This article, written for the lay reader, describes some studies, initiated in the author's laboratory in the late 1960s and pursued there for more than 15 years. The interested reader can find a full technical description in the bookNuclear Magnetism. Order and Disorderby A. Abragam and M. Goldman. The present account is an abridged version of the chapterNuclear Magnetic Orderfrom my bookTime Reversal, an Autobiography.