All About Roubo. Leitz Elmarit 90mm

As I have faced the prospect of ripping and resawing - by hand - quite a few linear feet of South African Yellowwood for my current project, I have turned to the history books.  After all, there were not always sophisticated woodworking machines which can dimension rough lumber to within a fraction of a millimeter of spec. in the matter of a few minutes.  Before their advent, skilled, specialist sawyers - working in pairs -, attacked raw logs with huge frame saws, and reduced them to dimensioned lumber or veneer, all in a day’s work. 
The place to start is André Jacob Roubo’s four volume treatise: L'Art du Menuisier, which has reached us from pre-Revolutionary 18th Century France.  Clearly, Roubo, a 3rd generation carpenter/cabinet maker possessed an intellect way above that demanded by his station.  For those interested, Wiki provides a most informative article.  I am interested in the saw which he describes:  the vicious rip-tooth blade is mounted in a frame like the saw I Blipped yesterday.  The difference is that it is situated in the center of the frame so that the saw is balanced.  The sawyer can use both arms and the strength of his entire body to guide the saw, while letting the weight of the frame and gravity do the work.  It’s a small difference, but ingenious.
In a previous Blip, I wrote of Frank Hubbard’s seminal work from 1965: Three Centuries of Harpsichord Making.  In it, he reproduces several of the beautiful engravings from Roubo’s treatise, including one depicting the saw, and how to use it efficiently.  The Extra shows this illustration.
As the Main for today, I photographed the cover of a book in my little library.  It is the volume from Denis Diderot’s Encyclopedie from almost exactly the same time and place as Roubo’s treatise. I gather that Roubo was not asked by Diderot to contribute for the chapter on carpentry, cabinet making and veneering.  Yet, somehow the engraved illustrations look remarkably similar to Roubo’s…  One can only surmise that copyright law in 18th Century France was not a developed discipline.  But how did Diderot get his hands on Roubo’s engraving plates??  Material for an historical novel?