288 Proximate Causes of certain Winds and Storms. 



of the view from its summit on the 14th of July, 1820. "From 

 the summit of the peak, the view towards the north, west and south- 

 west is diversified with innumerable mountains, all white with snow, 

 and on some of the more distant it appears to extend down to their 

 bases." These high ridges extend down as far as Santa Fe,lat. 36° 

 and there are good reasons for believing, that there are others still 

 more elevated west of that town, and of the sources of the Rio del 

 Norte. 



[b.) Lewis and Clarke crossed at a gap or low place in the ridge, 

 at the head of the Missouri, and between the latitudes of 43° 30' 

 and 46° 41', were surrounded on every side by mountains covered 

 with snow, between the 12th of August and 9th of September ; they 

 also travelled over deep snow on their return in the last days of June. 



(c.) Mackenzie crossed in latitude 52° 6'. Notices of moun- 

 tains covered with ice and snow, occur in his Journal, under the 

 dates of May 26 ; June 5, 12 ; July 17, 27 and August 13, 17. He 

 appears also to have crossed at a gap. 



(d.) The northern extremity of these mountains, lat. 70^, was 

 seen by Capt. Franklin, covered with snow in the beginning of Au- 

 gust. The accounts obtained of intermediate points, are such as to 

 create a belief that they are still more elevated. 



Over this lofty barrier, a cause as constant as the revolution of the 

 sun, is urging the air from the west and (if the views taken in this 

 communication of the specific manner in which this cause operates 

 are correct) urging especially, the upper strata of the atmosphere. 

 But however this may be, it is at least certain, that only the upper 

 strata can pass. I may add that the lower strata do not pass, for if 

 they did they would melt the snow. The air which has had a mild 

 temperature, communicated to it on the bosom of the Pacific, is stop- 

 ped and a deluge of air having a temperature never elevated much 

 above 32°, and often depressed very far below it, is poured over upon 

 the region on the east side of the mountains, from the icy sea, quite 

 down to Mexico. This air imbibes heat from the soil of the eastern 

 part of the continent, and continuing its course, carries it off over the 

 Atlantic. This country therefore communicating heat to the prevail- 

 ing winds, and receiving none from them, has its temperature de- 

 pressed. This cold deluge must exist and produce the effects as- 

 cribed to it, unless a law of nature, which we have shewn to obtain 

 in other parts of the globe, is arrested in the case of North America. 

 Its existence is also proved by observations, made in the immediate 



