1874.] The Iowa and Illinois Tornado. 381 
main funnel, and occasionally making a dip, would produce 
no appreciable discord in the disposition of the ruins. An 
insuperable objection to this theory was found in the 
unanimous testimony of the eye-witnesses that the funnels 
approached each other and combined to form one. Another 
objection was found in the lack of unity thus introduced 
into the conception of the magnificent whole. Finding this 
explanation untenable, I endeavoured to think the possibility ~ 
of smaller auxiliary funnels, each of them a perfect whirl, 
moving in spirals nearly or altogether identical with those 
pursued by the confluent winds. This I found to be more 
difficult than the first. The chief objection was the total 
lack of a conceivable cause of the existence of these smaller 
whirls. The second was the peculiar circumstance that 
while one observer saw two funnels, another in the same 
position saw only one, or saw two superimposed with the 
smaller ends together. No possible arrangement of two 
independent funnels with the smaller ends down could pro- 
duce the optical illusion of the funnels superimposed with 
the smaller ends together. I found what I believe to be the 
key to the difficulty given by Mr. Marbourg while considering 
the delineation of the two funnels joining in one funnel. 
The other observers who saw two or more funnels evidently 
had the whole of their attention confined to these, and did 
not observe what was above them. He saw the two com- 
bine at what he estimated an altitude of 50 feet, and form 
one. Another witness at the same place and time saw only 
one funnel. At Lancaster some saw only one, others saw 
two superimposed, and others saw two side by side and all 
at the same time. ‘There is, therefore, an unavoidable 
necessity for some explanation to reconcile these antagonistic 
appearances. 
There is excellent evidence to show that the funnel moved 
at its base with a sort of pendulum motion; that it seemed 
to stand still for a moment and then to bound suddenly 
forward. ‘The evidence on this point is so general that we 
need not recapitulate it. But we have no reason for 
supposing that this oscillating motion extended to any con- 
Siderable distance above the ground, for it is only in the 
want of homogeneity of the atmosphere and the resistance 
opposed to the free course of the winds by the earth’s sur- 
face that we can find a cause for this pendulum motion. 
Let us suppose that the funnel is over a well-watered and 
well-wooded ravine, with its path at right angles to it. It 
is evident that the air at some distance above the ground 
wiil offer much less resistance to the forces drawing it into 
VOL. IV. (N.S.) Z¢ 
