Page:Cyclopaedia, Chambers - Volume 1.djvu/910

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S° Hang the Globe within the Meridian, in the Poles of the Ecliptic, a« before in the Poles of the World ; and ap- plying a Style to E, turn it round: By this means will the Ecliptic be delineated ; which remains to be divided into 12 Signs 5 and each of thefe into 30 Degrees.

9 While the Globe remains thus fufpended, bring the De- gree of Longitude of any Sra-r under the Meridian ; and in the Meridian, number as many Degrees towards the Pole as is the Degree of Latitude of the Place : The Point of In- terferon is the Place of that Star on the Surface of the Globe. After the like manner is the Place of the Star de- termined from the right Afcenfion and Declination given; the Globe being fuppofed fufpended from the Poles of the World, or the ./Equator.

io° All the Stars of a Conftellation thus laid down 5 the Jigure of the Conftellation is to be defign'd ■ after which it may cither be colour'd, or engraven.

ii° Place the Globe with the Meridian, in a wooden Frame or Horizon D B L, fupported on four Feet ; in fuch manner, as to be divided thereby into two Hemifpheres; and that the Pole A may be rais'd or deprefs'd at pleafure.

12 On the Limb, or Edge of the Horizon defcribe a Circle, which divide into 360 Degrees, and infert the Ca- lendars, and Winds.—

1 3 Laftly, to the Pole A, fit a Brazen Semicircle, di- vided into 24 horary Parts, and number'd twice twelve, fo that the Lines or Divifions of XII, may be in the Plane of the Meridian, on either Side the Pole. And on the Pole it- felf apply an Index, to turn round with the Globe.- — Thus is the Globe compleat.

It may be here obferv'd, that as the Longitude of the Stars is continually growing, a Globe does not remain of per- petual Ufe : But the Increafe in 72 Years only amounting to a Degree, it will make no considerable Error in an hundred Tears ; the Defign of a Globe being only to reprefent things fomething near the Truth.

To make a Celeflial Globe the ufual way.

This Method is that the moft frequently ufed ; and we only premis'd the former as being the moft eafily conceived5 and leading more naturally to this. — ■

i° From the given Diameter of the Globe, find a Right Line A B, Fig- 59- equal to the Circumference of a great Circle 5 and divide it into twelve equal Parts.

i° Thro' the feveral Points of Divifion, 1, 2, 3,4, &c. with the Interval of 10 of them, defcribe Arches mutually, interfering each other in D and E.' — Thefe Figures, or Pieces duly pafted or join'd together, will make the whole Surface of the Globe.

3 Divide each Part of the Right Line A B, into 30 equal Parts; fo that the whole Line A B, reprefenting the Peri- phery of the Equator, may be divided into 36b Degrees.

4 From the Poles D, and E, with the Interval of 23!- Dcg. defcribe Arches a b 5 thefe will be twelfth Parts of the Polar Circles.

5 After the like manner, from the fame Poles D, and E, Fig. 59, 60. with the Interval of 66£ Deg. reckon'd from the Equator, defcribe Archesc d; thefe will be twelfth Parts of the Tropicks.

6° Thro' the Degree of the iEquator c correfponding to the right Afcenfion of any given Star, and the Poles D and E, draw an Arch of a Circle; and taking in the Compaffes the Complement of the Declination from the Pole D, de- fcribe an Arch, interfecting it in / 5 this Point i will be the Place of the Star.

7° All the Stars of a Conftellation thus laid down, the Figure of the Conftellation is to be drawn according to Bayer, Hevelius, or Flamftecd.

8° Laftly, after tha fame manner, are the Declinations, and Right Afcenfions of each Degree of the Ecliptic d g determined.

9 The Surface of the Globe thus projected on a Plane, is to be engraven on Copper, to fave the Trouble of doing this over again for each Globe.

io° A Ball, in the mean time, is to be prepar'd of Paper, Plafter, &c. after the manner above directed, and of the intended Diameter of the Globe. On this, by means of a Semicircle, and Style, is the iEquator to be drawn ; and thro* every 30 th Degree, a Meridian. The Ball thus divided in- to twelve Parts, correfponding to the Segments before pro- jected ; they are to be cut out from the printed Paper, and pafted on the Ball.

ii° Nothing now remains but to hang the Globe as before in a Brazen Meridian, and Wooden Horizon. To which may be added a Quadrant of Altitude H I, Fig. 61. made of Brals, and divided in the fame manner, as the Ecliptic and ./Equator, —

If the Declinations, and Right Afcenfions of the Stars be not given; but their Longitudes, and Latitudes, in lieu thereof; the Surface of the Globe is to be proje&ed after the fame manner as before ; except that in this cafe D, and

E, Fig. 59. are the Poles of the Ecliptic, and fh the Ecliptic itielf ; and that the Polar Circles, and Tropicks, with the Equator q d, and the Parallels thereof, are to bedetcrmin'd from their Declinations.

The lateft. Catalogue of the Stars is that of Mr. Flamflccd, wherein the Right Afcenfions and Declinations, as well as the Longitudes, Latitudes, &c. are every where exprefs'd. See Catalogue.

Ufe of the Celeflial Globe.

The Ufe of this Inftrument is very extenfive : Scarce any thing in the fphcrical Aftronomy but may be exhibited thereby. See Astronomy.

The principal Points are contain'd in the following Pro- blems, with their Solutions; which will let the Reader enough into the Nature and Reafon of thisnobic Inftrument to apply it, of his own Accord, in any other Cafes. —

Problem I. To find the Right Afcenfion, and 'Declina. tion of a Star, reprefented on the Surface of the Globe.

Bring the Star to the graduated Side of the Brazen Me- ridian: Then, the Number of Degrees intercepted between the JEquator, and the Point of the Meridian cut by the Star, gives its 1)eclination ; and the Degree of the .(Equator, which comes under the Meridian together with the Star, is its Right Afcenfion. See Ascension, and Declination.

II. To find the Longitude and Latitude of a Star.

Apply the Centre of the Quadrant of Altitude over the" 1 Pole of the Ecliptic in the fame Hcmifphere with the Star; and bring its graduated Edge to the Star: The Degree on the Quadrant cut by the Star is its Latitude^ reckon'd from the Ecliptic ; and the Degree of the Ecliptic cut by the Quadrant, its Longitude. See Longitude, and Latitude.

III. 2*0 find the Sun's Place in the Ecliptic.

Seek the Day of the Month in the proper Calendar on the Horizon ; and againft the Day in the Circle of Signs is the Sign and Degree the Sun is in for that Day. This done, find the fame Sign upon the Ecliptic, on the Surface of the Globe ; This is the Sun's 'Place for thatDay.— See Place.

IV. To find the ^Declination of the Sun,

The Sun's Place for the Day given being brought to the Meridian 3 the Degrees of the Meridian intercepted be- tween the Equinoctial and that Place, is the Sun's declina- tion for that Day, at Noon.

V. To find the "Place of a Planet, with its Right Af- cenfion and ^Declination 5 its Longitude, and Latitude, for the Time being given.

Apply the Centre of the Quadrant of Altitudes on the Pole of the Ecliptic (the Pole, we mean, of the fame De- nomination with the Latitude); and bring it to the given Longitude, in the Ecliptic : This Point is the Planet's 'Place : And bringing it to the Meridian, its Right Afcenfion, and ^Declination will be found as already fhewn of a Star.

VI. To rectify the Globe, or adjufl it to the Place, Sec. Jo as it may reprefe?it the prefent "State, or Situation of the Heavens.

i° If the Place be in North Latitude, raife the North Pole above the Horizon, if in South, the Sou,th Pole ; till the Arch intercepted between the Pole and Horizon be e- qual to the given Elevation of the Pole. z° Fix the Qua- drant of Altitude on the Zenith, i. e. on th» Latitude of thu Place. 3 C By means of a Compafsor Meridian Line'placs t\ie.Globe in fuch manner as that the Brazen Meridian may be in the Plane of the Meridian. 4 Bring the Degree of the Ecliptic the Sun is in, to the Meridian, and fet the ho- rary Index to XII : Thus will the Globe exhibit the Face of the Heavens for the Noon of that Day. 5 Turn theGtobc till the Index come to any other given Hour : Thus will the Globe fhew the Face of the Heaven for that time. See Rectifying.

VII. To know all the Stars. Globe.

f Planets by means of the

i° Adjuft the Globe to the State of the Heavens, for that Time. 2 C Look on the Globe for fome one Star, which you know ; e.gr. the middlemoft Star in the Tail of tha Great Bear. 3 Obferve the Pofirions of the other more confpicuous Stars in the fame Conitellation; and by tranf- ferring the Eye from the Glybe to the Heavens, you will

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