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THE FARMER'S MAGAZINE. 



tracted the attention of mankind. One can hardly 

 read the observations of holy writ, without being 

 struck by the remarks of the sacred writers ; ob- 

 servations which modern investigations seem often 

 so well to verify. We have seen how currents 

 of air have been proved to cross each other, and so 

 return back to their sources the streams of air 

 which " the trades " and other winds have with- 

 drawn. Thousands of years since, we find it ob- 

 served that "the wind goeth towards the south- 

 and turneth about unto the north, it whirleth about 

 continually, and the wind returneth again according 

 to his circuits" {Ecclesiastes \, 6.). Job seems 

 to have regarded as a mystery "the balancing of 

 the clouds " (xxxvii. 16). But he was aware of 

 how rain exhausted those clouds (xxxvii. 11). 

 But how that rain was produced out of the cloud 

 he merely inquires (xxxviii. 28). The sraallness 

 and gentle falling of the drops of rain had not 

 escaped his attention (xxxvi. 27). Modern 

 philosophers once disputed whether dew descended 

 from heaven, or was emitted from the earth. It 

 has long been decided that Solomon was right 

 when he said that the dew " drops down " {Pro- 

 verbs iii. 20); and as Zechariah says (viii. 12) 

 " from Heaven." There are many other observa- 

 tions scattered through Holy Writ which seem to 

 be not a little remarkable, when viewed in connec- 

 tion with modern scientific researches. For 

 instance, it is now more than suspected that the 

 sun, with all its planets and their satellites, are 

 moving around one vastly larger centre, and that 

 that central sun, is very likely to be one of the 

 Pleiades. Job asked, thousands of years ago, 

 (xxxviii. 31) " Canst thou bind the sweet influences 

 of Pleiades ?" 



Dew. 



The insensible vapour, of which we have noted 

 the birth, in the evaporation from the earth's sur- 

 face, appears again on the earth in its first and 

 softest way in dew — a phenomenon full of interest. 

 Travel where we may, dew seems to be ever ready 

 to descend ; to bless our thirsty soils, and give life 

 to the vegetable world. With us, it has been cal- 

 culated to amount, soft and insensible as is the 

 descending stream, to five inches of water in depth 

 every year, or 500 tons per acre. Many interesting 

 observations rivet our attention with regard to dew. 

 Its deposition is found to be greater in valleys, and 

 near to running waters, than in dry elevated situa- 

 tions ; in fact dew is almost always to be found in 

 such low lying situations after the sun is down. 

 This dew sometimes extends to considerable 

 distances from the stream. Similar observations 

 have been made in the East Indies. Colonel Sykes 

 {Trans. Roy, Soc. 1850, ^j. 343), observed in 

 Mohol that garden produce, which is there usually 

 irrigated during the day time, is covered with a 

 copious dew every morning. The lands bordering 

 the gardens for 40 or 50 yards around were shghtly 

 sprinkled with it, but there was not a vestige of it 

 beyond that distance; hence he inferred that 

 aqueous vapour had been taken up by the action of 

 the sun during the day, suspended over the spot, 

 and deposited by the lower temperature of the 

 night as dew upon the land. In other observations 



made at Poonah, he found that in September and 

 October, when there was not any dew in the can- 

 tonments, or in the fields of standing grain, it 

 would yet be found on the banks of rivulets ; but 

 in these, 15 to 20 feet from the water were the 

 limits of the deposition. These phenomena are 

 chiefly remarkable in calm weather. 



When by the cooling of the surface of the earth 

 the aqueous vapour is condensed and becomes 

 visible, we call it dew; if the temperature of the 

 earth is reduced below 32*^ that dew becomes 

 frozen, and then we call it hoar-frost. This was 

 another of the meteorological mysteries which 

 sorely puzzled the early dreamers of philosophy.- 

 The alchemists had a wild notion that dew was an 

 exudation from the stars ; they manipulated upon 

 it in all kinds of unmeaning ways, since they hoped 

 to find in it gold ; great were the disputes amongst 

 later enquirers as to whether it came from the at- 

 mosphere or the earth. The explanation originally 

 given by Wells is that now commonly received, 

 viz. : — that it is an effect of a decreased tempera- 

 ture of the portion of air in immediate contact with 

 the soil. When the earth, during the day, becomes 

 heated, the vapours ascend in a current ; but when 

 towards evening the force of this ascending stream 

 diminishes, they descend again towards the earth. 

 After the sun is set, the weather calm, and the sky 

 serene, the soil radiates, and thus its temperature 

 descends several degrees lower than that of the 

 stratum of air immediately resting upon it, then, as 

 Von Kaemtz observes, the phenomenon of the 

 precipitation of vapour on a cold glass, when 

 brought into a heated room, takes place on a grand 

 scale, and the grass is covered with dew. This fall 

 of temperature always precedes the formation of 

 dew. The greater the fall of the thermometer on 

 the surface of the soil, the greater is the amount of 

 dew deposited. The agriculturist and the gardener 

 are well aware that nights with heavy dews are very 

 cold ; but this cold is the cause not the effect of 

 dew. 



Everything which opposes the radiation of heat, 

 a screen either above or beside the object, for 

 instance, prevents the formation of dew. Plants 

 placed beneath a tree are less wetted than others 

 which are unshaded. I have constantly noted that 

 the deposition of dew under trees on my lawn 

 varies considerably with the kind of tree. Under 

 a wych elm there is rarely any deposition on the 

 grass beneath ; under the oaks immediately adjoin- 

 ing, the deposition is early and copious. It is 

 necessary for the deposition of dew, that the sky 

 should be unclouded, and little or no wind. When 

 the sky is clouded indeed, there is but little radia- 

 tion, so there is no cooling of the soil, and conse- 

 quently no condensation of dew. When there is 

 wind, the same effect is produced, for then a cur- 

 rent of warmer air carries off or preserves the 

 temperature of that which is immediately |in|(Contact 

 with the cooling soil. The accumulated clouds 

 often portend rain, and as they prevent the forma- 

 tion of dews, hence comes the old weather observa- 

 tion, that " absence of dew on the grass portends 

 approaching rain." 



The deposition of atmospheric moisture in dew 

 is not confined to the surface of the soil ; wherever 



