Memoirs for a natural history of animals. Containing the anatomical descriptions of several creatures dissected by the Royal Academy of Sciences at Paris / Englished by Alexander Pitfeild [!] ... To which is added an account of the measure of a degree of a great circle of the earth, published by the same Academy, and Englished by Richard Waller.

French Academy of Sciences

Date:: 1688

Credit: Memoirs for a natural history of animals. Containing the anatomical descriptions of several creatures dissected by the Royal Academy of Sciences at Paris / Englished by Alexander Pitfeild [!] ... To which is added an account of the measure of a degree of a great circle of the earth, published by the same Academy, and Englished by Richard Waller. Source: Wellcome Collection.

403/428 page 27

$CE M ARE Le ane 5 ue ee à res Crees y catty The Meafuresof the Earth. -Kelefcope of theInftrument with; that of the Alid lade. | tht4sjnecel- Mary here .that.they, mult be both well adjatted, together : at onerand the! fame: far. diftant -Obje@.. This being fuppofed, one, ebferves Ark withthe Plumbs and with the ‘Lelefeope, faftned to, the, Inftru- . teats) the Meridional. diflince: between the Zenith and the:S Star pro- pofed, next one! fixes! thus, Ingerument : in the, plain, of. the Meridian, sin the preceding manner, -«but-in fuch el that it:may. be.coux- -twere,for -obférving -tow ards the North; and one obferyes. exactly sthe, Degregandi Minute of the Limb; where the Plumb beats. . After this the the Plumb being taken.off, bne applies the Alidade,..with -which,one obfer ves the] Meridional Diftance between the, Zenith and .the.Star, counting for this effect the Degree and Minutes which. are found betw: een the fiducial linciof,the Alidade,and the part of the limb where the plumb did beat before. The, firft: diftance that was found being compared with this laft, fhall be too little if the Inftrument ele- vates; and on the contrary, it fhall be toobig if it deprefies in fuch fort that the half of the difference fhall be the error of the Inftrument. … After ong has known,,the-error,of the laftruament; and that-one is aflured that.it comes.not1but.by.the.Telefcope,. the. fhorteft and eafieft. way.is.to let.it alone,” and, to, have, regard toit in the. Ob- {ervations ; but. if.one would correct, it; this maybe done et ther:by.-difplacing, the) Filaments,of:the Telefcope, or..by turning the Object Glafs upon its Center ; fo far as one knows by experi- and. the fame .diftant Obie, ‘as, well the ‘Lelefcope of hic Alidade as-that of the Inftrument.,,,..Next, if the,-error: is, for example, of on the contrary, one puts it nearer it, as muchyif, the error be. in de- preffing,s, and having faftned it in. this pofition, by removing, the Inftrument all together, one makes the Telefcope of this Alidade to {tand pointed at ‘the fame Object as before ; after which you mutt turn, the Object Glafs of the Telefcope, w hich, is faftned.to. the In- ftrume ent upon its Center, till fuch time as it be found. pointed to the: fame PS and by this means: one.may-be_aflured, that a ight line. which {hall be drawn from the Object by..the. Center, .of the Infirument;.comes to-meet, the point B, which we fuppofe.to have been eflablifhed for the beginning of the decifion. But for avoiding. as much.as.is poflible the refractions. of the. Tele- fcope, care. muft.be taken that. the Object Glafs be well ‘centred, which may be difcovered by making it refleét the Rays:of the Sun, becaufe if it be well centred, the little focus which it makes by re- flection at a certain dittance, will be found.exadtly. in the middie of a much.greater round of ‘ligh ht. ,Orielfe one may obferve that the, two Images which. the, Glafs reflects, of the fame Object, come to unite.in the middle of: its furface. ;. | | IE After a eee ==$

Licence and re-use

Contents