GLOBE. 



nautical problems. On the celeftial globe, all the foutliern 

 cotiilellations, lately obferved at the Cape of Good Hope 

 by M. de la Caille, and all the ftars in Mr. Flamltted's 

 Britilh Catalogue, are accurately laid down ajid marked with 

 Greek and Roman letters of reference, in imitation of Bayer. 

 Upon each fide of the ecliptic are drawn eight parallel 

 circles, at the diltancc of one degree from each other, includ- 

 ing the zodiac ; and thefe are crofTed at right angles with 

 fegments of great circles at every fifth degree of the eclip- 

 tic, for the more readily noting tlie place of the moon, or of 

 any planet upon the globe. The author has a!fo infertcd, 

 from Ulngh Beigh, printed at Oxford in'i665, ^'"^ manfions 

 of t'p.e iVIoon of the Arabian Aftronomers, fu called, be- 

 caufe they obferved the moon to be in or near one of thefe 

 every night during her monthly courfe round the eartli, to 

 each of which the Arabian characlers are fixed. On the 

 ftrong brai's circle of the terreftrial globe, and about 23^n 

 on each fide of the north pole, the days of each month are 

 laid down according to the fun's declination ; and this brafs 

 circle is fo contrived, that the globe may be placed with the 

 north and fouth poles in the plane of the horizon, and with 

 the fouth pole elevated above it. The equator, 0:1 t!ie fur- 

 face of either globe, ierves the purpofe of the horary circle, 

 by means of a femi-circular wire placed in tlie plane of the 

 equator, carrying tv.-o indices, one of which is occafionally 

 to be ufed to point out the time. For a fartlier account of 

 thefe globes, with the method of ufing them, the reader 

 may confult Adams's Treatife on their ConllruiSion and Ufe, 

 &c. 1769. 



Globe, Celejlial, is an artificial fphere, on whofe convex 

 furface the fixed ftars are laid down, at proportionable 

 diftances, together with the principal circles of the 

 fphere. 



The furfaceof the celeftial globe may be efteemed a juft 

 reprefentaticn of the concave expanfe of the heavens, iiot- 

 withltanding its convexity ; for if the eye were placed in the 

 centre of it, and the globe made of glafs, the ilars that 

 are drawn upon it would appear in a concave furface, exaftly 

 correfponding to thofe in the heavens. The ufe of thefe 

 globes is to exhibit the phenomena of the motions of the 

 fun and ftars, in an eafy and obvious manner ; which, tliough 

 fomewhat inaccurate, is yet exafl enough for the common 

 ufes of life, and may favethe trouble of trigonometrical cal- 

 culations. 



To exhibit the JIari, circles, isfc. on the furface of a given 

 fphere or ball, and fit for the ufes of ciflronomy. — I. AlTnme 

 any two points diametrically oppofite to each other, as P and 

 Q (Plate XIV. j}Jlronomy,fig. 1 17.) and in thefe fix up axes, 

 P A and Q C, tor the bail to turn round on. The points 

 P and Q, or A and C, will exhibit the poles of the 

 world. 



2. Divide a brazen circle A B C D into four quadrants, 

 A E, E C, C F, and F D ; and fubdivide each quadrant 

 into go degrees, numbered from the points E and F, to- 

 wards the poles A and C. 



3. Inclofe the globe in this circle, as in a meridian, at the 

 points A and C, fo as it may freely turn therein. 



4. Apply a ftyle or pin to the furface of the globe, in the 

 firft degree of the meridian, and turn the ball round ; by 

 this means will a circle be defcribed on the furface, repre- 

 fenting the equator to be divided into degrees. 



5 From the pole of the world P towards M, and from 

 the other pole C towards N, number 23^ degrees ; the 

 points M and N will be the poles of the ecliptic. 



6. Apply a ftyle to the meridian, in the point M, and 

 turn the globe round ; by this rotation \vill the arii\ic polar 



circle be acfcribed : and after the fame manner it the an- 

 tarftic polar to be defcribed about the point N. 



7. Number 23J: deg. from the equator towards the poles 

 P and Q, and note the points H and I ; then applying a 

 ftyle to tiie meridian, as before, two circles will be defcribed 

 parallel to the equator, whereof that drawn tlirough H will 

 be the tropic of Cancer, and the other through I the tropic 

 ot Capricorn. 



8. Flang the g'obe within the meridian, in the poles of 

 the ecliptic, as before in the poles of the world ; and ap- 

 plying a ftyle to E, turn it round: by this means will the 

 ecliptic be dehneated, which remains to be divided into 

 twelve iigns ; and each of thefe, again, di%ided into thirty 

 degrees. 



9. AVhile the globe remains thus fufpended, bring the 

 degree of longitude of any ftar 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- 

 terfeClion is the place of that ftar on the furface of the 

 globe. After the like maimer may the place of the ftar be 

 determined from the right afcenfion and dechnation given, 

 the globe being fuppofed fufpended from the poles of \.\e 

 world, cr the equator. 



10. All the ftars of a conftellation tluis laid down, the 

 figure of the conftellation is to be defigncd ; after which it 

 may either be coloured or engraven. 



11. Place the globe with the meridian, in a wooden frame 

 or horizon, DEL, fupported on four feet, in fuch manner 

 as to be divided thereby into two hemilpheres, and that the 

 pole A may be raifed or deprcfTed at pleafure. 



12. On tlie limb or edge of the hori/on dcfcribe a circle, 

 which divide into 360 degrees, and infert the calendars and 

 winds. 



1 3. Laftly, To the pole A fit a brazen circle, divided 

 into twenty-four horary parts, and numbered twice twelve, 

 fo that the line of divifion of XII. may be in the plane of 

 the meridian, on either fide tlie pole ; and on the pole itfelf 

 apply an index, to turn round with the globe. See Horary 

 Circle. Thus is the globe complete. 



It may be here obferved, that as the longitude of the 

 ftars is continually increafing, a common globe does not 

 remain of perpetual ufe : but the increafe in feventy-two 

 years only amounting to a degree, the whole will make 

 no confidcrable error in a hundred years ; the defign of 

 a globe being only to reprefent things fomcthing near the 

 truth. 



Globe, to make a celejlial. This method is that the moft 

 frequently uied ; and we only premifed the former as being 

 the moft ealily conceived, and leading more naturally to 

 this. 



1. From the given diameter of the globe, find a right 

 line A B, fg. llS. equal to the circumference of a great 

 circle, and divide it into twelve equal parts. 



2. Through the feveral points of divifion, 1, 2, 3, 4, 

 S:c. with the interval of ten of them, deicribe arches, mu- 

 tually intcrfccting each other in I) and E : thefe figures or 

 pieces, duly pafted or joined together, will make the whole 

 furface of \\\i globe. 



3. Divide each part of the right line A B into thirty 

 equal part.^, fo that the wliole line A B, reprefenting the 

 periphery of the equator, may be divided into 360 de- 

 grees. 



4. From the poles D and E, _^^. 119. wiili the interval of 

 23.t deg. defcribe arches a, b ; thefe will be twelve parts of 

 tlie polar circles. 



5. After the like manner, from the fame poles D and E, 

 with the interval of 66; deg. reckoned from the equator, 



dcfcrilc 



