Elements of geometry : containing the first six books of Euclid, with a supplement on the quadrature of the circle, and the geometry of solids : to which are added, Elements of plane and spherical geometry (1826)
Playfair, John, 1748-1819, Euclid · Philadelphia : Marot & Walter · leaf 290
.pendiculars drawn from the one of these lines to the other are equal.(Encychpedie Art. Par allele.) Another definition that has been given of parallels is, that they arelines which make equal angles with a third line, toward the sameparts, or such as make the exterior angle equal to the interior… … parallel, are such as make equal angels with z certain third line, butnot with any line that falls upon them. It remains, therefore, tobe demonstrated, That if AB and CD make equal angles withGH, they will do so also with any other line whatsoever. Thedefinition, therefore, must be thus understood,…
Euclid's Elements · Geometry · Trigonometry
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