Though the first sextants were built by the 1790s, most navigators were still used a Hadley's Quadrant, or Octant, up into the middle of the 19th century. The quadrant's legs subtended a 45 degree angle, but with the double reflecting system enabled measurement of angles up to 90 degrees. The sextant could measure angles up to 120 degrees.
Box chronometer, used in navigation to find a ship's longitude at sea. Made by T.S. and J.D. Negus, No. 586. An immigrant, Thomas S. Negus began making and selling chronometers in New York in 1848. In 1864, 100 Wall Street was listed as its location, and it became Thomas S. and John D. Negus in 1869. The company continued into the 1960s. Down Easter captains bought these if they could afford them.
The Astronomer Royal, Nevil Maskelyne, is credited with checking and publishing calculated positions of the moon in the first British Nautical Almanac, in 1767. The Lunar Distances tables were fundamental to the finding of longitude at sea without a chronometer.
Astronomer Royal Nevil Maskelyne is credited for checking and publishing calculated positions of the moon in the first British Nautical Almanac, in 1767. The Lunar Distances tables were fundamental to the finding of longitude at sea without a chronometer.
The Gunter’s Scale uses logarithmic and other scales to assist in numerical and trigonometric calculations. Instead of using a sliding scale like the later slide rule to assist in the addition or subtraction of logarithms, the user of a Gunter’s Scale uses dividers to mark sums and differences. The Gunter’s Scale is particularly specialized for nautical use, as some of its scales make direct solution of dead reckoning problems relatively easy. Developed by Edmund Gunter in 1623, Gunter's Scales or Rules continued to be made and used into the 19th century.
After returning from an unsuccessful exploration trip to Labrador, in 1602 George Waymouth set down to write and illustrate his book The Jewell of Artes. Two copies were apparently presented to the new king, James I, in 1604, possibly as part of a search for employment. Two manuscripts exist, one at the Beineke Library at Yale University, the other in the British Library. James Baxter, founder of the Maine Historical Society, had a copy of the British Library volume made, which was on display at the Tercentenary of Waymouth’s voyage but since has disappeared.
The cross staff measures the angle of altitude of the sun or moon or a star by sighting from one end of a staff, past ends of a cross piece, towards the horizon and the celestial object. The cross arm is moved up or down a graduated staff so that when sighting along the staff the user sees the sun or star and horizon at the ends of the cross arm. The altitude is then read off the staff. The altitude is measured on a scale along the staff.
This illustration comes from Medina's Arte De Navegar, 1545.
This working reproduction of a cross staff shows a scale along the staff and four different length cross pieces, so that different altitudes may be measured precisely. The height of the celestial body to be observed over the horizon determines which scale and arm is used.