Defining the Straight Line and the Four Kinds of Angle
The straight line as the shortest path between two points; four angle types a, b, c, d
Leonardo argues over the definition of a straight line, rejecting the idea that it is a line 'receiving three points of equal height' and concluding that the true definition is the shortest extension between two given points. Below, four small figures labelled a, b, c and d illustrate his statement that there are four kinds of angles. The page continues the notebook's Euclidean study of lines and angles.
On this page
The straight line defined as the shortest path
Leonardo rejects the notion that a straight line is one that receives three points of equal height in its extension, calling that wrong. He concludes that a straight line is the shortest extension between two given points, which he calls its true definition.
The four kinds of angle (a, b, c, d)
Four small figures labelled a, b, c and d are drawn in a row. The accompanying note states that there are four kinds of angles.