'Evening and Morning Dbiv. 1 1 9 



menon will be renewed on the €aft fide of the obferver, vvitli 

 the f^me circumfiauces as the preceding evening, and with 

 the fame gradations and the fame eflc£t when the fun is ftiU 

 below the horizon ; but with this very remarkable difference, 

 that the effefts will be much ftronger than thofe of the even- 

 inc : there will therefore be more wind, more moifture de- 

 pofited, and a more fenfible cold. The reafon of this is, that 

 in the evening the precipitation of water, the wind, and the 

 cold, which accompany it, muft be diminiilied, becaufe the 

 whole takes place in the neighbourhood and by the mix- 

 ture of air, which the fun has heated during the day; while 

 in the morning the coolnefs of the night-air leaves or gives 

 to the phenomenon a little more effeft. 



We fee alfo that in the two temperate zones, where there 

 is a greater difference between the temperature of fummer 

 and winter, and where the length of the days and nights 

 vary a great deal, the cffciSts of the evening and morning dew 

 will be varied and irregular. In fummer, if the air has 

 diffolved more water during the day, the diftillation of dew 

 takes place in air ftrongly heated, and that of the morning 

 dew in air which the fliort duration of the night has cooled 

 only to a certain point : in that cafe, the folution of water is 

 confiderable, and the precipitation of dew leffened. In win- 

 ter, on the other hand, the caufe of the folution is Icfs, but 

 that of precipitation greater. Local circumitances, and par- 

 ticularly the neighbourhood of water, muft alfo have an in,- 

 fiuence on thcfe effeiSls. Fine weather increafes them, and 

 renders them more fenfible, but cloudy weaiher leffens or 

 annuls them. 



Under the torrid zone a greater equality prevails belvveen 

 the days and the nights, fince at the equator they confift of 

 twelve hours each throughout the year. The difference of 

 temperature in fummer and winter is lefs ; that of the day in 

 comparifon of the night is greater than in our latitude, the 

 heat of the day is iar more intenfe, and the Iky is almoll al- 

 ways fercne and uni;louded. It ought thence to follow, that 

 the evening and morning dew will be more fenfible m fuch 

 a fcorched climate than in any other part of the earth. This 

 lias indeed been obfervcd by travellers. In Egypt, Turkey, 

 , 9 ^^'^^* 



