Umbra Versa.-->
Another maner of the werkinge, by umbra versa-->. Yif so
be that thou may nat come to the bas of the tour, I see him thorw
at the nombre of 1; I sette ther a prikke at my fot; than go I
neer to the tour, and I see him thorw at the poynt of 2, and
there I sette another prikke; and I beholde how 1 hath him to 12,
and ther finde I that it hath him twelfe sythes; than beholde I
how 2 hath him to 12, and thou shalt finde it sexe sythes; than
thou shalt finde that 12 passith 6 by the numbre of 6; right so
is the space between thy two prikkes the space of 6 tymes thyn
altitude. And note, that at the ferste altitude of 1, thou
settest a prikke; and afterward, whan thou seest him at 2, ther
thou settest another prikke; than thou findest betwyx thes two
prikkys 60 foot; than thou shalt finde that 10 is the 6-party of
60. And then is 10 feet the altitude of the tour. For other
poyntis, yif it fille in umbra versa-->, as thus: I sette
caas it fill upon 2, and at the secunde upon 3; than schalt thou
finde that 2 is 6 partyes of 12; and 3 is 4 partyes of 12; than
passeth 6 4, by nombre of 2; so is the space between two prikkes
twyes the heyghte of the tour. And yif the differens were thryes,
than shulde it be three tymes; and thus mayst
thou werke fro 1 to 12; and yif it be 4, 4 tymes; or 5, 5 tymes;
et sic de ceteris-->.
