ON THE PHENOMENON OF DEW. 
69 
part of a moist meadow happen to be covered by a garden-hand or bell- 
glass, or by any impervious covering, transparent or opaque, a copious 
dew will be found beneath, while the herbage around is quite dry. 
If two pieces of arable or garden ground be sown at the same time, 
and with the same kind of seed, but having been differently prepared 
for the crops—one of the pieces by trenching, say eighteen inches deej), 
and the other by common digging only—the seedlings will rise on both 
at first equally strong ; but the plants on the trenched part will not 
only outgrow those on the digged ground, but will always be seen to 
carry much more dew, though both are exposed to the same atmospheric 
influences. The same effect may be seen on waste or on uncultivated 
lands, where a stratum or bed of rock lies near or just within the sur¬ 
face. Over the bed of rock dew is always less plentiful than it is where 
there is no rock, or where it lies at a greater depth. 
Dew-drops are iridescent when seen between the sun and the eye; 
and when a person’s shadow is, on mornings, thrown on a bedewed sur¬ 
face of grass or young corn, a halo or glory appears to surround the head 
of the observer’s shadow. 
Dew is formed during clear frosty nights as plenteouslv as it is in 
warm weather, only, in such a chilled state of the air, each floating 
vesicle of water is frozen either before or immediately after it is united 
to the previously-formed globules on the green herbage. 
It has been already observed, that dew-drops are attached to the 
points and acute angles of the leaves of all healthy plants near the sur¬ 
face of the ground. The presence of dew upon a plant is the strongest 
indication of its perfect health and luxuriance. What, it may be asked 
is the cause of this ? Is it because the acute angles, being more promi¬ 
nent, catch the floating vesicles more readily? We may easily conceive 
that, when a larger globule of dew is once formed, it will readily attract 
the smaller globules or vesicles floating near it, and so become larger 
and larger, till it falls by its own weight. But may not these attrac¬ 
tions and condensations of the vapour be caused by some inductive 
power of the vegetable organisation ? Electric or gaseous currents of 
some kind may be absorbable by the plant, and the points, as they 
always contain the end of a vascular branch of the structure, may 
exhibit some inhaling agency which may carry the vesicles of vapour to 
the inlet. 
I am the more inclined to suggest these questions, because, although 
dew-drops are most commonly seen on the acute angles of leaves, they 
are not always so disposed. The leaves of the common nasturtium, or 
Indian cress (Tropceolum majus ) are what botanists call peltate, that 
is, the foot-stalk is fixed, not in the edge, but to the centre, whence 
