THE ROSE OF THE WINDS : THE ORIGIN AND DEVELOPMENT OF THE COMPASS-CARD ([1914])

ALTHOUGH the construction of the compass lies outside the scope of this inquiry, some preliminary considerations are necessary concerning the origin of the compass itself ; and these must be stated briefly.

The mariners' compass, as we know it to-day, consists of a light
circular disk or card, beneath which is attached a magnetic needle or system of magnetic needles. The card is provided at its centre with a small cap, by which it is poised movably upon a pin. The whole is enclosed in a hollow box or bowl covered with a flat lid of glass ; and the compass box or bowl is suspended within two hinged rings of brass to enable it to conserve its proper horizontal position in spite of any tilting movement to which it is subjected by the rolling or
pitching of the ship on which it is carried.

The card is divided out into thirty-two ( points ' or c rhumbs 3 of
equal angular breadth forming a rose or star, and to these are affixed the initials of the names of the thirty-two points. The magnet needle, or system of needles, is affixed to the card parallel to the direction marked NS on the card, so that when left to itself, the card, obeying the directive force which acts on the needle, sets itself in a direction pointing (magnetically) North and South ; the several points (or, strictly, pointers) marked on the card then indicating the several directions that the mariner may know in which way to steer in order to follow his desired course. The card is also usually marked at its North point with a fleurdelis or other distinctive sign. The magnetic needle is controlled in its pointing by the magnetism
of the earth's globe.

Silvanus Phillips Thompson (19 June 1851 – 12 June 1916) was a professor of physics at the City and Guilds Technical College in Finsbury, England. He was elected to the Royal Society in 1891 and was known for his work as an electrical engineer and as an author. Thompson's most enduring publication is his 1910 text Calculus Made Easy, which teaches the fundamentals of calculus, and is still in print. Thompson also wrote a popular physics text, Elementary Lessons in Electricity and Magnetism, as well as biographies of Lord Kelvin and Michael Faraday.