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ASTRONOMY

from it; and whatever place he paes vertically over when in the equator, one day’s revolution will remove him 36$1/4$ degrees from it. So that the un 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 un’s heat, (which is twice as great on Venus as on the earth), o that he cannot hine perpendicularly on the ame places for two days together; and by that means the heated places have time to cool.

If the inhabitants about the north pole of Venus fix their fouth or meridian line through that part of the heavens where the un comes to his greatet height, or north declination, and call thoe the eat and wet points of their horizon, which are 90 degrees on each fide from that point where the horizon is cut by the meridian line, thefe inhabitants will have the following remarkable things.

The un will rie 22$1/2$ degrees north of the eat; and going on 112$1/2$ degrees, as meaured on the plane of the horizon, he will cros the meridian at an altitude of 12$1/2$ degrees; then making an entire revolution without etting, he will cros it again at an altitude of 48$1/2$ degrees; at the next revolution he will cros the meridian as he comes to his greatet height and declination, at the 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 defeend in the like piral manner, croing the meridian firt at the altitude of 48$1/2$ degrees; next at the altitude of 12$1/2$ degrees; and going on thence 112$1/2$ degrees, he will let 22$1/2$ degrees north of the weft; o that, after having been 4$5/8$ revolutions above the horizon, he decends below it to exhibit the like appearances at the outh pole.

At each pole, the fun continues half a year without etting in ummer, and as long without riing in winter; conequently the polar inhabitants of Venus have only one day and one night in the year, as it is at the poles of our earth. But the difference between the heat of ummer and cold of winter, or of mid-day and mid-night, on Venus, is much greater than on the earth; becaue in Venus, as the un is for half a year together above the horizon of each pole in its turn, o he is for a coniderable 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 leat 70 degrees from it. Whereas, at the poles of our earth, although the un is for half a year together above the horizon, yet he never acends above, nor decends below it, more than 23$1/2$ degrees. When the fun is in the equinoctial, or in that circle which divides the northern half of the heavens from the outhern, he is een with one half of his dik above the horizon of the north pole, and the other half above the horizon of the outh pole; o that his centre is in the horizon of both poles: and then decending below the horizon of one, he acends gradually above that of the other. Hence, in a year, each pole has one pring, one harvet, a ummer as long as them both, and a winter equal in length to the other three eaons.

At the polar circles of Venus, the eaons are much the ame as at the equator, becaue there are only 15 degrees betwixt them; only the winters are not quite o long, nor the ummers o hort; but the four eaons come twice round every year.

At Venus’s tropics, the un continues for about fifteen of our weeks together without etting in ummer, and as long without riing in winter. Whilt he is more than 15 degrees from the equator, he neither ries to the inhabitants of the one tropic, nor ets to thoe of the other; whereas, at our terretrial tropics, he ries and ets every day of the year.

At Venus’s tropics, the eaons are much the fame, as at her poles; only the ummers are a little longer, and the winters a little horter.

At her equator, the days and nights are always of the ame length, and yet the diurnal and nocturnal arches are very different, epecially when the un’s declination is about the greatet; for then his meridian altitude may ometimes be twice as great as his midnight depreion, and at other times the revere. When the fun is at his greatet declination, either north or outh, his rays are as oblique at Venus’s equator, as they are at London on the hortet day of winter. Therefore, at her equator there are two winters, two ummers, two prings, and two autumns every year. But becaue the un tays for ome time near the tropics, and paes o quickly over the equator, every winter there will be almot twice as long as ummer; the four eaons returning twice in that time, which conits only of 9$1/4$ days.

Thoe parts of Venus which lie between the poles and tropics, and between the tropics and polar circles, and alo between the polar circles and equator, partake more or les of the phenomena of thee circles as they are more or les ditant from them.

From the quick change of the un’s declination it happens, that if he ries due eat on any day, he will not et due wet on that day, as with us; for if the place where he ries due eat be on the equator, he will et on that day almot wet-north-wet, or about 18$1/2$-degrees, north of the wet. But if the place be in 45 degrees north latitude, then on the day that the fun rifes due eat he will et north-wet by wet, or 33 degrees north of the wet, and in 62 degrees north latitude. When he ries in the eat, he ets not in that revolution, but jut touches the horizon 10 degrees to the wet of the north point, and acends again, continuing for 3$1/4$ revolutions above the horizon without etting. Therefore, no place has the forenoon and afternoon of the ame day equally long, unles it be in the equator, or at the poles.

The fun’s altitude at noon, or at any other time of the day, and his amplitude at rifing and letting, being very different at places on the ame parallel of latitude, according to the different longitudes of thoe places, the longitude will be almot as eaily found on Venus as the latitude is found on the earth; which is an advantage we can never enjoy, becaue the daily change of the un’s declination is by much too mall for that important purpoe.

On this planet, where the un croes the equator in any year, he will have 9 degrees of declination from that place

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