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GNomonica est ars construendi horologia solaria.
Horologia solaria dividuntur in pendula, & fixa: Pendula sunt ea quae appensa, aut manu suspensa, ho∣ras indicant ope altitudinis solaris: Cujusmodi sunt Astrolabium, Cylin∣drus, Quadrans, Annuli Astronomici, aliaque ejusdem generis.
Horologia stabilia, seu fixa, requi∣runt situm quemdam ut ostendant ho∣ras ope motus solis ab ortu in occa∣sum, ideoque accuratiora sunt pen∣dulis.
Centrum horologii est punctum plani horologii, in quo axis mundi se∣catura plano.
Stylus perpendicularis est recta a centro terrae ad planum horologii du∣cta, unde centrum mundi, sive terrae in horologio est vertex styli plano ho∣rologii normalis.
Polus plani horologii, est polus magni circuli paralleli plano horo∣logii.
In omni horologio Astronomico ea pars styli quae umbra horam ostendit, debet esse in axe mundi.
Itali numerant horas 24 initio du∣cto ab occasu solis; Babylonii nu∣merant totidem initio ducto ab ortu
solis; sed in antiquis horologiis horae diei, noctisque separatim enumeran∣tur, duodecim scilicet enumerantur ab ortu solis ad occasum, totidemque ab occasu ad ortum.
Maurolycus, Ptolomaeus, Kircherus, &c.