In the spring of 2010, Amazon's sales of e-books surpassed its sales of hardback books. This is not surprising when one considers the prices of hardback books. In December, 2010, sales of e-books through Amazon overtook its paperback sales. This indicates a major change in the way that the world reads books. Academics have been at the forefront of this change from print to electronic documents. For more than a decade, it has been standard for academics to share preprints of articles via e-mail. Most of us use some sort of LaTeX implementation to produce our journal articles and lecture notes. Then we simply send the DVI or PDF files to our colleagues or students by e-mail.

Unfortunately, most academics and students then print on paper the files they receive because it yields the most readable and portable document. Few—if any—have the will power to read an entire 35-page journal article on a computer monitor, and until recently there did not exist a portable device which made it easy to read an electronic version of an article or textbook, especially one with a significant amount of mathematics in it.

With the tremendous rise in popularity of various e-book readers such as the Kindle, Sony Reader, Nook—to name only a few—textbook publishers have begun to make their titles available as e-books. DSWeb's book reviews editor tested e-books from some of the biggest mathematics and engineering textbook publishers. We tested e-books on four devices: the Apple iPad, Apple iPod, the Nook Color, and the Motorola Droid A-855.

Kindle

Our first test used Rufus Bowen's classic text Equlibrium States and the Ergodic Theory of Anosov Diffeomorphisms, [Bow08] which was meticulously retyped in TeX and republished by Springer in 2008. We tested this book on the Apple iPad and the Motorola Droid, using the Kindle app on both devices. Both devices rendered the book excellently. The in-line mathematical symbols were displayed neatly and correctly with the proper size relative to the surrounding text. Some subscripts and superscripts were slightly washed out but still readable; furthermore, this was completely independent of the device since the defective subscripts were rendered in exactly the same way on both the iPad and the Droid.

Our second test of the Kindle app used Global Riemannian Geometry: Curvature and Topology [MM03] by Steen Markvorsen and Maung Min-Oo, published by Birkhäuser Verlag in 2003. The results were not impressive. Even plain text rendered horribly on both the iPad and the Droid. While the "old-fashioned" bound print copy would certainly be a good book for one to have as a reference, reading the e-book on the Kindle app would test anyone's patience. The text looks as if someone photocopied the original book on a very cheap photocopier. Every letter on every page washes out a bit. Even the umlauts were missing from "Birkhäuser" on the title page.

The verdict: Some books are quite readable on the Kindle app, but some are not ready for release as e-books yet. If the option is available, try the free sample available from Amazon before deciding whether to buy the print copy or the e-book.

Nook

The results for the Barnes and Noble Nook were just as favorable as they were for the Kindle. The first book we tested was Ruey S. Tsay's Analysis of Financial Time Series, [Tsa05] published by Wiley and Sons. We tested this book on the iPad, the Droid, and a Barnes and Noble Nook Color. On all three devices, this book was very readable. Both plain text and equations were rendered very clearly. In-line mathematics symbols were generally the same size as the surrounding text but they were not aligned vertically with the rest of the line. Centered equations were smaller than the regular text, but all characters—including subscripts and superscripts—were clear and complete. Both centered and in-line equations appear as though they have been converted into images. While not as aesthetically pleasing as the print copy, the e-book version for the Nook was certainly every bit as readable as the print version.

Our second Nook e-book was Raymond M. Smullyan's Gödel's Incompleteness Theorems [Smu92]. Plain text was displayed perfectly. Small in-line mathematics symbols were difficult to read, but this was corrected by increasing the font size.

The verdict: Books are quite readable on the Nook Color and on the Nook apps; however, if the option is available, try the free sample available from Barnes and Noble before deciding whether to buy the print copy or the e-book.

Borders Reader

In all of our tests, we have been testing books for which free samples are provided, so it wasn't always possible to test advanced texts. Also, the free previews provided by Borders were ridiculously short with none of the ones we found extending beyond the preface. This made it impossible to judge how well the Borders Reader app for iPad renders mathematical texts. In fact, the all-too-brief free previews make it entirely impossible to decide whether to buy the book at all.

Despite a rather time-consuming search for an e-book which would give us any mathematical content in the free preview, we could find only one book which used one symbol in its preface: David S. Moore's Essential Statistics [Moo10]. One mathematics symbol in the preface was treated as an in-line image, so it was displayed clearly, but it was not aligned correctly to the rest of the line of text.

Books formatted for the Borders Reader app seem to be divided into a number of files, one for the title page, one for the table of contents, one for the preface, and so on. This made the Borders Reader app considerably slower than the Kindle or the Nook apps. Also, the Borders app locked up on a few occasions when the iPad had no internet connection, but the Kindle and Nook apps seem to have no such problem.

The verdict: The Borders Reader app for the iPad is the quirkiest of all the readers we tested, and the lack of free previews makes it difficult to decide whether a book is worth buying. Essentially, one must already know the book, or one must decide from the title and author alone whether to buy the book.

Conclusions

Publishers seem to be intent upon selling their books in Amazon's AZW, Nook's PDB (eReader), or ePub formats, which are fine for books written only in plain text. Mathematicians, physicists, engineers, chemists, etc., have become accustomed over the last couple of decades to reading documents created by LaTeX and rendered in PDF (portable document) format. Beginning with Donald Knuth and continuing for 40 years now, a very large group of mathematicians, computer scientists, physicists, engineers, chemists, musicians, and many others have worked to expand upon the power of the TeX engine to produce beautiful documents. Publishers seem intent upon taking us back to the pre-TeX years.

The solution is simple: publish mathematics texts in PDF format. All of the readers currently on the market, except perhaps for the Azbooka WISEreader, support the PDF format. So why are publishers, even the big mathematics publishers like Springer and Birkhäuser, avoiding the PDF format? Some publishers—Taylor and Francis, for example—are making their e-books available in PDF format so that they read naturally on the screen of an iPad or computer, but they can be difficult to read on an iPod or a smart phone because the flow of the text across lines may be unnatural. (This is a function of how the PDF file was created.) Most of us probably create our PDF files using pdflatex or dvipdfm. Files created in this way are not easily read on small-screen devices such as the Sony PRS-700, the Nook Color, the iPod, or smart phones because lines do not wrap correctly. The screens of the Apple iPad and the larger ebook readers, though, make them quite sufficient for reading PDF files created by dvipdfm or pdflatex.

In short, it seems that publishers have made the decision to sacrifice the quality of the reproduction of mathematics symbols in return for good line wrapping. They have dispensed with one aesthetic quality in favor of another which is presumably more valued by those in the publishing profession. We in the sciences, though, feel that this compromise need not be made. Publishers and e-book reader developers are trying to reinvent the wheel; in this case, they are trying to reinvent PDF.

Finally, some e-books sold by one major bookseller might not be sold by the others. This potentially forces the reader to choose arbitrarily among the three major devices—Kindle, Nook, or Borders Reader. Until publishers start selling e-books in PDF format, the best bet for the reader is to use one of the new tablet devices such as the iPad or an Android tablet.