Last two propositions before parallel lines! – an exciting transition in Book One. Proposition 25 describes another relationship between sides of triangles and the angles contained by those sides: in this case, a larger base indicates a larger subtending angle.
The collage elements in this piece (and the next one) relate to navigation. Congruent and similar triangles as well as correlating a larger side to a larger subtending angle has determined unknown distances for many centuries. The image I’ve overlaid on the collage here is a piece of a vintage navigation diagram, slightly adjusted so one triangle has a larger base than the other.