This interactive mathlet is an adaptation of the drawing that Leonardo da Vinci made of the augmented rhombicuboctahedron (Vigintisex basium elevatus) for Luca Pacioli's book 'De Divina Proportione'.
The process of adding pryramids to a polyhedron is called 'augmentation'.
We have already used this technique when we study the rhombicdodecahedron as an augmented cube:
In this page we are going to study the augmented rhombicuboctahedron.
The rhombicuboctahedron was also discribed by Luca Pacioli and was drawn by Leonardo:
Pacioli wrote about this 'elevatus' or augmented polyhedron (Spanish translation):
"El cuerpo de veintiséis bases sólido o hueco elevado recibe en su formación ciento cuarenta y cuatro líneas que, unidas entre sí, según las oportunas exigencias, originan en él doscientos ochenta y ocho ángulos superficiales y veintiséis sólidos elevados piramidales, dieciocho de los cuales son deterinados por cuatro ángulos agudos superficiales y ocho por tres agudos. Está compuesto dicho cuerpo por veintiséis pirámides lateradas, dieciocho de las cuales son cuadrangulares y ocho triangulares, que se pueden discernir por la vista en el exterior, y por el mencionado cuerpo de veintiséis bases sólido plano, interior, que solamente puede ser captado por la imaginación. Sus veintiséis bases son igualmente bases de las antes mencionadas veintiséis pirámides, es decir, las dieciocho cuadrangulares de las dieciocho pirámides cuadrangulares y las ocho triangulares de las ocho pirámides cuadrangulares."
('La divina proporción' de Luca Pacioli, page 98, Spanish translation by Juan Calatrava, Editorial Akal, 4th edition, 2008)
Leonardo da Vinci's drawing of the augmented rhombicuboctahedron (Vigintisex basium elevatus solidus) for Luca Pacioli's book 'De divina proportione'. (There is an Spanish version, 'La divina proporción' Editorial Akal. Image used with permission of Editorial Akal).
Leonardo da Vinci's drawing of the augmented rhombicuboctahedron (Vigintisex basium elevatus vacuus) for Luca Pacioli's book 'De divina proportione'. (There is an Spanish version, 'La divina proporción' Editorial Akal. Image used with permission of Editorial Akal).
Interacting with the application you can rotate the polyhedron and play with the "hole" in each face:
We can play with a second versión of this interactive application and see the interior of this polyhedron.
We can compare Leonardo da Vinci's drawing with the image generated with the application.
Dutch mathematician and sculptor Rinus Roelofs pointed out an error in da Vinci's drawing. Dirk Huylebrouck wrote an article that was published in Scientific American magazine about this mistake: Lost in Triangulation: Leonardo da Vinci's Mathematical Slip-Up,
Leonardo da Vinci was a genius, his drawings for Pacioli's book are wonderful and this is only an anecdote that alow us to study and enjoy this beautiful polyhedron.
If we look at the two pyramids that point directly left and right we see something odd. They should be two cuadrangular pyramids but it is not clear if they are triangular or quadrangular. Perhaps it depends on the observer's point of view.
The apexes of two triangular pyramids at the bottom left and right seem to be missing.
The main difference is that the pyramid at the bottom should be triangular but it is quadrangular in Leonardo's drawing.
The two pyramids adjacent to it should be quadrangular and symmetric.
As Huylebrouck pointed out, Leonardo da Vinci was the first to draw the rhombicuboctahedron for print and then he had to add pyramids and then draw this augmented star-shaped polyhedron (Pacioli called this kind of polyhedra 'elevatus'). We do not know if he had a model.
A different opinion was published by Carlo H. Sequin. He thinks that Leonardo was depicting an augmented pseudo rhombicuboctahedron rather than an augmented rhombicuboctahedron.
You can learn more about the pseudo-rhombicuboctahedron following this link:
Then the main problem, the pyramid at the bottom, is now a quadrangular pyramid and Leonardo was right.
We are going to take a look comparing Leonardo's drawing and the augmented pseudo-rhombicuboctahedron. But there is a big objection to this point of view: if we read Pacioli's book he wrote about several polyhedra in the same order ('planus solidus', 'planus vacuus' 'elevatus solidus' and 'elevatus vacuus'). Then he explained the reader the rhombicuboctahedron ('planus solidus and vacuus') and the augmented rhombicuboctahedron ('evelatus solidus and vacuus') and those are the drawings that we expect from Leonardo.
The next application is an adaptation of Leonardo's drawing but in this case we are using a pseudo-rhombicuboctahedron as the polyhedron base of the augmentation.
If we use a pseudo rhombicuboctahedron the problem with the pyramid at the bottom is solved but Leonardo's drawing is still not symmetric and we expect an augmented rhombicuboctahedron and not an augmented pseudo rhombicuboctahedron as an illustration for Pacioli's book.
Luca Pacioli - La divina proporción - Ediciones Akal, 4th edition, 2004. Spanish edition of 'De divina proportione'. Translation by Juan Calatrava.
Rinus Roelofs' web site. Sculptor and Mathematician Rinus Roelofs has a wonderful web site full of beautiful ideas and resources. One example, his article A Mistake in a drawing by Leonardo da Vinci.
Dirk Huylebrouck, Lost in Triangulation: Leonardo da Vinci's Mathematical Slip-Up, Scientican American, March 2011.
Carlo H. Squin, Lost in Triangulation?? No, -it is not a mistake, -it is a Pseudo Rhombicuboctahedron!.
W.W. Rouse Ball and H.S.M. Coxeter, 'Matematical Recreations & Essays', The MacMillan Company, 1947.
Peter R. Cromwell, 'Polyhedra', Cambridge University Press, 1999.
Leonardo da Vinci's Geometric Sketches Frank J. Swetz's article in MathDl, Loci:Convergence.
Leonardo da Vinci's Polyhedra George Hart's excellent website about polyhedra.