Full text: Bithynius, Theodosius: Theodosii Tripolitae Sphaericorum libri tres

quin{que} libris diffusè explicatam, & à Gebro Hi-
ſpalenſi Arabe, necnon à Nicolao Copernico bre-
uiter quidem, ſed paulò obſcurius traditam, pro
virili etiam exponamus, cum incredibilis ſit eo-
rum vtilit as cum in rebus omnibus Mathema-
ticis, tum præſertim in cæleſtibus motibus, & in
ijs rebus, quæ ex illis pendent, rectè intelligendis,
velinueſtig ãdis, vt dictum est, & partim etiam
non obſcure ex noſtra Gnomonica colligi poteſt,
vbi permulta ad horologia pertinentia ex trian-
gulis à nobis ſunt demonſtrata. Exordiemur
autem à triangulis rectilineis, tanquam facilio-
ribus, de quibus eaſolum demonſtr abimus, quæ
ad res Aſtronomicas, & Geometric as recte per-
cipiend as neceſſaria eſſe iudicamus: Id quod e-
tiam in ſphæricis triang ulis obſeruauimus. Qui
plur a deſider at, leg at Menelaum, & Mauro-
lycum de sphæricis triangulis, de rectilineis ve-
ro Ioannem Regiomontanum. Ante omnia au-
tem explicandum erit, penes quid angulorum
rectilineorum quantitas ſumenda ſit.

450.1.

vſus ſinu@,
linearũ tan
gentium, &
ſecantium
in doctrina
triangulo-
rum potiſ-
ſimum con
ſiſtit.

PENES QVID ANGVLI rectilinei magnitudo ſumatur.

Angulorũ
rectilineo-
rũ magni
tudo penes
quid ſuma
tur.

ANGVLI cuiuſuis rectilinei magnitudo ſumitur penes arcum circuli ex ipſo
angulo, vt centro, deſcripti ad quodcunq; interuallum, inter rectas lineas angulum
comprehendentes interceptum. Nam quilibet angulus rectilineus tantus eſſe dicitur,
quantus eſt arcus circuli, cuius centrum eſt inipſo angulo, inter duas lineas rectas,

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