Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/550

 460 . ASTRO N O M Y. enters Libra; and the 21ft of December, when he en- the patches from Aries-to Cancer come to the brazen meters Capricorn. But, as there is only one fun, and his ridian fooner than the correfponding patches on the equa* apparent motion is always on the ecliptic, let us hence- tor ; all thofe from Cancer to Libra will come latter to forth call him the real fun ; and the other, which is fup- the meridian than their correfponding patches on the e.poied to move in the equator, the fitlilious ; to which quator; thofe from Libra to Capricorn foqner, and ialt, the motion of a well-regulated clock always an- thofe from Capricorn to Aries latter: And the patches fwers. at the beginnings of Aries, Cancer, Libra, and CapriIn PlateXLII. fig. 4. let Z'YzQ be the earth, ZFRz corn, being either on, or even with thofe on the-equa•its axis, abcde <bc. the equator, ABCDF. ilc. the northern tor, {hew that the two funs either meet there, or are ehalf of the ecliptic from or Q on the fide of the globe ven with one another, and fo come to the meridian at next the eye ; and MNOP See. the fouthern half on the fame moment. the oppolite fide from ;Q; to °f. Let the points at Let us fuppofe that there are two little balls moving jJBCQEF See. quite round from to ‘Y’ again bound equably round a celeftial globe by clock-work, one alequal portions of the ecliptic, gone through in equal ways keeping in the ecliptic, and gilt with gold, to retimes by the real fun ; and thofe at abedef <bc. equal prefent the real fun ; and the other keeping in the equaportions of the equator, deferibed in equal times by the tor, and filvered, to reprefe'nt the fictitious fun: And fictitious fun ; and let Z°<Fz be the meridian. that whilft thefe balls move once round the globe, acthe real fun moves obliquely in the ecliptic, and cording to the order of figns, the clock turns the globe the fidlitious fun dire&ly in the equator, with refpeft to 366 times-round its axis weftward. The ftars will make the meridian; a degree, or any number of degrees, be- 366 diurnal revolutions from the brafen meridian to it atween hf and F on the ecliptic, mull: be nearer the me- gain; and die two balls reprefenting the real and ficridian Z'Y'z; than a degree, or any conelponding num- titious fun always going farther eaftward from any giber of degrees on the equator from to f; and the ven liar, will come later than it to the meridian every folmote fo, as they are the more oblique : And therefore lowing day; and each bail will make 365 revolutions to the true fun comes fooner cto the meridian every day the meridian; coming equally to it at the beginnings of whilif he is in the quadrant ■ f F, than the fi&itious fun Aries, Cancer, Libra, and Capricorn: But in every odoes in the quadrant CY> f; for which reafon, the folar ther point of the ecliptic, the gilt ball will come either noon piecedes no:', by the clock, until the real fun fooner or latter to the meridian than the filver bail, like comes to F, and the fi&itious to f; which two points, the patches above mentioned. being equidiftant Bom the meridian, bo;h funs will come This would be a pretty enough way of {hewing the reafon why any given liar, which, on a certain day of the ,to it precifely at noon by the clock. Whilft the real fun deferibes the fecond quadrant of the year, comes to the meridian with the fun, paffes over it ecliptic FGHIKL from F to £2, he comes later to fo much fooner every following day, as on that day the meridian every day, than the fiflitious fun moving {welvemonth to come to the meridian with the fun again ; through the fecond quadrant of the equator from f to and alfo to {hew the reafon why the real fun comes to urn ; for the points at GHIK and L, being farther from the meridian fometimes fooner, fometimes later, than it the meridian than their correfponding points xtghik and is noon by the clock; and, on four days of the year, at l, they mull: be later of coming to it: And as both funs the fame time; whilft the fictitious fun always comes to come at the farne moment to the point they come the meridiafi w"hen it is twelve at noon by the clock. to the meridian at the moment of poon by the clock. This would be no difficult tafle for an artift t'o perform ; In departing from Libra, through the third quadrants, for the gold ball might be carried round the ecliptic by the real fun going through towards rs at R, a wire from its north pole, and the filver ball round and the fiftitious fun through mnopq towards r, the the equator by a wire from its fouth pole, by mein of. former comes to the meridian every day fooner than the a few wheels to each. latter, until the real fun comes to m, and the fiftitious It is plain, that if the ecliptic were more obliquely pothe to and then they both come to the meridian at the fited to the equator,t )ast0the doted circle equal divifions from Y X would come ftill foonei to fame time. Laftly, as the real < 5 fun moves equably through STUVIV, the meridian ZoT than thofe marked ABCD and E do ; from rs towards Y ; and the fidlitious fun thro’-rrauw, for two divifions containing 30 degrees, from ‘T'to the from r towards ; the former comes later every day fecond dot, a little ffiort of the figure 1, come fooner to to the meridian than the latter, until they both arrive at the meridian than one divifion containing only 15 degrees the point °f, and then they make noon at the fame time from T to ^-does, as the ecliptic now ftands; and thofe with the clock. of the fecond quadrant from X to would be fo much This part of the equation of time may perhaps be later. The third quadrant would be as the firft, and fbmewhat difficult to underftand by a figure, becaufe the fourth as the fecond. And it is likewife plain, that borh halves of the ecliptic feem to be on the fame fide where the ecliptic is moft oblique, namely, about Aries and of the globe ; but it may be made very eafy to any per- Libra, the difference would be greateft ; and lead about and Capricorn, where the obliquity is leaft. fun who has a real globe before him, by putting fmall Cancer patches on every tenth or fifteenth degree, both of the Having explained one caiife of the difference of time equator and ecliptic, beginning at Aries T ; and then, (hewn by a well-regulated clock and a true fun-dial; turning the ball ilowly round wdhvard, he will fee all and confidered the fun, not the earth, as.movingecliptic in the