330 Mr. Hinds on Climate in conneooion 



after sunrise, but at this time decreasing in quantity. That 

 more dew falls on clear, calm nights than under opposite cir- 

 cumstances, is as old an observation as the days of Aristotle, 

 though he was unable to account for it with the correct yet 

 curious intricacy of the present day. A still state of the at- 

 mosphere favours the terrestrial radiation in which dews ori- 

 ginate ; breezes of wind disturb the formation : thus, in 

 spots which are sheltered, dew forms with most rapidity and 

 freedom. 



A small diminution of temperature is sufficient for the 

 existence of dew ; hence most substances are capable of appro- 

 priating some to themselves during the night. Vegetation 

 surpasses all others in the depression it is capable of produ- 

 cing ; with us this can be observed from 10° to 20° below the 

 temperature of the air, and in the tropics it is still greater. 

 When the atmosphere is for the time so constituted that some 

 of the bodies on the surface of the earth cannot radiate suffi- 

 ciently to attach dew, whilst others are covered with a thin 

 film, the different substances become so many indices of their 

 respective powers in facilitating deposition, and it is not diffi- 

 cult to appreciate the different shades of their radiating pro- 

 perties in this way. 



Not only is vegetation within the tropics dependent on dew 

 for a large proportion of its moisture, but in all latitudes it is 

 the same ; it is here perhaps that the most visible effects are 

 seen ; and, before the heat of the day plants exhibit much 

 vigour and freshness ; yet beyond the tropics, and in those 

 bright latitudes where clear blue skies prevail, the dews are 

 also intense. In California and Chili, countries in similar 

 situations in each hemisphere, a person exposed to the dews 

 soon becomes as wet as after a shower of rain ; it is late in the 

 day in the latter before the sun has obliterated the dew of the 

 previous night. The soil in sheltered situations seems to 

 retain a perennial moisture, and the rains are rare and of short 

 continuance, 



III. Moisture is so great a blessing to the earth, that na- 

 ture everywhere acknowledges its beneficial properties ; and 

 those parts of the world without it are so dreary and desolate 

 as to be totally unfitted for the habitation of man, and even 

 for the existence of animated beings or plants. The large 

 desert tracts which cover occasional portions of the earth, 

 without water, are rendered so thoroughly destitute of life, 

 that not an insect occupies the air or an animal lives on the 

 surface ; man alone, urged by the love of gain, hastily traverses 

 them, taking with him every necessary for the support of life. 

 Yet perhaps there are few situations which, with a plentiful 



