1874.] The Iowa and Illinois Tornado. 377 
to all and sundry: Did you observe any pointed objects, 
such as lightning-rods, posts, &c., tipped with flame, during 
the progress of the tornado? but the replies being uniformly 
in the negative, have not been formally inserted in the state- 
ment of facts. Also a description of the sound was ex- 
acted from all witnesses, but only a few typical ones have 
been inserted. I regret this at present, because I have 
learned from experience that very important questions may 
attach themselves to a description of the sound. While 
interrogating parties the utmost vigilance was exercised to 
prevent them from giving conclusions for what they saw 
and heard. This was a very troublesome point and caused 
the interrogator to appear in many cases in the highest 
degree rude; while it also excludes from these pages the 
names of persons who observed accurately, but who are 
unable to distinguish between the esse and the ergo. 
The statement of facts for Iowa is much more exhaustive 
and instructive than that for Illinois. There are several 
reasons for. this. 
1. Some weeks had already elapsed since the tornado, 
and its traces were becoming rapidly obliterated, both in 
the memories of the witnesses and upon the surface of the 
earth. 
2. It was later in the day when it occurred, thus hiding 
the light of the sun more completely by the tornado clouds 
as they approached, and rendering it more difficult to ob- 
serve accurately their forms and proportions. 
3. The storm in Illinois seems to have been of a some- 
what different character from that in Iowa, by its form 
rendering observation more difficult. 
With regard to the angles of elevation given, it must be 
borne in mind that they are only approximations. Very few 
indeed of the witnesses have accurate conceptions of angles. 
I generally made them point in the direction in which an 
object was seen, and so estimated the angle. 
CALCULATIONS AND CONCLUSIONS. 
The Idea of a Tornado in General.—The tornado consists 
essentially of a rapidly ascending current of air. This in- 
volves two other fun¢tions—(r) a rushing in of the air at 
the under part of the ascending current or column; (2) an 
out-rushing at the upper. Upon the former of these 
functions, combined with modifying circumstances, depends 
the peculiar character and career of the under currents and 
of the clouds they bear; upon the latter, combined with 
the same circumstances, the proportions and direétion of 
