The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1881-05-28


time, when the energy of the system is
suddenly spent.
The formation of large hailstones by
coucentric layers of clear ice and white
snow, laid on like the coats of an onion,
will be readily understood from the fore
going. As many as thirteen layers have
been observed in large hailstones, showing
that they must have made half a dozen
circuits, being successfully thrown out of
the frosty vortex above and sucked in below
by the infowing currents, each time ad-
ding to their coatings of snow and ice be-
fore their final fall to earth.
When the tornado is very small in the
area covered by the gyratory motion,
land spout or water spout is formed, as
it may happen to occur on land or at sea.
In these the gyratory velocity rapidly di-
minishe with distance from the center.
Their destructive effects are sudden and
often great, but the area of violence is
small. In the center of waterSpout, as
in that of tornado when in full force, no
rain falls or water descends in any form,
though heavy shower often falls in the
vicinity. On land dust and light sub
stances are carried up, and as they are
being collected from all sides by inhowing
currents toward the vortex below, they as
sumo the form of cone, which meets the
descending spout, falling apparently from
the clouds, and thus give the whole phe-
nomenon the appearance of an hour-glass.
The observed diameters of water-spouts
range between two and two hundred feet
or more, and their heights from thirty to
fifteen hundred feet, sometimes very much
more: but none of these observations can
be regarded as at all exact. With high
temperature and very low dew point Mr.,
Ferrel calculates that water spout might
reach mile in height, but such conditions
must occur rarely. Water spouts are often
observed to drop down from cloud in an
incredibly short space Of time, aud to be
drawn up again in the same manner; but
this is all an illusion. When the gyratious
are such as to not quite reduce the tension
and temperature in the center, so as to
condense the aqueous vapor and make it
visible, very slight increase at once re-
duces the temperature sufficiently, and the
spout appears from top to bottom almost
instantsneously. Just the reverse Of this
takes place, when the spout breaks, and it
seems to be drawn up instantly; it is dis
solved, not lifted. Tornadoes and water
spouts originate only in an unstable state
Of equilibrium Of the air, which requires
an unusually rapid decrease oftemperature
with increase Of altitude. This can take
place only when the strata nearest the
earth are unusually heated; accordingly
they never occur at night, or in the win
ter, aud but rarely in cloudy weather. If
any agitation Of the air, such as that aris-
ing from the discharge Of cannon, tends
to break up these meteors, then any con-
siderable disturbance of the air from any
cause must tend to prevent their forma-
ton. Hence they occur at sea and on the
lakes only when there is little or no wind
White squalls are invisible spouts. In
such cases the dew point is so low, and
the cloud when formed so high, that the
gyrations are invisible. Still the gyrations
and the rapidly ascending current in the
central part are there, aud also the rising
and boiling Of the sea Over the boiling
sea, high up in the air, is patch of white
cloud, formed by the condensation of the
vapor when ii reaches the required height.
The bulls-eyc squalls on the west coast of
Africa are Of precisely the same nature.
In these cases the air is too dry to furnish
the cloud necessary to make the spout, or
center Of the gyratory movement, visible.
In hot dry climates these ascending
whirls of air form sand spouts or pillars of
saud. Both water spOuts and sand spOuts
are hollow