and great declination. To deter points of natural day, or nearly in 18% of our days and nights. 33. Because her day is so great a part of her year, the Sun changes his declination in one day so much, that if he passes vertically, or directly over head of any given place on the tropic, the next day he will be 26 degrees from it; and whatever place he passes vertically over when in the Equator, one day's revolution will remove him 36 degrees from it. So that the Sun changes his declination every day in Venus about 14 degrees more, at a mean rate, than he does in a quarter of a year on our Earth. This appears to be providentially ordered, for preventing the too great effects of the Sun's heat, (which is twice as great on Venus as on the Earth,) so that he cannot shine perpendicularly on the same places for two days together; and on that account, the heated places have time to cool. 34. If the inhabitants about the north pole of mine the Venus fix their south, or meridian line, through that the com- part of the heavens where the Sun comes to his her poles. greatest height, or north declination, and call those pass at the east and west points of their horizon, which are 90 degrees on each side from that point where the horizon is cut by the meridian line, these inhabitants will have the following remarkable appearances The Sun will rise 223 degrees north of the east, and going on 1124 degrees, as measured on the plane of the horizon, he will cross the meridian at an altitude of 12 degrees; then making an entire revolution without setting, he will cross it again at an altitude of 48 degrees. At the next revolution he will cross the meridian as he comes to his greatest height and declination, at the The limit of any inhabitant's view, where the sky seems to touch the planet all round him. altitude of 75 degrees; being then only 15 degrees from the zenith, or that point of the heavens which is directly over head: and thence he will descend in the like spiral manner, crossing the meridian first at the altitude of 48 degrees, next at the altitude of 123 degrees; and going on thence 112 degrees, he will set 24 degrees north of the west. So that, after having made 4 revolutions above the horizon, he descends below it to exhibit the like appearances at the south pole. 35. At each pole, the Sun continues half a year Surprising apwithout setting in summer, and as long without pearances rising in winter; consequently the polar inhabitants at her of Venus have only one day and one night in the poles. year; as it is at the poles of our earth. But the difference between the heat of summer and cold of winter, or of mid-day and mid-night, on Venus, is much greater than on the Earth: because on Venus, as the Sun is for half a year together above the horizon of each pole in its turn, so he is for a considerable part of that time near the zenith; and during the other half of the year always below the horizon, and for a great part of that time at least 70 degrees from it. Whereas, at the poles of our Earth, although the Sun is for half a year together above the horizon; yet he never ascends above, nor descends below it, more than 23 degrees. When the Sun is in the equinoctial, he is seen with one half of his disc above the horizon of the north pole, and the other half above the horizon of the south pole; so that his centre is in the horizon of both poles: and then descending below the horizon of one, he ascends gradually above that of the other. Hence, in a year, each pole has one spring, one autumn, a summer as long as them both, and a winter equal in length to the other three seasons. 36. At the polar circles of Venus, the seasons At her po lar circles. At her tropics. At her equator. are much the same as at the equator, because there are only 15 degrees between them, 31; only the winters are not quite so long, nor the summers so short but the four seasons come twice round every year. 27. At Venus's tropics, the Sun continues for about fifteen of our weeks together without setting in summer; and as long without rising in winter. While he is more than 15 degree from the equator, he neither rises to the inhabitants of the one tropic, nor sets to those of the other; whereas, at our terrestrial tropics, he rises and sets every day of the year. 38. At Venus's tropics, the seasons are much the same as at her poles, only the summers are a little longer, and the winters a little shorter. 39. At her equator, the days and nights are always of the same length; and yet the diurnal and nocturnal arches are very different, especially when the Sun's declination is about the greatest: for then, his meridian altitude may sometimes be twice as great as his midnight depression, and at other times the reverse. When the Sun is at his greatest declination, either north or south, his rays are as oblique at Venus's equator, as they are at London on the shortest day of winter. Therefore, at her equator there are two winters, two summers, two springs, and two autumns every year. But because the Sun stays for some time near the tropics, and passes so quickly over the equator, every winter there will be almost twice as long as summer: the four seasons returning twice in that time, which consist only of 91 days. 40. Those parts of Venus which lie between the poles and tropics, between the tropics and polar circles, and also between the polar circles and equator, partake more or less of the phenomena of those circles, as they are more or less distant from them. ference of and set ting. 41. From the quick change of the Sun's declina- Great dif tion it happens, that if he rises due east on any day, the Sun's he will not set due west on that day, as with us, amplitude For if the place where he rises due east be on the at rising equator, he will set on that day almost west-northwest, or about 18 degrees north of the west. But if the place be in 45 degrees north latitude, then on the day that the Sun rises due east he will set north-west-by-west, or 33 degrees north of the west. And in 62 degrees north latitude, when he rises in the east, he sets not in that revolution, but just touches the horizon 10 degrees to the west of the north point; and ascends again, continuing for 31 revolutions above the horizon without setting. Therefore no place has the forenoon and afternoon of the same day equally long, unless it be on the equator, or at the poles. places ea 42. The Sun's altitude at noon, or any other The longitime of the day, and his amplitude at rising and tude of setting, being very different at places on the same sily found parallel of latitude, according to the different longi. in Venus. tudes of those places, the longitude will be almost as easily found on Venus, as the latitude is found on the Earth. This is an advantage we can never have, because the daily change of the Sun's declination, is by much too small for that important purpose. a quarter every 43. On this planet, where the Sun crosses the Her equiequator in any year, he will have 9 degrees of de-noxes shift clination from that place on the same day and hour of a day next year, and will cross the equator 90 degrees far- forward ther to the west; which makes the time of the equi- year. nox a quarter of a day (or about six of our days) later every year. Hence, although the spiral in which the Sun's motion is performed be of the same sort every year, yet it will not be the very same; because the Sun will not pass vertically over the same places till four annual revolutions are finished. G Every fourth year to to Venus. When she will appear on the Sun. 44. We may suppose that the inhabitants of Veyear a leap nus will be careful to add a day to some particular part of every fourth year; which will keep the same seasons to the same days. For, as the great annual change of the equinoxes and solstices shifts the seasons a quarter of a day every year, they would be shifted through all the days of the year in 36 years. But by means of this intercalary day, every fourth year, will be a leap-year; which will bring her time to an even reckoning, and keep her calendar always right. 45. Venus's orbit is inclined 3 degrees 24 minutes to the Earth's; and crosses it in the 15th degrees of Gemini and of Sagittarius; and therefore, when the Earth is about these points of the ecliptic at the time that Venus is in her inferior conjunction, she will appear like a spot on the Sun, and afford a more certain method of finding the distances of all the planets from the Sun, than any other yet known. But these appearances happening very seldom, will be only twice visible at London for one hundred and ten years to come. The first time will be in 1761, June the 6th, in the morning; and the second in 1769, on the 3d of June, in the evening. Excepting such transits as these, she exhibits the same appearances to us regularly every eight years; her conjunctions, elongations, and times of rising and setting, being very nearly the same, on the same days as before. She may have a see it. 46. Venus may have a satellite or moon, almoon, al- though it be undiscovered by us. This will not though appear very surprising, if we consider how inconwe cannot veniently we are placed for seeing it. For its enlightened side can never be fully turned toward us, except when Venus is beyond the Sun; and then, as Venus appears but little larger than an ordinary star, her moon may be too small to be perceived at such a distance. When she is between us and the Sun, her full moon has its dark side toward us; and then we cannot see it any more than we can our own moon at the time of change. When |