To prove evidently the latitude of eny place in a regioun
by the preve of the height of the pool artik in that same
place.
In som wynters nyght whan the firmament is cler and thikke
sterred, wayte a tyme til that eny sterre fix sitte lyne-right
perpendiculer over the pool artik, and clepe that sterre A; and
wayte another sterre that sitte lyne-right under A, and under the
pool, and clepe that sterre F. And understond wel that F is not
considrid but oonly to declare that A sitte evene over the pool.
Tak than anoon-right the altitude of A from the orisonte, and
forget it not; let A and F goo fare wel tyl ageynst the dawenyng
a gret while, and com than ageyn, and abid til that A is evene
under the pool, and under F; for sothly than wol F sitte over the
pool, and A wol sitte under the pool. Tak than eftsonys the
altitude of A from the orisonte, and note as wel his secunde
altitude as hys firste altitude. And whan that this is doon,
rekene how many degrees that the firste altitude of A excedith
his secunde altitude, and tak half thilke porcioun that is
excedid and adde it to his secunde altitude, and tak there the
elevacioun of thy pool, and eke the latitude of thy regioun; for
these two ben of oo nombre, this is to seyn, as many degres as
thy pool is elevat, so muche is the latitude of the regioun.
Ensample as thus: Peraventure the altitude of A in the
evenyng is 56 degrees of height; than wol his secunde altitude or the
dawenyng be 48 degres, that is 8 degrees lasse than 56, that was
his first altitude att even. Tak than the half of 8 and adde it
to 48 that was his secunde altitude, and than hast thou 52. Now
hast thou the height of thy pool and the latitude of the regioun.
But understond wel that to prove this conclusioun and many
another faire conclusioun, thou must have a plomet hongyng on a
lyne, heygher than thin heved, on a perche; and thilke lyne must
hange evene perpendiculer bytwixe the pool and thin eye; and than
shalt thou seen yf A sitte evene over the pool, and over F atte
evene; and also yf F sitte evene over the pool and over A or
