Page:Encyclopædia Britannica, first edition - Volume II, C-L.pdf/644

676 , and through the points  and, in the. Each quarter of the former of thee is divided into 90 s, from the  to the s of the, for hewing the  of the , , and ; and each quarter of the latter, from the  at e and f, to its s b and d, for hewing the  of the.

In the of the  is a  b, to which is fixed one end of a al, and to the other end a mall  Y, which is carried round the  B B, by turning the ; and in the  of the  is a pin d, on which is another al , with a mall  Z upon it, which may be moved round by hand: but there is a particular contrivance for cauing the  to move in an  which croes the  at an  of 5 s, in two oppoite points called the s s; and alo for hifting thee points backward in the , as the s  hift in the.

Within thee s is a mall terretrial  I, fixt on an  K K, which extends from the  and  of the  at n and s, to thoe of the celetial phere at N and S. On this is fixt the flat celetial  L L, which may be et directly over the  of any place on the, and then turned round with the , o as to keep over the ame  upon it. This flat is graduated the ame way as the  of a common, and its ue is much the ame. To this is fitted the moveable  M M, o as to turn upon two trong s proceeding from its eat and wet points to the, and entering the  at the oppoite points of its , which is a moveable   let into the  in a groove all around its. The may be turned by hand within this, o as to place any given  upon it, directly under the celetial  L L. The is divided into 360 s all around its outermoft edge, within which are the points of the, for hewing the amplitude of the  and , both in s and points. The celetial L L paes through two notches in the north and outh points of the, as in a common : but here, if the  be turned round, the  and  turn with it. At the of the phere is a  of 24 s, fixt to the s, and on the  is an index which goes round that, if the  be turned round its.

The whole fabric is upported on a pedetal N, and may be elevated or depreed upon the joint O, to any number of s from 0 to 90, by means of the arc P, which is fixed in the trong arm Q, and lides in the upright piece R, in which is a  at r, to fix it at any proper.

In the box T are two wheels (as in Dr Long's phere) and two, whoe come out at V and U; either of which may be tumed by the mall  W. When the is put upon the  V, and turn backward, the terretrial, with its  and celetial , keep at ret; and the whole phere of s turns round from eat, by outh, to wet, carrying the  Y, and  Z, round the ame way, and cauing them to rie above and et below the. But when the is put upon the  U, and turned forward, the phere with the  and  keep at ret; and the, with its  and , turn round from wet, by outh, to eat; and bring the ame points of the  to the  and , to which thee bodies came when the  kept at reft, and they were carried round it; hewing that they rie and et in the ame points of the , and at the ame times in the  , whether the motion be in the  or in the. If the earthly be turned, the -index goes round its -; but if the phere be turned, the - goes round below the index.

And o, by this contruction, the is equally fitted to hew either the real motion of the, or the apparent motion of the.

To rectify the phere for ue, firt lacken the r in the upright tem R, and taking hold of the arm Q, move it up or down until the given  of  for any place be at the ide of the tem R; and then the  of the phere will be properly elevated, o as to tand parallel to the  of the world, if the  be et north and ourth by a mall : this done, count the  from the, upon the celetial  L L, down towards the north notch of the , and et the  to that ; then, turn the  b until the  Y comes to the given  of the  in the , and the  will be at its proper place for that : find the place of the 's acending , and alo the place of the , by an , and et them right accordingly: latly, turn the  W, until either the  comes to the  L L, or until the  comes to the  (according as you want the phere or  to move) and et the -index to the XII, marked , and the whole  will be rectified.&mdash;&mdash;&mdash;Then turn the , and oberve when the  or  rie and et in the , and the -index will hew the s thereof for the given.

As thoe who undertand the ue of the s will be at no los to work many other problems by this phere, it is needles to enlarge any farther upon it.

 Directions for uing

 In uing s, keep the eat ide of the towards you (unles your problem require the turning of it), which ide you may know by the word Eat upon the ; for then you have the graduated ide of the  towards you, the  of  before you, and the  divided exactly into two equal parts, by the graduated ide of the.

In working ome problems, it will he neceary to turn the whole and  about, that you may look on the wet ide thereof; which turning will be apt to jog the ball o, as to hift away that  of the  which was before et to the  or : to avoid which inconvenience, you may thrut in the feather-end of a  between the ball of the  and the ; which, without hurting the ball, will keep  it