'Vasari says, and rightly, in his Life of Leonardo, 'that he laboured much more by his word than in fact or by deed', and the biographer evidently had in his mind the numerous works in Manuscript which have been preserved to this day. To us, now, it seems almost inexplicable that these valuable and interesting original texts should have remained so long unpublished, and indeed forgotten. It is certain that during the XVIth and XVIIth centuries their exceptional value was highly appreciated. Thi ...