CLOUDS. 437 



When this lias considerably increased we see the lower clouds spread 

 themselves till they liuite in all x)oints and form one uniform sheet. It 

 will rain during this state of the two strata of clouds, one passing be- 

 neath the other and each continually tending to horizontal, uniform dif- 

 fusion, (the superior stratum is often seen in this case to i)artake of cirrus,) 

 although they should he separated by an interval of many hundred feet 

 in elevation. The intermediate space on these occasions is not sni)posed 

 to be at any time free from a conducting medium of different watery 

 particles, enabling the opposite electricities to neutralize each other." 

 Hence we see that this description of Howard's nimbus has no connec- 

 tion with that given by Kilmtz and the late writers, of a cloud inter- 

 mediate in form, which, according to the latter, is supposed to have the* 

 property of producing rain. It is not the property of any cloud to \)X0- 

 duce rain, but it is produced by the reunion by the electric action and 

 reaction upon the aqueous vapor of two superposed strata of clouds, the 

 superior being cirrus and the inferior cumulus. It is this latter cir- 

 cumstance that Howard has neglected to properly establish. All the 

 plates which have been published, not excepting that of Howard, give 

 no idea of this double stratum which constitutes the rain-cloud, that 

 is, the nimbus of Howard, or properly my pallium, (imMo -cirrus and 

 pallio-cumulus.) I now proceed to point out the error equally inherent 

 in the three orders of clouds denominated cumidus, cumulo-straius, 

 and strato-cumulus, and to show that they can all be reduced to 

 the second type of cumulus. I remark, in th'e first place, a great 

 confusion, or it may be a great similitude, between the cumulus 

 and the ctimulo-stratus ; afterward I observe in the sky other cumuli, 

 whose characters partake of more than these two types ; for example, 

 M. Kiimtz's definitions, which are generally accepted. M. Kiimtz says : 

 "The cumulus is often seen in the form of a hemisphere, reposing upon a 

 horizontal base. Sometimes these hemispheres are piled one upon the 

 other, forming those great clouds accumulated at the horizon, which 

 resemble at a distance mountains of snow." 



Now for the cumulo-stratus : "When the cumulus is x>iled up and 

 becomes more dense, it passes to the state of cumulo-stratus, which often 

 takes at the horizon a black or bluish tint and passes to the state of 

 nimbus or rain-cloud." Thus, it is sufiicient that the cumulus be piled 

 up and become more dense in order to be changed into cumulo-stratus, 

 strikingly implying great development in the horizontal base, which is 

 not mentioned, though it is one of the most essential characters of this 

 type of clouds. While, on the other hand, this horizontal base is 

 expressly pointed out in Kamtz's definition of cumulus. In a word, 

 these fundamental points are found equally in the formation of cumulus 

 and cumulo-stratus : 1st, a horizontal base ; 2d, a superior hemispherical 

 dome; 3d, a formation by increase from below upward. The points of 

 diflerence as to the cumulo-stratus rest upon the irregularity of the 

 base of the convex summits, and the aggregation from below upward ; 



