What did Eddy mean when referring to “useful” books?

The Mary Baker Eddy Library frequently receives questions regarding statements Mary Baker Eddy made, including those in Science and Health with Key to the Scriptures. Over the years, patrons have asked about this particular passage in the book’s Preface:

The first edition of SCIENCE AND HEALTH was published in 1875. Various books on mental healing have since been issued, most of them incorrect in theory and filled with plagiarisms from SCIENCE AND HEALTH. They regard the human mind as a healing agent, whereas this mind is not a factor in the Principle of Christian Science. A few books, however, which are based on this book, are useful.¹

What were the books Eddy was referring to as useful? Our research has not been able to determine any specific titles.

It may be worth noting, however, that our collection does reveal how Eddy revised this statement over time. Her first mention of this appeared in the 50th edition of Science and Health, published in 1891: “A few of these books, however, are helpful to humanity.”²

By the time of the 61st edition, also published in 1891, that sentence was changed to say, “A few of these books, however, which are based on this Book, are useful.”³

By the 108th edition, published in 1896, Eddy had made a further change: “A few books, however, which are based on this Book, are useful.”⁴

Then in the 240th edition, published in 1902, she changed the capitalization of “Book,” to what we read today.⁵