1874.] 



Thermometric Observations in the Alps. 

 I. Blackened bulb in vacuo. In sunshine. 



319 



This thermometer was clamped to an alpenstock at a height of about 

 five feet from the snow in all the observations recorded in this paper. 

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

 mum 12-8 C. (55 Fahr.); at 9 A.M., 8'5 C. (47'3 Fahr.); at noon 

 and at 3 P.M., 12'8 C. (55 Fahr.). The maximum in the shade was 

 10-4 C. (50 0< 7 Fahr.), and the minimum on grass in the shade 1*7 C. 

 (28-9 Fahr.). 



II. Plain mercurial thermometer with black glass bulb. In sunshine. 



III. Plain mercurial thermometer with black glass bulb. In shade. 



IV. Plain mercurial thermometer with black glass bulb, placed in a 

 box lined with padded black cloth and covered with plate-glass 

 inch thick. 



Thus in mid winter the unconcentrated solar rays at Davos are capable 

 of producing, under favourable circumstances, a temperature of 221 

 Fahr., 9 Fahr. above the boiling-point of water at the sea-level, or 

 21 Fahr. above that point at Davos, where I found water to boil at 

 200 Fahr. when the barometer stood at 627'3 millims. 



