536 



SNOW 



SNOW-BIRD 



a depth of 4 inches. Fresh-fallen snow in very 

 light, owing to it< looseness of structure a foot of 

 -ni'li snow gives only aliout an inch of water when 

 melted ; but it increases in density \vlicn lying, 

 partly l>y compression ilue to its own weight, 

 partlv by the filling of the interstices with condensed 

 and frozen moisture from the air, and greatly by 

 partial thawing and refree/iug. I" this w:iy the 

 .-now on mountain- that rise to a height -ullicient 

 to have a temperature mostly In-low tree/ing gct~ 

 hardened into ;/'. and ultimately into tin- ice of 

 the glacier, by which it is transferred to lower 

 icjion- ; Inn if the depth on a steep nlope gets too 

 great Ix-fore it ha- time to harden it i~ liable to 

 sweep down suddenly a an avalanche of dry snow. 

 On the other hand, the sudden melting of snow 

 may cause dangerous Hoods, such as occur when 

 tin- warm wind, called the Fnhn, hlowH over the 

 Alp* ; but the more gradual melting of the snow- 

 mantle of hills feeds the deep-seated springs of 

 rivers. The flooding of the Nile, the source of the 

 fertility of Egypt, is due to snow melting on the 

 mountains of Central Africa. The snow of the 

 Airtie regions, where solar radiation is weak, does 

 not compact together, hut remains dry and powdery; 

 in eastern Siberia the prevalent wind is north-west, 

 and all winter there is a continual drift of dry snow 

 along the surface towards the south-east. The 

 white colour of snow is due to reflection of the 

 light from the innumerable surfaces of the crystals, 

 each of which is composed of clear ice, just as glass 

 loses it* transparency when pulverised. Snow is 

 feebly phosphorescent, absorbing light during the 

 day and giving it out at night. The loose texture 

 of freshly fallen snow makes it an admirable non- 

 conductor of heat, and in the temperate zone it 

 often preserves the ground from the chilling action 

 of short spells of intense cold. The latent neat set 

 free when vapour condenses into snow also some- 

 times mitigates the severity of a frost. 



Snow is sometimes, in polar and alpine regions, 

 where it lies unmelted from year to year, and 

 the annual fall is small, coloured red by the 

 presence of innumerable small red plants. In 

 its native state the plant consists of brilliant reel 

 globules seated on a gelatinous mass. It is an 

 Alga, anil is now known as Prolococcug nivalit ; it 

 is probably near akin to the not uncommon Hcemato- 

 eoccint jduvalis. Hed snow seems to have been 

 observed by the ancients, as a passage in Aristotle 

 apparently' refers to it ; but it attracted no atten- 

 tion in modern times till 1760, when Saiissnre ob- 

 served it in the Alps, and from chemical experiments 

 concluded that the red colour was owing to the 

 presence of some vegetable substance, which he 

 supposed might lie the pollen of a plant The 

 next observations on red snow were mode in the 

 Arctic expedition under Captain Uoss, when it was 

 found extending over a range of cliffs on the shore 

 of Hattin Hay for 8 miles, and the red colour 

 penetrating the snow in some places to a depth of 

 12 feet. Less frequent is a green growth on snow, 

 iso BACTKHIA, HLIZZARD, ICE. 



SNOW-I.INB. This is the usual term employed 

 to signify the height below which all the snow that 

 falls during the year is melted in the course of the 

 summer, or, in other words, the limit above which 

 snow perpetually lies. It is no hard and fast line, 

 but varies greatly in different localities, and in 

 most localities varies more or less from year to 

 year. Hence it would be more appropriate to 

 speak of a zone, having superior (np|>er) and in- 

 ferior (lower) limits, within which the snow-line 

 move* up and down. The altitude at which this 

 line (or zone) falls depends upon several conditions 

 viz. the volume or i|iiantity of snow prccipitat'-d 

 during the winter, the amount of the rainfall and 

 the position of the mountain-slope with reference 



to the principal rain-bringing winds, the latitude- 

 or distance from the equator, the dcgiee nt 'exposure 



to the sun's rays, the angle of tin- -lo] r the 



relative steepness of the mountain side, and the 

 general humidity or dryness of the atino-phcn-. 

 Other things being i-ipial. the following rules hold 

 good : the snow line is higher in north latitudes 

 on the south than on the north side of mountains ; 

 higher on the east than on the west, owing to tin- 

 greater prevalence of westerly winds in regions 

 win-re snow accumulates; and higher in the in 

 terior of continents than near the sea, l-cause in 

 the former situations the precipitation is less and 

 the heat of summer greater. In each separate 

 locality the snow-line must 1* determined by a 

 proper series of olwervations. To the general rules 

 quoted above must be superadded those that depi-nd 

 ii|M>n the latitude : between 20 N. and 20 S. of 

 the equator the altitude is pretty uniform : from 

 20 to 70 on both sides of the same central girdle 

 it falls as the latitude increases in a pretty regular 

 manner ; but lieyond 70 N. and S. and up to 78 

 in both directions it sinks very rapidly. 



To these general rules there are of course in 

 actual fact some important exceptions. In the 

 Himalaya the snow-line runs 4000 feet higher on 

 the north than it docs on the south side: this is 

 caused by the greater depth of snow that falls on 

 the south side, by the greater dryness of the climate 

 of Tibet, which increases the evaporation and con- 

 sequently the heating power of the sun's rays, and 

 by the comparatively treeless rocks and "barren 

 soil on the northern side absorbing more heat ami 

 attracting less precipitation than the well- wooded 

 southern slopes. In the Andes the snow-line rises 

 very rapidly between the equator and 18 S. lat., 

 ancf more rapidly in proportion on the west than 

 on the east side, owing to the comparatively small 

 quantity of snow that falls on the Pacific side of 

 the mountains. The subjoined table gives the 

 snow-line on some of the most important mountain- 

 ranges and peaks on the globe. 



M.iunUuu. 



UtltuJf. 



624" 

 61 1' 

 69* 



Snow-line 

 In fret. 

 8,850 

 6,100 

 8,100 



8,M 



7,000 



. 



s.-.o.. 

 11,000 

 12,600 

 14.000 

 10,600 

 18,800 

 16,000 

 18,000 

 18.400 

 14,700 



6,600 



MM 



Greenland 76' N. 



Norway ( inu-rior) 



(coast) 



Kamchatka 



Altai ...60- 



Alps 46 < -4r 



Pyrenee* 48* 



Caucasus 48* 



Rocky Mountains 48* 



Atlas Mountains 82" 



Himalaya (north side) 80" 



(south side) 27' 



Kilimanjaro (East Africa) S' 8. 



Andes of Boll via ( east side \ 16* 



(west side) 16" 



Chill ST 



Australian Alps sr 



Andes of Patagonia 42* 



Snowball Tree. See GUELDER ROSE. 



Sliowberry (Si/inphoricarpot or Symphoria 

 I'liiiHosa), a bushy deciduous sfiruh of the natural 

 order CaprifoliaccH 1 , a native of the northern parts 



of North America, and now very com n in Hritish 



shrubberies. It has simple leaves, small flowers, 

 and white uneatable bernes about the size of black 

 currants, remaining on the bush after the leaves. 

 The name is also given to Gaultheria serpy Hi folia, 

 a native of North American bogs. 



Snow-bird ( /'</;////// hyemali* or hiidsmtia), 

 a North American bird of the Finch family ( Frin - 

 gilliihe). common from the Cull of Mexico to the 

 Arctic Circle, in all the eastern parts of North 

 America. The wings are rather short, the tail 

 slightly notched. The whole length is aliout six 

 inches; the upper parts are lead-colour, the lower 

 parts white, the two outer tail-feathers white, the 

 next white margined with black. This bird 



