Wheels within wheels

In the secure, humidity-controlled strongroom ‘A’ in St George’s Chapel Archives and Chapter Library, Windsor, far away from the secrets of the sea and all things nautical, are four precious books printed in Italian and written by Robert Dudley, the illegitimate son of the famous Lord Robert Dudley; Earl of Leicester, one-time favourite of Elizabeth I. The four volumes (SGC RBK D.210 i-iv) together form a work entitled Dell’Arcano del Mare (‘The Secrets of the Sea’). They were published in Florence, 1646-1647.

Dudley had turned his back on England and his family to start a new life in Florence and the publication of Dell’Arcano was the culmination of a lifetime’s interest in navigation, mathematics and engineering as well as practical seafaring.

The books contain over 200 engraved plates very well made by a Florentine engraver called Antonio Francesco Lucini. In addition to the detailed nautical maps and plans of forts and ships, there are dozens of working models of wheel charts, calculators, mathematical slide rules and the like. They are, in fact, moveable paper wheels-within-wheels, known as volvelles; all, in this case, designed and developed by Robert Dudley to help Italian naval commanders to negotiate and navigate their way to success in warfare at sea.

Some of the volvelles are designed to help the user determine the position of the sun and moon by turning the roundel and pointer so that their indexes, one for the sun and one for the moon, point to the appropriate days and locations. The paper calculators can be turned independently whilst attached to the page. Some of them determine longitude and latitude, whilst others help make astronomical calculations. This was a period in time when great strides were being made in Europe towards a better scientific understanding of our place in the world and how best to discover new horizons. In many ways it fell under the embrace of the Renaissance. The four fine volumes of Dell’Arcano held in the Chapter Library are testament to this important period of our history.

A further interesting fact about volvelles is that they are not only objects of the past but actually in use today. One example is in the form of wheels-within-wheels made of plastic or metal. Despite the advent of electronic calculators and fly-by-wire technology in the cockpits of modern aircraft, the United States Air Force use an E6B flight volvelle to help trainee pilots plan their flights before take-off. The device does much more besides, and there is an anecdote that, during World War II, if pilots of the USAF were a little lost on their mission the ditty ran “My eyes are dim I cannot see, I have not got my E6B with me “.

More about the history of St George’s Chapel’s Dell’Arcano del Mare can be read in this Image of the Month from September 2010. Examples of seventeenth century brass instruments copied from volvelles may be seen in most science museums and nautical museums in the form of compasses, protractors, nocturnals and astrolabes.

Peter Eley, Library and Archives conservator volunteer

The King's Free Chapel. The Chapel of the Most Honourable and Noble Order of the Garter. The Chapel of the College of St George.