well look upon them en bloc, inasmuch as one attribute of the asteroids concerns them generically rather than specifically, and is of great interest both from a mechanical

and an historical point of view. For, in fact, it is what led to their discovery. Titius of Wittenburg, about the middle of the eighteenth century, noticed a curious relation between the distances from the Sun of the then known planets. It consisted in a sort of regular progression, but with one significant gap. Bode was so struck by the gap that he peopled it with a supposed