Throughout the disturbed area, considerable variations were observed in the nature of the shock. These changes were due to the mere size of the focus, to its elongated form and, as will be seen, to its discontinuity, and also to the distance of the place of observation from the epicentre. At places near the epicentre, rapid changes in the direction of the shock were observed owing to the large angle subtended by the focus; while, at considerable distances, this angle being small, the changes of direction were imperceptible. A further variation with the distance was an increase in the period of the vibrations. Close to the epicentre, the general impression was that of crossing the wake of a steamer in a very short rowing-boat, or of riding in a carriage without springs. At distances of a hundred miles or more, the movement is described as being of a pleasant, gentle, undulating character, like that felt during the rocking of a ship at anchor or in a carriage with well-appointed springs. The most remarkable feature of the shock, however, was its division into two distinct parts or series of vibrations, separated by an interval, lasting two or three seconds, of absolute rest and quiet. And this was no mere local phenomenon. With the exception of a narrow band that will be referred to presently, records of the double shock come from nearly all parts of the disturbed area, even from districts so remote as the Isle of Man and the east of Ireland. The two parts differed in intensity, in duration, and in the period of their constituent vibrations. For instance, at Oaklands (near Chard), a shivering motion was first felt, and then, after about three or four seconds, a distinct rocking from side to side. At Exeter, there was a sudden tremor lasting about two seconds, followed, after two or three seconds, by another and more severe shaking lasting four or five seconds. Again, at West Cross (near Swansea), an undulatory movement for about four seconds was followed soon after by a tremulous shock. At Liverpool, the durations of the first part, interval, and second part were respectively estimated at about six, two, and four seconds. As a first result of the observations, then, it appears that in the south-east half of the disturbed area, the second part of the shock was the stronger, of greater duration and consisted of longer-period vibrations (as at _a_, Fig. 61); while, in the north-west half, the same features characterised the first part of the shock (_b_, Fig. 61). A closer examination of the records shows, however, that the boundary between the two portions of the disturbed area was not a straight line, but slightly curved, the concavity facing the south-east. The broken line on the map (Fig. 60), which is hyperbolic in form, represents roughly the position of this curved boundary.[64] [Illustration: FIG. 61.--Nature of shock of Hereford earthquake.]