OF THE ORIENTATIONS OF A NUMBER OF GREEK TEMPLES. 
807 
on one system are on the great circle which lies in the plane of the orbit, 
called the Ecliptic circle, and the measures taken at right angles to it are called 
latitudes. The coordinate measures round its circumference are called longitudes, 
exactly analogous to the measures of Geography, excepting that the longitudes are 
only reckoned in one direction, viz., from west towards east. The other system of 
measures employs the same imaginary sphere, but the great circle which is used is 
that which lies in the plane of the earth’s Equator, and the measures from it are called 
declinations instead of latitudes, and the coordinate measures are called right ascen¬ 
sions instead of longitudes, which are reckoned as in the other case, only from west 
towards east. Thus the place of a star may be given either in latitude and longitude, 
or in right ascension and declination; and if nothing occurred to disturb the 
mechanical conditions of the orbit, this alternative reckoning would remain constant, 
or altered only by the exceedingly slow proper motion of some of the stars ; and the 
summer and winter solstices and the spring and autumn equinoxes would occur in^ 
each succeeding year at the exact moment when the sun occupied the same longitude 
as on the previous one. This, however, is found not to be the case ; and the first 
recorded statement of the fact is attributed to the Greek astronomer, Hipparchus. 
It must, however, have been practically known to the Egyptians long before his time. 
The explanation was reserved for Newton, who showed that owing to certain gravi¬ 
tational reactions upon our planet, especially on the part of the Moon, the earth’s 
polar axis, whilst remaining nearly constant in its inclination to the plane of the 
ecliptic, is continually deflected in such a manner that the recurrence of the equinoxes 
(of which the exact moment can be more easily observed than that of the solstices) is 
accelerated to the extent of about the twentieth part of a degree annually. This 
movement necessarily disturbs the relation which exists at any particular epoch 
between the latitude and longitude, and the right ascension and declination 
reckonings. During the course of a few' years, indeed, the difference is not great, but 
when years are counted by thousands, the changes in right ascension have to be 
reckoned in hours. And although the latitude is not much affected, the changes in 
declination are generally large, sometimes northerly and sometimes southerly, according 
to the position of the object. It necessarily follows that, together with the declina¬ 
tion, the amplitudes of stars at their rising and setting are altered; and thus it has 
happened that stars once chosen for orientation purposes, after a few hundred years, 
could by no contrivance be retained in view, but as the law of the variation has been 
ascertained, the date can be computed when the amplitude of the star and the 
orientation angle coincided. 
In Greece nothing, so far as we know, has been recorded either in history or by 
inscriptions which offers a parallel to what has been found on this subject in the 
Egyptian hieroglypliics referred to above; but architectural evidence is not wanting 
of a character corresponding with that which has been found in Egypt, showing the 
changes of structure aidsing out of the precessional movement. The Greek examples, 
