Much of the information about Galileo’s books is incomplete, so the first scholar to work with these documents claimed that they contained “no information” to determine specific editions of over 40% of the books in the library.1 Admittedly, the two lists in Florentine archives (which indicate 280 titles) are documents of unstructured (sometimes illegible) data about books and they only have 84 titles in common. Some of the works listed in these inventories had fortunate publishing histories that included multiple editions over the course of many decades, but for early modern scholars, having a title is better than no information at all. In fact, a title alone suggests so many options that selection becomes overwhelming. What if a partial title can refer to 100 discrete editions of a book? Can a common set of characteristics be determined for the variants of a book? Can that book then be seen in relationship to a collection?
Early modern lists of books tend to express those volumes in terms of an idealized text with general properties that a contemporary audience was expected to know: Juvenal’s Satires, Virgil’s Aeneid, Dante’s Comedy, etc. were entries with sufficient information for the readers of the inventory. Nevertheless, historians, literary critics, material culture scholars, and anyone working in digital or computational studies all seek out, insist upon determining, and in some cases require the specific characteristics of a book in order to carry out their analyses. Without those details, essentially the metadata for the edition, some scholars might feel that they are left with incomplete data that must be discarded or omitted from a comprehensive presentation of their research question, but having just the title or the author is already a substantial amount of information.
“Galileo’s Library” is testing the hypothesis that chemistry offers the humanities a way to conceptualize, measure, and represent the general properties of the early modern book element in a way that recognizes the complexity and richness of its various iterations. Isotope, meaning “same place” in Greek, is a term typically reserved for descriptions of atoms that have the same number of protons but different numbers of neutrons. For example, chemists speak of the general properties of the idealized element carbon, which has six protons, but isotopes of carbon exist with six or more neutrons, which interact differently with other atoms in highly specific ways due to their unique masses. In this way an isotope can be a useful heuristic for considering the nature of an early modern book, especially when quantification and datafication alone simply do not account for the variability and uncertainty inherent in their identities.2 The chronology histogram and the map of publishing locations are limited in the dimensionality of information they can represent about what an early modern library was to its collector, to the person writing the inventory, and to scholars or students who want to use it today.
This cumulative identity of a book, which to a computational pessimist could also be seen as a lack of specific metadata, is essential to understanding how early modern readers conceptualized their libraries. It can help answer new questions: When Galileo started annotating his copy of Boccaccio was it because it was the first to be published in Florence in his lifetime or did he seek out an older, more philological, or less-censored edition? In the list of books that Galileo’s son inherited, when the notary indicates “Lucretius,” what possible geographic information does that information carry with it? How long were ideas percolating in printed Italian intellectual culture prior to reaching Galileo?
 I take for granted that the identification of these isotopes depends in large part on catalogs and records whose problematic status as representations of books has been outlined in Hugh Amory, “Pseudoxia Bibliographica, or When is a Book Not a Book?” The Scholar & the Database: Papers Presented on 4 November 1999 at the CERL Conference Hosted by the Royal Library, Brussels 2 (2001): 1-14. Print.