"To do this : 1st, start with the middle C of the keyboard, and narrow the first four fifths going up, until the fourth, E, makes a very true major third with the first note C; this is called'the proof'. 2nd, Continuing to tune by fifths, as soon as one has arrived at the sharp notes, one then widens the fifths even though the thirds suffer by it and one stops when one has arrived at G # . 3rd, Return to C and tune the fifths going down, that is, F, B flat, and so on, widening them all the time, until one has arrived at D flat, which when taken as C #-ought to be in harmony as a fifth with the G # where one stopped before.
