Smyrna times., 1899-02-15
lSOTHERMS.
Facts About IsOthermic Mnps That
Are Rarely Learned ot Schoo1

Facts About IsOthermic Maps That
Are Rarely Learned nt schooI
Here are some definitions of isotberr,s
that appear in American Textbooks Of
geography:
Those lines which are drawn through
places with an equal average of temper-
ature are called isOtherms.
''Isotherms are lines connac+;nc.
places having the same mean temnora,
ture for particular periods, as the whole
OF the year the winter or summer
months. etc
II upon map all places having
the same mean temperature are con-
nected by lines, such lines are called
lSo,hermal lines or simple isotherms -
These definitions are part of tbe
truth, but not the whole of il. If may
not be great calamity, but the fact is
that most boys and girls leave school
with a misconception as to what an
lsotherm Is, and they rarely find out in
later Years.
1hey all know that two elements.
latitude and altitude are the main fac.
Tors III determining the mean temper-
ature OF place; that the farther a
place is from the equator and the biobor
IL stands above sea level the cooler its
climate is. But they do not know that
lSothermlc maps take into account only
one OF these elements, and that is lati-
tude They eliminate the influence of
attitude. The isotherm passing over the
top OF Pixies peak does not show the
mean temperature at the summit of the
mountain, hut what the mean tomner-
ature would be in that immediate neiph.
borhood If the land, instead of rising
high above the sea, stood at the level Of
COney Island
DO you see the reason for this? It
may be easily explained. Most of the
Iand does not rise so high above the sea
that the temperature is greatly affected
by attitude. To the majority of man
KIND latitude is far more impOrtant
climatic element than altitude. Now
the effects on temperature of both lati-
tude and altitude cannot well be shown
on one man, and isOthermic mans were
devised to show the effects of latitude
ana some other element, such as posi-
ton near the sea or in the far interior
An lsothermic line, therefore, does not
show the actual mean temperature of a
place on 1t unless that place is at sea
level. But it is easy to deduce from the
isotherm the actual mean Temperature
OF a place, if we know its elevation
above the sea- How this is done is verv
clearly explained by Dr. H. R. Mill,
the British geographer. as follows:
1he air grows cooler by l degree F.
for every 210 feet of elevation above
sea level, but isothermic lines show the
sea level temperature. In using isother-
mic maps we must therefore remember
that places 600 feet above the sea level
have q temperature 2 degrees lower
than the isotherms Indicate; places
5000 feet above the sea, % degrees
lower; those 1900 feet above the sea.
40 degrees lower, and the mountain
slopes Is, 600 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 situated more than 1000 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. New York Sun