6 Dr Davy's Meteorological Observations. 



meter in the air was 28°, and on the grass 25''. On a low 

 parapet wall, about twelve feet from a house in the same 

 field, it rose to 31° ; and on the gi'ound, which was not 

 frozen, close to the wall of the house, it rose to 32-5. No- 

 where is the effect of a wall, especially of a southern wall, more 

 strikingly displayed than in this country, in the prevention 

 of hoar-frost, and in shielding tender plants from sudden 

 reduction of temperature, the consequence of radiation. 

 And the same remark is applicable to rocks and trees, 

 especially the dark Scotch fir and yew tree, with their 

 thick umbrageous mass of foliage, and also to the sides 

 of hills of moderate elevation, compared with the valleys 

 below. The natives, taught by experience the differ- 

 ence, almost invariably, in selecting a site for their dwel- 

 lings, avoid the latter, giving the preference to the 

 former. The hillside in early spring, in accordance with 

 what has just been stated, commonly shews signs of active 

 vegetation before the lower meadows ; and also in winter, 

 in fine weather, such as promotes radiation. In December 

 last, the contrast was striking between the fresh green of 

 the hill pastures, and the sad withered hue of the bottom 

 meadows, when not covered and whitened with hoar-frost, 

 as they very frequently were. I would add, that, to the 

 gardener and florist in this district, and, indeed, in our cli- 

 mate generally, the importance of attending to the influence 

 of radiation cannot be too much insisted on. To be convinced 

 of this, it is only necessary to go out on a still clear night 

 into a garden, and observe the condition of plants in different 

 situations as to exposure and protection. I may give an in- 

 stance in farther illustration. Here, at " the Oaks," on the 

 night of the 5th of April, which was beautifully serene, after 

 a warm day, hoar-frost was to be seen at an early hour on the 

 grass-plot, Vliere fully exposed ; but none near trees or walls. 

 At one o'clock A.M., a thermometer on the grass, in an ex- 

 posed situation, stood at 21° ; and in the air, about 4 feet 

 above, at 31° ; on a garden border, within a foot of a stone- 

 wall, it stood at 33° ; against the wall, at 35° ; on the grass, 

 under a yew tree, at 35° ; in the air, under it, at the same ; 

 and in a cavity of the trunk of the tree, about 2 inches deep, 



