The Logan Republican. [volume] (Logan, Utah) 1902-1924, 1914-04-30
the DsssjSSs,' yxs,sSs, . u 'als' IAt-
mosDhsrs 8hsss apsr.turss ne dffec-

mosphere& me Honap erstures the direc-
ton and svesocityeof the wind, the
ar9onnt ofFsiassince' the last report
and "a forth From this information
ting MsathS Msp II The United States
H. made sp-sshoxins the conditions
that prevail IN every part of the coun-
tfys sines tAeK are two maps for
each day It Is obvious that by com
pairing them the forecaster can keep
track Of the course and progress Of
both storms and periods Of clear
weather. From that, the next step
Is 70 predict what sort Of weather
viii prevail for day or two in any
given locality.
This map is the basis for all scien-
,tific weather forecasting. A glance
at it will show that 1t is divided into
high pressure areas and low pressure
areas. These are technical terms
used to describe the regions in which
the weight or pressure of the atmos-
phere is great (high) or small dow.
At sea level the barometer which Is
used to measure this weight, will reg
lister 30 inches under normal condi-
tons of the atmosphere. When 1t
registers more than this, say 30.5 or
81, the pressure is high; when 29.5
or less, low. In this way the height
of column of mercury in baro-
meter indicates the weight of the air
just as, in thermometer, it indicates
the temperature.
Low pressures usually mean strong
winds, rain, and rising temperature;
high presshres, cool, clear weather
For a reason to be explained later,
these highs and lows, as they are
called, travel In general direction
from west to east. The forecaster
notes their progress on the map, per-
ceives their speed and their route,
and then predicts the time of their
arrival at any specified point. II
they travelled, like ship steered by
an exact course to the east
and II they moved invariably at the
same speed, then weather forecasting
would be a simple sum in arithmetic,
like calculating the time when a rail
road train running fifty miles an hour
will arrive at station 500 miles
away. But storms are not railroad
trains. They travel in an easterly
but they do not travel due
east. Their speed is liable to change
and they are affected by the presence
of other storms by mountain ranges,
large bodies of water, and many other
things which make weather prophesy-
ing the complicated science that 1t
is. The skeleton of the science,
however. is the progress of those
highs and lows eastward across the
country.
This progress is caused by the
shape of the earth and the well known
fact that hot air rises. The tropical
sun In the regions along the Equator
heats great masses of air, which rise
and drift toward the North and South
Pole. AS the earth revolves from
west to east those masses are carried
along with It at the same speed. But.
dS ID also we'll huOWu, inc EqudtOT
revolves much faster than the poles,
which are practically stationary, in
much the same way rs the rim OF a
wheel revolves faster than the hub.
Therefor these masses of air, revolv-
Ing at the same rate as the Equator,
begin, as they approach the poles. to
move much faster than the earth be-
meath them. There is thus con-
slant movement OF the atmosphere
from west to east, a movement which
becomes more marked the nearer one
gets to the poles.
This, of course, does not mean that
the wind always blows from the west.
The great current flows in that direc-