“Secunda varias trianguli affectiones exhibet.”
Liber hic fere Lemmaticus est, quemadmodum & alter, qui de Circulorum variis proprietatibus tractat. Porrò quo magis materia Lectori admanum sint, omnem in tres partes dividere placuit.
Prima quidem maximè circa linearum proportionem versatur.
Tertia illas linearum contemplatur proprietates, quae earum potentias concernunt.
This book is generally concerned with a lemma [i. e. the harmonic ratio, whereby a line segment is divided internally and externally in the same ratio], as with the following one which draws out various properties of circles. Again, so that more material should be at hand to the reader, it was determined to set everything out in three parts.
The first part is mainly concerned with the proportions of lines.
The second shows the various uses of triangles.
The third considers these properties of lines which are concerned with powers.
Qvadratvrae circuli http://www.17centurymaths.com/contents/gregoriuscontents.html (1647) Books I & II, translated and annotated by Ian Bruce, quoted from Book I, Part I : Proportions between line segments http://www.17centurymaths.com/contents/gregorius/book1a%20pp1-20.pdf.
