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A TABLE of the Equation of Time, shewing how much a Clock should be faster or slower than the Sun, every Day of the Year, at Noon. The Third Year after Leap-Year.
Jan. Feb. March. April. | May. | June. M. S. M. S. M. S. M. S. M. S. M. S. 814 412 38 3 55 3 8 2 38 3614111225 336 315 2029 5 414171112 318 322 219 32142311591 300 328 2
2811 45 2 43 3 34 1 59
A TABLE of the Equation of Time, shewing how much a Clock should be faster or slower than the Sun, every Day of the Year, at Noon. The third Year after Leap-Year.
This table is near enough the truth for regulating common clocks and watches. It may be easily copied by the pen, and, being doubled, may be put into a pocket-book.
The Moon's Surface mountainous: Her Phases described: Her Path, and the Paths of Jupiter's Moons delineated: The Proportions of the Diameters of their Orbits, and those of Saturn's Moons, to each other; and the Diameter of the Sun.
Y looking at the Moon through an ordinary PLATE telescope, we perceive that her surface is diversified with long tracts of prodigious high moun- The tains and deep cavities. Some of her mountains, by Moon's comparing their height with her diameter (which is mountain2180 miles,) are found to be three times as high as ous. the highest mountains on our Earth. This ruggedness of the Moon's surface is of great use to us, by reflecting the Sun's light to all sides: for if the Moon were smooth and polished like a looking-glass, or covered with water, she could never distribute the Sun's light all round: only, in some positions, she would shew us his image, no bigger than a point, but with such a lustre as might be hurtful to our eyes.
253. The Moon's surface being so uneven, many have wondered why her edge appears not jagged as well as the curve bounding the light and dark parts. But if we consider, that what we call the edge of the Why no Moon's disc is not a single line set round with mountains, in which case it would appear irregularly in- her edge. dented, but a large zone, having many mountains lying behind one another from the observer's eye, we shall find that the mountains in some rows will be opposite to the vales in others, and fill up the inequalities, so as to make her appear quite round; just as when one looks at an orange, although its roughness be very discernible on the side next the eye, especially if the Sun or a candle shines obliquely on that side, yet the line terminating the vi sible part still appears smooth and even.
254. As the Sun can only enlighten that half of the Earth which is at any moment turned toward him, The Moon and being withdrawn from the opposite half, leaves it in darkness; so he likewise doth to the Moon; only with this difference, that the Earth being surrounded by an atmosphere, and the Moon, as far as we know, having none, we have twilight after the Sun sets; but the Lunar inhabitants have an immediate transition from the brightest sunshine to the blackest darkness, § 177. For, let t r k sw be the Earth, and A, B, C, D, E, F, G, H, the Moon, in eight different parts of her orbit. As the Earth turns round its axis, from west to east, when any place comes to t, the twilight begins there, and when it revolves from thence to r, the Sun S rises; when the place comes to s, the Sun sets, and when it comes to w, the twilight ends. But as the Moon turns round her axis, which is only once a month, the moment that any point of her surface comes to r (see the Moon at G) the Sun rises there without any previous warning by twilight; and when the same point comes to s the Sun sets, and that point goes into darkness as black as at midnight.
255. The Moon being an opaque spherical body phases. (for her hills take off no more from her roundness than the inequalities on the surface of an orange take off from its roundness), we can only see that part of the enlightened half of her which is toward the Earth. And therefore when the Moon is at A, in conjunction with the Sun S, her dark half is toward the Earth, and she disappears, as at a; there being no light on that half to render it visible. When she comes to her first octant at B, or has gone an eighth part of her orbit from her conjunction, a quarter of her enlightened side is seen toward the Earth, and she appears horned, as at h. When she has gone a quarter of her orbit from between the Earth and Sun to C, she shows us one half of her enlightened side, as at c; and we say, she is a quarter old. At D she is in her second octant, and by shewing us more of her