Page:Popular Science Monthly Volume 27.djvu/306

290 5. In most cases, transient or continued increase of appetite, ingestion of food, digestion and assimilation.

6. Thereby improved production of blood and nutrition of the organs.

7. Greater energy of nervous and muscular action.

8. In most cases, improvement of sleep.

9. Probable augmentation of tissue-change.

During last fall I became acquainted with an elevated plateau in the United States which rivals if it does not even surpass Davos in the excellence of its winter climatic conditions. I allude to that most interesting tract of territory—the Yellowstone National Park.

The beneficial effects of a winter climate like that of Davos depend upon the concurrence of several conditions which are difficult to secure at a lower elevation than that just indicated. In the first place, the sun's rays are far more powerful at great than at low elevations, and their intensity is much more equable throughout the day; thus the temperature in sunshine observed by me at Davos on the 26th of December was 89·2° Fahr. twenty-five minutes after sunrise, 108·5° Fahr. at noon, and 91·6° Fahr. at thirty-five minutes before sunset. And the intensity of solar radiation at Davos is such that, on the 22d of December, I obtained, in a box lined with padded black cloth and covered with plate-glass, a temperature of 221° Fahr., or 21° above the boiling-point of water at Davos (200° Fahr.).

Besides the intensity of solar radiation and its comparative uniformity during the day, the rarity and calmness of the air are important factors among the causes of the peculiar climate of Davos. With the barometer standing at 615 millimetres, the weight of air in contact with a given surface of the skin is about one fifth less than it is at the sea-level. The excessive dryness of the air at Davos has probably but little special influence upon the sensation of heat and cold, because the maximum proportion of aqueous vapor present in air near the freezing-point is everywhere small, and the specific heats of equal volumes of air and aqueous vapor are not widely different. On the other hand, the absence of suspended watery particles in the air has, no doubt, very considerable influence in preventing the chilling of the skin. Not only are such liquid particles present when there is visible fog, but they often exist in great numbers when the air presents a perfectly transparent appearance. The most important influence upon the sun-temperature, however, is the reflection of solar rays from the snow. The valley of Davos has precipitous sides and a flat sole, and the hotels are situated on the northwest slope of the valley; consequently they receive, in winter, the scattered solar rays reflected from a large area of snow. A considerable proportion of the thermal rays of the sun falling at an acute angle upon a surface of snow is known to be reflected.