The Washington herald., 1913-07-13

In the aerodynamical laboratory Of ths
indeed real. and the principal thing Il
to know when and where they are most
likely to occur, and how best to AVOID
them.
First there is the aerial fountains
These fountains are a mass Of air which
rises or falls according to the density
of the surrounding atmosphere. for the
same reason that a cork bobs up In water
and a stone goes down. Hence warm and
expanded or light air Is buoyed up when
ever the surrounding air at the same
level is colder: and the atmosphere is
heated mainly through contact with the
surface of the earth. The earth in turn
Is heated by sunshine These vertical up
rushes of the atmosphere. are most nu-
merous during warm clear weather.
The sides of these aerial fountains
may be almost as sharply separated from
the surrounding air as are the sides OF
a fountain Of water. and II Is altogether
possible for the swiftest of them TO pro-
duce effects more or less disconcerting
to the aviation.
Cataracts Are Met.
Then We come to aerial cataracts.
These cataracts are the counterpart OF
the aerial fountain, and most likely TO
occur at the same time. They are seldom
rapid, save in connection with thunder
storms. and such effect as they have is
exactly similar to, but in the opposite
direction from that of the rising column.
In the air there are even such things
as aerial cascades. This term Is applied
to the wind as It sweeps down the lee
side of a hill or mountain. II is most
pronounced when the wind Is at right
angles 10 the direction of the ridge. and
l. serI, av.l
steep. The swift downward sweep of the
air when the wind is strong may carry
an aeroplane with it and lead observers.
II not the pilot. to fancy that another
hole has been encountered, when of
course. there is nothing OF the kind. In
deed such cascades should be entirely
harmless so long as the aeronaut keeps
his machine well above the surface and
out of the treacherous eddies.
1T is a common thing to see two or
more layers of clouds moving in different
directions and at different velocities.
Judgment Of both the actual and the
relative speed of cloud layers may be
badly in error-the lower seems to be
moving faster. and the higher slower.
than is actually the case. Accurate
measurements. however. are possible and
have often been made.
Wind sheets are another danger to
the aviator. These are most frequent
during winter changes. especially as fine
weather is giving way to stormy. This
Is the time to be on ones guard against
the most dangerous of all holes in the
air II is also well to avoid making
great changes in altitude since wind
sheets, of whatever intensity. remain
parallel to the surface of the earth, and
the greater the change in altitude. the
greater the risk Of running into a treach-
erous hole
There are also billows in the air.
When one layer Of air runs over an
other Of different density, billows are set
up between them the same as upon the
ocean. OF course, warning clouds are
seldom present, and therefore even the
most cautious aeronaut may, with no
evidence Of danger before him, take the
very level of the billows themselves,
and before getting safely above or below
them. encounter one or more sudden
changes in wind velocity and direction
due. In part. to the eddy-like or rolling
motion within the pillows. with chances
in each case Of being suddenly deprived
Of large part Of the necessary sustain
ing force and he encounters a hole in
the air. There may be perfect safety
in either layer, but unless headed lust
right, there Is some risk in going from
one to the other. and since flying at the
billow level necessitates frequent chang
ing Of this dangerous nature, 1t should be
strictly avoided.
Air Drainage Exists.
"Eddies and whirls exist in every
stream Of water, from tiny rills to the
great rivers and even the ocean cur
rents, wherever the banks are euch as
to greatly change the direction Of now