Water-marks in Writing-paper

Can any of your correspondents indicate any guide to the dating of paper by the water-mark. I think I have read of some work on that subject, but have no precise recollection about it. I have now before me several undated MSS. written on paper of which it would be very desirable to fix the exact date. They evidently belonged to Pope, Swift, and Lady M.W. Montague, as they contain their autographs. They are all of that size called *Pro Patria*, and two of them have as water-mark a figure of Britannia with a lion brandishing a sword within a paling, and the motto *Pro Patria* over the sword. Of…