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Show 192 FORMATION OF DEW. composed, and has an efflorescence of salts of lime on it; and it will be found that the buds of the tre~s are black, and full of cankers, and rusty, and in sof!le places breeding fungi, unless they are natu~al mhabitants of moist atmospheres. The flags m the pavement, and even the granite in the streets, bear marks of this humid and corrosive nature; and an atmosphere which produces those effects cannot be the most salubrious for human beings. So much for the earth fogs. . Dew, it has been said, is produced much m the same way as these fogs, and the only difference is that the dew is produced only at or on the surfaces of the objects upon which it appears, and is really a product of the _atmospher~, though it _does not fall through it; while the fog IS, at least m the first mstance, a product of the surface over ~hich the air is ; though, after it has cooled the au down t? a certain temperature, it may, and often does, brmg about that state of things which produces dew. There are instances, however, in which the fog does not brino- the temperature of the air down to the dew-poi~t, and these are usually called "dry fogs," though they are composed of water, and, according to their densities, contain as much water as those fogs which are accompanied by dew. Dry fogs are day-foo-s rather than night-fogs, as, of course, the surfac~ of the earth does not cool so fast when it is merely veiled from the sun by a fog as when the sun is down. s "imple as the process of the formation of dew is, there have been some mistakes and disputes about it. Some have written and spoken about " rising" dew, and others about" falling" dew. But the ~ew, as dew, that is, as visible drops of water, neither rises nor falls, but is formed on the surfaces ;_ and. as the air has access to all surfaces except the mtenor · surfaces of air-tight vessels, the dew may form on the side of a substance or under it, just the ·same as MORNING DEW. 193 on the top; for while _the wa~er in the air is invisib~ e vapour, and floats m the au, it must go with the ~Ir whereve~ that goes; and thou~h :1 is under an Inverted basm on the g~ass, thP L • • s no reason, if the surface cools as rapidly, wh" , 11ere should not be dew_ th_er~ as well as anywhere else. If, indeed, the basm Is mverted before sunset there should be and really there is, more dew the're than upon th~ same surface of the _exposed grass. Take a large flower-pot? and_ turn 1t down a little before sunset, and leave It a little after. sunrise, on the same spot, for a week, and you will find a circle of strono-er and greener grass than that around. Even if you keep the pot constantly. on the place till the grass becomes yello~, you will find that it is light that has been wantmg, and not moisture. Every gardener knows that fact, and acts practically upon it '\\ ,e_'l he turns do_wn a flower-pot over his piping~ !>f J?IDk~ or car!latwns to make them strike, by nourlshmg them with the gentle dew which their own cool l~aves melt out of the warmer air. A shady tree will refre~h a man with dew when he escapes from the burn.mg sun, even though he be so hot t~at that dew Is evaporated again before it touches him. The dew forms i~to beaut~ful drops on those ( surfac~s between whiCh and It there is a sort of repulslon: Vegetable leaves when in action have that quality, and hence the beauty of the morning dew on the grass. If.those who are fond of looking at gems would get up m the morning, when the dewdrops ar~ large on the grass, and the sun's rays low and slant~ng, they would, by just sittino- or standing a fe~ l!lmutes with their back to th~ sun, et a grabs sight of a far finer casket than any mo~arch on earth can boast of possessing. Many eo le make a boast of having been at court and h p see!l t~e queen in her jewels; but if th~y woul~v~~~ up Ill tmle, they might, a~rnost any sunny morning, |