ASC 



ASC 



with the right ascension itself, and is the 

 same in all parts of the globe. The arch 

 of oblique ascension coincides with the 

 oblique ascension, and changes according 

 to the latitude of the places. 



The sun's right ascension in time is use- 

 ful to the practical astronomer in regular 

 observatories, who adjusts his clock by 

 sideral time. It serves also for convert- 

 ing apparent into sideral time ; as e. g. 

 that of an eclipse of Jupiter's satellites, in 

 order to know at what time it may be ex- 

 pected to happen by his clocks. For this 

 purpose the sun's right ascension at the 

 preceding noon, together with the in- 

 crease of right ascensionfrom noon, must 

 be added to the apparent time of the 

 phenomenon set down in the ephemeris. 

 The sun's right ascension in time serves 

 also for computing the apparent time of 

 a known star's passing the meridian : thus, 

 subtract the sun's right ascension in time 

 at noon from the star's right ascension in 

 time, the remainder is the apparent time 

 of the star's passing the meridian nearly; 

 from which the proportional part of the 

 daily increase of the sun's right ascen- 

 sion from this apparent time from noon 

 being subtracted, leaves the correct time 

 of the star's passing the meridian. The 

 sun's right ascension in time is also useful 

 for computing the time of the moon and 

 planets passing the meridian. The prac- 

 tical method of finding the right ascen- 

 sion of a body from that of a fixed star, 

 by a clock adjusted to sideral time, is 

 this : let the clock begin its motion from 

 O h 0' 0" at the instant the first point of 

 Aries is on the meridian ; then, when 

 any star comes to the meridian, the clock 

 would shew the apparent right ascension 

 of the star, the right ascension being esti- 

 mated in time at the rate of 15 an hour, 

 provided the clock was subject to no 

 error ; because it would then shew at any 

 time how far the first point of Aries was 

 from the meridian. But as the clock is 

 liable to err, we must be able at any time 

 to ascertain its error, or the difference 

 between the right ascension shewn by 

 the clock, and the right ascension of that 

 point of the equator which is at that time 

 on the meridian. To do this we must, 

 when a star, whose righ ascension is 

 known, passes the meridian, compare its 

 apparent right ascension with the right 

 ascension shewn by the clock, and the 

 difference will shew the error of the 

 clock. E. j-. Let the apparent right 

 ascension of Aldebaran be 4 h 23' 50", at 

 the time when its transit over the meri- 

 dian is observed by the clock ; and sup- 

 pose the time shewn by the clock to be 



VOL. II. 



4 h 23' 52", then there is an error of 2" 

 in the clock, as it gives the right ascen- 

 sion of the star 2" more than it ought, 

 If the clock be compared with several 

 stars, and the mean error taken, we shall 

 have more accurately the error at the 

 mean time of all the observations. These 

 observations being repeated every day, 

 will give the rate of the clock's going, or 

 shew how much it gains or loses. The 

 error of the clock and the rate of its going 

 being thus ascertained, if the time of the 

 transit of any body be observed, and the 

 error of the clock at the time be applied, 

 we shall have the right ascension of the 

 body. This is the method by which the 

 right ascension of the sun, moon, and pla- 

 nets, are regularly found in observatories. 

 To find the right ascensions mechanically 

 by the globe, see GLOBES, the use of. The 

 arch of right ascension is that portion of 

 the equator intercepted between the be- 

 ginning of Aries and the point of the 

 equator which is in the meridian : oritis 

 the number of degrees contained in it. 

 This coincides with the right ascension 

 itself. The right ascension is the same in 

 all parts of the globe. We sometimes 

 also say, the right ascension of a point of 

 the ecliptic, or any other point of the 

 heavens. The right ascension of the 

 mid heaven is often used by astronomers, 

 particularly in calculating eclipses by the 

 nonagesimal degree ; and it denotes the 

 right ascension of that point of the equa- 

 tor which is in the meridian, and is equal 

 to the sum of the sun's right ascension 

 and the horary angle or true time, re- 

 duced to degrees, or to the sum of the 

 mean longitude of the sun and mean time. 



ASCENSIONAL difference, the differ- 

 ence between the right and oblique ascen- 

 sion in any point of the heavens ; oritis 

 the space of time that the sun rises or 

 sets before or after six o'clock. 



The ascensional difference may be 

 found by this proportion, viz. As the ra- 

 dius is to the latitude of the place, so is 

 the tangent of the sun's declination to the 

 sine of the ascensional difference ; by 

 subtracting of which from the right as- 

 cension, when the sun is in the northern 

 signs, and adding it, when the sun is in 

 the southern ones, you will find the ob- 

 lique ascension. 



ASCENT offuids, is particularly un- 

 derstood of their rising above their own 

 level, between the surfaces of nearly con- 

 tiguous bodies, or in slender capillary 

 glass tubes, or in vessels filled with sand, 

 ashes, or the like porous substances. 

 This effect happens as well in vacuo as in 

 the open air, and in Crooked as well as 



F 



