NATURAL HISTORY. 91 



" ' Tis raging noon ; and, vertical, the sun 

 Darts on the head direct his forceful rays, 

 O'er heaven and earth, far as the ranging eye 

 Can sweep." THOMSON. 



235. Why do sudden storms destroy scent? 



Because they rapidly change the conditions upon which it 

 depends. Storms of rain produce a superabundance of wet ; storms 

 of wind dry the air, and disperse the effluvia ; storms of hail and 

 snow produce cold, and, if succeeded by an immediate thaw, result 

 in a wet surface, with sluggish evaporation ; but if no thaw occurs, 

 then a cold dry air rests over the earth. 



286. Wliy are sunshiny days not good for scent ? 



Because then there is a rapid movement of the vapours of the 

 earth, from the surface to a considerable elevation in the atmo- 

 sphere. This may be observed in what is called the " steaming " of 

 the earth on a hot day. The scent is, in such a condition, borne 

 away, and dispersed above the reach of the dogs employed in 

 the hunt. 



287. Why is a warm day without sunshine good for scent ? 

 Because then the evaporation from the earth's surface proceeds 



gradually. Instead of rising rapidly under the glaring heat of the 

 sun, the vapours lie for a time upon the surface ; and when the 

 Tapours lie the scent lies also. 



288. Why does scent lie badly upon fallows and beaten roads ? 

 Because there is nothing to detain it ; every blade of grass, or 



moss, or frond of fern, serves to give stillness to the stratum of air 

 immediately over the earth's surface. But where there are no such 

 checks to atmospheric motion, every impulse of the air spreads far 

 and wide, and disperses all local exhalations. 



289. Why is scent frequently good by hedgerows, when bad in 

 the coppice or in the open field ? 



Because the coppice may be too wet, and the scent be drowned ; 

 and the open field, being quickly dried by the sun, or swept by a 

 brisk wind, the scent may be dispersed ; while the hedgerow, 

 sheltered from the wind, and partially so from the sun, may 

 preserve the conditions required. 



