Scientist of the Day - Franz Reuleaux

Reuleaux mechanism O03, slide-crank mechanism, 1882, Cornell University (digital.library.cornell.edu)

Franz Reuleaux, a German mechanical engineer, died Aug. 20, 1905, at the age of 75. Reuleaux, who taught at the Technische Hochschule in Berlin, was one of the first engineers to approach engineering design from the vantage point of mathematics, rather than mechanics, which was quite a revolutionary slant in the mid-19th-century; engineers at that time were customarily craftsmen, not theoreticians. Reuleaux wrote a series of books on kinematics, the science of motion without regard to causes, a number of which we have in our Library. But to the non-engineer, one of his most interesting contributions to the field was the design, construction, and marketing of a series of engineering models, designed to help teach students about mechanisms.  Reuleaux designed over 800 models, and some 300 of these designs were manufactured by Gustav Voight in Berlin around 1880 and offered for sale.

Portrait of Franz Reuleaux, undated photograph, Digital Mechanism and Gear Library (dmg-lib.org)

Cornell University had been founded in 1865, and its first president, Andrew Dickson White, was very encouraging of educational innovation, and it was White's idea to purchase 230 of Reuleaux's models for use in instructing would-be engineers at Cornell. He did so, and amazingly, most of these still survive. They are made of iron, brass, and wood, are fully operational, and are quite beautiful to behold, if you like well-crafted machines, and who does not? White was the same Cornell president responsible for purchasing the Blaschka glass invertebrates at about the same time, which we discussed and displayed in a recent post on Leopold Blaschka

Reuleaux mechanism S34, Cartwright straight-line mechanism, 1882, Cornell University (digital.library.cornell.edu)

The Reuleaux models at Cornell seem to be the property of the Sibley School of Mechanical and Civil Engineering. The mechanisms have had a fitful web presence. Back in 2010 they were all imaged online, along with animations that showed how many of them work. Then the Reuleaux website disappeared for 10 years or so. Now it is back, with photos and some technical details for each of the mechanisms, but no animations, except for occasional gifs that are not helpful.  Here is a general introduction to the Reuleaux Collection, and here are the models in sequence with thumbnails.  They really need to bring the animations back, especially for those with elaborate linkages.  There are several animations on YouTube, and I chose the Cornell models to show here with those animations in mind. Each mechanism has been placed in a type class, identified by a capital letter, and then each mechanism in that class has a number. Our first image, a slide-crank mechanism labeled O03, can be seen in action in this animation.  Our second mechanism is called S34 (third image) and can be seen in motion here.

Reuleaux mechanism B2, Reuleaux triangle rotor, 1882, Cornell University (digital.library.cornell.edu)

Reuleaux is best known for a device used in mechanism B2 (fourth image). It has a rotor turned by a crank on the back, and its rotor has an unusual shape, like a fat equilateral triangle. You can see it better in a detail (fifth image). It is an example of a polygon of constant width, which means it can rotate between two parallel lines separated by that width, and continually touch both lines, even though visually it seems to wobble back and forth. This means that a Reuleaux triangle, as it is now called, can rotate in a square and continually touch all four sides (excepting a tiny space in each of the four corners), as it does in device B2.

Close-up view of Reuleaux mechanism B2, Reuleaux triangle rotor, 1882, Cornell University (digital.library.cornell.edu)

This peculiar property of the Reuleaux triangle was utilized in a design for a rotary internal-combustion engine built by German engineer Felix Wankel in 1957 (sixth image).  The combustion chamber was no longer a square, but the rotor was still a Reuleaux triangle, as you can see in this animation.

A Wankel rotary engine, made for Mazda, with a Reuleaux-triangle-shaped rotor, photograph (Wikimedia commons)

Wankel engines were used in several motorcycles and a few automobiles, including the Mazda RX-7 and RX-8 sports car, in the 1970s and the ensuing three decades. However, problems with the seals on the rotor, and with meeting emission standards, led Mazda to discontinue its use of rotary engines in 2012, and I doubt if they are going to come back.

Reuleaux mechanisms on display at Upson Hall, Sibley School of Mechanical and Aerospace Engineering, Cornell University (engineering.cornell.edu)

As for the Reuleaux models at Cornell, some, if not most, of them are on display in cases in the corridors of Upson Hall (seventh image).  I have not seen them in person, despite the fact that I visited Cornell and the Corning Glass Museum this spring.  I regret very much not having had the opportunity to look at the models firsthand. In my opinion, the Reuleaux model mechanisms have never been equaled in terms of beauty, elegance, ingenuity, and sheer variety. They deserve to be better known.

Room showing the Reuleaux mechanisms on display in 1885 at Sibley College, Cornell University, detail of front-cover set of wood engravings, Scientific American, vol. 53(10), p. 239, fig. 1,  Oct. 17, 1885 (Linda Hall Library)

At the last minute, I ran across a front-page story on Cornell’s Sibley School of Engineering in a Scientific American issue for 1885. The first of the 8 wood engravings on the front page undoubtedly depicts the recently-arrived Reuleaux mechanisms on display in fine glass cases, although Reuleaux is not mentioned by name in the accompanying article. I include an iPhoto as our last-but-one image.

Grave of Franz Reuleaux, with no sign of a Reuleaux mechanism anywhere, Technische Universität, Berlin (Wikimedia commons)

William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor emeritus, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to ashworthw@umkc.edu.