Mentioned throughout the first chapter is George Washington’s love of Philip Miller’s Gardeners Dictionary. I have found a free online copy from the lovely people at archive.org. You can read a copy of it right there on the page or download a free copy to your device or computer for better inspection.
I have also found Batty Langley’s New Principles of Gardening at archive.org. Same deal as the first book: you can read it (in full color!) on the page or download a free copy to yourself.