The Portland daily press., 1897-09-02
PHOToGEAPHENG THE SKIES.
Interesting Experiments To Be Made
by the Weather Bureau.

Pictures of Atmospheric Currents on Dry
TIates--Inportance of the Expected
Resuits-The Mystery of the Tornado
May Be Solved.
(From the ST. Louis Globe-Democrat.
Washington, Aug. 24.-The Weather
Bureau is about to enter upon wholly
new branch of scientific investigation,
namely, the photographing of the air.
Results are expected from it of the the
utmost Importance to meteorology,
throwing light upon many phenomena
which at present are not understood.
For it is fact that almost nothing is
known about the way in which the cur
rents of the atmosphere move and it is
easily seen what an important bearing
this qustion must have upon tn problems
which the Government forecasters are
Obliged to tackle. Take an ordinary
hurricane, for example, such as is apt to
run up the Atlantic coast from the West
Indies at about this time of the year.
The nature of the disturbance is compre-
hended in general way, but the working
mechanism of the storm is mystery A
whirling tornado plucks chicken clean,
drives scantling through man, strips
a woman naked and carries baby a mile
unhurt How does it do these thingsF
Nobody can say. afs
The Weather Bureau is going to- find
out all about such things by photograph
ing the air currents and studying their
movements as shown by the camera. For
instance the experts want to know how
tie air flows over houses, over mountains,
through bridges, etc. They will make
little model of a mountain, place. it before
the camera, and direct an imitation
breeze against it. When the wind strikes
a real mountain it flows up the slope;
that much is known. But what does it do
VIII it reaches the top Does it continue
t ascend, or where does it go to? No
body knows.
1t would seem to be an extremely diffi-
cult matter to photograph SO tenuous and
transparent a substance as air. However,
rnere is way of doing it which has been
worked out recently by an Austrian
scientist. Prof. e. Mach of Vienna. The
discovery is derived originally from the
experiments of two Frenchmen, Foucault
and Fizeau, who invented method OF
producing perfect lenses. They found
that if d bright point of light were placed
a considerable distance behind the lens,
the latter from the front would appear
TO be illuminated uniformly throughout
If there was any imperfection in the
shape IF the glass it would be shown by
~ irregularity of coloring. In such case
tn spot was marked and corrected.
Prof. Cleveland AbDe showed your cor
respondent yesterday a pho. 5graph OF
flying bullet made by Prof. Mach. 1t was
on piece of translucent gelatine, which
had to be held between the eye and the
light for observation. Not only was the
compression of the air in front of the bul
let clearly visible as dark spot, but one
could see the waves of air moving away
from the sides of the projectile and the
atmosphere rushing in behind the latter
to fill up the vacuum made by its pass
age. A photograph of a conical cannon
shot had an appearance somewhat similar.
Prof. Mach has been studying the way in
which the air affects the trajectory of
mortar shells and other kinds of projec-
tiles the results being most useful to
the Austrian artilleristS.
The method by which the photographs
are taken is quite simple. There is a
large and very perfect lens, at some dis
tance behind which are two electrodes so
placed that an electric spark can be made
lens is the camera. Avoiding details, it
is sufficient to say that the passage of a
bullet behind the lens causes a spark to
fly between the two electrodes, and the
result is photograph of the spark de-
formed by the disturbed air around the
projectile. Thus is produced picture of
the bullet and the atmospheric waves sur
rounding it. The same process is applied
with other objects. In some cases the
latter are stationary, being placed behind
the lens and exposed to an artificial
breeze. Prof. Mach has done this sort of
thing with the wings of birds, blowing a
current of air against theA The result
ing photographs show that Che resistance
of the air is utilized by bird with the
utmost economy of energy, none of it be-
ing wasted.
Following this method, the Weather
Bureau experts will set up little model
of building and blow against it with an
imitation wind. photographing the air
currents as they move around 1t. At
present nobody knows in what manner
air in motion flows around a house.
People often write to the Weather Bureau
asking how strong they ought to make a
certain structure, as q bridge, for ex-
ample. They want to know how to cal
culate the pressure per square foot OF
high wind. The experts are unable to
furnish the required information. No
way of ascertaining the pressure of wind
has been invented The Weather Bureau
receives and sends out reports every day
respecting the velocity of winds, but the
truth is that these are only crude guesses.
The machines called thermometers, used
for measuring wind velocity, are mere
makeshifts, made to reyolye by the NOV
ing air caught in little iron cups at the
ends OF horizontal arms. Nobody knows
what the air does when 1t strikes these
cups, but it must be thown into very
complex motions.
The Weather Bureau people are going
to try every imaginable sort of expert
ment with the apparatus described, They
will put little models of sailing vessels In
the machine, and supplying an artificial
breeze, will find out what becomes of
The air that strikes the sails. If any of it
is wasted, then the shape of the sails
ought to be modified. Much may be
learned in this way that will be of great
advantage TO navigation, and the yacht
of the future may be far superior in sail
ing power to the pleasure boat of today,
her sails being cut on scientific pattern
Recently the kite has hpan elevpted f-oy,