Description and use of a new constructed equatorial telescope or portable observatory / made by E. Nairne.

  • Edward Nairne
Date:
1771
Catalogue details

Licence: Public Domain Mark

Credit: Description and use of a new constructed equatorial telescope or portable observatory / made by E. Nairne. Source: Wellcome Collection.

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    To find the Meridian ofi the Place. [The inftrument remaining as in thelaft obfervation.] You firft move the plate K until the vernier on it cuts the 12 o’clock hour, and, difcharging the jfcrew to which the declination handle is fixed, turn the telefcope down to the horizon, and obferve the point which is then in the middle of the field of the tele¬ fcope, or cut by the interfedfion of the crofs wires, and a fuppofed line drawn from the center of this field, to that point in the horizon, is your meridian line, where a mark may be fet up in order to pre- ferve it; you may likewife preferve this line, by the azimuth circle, which being made moveable, fhould be turned fo as to bring the o of the azimuth plate to agree with its vernier, when the telefcope is point¬ ed to the meridian; this motion in the azimuth plate will be found very convenient, lince you may thus recover the meridian line by it, and it will fhew the exadt azimuth of any objedt the telefcope is dire&ed to, without difturbing any other part of the inftru¬ ment : the beft time of the day for making this obfervation for finding your meridian, is about three hours before noon, or as much after noon; the meri¬ dian of the place may be found by this method very nearly, and, if proper allowance be made for re- fradtion, it may be found to great exadtnefs ; this line once fettled will fave trouble afterwards, and is indeed the foundation of all aftronomical obfervations. To find .a known Star or Planet at any propofied injlant ofi time, whether in the day or night. The inftrument remaining redtified as in the laft obfervation; fet the declination femicircle to the declination
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