290 THE POPULAR SCIENCE MONTHLY. 



5. In most cases, transient or continued increase of appetite, inges- 

 tion 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 uni- 

 formity during the day, the rarity and calmness of the air are im- 

 portant 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 ; conse- 

 quently 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. 



