298 Tornado at Wisconsin. [April, 
proportions, having its motion of revolution in a direction 
opposite to that of the sun, or from the east to the north, 
west south, to the east again. 
According to the most reliable information as to the rate 
of the forward movement of the storm, it struck the earth at 
about 3 p.m., between which time and 5.30 p.m. it passed 
over a distance of sixty-four miles, which would be at the 
rate of twenty-six miles per hour. Any conclusions upon 
the velocity of the wind within the tornado can, as Prof. 
Daniells points out, only be reached by indirect methods. 
The wind’s rotatory velocity south of the axis would be 
increased, while north of the axis it would be diminished by 
the progressive movement of the storm. The amount of 
increase or diminution would, however, differ greatly in dif- 
ferent parts of the whirl. That the velocity of the motion 
of revolution increased from the outer edge toward the centre 
is shown by the fadt that buildings near the centre were 
reduced to the dimensions of kindling wood in a way which 
never occurred near the borders of the track. Hence the 
horizontal velocity of each particular volume of air was con- 
tinually changing as it occupied different positions relative 
to the axis and to the centre of the whirl. Again the wind 
had an upward motion, the perpendicular component of 
which adted upon bodies to hold them in suspension. The 
velocity of this upward motion also increased toward the 
centre of the whirls, and was comparatively slight near its 
limits. The adtual velocity of the wind at any point would 
be the resultant of the horizontal and perpendicular veloci- 
ties at that point. 
The perpendicular velocity can be approximated by the 
lifting force exerted upon bodies while holding them in sus- 
pension. For instance, a horse weighing about 1100 lbs. 
was carried over twenty rods. Another of about the same 
weight was carried about eighty rods. A horse of this size 
would not expose a lifting surface to the wind of over 14 
square feet. To lift such an animal would require then an 
upward pressure of the air of = 78*5 lbs. per square 
I 4 
foot. This pressure is produced by wind moving with a 
velocity of 124*6 miles per hour. In the township of Jeffer- 
son a granite boulder 15 in. square and more than 6 in. in 
thickness, and weighing more than 130 lbs., was carried 15 
rods. To hold this rock in suspension would require a 
lifting force of 852 lbs. per square foot of surface. This 
force would be exerted by wind moving with an upward 
velocity of 129 miles per hour. These examples show the 
