10
be-tween two prikkes hath him to the altitude of the thing.
COMMENTARY ("FOOTNOTES").
Little Lewis my son, I perceive that thou wouldst learn the Conclusions of the Astrolabe; wherefore I have given thee an instrument constructed for the latitude of Oxford, and purpose to teach thee some of these conclusions. I say some, for three reasons; (1) because some of them are unknown in this land; (2) because some are uncertain; or else (3) are too hard. This treatise, divided into five parts, I write for thee in English, just as Greeks, Arabians, Jews, and Romans were accustomed to write such things in their own tongue. I pray all to excuse my shortcomings; and thou, Lewis, shouldst thank me if I teach thee as much in English as most common treatises can do in Latin. I have done no more than compile from old writers on the subject, and I have translated it into English solely for thine instruction; and with this sword shall I slay envy.
The first part gives a description of the instrument itself.
The second teaches the practical working of it.
The third shall contain tables of latitudes and longitudes of fixed stars, declinations of the sun, and the longitudes of certain towns.
The fourth shall shew the motions of the heavenly bodies, and especially of the moon.
The fifth shall teach a great part of the general rules of astronomical theory.
Here begins the first part; i.e. the description of the Astrolabe itself.