Some morning a little army of men begins work where to the ordinary observer there is nothing but piles of steel and big timbers. From a distance the scene reminds one of a partly depleted lumber yard. On one side of this, and within a few yards of the water of a slip, are first set up with mathematical accuracy a number of square timbers called “keel blocks.” Upon these blocks will rest the bottom of the ship, and from them to the water’s edge run long shelving timbers, or “ways,” down which she will slide when ready for launching. [Illustration: This Shows Some of the 800,000 Rivets that Go to the Making of a 10,000-Ton Leviathan of the Inland Seas.] Children frequently play with blocks which, when placed together according to the numbers on them, form a map of the United States. This is modern shipbuilding--in a way. It is on the same idea. There is a proper place for every steel plate in the yards, and the numbers on them are what locate them in the ship. A giant crane runs overhead, reaches down, seizes a certain plate, rumbles back, to hover for a moment over the growing “floor,” lowers its burden--and the iron workers do the rest. Within a few days work has reached a point where you begin to wonder, and for the first time, perhaps, you realise what an intricate affair a great ship really is, and what precautions are taken to keep it from sinking in collision or storm. You begin to see that a Lake freighter is what might be described as two ships, one built within the other. As the vessel increases in size, as the sides of it, as well as the bottom, are put together, there are two little armies of men at work--one on the outer ship and one on the inner. From the bottom and sides of the first steel shell of the ship there extend upward and inward heavy steel supports, upon which are laid the plates of the “inner ship.” In the space between these two walls will be carried water ballast. The chambers into which it is divided are the life-preservers of the vessel. A dozen holes may be punched into her, but just as long as only this outer and protecting ship suffers, and the inner ship is not perforated, the carrier and her ten-thousand-ton cargo will keep afloat.