234 GEOGRAPHY AND ASTRONOMY. The longitude of a place has been therefore usually found out and determined by measuring the distance travelled on the earth or sea, from the west toward the east, supposing you know the longitudeof the place wlìence you set out. SECT. VI.-OfRight Ascension, Declination, and hour Circles. HAVING considered what respect the parts of th earth hear to these artificial lines on the globe, we come, secondly, to survey the several relations that the parts of the heavens, the sun or the stars, bear to these several imaginary points andartificial lines or circles. The right ascension of the sun or any star is its distance from that meridián which passes through the point aries, counted toward the east, and measured on the equator ; it is the same thing with longitude on the earthly globe. The hour of the sun or any star is reckoned also by the di- visions of the equator ; but the hour differs from the right ascen- sion chiefly in this, (viz.) The right ascension is reckoned from that meridian which passes through arises ; the hour is reckoned on the earthly globe, from that meridian whichpasses through the town or city required ; or it is reckoned on the heavenly globe from that meridian which passes through the sun's place in the ecliptic,. and which, when it is brought to the brazen meridian, represents noon that day; There is also this difference. The right ascension is often computed by single degrees all round the equator, and proceeds to360: The hour is counted by every 15 degrees from the me- ridianof noon, or of midnight, and proceeds in number to12, and then begins again : Though sometimes the right ascension is computed by hours also instead of degrees, but proceeds to 24. So the sun's right ascension the 10th of May is 59 degrees, or as sometimes it is called 3 hours and 56 minutes. The same lines which are called lines-of longitudeor meri- dians on the earth are called hour circles on the heavenly globe, if they be drawn through the poles of the world at every 15 de- grees on the equator, for then they will divide the 360 partsor degrees into 24 hours. Note,. As 15 degrees make one hour so 15 minutes of a de- gree make one minute in tine, and one wholedegree makes four minutes in time. Note, degrees are marked sometimes with (d) or with a small circle (°), minutes of degrees with a dash O mconds of minutes with adouble dash (`.'), hours with (h), minut ofhours sometimes with (°'.) and sometimes a dash, seconds with a dou- ble dash. By these meridians or hour-lines crossing the equator on the heavenly globe,the eye is directed to the true hour, or the degree
RkJQdWJsaXNoZXIy OTcyMjk=