The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1893-08-06

motion at the desired rate when they are
not disposed to move by natural forces.
This may be easily apprebended if the
simplest process of rain making be eX-
amined; such as is seen in our summer
thunder showers.
The first feature to be noticed in the
cloud of thunder shower is the manifest
ascent of its upper parts. Its outlines are
convex in many small curves, and if any
one OF the curves is carefully watched it
is seen to grow rapidly upward and out
ward. The summit of the cloud spreads
forward in a thin fbrous sheet, as if
OVERLOOKING at the top OF the ascending
current.
Anyone on the watch through the sum-
mer may find examples of such storm
clouds in all stages of growth. A small
cloud beginning to form in his neigh bor-
hood may drift away, growing as it re-
cedes to the east, and yielding rain to his
neighbors in the next county or state. A
cloud that began to grow a hundred miles
or so to the west, drifting along at the
rate of thirty or forty miles an hour, may
have attained rain making size when II
reaches his point of observation. A storm
that began about noon several hundred
miles to the west may reach the observer
after nightfall, generally weakening in
the absence of sunshine, perhaps dwindl-
ing away without giving him any rain,
although it refreshed hundreds of square
miles further west.
These local storms OF summer generally
have a brief life of six eight or ten hours,
seldom more. Their essential feature is
the ascent of a vast volume of air from q
higher level and the condensation of its
vapor by the cooling that accompanies
expansion in ascent.
! We will consider the case of large
cumulus or thunder cloud, whose war;.
current rises actively to a height of two
or three miles at least, and there spreads
out horizontally. having found air OF Its
own temperature, above which it will
/ ascend no higher. The cloud consists o.
innumerable minute particles of water
most of them less than hundredth of ar
inch in diameter. The question is, why
do the minute water particles grow to the
size of raindrops and fall to the ground
The most important conditions in thl
the process of rain making are, first the
difference in the size of the water par
tjcles, and second, the variation in activ'
ity of the ascending current.
The particles cannot be of equal size
the process of condensation from invisibi
vapor into visible water cannot be so uni
form as to produce particles all of Thu
same volume. A particle that was frs
] formed near the base of the cloud ant
then borne upward, grows as it ascend
by the condensation of more vapor upor
1t; near by, another particle just begun
will be smaller. The larger the particle
the more difficult it is for the ascending
current to buoy it and support it, and tn
more it tends to fall.
The unequal activity of the ascendin,
current in which a thunder cloud /
formed may readily be observed. On
part of the cloud is seen to grow upward
$ faster than another, while near the sum
nit the vertical current becomes almost
horizontal movement, and the clcu,
flows off, an outspreading sheet doatin,
eastward. When it is remembered tina
it is only the vertical component OF tn
ascending current that supports tn
water particles against the downwar
pull of gravity, it is more evident thai
before that, with the unequal size of tn
drops and the variation in the ASCENDING
current, the particles must be carried up
wards at different velocities.
Let us now follow the history of a clou
particle from the time of its first conden
sat1on, near the base of the cloud, till
falls to the ground as drop of rain.
When first formed the particle is minut
and easily borne aloft by the ascendin
currents in the core of the cloud. II !
happens to be caught in one of the de
scending eddies with which thunde
clouds are often fringed around the base
it will be carried downward, dissolvin
away into vapor again as it falls slowl
into the warmer lower air. The wastin
} away of the wisps OF descending clou
. edges is often noticeable in thunder show
ers, but the descending motion must
regarded as exceptional and local. CON
pared to the great ascending motion o
which the growth of the cloud depends.
The more unusual course of the partic
: is at first upwards. AS it rises with tt
cooling air it's size increases by the ful
Their condensation of vapor upon it, ais
by occasional collisions with other drop'
When near the top of the cloud it may
!. frozen in the low temperatures there pr
: vailing, and while thus icy it may recei7
coating of snow; but all this withol
!, reaching any considerable diameter, prof.
, ably not a fiftieth of an inch.
, On approaching the summit of th
cloud, where the vertical ascent of tt
| air is changed to the horizontal outflow
/ the particle is less supported and may b.