is of better quality more or less, and stronger to endure in one effect more than in another, being subject to the nutriment of the heat, which is our life, it happens that the arch of the life of one man is of less or of greater extent than that of another, life being shortened by a violent death or by some accidental injury; but that which is called natural by the people is that span of which it is said by the Psalmist, “Thou settest up a boundary which it is not possible to pass.”  And since the Master among those here living, Aristotle, had perception of this arch of which we now speak, and seems to be of opinion that our life should be no other than one ascent and one descent, therefore he says, in that chapter where he treats of Youth and of Old Age, that Youth is no other than an increase of life.  Where the top of this arch may be, it is difficult to know, on account of the inequality which has been spoken of above, but for the most part I believe between the thirtieth and the fortieth year, and I believe that in the perfectly natural man it is at the thirty-fifth year.  And this reason has weight with me:  that our Saviour Jesus Christ was a perfect natural man, who chose to die in the thirty-fourth year of His age; for it was not suitable for the Deity to have place in the descending segment; neither is it to be believed that He would not wish to dwell in this life of ours even to the summit of it, since He had been in the lower part even from childhood.  And the hour of the day of His death makes this evident, for He willed that to conform with His life; wherefore Luke says that it was about the sixth hour when He died, that is to say, the height or supreme point of the day; wherefore it is possible to comprehend by that, as it were, that at the thirty-fifth year of Christ was the height or supreme point of His age.  Truly this arch is not half distinguished in the Scriptures, but if we follow the four connecting links of the differing qualities which are in our composition, to each one of which appears to be appropriated one part of our age, it is divided into four parts, and they are called the four ages.  The first is Adolescence, which is appropriated to the hot and moist; the second is Youth, which is appropriated to the hot and dry; the third is Old Age, which is appropriated to the cold and dry; the fourth is Extreme Old Age, which is appropriated to the cold and moist, as Albertus Magnus writes in the fourth chapter of the Metaura.  And these parts or divisions are made in a similar manner in the year—­in Spring, in Summer, in Autumn, and in Winter.  And it is the same in the day even to the third hour, and then even to the ninth, leaving the sixth in the middle of this part, or division, for the reason which is understood, and then even to vespers, and from vespers onwards.  And therefore the Gentiles said that the chariot of the Sun had four horses; they called the first Eoo, the second Piroi, the third Eton, the fourth Phlegon, even as Ovid writes in the second book of the Metamorphoses concerning the parts or divisions of the day.