SECTION VIII. 241 Thus z e N, is the vertical circle of east or west. And in this scheme s a or f it will be the arch of the altitude of thestar s, and rn a will be its azimuth from the meridian ; and c a will be its azimuth from the cast to west. But if the line x it be supposed to represent the equator, then z and N will be the two poles of the world, and then d b, f g, 83.c. will be parallels of latitude on earth, or parallelsof de- clination in the heavens. Then also the arches z H N, z a N, z e N, z o N, z e a will be meridians, or lines of longitude on earth, and our circles in theheavens. In figure vii. Let the utmost circle be the meridian, H R the horizon, z the zenith, N the nadir, E Q the equator, P L the axis of the world, or rather the two poles, north and south ; then zrtN,zaN,zeN,ZCN will be circles of azimuth; PE L,P0L, P ii L, P C L, &c. will be hour circles. And in this position the star s will have T s, i. e. equal to e o for its hour from noon or the meridian ; but its azimuth from noon or the south or meridian will be x e. Or if you reckon its azimuth from the east or west vertical (which is z c a) it will be found to be a e, while its hour reckoned from P 6 e L (which is the six o'clock hour line) will be found to be 6 s or c o. Thus it will appear how the hour of the sun differs from its azimuth and that both of them are numbered, or counted from the meridian P Z a n L N; yet they do not by any means keep equal pace with one another, one being numbered along the equator E e, the other numbered along the horizon it R. Thus you see most evidently that if you suppose the suns to be in the tropic of cancer represented by the line T lr, the difference between the hour and azimuth will appear to be very great ; and that the sun's azimuth from noon x e increases a deal faster than his hour T s doth in the middle of sum.oer. And if another line it Vß were drawn to represent the tropic of Ca- pricorn, the sun's azimuth from non will appear to increase a great deal slower than his hours do in the middle of winter. I think it should not utterly be omitted here what is men- tioned in almost all writings of this kind, (viz.) that a star is said to rise or set cosmically when it rises or sets at sun-rising. It is said to rise or set achronically if it rise or set at sun -setting. A star is said to rise heliacallywhen it is just come to such a distance from the sun as that it is no longer hid by the sun- beams. And it is said to set heliacally when the sun approaches so near to it as that it begins. to disappear from our sight being hid by the beams of the sun. The fixed stars and the three superior planets, mars,jupiter, and saturn, rise heliacally in the morning, but the moon in the Vol,. vim. Q
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