290 Wisconsin Academy of Sciences, Arts and Letters. 
to the winter cold-wave, and might he dignified by the name 
“cool-wave/’ the minimum temperature reached not being suf¬ 
ficiently low to be considered cold by anyone except a denizen 
of the tropics. 
It is interesting to note that cold-waves occur, under various 
names, in all regions of the world except the tropics. In 
our Northwest, when attended by high winds and snow at 
low temperatures, they are called “blizzards.” In Texas and 
over the Gulf of Mexico they are known as “northers.” In 
Europe the cold-wave is less severe than in the United States, 
usually coming from the northeast, and is called “mistral” in 
Erance) “bora” at the head of the Adriatic Sea, and “bura” 
or “purga” in Russia. In South America the “pampero” and 
in Australia the “burster” are identical with our cold-wave, 
though in those countries they accompany southerly winds. 
WINTER TEMPERATURE CONDITIONS IN THE NORTHWEST. 
During the winter, temperature conditions are much more 
variable from day to day than at other seasons. The rapid 
and frequent movement of cyclonic areas across the country 
causes many decided changes in temperature. The mean 
variability of temperature, by which is meant the average 
change from the temperature mean of one day to that of the 
next, at Madison in January is over 6°, while during July 
it is 1’ess than 3°. February’s mean variability is even greater 
than January’s, while that of December is but little less. 
A consideration of the average monthly temperatures over 
the United States during January (see Plate XV) reveals 
decided differences in temperature within comparatively short 
distances. The coldest region in the country is the Red River 
Valley, with an average January temperature of zero or lower. 
During this month the mean temperature at Madison is 16°. 
Under average temperature conditions then, any cause, such 
as the northwest wind, which will transfer the cold air of the 
Red River Valley to Madison, a distance of 400 miles, would 
produce a fall of 16° in temperature, almost enough to verify 
