Karezza: Ethics of Marriage is a book by Alice Bunker Stockham, MD, one of the first women medical school graduates in the USA. This second edition was published in 1903. A highly-principled Quaker distressed by all the unwanted pregnancies among her patients, she saw controlled intercourse as a way to prevent reckless procreation, increase the harmony between couples, and raise spiritual awareness. (Her earlier book on women's reproductive health, Tokology: A Book for Every Woman is also available online.)
With Karezza, satiety is never known, and the married are never less than lovers; each day reveals new delights....In the physical union of male and female there may be a soul communion giving not only supreme happiness, but in turn [leading] to soul growth and development.
For more on Stockham, see "Finding the Kingdom of Heaven in Your Own Hearts."
If you wish, the same book is also available at the Internet Sacred Text Archive in another format. The version at the Sacred Texts Archives includes the original page numbering, which may be useful for academic purposes. The Internet Sacred Text Archive has thousands more e-books available. (PDF version)