METEOROLOGY, 313 
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 Snoqualmoo 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 ata 
greater distance from the sea. And in consequence also of its great elevation there would be a 
rarefaction and coldness in the atmosphere which would 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 others 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 none 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 drifts lodging against 
them, and the Indians walking over the surface on snow-shoes 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 
off about as early, while the rest of the route is never liable to be impeded by snow. pe 
On no other point of the route between the Mississippi and the Unas Vates is the 
precipitation of snow as great as in this interval. At Fort Snelling, admitting that an the 
moisture of the three winter months should fall in the form of snow, we find that the maximum 
of nineteen years' observations is only 5.47 inches melted, or ыо inches snow, (4% feet, ) sad 
the minimum 4 an inch of snow. The mean for the same period is only 19.20 Mehes: Going 
westward, the deposition rapidly decreases until approaching the Rocky mountains, whore 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; E 
January 71 inches, (1.6 inches moisture;) February, including both snow "d 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 snow in the end of February, although the accumulated snows of 
the winter were 23 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 
0s 
