CHAPTER IV.
T H E M O U N T A I N S.
“Blue, and baseless, and beautiful,
Did the boundless mountains bear
Their folded shadows into the golden air.
The comfortlessness of their chasms was full
Of orient cloud and undulating mist,
Which, when their silver cataracts hissed,
Quivered with panting colour.”
Ruskin.
FROM the Polar deserts to the icy crests of the mountains the transition is natural. There are here, so to speak, two varieties of a single class of deserts, which we might call the Deserts of Cold, since the coldness of the climate is the dominant cause which in both renders the soil more and more unproductive and uninhabitable. In effect, it is not only in departing from the Tropic Zone that we see the mean temperature gradually sinking even to the point whereat all liquids congeal and all terrestrial life becomes impossible. The same phenomenon occurs in proportion as we ascend in the atmosphere. It is a consequence of the properties of the gaseous medium which envelops our globe, and takes place in obedience to certain laws which science has been able to ascertain and define. We know now that the decline of the temperature is always in proportion to the elevation of places or of the atmospheric strata; but the value of the relation which exists between the two terms may be modified by various circumstances—such as the direction of the prevailing wind, the hygrometrical state of the atmosphere, the hour of the day, and particularly the climate, or, to speak more exactly, the thermic latitude. The warmer the climate, the more sensible the difference between the temperature of the air at the level of the sea and that which we observe at a certain height; greater, nevertheless, is the height to which we must rise to find the region where the thermometer never descends below 0°, and where, consequently, the snows and ices of the mountains do not melt in any season.
As a mean, we estimate every 580 feet of elevation in the Torrid Zone as equal to one thermometrical degree, and in the Temperate Zone at one degree for every 450 feet, the cooling of the air. That is, for every 580 feet in the one instance, and every 450 feet in the other, as we ascend above the sea’s level, the temperature decreases one degree. In the Polar regions the decrease of temperature is insensible up to a certain height, which has not yet been ascertained. At Ingloolich, in 69° 21´ north latitude, Captain Parry flew a kite to a height of 400 feet, with an à minima thermometer attached. At this elevation the temperature of the air was 31° below zero, or the same as on the ice-fields of the sea. Humboldt counted one degree of declination for every 550 feet on Chimborazo. De Saussure obtained one degree for every 440 feet on Mont Blanc.
The limit of eternal snows, or perpetual snow-line, which at the Pole sinks to the very level of ocean, rises higher and higher as it approaches the lower latitudes, and attains its maximum elevation towards the Equinoctial Line. It follows, that in the countries bordering on the Arctic Circle, mountains of very moderate altitude show themselves all through the year in a shroud of radiant snow; while, under the Tropics, if we would meet with masses of eternal ice, we must mount to a height of 13,500 feet and more. The limit of the permanent snows is, however, affected by a variety of local circumstances, such as the neighbourhood of great seas or forests. The subjoined table, therefore, which shows the height of the curve of congelation in different latitudes, is founded upon the known law of the decrease of heat by elevation, and must be regarded rather as approximatively correct than strictly accurate.
TABLE OF SNOW-LINE.
| LATITUDE. | MEAN TEMPERATURE AT THE LEVELOF THE SNOW-LINE. | HEIGHT OF THE SNOW-LINE. | |
| Degrees Centrigrade. | Degrees Fahrenheit. | Feet. | |
| 0 | 29·00 | 84·2 | 15,207 |
| 1 | 28·99 | 84·2 | 15,203 |
| 2 | 28·96 | 84·1 | 15,189 |
| 4 | 28·86 | 83·9 | 15,135 |
| 5 | 28·78 | 83·8 | 15,095 |
| 6 | 28·68 | 83·6 | 15,047 |
| 7 | 28·57 | 83·4 | 14,989 |
| 8 | 28·44 | 83·2 | 14,923 |
| 9 | 28·29 | 82·9 | 14,848 |
| 10 | 28·13 | 82·6 | 14,764 |
| 15 | 27·06 | 80·7 | 14,220 |
| 20 | 25·61 | 78·1 | 13,478 |
| 25 | 23·82 | 74·9 | 12,557 |
| 30 | 21·75 | 71·1 | 11.484 |
| 35 | 19·46 | 67·0 | 10,287 |
| 40 | 17·02 | 62·6 | 9,001 |
| 45 | 14·50 | 58·1 | 7,671 |
| 50 | 11·98 | 53·6 | 6,334 |
| [195]51½ | 11·24 | 52·3 | 5,950 |
| 54 | 10·02 | 50·0 | 5,290 |
| 55 | 9·54 | 49·2 | 5,034 |
| 56 | 9·07 | 48·3 | 4,782 |
| 57 | 8·60 | 47·5 | 4,534 |
| 58 | 8·14 | 46·6 | 4,291 |
| 60 | 7·25 | 45·0 | 3,818 |
| 65 | 5·18 | 41·3 | 2,722 |
| 70 | 3·39 | 38·1 | 1,778 |
| 75 | 1·94 | 35·5 | 1,016 |
| 80 | ·87 | 33·6 | 457 |
| 85 | ·22 | 32·4 | 117 |
| 86 | ·14 | 32·3 | 76 |
| 87 | ·08 | 32·2 | 44 |
| 88 | ·04 | 32·1 | 20 |
| 89 | ·01 | 32·0 | 5 |
| 90 | ·00 | 32·0 | 0 |
That the foregoing table needs considerable modification in particular localities is evident from the following facts:—In the Scandinavian Alps, lat. 65° north, the snow-line occurs at an elevation of 5200 feet, instead of 2722; in the Alps of Savoy, lat. 45° north, it is found at 7650 feet, which is nearly that of the table. On the southern slope of the Himalayas the traveller ascends to an elevation of upwards of 15,000 feet before he enters the realms of snow and ice, and on the northern slope to 12,750 feet. Finally, in the Andes of Bolivia, according to Pentland, the curve of congelation lies between 14,400 and 14,800 feet.
Thus, then, in the mid Torrid Zone, we must accomplish a weary ascent of 13,000 to 15,000 feet before we can find ourselves transported from the calcined plains whose sands scorch and blister our feet, or the dense forests whose innermost depths teem with the most exuberant and beautiful floral life, to the heart of icy deserts and the sublime silence of the mountains. And in passing from one to the other of these extremes, we traverse in a few hours all the climates which succeed one another from the Equator to the Pole. Nevertheless, I must point out an important difference between the Polar deserts and the snowy regions of the mountains, which is wholly to the advantage of the former.