Charles Winfred Douglas (not Winifred—this is a man, not a woman) was one of the most respected scholars of hymnody in the 20th Century. Church Music in History and Practice is a thorough introduction to the history of Church music up until the middle part of the last century. (Thomas Day's somewhat abrasive Why Catholics Can't Sing does much to explain the musical train wreck of the second half of the century.)
Douglas was an Episcopal priest, and the book can be at times a little tendentious toward Catholicism, but not nearly so much as to obscure its value. If you want to know why classical Church music sounds the way it does, both the text and the music, Douglas's book will explain.
Sadly, it's long out of print. Even more sadly, there's a revised edition (ca. 1962, also OOP) whose reviser was far too kind to the growing incursion of bad taste into Church music. Fortunately he seems to have restricted most of his revising to adding chapters at the end.
The good news is that used copies, even of the first edition, are available at fairly reasonable prices.
