The fair Urania
We have seen how the astrolabe was one of the first devices to aid computational navigation; by the seventeenth century, as sea-travel expanded, so appeared printed guides to assist the would-be navigator and orientator.
One such is the volume entitled Urania Practica, or, Practical Astronomie, whose title-page grandly claims that it provides
(for the benefit of Sea-men) diverse Rules and Tables, of extraordinary use in Navigation. All which Rules, Tables, and Calculations, have been compared with the best approved Authors and Observations, and made more compendious then any hitherto bin publish- [sic] Nothing of this nature being extant in the English Tongue. Calculated for the Meridian of London.
The authors were Vincent Wing, and William Leybourn, ‘practitioners in the mathematicks’ as they described themselves. Leybourn, with his brother Robert, also printed the work. The first edition appeared in 1649; this, the second, followed in 1652.
Urania is the goddess of astronomy and stars, her attributes being the globe and compass. On the title-page she is illustrated standing on the pedestals of astronomy and geometry, brandishing the globes of science. Two seafarers look on, clutching rolled-up navigational charts.
The contents of the book are varied; there are tables of moveable feasts, sun-rises and sun-sets for the next 19 years, explanations of eclipses, the moon’s latitude and numerous astronomical computations. On page 125, we have a printed volvelle. A volvelle is a moveable device for calculating the position of the sun and moon in the zodiac.
One of the most noted proponents of the volvelle was the thirteenth-century scholar Johannes de Sacrobosco. Around 1230 his best-known work, the Tractatus de sphæra (Treatise on the sphere) appeared in manuscript form. The ‘sphere’ to which he refers is the celestial sphere, an imagined backdrop of the stars in the sky. Though principally about astronomy, in its first chapter the book also contains a clear description of this planet as another sphere. To illustrate his point Sacrobosco included a volvelle. Our fourteenth century manuscript 336/725 (like 428/428, given by William Moore) includes a fine, coloured volvelle, with the points of the compass in English.
A rather stilted frontispiece poem appeals to the reader’s latent wanderlust. The authors
[Have] made this Sun of knowledge to arise
In our Horizon, seen by English eyes;
Yet not so perfectly, but there remains
Some Terra incognita for after-pains[.]
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