Drawing of an astrolabe from Medina's Arte de Navegar, 1545. The seaman's astrolabe was a graduated ring or disc fitted with a sighting rule pivoted at the center. The instrument was suspended so that it hung vertically. The user then turned the sighting rule so that the sun or star could be sighted along it and the altitude read off the ring. It dates back to ancient Greece and was heavily used in the Islamic world. The first records of a seagoing version date to around 1481.
The seaman's quadrant was first used at sea around 1460, about twenty years before the astrolabe. It is a quadrant of a circle, made of wood, with a sight up one side, a scale along the arc, and a hanging weight on a string from the apex of the quadrant. The quadrant was used to tell relative distance traveled north or south from a port of departure, something done more easily than measuring an accurate sun height to determine latitude.
Title page of The English Pilot, Fourth Book, anEnglish sea atlas published from 1671 to 1803, initially by John Seller who was appointed Royal Hydrographer in 1671. These were intended as working charts. The Fourth Book, first issued in 1689 covered North America and Canada.
This edition was published in 1767 and has the water stains that show it went to sea.
It was the first detailed set of sailing directions for the North American coast.
The other books gave charts and sailing directions for England, Europe, and the East Indies.
Edward Wright broke new ground in navigation with the publication of his book, Certaine Errors in Navigation, Detected and Corrected. It was particularly strong in its mathematical treatment of navigation, the application of Mercator's projection to chart making, and the necessity of noting compass variations when taking bearings. This is the 1610 edition.
University of Virginia Map Library Collection has additional information on Wright's work.
The traverse board is used to keep track of changes in a vessel's speed or course over the period of a four-hour watch. At the end of each watch, the courses and speeds are added together, with the help of traverse tables, or by estimation, and marked in the logbook or on a chalkboard. A peg is put into a hole every half hour for the course steered, and another is inserted to reflect the approximate speed sailed. The traverse board, though used some in the sixteenth century, was more common in the seventeenth century.
The chip log, a log line reel, and the sand glass used for measuring the speed of a vessel through the water. The chip is tossed, the sand glass turned, the line let out, and the number of knots in the line are counted until the sand glass empties. The number of knots that have passed is the speed of the vessel in knots or nautical miles per hour.
This illustration is from Bowditch's New American Practical Navigator,1868, Plate VI.
Sixteenth-century rendition of a compass rose, with 32 points.
North North by East North North East Northeast by North Northeast Northeast by East East North East East by North East
is the system which repeats in each quarter. The points are 11 1/4 degrees apart: the result of dividing 360 degrees by 8 which is what happens when a circle is quartered 4 times.
Mariner's dry card compass, from the schooner Gloucester of Stockton Springs, Capt. George A. Erskine, 1878. This compass may have been made in 1876, the year of the centennial, considering the patriotic artistry on the North point. Like most compasses prior to the 20th century it is laid out in points of 11 1/4 degrees. These 32 points are the result of continually dividing a circle of 360 degrees by 4. Learning the names of the points, called boxing the compass, was an essential skill for a sailor.
This portrait of Copernicus comes from the Nicolaus Copernicus Museum in Frombork, Poland. Copernicus showed that the earth was not the center of the universe, but that the sun was the center of a solar system.
This diagram shows the earth inside an imaginary celestial sphere, along with the names of coordinate systems: declination and right ascension. This also shows the Sidereal Hour Angle, which is 360 degrees minus the Right Ascension.
The drawing is from Bowditch's American Practical Navigator, H.O. Pub. No. 9, 1962, p. 382.
