due east. _Second._ That the destruction of property was generally
greater as the cloud moved across a valley. _Third._ That the velocity
of the moving mass varied at different periods from 5 to 15 miles an
hour, but twelve miles an hour would be considered a fair average.
_Fourth._ That the trees along the southern side of the track of
desolation were generally thrown with their tops towards the north, or
at right angles to the direction of the progressive motion of the
cloud, while those on the northern side were thrown in the opposite
direction. _Fifth._ That in some instances houses and buildings near
the _centre_ of the track were but slightly injured. These cases,
however, were rare. _Sixth._ That from local and other causes, the
lower part of the conical cloud frequently moved out of a straight
course, while the upper or larger part of the cone kept in a line very
nearly direct. _Seventh._ That as soon as the cloud was formed, a
roaring sound commenced, which continued without interruption during
its entire course. This sound was not unlike continuous thunder.
_Eighth._ That the movement of the storm-cloud was unaccompanied with
much rain or hail, though one or the other fell at some distance north
or south of the track, the sun frequently shining at the time. To
explain some of these phenomena, even with the aid of science, is
difficult. The storm-cloud itself was an entirely exceptional
phenomenon in this latitude. Such an event had never occurred before
in eastern Pennsylvania, and we are without the benefit of previous
observation and experience. The great destruction of property in
crossing valleys has excited marked attention. The cloud undoubtedly
required an immense amount of air to feed it as it went along. Persons
near its track say that they breathed with the greatest difficulty.
The surrounding air must have been very rare; in fact, a partial
exhaustion must have resulted from the absorption of air by the moving
mass. In crossing a valley at right angles, or nearly so, the dense
air up and down on either side, would be at hand to furnish it with
the necessary material, thus increasing its power and devastation;
this is one explanation. Another theory, which is probably the correct
one, could safely be advanced upon plausible grounds. Supposing
electricity to be the primal cause of the cloud itself, in passing
across deep and irregular valleys with rugged surface, more
electricity would be developed, a