Page:The chronology of ancient nations (IA chronologyofanci00biru).djvu/33

I say: Year means one revolution of the sun in the ecliptic, moving in a direction opposite to that of the universal motion, and returning to the same point which has been assumed as the starting-point of his motion, whichsoever point this may be. In this way the sun includes in his course the four seasons, spring, summer, autumn, winter, and their four different natures; and returns always to the point whence he commenced.

According to Ptolemy these revolutions are equal, because he did not find that the apogee of the sun moves; whilst they are unequal according to the authors of Sindhind and the modern astronomers, because their observations led them to think that the apogee of the sun moves. In each case, however, whether they be equal or different, these revolutions include the four seasons and their natures.

As to the length of such a revolution in days and fractions of a day, the results of the astronomical observations do not agree, but differ considerably. According to some observations it is larger; according to others less. However, in a short space of time this difference scarcely becomes perceptible; but in the long run of time, when this difference is being redoubled and multiplied many times, and is then summed up into a whole, a very great error becomes clearly manifest, on account of which the sages have strongly recommended us to continue making observations, and to guard against errors which possibly might have entered into them.

The difference of the observations regarding the length of one annual revolution of the sun does not arise from this cause, that people do not know how properly to institute such observations, and to gain thereby an accurate knowledge of the real state of the thing; but from this cause, that it is impossible to fix the parts of the greatest circle by