Though some have criticized Google's efforts to digitize books, I think it is the greatest thing since sliced bread. Over time, I have been able to acquire many original Victorian and Edwardian knitting resources but now there are countless books available for us online at books.google.com. It may not be the same as having the real thing in your hand but it sure is a treasure trove of knitting information and primary resources. Here is a great example: I think this is the oldest knitting book I have found on Google books...The ladies' knitting and netting book By Miss Watts 1840.
When you sign into Google, you can set up "bookshelves" to organize what you find. Give Google Books a try and see if you can find something older that 1840 and post it here for all of us to enjoy.