Today, books with pop-up illustrations—flaps to be lifted, tabs to be pulled, and wheels to be turned—form a small niche of the book market. Mostly, pop-up books are meant to get young children interested in books and reading. Once that interest is kindled, pop-ups are discarded for more sophisticated reading material.
The charm and whimsy of pop-up books might seem far removed from the dry seriousness of technical literature. But during the first three centuries of printing, from about 1450 to 1750, most pop-ups appeared in scientific books. Movable paper parts were once used to explain the movements of the moon, the five regular geometric solids, the connections between the eye and the brain, and more. Although there are examples in medieval manuscripts, pop-ups became prominent during the age of print, when there was a rising demand for books on scientific subjects.
The invention of printing was accompanied by a surge in literacy and book ownership. Readers expanded beyond the small, wealthy, educated elite that held medieval manuscripts. These new readers were hungry for knowledge. Scientific, technical, and medical books aimed at the general public (as opposed to academic or specialist readers) were among the most popular types of books produced during the early era of print.
But popular science books posed some new challenges for both authors and readers. Since antiquity, teachers had held that scientific subjects were best learned through pictures and working models. Beginners needed to see, touch, and manipulate the objects of study. Teachers of astronomy and mathematics, for example, had long employed three-dimensional models and instruments in their classrooms. Anatomy instructors had used the bodies of humans and animals to illustrate their lessons. For this reason, many scientific, mathematical, and medical books were richly illustrated.
But for the reader to understand the intricate motions of the heavenly bodies, complex geometrical shapes, or the depths of the human body, a two-dimensional illustration might not do the trick. Movable paper parts did.
Authors of popular astronomy texts were among the first to utilize them. Astronomy in this period was geocentric; the sun, moon, and five visible planets were thought to move around the Earth. Each body’s overall motion combined several circular motions. To take the simplest example, the sun was thought to have two motions: It spun around the Earth from east to west every 24 hours, and it moved across the celestial sphere from west to east over the course of a year. Visualizing an object that is simultaneously rotating in two different directions at two different speeds around two different axes was (and is) no mean feat. Michael Crowe, a historian of astronomy, suggests imagining spinning a basketball on your finger while an ant crawls around the ball in the opposite direction. The motion of that ant is the combination of two circular motions. In the classroom, three-dimensional models of the cosmos (armillary spheres) helped students grasp these motions.
The authors of popular astronomy books used a simplified, paper-craft version: paper wheels called volvelles. These could be used to demonstrate the motions of heavenly bodies or to make calculations about those motions. Assembled from layers of paper circles that could be rotated by the reader, volvelles served the same function as armillary spheres in a more affordable, portable format.
One of the most successful popular astronomy books of the 16th century was Peter Apian’s Cosmographia, a work that went through almost 40 editions in Latin, Dutch, French, and Spanish. Apian included five different volvelles in the book. One of these volvelles demonstrates the relationship between the moon and the sun and the phases of the moon.
The volvelle consists of two paper wheels connected with a small piece of string to a printed circle. The topmost wheel has a circular hole, revealing the lower wheel beneath. Both wheels can be rotated freely in either direction. The top wheel of the volvelle has an indicator with the moon on it. Spinning this wheel represents the moon’s west-to-east monthly circuit around the Earth. The lower wheel has an indicator with the sun on it. Spinning this wheel represents the sun’s yearly west-to-east motion. When the reader moves the two wheels, the phases of the moon appear in the hole cut out of the top wheel.
This same volvelle also allows a rough calculation of the time at night. To do this, the indicator on the inner wheel is made to point to the lunar hour (lunar hours are longer than 60 minutes, because it takes the moon longer than 24 hours to complete a circuit around the Earth). Then the indicator on the outer wheel is moved until the correct phase of the moon shows through the hole in the top wheel. When aligned in this way, the indicator on the outer wheel points to the hour of night. The calculation was not very accurate, but precision was not the point. Rather, manipulating these two paper circles helped the reader grasp the relationship between the motions of the two most visible celestial bodies.
The Spanish navigator Martín Cortés included a modified version of a different Apian volvelle in his Brief Compendium on the Sphere and on the Art of Navigation, published in 1551. Cortés’s volvelle allowed the reader to figure out which sign of the zodiac the sun and moon were in on any given day of the year. As an observer watches the sun rotate around the Earth over the course of a year, it will appear to change positions relative to the stars that make up the zodiac. The sun appears in a new sign of the zodiac about once a month. In Cortes’s volvelle, the names of the months, the numbers of days, and the corresponding signs of the zodiac are printed on the page in a circle. Two wheels are superimposed on this circle. If you turn the middle wheel so that the indicator, which has a picture of the sun on it, points to the month and day, you can read off which sign of the zodiac the sun is in at that time. Again, this doesn’t allow for very precise calculations, but the point was explanatory clarity.
Geometry was another subject where learners benefited from drawings and models. The first English translation of Euclid’s Elements of Geometry in 1570 had a striking set of pop-up illustrations depicting various geometrical solids. The illustrations include some simple flaps illustrating lines and planes, where the plane is represented on the flat page of the book and the flap can be raised to demonstrate the position of a line or a plane perpendicular to the plane of the page. There are also illustrations with multiple triangular flaps that, when raised by the reader, form the shape of pyramids with three, four, and five sides. To illustrate more complex shapes, there are 10 patterns that the reader could trace onto stiff paper and fold into solids, including a tetrahedron, an icosahedron, and a parallelepiped.
But anatomy was the visual and experiential science par excellence. Medical students were not expected to learn anatomy from books alone. Since at least 1300, university lectures on anatomy had been accompanied by dissections of human and animal bodies. To accommodate curious readers of the 16th and 17th centuries who had no opportunity to attend dissections, printers all over Europe made flap anatomies.
Large sheets of paper were printed with male and female figures and a small amount of explanatory text. Flaps of paper representing different organs were pasted in layers on top of the figures. The top flap represented the skin and external anatomy; when it was down flat, the figures looked like ordinary nudes. By lifting the flaps, the viewer performed a virtual dissection, revealing successive layers of internal organs. The top flap was most commonly lifted from the crotch region of the figures, adding an erotic frisson that undoubtedly contributed to their enormous popularity.
Flap anatomies also appeared inside medical books. In 1583, the German surgeon and eye doctor Georg Bartisch published Opthamoduleia, a massive tome on diseases of the eye and their treatments. He included two flap anatomies in the text. The first showed the anatomy of the brain: The viewer lifted the skin and hair, the skull, and the cerebrum to reveal the brain stem and optic nerves. The second was a seven-layer anatomy of the eye. The French philosopher René Descartes also included a flap anatomy of the heart and lungs in his Treatise of Man of 1664.
The most elaborate flap anatomies are found in the works of the Dutch anatomist Johann Remmelin, whose book Microcosmic Mirror went through multiple editions from 1613 to 1744. Most contain three pages of flap anatomies: The first has a male and a female figure and a pregnant torso, the second a male figure, and the third a female figure. These all have multiple sets of flaps, many of which open in different directions and have printing on both sides.
Pop-ups weren’t completely unique to printed scientific books. Printers exploited wheels and flaps for a variety of uses, like games of chance, the creation of codes, and mildly salacious prints that allowed the reader to lift up a courtesan’s skirt and see her undergarments. But it took until the early 19th century for pop-ups, flaps, wheels, tabs, and other moving parts to become a feature of children’s books.
Pop-up science texts were a creative response to the demands of an expanding base of readers, hungry for information about the natural world. The appetite for such books remains strong today, as the popularity of books by Neil deGrasse Tyson and Stephen Hawking demonstrates. Although Tyson and Hawking do not include movable paper parts in their books, they grapple with the same challenge their forebears faced: how to make scientific subjects accessible to general readers.
Pop-ups are no longer used to do this, in part because of changes in print technology. But at a deeper level, the abandonment of flaps and volvelles and their ilk in books for adults also reflects changes in reading practices. Modern readers think of reading primarily as a mental activity. Earlier readers saw it as a physical activity as well. They did not just turn the pages of their books. They wrote in the margins, underlined and annotated, used blank space for recipes and handwriting practice, kissed religious images, and copied out quotes. Pop-up science books evoke a period in which reading always meant physical engagement, and they remind us that reading was—and still is—an embodied experience.