Thus we can tell how much to take away from him who has more or too much, and how much to add to him who has less or too little: to the latter’s portion must be added that by which it falls short of the mean, and from the former’s portion must be taken away that by which it exceeds the mean.

To illustrate this, let AA′, BB′, CC′ be three equal lines:⁠—

From AA′ let AE be cut off; and let D [equal to AE] be added to CC′; then the whole DCC′ exceeds EA′ by CD and CZ [equal to AE or CD], and exceeds BB′ by CD.

And this 107 holds good not only in geometry, but in the arts also; they could not exist unless that which is worked upon received an impression corresponding in kind and quantity and quality to the exertions of the artist.