190 Astronomical and Nautical Collections. 
of the refraction for this corrected altitude: thus, adding, in 
the first example 3,54 to the mean altitude 1° 31’, the re- 
fraction ought to become less by about 34, x 5”,9 x 3.54 
== ",35, and the true correction for — 1° F. is therefore 3’,89. 
In the same manner we find, for 2”,81, 3”,01; and for 1”,07, 
1”,09. It is impossible for unselected’ examples to agree better 
with a theory than these do with the table in the Nautical 
Almanac, of which the numbers are 3”,88, 2”,85, and 17,10 
respectively ; while the French tables give us 2”,5, 2”,0, and 
0”,98 only. 
iv. Remarks on the Astronomical Measurements of the Ancients. 
There is a passage in Plutarch, as quoted by Eusebius in his 
Evangelical Preparation, which determines the distance of the 
sun from the earth to be about 95 millions of miles, according 
to Sir William Drummond’s computation of the length of the 
stadium, published a few years since in the Classical Journal. 
The circumstance must:be allowed to be very remarkable, and 
‘seems at first sight to indicate an astonishing precision of 
observation, without the possession of any accurate instruments : 
but a little consideration is sufficient to convince us, that to an 
astronomer unprovided with a telescopic micrometer, it was 
utterly impossible to ascertain an angle of any kind even with- 
out a probability of error of half a minute, much more to come 
within one-tenth of a second of the truth in the measurement 
of seven or eight seconds. Indeed the very utmost that could 
be expected from the observation of the moon’s disc at the 
quadratures, would be to make it probable that there was a 
sensible though a very small parallax, but whether of a second 
or a minute could certainly not be conjectured without a teles- 
cope; and the perfect coincidence of Plutarch’s report of the 
determination of Eratosthenes with the true measure must have 
been wholly accidental : a conclusion which is still further 
confirmed by the extreme inaccuracy of the statement of the 
moon’s distance in the same passage, though the moon’s paral- 
lax was pretty well known to Eratosthenes, as well as the 
earth’s ‘dimensions. 
