242 



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 genera,lly used east 

 of the mountains, where the idea of dryness is a fundamental one, tlie 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 Cbinook the winter appears to yield, the 

 air becomes mikl and spring-like. This effect appears in the winter isocherms, mak- 

 ing the average winter temperature on the plains east of the Eocky 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 plain and 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 foliage, 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 important part 

 in the treelessness of the Western plains and interior basins." 



MOYEMENT OF THE SNOW, FORMATION OF AVALANCHES. 



On the plain the snow moves oul^^ 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 temi^erature 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 sucit an extent that like a cyclone it precedes the 



