VALUE OF WEATHER OBSERVATIONS 135 



and Captain Lewis was " astonished that more have not suffered in a 

 similar manner." 



Our general understanding of the essential climatic characteristics 

 of the country through which the expedition passed, already reasonably 

 accurate although 02ily in outline, becomes clearer as we pick out other 

 details which are noted in the journals. " The air is remarkably dry 

 and pure in this open country. . . . The atmosphere is more transparent 

 than I ever observed it in any country through which I have passed," 

 Captain Lewis says, thereby bringing out very clearly one of the great 

 climatic advantages of the region. The rapid evaporation, which has 

 its disadvantages as well as merits, was frequently observed. Thus 

 (September 23, 1804) on one occasion "in 36 hours 2 spoonfuls of 

 water evaporated in a saucer," and elsewhere in the " Journals " we note 

 that the rapidity with which Captain Lewis's ink dried up was recorded 

 as furnishing a striking illustration of the dryness of the air. Surely 

 that gives us a hint as to what can be done by a traveler who is alive to 

 what is going on around him. The difficulty of making any accurate 

 estimate of distances in the air of the mountain country, so much drier 

 and purer than that to which he had been accustomed, struck Captain 

 Lewis forcibly. Similar difficulty has been experienced by many per- 

 sons whose eyes have become trained to estimate distances in turbid 

 air near sea-level, and find, on mountain tops, that their whole scale of 

 distances must be revised in order to allow for the greater clearness of 

 the mountain air. Although the winter was spent on the Pacific coast, 

 there was no lack of opportunity to observe frost and cold on the Plains 

 and northern plateaus. Frost we find recorded as " white," " hard," 

 " very hard." The thickness of ice frozen in a day is often recorded. 

 On October 18, 1804, we note that water in vessels exposed to the air 

 was frozen, as was " the clay near the water edge." And on another 

 occasion (April 15, 1805) "the earth at the depth of about 3 feet is 

 not yet thawed, which we discover by the banks falling in and dis- 

 closing a strata of frozen earth." It was recorded that snow fell on 

 the mountains while rain fell at lower levels — a common phenomenon 

 resulting from the lower temperatures aloft. The occurrence of noc- 

 turnal radiation fogs; the prevalence of cold northwesterly winds in 

 the colder months (as contrasted with the warm southerly and south- 

 easterly winds of summer) ; the depth of snowfall; the appearance of 

 auroras, and of haloes and other optical phenomena ; the migrations of 

 birds; the coming of rains with northwesterly winds (this being a 

 combination which is not very common in the eastern United States, 

 but occurs more frequently in the west) — these are a few of the many 

 instructive observations which have been picked out in a rather hap- 

 hazard way from the very rich harvest in the " Journals." The occur- 



