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in the American Meteorological Journal for 1887; from which we cite only a few 
points: 
‘¢The dry character of these winds is usually seen only to the eastward of the mount- 
ains. In western Oregon and Washington they are moist, and the same is true of the 
western slopes of Idaho and Montana. But as the name is more generally used east 
of the mountains, where the idea of dryness is a fundamental one, the Chinooks are 
defined as warm, dry westerly or northerly winds occurring on the eastern slopes of 
the mountains of the Northwest, beginning at any hour of the day and continuing 
from a few hours to several days. Their effects are felt at least as far as 500 miles 
east of the divide. On the arrival of the Chinook the winter appears to yield, the 
air becomes mild and spring-like. This effect appears in the winter isotherms, mak- 
ing the average winter temperature on the plains east of the Rocky Mountains in the 
great interior basin and the narrower interior valleys to the north, notwithstanding 
their continental position and high elevation, actually higher than on the same lati- 
tudes east of the Mississippi River; yet at the same time the range of temperature for 
the northwestern plainand the changes more sudden and severe. These changes are 
injurious to tree life, and in them can be found one reason for the difference between 
the eastern and western slopes of the mountains. The eastern slopes are bare, rugged, 
and somber; the western heavily clothed with timber. These trees, largely conifers, 
which can endure without injury very low temperatures, are very sensitive to ex- 
treme dryness. The dry air injures the folhage, and when accompanied by wind may 
kill the cambium on the windward side of the trunk, thus permanently injuring and 
in time destroying the tree. The Chinooks have probably played an he part 
in the treelessness of the Western plains and interior basins.” 
MOVEMENT OF THE SNOW, FORMATION OF AVALANCHES. 
On the plain the snow moves only by settling and by drifting. On 
an incline, even if only slight, there is a side movement, following the 
law of gravity and depending in its amount on the angle of inclination, 
configuration, and especially cover of the ground, and also on the nat- 
ure and amount of the snow. If the snow is frozen to the soil, it can 
not of course move. Otherwise, even if the conditions are not favor- 
able to motion, and a movement may be hardly noticeable, yet it exists 
within the mass, and becomes apparent by the formation of horizontal 
rills on the surface of the snow. This movement and the pressure due 
to it is capable of displacing buildings without much injuring them. 
The more favorable the conditions are for motion the greater becomes 
this movement, until at last a slide occurs, moving in larger or smaller 
masses, more or less rapidly over the incline. = 
According to the temperature or the nature of the snow dependent 
thereon, the form and effect of the avalanche vary. 
If in cold temperature a large amount of dry snow falls on a steep, 
deforested mountain side, it behaves like a sand-heap, the particles get- 
ting into motion for lack of stability in the mass, and moving forward, 
the mass carries with it any other masses of snow that are in its way. 
The heavy particles arrange themselves towards the soil, the finer par- 
ticles forming a cloud of snow bursting into the air and like dust set- 
tling down only gradually. 
This falling cloud, which obscures the mountain view for some time, 
compresses the air to such an extent that like a cyclone it precedes the 



