SPHERE. 



rings of brafs, or other matter, called by the Latins armilU, 

 from their refemblance to bracelets, or rings for the arm. 



By this it is diflinguiflaed from the globe, which, though 

 it hath all the circles of the fphere on its furface ; yet is not 

 cut into armillx or rings, to reprefent the circles fimply and 

 alone ; but exhibits alfo the intermediate fpaces between 

 the circles. 



Sphebe, The ylrm'tUary, of Mr. Fergufon, conftrufted 

 after the model of the glafs fphere of Dr. Long, is repre- 

 fented Plate XX. Ajlronomy.,Jig. 5. 



The exterior parts of this machine are a compages of brafs 

 rings, which reprefent the principal circles of the heavens, 

 wz- I. The equinoctial A A, which is divided into 360 

 degrees (beginning at its interfeftion with the ecliptic in 

 Aries), for (lie wing the fun's right afeenfion in degrees ; 

 and alfo into twenty-four hours, for (hewing his right afeen- 

 fion in time. 2. The ecliptic B B, which is divided into 

 12 figns, and each fign into 30 degrees, and alfo into the 

 months and days of the year, in fuch a manner, that the de- 

 gree or point of the ecliptic in which the fun is, on any 

 given day, ilands over that day in the circle of months. 

 3. The tropic of Cancer C C, touching the ecliptic at the 

 beginning of Cancer in e; and the tropic of Capricorn DD, 

 touching the ecliptic at the beginning of Capricorn iny"; 

 each 235 degrees from the equinodlial circle. 4. The arftic 

 circle E, and the antardlic circle F, each 23! degrees from 

 its refpeftive pole at N and S. 5. The equinoftial colure 

 G G, paffing through the north and fouth poles of the 

 heaven at N and S, and through the equinoftial points 

 Aries and Libra, in the ecliptic. 6. The folftitial colure 

 H H, palling through the poles of the heaven, and through 

 the foUtitial points Cancer and Capricorn, in the ecliptic. 

 Each quarter of the former of thefe colurea is divided into 

 90 degrees, from the equinoftial to the poles of the world, 

 for (liewing the declination of the fun, moon, and Itars : and 

 each quarter of the latter, from the ecliptic at e and/, to its 

 poles b and d, for {hewmg the latitudes of the ftars. 



In the north pole of the ecliptic is a nut /;, to which is 

 fixed one end of a quadrantal wire, and to the other end a 

 fmall fun Y, which is carried round the ecliptic B B, by 

 turning tiie nut : and in the fouth pole of the ecliptic is a 

 pin at d, on which is another quadrantal wire, with a fmall 

 moon, Z, upon it, which may be moved round by hand : but 

 there is a particular contrivance for caufing tlie moon to 

 move in an orbit which croflcs the ecliptic at an angle of 54^ 

 degrees, in two oppofite points, called the moon's nodes ; and 

 alfo for fhifting thofe points backward in the ecliptic, as the 

 moon's nodes (hift in the heaven. 



Within thcfe circular rings is a fmall tcrrellrial globe I, 

 fixt on an axis K K, which extends from the north and fouth 

 poles of the globe at n and s, to thofe of the cclcftial fphere 

 at N and S. On this axis is fixt the flat celeftial meridian 

 L L, which may be fet direftly over the meridian of any 

 place on the globe, and then turned round with the globe, fo 

 as to keep over the fame meridian upon it. This flat me- 

 ridian is graduated the fame way as the brafs meridian of 

 the common globe, and its ufe is much the fame. To this 

 globe is fitted the moveable horizon M M, fo as to turn 

 upon two llrong wires proceeding from its eaft and well 

 points to the globe, and entering the globe at oppofite 

 points of its equator, which is a moveable brafs ring let into 

 the globe in a groove all round its equator. The globe 

 may be turned by hand within this ring, fo as to place any 

 given meridian upon it, direftly under the celcltial meri- 

 dian L L. The horizon is divided into 360 degrees all 

 round its outermofl edge, within wliich are tlie points of 

 the compafs, for fliewing the amplitude of the fun and 



moon, both \n degrees and pomts. The celeftial meridian 

 I^ L paffes through two notches in the north and fouth 

 points of the horizon, as in a common globe : but here, if 

 the globe be turned round, the horizon and meridian turn 

 with it. At the fonth pole of the fphere is a circle of 

 24 hours, fixt to tlie rings, and on the axis is an index 

 which goes round that circle, if the globe be turned round 

 its axis. 



The whole fabric is fupported on a pedcftal N, and may 

 be elevated or dcprefled upon the joint O, to any number 

 of degrees from o to 90, by means of the arc P, which is 

 fixed into the itrong brafs arm Q, and Aides in^o the up- 

 right piece R, in which is a fcrew at r, to fix it at any pro- 

 per elevation. 



In the box T are two wheels (as in Dr. Long's fphere), 

 and two pinions, whofe axes come out at V and U ; either 

 of which may be turned by the fmall winch W. When the 

 winch is put upon the axis V, and turned backward, the 

 terreftrial globe, with its horizon and celeltial meridian, keep 

 at reft ; and the whole fphere of circles turns round from 

 eaft, by fouth, to welt, carrying the tun Y, and the moon Z, 

 round the fame way, and caufing them to rife above and fet 

 below the horizon. But when the winch is put upon the 

 axis U, and turned forward, the fphere with the fun and 

 moon keep at reit ; and the earth, with its horizon and me- 

 ridian, turn round from welt, by fouth, to eaft ; and bring 

 the fame points of the horizon to the fun and moon, to 

 which thefe bodies came -wlien the earth kept at reft, and 

 they were carried round it ; fliewing that they rife and fet in 

 the fame points of the horizon, and at the fame times in the 

 hour-circle, whether the motion be in the earth or in the 

 heaven. If the earthly globe be turned, the hour-index goes 

 round its hour-circle ; but if the fphere be turned, the hour- 

 circle goes round below the index. 



And fo, by this conftruftion, the machine is equally fitted 

 to ftiew either the real motion of the earth, or the apparent 

 motion of the heaven. 



To reftify the fphere for ufe, firft flacken the fcrew r in 

 the upright ftem R, and taking hold of the arm Q, move 

 it up or down until the given degree of latitude for any 

 place be at the fide of the Item R ; and then the axis of the 

 fphere will be properly elevated, fo as to ftand parallel to 

 the axis of the world, if the machine be fet north and fouth 

 by a fmall compafs : this done, count the latitude from the 

 north pole, upon the celeftial meridian L L, down towards 

 the north notch of the horizon, and fet the horizon to that 

 latitude ; then turn the nut b until the fun Y comes to the 

 given day of the year in tlie ecliptic, and the fun will be at 

 its proper place for that day : find the place of the moon's 

 afcending node, and alfo the place of the moon, by an Ephe- 

 meris, and fet them right accordingly : lallly, turn the 

 winch W, until either the fun comes to the meridian L L, 

 or until the meridian comes to the fun (.iccording as you 

 want the fphere or earth to move), and fet the hour-mdex to 

 the XII, marked noon, and the whole machine will be rec- 

 tified. Then turn the winch, and obfrrve when the fun or 

 moon rife and fet in the horizon, and the hour-index will 

 (hew the times of them for the given day. See Fergufon's 

 Leftures, p. 194, &c. 



Armillary fphcres are of diflercnt kinds with regard to 

 the polition of the earth in tht-m ; whence they become dif- 

 tinguifticd into Ptolrniaic and Copernican fphcres : in the firit 

 of whieii the earth is in the c-cntre, and in the latter near the 

 circumference, according to tlie pofition which that planet 

 obtains in thofe fyftems. 



Sphere, The Ptolemaic, ii that commonly in uCc, and is 

 reprcfcnted {Plate XX. /Ijlrunomy, fi^- 6.) with the samcs 



