An Ancient Rule for Making Portable Altitude Sundials from an ‘Unedited’ Medieval Text of the Tenth Century
Mario Arnaldi
The use of altitude dials that worked on same principle as cylinder for travellers may be proved Christian Europe between tenth and eleventh centuries by 'Canterbury Pendant': a little portable sundial made silver gold found in 1938, during work ground levelling cemetery inside cloister cathedral Canterbury. This shows only third, sixth ninth hour day' series points along vertical columns assigned to months year.The existence other sundials kind seems confirmed words used Byrhtferth Ramsey (c. 970 - c. 1020) passage his Manual: the sun ascends point sundial, again Observe, O clerk, how sundial.2 To monk was attributed, 1563, Glossae De temporum ratione Venerable Bede (627-735);3 these we read: 'The [one fractions one hour] is so called from word 'pungendo'; because this they make some sundials. horologium hours shown after point.4 Hermann Lame (Hermannus Contractus, 1013-54) described instrument first time short but complete treatise.5Then there text, which until now has escaped attention scholars, describes clear way construction an dial kind. It inserted treatise doubtfully attributed Bede: Libellus de mensura horologii. brief composition (for convenience hereafter simply Libellus) published 1563 tome big edited Iohannes Hervagius (Johann Herwagen) Basel6 reprinted second half nineteenth century vol. xc well known patristic Latin texts J. P. Migne.7 Libellus, fact, collection different (not all gnomonics) gathered under seven rubrics order:1. does not seem have title it starts with: Si quem delectat componere.82. second, Ad merithem inveniendum, method finding meridian line with 'correspondent altitudes' sun, also 'Hindu circles'.3. Horologium quod contra unumquemque mensem habet ad umbram humani corporis pede singularum horarum diei, drawing 'shadow scheme' falsely Bede. represented instrument.94. Then follows Concordia xii mensium, where preceding shadow scheme reported textual way.105. fifth, signis et horis diagram length days, equal hours, every month corresponding zodiacal sign.6. Then, tribus diebus periculosis lists three dangerous days year, when risks death.7. last one, Aegyptiacis diebus, text about 'Egyptian days', 22 year are disadvantageous human activities.12The item no. 3 next (no. 4) often together single folio,13 while 2 added many medieval gnomonical works independently described.The contiguity items 2, 4 always drawn, automatically, researchers schemes', were popular times.'4 For reason been studied carefully sometimes entire compilation even mistreated disappointing gnomonic work.We do know source consulted work, whatever irreparably lost. sections relating computus, Charles Jones suggested thirteenth-century manuscript, or manuscripts, southern Germany, anything manuscript publication Libellus. …
Journal for the History of Astronomy