Full text: Musschenbroek, Petrus: Physicae experimentales, et geometricae de magnete, tuborum capillarium vitreorumque speculorum attractione, magnitudine terrae, cohaerentia corporum firmorum dissertationes

DE MAGNETE. tem perpendiculariter erecta ſponte vi eâ donari; craſſa tamen & brevia non niſi longinquitate temporis; craſſa & longa citius; ſed
tenuia & longa nequidem horæ minutum poſtulare, cape enim vir-
gam 6 pedes longam, diametri {1/5} pollicis, ad horizontem perpen-
diculariter tene, & cuſpide inferiori polum Verſorii Auſtralem at-
trahet, fugabit Boreum: cuſpide ſuperiori attrahet polum Boreum,
fugando Auſtralem: ſtatim virgam inverte, & intra Minutum ob-
ſervabis, cuſpidem inferiorem attracturam polum Verſorii Auſtra-
lem, quem modo ante reſpuerat, adeo ut poli in ejuſmodi Virga
ocyſſime mutentur: Idem in Virga breviori, ſed ſimul multum te-
nuiori animadverti poteſt. Horum nonnulla adnotavit quondam
Grimaldi in Tract. de Lumine Prop. 6. §. 51. tum Boyle, Poli-
nierius in Exper. Phyſiq. pag. 283. & nuperrime Reaumurius in
L’Hiſt. de L’Acad. Roy. A°. 1723. Addendum præterea eſt, dari
nonnunquam lamellas Chalybeas, quæ in aquâ perpendiculariter
ad horizontem extinctæ, acquirunt polos fixos, non mutabiles,
lamellis quomodocunque inverſis: dantur quoque aliæ, quæ po-
los quidem fixos conſervant, verum inverſæ, non adeo vehemen-
ter vim ejuſdem poli exercent, quam antea, & potius inclinatio-
nem tantum ejuſdem poli oſtendunt: imo aliæ, poſtquam conver-
ſæ ſunt, evadunt indifferentes, ita ut nauticæ Acui admotæ, ver-
ſus Ortum & Occaſum eam dirigant, atque in æquilibrio quaſi
teneant: hæc autem omnia modo obtinent in tenuibus Chalybeis
lamellis; nam in craſſioribus ferramentis ea, quæ ſuperius attuli,
tantum dantur, hujus obſervationis potiſſimam partem vide in Phi-
loſ. Tranſ. N°. 246.

Quod ſi ferramenta diu fixa ſteterint, quemadmodum cancelli
ferrei feneſtrarum, qui in ædibus antiquis per centenos hæſerunt
annos, hi vim maximam agendi in Acum Nauticam, imo ad di-
ſtantiam quidem 4 ulnarum & amplius acquirunt, quemadmodum
Mantuæ obſervavit Cabeus Lib. 1. Cap. 17.

Ex his experimentis iterum conſtat, ſemper Verſorium haberi
poſſe, quod cuſpides ſuas dirigat verſus plagam cæli Boream & Au-
ſtralem, etiamſi non affricetur Magneti, modo ſtet aliquamdiu ver-
ticaliter erectum, aut ignitum immergatur aquæ perpendiculari-
œ [?] r.

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