METEOROLOGY. 2 1 



found by Mr. Tinkham, or as 26 : 6 : : 39 : 9; thus showing that the whole amount falling in 

 the five months does not probably exceed nine feet, and this can only remain during the coldest 

 weather — since the mean for December and January is, at the height of Snoqualme Pass, only 

 four degrees below freezing. 



It is not probable that as much moisture is deposited in the pass as at the sound. It is at a 

 greater distance from the sea. And in consequence also of its great elevation there would be a 

 rarefication and coldness in the atmosphere which woidd tend to make it less humid. It is a 

 fact, ascertained by experiment, that in the same storm rain-gauges near the surface of the 

 ground are made fuller than othevs at a few hundred feet elevation directly above them, 

 showing probably that the drops of rain must increase in size as they descend, by accumulating 

 moisture. 



The western spurs of the Cascade range must intercept much of the snow (or moisture) 

 before it reaches the pass; and if we should admit the hypothesis that the amount of moisture 

 falling in the pass is the same as at the sound, we must also admit that the same amount falls 

 on the plains east of the mountains, contrary to actual observation. 



The depth found in February, by Lieutenant Grover, along Clark's Fork, two and one-half 

 feet, would be produced by two and one-half inches of moisture ; and it is stated expressly by 

 him that there was 7wne on the plains from Spokane river southward, while east of the Bitter 

 Root range none was seen by him or by Lieutenant Mullan over a foot in depth. 



Snow lines, at a height of twenty-five feet, on trees are produced by drilts lodging against 

 them, and the Indians walking over the surface on snow-shges would be unable to determine 

 whether the snow was drifted on a surface everywhere uneven and remote from their winter 

 homes where they are acquainted with the ground. Hence probably arose the information 

 derived from them, that the depth of snow was usually so great. 



The presence of the evergreen spruce and pine timber prevents thawing, and thus assists in the 

 accumulation of drift upon drift, while the effect to be expected from opening the surface to 

 the sun may be estimated by the fact that, as just stated. Lieutenant Grover found no snow on 

 the Spokane prairie, while just before he came out of the timber there was a depth of two 

 feet. 



The whole evidence favors the belief that there is not a greater depth of snow in the highest 

 six miles of the pass than on the line of the Portland and Montreal railroad, and that it passes 

 oft' about as early, while the rest of the route is never liable to be impeded b}- snow. 



On no other point of the route between the Mississippi and the Cascade mountains is the 

 precipitation of snow as great as in this interval. At Fort Snelling, admitting that all the 

 moisture of the three winter months should fall in the form of snow, we find that the maximvm 

 of nineteen years' observations is only 5.47 inches melted, or 54.70 inches snow, (4^ feet,) and 

 the minimum | an inch of snow. The mean for the same i^eriod is only 19.20 inches. Going 

 westward, the deposition rapidly decreases until approaching the Rocky mountains, where the 

 influence of the west winds probably causes an increase, but at the same time mostly in the 

 form of rain. Mr. Doty records : "December, 1853, no snow or rain during this month ;" in 

 January 7^ inches, (1.6 inches moisture;) February, including both snow and rain, 11 inches, 

 (3.4 inches,) none of which remained long on the ground. On the Great Plain of the Columbia 

 Lieutenant Grover found no snoiv in the end of February, although the accimiulated snows of 

 the winter were 2^ feet deep in the woods along Clark's Fork, the deepest he met with. The 

 mildness of the winters, compared with Fort Snelling, will not permit us to make the same 



