292 
NATURE 
(¥an. 26, 1882 
Certain tracts of the ocean are known by the absence, | when sailing through a region overspread by the anti- 
or comparative absence, of rain, such rainless regions of 
the ocean being included within what may be called per- 
manent anti-cyclones; that is, tracts of sea over which 
atmospheric pressure is higher than it is all round. Such | 
regions are also remarkable for peculiarly bright clear 
skies and strong sunheat. Similarly the anti-cyclones 
which occur between, or in the immediate neighbourhood 
of cyclones are characterised by dry air and clear skies; 
and it is under such conditions that the strongest direct 
sun-heat is experienced. When in the warmer months of 
the year these anti-cyclones remain practically stationary 
for some time, which at that season of the year not unfre- 
quently happens, it follows that the lowermost strata of 
the atmosphere become abnormally heated; thus bringing 
about a vertical disturbance of the equilibrium of the 
atmosphere, out of which whirlwinds originate. It is 
under these conditions, in all probability, that w/zte 
squalls, or fair-weather whirlwinds occur, the originating 
cause of this special form of the whirlwind being the 
great dryness of the air due to its place in the anti-cylone, 
and the abnormally rapid diminution of temperature with 
height owing to the strong insolation through the clear, 
dry atmosphere. Any cloud that may happen to be 
formed is at a great height. The character of the cloud, 
also, and the commotion and boiling of the sea which is 
observed immediately under it, and accompanies it as it 
moves onward in its course, are clear proofs that the inter- 
space between the sea and the cloud is filled with the 
gyrations of the rapidly-ascending air-currents of a whirl- 
wind, which does not appear as a water-spout simply 
because the air of the ascending currents is too dry or 
the gyrations of the whirlwind are not sufficiently rapid 
to bring about condensation of the vapour into visible 
cloud. 
One of the best marked of the permanent anticyclonic 
recions of the globe is that large region of the Atlantic 
which lies to the west of Northern Africa. Over this 
wide tract of ocean the portion most liable to be struck 
by the white squall or the tornado will evidently be where 
the general drift of the wind issuing from the anticyclonic 
region is approximately antagonistic to the prevailing 
wind as observed at the surface. During the summer 
months, for example, no such antagonism exists between 
the winds of Florida, the southerly winds prevailing there 
being in accordance with the general drift of the winds for 
that side of the anticyclonic region of the Atlantic on the 
one hand, and on the other in equal accordance with the 
monsoonal wind of that coast towards the heated interior 
of the Southern United States. Quite otherwise, how- 
ever, is it with the ocean off the west coast of Northern 
Africa. There the general drift of the winds over that 
part of the region overspread by the Atlantic anticyclone 
is north-easterly; and that this wind prevails at no very 
great height is abundantly shown by the quantity of African 
dust which falls on this part of the sea; whereas the 
surface wind is from the south-west, being strictly mon- 
soonal in its character, or is an inflow towards the heated 
interior of’ North Africa. This is the region of the 
Bull’s-eye Squalls of the African coast—a form of the 
whirlwind which deserves to be more accurately de- 
scribed and investigated than it has yet been, from its 
evident relations to the two great wind-systems referred 
to above, and to the very different states of atmosphere, 
which these imply over the restricted region where the 
bull’s-eye squalls occur. 
The white squall accompanies fine weather, and is 
preceded immediately, and for a space of time more or 
less extended, by a clear sky and calm, or all but calm, 
weather. Its appearance is sudden, its duration brief, 
but its destructive power is occasionally so dreadful, that 
it has been known to strip a ship of every sail and mast 
in afew seconds, and leave it lying a helpless log amidst 
the tremendous seas which* follow it. 
cyclone, to make the outlook too close and sharp, particu- 
larly when the weather looks singularly fine, the skies 
beautifully clear, the air calm or all but calm, and she. 
temperature and moisture of the air noticeably high. 
On May 17, 1763, Cook saw six waterspouts on Queen 
Charlotte Sound, in one of which a bird was seen, and in 
arising was drawn in by force and turned round like a 
spit ; an important observation, as Prof. Ferrel remarks, 
as showing that there is draught and an inflowing of air 
from all sides to supply the ascending current. In other 
words, the behaviour of the air-currents of a waterspout 
is precisely that of the air-currents of a duststorm, as 
actually seen in its dust-laden currents. 
Another observation of great importance was made by 
Prof. F. E. Nipher, near Schell City, Missouri, and pub- 
lished in NATURE, vol. xx. p. 456, which, from its great 
importance in the study of whirlwinds, we here quote :— 
‘* While making magnetic determinations at Schell City, Mo., 
a whirlwind of some violence passed near our tent, moving with 
the characteristic swaying and halting mo‘ions of the tornado. 
Its base was quite pointed, and about 2 feet in diameter. 
“ Unlike those seen last year, and decribed in NATURE abouta 
year ago, there were no surface-winds strong enough to bear 
dust along the surface of the ground, but the dust carried up in 
the vortex was collected only at the vertex of the whirl. The 
dust-column was about 200 feet hizh, and perhaps 30 or 40 feet 
in diameter at the top. The direction of rotation was the same 
as that of storms in the northern hemisphere. Leaving the road 
the whirl passed out on the prairie, immediately filling the air 
with hay, which was carried up in somewhat wider spirals, the 
diameter of the cone thus filled with hay being about 150 feet at 
the top. It was then observed, also, that the dust-column was 
hollow. Standing nearly under it the bottom of the dust-column 
appeared like an annulus of dust surrounding a circular area of 
perfectly clear air. This area grew larger as the dust was raived 
higher, being about 15 or 20 feet wide when it was last ob- 
served. This whirl could be observed half a mile, finally 
disappearing over a hill.” 
Hence in this whirlwind the behaviour of the wind was 
exactly what is seen to obtain in the dust-storm. The 
light objects on the surface of the earth were lifted and 
carried up in whirling gyrations with a velocity so con- 
siderable that the hay and dust were driven outward by 
the centrifugal force of these gyrations to some distance 
from the axis of the whirlwind, leaving round the axis a 
shaft of perfectly clear air, the diameter of which gradu- 
ally increased as the gyrating air-currents ascended, and 
friction was thereby diminished. An increase in the 
velocity of the ascending gyrations would, if sufficiently 
great to produce the required rarefaction, have filled the 
clear axial shaft of the whirlwind with cloudy vapour. 
ELECTRICITY AT THE CRYSTAL PALACE 
I. 
C Been work of installing the apparatus and machines at 
the Crystal Palace Electrical Exhibition is pro- 
gressing very slowly, owing perhaps to the absence of 
any formal day of opening to hasten it. Before every- 
thing is fairly in its place, at least another fortnight will 
have elapsed, for a great deal of time is necessarily con- 
sumed in making electrical connections. Enough bas 
been done, however, to give a fair idea of what the ex- 
hibition will be like. The official catalogue has been 
published in advance, and there are about five hundred 
exhibitors enumerated in its pages. Of these only about 
a hundred are from abroad, including America, so that 
the exhibition is rather an English than an “ interna- 
tional” one. At the Paris International Exhibition of 
Electricity there were over two thousand exhibitors, aud 
of these only one-half were French, the remainder being 
from every other civilised country, including Japan, which 
It is not possible, | offered the first fruits of its electrical science in the shape 
