Nicholas Tartaglia, in his “Three Bookes of Colloquies concerning the Arte of Shooting,” published in the year of the Armada, gives an interesting illustration to indicate how one could know by the help of a gunner’s circle the number of miles or feet any ship lying in the roadstead was distant; and also how to measure height with a geometrical square. And Bourne, in his “Treasure for Traueilers” (1578), had a method for ascertaining the “waight of any shyp swimmyng on the water.” The reader will remember that when we were discussing Columbus we pointed out the lack of that useful instrument, the log and line, for indicating the distance which a vessel sailed. It was William Bourne who first published an idea for overcoming this difficulty in a somewhat ingenious manner. In his “Inventions and Devices” (1578), he gives a method whereby “to know the way or going of a ship, for to knowe how fast or softly that any ship goeth.” The idea is too complicated to be given here in detail, but practically it amounted to towing astern a tiny boat containing a paddle-wheel which revolved, and so by a species of clockwork registered the speed. Excepting that the patent log of to-day is helicular, there is much resemblance between the old and the new in at least the bare idea. But a little later--in the year 1637--Richard Norwood published, in his “Seaman’s Practice,” a whole chapter on the subject “Of dividing the Log-line and reckoning the Ship’s way.” The log-line was to be used in conjunction with the glass, and this method was little altered until the nineteenth-century invention of the patent log had to be brought about owing to the great speed of steamships. [Illustration: SIXTEENTH-CENTURY SHIP BEFORE THE WIND. By a Contemporary Artist. Notice the square lids over the portholes.]