METEOROLOGY. DEW. 491 



is bv SO much the greater as the temperature is higher. In very 

 warm climates the^dew is so copious as to assist vegetation essen- 

 ^allv supplvino- the place of rain during a great part of the >ear 



Accordn^ to soml meteorologists dew is most copious near the 

 «pn hmrd of -i country ; very little flills in the interior of great con- 

 iTel'and iKle dt'said oiJiy to be apparent in the vicinity ot lakes 

 and HveTS.* I cannot agree in any statement of this kind made so 

 absolutely I have ne^er had occasion to see more copious dexs 

 than those which occasionally fall in the steppes of ban Martin to 

 the e\rof tl^e eastern Co'rdilleras, and at a very great dis ance 

 from tht sea -the dew was so copious that for several nights I found 

 [[TrnpossS'to employ an artificial horizon of black g ass in order 

 to t^ke the meridian altitude of the stars ; the moment the apparatus 

 was exioseT there was such a quantity of water deposited on the 

 rurfaceE t soon gathered into drops and trickled oif. I found it 

 neceiary to have recourse to mercury to reflect the star under ob- 

 "ervitToif During the clear cahn nights the turf of these immense 

 ph ns ?ecei^^s a considerable quantity of moisture in tlie form ot 

 Sew whlh materially assists vegetation, and by its evaporation 

 fem^ers the excessive heat of the ensuing day. In tropical coun- 

 tries the forests contribute to keep down the temperature. In very 

 hot countries it is rare to be out in a cleared spot, when the mght 

 s favorable to radiation, without hearing drops ot water, produced 

 by theTop ousness of the dew, falling continually from the surrourid- 

 inVtiees so that forests contribute further to produce and to main- 

 am spri^as by acting as condensers of the watery vapor dissolved 

 n the air^ I midit cite a number of observations upon this point 

 m the air. i mi a bivouac between the 



St] 5™ oVjU 18 7 tte mgh'vas .magnificent ; nevertheless, 

 fn the fo.^stvvhich began at the distance o( a few yards from our 

 encampmenjt™i«./afr«-/«"''y.- by the l.ght of the unclouded 

 mooTw" could see the water running from the branches. 



Tt is DOSsMe that the transpiration from the green parts of the 

 trees mlh have been added to the dew condensed, and ^o 'ncreased 



» Kaemtz, Meteorology, translates! Uy W. Walker. London, 1844. 



