, 1874-11-14

amount OF rain falls upon the ocean lar
away from land, and it may be thought
by some that the absence Of trees cannot
reduce the rainfall to an amount less than
the tall at sea, which may be considered
the normal fall. That from some cause
or other a less amount OF rain may tall
upon land than,sea is evident from the ex-
istence of the r~ainless districts Of North
Africa, of Thibet, of Mexico, and OF Peru.
In order to attract rain it has been shown
that the surface must be covered with OBJ
jects (ike trees) which produce a dlmlnu-
ton of temperature which can intercept
the currents of air, and which are good con-
ductors Of electricity. 1t is evident that
as the currents of air nov more rapidly
in proportion to their altitude, that the
more elevated the objects the more power
ful will be the influence exerted by them
tor better or for worse. The whole
amount of moisture raised into the atmos-
phere from the surface of the ocean, and
OF moist earth, vegetation, and fresh water,
must OF necessity be precipitated again,
and that which is not discharged upon the
land IS poured upon the water. The land
from the character Of its surface and the
nature Of its covering as well as from the
degree OF it's elevation presents u selectlye
influence which determines within certain
limits, the amount of water that will be
prccipitatod upon its surface.
Let US imagine three different islands in
the same tropical latitude, distant from
each other, and from other land.
One island shall be covered with
wooded mountains; the second with
bare mountain, and the third covered with
grass. The first island will receive the
normal amount Of rainfall, that is the
amount that would fall upon an equal area
of ocean, and besides this it will receive a
second supply that will have been induced
by the influence of the trees, this influence
being increased by their elevation above
the sea level. The bare rock Of the second
island will receive abundant heat by the
suns rays, and being unable to convert it
into latent heat by the evaporation Of
moisture from vegetation it will discharge
it in the form Of radiant heat both by day
and night. 1t has been shown however
hat the fail Of rain often depends upon the
clothing Of the ground being cooler than
the air but where heated rock is present
Cd the temperature will be actually raised,
and an active repellent action will be set
upin consequence. Dry rock is a bad con-
ductor of electricity and therefore cannot
induce rain by restoring the equilibrium
when it is disturbed by the presence Of n
thunder cloud Neither does it offer the
multitude of points presented by foliage.
Thus none of the rain that trees would
have attracted will be received, and even
q considerable portion Of the normal rain
will be repealed. That part OF tho normal
portion which is not influenced by the
of the surchargcd air with The
surface of the ground, but which is pre-
cipitated from the tropical regions, will
still fall upon the island, and this is the
most violent portion Of the rainfall. The
third island will also receive this violent
portion Of the rainfall which is not depen-
dant upon tho character Of tho surface.
In addition to this when the grass is green
it will attract rain in the same manner os
trees, but to q less extent, because the
eyaporating surface is smaller and the We
getable electrical conductors are fewer
and less elevated. But when the grass be-