Full text: Apian, Petrus: Cosmographia

106. Inſtrumentum ſiderale.

QValiter ex ſtellarum fixarum motu, nocturno tem
pore horæ venandæ ſint, paucis abſoluam: Fiat pri
mùm rotula parua cum manubrio in ſimilitudine
rotulæ ſequentis, quam diuide in vigintiquatuor
horarum ſpacia. His perfectis, aptabis regulam ſeu
indicem in longitud. tanta, vt à centro rotulȩ vltra
limbum protendatur. Hanc itaq; regulam pone ſu
per centrum rotulæ, & fac vnum foramen rotundum, in quod mitta
tur clauus cum foramine rotundus, qui ambo conſtringat, ita vt in-
dex hac atque illac volui poſſit. Vt patet in Figura ſequenti.

106-01

107. ¶ Vſus huius Inſtrumenti.

IN ſtellifera noctis claritate ſubleua rotulam cum manu [?]
brio verſus ſeptẽtrionem, & moue rotulam huc & illuc,
donec radius viſualis ab oculo tuo per centrum inſtru-
menti ad ſtellam polarem tranſeat: ſimiliter extra rotu-
lam idem radius ad extremas duas ſtellas maioris vrſæ ſeu rotas plau
ſtri protendatur, & tam diu leua aut ſummitte indicem, donec eius
linea fiduciȩ ſuper radialem lineam incidat. Tunc enim cõſidera ho-
ram limbi & eius partem, quã regula abſcindit, cum qua intra figu-
ram præcedentẽ, hoc pacto: Pone indicem maioris vrſæ ſiue plauſtri
ſuper horam iam inuentam, indice inuariato manẽte, ſituetur regula
Solis ſua fiduciæ linea ſuper diem tuæ conſiderationis, & oſtendit in
inferiori parte limbi horam quæſitam, quam inuenire oportebat.

108. ¶ Libri de Geographicis principijs
FINIS.

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