1874.] 



Thermometric Observations in the Alps. 



321 



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

 maximum 19-5 C. (67-l Fahr.) ; at 9 A.M., 9-6 C. (49-3 Fahr.) ; at 

 noon, 18-6 C. (65-5 Fahr.) ; and at 3 P.M., 19-5 C. (67'l Fahr.). The 

 maximum in the shade was 10'5 C. (50- 9 Fahr.), and the minimum on 

 grass in the shade -3-l C. (26-5 Fahr.). 



December 25th. The sky was again deep blue and perfectly cloudless. 

 The air was also apparently clear, except at about 9 A.M., when the village 

 and valley became immersed in a light fog, which consisted of minute 

 snow crystals. On this and most subsequent days isolated crystals could 

 be distinctly seen floating in the air, by placing the eye in shadow and 

 then looking into the sunshine. The abundance or paucity of these 

 suspended and, under ordinary circumstances, invisible snow crystals 

 must exercise a powerful influence upon the intensity of solar radiation. 

 To this cause, for instance, it was probably due that at 1.45 P.M. on this 

 day, although the sky was perfectly clear and the sunshine most intensely 

 brilliant, the blackened bulb in vacuo only stood at 35 C. in the sun, 

 whereas at noon, when all the conditions were apparently the same 

 (except, of course, the sun's altitude), the temperature was 5 C. higher. 

 The following readings were taken : 



I. Blackened bulb in vacuo. In sunshine. 



II. The black glass bulb on the snow eight minutes before sunrise 

 marked 12-8 0. At noon in the shade it stood at -9-l C. Height 

 of barometer 630 millims. 



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

 maximum 10-4 C. (50-8 Fahr.) ; at 9 A.M., 46 C. (40-3 Fahr.) ; at 

 noon and at 3 P.M., 10-4 C. (50'8 Fahr.). The maximum in the shade 

 was 7'5 C. (45-5 Fahr.), and the minimum on grass in the shade 

 -2-7 0. (27-2 Fahr.). 



December 26th. Not the smallest cloud was visible during the whole 

 of this day. The sky was intensely blue and the air perfectly calm. 

 Atmospheric pressure 630 millims. Fifteen minutes before sunrise the 

 thermometer on the snow marked 16*7 C. At 1.50 P.M. the same 

 thermometer in the shade stood at 4'l C. The following readings in 

 the sunshine were made with the blackened bulb in vacuo \ 



