Proportion, or, The geometric principle of beauty, analysed (1843)
Hay, D. R. (David Ramsay), 1798-1866 · Edinburgh and London, W. Blackwood and Sons · leaf 38
GEOMETRIC PRINCIPLE OF BEAUTY ANALYSED. 22 these arcs contain 90 degrees, right angles are called angles of 90°, Fig. 15. figure 15. But if the radius touch the circumference at any other point than the centre, two different angles are form- ed; one an acute angle, and the other an obtuse angle,… … this division of the circumference of the circle depends the cha- racter and direction of every straight line, as well as every rec- tilinear figure. This simple account of the mode in which angles are reckoned, will make the following description of geo- metric figures more easily understood to…
Proportion (Art)
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.