Mr. W. S. Jevons on the Cirrous form of Cloud. 38 
another; and as the two portions of air would mix more at one 
part of each undulation than any other, long waves of cloud 
would be the result. Ripple would, I think, be a convenient 
term for this appearance in descriptions of clouds. . 
The only other fundamental form of cloud besides the cirrus 
and the stratus is the cumulus, the nature of which is too well 
known to need any remarks here. The fundamental cloud- 
actions of the atmosphere may then be laid down as follows :— 
Ist. Cumulus, produced by the elevation and rarefaction of 
large masses of air. 
2nd. Stratus, produced by the mechanical mixture of different 
portions of moist air at their common surface. 
8rd. Cirrus, produced by the interfiltration of different por- 
tions of moist air. 
Howard felt and marked the fundamental differences of these 
by giving them these distinct and admirably chosen names. 
They were not laid down as fundamental in obedience to any 
theory or deduced system of classification whatever, but because 
their appearance and conditions of occurrence in the atmosphere 
are so entirely distinct as at once to point to essential differences 
of nature, whatever these may be. Howard, indeed, had very 
little conception of how these clouds were formed; and carried 
away, perhaps, by the success of his first attempt at classification, 
he completed his nomenclature by applying to a number of other 
subordinate species of cloud, systematic terms obtained by the 
combination of these three principles, viz. cumulostratus, cirro- 
cumulus, cirrostratus, and cumulo-cirrostratus or nimbus. 
Now these compound terms will not be at all philosophical or 
advantageous unless the species of cloud they represent are actu- 
ally formed by the amalgamation of the cloud-actions denoted by 
the component parts of the term. In adopting a theory of these 
actions, we should therefore have to re-examine and perhaps 
remodel these terms with a view to render them true and con- 
sistent. 
Now it seems to me that the cirrous and stratous actions are 
those only which can be truly amalgamated, and take place in 
the same portion of air; and that if the other actions do ever 
unite, the result will not be the clouds universally denoted by 
the terms used. Cirrostratus is, indeed, a true intermediate 
species of cloud, and the only commonly occurring species of the 
kind. Not only in the second experiment did we produce a di- 
stinct streaked sheet of cloud, which is the exact appearance of 
cirrostratus, but it is evident, that, supposing the above theory 
of cirrus to be correct, the cirrous mixture of two portions of air 
in motion upon each other will seldom go on without a certain 
amount of mechanical mixture taking place at the same time 
Phil. Mag. 8. 4. Vol. 14, No. 90, July 1857. D 
