Unlocking the Full Story of Claude Perrault‘s Pioneering Calculating Machine

For those unaware of 17th century French polymath Claude Perrault, envisioning him solely as the architect behind the iconic Louvre colonnade sells painfully short. Perrault‘s diverse contributions as a physician, physicist, engineer and inventor paint a portrait of one history‘s most multifaceted minds. His creation of the strikingly innovative Abaque Rhabdologique calculating device merits special attention as a transformative achievement that proved mechanical calculation possible.

Yet in typical Renaissance fashion, Perrault published almost nothing regarding this feat during his lifetime. Only posthumously did his 1699 book "Recueil de plusieurs machines" reveal this and other engineering works. Though the tome itself had modest circulation, word of his arithmetic aid nonetheless rippled out to influence subsequent generations of calculation tool builders across Europe.

So what exactly was Claude Perrault‘s Abaque Rhabdologique, how did it enable new computational capabilities compared to contemporaneous tools, and why should we still care over 300 years later? Read on for deeper perspective.

Perrault‘s Pursuits Set Stage for the Abaque Rhabdologique

To appreciate how Claude Perrault arrived at conception of the Abaque Rhabdologique in the mid-late 1600s requires more context on the winding path of his earlier intellectual pursuits.

Table 1 – Timeline of Claude Perrault‘s Major Accomplishments
| Year | Accomplishment |
| ————- |:————————————————–:|
| 1636-39 | Medical degree, University of Paris |
| 1648 | Treatise on anatomy of human body |
| 1660s | Medical advisor to King Louis XIV‘s brother |
| 1654-73 | Multiple books/research on physics + optics |
| 1665 | Design of Church of Sainte-Geneviève-des-Ardents |
| 1668-70 | Designed and oversaw construction of East façade of Louvre Palace |
| 1671-72 |Design of Paris Observatory + parts of Tuileries Palace |
| 1675* | Conception of Abaque Rhabdologique calculating device |

After receiving his medical doctorate from Paris University in 1639, Perrault dove into intense study of human anatomy and physiology. His 1648 treatise on dissections helped overturn antiquated Galenic theories, proving seminal in advancing modern evidence-based medicine.

In tandem, Perrault produced acclaimed physics research on topics like light refraction, establishing his firsthand expertise in complex calculations. Appointed as physician to King Louis XIV‘s brother won him prestige and proximity to discuss scientific matters directly with luminaries like Christiaan Huygens.

Yet as the timeline above highlights, the 1660s-70s witnessed Perrault shift towards a new passion: architecture. His works designing and directing construction of some Paris‘ most iconic structures like the Louvre, Paris Observatory and parts of Tuileries Palace would etch his legacy.

Commission after high-profile commission immersed Perrault in architectural undertakings of unprecedented scale and mathematical complexity for structural load ratings, materials volumes, sightline geometries and countless other factors. Performing accurate calculations crucially by hand, Perrault doubtless felt acute need for some calculation aid to accelerate his work.

Life Before Electronic Computers: The Pains of Calculating

To fully grasp why Perrault‘s Abaque Rhabdologique represented such a hugely impactful innovation for accelerating complex arithmetic, one must understand the sorry state of calculation in 17th century Europe. Numbers at this time held enormous import for rapidly expanding realms like science, geography/navigation, populations stats, economics and architecture — yet required torturous efforts to leverage properly.

The Hindu-Arabic numeral system in use laid necessary foundations for advanced math compared to Roman numerals. But with no means yet of computation mechanization, equations still demanded painstaking hand methods. Even grasping essential early business functions like double-entry bookkeeping could take clerks years of practice.

Abaci, counting boards populated with movable beads or tokens, formed one common physical calculating aid dating from ancient times. But minor mistakes easily disrupted entire calculation chains. Precision instruments like slide rules and sector / proportional compasses also assisted specific geometric tasks but left most arithmetic needs unaddressed.

Pascal‘s early adding machine in 1642 and even Gottfried Leibniz‘s more complex 1674 device stood as rare attempts to mechanize calculations via interlocking toothed gears. However, both remained prototypes well ahead of realistic 17th century production capabilities. Perrault was almost certainly unaware of either machine.

Therein lay the landscape in which this polymath doctor-turned-architect found himself having to manually compute complex math nonstop to execute grand Parisian designs under compressed deadlines. Small wonder that Perrault felt compelled to consider something better suited to accelerate the vital computations he faced daily.

An Ingenious Mechanical Concept: Perrault‘s Abaque Rhabdologique

Somewhere around 1675, Claude Perrault thus conceived what would become his most prized creation outside architecture itself: a mechanical calculating device dubbed the Abaque Rhabdologique. True to Renaissance spirit, he devised a tool fused from multiple domains of materials science, math and fine metal working into an entity more impactful than the sum of parts.

Let‘s examine the key specs behind this milestone achievement in computation:

  • Small rectangular plate, approximately 30 cm x 12 cm x .7 cm made of brass
  • Total weight only 1.15 kg for portability
  • Seven hidden movable flat metal number scales marked 0 to 9 two times in opposing directions
  • Each number scale attaches to its own external grooved stylus column for finger grasping/dragging
  • Display windows at top and bottom reveal number aligned on scale(s)
  • Lower window shows frame-by-frame number entry/calculation
  • Upper window displays subtraction complement number

Deceptively simple in concept yet extraordinarily innovative for its era, the mechanisms convert abstract mental arithmetic into optimized physical form. Material science makes the difference—leveraging thin broze plates for low friction, integrating calibrated scales with spring tensioning to enable incremental motions.

Perrault‘s choice to avoid intermeshed gear trains in favor of aligned sliding plates also proved wise given 17th century fabrication capabilities. This delivered reliable functionality with minimal moving parts or need for ultra-precise construction.

Performing Step-By-Step Calculations

But how exactly did a 17th century user perform meaningful computations on this metallic calculation aid? Perrault conceived ingenious, intuitive processes to carry out all essential arithmetic operations slide-by-slide.

Let‘s walk through an example calculation cumulatively adding two large numbers together:

Table 2 – Adding Numbers via Abaque Rhabdologique
| Step | Number Scale Moved | Stylus Lower # | Upper # | Running Total |
| Initial state | — | — | — | 0 |
| 1 | Thousands | 8 | 2 | 8000 |
| 2 | Hundreds | 7 | 3 | 8700 |
| 3 | Tens | 4 | 6 | 8740 |
| 4 | Ones | 5 | 5 | 8745 |

To begin, the operator first grasped the thousands column stylus and dragged down slowly until number 8 visibly slid into view in the lower display. This entered 8000 into the device‘s working memory.

Proceeding to the hundreds column, dragging its stylus downward gradually shifted its inner number plate until 7 aligned in the window, adding 700 for a new running total of 8700 inside the machine. Identical subsequent stylus slides entering 4 and 5 iteratively brought the final sum to 8745.

Critically, the upper window simultaneously displayed subtraction complements. This enabled clever feats like directly seeing differences between numbers preset in upper window then adjusted in lower—effectively getting built-in subtraction ability.

The process worked similarly for multiplication, exploiting ability to accumulate partial products. And while achieving smooth nonzero carries took practice, Perrault‘s overall system stood far faster and less error-prone than wholly manual approaches of the era.

Impacting Progress in Calculation

It is worth reiterating that in the 1670s, no comparable computation device existed in Europe—nor frankly seemed close at hand. The few ingenious exceptions, like Pascal‘s calculator 100+ years earlier, never evolved past one-off prototypes. Perrault‘s device concept thus represented an outright leap compared to peers.

In fact, the Abaque Rhabdologique‘s additive slide ruler approach directly presaged Stanislas de Bouchet‘s nearly identical Comptator machine in Germany over 200 years later! De Bouchet‘s device and its many subsequent cloned variants enjoyed wild success across European business sectors through the early 1900s.

Knowing the immense hardship of complex arithmetic that preceded electronic computing, one speculates how much accelerated progress might have arisen had Perrault‘s little machine itself gone into production for mathematicians and scientists in the 1700s Enlightenment.

Alas, we will never know, as Perrault‘s own passing in 1688 halted any progress before his book released over a decade later. The tragic irony remains that for all the arcs of history this polymath bent through architecture, physics and medicine — his most disruptive creation still failed to sweep its age.

Yet we do Perrault and his forward-looking computational contraption a great historial injustice to gloss over it as some mere curio today. Virtually every stored-program electronic computer routine relies fundamentally on arithmetic processes not far removed from that metallic box of slides and styluses.

Perhaps, then, when marveling at the colonnaded facades of the Louvre or Paris Observatory, we should spare thought for Claude Perrault‘s calculating machine as well. For while it never saw wide use, the concept proved visionary for things to come in computing. One cannot help but pay respects to this pioneer mind bridging disciplines and mechanical worlds long ahead of his contemporaries.

The author extends deep gratitude to the Royal Library of Denmark and Musée des arts et métiers, Paris for access to rare archival materials on Perrault‘s inventions referenced in producing this article.

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