_The invention of the Mariner’s Compass_ must be reckoned of still greater importance, and yet it is absolutely unknown to whom we owe it. That honor has been often bestowed on Gioia, a citizen of Amalphi, who lived about the commencement of the fourteenth century. But the polarity of the magnet at least was known to the Saracens two hundred years before that time; though even after the time of Gioia, it was long before the magnet was made use of as a guide in navigation. ‘It is a singular circumstance,’ says Mr. Hallam, ‘and only to be explained by the obstinacy with which men are apt to reject improvement, that the magnetic needle was not generally adopted in navigation till very long after the discovery of its properties, and even after their peculiar importance had been perceived. The writers of the thirteenth century, who mentioned the polarity of the needle, mention also its use in navigation; yet Campany has found no distinct proof of its employment till 1403, and does not believe that it was frequently on board Mediterranean ships at the latter part of the preceding age.’ The Genoese, however, are known in the fourteenth century to have come out of that inland sea, and steered for Flanders and England. But by far the greatest sailors of the age were the Spaniards and Portuguese. This latter nation had little or no existence during the greater part of the middle ages, but in the twelfth, thirteenth, and fourteenth centuries, they were able to expel the Moors from a great part of their country; and in the beginning of the fifteenth, John, surnamed the Bastard, who was then their king, was the first European prince who exhibited a respectable navy. It was in 1486 that this adventurous people first doubled the Cape of Good Hope. _The discovery of America_ (1493) may be mentioned supplementarily to the invention of the mariner’s compass, as an event which, without it, could never have taken place. The immortal honor of that discovery rests with Christopher Columbus, a sailor of Genoa. After unsuccessful applications at almost every court in Europe, and braving obloquy and contempt, Columbus at last obtained a miserable force from Ferdinand and Isabella of Spain; and with no landmark but the heavens, nor any guide but his compass, he launched boldly into the sea, and at last conducted Europeans to the great western hemisphere. In the course of the fourteenth and beginning of the fifteenth centuries, various discoveries in the arts were made, which powerfully tended to the advancement of society; among these the more important were the invention of gunpowder and firearms, clocks and watches, paper-making and printing. This last, the greatest of all, prepared the way for the Reformation in religion, in the sixteenth century, by which religious was added to civil freedom, and a great spur given to individual activity. HISTORY OF GREAT BRITAIN AND IRELAND. CONQUEST BY THE ROMANS.