August i -j, 1882] 



NATURE 



381 



This heated matter is :— (1) Sea or land. (2) Suspended matter 

 in the air— cloud, dust, smoke. (3) Aqueous vapour. 

 These two factors were first considered in their relation to 



Country Climate 

 The feeling of warmth and comfort in the open air is produced 

 either by direct solar radiation, even if the air be very cold ; or 

 by the warmth of the air itself. Upon both of these, the nature 

 of the surface upon which the sunlight falls has a paramount in- 

 fluence, as is seen from the results of experiments on sun tem- 

 perature recorded in the following table : — 



Influence of Surface 



Norway. 



Green grass 



Parched grass 



Bare soil 



Newly-mown grass ... 



White paper 



Hesse Cassel. 



Black caoutchouc ... 



Black silk 



Plane glass mirror ... 



Slightly concave metallic mirror ... 



Green grass ... 



White paper... 



Switzerland. Mortaratsch Glacier. 



Black caoutchouc^ ... 



Bare white ice 



White paper 



Summit of Gornergra!. 



Dazzling white snow 

 White paper 



Pontresina. 



White paper... 



Grass 



Grey rock ... 



Black caoutchouc 



Black caoutchouc 

 Snow... 

 White paper 



Black caoutchouc 

 Black merino 

 White linen .., 

 White paper 



Italy. Bdlagio. 



57'3C 



612 



606 



56-5 



735 



547 C. 



56-5 



64 o 



640 



5»-5 



677 



39 o C. 



47-5 



53° 



59 o C. 

 612 



662 C. 

 54"° 

 54 o" 

 564 



39-1 C. 



619 



658 



600 C. 

 59-0 

 660 

 66.3 



These 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 

 leait. The nearer the colour of the ground approaches to white, 

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

 will be the air. The nearer it gets to black, 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 reflection. The difference is substan- 

 tially 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 following table illustrate this 

 effect of reflection from surrounding objects : — 



Influence of Reflection from Surrounding Objects 

 From a while-washed wall. Pontresina. 



On white paper 10 feet from wall 



in adjoining meadow 



387 C. 



277 



From water. Top of cliff at Alum Bay, hit of Wight. 



Direct and reflected rays 

 Direct rays only 



Zurich. One mile from Lake. 



Direct and reflected rays 

 Direct rays only 



312 C. 

 257 



34 -o C. 

 3i'5 



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

 Geneva between Lausanne and Vevay. He has measured the 

 proportions of direct and reflected heat at five different stations 

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

 in the follow ing table : — 



Dufour's Observations 



Altitude of Sun. Proportion of direct to reflected^heat. 



3° 34' to 4° 38' 

 7° 

 16° 



IOO : 6&. 



too -.40 to 50. 



100 : 20 to 30. 



When the sun was higher than 30° the reflected heat was 

 hardly perceptible. Hence this reflection is of the greatest 

 value in w inter, when it is most wanted, and it also tends to 

 equalise temperature during the day ; for in the early morning 

 and evening, when the sun is low, and his direct heat is small, 

 the reflected heat is greatest. 



The bearing of these observations upon winter refuges for 

 invalids is obvious. While the primary conditions to be secured 

 must ever be fine weather and a sheltered position, the next in 

 importance is, doubtless, exposure all day long to reflected, as 

 well as direct, solar radiation. To realise this, a southern 

 aspect and a considerable expanse of water or snow are necessary, 

 and it is important that the sanitarium should be considerably 

 and somewhat abruptly elevated above the reflecting surface, so 

 that it may receive, throughout the entire day, the uninterrupted 

 reflection of the sun's rays. At or near the sea-level, however, 

 it is impossible, owing to solid and liquid matters floating in the 

 lower regions of the atmosphere, to enjoy anything approaching 

 to a uniform temperature from sunrise to sunset. 



Although this suspended matter exists even at great altitudes, 

 the bulk of it floats bebw 5,000 feet, and whilst only one-sixth 

 of the atmosphere is below this height, there is probably much 

 more than one-half of the suspended matter at a lower elevation. 

 As might be expected, therefore, solar intensity is much greater 

 at high than at low elevations, although the temperature of the 

 air continually decreases as it is further removed from the 

 earth's surface. The following tables contain observations illus- 

 trative of this point : — 



