20 Dr. E. FranJcland [Feb. 10, 



Diavolezza. o 



Black caoutchouc 39'1 0. 



Snow 61-9 



White paper 65 • 8 



Italy. Bellagio, o 



Black caoutchouc 60 • C. 



Black merino 59 • 



White linen 66-0 



White paper 66 " 3 



Tliese results may be imitated with the powerful light from a 

 Siemens' dynamo-machine. [Experiments shown.] 



The warmth of the air over these surfaces was in the inverse 

 order, caoutchouc heating the air most, white paper and snow least. 

 The nearer the colour of the ground approaches to ivhite, the more 

 genial will be the climate from radiation and the cooler will be the 

 air. The nearer it gets to hlach, the warmer will be the air and the 

 less will temperature be due to radiation. Dark surfaces warm the 

 air ; light surfaces keep it cool, but warm the body by radiant reflec- 

 tion. The diflference is substantially the same out of doors as that 

 produced indoors by a close stove on the one hand, and an open fire 

 on the other ; but calm air is required for the enjoyment of radiant 

 heat. 



The sun's radiant heat may be greatly reinforced by reflection 

 from surrounding objects. There are two kinds of reflectors ; those 

 which, like white paper, white linen, and whitewash, scatter the solar 

 heat in all directions, and those which, mirror-like, reflect it in one 

 direction only. To the former belong snow, chalk, light-coloured 

 sand, and light-coloured earth ; to the latter, water. The former are 

 useful on whatever side they may be, the latter only when they are 

 between the observer and the sun. The observations in the fol- 

 lowing table illustrate this effect of reflection from surrounding 

 objects : — 



Influence of Keflection from Surrounding Objects. 



From a white-washed wall. Pontresina. 



o 



On white paper 10 feet from wall 38-7 C. 



„ in adjoining meadow 27 "7 



From water. Top of cliff at Alum Bay^ Isle of Wight. 



o 

 Direct and reflected rays 31 • 2 C, 



Dhect rnys only 25 '7 



Zurich. One mile from Lake. 



o 

 Direct and reflected rays 34 • C. 



Direct rays only 31 ' 5 



M. Dufour has observed the same phenomenon on the lake of 

 Geneva between Lausanne and Vevay. He has measured the propor- 

 tions of direct and reflected heat at five different stations on the 

 northern shore of the lake, and the results are condensed in the 

 following table : — 



