You therefore naturally and rightly come to the conclusion that far more vapour rises out of the ground during the night than condenses as dew on the grass, and that this vapour from the ground is trapped by the tray. Much of the rising vapour is generally carried away by the passing wind, however gentle; hence we have it condensed as dew on the roofs of houses, and other places, where you would think that it had fallen from above. The vapour rising under the tray is not diluted by the mixture with the drier air which is occasioned by the passing wind; therefore, though only cooled to the same extent as the air outside, it yields a heavier deposit of dew. If you place the tray on bare ground, you will find on a dewy night that the inside of the tray is quite wet. On a dewy night you will observe that the under part of the gravel of the road is dripping wet when the top is dry. You will find, too, that around pieces of iron and old implements in the field, there is a very marked increase of grass, owing to the deposit of moisture on these articles--moisture which has been condensed by the cold metal from the vapour-charged air, which has risen from the ground on dewy nights. But all doubt upon this important matter is removed by a most successful experiment with a fine balance, which weighs to a quarter of a grain. If vapour rises from the ground for any length of time during dewy nights, the soil which gives off the vapour must lose weight. To test this, cut from the lawn a piece of turf six inches square and a quarter of an inch thick. Place this in a shallow pan, and carefully note the weight of both turf and pan with the sensitive balance. To prevent loss by evaporation, the weighing should be done in an open shed. Then place the pan and turf at sunset in the open cut. Five hours afterwards remove and weigh them, and it will be found that the turf has lost a part of its weight. The vapour which rose from the ground during the formation of the dew accounts for the difference of weight. This weighing-test will also succeed on bare ground. When dealing with hoar-frost, which is just frozen dew, we shall find visible evidence of the rising of dew from the ground. You know the beautiful song, "Annie Laurie," which begins with-- "Maxwelton's braes are bonnie, Where early fa's the dew"-- well, you can no longer say that the dew "falls," for it rises from the ground. The song, however, will be sung as sweetly as ever; for the spirit of true poetry defies the cold letter of science. CHAPTER III TRUE AND FALSE DEW Ever since men could observe and think, they have admired the diamond globules sparkling in the rising sun. These "dew-drops" were considered to be shed from the bosom of the morn into the blooming flowers and rich grass-leaves. Ballantine's beautiful song of Providential care tells us that "Ilka blade o' grass keps it's ain drap o' dew."