e of low storm-cloud, or
seud, showing very sharp and white on the dark back ground all along the
southern sky. This line continues until noon about 10d at the highest,
showing the northern boundary of the storm to the southward; 8 P.M.,
same bank visible, although in rapid motion eastward; same time clear
overhead, with cirrus fringe pointing north from the bank; much
lightning in south (W. fresh); so ends.

15th. Last night a black squall from N.-W. passed south without rain; at
3 A.M. clear above, but very black in south (calm below all the time);
9 A.M., the bank in south again throwing off rays of cirri in a
well-defined arch, whose vortex is south: these pass east, but continue
to form and preserve their linear direction to the north; no lightning
in south to-night.

16th. Clear all day, without a stain, and calm.

17th. Fine and clear (N.-E. light); 6 P.M., calm.

18th. Fair and cloudy (N.-E. light); 6 P.M., calm.

19th. Fine and clear (N. fresh); I. V. visible in S.-W.

20th. 8 A.M., bank in N.-W. with beautiful cirrus radiations; 10 A.M.,
getting thick with dense plates of cream-colored cirrus visible through
the breaks; gloomy looking all day (N.-E. light).[21]

Appearance of the Inner Vortex at 8 A.M., July 20th, 1853, including the
whole sky. (See Fig. 19.)

[Illustration: Fig. 19]

This was a different passage of the Inner Vortex ascending as compared
with the same 28 days before. At that date (June 22) it did great damage
in the central parts of Illinois. Still this last passage was very
palpable--the clouds were very irregularly assorted--plates of cirrus
above and beneath cumulus--various kinds of cirrus clouds, and that
peculiar prismatic haze which is a common sign of the passage of a
vortex. The appearance depicted above is a very common, although a very
evanescent appearance. When the sky appears of a clear blue through the
cirri, there will be generally fresh gales without any great electrical
derangement; but if the clear spaces are hazy, gradually thickening
towards the nucleus, a storm may be expected. Any one who wishes to
understand the indications of the clouds, must watch them closely for
many years, before he can place much reliance upon them. But we shall
again advert to this point.

We have now passed through one sidereal period of the moon. We might
continue the record, but it would be tedious. The passages of these
vortices vary in violence at different times, as we might exp