As I was researching Ms. Mary Brooks Picken, I found that the entire contents of four of her instructional books, including The Mary Brooks Picken Method of Modern Dressmaking are available online at the Home Economics Archives at Cornell University. This archive, whose full name is actually Home Economics Archives: Research, Tradition, History (HEARTH) is a great resource, as many of the educational books created at WIDAS and many other vintage publications on home sewing are available there.
I tried a few search terms and here are some of the books I found that HEARTH has available:
Pattern making by Agnes K. Hanna, 1921.
The dressmaker: a complete book on all matters connected with sewing and dressmaking from the simplest stitches to the cutting, making altering, mending and caring for the clothes Butterick Publishing Company, 1916.
The elements of dress pattern-making: Magyar dress-cutting for technical classes, home workers & professionals by Amy J. Reeve, 1912.
The dress you wear and how to make it by Mary Jane Rhoe, 1918.
Note to Gertie: Don't think I wasn't secretly hoping that Vogue's New Book for Better Sewing was among these free downloadable books!!