The Rules of Navigation

Two manuscript volumes produced by different students cast light into the world of navigation. Both are in the archives of the Essex Society for Archaeology and History. The student’s names are unknown, it is uncertain that these relate to Essex, but both are likely to be of late eighteenth century date.

Having only rowed a boat on the water of Billericay Lake Meadows and more recently steered for five minutes, under very close supervision, a Thames Sailing Barge on the River Blackwater, I was interested to see how a would-be mariner learned his craft.

The larger bound volume of over 500 pages begins with the basic principles of geometry. The student is taught to draw and label circles then triangles of various shapes before going on to calculate longhand, the area of a square, rhomboid, then circles, for example, “What is the circumference of a circle whose diameter is 40?”

He is then required to master three dimensional objects: the solidity of cones, spheres, spindles, paraboloids - things that look like rugby balls and sections of them. The longhand calculations run to a few rows in the student’s best book as the mental gymnastics becomes ever greater.

At about a third of the way through the book, the student writes “Of Artificer’s Work” having explained that “artificers estimate, or compute the value of their works by different measures”. Glazing and masons, painting and plastering, flooring partitioning and roofing, brickwork & c. are all considered. A number of exercises follow.

Next the student encounters “logishalls sliding rule” with a lengthy explanation of its use. As an ‘O’ Level Maths pupil in the 1970s, when exams forbade the use of calculators, I remember using ‘Logarithm Tables’, never being able to master a slide rule. I have not had cause to use either since.

At about halfway through the manuscript volume the student, probably an apprentice, titles a page ‘Navigation’ and defines the topic “how to conduct a ship through the wide and pathless ocean, to the smallest part of the world the safest and shortest way in passage navigable”. He learns of latitude distances from London to Rome, Finisterre and Cape Rogue in South America, and longitude between Cape Finisterre and Barbados, Barcelona and Lisbon. A Mariner’s Compass is then drawn showing 32 points and angles.

‘Plane sailing’, the simplest form of navigation is then explored, the student illustrating one diagram with a ship in full sail. At this point all those exercises in geometry begin to be applied. The student is then taught to master a complex course by means of further exercises.

Winds and tides are then considered. It is here “the immortal Sir Isaac Newton” is mentioned in connection with “his great principal or gravity and attraction” and an understanding of “all bodies within
the solar system”: the moon, sun, earth, stars. The class then defines a leap year (using the year 1806 as an example), epact of a year, and “the moons age” (using the example 29 April 1784, and epact in the calculation). It is at this point the student mariner is able to calculate high water at any place using the moon’s age and produce a “table of times” for a given place. Equipped with this “At what time will it be High water at London August 29th 1796?” is then calculated, followed by Dover and Torbay on different days.

In the final section of the course, the student learns how to adjust the course of the ship caused by wind, swell, current etc. The final pages are devoted to ‘A Journal of a Voyage from London to Madeira In The Nancy of London, A B Commander. Kept by George Foster Mate”.

It is not known whether George Foster was the student.

The second manuscript book, with a coloured frontispiece of a sailing boat upon the high seas, is about half the size of the former. It begins with the title ‘Navigation’, considering much the same syllabus. The illustrations are of better quality: one of a map showing
the navigation of St Georges Channel, the coastline of England, France Spain and Portugal and Barbary coast, where the Cape Nord Islands are situated and drawn with a little more accuracy than the African coastline. The year 1810 is mentioned and at the end is a log,

“In the Brig Nancy of Mary Port. William Harkness Commander. Kept by William Johnstone Mate”.

The vessel left Lizard Point bound for Maderia on April 25th 1813.