Via the wonders of Wikipedia, we can experience a tesseract through a variety of descriptions: by its Schlaäfli symbol, Coxeter-Dynkin diagram, or an animated computer projection. I first experienced the word “tesseract” in the great book A Wrinkle in Time. Its author Madeleine L’Engle has recently passed away, but her wonderful book endures and its fourth-dimensional musings seem all the more poignant in her passing.