A S C 



A S C 



AR (ri:rlu afcenfion) nearer III and IX figns than! 

 oaiid \l l%ns, i'uK AR+tanp;. B ( _ 



AR noaiL-r o and VI figiis than III and IX figns, 1 

 tang. A R +cof. A R + tang. B > 



tang, declination of fumo thle as B, true to the ncared fe- 

 cund by Taylor's logarithms, to ncarell lo" by Gardiner's 

 logarit-hm-:, or to iicarcll minute by Sherwin's or Mutton's 

 logarithms, without proportioning. 

 Example. 



Let the moon'slong.be 7' i4"26'2i",andlat. 4°©' 3.i."N. 

 and the obliquity of the ecliptic 23° 27' 4S". Required 

 the right afcenfion and declination ? 

 Lat. D 4° o' 34" tang. 8.3456713. 



Long. 2 24 26 21 fine 9.8451920 — tang. — 9.9914974 

 A= 5 43 o. 7 tang. 9.:oo4793 ar. co.cof. 0.0021654 



O = 23 2748. S 



B — 17 4447. 3 S.— cof. — 9.978 S260 tang:'^.505 1 970 

 RA- 223 21 II. 2 — tang. — 9.97248S8 fine 9. 3852940 

 Decl. 12 21 14. 6 S. tangent. - - 9.3464910 



K.r>. The ritrht afcenfion and declination may be found 

 by the following formuhe : 



Co-v. f. Decl. = V. f. long, a es X f . co. lat. X f. ob. 

 eel. + V. f.co. lat. w f. ob. eel. 



Cof. Right afcenfion from fy or =^ = 



fccant decl. X cof. lat. X cof. long, from '■f or ^. 

 Mackay's Theory and Praclicc of finding the Longitude &c. 

 vol. i. p. 42. 



For other methods of determining the right afcen- 

 fion of a fixed liar by Mr. riamllcad, and Dr. Ma(!<elyne, 

 illufhated by examples, fee Vincc's Ailronomy, vol. i 

 p. 31, &c. 



The praftical method of finding the right afcenfion of a 

 body from that of a fixed ftar, by a clock adjulled to fiderenl 

 time, \i this : — I>et the clock begin its motion from o'' o' c" 

 at the inllant the firil point of aries is on the meridian ; 

 then, when any ftar comes to the meridian, the clytk would 

 ftiew the apparent right afcenfion of the ftar, the right 

 afcenfion being cftimated in time at the rate of 15" an h.our, 

 provided the clock was fubjecl to no error, bccaufe it would 

 then (hew at any lime how far the firft point of aries was 

 from the meridian. But as the clock is \uh\e to err, we 

 muft be able at any time to afcertain its error, or the dif- 

 ference between the right afcenfion (hewn by the clock and 

 the right afcenfion of that point of the equator which is at 

 that time on the meridian. To do this, we muft, when a 

 ftar, whofe apparent right, afcenfion if known, paffcs the 

 meridian, compare its apparent right afcenfion with the right 

 afcenfion fliewn by the clock, and the difference will fliew 

 the error of. the clock. E.g. let the apparent right afcenfion 

 of Aldcbaran be .\.^ 23' 50" at the time when its tranfit over 

 the meridian is obferved by the clock ; and fuppofe the time 

 {hewn by the clock to be 4'' 23' 52", then there is an error 

 of 2" in the clock, as it gives the right afcenfion of the ftar 

 2" more than it ought. If the clock be compared with 

 feveral ftars, and the mean error taken, we ftiall have more 

 accurately the ei ror at the mean time of all the oblei-vation<. 

 Thefc obfervations, being repeated every day, will give the 

 rate of the clock's going, or (hew how much it gains or 

 lofes. The error of the clock, and the rate of its going, 

 beino- thus afcertained, if the lime of the tranfit of any body 

 be obferved, and tl-.e error of the clock at the time be ap- 

 plied, we (liall have the right afcenfion of the body. This 

 is the mctliod by which the right afcenfion of the fun, moon, 

 and planets arc regularly found in obfcrvatories. 



To findthe right afccnfions mechanically by the globe, fee 



Gl.OBK. 



Thi: /irr/j of ri^ht tjfcenfwins that portion of the equator 

 intercepted between the beginning ot aries, and the point 

 of the equator which is in the meridian : or, it is the num- 

 ber of degrees contained in it. Tiiis coincides with the 

 riglit afcenfion ilfelf. — The right alcenfioii is the fame in 

 all parts ot the globe. 



We fometimcs alfo fay, the right afcenfion of a point of 

 the ecliptic, or any other point of the heavens. The right 

 afcenfion of the mid-heaven i.-i often ufed by aftronomers, 

 particularly in calculating eclipfes by the nonagcfimal de- 

 gree ; and it denotes the right alcenfiun of that point of 

 the equator which is in the meridian, and is equal to the 

 fum of the lun's right aicenfion and the horary angle or 

 true time reduced to degrees, or to the fum of the mean 

 longitude of the fun and mean time. 



AsctNsioN, an^le of right. See Angle. 



Ascension, rjlitque, is an arch of the equator intcrccpt«l 

 between the firft point of aries, and that point of the equa- 

 tor which rifes together with a ftar, &c. in an oblique 

 fphere. 



The oblique afcenfion is numbered from weft to caft ; and 

 is greater or lefs, according to the difterent obliquity of tlie 

 fphere. 



To find the oblique afcenfion of the fun by the globe, 

 fee Globe. See alio Ascensional Difference, 



The arch of oblique afcciifion, is an arch of the horizon in- 

 tercepted between ihe beginning of aries, and the point of 

 the equator, which rifes with a ftar or planet in an oblique 

 fphere. — This coincides with the oblique afcenfion itfelf. 

 — The oblique afcculions change according to the latitude of 

 the places. 



Ascension and Defcenfon, Refratiion of. See Refrac- 

 tion. 



Ascension, Jfle of, in Geography, one of the African 

 iflands iltuate in the Southern Atlantic ocean. S. lat. 7" 

 56' 30". W. long. 14° 22' 31''. 'I'liis dreary defolate ifland 

 was tuft difcovtred in 1501, by J. de Nova Galego, a Portu- 

 guefe navigator, wlio called it " Una de NotTa Senhora dc 

 Conceirao ;" and it was feen a fccond time by Alfonlo d' 

 Albuquerque, on his voyage to India in 1503, probably on 

 Alcenfion-day when it received its prcfent name. Capt, 

 Cook ftoppcd at this ifiand in 1775 ; and he fays that it is 

 about ten miles in length, from north-weft to foutli-caft, and 

 about five or fix in breadth. Its furface is compofed of bar- 

 ren liilli and vallies, or a collection of rocks and hollows, 

 without a ftirub or plant for feveral miles, and exhibiting by 

 the ftones and adies which abound in it, fufiicient evidence 

 that at fome period or other it was a volcanic production. 

 Mr. Forfter, in his account of tliis ifland, fays, that they 

 could difcern from the fliip, near the centre of it, a broad 

 white mountain of confideiable elevation, on wliicli there 

 was fome verdure, and from this circumftance it obtained the 

 name of the " Green Mountain." When they landed on 

 the beach, through a high furf, they found themfelves amidll 

 rocks, which confilled of minute fliell-fand, chiefly of a fiiowy 

 white, deep and dry, and by the reflection of the fun intole- 

 rable to the eyes. In their progrefs, they afcended through 

 heaps of black cavernous ftone, which perfeftly refembled the 

 common lavas of Vefuvius and Iceland. After a perpendi- 

 cular afccnt of about twelve or fifteen yards, they arrived at 

 an extenfivc level plain, about fix or eight miles in circuit, 

 at the diflerent corners of which they obferved large hills, of 

 a conical thape, and of a reddifh colour, which were perfeClly 

 iiilulatcd. Between thefe hills the plain was covered with a 



great 



