S E P T ~E R , 1908. MON!CEliY WEATHER BEVIEW. 277
6th to 27th. A decided change to colder came with the rain-
storm of the 27th, and the last three days of the month were
unusually cold, with frost generally in Kentucky and parts of
Tennessee. Special warnings were isclued for the frost.-
F. J. Walz, District Forecaster.
[ Indlana, Illinois. Mlchlgan, Wlsconsln, Minnesota, Iowa, Ml6SOUrf, North Dakota, South Dakota, Nebraska, Kansas, and Montana.]
Except during the last few days of the month September
was unusually warm. The change to cooler weather set in
over the Western States on the 25th and advanced slowly
eastward, bringing unseasonably cold weather and general
frosts for which warnings were issued well in advance. Frost
warnings were again issued on the 30th in advance of another
cool area. Special frost warnings were issued to the cranberry
marshes of Wisconsin on the 1st. 2d, and (ith, and in each
case frost and freezing temperatures were reported in the
bogs. The drought conditions continued from the previous
summer months, and they were not effectually broken until
the passage of the storm of the last week. The only disturb-
ance that justified storm warnings crost the upper Lakes on
the 30th, and warnings were issued for this storm on the
morning of that day.
The following action was taken by the South Dakota State
Board of Agriculture in connection with a special forecast
telegraphed from Chicago to the Local Office of the Weather
Bureau at Huron, 8. Dak., on September 8:
By resolution of the State Board of Agriculture, it is my duty and pleasure to express to you, and through you to the U. S. Weather Bureau, our sin ere thanks for the long forecast given us for the week d our
Fair. It was of great value for us to know this as i t saved muoh expense in preparing for rain as we felt we should. Besides this it was a great
relief of mind to the management to know that we could expect such fine weather.
(IHICAQO FORECAST DISTRI(IT.*
J. W. CAMPBEEL, Preaidmt,
H. J. Car, Proj>sanr and District Forecastrr.
DENVER FORECAST DISTBICT.*
[Wyoming, Colorado, Utah, New Mexico, and Arizona.]
Except during the closing week the month was warm and
dry. From the 23d to 26th a heavy storm of snow and rain
moved from Wyoming to southern New Mexico. The storm
was followed by one of the most severe cold spells on record
during September in eastern portions of Wyoming, Colorado,
and New Mexico. Timely warnings of frost and freezing tem-
perature were issued in connection with the cold spel1.-
P. IllcDonough, Local Forecaster, teniporarily in charge.
SAN FRANCISCO FORECAST DISTRI0T.t
[California and Nevada.]
The most striking feature of the month was the storm that
prevailed over southern California on the 23d to 25th. Gen-
erally speaking the rainfall was the heaviest during September
since records have been kept. It varied in amount from half
an inch to several inches. The raisin-making section had
ample warnings of the rains and the benefit of the service bas
been acknowledged. No frost nor storm waruings were issued
during the month.-A. a. Mctldie, Professor and DWrict Fore-
caster.
PORTLAND, OREG., FORE(IAST DISTBICT.~
[Oregon, Washington, and Idaho.]
The month was unusually dry in western and northern sec-
tious, and temperature was slightly above normal east of the
Cascade Mountains. A moderate disturbance crost the northern
portion of the district the last day of the month. Light frosts
occurred on the 23d and 24th and heavy frosts on the 25th
and 26th. Warnings of the storm and frosts were issued in
time to be of service to those interested in them-E. A. Real#,
Daltlrict Forecaster.
RIVERS AND FLOODS.
The feature of the month was the general drought that pre-
vailed over the middle and northern district3 east of the Rocky
Mountains. Little or no rain fell over this extensive area
until the end of the month, and all streams, escept the Missis-
sippi and Missouri, were at very low stages. The two larger
rivers were not lower than usual for the season of the year.
The drought conditions were most severe in the Ohio Val-
ley and the Middle Atlantic States, and in many places rivers
were lower than ever before. Navigation was practically sus-
pended on the Ohio, and many manufacturing plants in the
upper Ohio Valley were compelled to suspend operations on
account of lack of water.
Delayed reports of the flood of August and early September
in the rivers of eastern South Carolina show that the damage
caused thereby amounted to over $900,000, divided as follows:
Property loss, excluding crops, $200,000; losses of crops,
$700,000. The losses due to erosion of land and suspension
of businew were reported great, but detailed reports were not
available.
The highest and lowest water, mean stage, and monthly
range at 211 river stations are given in Table IV. Hydro-
graphs for typical points on seven principal rivers are shown
on Chart I. The stations selected for charting are Keokuk,
St. Louis, Memphis, Vicksburg, and New Orleans, on the Mis-
sissippi; Cincinnati and Cairo, on the Ohio; Nashville, on the
Cumberland; Johnsonville, on the Tennessee; Kansas City, on
the Missouri; Little Rock, on the Arkansas; and Shreveport,
on the Ked.-H. G. Frankenfild, Profwor of Meteorology.
* Morning forecasts made at district center; night forecasts made at
+ Morning and night forecasts made at dietrict center. Washington, D. C.
-
~
SPECIAL ARTICLES, NOTES, AND EXTRACTS.
R &S m OF EXPERIMENTS IN AEBODYNAMICS
By Dr. A. F. ZAHM. Dated Waahlogtoo, D. C., August 8.1, 190S.
INTRODUCTION.
Aerodynamics may be defined broadly as the science of
motion of air, or an aeriform fluid. Commonly air alone is
implied in the word. This is especially true when the name
ie used by engineers. With them it is the analog of hy-
draulics, which is the science of motion of water. Both
sciences treat not only of the movement of their peculiar
media, but also of its effects on objects, or machinery, con-
nected with the fluids.
Bn important function of aerodynamics is to determine the
velocity and stress of air at every point of this medium, when
it flows past an obstacle, the physical conditions of the fluid
being given or observed by means of suitable instrumeuts.
From the point-velocity the stream-lines may be mapped; from
the point-stress about an object the resultant pressure and
friction may be found by integrating over its surface.
Equivalent results may be obtained if the object move
against the fluid, since only the relative motion is of conse-
quence. Devices are in use, also, for revealing these inte-
grated effects directly, without first finding the point-velocity
and point-stress. Some of these will be described presently.
Experimental aerodynamics may be studied in its elements,
as diatinguished from its applications, by considering it under
these heads: (1) velocity and stream-lines; (2) normal stress
and resultant pressure; (3) shearing stress and resultant
friction; (4) combined pressure and friction. To trace the
development of even this much of the science would require
a large volume.
The following pages present a brief sketch of such of the
writers experiments as may be classed under the above heads,