on the Temperature of Soils. 
133 
ing: streams and rivers. The atmosphere, in the neighbour- 
hood of currents of water, becomes more highly charged witbi 
aqueous vapour than that of the uplands ; and as the air trans- 
ports and disperses this moisture over the adjoining fields, it 
is condensed and precipitated during the night by the process 
discovered and illustrated by Dr. Wells.* The finely-di- 
vided and filamentous structure of the grasses renders them, in 
addition to their demand for aqueous nutriment, peculiarly 
suitable for culture in these localities. It is worthy of notice that 
the leaves of different plants appear to act in somewhat different 
ways as to their mode of receiving and disposing of dew. A 
blade of grass is sometimes spangled over with dew-drops, but it 
usually becomes wetted throughout its whole surface by the run- 
ning together of the drops, and thus conducts the water to the 
earth in minute streamlets ; whereas, the leaves of the clover, 
cabbage, nasturtium, and many other plants, will be found to col- 
lect it in distinct globules, which may be rolled about on the leaf 
without appearing to moisten it. These drops, in fact, do not 
touch the leaf, but rest and roll upon a pillow of air interposed 
between them and the substance of the leaf. I have not unfre- 
quently procured a tea-cup full of dew, early in the morning, 
from the leaves of a single cabbage-plant; and, on very trans- 
lucent nights, I have seen, whilst watching this elegant and in- 
teresting process, the tender clover-leaf bend beneath the weight 
of its crystal load, discharge it on the ground, and immediately 
begin to accumulate another globule. In the course of three or 
four hours I have observed as many collections and discharges 
of dew by the same leaf. The gradual diminution of the size of 
these drops of water, by evaporation, as the sun exerts its influ- 
ence, has often struck me to be the means provided by nature for 
preparing plants to sustain his increasingly-ardent rays without 
injury ; and it is generally after nights of copious deposition of 
dew that the mornings are the brightest, and the sun's heat the 
most powerful. Cup-formed and horizontal leaves and flowers 
seem to retain all, or nearly all, their collected dew for their spe- 
cial use, as if it were more beneficial to them when so applied than 
to their roots. 
* The French expression, that a river bedeu s (arrose) a country, is more 
correct than the English one, that it waters it. The watering of land is, 
properly, an artificial, the bedewing of it, a natural, process. The dis- 
tance from its banks to which a river can saturate soil with water is rarely 
great; though it is in this acceptation that I have known many persons 
and authors to understand and use the phrase watering. A river, deep 
within its banks, will bedew a country as well as one bank-full ; but the 
former acts as a drain to the land, and therefore does not directly moisten 
the surface of the soil. The term watering, in agriculture, should be 
limited to what we understand by irrigation. 
