128 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



adjunct even there, and such methods of navigating were makeshifts 

 at best. 



The general adoption of the mariner's compass, about 1100 A. D., 

 was followed by a period of progress in navigation, particularly 

 among the Portuguese, whose exploring expeditions during the fif- 

 teenth century led to important discoveries in the Atlantic. Prior 

 to this time the methods in use were very rude, uncertain, and dan- 

 gerous. When a fleet of merchant vessels was sent to distant ports 

 the trader was content if one or two returned and he fixed the prices 

 on his precious imports accordingly. 



But even at the beginning of the seventeenth century, navigation 

 was still in a very backward state. That the compass needle does not 

 point true north had been noticed early ; that the amount of variation 

 from north was different for different localities had been noted by 

 Columbus or Cabot about 1490; but that the variation of the com- 

 pass changes from year to year at the same base was not known 

 until 1635. 



At this time (about 1600) a navigator's equipment included a com- 

 pass for directing the course; a rough weight and line for making 

 soundings; a cross-staff or astrolabe for measuring angles; a fairly 

 good table of the sun's distance north or south of the equator; and 

 corrections for the altitude of the pole star. The last four appliances 

 were used solely to determine the latitude or the distance on the 

 earth's surface north or south of the terrestrial equator. Occasion- 

 ally a very incorrect chart helped determine the ship's position. In 

 this connection the motion of the ship was usually determined by 

 estimating the speed every two hours or so, or, in some cases, by 

 throwing out a float from the bows of the ship and noting the inter- 

 val of time between its passage abeam of two observers standing on 

 the deck at known distances apart. 



By observations with the cross-staff and astrolabe on the sun or the 

 pole star, latitude could be measured at sea with sufficient accuracy 

 to fix the observer's position north or south of the equator within 20 

 miles or so, but no method was available for finding longitude or 

 position east or west on the earth, except the rough expedient of esti- 

 mating the run of the ship, taking wind, tide, and current into ac- 

 count. The only mode of arriving at a port of destination was to 

 steer so as to get into the latitude of such a port either to the east- 

 ward or westward of its supposed position, and then to approach it 

 on its parallel of latitude b} T steering a course due east or west. Ob- 

 viously this method, though the best then available, might prove 

 fatal if the error in longitude were too great. 



The advice on longitude finding given by a nautical authority of 

 repute at this time illustrates well the status of the problem up to 

 the eighteenth century. He observes: 



