30 Mr. W.S. Jevons on the Cirrous form of Cloud. 
lightning proceed, the whole moving in the same direction as the 
cirrus above. Squalls or a decided change of wind and weather 
after the storm show that the latter arises from the conflict of 
two currents, the lower one always moist and sultry. At the 
point of conflict, this lower current, as I suppose, is turned up- 
wards, and then probably swept backwards by the other current 
which is replacing it. The upward motion produces a vast pre- 
cipitation of vapour in the cumulous form, leading to rain and 
electrical excitation ; while at a higher level, the air proceeding 
from the summits of these cumuli still preserves sufficient warmth 
and moistness to cause it to filter upwards into the other por- 
tions of the colder upper current. Would not an advancing 
cirrous crest be exactly the form of cloud produced on this 
theory ? 
Imaginary Section of a Thunder-cloud near Sydney. 
4 oe D z 
; = = Dioist Basteriy Wierd 
West 5 a5 (= = <A mist 
Dry Westerly Wind. 5 —- “ 
D is Bi 7 
D (dotted line) shows junction of two currents of air, the directions of 
these being indicated by arrows (A A). 
B B, arrows showing upward and backward current of moist air. 
L, lightning striking from thunder-cloud to earth. 
CC, cirrous crest moving with upper current. 
S, scud moving in lower moist current. 
E, the appearance of dropping portions of cloud at foot or back of storm. 
To proceed a little further in this explanation of the produc- 
tion of a thunder-storm, to which our cirrous theory has partly 
led us, may not the electrical excitation of the thunder-cloud be 
easily accounted for by supposing it to collect, like a conductor, 
the whole electrical charge of the lower moist and electrified 
current as successive portions of this reach the point of conflict 
and rise upwards? Electricity probably exists in the air pre- 
cisely as on the surface of the excited glass plate of an electrical 
machine. There are large quantities of the electrical fluid or 
force distributed among individual particles; but these are so 
far separated by masses of non-conducting air, that no large 
quantity can be discharged at any one moment. When the 
whole mass of air, however, passes upward and throuyh the 
cloud, the watery particles which are precipitated assume all the 
electricity of the particles of air, just as the metallic points of 
the conductor collect the whole electrical charge of the surface 
