in itself sufficed to explain them, I want to suggest that it is not enough, at least at anything other than a general perfunctory level. It is a second ingredient in Bacon's criticisms which I believe should bear the explanatory weight: This is the fact that his criticisms are very specifically those of a Renaissance humanist.

In Chapter 2, we saw that the two principles to which both Italian and northern humanists were committed were the importance of sound learning for sound government, and the responsibilities of humanists to provide such sound learning in the practical context of government.

The idea of mathematics or mechanics as a model for natural philosophy was something that took shape gradually during the seventeenth century. By contrast, during the Renaissance the models were taken from a variety of areas in which argument, persuasion, discovery, and the many other things that one expected of natural philosophy were pursued. Law and textual criticism figured predominantly here, for these were areas in which major reforms were being introduced and which were continuing to yield benefits. For Renaissance thinkers – even those who, like Bacon, can take a significant share of the responsibility for the transition to modernity – it is above all the legal-rhetorical tradition that shapes their theoretical sensibilities. In the first instance, Bacon set out not to reform natural philosophy but to reform law and, through this, politics. His shift from the reform of law to the reform of natural philosophy is possible and, in a way that is initially very difficult for us to understand, natural, because what Bacon sees as the problems in law and natural philosophy have a number of shared – or at least analogous – sources. These sources are something embedded in English Renaissance culture, and Bacon very largely uses the resources of that culture to unearth and transform them. Consequently, our first priority must be that culture.

An education in rhetoric

Bacon was born into one of the most illustrious families in England. His father, Sir Nicholas Bacon, although from humble origins, was Lord-Keeper of the Great Seal of England, and was both eloquent and cultured.

Matter theory and natural philosophy

In Chapter 5 we saw that Bacon's account of method is closely tied to his advocacy of matter theory as the foundational natural-philosophical discipline. His natural-philosophical interests range across what we might now think of as cosmology, chemistry/alchemy, and physiology, and we can consider the means by which natural philosophy was pursued in these three areas in the seventeenth century in terms of two fundamental disciplines, mechanics and matter theory. The first deals with physical processes in terms of the motions undergone by bodies and the nature of the forces responsible for these motions. The second deals with how the physical behaviour of a body is determined by what it is made of, and in the seventeenth century it typically achieves this in a corpus-cularian fashion, by investigating how the nature and arrangement of the constituent parts of a body determine its behaviour. Traditionally, matter theory had been constitutive of natural philosophy, and it was generally assumed from the Presocratics up to the seventeenth century that the key to understanding physical processes lay in understanding the nature of matter and its behaviour, whether this understanding took the form of a theory about how matter is regulated by external immaterial principles, internal immaterial principles, or by the behaviour of the internal material constituents of macroscopic bodies.

Around the beginning of the seventeenth century, however, there was an attempt to draw on the traditional disciplines of practical mathematics – geometrical optics, positional astronomy, harmonics, and statics were the best developed – and to incorporate these into natural philosophy.

Cicero tells us that Cato had applied himself to philosophy, not that he might dispute like a philosopher, but that he might live like one. Bacon quotes this remark on a number of occasions, and it invokes a conception of philosophy that dominated not just antiquity but also the early-modern era. It is a conception according to which there is a way of engaging intellectual, cultural, moral, scientific, and aesthetic problems which is not only distinctive, marking out the philosophical treatment of these problems from that of the theologian or the statesman or the artist, for example, but whereby the philosopher is someone who has a particular standing, a particular claim to be heard. Rightly or wrongly, the scientist has now largely usurped much of this role from the philosopher – it is now the scientist, rather than the philosopher, who lays claim to a ‘theory of everything’, for example – and although this shift was consolidated only in the nineteenth century, the influence of Bacon has been such that it is to him, more than anyone else, that we must trace its origins. For it is Bacon who, more than anyone else, urges and guides the transformation of philosophers into what later came to be known as scientists, inducing the birth of a new discipline quite different from philosophy as traditionally practised, and leaving not just philosophy, but the humanities generally, with the problem of forging a new identity for themselves.

From the time of his death in 1626 onwards, Bacon's fortunes have risen and fallen dramatically.

From arcane learning to public knowledge

Bacon's project was to harness firmly to the yoke of the state a new attitude to knowledge, and in the course of attempting to do this, he was led to think through and transform this new attitude to knowledge. At the most elementary level, his aim was to reform natural philosophy, but what exactly he was reforming, and how he envisaged its reform, are not straightforward questions. The object of this reform was both the practice and the practitioners of natural philosophy. He was concerned to reform a tradition of natural philosophy in which the central ingredients were areas such as natural history and alchemy: empirical, labour-intensive disciplines.

In a pioneering essay, Kuhn attempted to distinguish between what he referred to as the mathematical and the experimental or ‘Baconian’ traditions. This is a useful first approximation, and it indicates a divergence of research in the seventeenth and eighteenth centuries (although Newton, for example, was considered to have produced models in both traditions, in his Principia and his Opticks, respectively). It is only to be expected that this characterisation is of less help in understanding the way in which fields of research were structured at the time Bacon was writing – and of course it is this that we need to understand if we are to comprehend what Bacon's reforms were directed towards – but there is a similar divergence between two broad kinds of discipline.

Charles Webster has noted that, unlike Descartes, Bacon wrote nothing that could be translated into textbook form; but Bacon's contribution was not really the kind of thing that could have been encapsulated in such a form. Even his account of inductive procedures is so geared to the particular problems faced in pursuing the matter theory of his time that, although some insights are undeniably generalisable, unlike the theories of method of nineteenth- and twentieth-century philosophy of science the attractiveness of his account lies primarily in the attention to detailed problems facing the isolation of particular properties of matter, a detail which was gradually superseded as the discipline became transformed and its role in physical inquiry rethought. Bacon's main contribution is not one to be described as lasting so much as irreversible. He inaugurated the transformation of philosophy into science, and philosophers into scientists, for even though the ideas of ‘science’ and ‘scientists’ in the modern sense are only really established in the nineteenth century, their genealogy goes back to Bacon's attempt to effect a fundamental reform of philosophy from a contemplative discipline exemplified in the individual persona of the moral philosopher, to a communal, if ultimately centrally directed, enterprise exemplified in the persona of the experimental natural philosopher. In turn, observation and experiment are lifted out of the purview of the arcane and the esoteric, and planted firmly in the public realm.

The ‘Great Instauration’

When Novum Organum was first published in 1620, among the various short pieces with which it was prefaced was a general plan of the parts of the projected ‘Great Instauration’. This Distributio Operis divides the project into six parts. The first, which Bacon describes as ‘a summary or general description of the knowledge which the human race at present possesses’, was entitled ‘division of the sciences’, which had been the theme of the Advancement of Learning, and would be covered in a comprehensive way in the revised Latin version, De Dignitate & Augmentis Scientiarum. The latter was written for a continental audience and revised accordingly, and it was indicative of Bacon's realisation that little was likely to be done to implement his scheme in England, and of his desire to reach a wider audience.

The second part is ‘the New Organon, or Directions concerning the Interpretation of Nature’. The aim here is to equip the intellect to pass beyond what is already known. It is covered in Novum Organum, and although much earlier work on method is incorporated into Novum Organum, its detailed and comprehensive treatment makes it invaluable, and it has been widely regarded as Bacon's principal lasting contribution to natural philosophy – an assessment which I believe is entirely correct. Nevertheless, it is incomplete and was clearly intended to comprise more than the two books which Bacon managed to complete: In Book 2, he sets out nine major topics he will take up, the first seven of which seem relevant to the second part of the project, but he deals only with the first of these.

The psychology of knowledge

In 1597, at the age of thirty-seven, Bacon published his first book, a slim octavo collection containing three works: a collection of ten brief English Essayes, the short Latin essay Meditationes Sacrae, and Coulers of Good and Evill a Fragment. The term ‘essay’ literally means ‘attempt’ (Fr. essai), and essays were generally aphoristic and thought-provoking: They were not designed to survey a field in any detail. It was Montaigne who had made the essay form such a success in the early-modern era, but although there can be little doubt that Bacon would have read Montaigne by 1597, he does not mention him as a source. Also, there are significant differences between Montaigne's essays and those of Bacon. Whereas Montaigne is enticing, drawing the reader in, shifting from the personal to the general, from the serious to the capricious, Bacon's tone is didactic throughout. Montaigne aims at a broad audience, while Bacon seems to be writing for the court: The Essayes are much closer to Castiligione than Montaigne, both in genre and in tone.

The Essayes proper – which deal briefly with study, with speech (‘discourse’), ceremonies, followers and friends, lawsuits, spending money, health, honour and reputation, political factions, and negotiation – are resolutely practical. The first, ‘Of Studies’, does, however, draw attention to two enduring themes in Bacon, namely, the superiority of the learned in making judgements, and the notion that the value of studies is to be tied to their usefulness. Moreover, the instruction that we must ‘reade not to contradict, nor to belieue, but to waigh and consider’ is surely an implicit rebuke to Scholastic methods of teaching.