Washington standard. [volume] (Olympia, Wash. Territory) 1860-1921, 1901-02-01
ISOTHERMS.
Facts About lsothsrmic Maps That Are Rarely
Learned at School.
New York Sun.

New \ Ork sun.
Here are some definitions OF iso-
therms that appear in American text.
books of Geography:
"Those lines which are drawn
through places with an equal average
OF temperature are called isotherms.
"Isotherms are lines connecting
places having the same mean temper
ature for particular periods, as the
whole of the year, the winter or sum-
mer months, etc.
eff upon a map all places having
the same mean temperature are con-
nected by lines, such lines are called
isothermal lines or simple isotherms."
These definitions are part of the
truth, bat not the whole of it. 1t may
not be a great calamity, but the fact
is that most boys and girls leave school
with misconception as to what an
Isotherm is, and they rarely find out
in later years.
They all know that two elements,
latitude and altitude, are the main
factors in determining the mean tenn
perature of a place; that the farther a
place is from the equator and the
higher it stands above sea level the
cooler its climate is. But they do not
know that isothermic maps take into
account only one of these elements,
and that is latitude. They eliminate
the influence oil altitude. The iso.
therm passing over tho top of Pixies
peak does not show the mean temper
ature at the summit of the mountain,
but what the mean temperature would
be in that immediate neighborhood if
the land, instead Of rising high above
the sea, stood st the level OF Coney
Island.
Do you see the reason for this? 1t
may be easily explained. Most of the
land does not rise so high above the
sea that the temperature is greatly
affected by altitude. To the majority
of mankind latitude is q far more i'm
portant climatic element than altitude.
Now, the objects on temperature of
both latitude and altitude cannot we'll
be shown on one man, and isothermic
maps were devised to show the effects
of latitude and some other element,
such as position near the sea or in the
far interior.
An isothermic line, therefore, does
not show the actual mean temperature
of place on it unless that place is at
sea level. But it is easy to deduce
from the isotherm the actual mean
temperature of place, if we know
its elevation above the sea. How
this is done is very clearly explained
by DR.. H. Il. Mill, the British geo.
grapher, as follows:
"The air grows cooler by l degree F.
for every 270 feet of elevation above
sea level, but isothermic lines show
the sea level temperature. In using
isothermic maps we must therefore
remember that places 600 feet above
the sea level have temperature 2 de-
grees lower than the isotherms indi-
cate; places 5000 feet above the sea
% degrees lower; those $4,000 feet
above the sea, 40 degrees lower, and
the mountain slopes $4,000 feet above
the sea no less than 66 degrees lower
than the sea level temperature shown
by the isotherms. This accounts for
the fact that none of the important
towns in the temperate zones is sit
uated more than 2,000 feet above the
sea, while in the tropics they are built
at as great elevations as 5000 or 10,-
600 feet"
Weather charts are an exception to
this rule. They record the actual
thermometrical readings at the points
Of observation.