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references to those passages in the writings of the ancients which appear to bear upon the subject.
I shall not pretend, however, to give exactly M. Howard's observations, but only an abstract of the principal facts, as far as they immediately relate to the origin and appearances of the clouds; for further particulars, I refer the reader to the original paper printed in the Philosophical Magazine.
Of the artificial Distinction of Clouds.
CLOUDS are distinguished by seven modifications, the peculiarities of which seem to be caused by the agency of electricity: for example, three primary modifications, the CIRRUS, the CUMULUS, and the STRATUs; two, which may be considered as intermediate in their nature, the CIRROCUMULUS and CIRROSTRATUS; one, which appears to be a compound, the CUMULOSTRATUS; and, lastly, the CUMULOCIRROSTRATUS, or NIMBUS, a state which immediately precedes and attends the resolution of clouds into water, and is therefore called the RAINCLOUD.
Of the Cirrus or Curlcloud. Pl. I. Fig. 1.
CIRRVS. Def. NVBES CIRRATA TENVISSIMA QVAE
THE cirrus is a cloud which appears to have the least density, and generally the most elevation, and which has the greatest variety of extent and direction. It may truly be called the Proteus of the skies; for, in some kinds of weather, its figure is so rapidly and so continually changed, that after turning the eye away from it for a few minutes, it will frequently be found so completely altered, as scarcely to be identified as the same cloud. This, however, is not always the case; it is sometimes visible for many hours and even days together, without much changing its appearance. I shall briefly mention some of its most common varieties, together with the circumstances under which they generally ap
After a continuance of clear weather, the cirrus is frequently the first cloud which is seen. In this case it often looks like a fine whitish thread pencilled, as M. Howard expresses it,
on the clear blue sky: to this other, faint lines of the same kind are added laterally; they increase in size and length, and often serve as stems from which numerous branches proceed and become other cirri of the same kind. These linear cirri will generally be found to be very high in the air, the lines frequently extend quite across the welkin, while their ends, being lost in either horizon, appear, from a well known optical deception, to converge into one point. They do not always extend in parallel lines; they frequently diverge, or increase obliquely downwards. Sometimes transverse lines are formed, which intersecting the others at right angles, give to the sky the appearance of being covered with a beautiful network. Of late, by way of distinction, I have used certain specific names for the various forms of each modification. I have called this netlike feature the reticular cirrus. Those which are local and detached, and which ramify in many directions, giving the idea of a distended lock of hair, may be denominated comoid cirri. Sometimes numerous little filaments appear like bundles of thread, which I have called filiform cirri. In fair, dry weather, with light gales, obliquely descending bands of fibrous texture are often seen, and fre
quently move slowly along from the leeward in a supervening current. I by no means intend, by the above account, to infer that the appearances of the different kinds of cirri, or indeed of any cloud, are ever quite uniform; on the contrary, scarcely two occur exactly alike; and there are many features so various and so mixed, that a particular description of each can scarcely be attempted. In some kinds of weather, the numberless and everchanging figures which this cloud is continually presenting to the eye, baffle all attempt at description. Practical observation affords the only means of becoming acquainted with them.
The observations of M. Howard, as well as those which I have made since the perusal of his meteorological papers, have induced me to believe, that, under whatever form the curlcloud may appear, it must always be regarded as a conductor of the electric fluid. Its very texture seems indicative of its particular office. The long parallel and elevated lines are probably equalizing the electricity of masses of air very remote from each other. The detached comoid cirri equalizing their own electricity with that of the surrounding air, while oblique or depending tufts appear to be conducting from an upper to
a lower stratum. The cirrus, too, is sometimes interposed and conducting between two other clouds at some distance from each other. All the phenomena which I have witnessed, since my attention was directed to nepheology, are reconcileable with this supposition: and it is probable that a cirrus ceasing to conduct, ceases to be a cirrus, and that it either evaporates, or passes to some of the other modifications: in doing which, it may often be seen in an intermediate state, partaking more or less of the modification into which it may be changing, and exhibiting, in the progress of its metamorphosis, very various and very beautiful appearances.
I have elsewhere had occasion to notice the long continued appearance, and the multiform and everchanging configurations of this and the other modifications, unattended by rain, and accompanied by dry, variable, and generally easterly winds, the abundance of nocturnal meteors, and the intermitted actions of De Luc's aërial electroscope, as indicative of a very peculiar state of the electric atmosphere; and, I believe, not a very healthy one.