The morning news., 1897-08-28
PHOTOGRAPHING THE AIR.
The Weather Bureau to Begin a Sc
ries of Wonderful Experiments.

branch OF scientific investigation, namely,
the photographing of the air. Results are
expected from it of the utmost importance
to meteorology, throwing light upon many
phenomena which a present are not un-
derstood. For it is a fact that almost moth
ing is known about the way in which the
currents of the atmosphere move, and il is
easily seen what an important bearing
this question must have upon the problems
which the government forecasters are
obliged to tackle. Take an ordinary hur-
ricane for example, such as is apt 10 run
up the Atlantic coast from the West Indies
at about this time of year. The nature Of
the disturbance is comprehended in a gen
eral way, but the working mechanism OF
the storm is a mystery. A whirling lorna
do pluckS chicken clean, drives a scaut-
ing through a man, strips a woman naked
and carries baby a mile unhurt. How
does it do these things? Nobody can say.
The weather bureau is going to find out
all about such things by Photographic
the air currents and studying their move
ments as shown by the camera. For in
stance, the experts want to know how the
air flows over houses, over mountains,
through bridges etc. They will make a
little model of a mountain. place it before
the camera and direct an imitation breeze
against il. When the wind strikes real
is known But what does it do when it
reaches the top? Does it continue to as
cend, or where does it so TO? Nobody
knows.
1t would seem to be an extremely difficult
matter to photograph so tenuous and
transparent substance as air. However,
there is a way of doing it which has been
worked out recently by an Austrian scien-
tist Prof. f. Mach, of Vienna. The dis
covery is derived originally from the ex-
periments of two Frenchmen, Fourcault
and Fizeau who invented me hod of pro-
ducing perfect lenses. They found that if
a bright point of light were placed a con
siderable distance behind the lens, the lat
ter from the front would appear to be il.u-
minated uniformly throughout. II there
was any imperfection in the shape OF the
glass, it would be shown by an Irregular
ity of cOlorng. In such case the spot was
marked and corrected.
On bad days, however the most perfect
lens was apt to appear streaky when sub
jected to this optical test, and it was found
that the phenomenon was due to warm
and cold currents of air moving over the
glass. This was a serious annoyance to
the lens makers, but some years later it
struck another scientific man named Toep-
Ter that the trouble could be turned to
profitable account for the study of mo
tions of air currents. He did something
at it, but the important work in this line
has been accomplished recently by Prof.
Mach, who has made a great number of
photographs of air moving around objects
of all kinds. His photographs Of flying
cannon balls, for example, have caused
certain notifications in the ordnance en-
ployed in the Austrian artillery.
Prof. Cleveland Able showed your cor
respondent yesterday a photograph of a
flying bullet made by Prof Mach. 1t was
~, nia ~
had to be held between the eye and the
light for observation. Not only was the
compression of the air in front of the
bullet clearly visible as a 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
passage A photograph of a conical cam
non shot had an appearance somewhat
similar. Prof. Mach has been studying
the way in which the air affects the traj-
ecIory or mortal shells and other kinds
of projectiles. the results being most use
full to the Austrian artillerists.
The method by which the photographs
are taken is quite simple. There is
large and very perfect lens, at some dis
tance behind which are two electrodes so
placed that an electric spark can be made
to flash between them. In front of the
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 a photograph of the spark, de-
formed by the disturbed air around the
projectile. Thus is produced a picture of
the bullet and the atmospheric waves
surrounding it, The same process is ap-
piled with other objects. In some cases
the latter are stationary being placed be-
hind the lens and exposed to an artificial
D,nf hoe d fg orf Of
thing with the wings of birds. blowing
current of air against them. The re-
sulting photographs show that the re-
sistance of the air is utilized by a bird
with the utmost economy of energy. prac-
tically none of it being wasted.
Following this method, the weather bu-
reau experts will set up a little model
of a 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. Peo-
pie often write to the weather bureau
asking how strong they ought TO make
certain structure, as a bridge, for exam
ple They want to know how to calcu-
late the pressure per square foot Of
high wind. The experts are unable to fur
nish the required information. No way
Of ascertaining the pressure of wind has
been invented. The weather bureau re-
ceiVes and sends out reports every day
respecting the velocity of winds, but the
truth is that these are only crude guesses
The machines called anemometers, used
makeshifts, made to revolve by the NOV
ing air caught in little iron cups at the
ends of a pair OF horizontal arms. No
body knows what the air does when It
strikes these cups but It must be thrown
into very complex motions.
The weather bureau people are going to
try every imaginable sort OF experiment
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. II any Of II 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 fu-
ture may be far superior In sailing power
TO the pleasure boat Of to-day. her sails
being cut on scientific pattern. Recently
the kite has been elevated from the con-
dltion OF a toy 20 that Of a scientific ap-
paratus. The weather bureau experts,
however. are Of the opinion that lts evo-
luton is not yet complete. They propose
10 study small models Of kites Ia the same
,,...t Adding auf Ia what manner tho air