The Mathematicall Praeface to Elements of Geometrie of Euclid of Megara — Edition Insights

The Hierarchy of Mathematical Sciences

Dee divides mathematics into two main branches: 'Arithmetic' (dealing with number) and 'Geometry' (dealing with magnitude). From these spring a host of 'derivative' arts: 'Perspective,' 'Astronomy,' 'Music,' 'Cosmography,' 'Astrology,' 'Statics,' 'Anthropography,' 'Trochilike' (the study of wheels), 'Helicosophie' (spiral lines), 'Pneumatithmie' (the art of weighing air), and 'Menandrie' (the art of measuring the earth). Each is given a precise definition and a claim to practical or philosophical value. For instance, 'Perspective' is 'the art of seeing by natural lines,' while 'Astronomy' is 'the science of the stars' motions.' Dee's taxonomy is not merely descriptive; it is a rhetorical tool to argue that mathematics underpins all knowledge, from theology to mechanics. He insists that these arts are 'not only speculative but also operative,' meaning they yield tangible results. This classification serves as a map for the reader, showing how Euclid's geometry is the foundation for a vast network of disciplines.

The Role of Experiment and Mechanical Practice

Dee repeatedly urges the reader to test theoretical claims through physical experiment. In a striking passage, he describes how to determine the ratio of a cube to a sphere by weighing models: 'Way your Cube. Note the Number of the waight. Way, after that, your Sphære.' He then shows how this empirical ratio (21:11) can be used to approximate the squaring of the circle, a problem that had vexed mathematicians since antiquity. Dee emphasizes that the mechanic, 'without Geometrie and Demonstration,' can come 'as nerely in effect' to the truth as the geometer. This is not a rejection of theory but a call to integrate hand and mind. He advises the reader to 'chaunge your Sphære and Cube, to an other matter: or to an other bignes: till you have made a perfect vniuersall Experience.' The language is direct and procedural, almost like a recipe. Dee's confidence in the power of repeated trial—'Often, try with the same Cube and Sphære'—reflects a belief that nature's secrets yield to persistent, methodical inquiry.

The Squaring of the Circle as a Case Study

A central example in the preface is the squaring of the circle, which Dee claims can be achieved 'without hauing knowledge of the proportion, of the Circumference to the Diameter.' He presents a mechanical method: from a square plate, cut out the inscribed circle and compare weights. The ratio of square to circle, he notes, is approximately 14:11. Dee then extends this to find the volume of a cylinder and sphere, showing how one result leads to another. He references his own annotations on Euclid's twelfth book, directing the reader to 'my third Probleme there.' This intertextuality reveals Dee's project as part of a larger scholarly conversation. He also notes that 'many haue cumberd them selues superfluously' by tackling the circumference first, implying that his method is more direct. The passage is dense with numerical ratios and geometric relationships, but Dee's tone remains encouraging: 'Your diligence may come to a proportion ... nerer the truth.' He presents the squaring of the circle not as a finished achievement but as an ongoing inquiry, open to refinement.

The Reader as Active Participant

Throughout the preface, Dee addresses the reader as a collaborator in the pursuit of knowledge. He uses imperatives—'way,' 'note,' 'procede,' 'inferre'—that transform reading into doing. The text is punctuated with marginal symbols (pointing hands, asterisks) that guide attention, and the original printing included foldout diagrams. Dee's rhetoric is designed to empower: he assures the reader that 'you may begyn at the Circle and Square, and so come to conclude of the Sphære.' The preface is not a passive exposition but a training manual for the mind. Dee also defends the dignity of the mathematical arts against those who dismiss them as mere craft. He argues that mathematics 'beautifieth and adorneth the soule' and leads to contemplation of God's creation. This dual appeal—to practical skill and spiritual elevation—is central to Dee's project. The reader is invited to see themselves as both a philosopher and a mechanic, capable of uncovering the mathematical order underlying the universe.

Dee's preface rewards a reading that moves between his grand claims for mathematics and the specific experimental procedures he describes. Pay attention to the marginal notes and diagrams (where present), as they are integral to his argument. The text is best approached not as a linear treatise but as a network of interconnected arts, each illuminating the others. Dee's voice is that of a teacher eager to share a method, not just a doctrine. Let his enthusiasm for 'naturall veritie' guide your engagement with Euclid's geometry.

The rain tapped against my window that afternoon, and I found myself lost in John Dee’s preface, his insistence that mathematics demanded not just thought but touch. His words felt like a nudge toward the workbench, a gentle push from contemplation into craft. Closing the book, my hand drifted to another volume by my chair, Archimedes — Key Ideas to Explore, and the quiet pleasure of that accidental shift stayed with me long after the sky cleared.