But once the shipwrights of England and Holland and France began to see the advantages of even the crude ships that were occasionally sailed by the Venetians and the Genoese to the bleak northern waters, the improvement in northern ships began. The single mast with its simple square sail was supplemented by another mast and by the slanting mast at the bow that became the bowsprit, and it became the custom in northern waters, as it already was the custom in southern, to use two or three masts carrying square sails and one mast carrying the triangular lateen sail. The bowsprit was a crude affair but was highly important, which was the reason for its continued use despite the fact that even in ordinary weather in the open sea the pitching of the dumpy hulls often drove the spritsail into the waves. Perhaps this troublesome feature of the spritsail was partially responsible, as the desire for more head sails certainly was, for the addition at the end of the bowsprit of a short, vertical spar on which a new sail called the “sprit topsail” was spread. In heavy weather this sail could be carried without plunging it into the sea long after the spritsail, which was spread on a spar mounted below the bowsprit, had to be taken in. And now the masts of these ships began to undergo an important change. Hitherto a mast was simply a long sturdy spar made of a single tree, with a single square sail mounted on a single yard. The desire for more canvas led at first to the setting of a triangular sail above the square sail. This new sail was set with its lower corners made fast to the extremities of the yard and with its apex at the apex of the mast. Soon, however, a short yard appeared at the top of this sail, which in the course of later developments became more and more rectangular until finally it became the highly important topsail of the square-rigged ships of to-day. As still other sails were added this topsail became the sail that is carried for a greater part of the time than any other of the square sails, for in heavy weather it is the last to be taken in, and continues to hold its place long after its predecessor, the great square sail below it, has been furled.