1874.] Thermometnc Observations in the Alps. 325 



At Greenwich the readings were, with blackened bulb in vacuo : 

 maximum 23- 8 C. (74-9 Fahr.) ; at 9 A.M., 7-2 C. (44-9 Fahr.) ; at 

 noon 10-4 C. (50-8 Fahr.) ; and at 3 P.M., 23-8 C. (74-9 Fahr.). The 

 maximum in the shade was 9-2 C. (48- 6 Fahr.), and the minimum on 

 grass in the shade was --4 C. (31-3 Fahr.). 



During the winter of 1870-71 a series of meteorological observations 

 were made at Davos by Mr. Arthur Wm. Waters, F.Q.S., but I am not 

 aware whether the instruments used were verified. The minimum 

 temperatures observed with a Hermann's metallic spiral thermometer 

 were : 



At Davos. ^StfSr 



November, 1870 -10-7 C. - 5-5 C. 



December, 1870 -29-5 G. - 15- 7 C. 



January, 1871 - 20'7 C. - 11-1 C. 



February, 1871 - 187 C. - 5-0 0. 



The maximum sun-temperatures observed with a blackened bulb in 

 vacuo were : 



. , -r> Corresponding tempera- 



At Davos. tur^t Greenwich. 



November, 1870 46-3 C. 35-l C. 



December, 1870 46-l C. 26-0 C. 



January, 1871 47'3 C. 26-6 C. 



February, 1871 52-2 C. 38-8 C. 



The chief remarkable things about the observations made last winter 

 are, first, the very high sun-temperatures prevailing contemporaneously 

 with very low air- or shade-temperatures, and secondly, the compara- 

 tive uniformity of the solar heat from sunrise to sunset. Thus on the 

 29th of December, whilst the temperature of the air was 18'l C., the 

 sun-thermometer stood at +37 C., and on the following day, with an air- 

 temperature not exceeding 12-8 C., the sun-temperature was 38-5 C. 

 Again, the sun-temperatures observed on the 26th of December illustrate 

 the comparative uniformity of solar radiation during the day, when the 

 sky remains cloudless. Twenty-five minutes after sunrise the solar 

 thermometer indicated 31-8 C. ; at noon it stood at 42-5 C., and at 

 thirty-five minutes before sunset it recorded 33 0< 1 C. 



Besides the intensity of solar radiation and its comparative uniformity 

 during the day, the rarity and calmness of the air are important factors 

 amongst the causes of the peculiar climate of Davos. With the baro- 

 meter standing at 615 millims. 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 influ- 

 ence upon the sensation of heat and cold, because the maximum proportion 

 of aqueous vapour present in air near C. is everywhere small, and the 

 specific heats of equal volumes of air and aqueous vapour are not widely 



TOL. XXII, 2 C 



