It is reported that in 643 the Emperor Theodosius sent an envoy to China with presents of rubies and emeralds. Nestorian missionaries also presented themselves at court. The Emperor received them with respect, heard them recite the articles of their creed, and ordered a temple to be erected for them at his capital. This was in the palmy period of the Tangs, when the frontiers of the Empire had been pushed to the borders of the Caspian Sea. If China in part or in whole was sometimes conquered by Tartars, it is only fair to state that the greatest of the native sovereigns more than once reduced the extramural Tartars to subjection. Between the two races there existed an almost unceasing conflict, which had the effect of civilizing the one and of preventing the other from lapsing into lethargy. About B.C. 100, Su Wu, one of China's famous diplomatists, was sent on an embassy to the Grand Khan of Tartary. An ode, which he addressed to his wife on the eve of his perilous expedition, speaks alike for the domestic affections of the Chinese and for their ancient literary culture. "Twin trees whose boughs together twine, Two birds that guard one nest, We'll soon be far asunder torn As sunrise from the west. "Hearts knit in childhood's innocence, Long bound in Hymen's ties, One goes to distant battlefields, One sits at home and sighs. "Like carrier dove, though seas divide, I'll seek my lonely mate; But if afar I find a grave, You'll mourn my hapless fate. "To us the future's all unknown; In memory seek relief. Come, touch the chords you know so well, And let them soothe our grief." II. INTERCOURSE BY SEA. In 1388 the Mongols were expelled. The Christian bishopric was swept away, and left no trace; but a book of the younger Polo, describing the wealth of China, gave rise to marvellous results. Together with the magnetic needle, which originated in China, it led to centuries of effort to open a way by sea to that far-off fairyland. It was from Marco Polo that Columbus derived his inspiration to seek a short road to the far East by steering to the West,--finding a new world athwart his pathway. It was the same needle, if not the same book, that impelled Vasco da Gama to push his way across the Indian Ocean, after the Cape of Good Hope had been doubled by Bartholomew Diaz. A century later the same book led Henry Hudson to search for some inlet or strait that might open a way to China, when, instead of it, he discovered the port of New York. The mariner's compass, which wrought this revolution on the map of the world, is only one of many discoveries made by the ancient Chinese, which, unfruitful in their native land, have, after a change of climate, transformed the face of the globe.