a 
17 
of our star through the whole period, half the sum of the 
precessions registered for « Hydrz now, and for the other star 
in the catalogue. Or, if we cannot find one such star we may 
find two stars, the ar and declination, of one of which are larger, 
and those of the other smaller by an equal amount than were 
the supposed AR and declination of « Hydre then. The 
table printed below shows the Ar and declination of a Hydr 
now, and the same at the time sought, also of two other stars. 
mentioned in the Edinburgh Catalogue,* the Ar of one of which 
is less than and that of the other exceeds the ar of a Hydre by 
the same amount. The table also shows the annual precession 
of each of these two stars, and of a Hydre. Half the sum of the 
first and the mean of the two last of these three annual 
precessions will fairly represent the mean annual precession 
of a Hydre during the whole period. 
Right Ascension. Annl. Precession. Declination. Annl.Varn.. 
a Hydre ] 140° 37’ 52" 44°25 (2°95) S.8°12' 44" 15'"5. 
A.D. 1897 f (9° 22" 3155) 
a Hydre \ 107° 50’ 2” 
B.C, 891 f (7° 11™ 0*5) 
e Canis Majoris N.P.D.115°44' 47" 
1109 E.A.0.8S.C, ; (6" 31™ 568) 35''°34 (29356) S.25° 4447" 4"-66. 
29 Monocerotis N.P.D. 92° 29’ 38" 
1248 E.A.O.8.C. f (880™2°) 45'"30 (3°'020) §8.2° 29’ 38" 10” 
Then 35: 34445 30 nd 40°32 + 44:25 
— = 40°32 ;* — 42285 
Also 4°66 + 10: and 7°33 + 15°5 7 
88 
Therefore the mean annual precession of a Hydre during the 
required period, which we shall find was 2,788 years, was. 
42'285. Also the mean annual variation in declination was 
11”-415. Let us multiply this by 2,788. The result is 
31825" =8° 50’ 25". Deducting this from 8° 12’ 44”, the present 
* Edinburgh Astronomical Observations, Vol. XV., published by Order of 
H.M. Government, 1886, 
B 
