If the question is asked why a unit distance measurement is not applied to differentiate these varieties, the answer is that the spacing of the letters of the inscription is nearly alike. Of course the slant of the letters differs. Such differences as are helpful and noticeable will be mentioned. The system of line prolongation, for example, the downward prolongation of the "T" of "THREE", discloses certain groups in the writer's opinion, but the differences obtained thereby are not of sufficient practical value for establishing groups. For a quick and reliable identification of these varieties an intimate knowledge of the heads is required. It having been decided to reproduce the heads, the question arose: Shall we draw every feature and every detail, or is it preferable to indicate merely such portions of the face as are different in the various dies? Evidently, many minor points could be omitted without in any way detracting from the usefulness of the drawings. Indeed, the adoption of this plan permitted the artist to emphasize and to bring out more strikingly such features as constitute the real differences. There are three prominent features in each of the ten heads. The first is the side-lock, which may be either single or double, straight or hooked, short or long. Second in importance is the distance between the end of the side-lock and the ear-lobe. Even a casual observation shows that the distance between the ear-lobe and the end of the side-lock varies greatly; very wide, near and close. The third feature is the lowest front-lock, which, by the taste or art of the die cutters has been, like man, "wonderfully and fearfully made", short or long, thin or full, single or double. In good specimens the eyebrow constitutes a valuable adjunct, and in all dies where this feature plays a prominent part it will be noted. Finally the attention of the collector is directed to the fact that only Head 1 shows Washington with circularly cropped hair, or, as the barber would express it, a "Dutch clip". This head was used for varieties 1, 2 and 3, the first being a rather scarce article. If the student fixes his attention on the above three main features, and does not attempt to get the entire ten heads fixed in his mind at a glance, it will be found that the task of differentiation is not at all a burden even to the youngest collector of cut square specimens. A certain amount of patience is, however, required; likewise a certain amount of willingness to be taught, but the collector possessing these two virtues--and it is one of the crowning glories of stamp collectors to be both studious and patient--will soon have the various Nesbitt heads of Washington engraved upon his memory. Taking the distance between the end of the side-lock and the ear-lobe as our main feature, the various heads may be grouped into three distinct classes: CLASS I. Distance between side-lock and ear-lobe very wide. Heads 1a, 3, 4, 6, 7.