Fig. 210. Snow crystals
Snow is usually from ten to twelve times as light as water, bulk for bulk; so that where the snow falls pretty evenly, the corresponding rainfall is readily determined by merely measuring the depth of snow and taking one tenth of the result. The more accurate plan, however, is to thrust the open end of a cylindrical vessel into the snow, invert the cylinder, and then melt the snow in it.
Snow plays an important part in the economy of nature. In the first place, the mere transformation of the water particles into ice is a process during which a large amount of heat is given out; so that we may regard the formation of snow renders the air currents warmer than they would otherwise be. Fallen snow serves to protect the ground, for, owing to its loose texture, it is a bad conductor of heat; so that, while checking the radiation of heat from the earth into space, it does not draw off the earth's heat by conduction. The ground is thus often 23 degrees to 30 degrees warmer than the surface of the snow above, and sometimes the difference of temperature has been more than 40 degrees.
Red snow and green snow have been met with, more commonly in Arctic regions, but also in other parts of the world. These colours are caused by the presence of minute organisms—a species of alga called Protococcus nivalis.
The snow line of mountains is on the slopes below which, all the snow which falls in the year, melts during the summer. Above the snow line, therefore, lies the region of perpetual snow. The altitude of the snow line depends on a variety of conditions. The latitude of a snow range is, of course, important in determining the position of the snow line, but many other circumstances have to be considered, as the shape and slope of the mountain, the aspect of either side of the range, the character of the surrounding country, the prevalent winds, and so on.
The following table shows the observed height of the snow line in feet above the sea level in different places:
| Place | Latitude | Height | |
| Spitzbergen | 78 | N | 0. |
| Sulitelma, Sweden | 67 | 5´ | 3.835 |
| Kamtchatka | 59 | 30 | 5.240 |
| Unalaschta | 56 | 30 | 3.510 |
| Altai | 50 | 7.934 | |
| Alps | 46 | 8.885 | |
| Caucasus | 43 | 11.063 | |
| Pyrenees | 42 | 45 | 8.950 |
| Rocky Mountains | 43 | 12.467 | |
| North Himalaya | 29 | 19.560 | |
| South Himalaya | 28 | N | 15.500 |
| Abyssinian Mts. | 13 | 14.065 | |
| Purace | 2 | 2´ | 15.381 |
| Nevades of Quito | 0 | 15.820 | |
| Arequipa, Bolivia | 16 | S | 17.717 |
| Paachata, Bolivia | 18 | 12.079 | |
| Portillo, Chili | 33 | 14.713 | |
| Cordilleras, Chili | 42 | 30 | 6.010 |
| Magellan Strait | 53 | 30 | 3.707 |
DESIGNING, MAKING, AND INFLATING PAPER BALLOONS
