[AD COGNOSCENDUM SPECIALITER LATITUDINEM NOSTRI REGIONIS, SCILICET LATITUDINEM OXONIE, ET ALTITUDINEM POLI NOSTRI.] Understond wel, that as fer is the heved of Aries or Libra in the equinoxial from oure orisonte as is the senith from the pole artik; and as hey is the pol artik fro the orisonte, as the equinoxial is fer fro the senith. I prove it thus by the latitude of Oxenford. Understond wel, that the heyghte of oure pool artik fro oure north 5 orisonte is 51 degrees and 50 minutes; than is the senith from oure pool artik 38 degrees and 10 minutes; than is the equinoxial from oure senith 51 degrees and 50 minutes; than is oure south orisonte from oure equinoxial 38 degrees and 10 minutes. Understond wel this rekning. Also for-get nat that the senith is 90 10 degrees of heyghte fro the orisonte, and oure equinoxial is 90 degrees from oure pool artik. Also this shorte rewle is soth, that the latitude of any place in a regioun is the distance fro the senith unto the equinoxial. And for more declaracioun, lo here thy figure. 15 23. TO PROVE EVIDENTLY THE LATITUDE OF ANY PLACE IN A REGIOUN, BY THE PREVE OF THE HEYGHTE OF THE POL ARTIK IN THAT SAME PLACE. [AD PROBANDUM EVIDENTER LATITUDINEM ALICUIUS LOCI IN ALIQUA REGIONE, PER PROBACIONEM ALTITUDINIS DE POLO ARTICO IN EODEM LOCO.] In some winters night, whan the firmament is clere and thikke-sterred, waite a tyme til that any sterre fix sit lyne-right perpendiculer over the pol artik, and clepe that sterre A. And wayte a-nother sterre that sit lyne-right under A, and under the pol, and clepe that sterre F. And understond wel, that F is nat 5 considered but only to declare that A sit evene overe the pool. Tak thanne a-non right the altitude of A from the orisonte, and forget it nat. Lat A and F go farwel til agayns the dawening a gret whyle; and come thanne agayn, and abyd til that A is evene under the pol and under F; for sothly, than wol F sitte over the pool, 10 and A wol sitte under the pool. Tak than eft-sones the altitude of A from the orisonte, and note as wel his secounde altitude as his firste altitude; and whan that this is don, rikne how manye degrees that the firste altitude of A excedeth his seconde altitude, and tak half thilke porcioun that is exceded, and adde it to his seconde 15 altitude; and tak ther the elevacioun of thy pool, and eke the latitude of thy regioun. For thise two ben of a nombre; this is to seyn, as many degrees as thy pool is elevat, so michel is the latitude of the regioun. Ensample as thus: par aventure, the altitude of A in the evening is 56 degrees of heyghte. Than 20 wol his seconde altitude or the dawing be 48; that is 8 lasse than 56, that was his firste altitude at even. Take thanne the half of