The following books are freely available on-line. Nick Hopton has made me aware of them - thank you Nick!
If you come across any others, let me know and I'll be glad to add them to this page.

Church architecture considered, in relation to the mind of the Church
since and before the Reformation, by Richard Mant, 1843.

Decorated Windows - A Series of Illustrations of the Window Tracery of the Decorated Style of Ecclesiastical Architecture, by Edmund Sharpe, 1849.

A Glossary of Terms Used in Grecian, Roman, Italian, and Gothic
Architecture, by John Henry Parke, 1838.

A History of Ecclesiastical Architecture in England, by George Ayliffe Poole, 1848.

The Present State of Ecclesiastical Architecture in England, by Augustus Welby Northmore Pugin, 1843.

A Treatise on the Ecclesiastical Architecture of England, During the
Middle Ages, by John Milner,  1835.