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The Dewey Decimal System was created by Melvil Dewey in 1876 while managing the Amherst College Library. Unlike Callimachus’s system, Dewey’s is hierarchical with a numeral for each subject, including fiction. Many libraries, however, maintain a separate section for fiction that is shelved alphabetically by the author’s surname.

As you can see in the picture, there are ten main classes of disciplinary knowledge, such as philosophy and science. Each of these classes is split into ten divisions, with each having ten sections. The system uses Arabic numerals, with three whole numerals designating the class, division, and section for a particular item in the library’s catalogue. Further divisions into more specific subgroups are designated by adding numerals to the right of the decimal point.

So, as a biologist looking for a book about bats, I would first go to the aisles in the 500’s for science. Then I would focus on the 590’s for the books on zoology. Next, I’d zero in on the 599’s for the books about mammals, and the 599.4's for the books about bats. If the library has a huge collection, I might find books specific to vampire bats. They would have the number 559.45. And that same set of numerals would bring me to books about vampire bats in thousands of libraries. The advantage of Dewey's system is that it can be expanded by adding digits to the right of the decimal point to accommodate ever more specific topics, such as the hibernation of vampire bats.

In my book The Deadliest Fever, the culprit is bitten by a rabid bat. Can you guess which Dewey Decimal numeral I searched for information? Speaking of The Deadliest Fever, you can click here to find out more about a jewel heist in Ephesus and the death of a hard-breathing sea captain.

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