SECTION XIX. 285 as little black patch and then for that day and that night yoh may perform any problem by that planet in the same manner as you did by a fixed star. But-if you would be very exact you must not only seek the planet's place in the sign for that day, which is its longitude, but you must seek its latitude also in the ephemeris '(which indeed in the superior planets, Jupiter, Saturn, Mars, alters but very little for whole months together) and thus set your mark in that point of latitude, or distance from its supposed place in the eclip- tic, whether northward,or southward, and then go to work your problem by this mark. I shall give but one instance, which will sufficiently direct to solve all others of 'the samekind that relate to the planets. On the 3dof April 1723, I find by an ephemeris that the sun is about the end of the 23d degree of cries, Jupiter enters the 8th degree of capricorn, and (if I would be very exact,) I observe also that the latitude of Jupiter that day is 15 minutes or a quarter of a degree to the north : There I make a mark or put on a small black patch: on the globe to stand for Jupiter. Then having rec- tified the 'globe for the latitude v. c. of London, and for thesun's place, April the 3d, 1 turn the mark which I made for Jupiter to the eastern edge of the horizon, and I find Jupiter will rise near the south-east at a little past one in the morning : He will come to the meridian at a very little past five : Hewill set near the south-west, about nine in the morning. Then if I rectify the globe for the zenith, the quadrant of altitude being brought down to the horizon, will tell you whatis his altitude, and what his azimuth, at any given hour of the morn- ingby 'the help of the dial and index. Or his altitude or azimuth being given you may find what itis o'clock. By this means you mu y find the hour when the moon will rise and set, together with her southing, or the time of her coming to the meridian. But let it be noted, that'the moon changes her place in the zodiac so swiftly, that she moves through 13 degrees of one sign every day, or thereabout ; and therefore you cannot find the precise hour and minute of her rising, setting, southing, &c. upon the globe without much more trouble than most of the other planets will give you, which change their places in the zodiac much more slowly. ProblemXXXVIII. 0° The day and hour of a solar eclipse being known to find all those places in which that eclipse will be visible." By the 13th problem findout at what place the sun isvertical at that hour of the day. Bring that place to the pole or vertical point of the wooden horizon, that is, rectify the globe for the latitude of that place ; then the globe heing in that situation, ob- serve what places are in the upper hemisphere; for if it bea large eclipse the sun will be visibly eclipsed in most of them.
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