The form of cirrus shown in Plate 9 is far more frequently seen than either of those which have been described. In this the fibrous texture is very imperfect, and the cloudlets show a tendency to arrange themselves in a kind of ribbed structure in two directions almost at right angles to each other. But this last is an accidental feature of the particular example, and not in any way a specific character of the cloud. The reason for regarding it as a distinct variety is the total absence of sharply defined lines, not only the heads of condensation, but even the long streamers attached to them being uniformly hazy and ill-defined. It is a form of cirrus which comes at all seasons, but most frequently in summer; it moves always with great slowness, indicating a quiet atmosphere free from disturbance of any kind. The conditions necessary for its appearance are a nearly uniform distribution of pressure over a considerable area, chequered by little shallow depressions of some trifling fraction of an inch. In hot weather these are the conditions under which thunder-storms develop, and this hazy cirrus, or cirrus nebulosus, may be taken as a certain sign of such an atmospheric state. [Illustration: Plate 9. HAZY CIRRUS. (_Cirrus Nebulosus._)] So far as permanency of form is considered, hazy cirrus is one of the most persistent, and affords a marked contrast to the species shown in Plate 10, which represents the most fugitive. Five minutes before the photograph was taken the same part of the sky was a deep, clear blue, without any trace of cloud. Suddenly a few short curling wisps made their appearance. These rapidly increased in number, until a delicate filmy network extended over the greater part of the field of view. But while the camera was being adjusted for an exposure, part of the net had broken up into the granular structure shown in the lower part of the photograph. The granulation rapidly spread through the net, almost as if the fibres had been curdled, and five minutes later the whole had been converted into a patch of cirro-cumulus which soon fused into a uniform sheet. Meanwhile the same series of phenomena were taking place in other parts of the sky. [Illustration: Plate 10. CHANGE CIRRUS. (_Cirrus Inconstans._)] On other occasions exactly the same set of events have been seen to follow each other in the inverse order. Beginning with a fairly even sheet, this broke up into granules, and they in turn seemed to be frayed out into short hazy and wavy fibres which slowly melted away.