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III. On the Orientation of certam Greek Tenijoles and the Dates of their Foundation 
derived from Astronomical Considerations, being a Supplement to ct Paper on the 
same subject published in the Transactions of the Roycd Society in 1893. 
By F. C. Penrose, F.R.S. 
Received Febraaiy 24,—Read March 11,—Revised June 28, 1897. 
The jDaper now presented to tlie Poyal Society is a sequel to one on tlie same 
subject read here on A^Dril 27, 1893, and published in the Transactions for that year. 
In that paper the subject was explained at some length; it will, therefore, be 
unnecessary in this to repeat more than a very few explanatory observations. 
The aim of this inquiry is to deduce the date of the foundation of a Greek (or 
Egyptian) temple from its orientation, but I confine myself entirely to Greek temples, 
in which, however, the same practice was followed which liad previously been reduced 
to a system in Egypt {vide ‘ Dawn of Astronomy,’ by Sir J. N, Lockyer). Almost 
all the temples in Greece and its Colonies had an Easterly frontage, and the principal 
religious function in each temple took place oir the morning of the day when the 
sun, as it rose above the visible horizon, shone through the open Eastern door 
directly upon the sanctuary, where there was usually a statue of the deity in the 
centre. As some time was requisite for the priests to prepare for the ceremony, 
the orientation of the temple was so directed as to combine with the sunrise the 
jDrevious heliacal rising or setting of some conspicuous star which could also be 
observed from the sanctuary. In the absence of clocks the heliacal rising or setting 
of stars was very greatly observed by the ancients—the meaning of the term being 
that the star, when very slightly above the horizon, should just be visible in the 
twilight, before being extinguished l)y the dawn. The angle of the orientation 
depended primarily on the time of year chosen for the principal festival, but it would 
be liable to a slight modification for the sake of combining an heliacal star with the 
sunrise, and it is the latter consideration which ofters the means of determining the 
date of foundation, because the stars, owing to the precession of the equinoxes, are 
affected by a slow, but steady movement, which alters the amplitude, as it is called, 
of their risiim or setting:—viz., the angular distance from the true East or West as 
the case may be, and which is reckoned positive if towards the North, and negative 
if towards the South. 
A journey to Greece and my return by way of Calabria and Sicily during the 
spring of 1896 has enabled me to add the orientations of a considerable number 
G 2 7.9.97 
