, 1891-11-04

battles Of Dresden and Waterloo the concus-
sion of the air by the cannonade led to the de-
scent of torrential showers; and we are remind
ed that 'in the same way rain follows a peal
of thunder caused by the passage of lightning
flash through a moisture Laden atmosphere DC.
Now, all this noise and disturbance have no
more to do with the production ofrainfall than
has the thrashing which the village rain
maker of Central India receives from his fellow
villagers to stimulate him to fresh e~xertions
when he is thought to have neglected the per-
formance of his official duties, or the London
street boys whistle, with which Sir Samuel
Baker started a rain-making king in the Sou
thern Soudan, and which was followed by
such, a deluge that even the rain-making po-
tentate implored him to arrest the working of
the spell. = The effect of a conclusion, as
such is to produce an instantaneous compress
sion of the air, and a momentary heating in a
wave which travels away at the rate of about
1000 feet per second, and is incapable of general
ing any transitional movement of the atmos-
phere and certainly of promoting condensation.
Nordo we know of any recorded observations in
support of the idea that it can cause the coale-
scence of cloud corpuscles into raindrops.
Neither does the conclusion of the air by a
thunder clap stand to the %downpour that fol-
lows it in the physical relation of cause to eff
feet. In this case Sir John Herschel adopts
the opinion originally put forward by Eeles,
that the order Of ucecssion is the reverse of
that here assumed, that the formation of the
rain-drop is the antecedent phenomenon and
the lightning-fash land ergo the thunder) the
consequent; the electrical discharge being
dete rmined by the sudden concentration of the
electricity Of SAY one thousand corpuscles on
the surface of the single resulting raln-drop
in which case it's intensity would be increased
ten-fold. What causes the coalescenco Is still
a matter of much obscurity, though some light
has been thrown upon it by the ingenious ex-
pertinent exhibited by Mr.. Shelford Bid
we'll at the Royal Society's com0ersazione
on May II, 1890, and described in vol.
xiii, (p. 91.) of this journal. When the shadow
of a small (condensing) steam jet was thrown
upon a white screen, under ordinary conditions
it was of feeble intensity and of a neutral tint;
but when the Jet was electrified, the density
of the shadow was at once greatly increased,
and it assumed a peculiar orange-brown tint.
It appeared that identification promoted the
coalesCence Of the exceedingly minute partl-
Giles of water contained in the jet, thus form
ing drops large enough to obstruct the more
~refrangible rays of light. On this view, then,
identification would appear to be the cause OF
coalescence, and the electrical discharge the
Interior result; but as yet we know too little
of the molecular processes concerned. IN the
formation of a rain drop to attempt anything
like a complete theory.
In conclusion, while we cannot but recog-
nize the high interest of General Dyrenfurth's
results, with the imperfect information at pre-
sent before us we cannot regard them as conclu-
sive. It is the characteristic weakness OF all
experiments of the kind that many of the es-
sential circumstances are scarcely ever re-
corded, or perhaps even capable OF beng
brought within the limits of observation: and
thus the logical conditions of a proved con-
clusion cannot be fulfilled. For instance, 1t
is very unlikely that anything Is known OF
the state Of the atmosphere in respect OF It's
humidity and it's vertical temperature deere
ment at the elevation at which the balloons
were exploded, and yet as we have seen, these
data lie at the very root of the whole matter.
However, arrangements are being made for
further operations at Ell Paso and in Western
Kansas, SO that it will not be long before the
highly interesting and practically important
problem of stimulating the precipitation OF
rain will receive a more satisfactory solution.
II. f. B.
x This story has probably been told by Sir
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