Page:Popular Science Monthly Volume 27.djvu/309

 {|
 * width=350 |White paper
 * width=70 |116·6°
 * width=30 |Fahr.
 * White linen
 * 116·1
 * Snow
 * 111·0
 * Metallic minor
 * 97·5
 * Common mirror
 * 97·5
 * Light-colored soil
 * 96·3
 * Parched grass
 * 95·3
 * Gray rock
 * 88·4
 * Green grass
 * 88·2
 * Black silk
 * 84·0
 * Black caoutchouc
 * 82·2
 * Black merino
 * 80·4
 * }
 * 95·3
 * Gray rock
 * 88·4
 * Green grass
 * 88·2
 * Black silk
 * 84·0
 * Black caoutchouc
 * 82·2
 * Black merino
 * 80·4
 * }
 * 84·0
 * Black caoutchouc
 * 82·2
 * Black merino
 * 80·4
 * }
 * Black merino
 * 80·4
 * }
 * }
 * }
 * }

White paper and white linen were therefore the most perfect reflectors of solar heat; but the efficiency of snow was but slightly inferior, while it greatly surpassed that of even polished metal.

The relative proportions of direct and reflected solar heat, falling upon a body in sunshine surrounded with snow, has not been determined, although it has been ascertained where water is the reflecting surface. Thus, M. Dufour has measured the proportions of direct and reflected solar heat incident at five different stations on the northern shore of the Lake of Geneva. He found that the proportion of reflected heat was as much as sixty-eight per cent of the heat directly incident from the sun, when the sun's altitude was between 4° 38" and 3° 34". At about 70° altitude, the proportion was between 40 and 50 of reflected to 100 of direct heat; and, even at an altitude of 16°, the proportion was between 20 and 30 of reflected to 100 of direct heat; but when the sun was higher than 30° the reflected heat was hardly appreciable. My own observations confirm these results, for I found at Alum Bay, Isle of Wight, that the reflection from a ruffled sea, at 6.45, in May, added no less than forty-four per cent to the direct solar heat.

It is obvious, therefore, that the Davos sanitarium is much indebted to its snow-covered valley for a winter day-climate which is so genial as to allow the patients to spend nearly the whole of every sunny day in the open air, although the temperature of the air may be 15° or 20° below the freezing-point. Five minutes after sunrise, many of the patients walk in the open air without any special wraps, and some of them even without overcoats. In the brilliant sunshine, one feels comfortably warm sitting in front of the hotel in a light morning coat.

3. —Davos is well sheltered from general atmospheric movements, and, as the surrounding snow can not be warmed above the freezing-point, no local currents or valley-winds can be set up. An almost uniform calm, therefore, prevails during the continuance of snow. This immunity from air-currents is of the highest importance to the patients, for, without it, they would not be able to sit out-of-doors and enjoy the free and comparatively germless air as already described. In still though cold air the skin is less chilled