32 Mr. W.S. Jevons on the Cirrous form of Cloud. 
effect produced by a rapid upper current into which, at some 
point or points, moist streamlets of warm air were filtering up- 
wards from another current. Watery particles would be preci- 
pitated, and then rapidly swept away in long, flat, and nearly 
horizontal streaks. 
An indirect electrical origin for the cirrus is not incompatible 
with this theory, and we may thus perhaps have a cue to the 
supposed connexion of cirrus and cirrostratus with auroral dis- 
plays. It is not inconceivable that electrical or magnetical eur- 
rents passing among moist and varying currents of air in the 
higher parts of the atmosphere, might occasion some rise of tem- 
perature in particular portions. If this amount only to {5th of 
a degree Fahrenheit, or say only ;35th or ;4,th of a degree, 
this would be quite sufficient to originate a very gradual and 
slow filtering action in these tranquil regions, and produce those 
very rare but exceedingly lofty scrolls of cirrus which are said to 
last sometimes for days together unchanged. 
To follow out these speculations into their full results would 
require volumes; the object of the present paper is fulfilled in 
merely suggesting a filtering action as the explanation of many 
important phenomena of the atmosphere. 
I will add a few remarks concerning the other well-known 
forms of clouds. 
In our second experiment, the meteorologist cannot avoid 
recognizing a striking resemblance between the sheet-like white 
precipitate, only produced when the strata are disturbed and 
mixed by internal causes, and the cloud known as stratus, which 
has a flat or lenticular shape, and invariably a nearly horizontal 
position. Cirrostratus is often, indeed, the more proper name 
for the cloud artificially produced in our experiment, since acci- 
dental cirrous mixture of the strata nearly always takes place 
from imperfect manipulation; but the fibres thus produced 
always quickly settle into the horizontal position, and form a 
streaked sheet which exactly represents the cirrostratus. 
The stratus, it is already well known, is produced by the mix- 
ture of portions of air saturated with moisture but differmg in 
temperature ; and we may now pronounce more precisely from 
the conditions of our experiment, that it is formed when strata, 
moving in contact with each other, are caused to mix at their 
common surface by friction or other similar mechanical causes. 
This is shown, too, by the form which it often assumes of parallel 
transverse bars or waves; for just as a breeze ripples the surface 
of water over which it blows, or as the latter again occasions 
ripple-marks on the sandy bottom over which it moves, one cur- 
rent in the atmosphere may produce a ripple in flowing over 
