Page:Tasman A Forgotten Navigator.djvu/7

 Viewed from our standpoint, the appliances for the navigation of their vessels were of the rudest description. The latitude was found in a very rough manner up to the end of the sixteenth century by a very primitive instrument, termed a cross-staff. Captain John. Davis, just mentioned, invented a superior instrument, called a back-staff. Hadley's quadrant, now in use, did not make its appearance until nearly a century and a half later. The speed of the vessel was found by flinging overboard, astern, what is termed a logship, with line attached. As the vessel sailed onward the line was allowed to run out. The line was marked by knots, and the time of its running out measured by a minute glass. Therefore, as sixty seconds are to an hour, so was the distance between each knot to a nautical mile. This was termed "heaving the log," and is the origin of our present way of denoting the speed of a ship as so many knots or miles an hour. This method was in universal use from that period until our steamboat age. Now we have what is known as the patent log, which measures a far greater speed than did its old-fashioned predecessor.

To ascertain the longitude was the supreme difficulty. The method had been proposed of observing the distance of the moon from the sun, with simultaneous altitudes—what is now known as taking a lunar. But the instruments necessary were then too rough for such a delicate operation.

In 1605 a Spanish expedition sailed from Peru for "the discovery of lands and seas in Southern parts." It was commanded by Quiros and Torres, two eminent navigators. The narrative of the voyage was written by Torres. He gives the latitude of the various positions of his vessels no less than seventeen times, but never once alludes to longitude.

The charts then in use were rude and unreliable. Map-making was known to the Greeks and Romans. The most celebrated geographer of ancient times was Ptolemy, an Alexandrian of the second century, who originated a system which, strange to say, was for thirteen centuries, with some slight variations, accepted as representing the true configuration of the earth's surface.

His geography dealt not only with the known, but the unknown. Outside of the Roman world, as Indo-China, Northern Europe, and the greater part of Africa, his system of geography, owing to lack of scientific observation, was rough and incorrect. It was principally based on vague rumours, or the grotesque tales of adventurous travellers.

During the Middle Ages his system obtained universal credence. Very little was done during those dreary centuries to expand or improve his conceptions. Original thought was not a characteristic of those times. It was dangerous to be original.