6 
INTRODUCTORY 
Greeks called a ‘swallow’, will agree that the latter is 
the more accurate description. Or again, what exactness 
of perception must have been possessed by the architects and 
- workmen to whom we owe the pillars which, seen from below, 
appear perfectly straight, but, when measured, are found to 
bulge out {’¿vrao-is). 
A still more essential fact is that the Greeks were a race of 
thinkers. It was not enough for them to know the fact (the 
on); the} 7 wanted to know the why and wherefore (the Sia tl), 
and they never rested until they were able to give a rational 
explanation, or what appeared to them to be such, of every 
fact or phenomenon. The history of Greek astronomy fur 
nishes a good example of this, as well as of the fact that no 
visible phenomenon escaped their observation. We read in 
Cleomedes 1 that there were stories of extraordinary lunar 
eclipses having been observed which ‘ the more ancient of the 
mathematicians ’ had vainly tried to explain; the supposed 
‘ paradoxical ’ case was that in which, while the sun appears 
to be still above the western horizon, the eclipsed moon is 
seen to rise in the east. The phenomenon was seemingly 
inconsistent with the recognized explanation of lunar eclipses 
as caused by the entrance of the moon into the earth’s 
shadow ; how could this be if both bodies were above the 
horizon at the same time? The ‘more ancient’ mathemati 
cians tried to- argue that it was possible that a spectator 
standing on an eminence of the spherical earth might see 
along the generators of a cone, i.e. a little downwards on all 
sides instead of merely in the plane of the horizon, and so 
might see both the sun and the moon although the latter was 
in the earth’s shadoV. Cleomedes denies this, and prefers to 
regard the whole story of such cases as a fiction designed 
merely for the purpose of plaguing astronomers and philoso 
phers ; but it is evident that the cases had actually been 
observed, and that astronomers did not cease to work at the 
problem until they had found the real explanation, namely 
that the phenomenon is due to atmospheric refraction, which 
makes the sun visible to us though it is actually beneath the 
horizon. Cleomedes himself gives this explanation, observing 
that such cases of atmospheric refraction were especially 
1 Cleomedes, De motn circulari, ii. 6, pp. 218 sq.