ASTRONOMY. 343 



motion of the sun r and the other of the solar anomaly. The fourth 

 book of the ' Almagest ' is employed in treating of the motion of the 

 moon, being prefaced by a few remarks respecting the observations 

 which are most useful for that purpose : he then gives an abstract of 

 all the lunar motions, with a table of them ; in the first of which the 

 motion is exhibited for periods of eighteen years : in the second for 

 years and hours ; and in the third for Egyptian months and days. 

 Four other columns of the same table present the number of degrees 

 which belong to each of the times indicated in the first column ; viz. 

 the second, the longitude ; the third, the anomaly ; the fourth, the 

 ktitude ; and the fifth, the elongation. 



The author next treats of various subjects connected with the Lunar 

 lunar motion ; as, for instance, its general anomaly ; its eccentricity ; motlon - 

 the lunar parallax ; the construction of instruments for observing the 

 parallax ; the distance of the moon from the earth, which he states at 

 38'4i terrestrial radii, when in the quadratures ; the apparent 

 diameters of the sun and moon ; the distance of the sun from the 

 earth, which is stated at 1210 radii of the latter; and the relative 

 magnitudes of the sun, moon, and earth. The diameters of these are 

 stated to be to each other, as the numbers 18 '8, 1, and 3| ; also 

 their masses as 6644J, 1, and 39. 



The next book is entirely occupied with the doctrine of eclipses 

 of the sun and the moon ; the determination of their limits and 

 durations ; tables of conjunctions ; and methods of computation and 

 construction, &c. 



We cannot extend the analysis of this important work to a greater Particular 

 length ; but must content ourselves with a few remarks relative to jJfpJUJjUJ 

 some of the deductions to which we have referred. We have seen 

 that Ptolemy made the length of the year to be more than 365 days, 

 5h. 55m., which is about 6 minutes longer than it really is ; but 

 considering that the observations before his time, with the exception 

 of those of Hipparchus, were very imperfect ; and that the distance 

 of time between these two celebrated astronomers, was not sufficient 

 to determine such a question, with the means they possessed, to the 

 greatest nicety, we may rather admire the near approximation to the 

 truth, than be astonished at the difference between his result and 

 that deduced from numerous and long-continued observations. 



His researches on the theory of the sun and moon were, however, -j^ ev ection 

 attended with better success. Hipparchus had shown that these two discovered, 

 bodies moved in orbits, of which the earth was not the centre ; and 

 Ptolemy demonstrated the same truths by new observations. He, 

 moreover, made another important discovery, which belongs exclusively 

 to him, except so far as relates to the observations of Hipparchus, by 

 a comparison of which with his own, his conclusion was deduced, 

 we allude here to the second lunar inequality, at present distinguished 

 by the term evection. It is known, generally, that the velocity of the 

 moon in its orbit, is not always the same, and that it augments or 



