He took verbatim notes of his teacher's lectures, which he subsequently published under the title of The Dissertations (L ta-**rpc**,6ai), in eight books, of which the first four are extant and constitute the chief authority for Stoic ethics, and The Encheiridion (i.e.

129) be the axis of a pivot, and let **RPC** be a portion of a curve such that at any point P the secant of the obliquity to the normal of the curve of a line parallel to the axis is inversely proportional to the ordinate PY, to which the velocity of P is proportional.