These two visualizations spark two interesting questions: What do people read during a revolution? What is the connection between what people read and political events? Both images spike dramatically around moments of upheaval in the Western World: The English, American, and French Revolutions, the mid-19th-century Europe-wide overthrow of governments, and World War I, to name just a few. These images are all the more striking because they did not arise from a historical study of warfare or publishing, but from a more workaday task—that of categorizing all books from 1600 to 2010 according to Library of Congress subject headings. (The source of the data was Google’s catalog of books as of 2010.) The visualizations were shown in passing during a 2010 meeting between researchers at Google, where the data had been produced, and a group of humanities scholars and advocates, who were meeting with the Google team to exchange ideas. When Google’s Jon Orwant flashed this image on the screen, the professors in the assembly gasped. Genuinely gasped. We could see in this visualization of data things that had been debated for centuries, but that had never been seen: a connection between the world of print and the world of political action, a link between revolution and reading a certain kind of book.
We are experienced readers of books, book history, and—we like to think—of book diagrams. Humans invented stream charts well before the age of computing; this style of conveying information is at least 250 years old and draws on sources that are even older. (See Rosenberg and Grafton, Cartographies of Time, 2010.) However, the union of technologies—modern cataloging systems, the increasingly systematized concatenation of library catalogs worldwide, and the capacity to render data chronologically in the style of a geological diagram—produces a compact vision of Western print culture hitherto unseen. Simple in execution, the visualization prompts new thinking.
Like any metaphorical or mathematical rendering, the diagram below should be read with care: the strata are normalized so that the spikes do not necessarily indicate a greater number of books published, but rather a shift in the proportion of books composed of a given subject. A spike in one layer of the diagram can give the illusion that all strata of the diagram have increased in size, a trick of the eye that the mind needs to combat. The second visualization helps with this by zooming in and thereby singling out the area of greatest mathematical change, but it, too, needs to be viewed critically.
Now that the caveats have been put to one side, we return to the original questions and then offer a reformulation.
What are people reading during a revolution? Poetry? Books on military technology? Theology? No. If we take the first spike, the years leading up to the English Revolution, the answer in the years leading up to the 1642 regicide seems to be “Old World History.” The second chronological peak—in the decades around the American (1776) and French (1789) Revolutions—shows the same pattern. In periods that historians would link to major political upheaval, the world of print shows similar disruptions: publishers are offering more history for readers who, perhaps, think of themselves as living through important historical changes.
We should be precise: these data don’t indicate that more people are reading history, but that a higher proportion of books published by presses can be classed by cataloguers as history. There are many follow up questions one might ask here. Does publication tie strongly to actual reading, or are these only loosely connected? Are publishers reducing the number of books in other subject areas because of scarcity of resources or some other factor, which would again lead to the proportional spikes seen above? Are the cataloguing definitions of what counts as Old World History or history in general themselves modeled on the books published during the spike years?
One has to ask questions about the size and representativity of the dataset, the uniformity of the classifications, and the nature of the spatial plot in order to understand what is going on. And, crucially in this case, one has to have the initial insight—born of a reading knowledge of history itself—that the timing of the spikes is important. But if you’ve got that kind of knowledge in the room, you might see something you haven’t seen before.