Page:The American Cyclopædia (1879) Volume IV.djvu/724

 712 CLOUDS classification, at least in its adaptation to Amer- ican meteorology. (" Journal of Science," vol. xli., p. 325.) Prof. Andre Poey, late director of the observatory at Havana, published a me- moir in the report of the Smithsonian institu- tion for 1870, in- which he proposes a new classification, which includes only two classes or types in place of the three of Howard, re- jecting the stratus on the ground that it is some other form viewed in perspective, or is no proper cloud, but a mist or hoar frost. The following tables show the comparison of the two classifications : NOMENCLATIVE OF HOWABD. First type Cirrus. nrivaHv J Cirro-stratus. Derivatives -J Clrro. cumulua Second type Cumulus. Derivative Cutnulo-stratus. Third type Stratus. Derived from other types Nimbus. NEW NOMENCLATURE OF POET. First type Cirrus. ( Cirro-stratus. ) _ Derivatives 1 Cirro-cumulus. V *? j Pallio-cirrus. f cloudfl ' Second type Cumulus. Derivatives ! Pallio-cumulus. I Vapor Derivatives -j Fracto-cumulus. f clouds. Prof. Poey's principal reasons for making this classification are stated by himself as follows : "When certain clouds spread out uniformly over the whole face of the heavens and assume a gray or ash color, under which state rain may occur for hours or whole days, what name do we give them ? They are not Howard's nimbus, as we conceive them and as they are generally described; they are neither stormy nor electrical ; they yield only a fine and con- tinuous rain. Under this stratum we see con- stantly other clouds of more or less extent, but always isolated, becoming lost in it and in- creasing its thickness. But just before this stratum begins to break up, and during this operation, we see these same formless fragments detach themselves and fly to other regions. This inferior stratum is not alone ; for when its disruption is completed we see through it another stratum of clouds, whiter and less dense, which breaks up in its turn, and ends by disappearing in an opposite direction to that of the inferior stratum. Have we a name for this variety of cloud, so common in time of rain from the intertropical regions to higher lati- tudes, especially in winter during the fall of snow ? Does Howard's term nimbus and his description -of it answer for its designation ? Certainly not. We apply the name nimbus to the single storm cloud as well as to this in- ferior stratum, or to the united strata, and this without electrical manifestations. To this cloud I give the name of pallium. When the superior stratum is formed" of cirrus, it con- stitutes the pallio-cirrus ; and when the inferior stratum is formed of cumulus, it constitutes the pallio-cumulus. The fragments of clouds which differ entirely from the cumulus or cumulo- stratus are the fracto-cumulus." Whether Prof. Poey's classification is well founded time will decide. The propriety of rejecting the third class or type of Howard, the stratus, is rather questionable in the light of the opinions held by Prof. Loomis, some of which have been quoted, and also when we take into considera- tion the use Prof. Poey himself makes of the word stratum in the explanation of his theory. The name fracto-cumulus appears to be ap- plicable to some forms of cloud not otherwise clearly denominated, such as we often see at sunset; but the placing of the gray vapor cloud, which Prof. Poey calls pallium, in the third division, stratus, by Prof. Loomis, would seem to supply the deficiency in Howard's classification with as near an approach to accuracy as the subject is perhaps capable of admitting. An interesting feature in the phenomena of clouds is their gathering in the equatorial regions in a vast belt, which en- circles the globe, and continues permanent and of nearly uniform breadth. This belt covers the region of equatorial calms, or the "dol- drums," and vibrates with this, as the seasons change, from one side of the equator to the other, its range being from lat. 5 S. to lat. 15 N. It has been observed of various widths, ranging from 60 to several hundred miles. The cloud belt is produced by the vapors gath- ered up and brought in by the N. E. and S. E. trade winds from each side of the equator, and diverted in the belt of calms, where they meet, into the upper regions of the atmosphere. There, continually fed by new supplies from below of heated air saturated with moisture, the cloud spreads in one vast body over seve- ral degrees of latitude, passing even beyond the margin of the calms, seeing that its rains stretch out on each side into the region of the trade winds. Borne upward into the cooler strata of the atmosphere, the heated airs shed their moisture, which falls in frequent torrents of rain. But immense volumes of vapor upon the upper surface of the cloud, exposed in the heat of the day to the direct rays of the sun, are retained in an invisible state, and thus are wafted away to reappear as clouds, and precipitate their waters upon distant portions of the earth. This cloud belt serves another important purpose in protecting the torrid re- gion it overshadows from the scorching heat of the sun ; which, if continued without inter- ruption, would in one season render the equa- torial belt a barren, uninhabitable waste. It is the N. and S. vibration of the cloud ring that causes the fluctuations of the rainy seasons on the parallels of latitude within its range. When it has swung near to its extreme polar limit, the sky about the equator is clear, and the crust of the earth then begins to grow hot. "The dry season continues, the sun is vertical, and finally the earth becomes parched and dry ; the heat accumulates faster than the air can carry it away ; the plants begin to wither and the ani- mals to perish. Then comes the mitigating