Nomnumm, 1902. MONTHLY WEA!I!ECER REVIEW. 6%
instruments and work of the Weather Bureau to the class in
physical geography of the high school in that city on Novem-
ber 4.
Mr. Charles Stewart. Observer, Vnited States Weather Bureau,
Spokane, Wash., reports that on March 31 he addressed the
pupils of the Spokane High School, on Weather Changes and
their Causes. On April 21 and 22 the pupils visited the
Weather Bureau station and were instructed in the nature and
use of the apparatus and in other matters connected with
meteorology.
MI.. J. B. Marbury, Section Director, Atlanta, Ga., writes. as
follows :
On November 13 of this year I delivered a lecture to a clz~qs at the
Boys' High School in this city. The Weather and the science of forecasting." My talk was mainly a preface to others that I
hare promised togire froiii time to time as my dutieljwill permit. Murh interest was shown in my remark*, wliirh the teacher has sinre infnrniwl
me macle a deep impression upon his class. The increasing interest
shown in the Bureau is. I think. largely due to the lectures and talks
given froin time to time by the various Weather Bureau otticials through-
out the country.
My subject was
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SAMUEL B. PFANNER.
In the death of Observer Samuel B. Pfanner, which occurred
at Toledo, his native city, on November 2, 1902, the Weather
Bureau sustains the loss of a faithful and efficient member of
its observing force. Mr. Pfanner was born May 31,1862. He
entered the Weather Service September 2,1890, and performed
duty at Chicago, Ill., Cincinnati, Ohio, New Orleans, La., San
Antonio, Tex., and Toledo, Ohio. Recently, his health failing
him, his transfer to Phoenix, Ariz., was promptly arranged for
at his request, but his illness took a sudden change for the
worse, and he died before he could esecute the official orders
for his transfer which he had received-D. J. C.
AUSTRALIAN DROUeHTS AND THE MOON.
Mr. H. C. Russell, Director of the Observatory at Sydney,
New South Wales, has published in the Journal and Proceed-
ings of the Royal Society of New South Wales, for the year
1901, a memoir on the relation of the moon's motion in decli-
nation and the quantity of rain in that colony, in which the
author concludes "that rain is clearly shown to come in abuncl-
ance when the moon is in certain degrees of her motion
south; but when the noon begins to go north then droughty
conditions prevail for seven or even eight years. This phe-
nomenon repeated for three periods of nineteen years each
constitutes a marvellous coincidence such that there must be a
law connecting the two phenomena."
The influence of the moon on the weatlier is a matter that
will not be downed by the exercise of any Rmount of commoii
sense. According to the most ancient notions, the moon ought
to have and must have a controlling influence in escess of the
sun's, and every one who seeks to demonstrate its power is liable
to become infatuated with the study. The moon has so many
variations north and south of the equator, north and south of
the ecliptic, to and from the earth, from new moon to full
moon, conspiring with the sun and opposing the sun, that it
does seem as though one ought to be able to iiiake its periocl-
ical oscillations agree with some of the inany variations in the
aspect of the weather. However, we know of but one relation
between the moon and the earth's atmosphere that can be said
to have been settled upon a rational basis and that is the mat-
ter of atmospheric tides. Laplace stated that the semidiurnal
lunar tide in the atmosphere ought to amount to about 0.003
inches of barometric pressure for equatorial stations, and this
agrees with the results of observations carried on at Batavia,
Java. His formule also showed, although we belieye he did
not state the fact, that as the moon moves north and south of
the equator monthly, there ought to be a fortnightly tide, or a
general pull of the atmosphere southward for two weeks and
northward for two weeks. This we believe was first demon-
strated as an observable quantity by A. PoincarB. a civil engineer
of Paris ancl a member of the Meteorological Society of France.
From his articles published by that Society in 1885-1888, we
learn that the average barometric pressure on parallels of lati-
tude around the whole globe, as measured on the International
Map published by the United States Weather Bureau, give
the following results: The pressure on latitude PO0 minus that
on latitude loo is -f- 1.88 millimeters when the moon is in the
estreine south and + 4.8a millimeters when the moon is in the
estreme north. The normal difference is + 3.35. This indi-
cates that when tlie moon is furthest north there is a slight
accumulation of atmosphere in the Northern Hemisphere,
nmounbing to an increase of 1.47 millimeter, or 0.06 inch of
pressure on tlie parallel of -10'.
Now, all lunar phenoinena go through rather rapid periodic
changes. What happens in one part of a lunar month is off-
set by an opposite effect in the other half of that month, or
what happens at the time when the sun and moon conspire is
offset by an opposite effect a few months or years later when
the sun and moon oppose each other. When the moon is far
south and begins to go north, according to Mr. Ruesell,
droughty conditions prevail and continue.for seven or eight
years. But the strange part is that the moon begins ti3 go
north from her estreme southern position every month without
esception, not only just before the seven or eight year drought,
but during the whole of that long period, and continues to do
so during the whole of the succeeding rainy period. How can
her beginning to go north be rationally supposed to be a basis
for predicting droughts in one case and rains in another?
But if we lay aside all these vagaries about the moon, and
recognize Mr. Russell's meteorological induc.tion that droughty
conditions do prevail for seven or eight years in Australia, fol-
lowed by years of rain, and that this cycle of droughts and
rains has been repeated about three times since 1840, then, we
have a fair observational basis upon which to build a rational
axplanation. NOW, this periodicity, or rather the irregular
succession of good seasons and bad seasons is a fact recognized
in every portion of the world. We have also enough data to
show that in most cases a drought in one portion of the
globe is accompanied by rains in other portions, and that the
regions of excess ancl deficiency of rain move over the surface
of the globe month by nionth and year and year. They do not
move in course0 so nearly parallel as to justify long range
predictions any more than do our storm centers, but the move-
nients are certainly governed by laws, and we can begin to
generalize as a first step in the process from induction to de-
duction. For instance, floods in the upper Nile, due to rains
in the highlnncls of central Africa, mean that an unusual pro-
portion of moisture has been taken from the southeast trade
wind current, and that, therefore, when that has turned north-
eastward over tbe Indian Ocean, and has become the southwest
nionsoon of India, i t will bring droughts over the western yor-
tion of that country. A drought in New South Wales, or on the
southeast side of Australia, means a de6ciency in the easterly
winds blowing on that coast, and especially so in the rainy
season, or December, January, February, and Marcli. But
this means that the great area of high pressure over the Indian
Ocean at latitude 30' soiitli has been pushed farther west than
usual, or in other words that the general circulation of the at-
mosphere in that region has been disturbed. NOW, such R dis-
turbance, continued over several months or even years, can
hardly be produced I1y the rapidly changing moon; it might
be due to secular changes in the quantity and quality of the
solar heat, but is most of all, likely to be simply the result of
accumulations of pressure, temperature, and moisture in vari-
ous portions of the earth's atmosphere. Australia has about
the sltme' area as the United States, but lies on the average
626 MONTHLY WEATHER REVIEW. NOWBEE, 1902
about 15O nearer the equator. This latter feature gives i t soil
temperatures and monsoon influences similar to those that pre-
vail in northern Africa, so that it may itself produce an appre-
ciable disturbance of the general circulation in the southern
half of our atmosphere. But the principal cause of the
droughts in Australia and India is undoubtedly to be found
in the changes going on periodically in the relation lietween
the general atmospheric pressure and resultant circulation in
the south and in the north, or between Cape Colony and Ans-
tralia, China and eastern Siberia. In this large portion of
the globe a system of circulation prevails that is affected
but comparatively little by what goes on to the west of it and
north of it. A large quantity of air enters into dhis kegion
from the Antarctic Ocean and passes out of it ah: the sout,h-
west monsoon of southern Asia to eventually become the west-
erly winds of the North Pacific. We may, therefore, look for
some connection by this roundabout way between the droughts
and rains of Australia, or southeastmu Asia, ancl those of
northwestern America.-C. A.
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SHADOW BANDS; SCINTILLATION; INTERFERENCE BANDS.
Among the optical phenomena observed in the atmosphere the
shadow bands seen on the ground during total solar eclipses
just before the beginning and just after the end of totality have
elicited considerable attention. During the total eclipse of
May 28,1900, they were made the special subject of investigx-
tion in connection with Weather Bureau work, as it is highly
probable that they originate in the earth's atmosphere. It is
very rare that there do not exist in the atmosphere ascending
and descending currents of air, which may be on a very minute
scale as well as on a large scale. We conceive of the atmosphere
as filled with minute masses of smaller density slowly ascend-
ing amidst equally minute descending masses of greater density.
This misttire of rarer ancl denser portions produces in general
a loss of 'light and a diminution of sound, which we know under
the familiar name of heat-haze and acoustic opacity, respect-
ively. Another effect is perceived when one views a minute
source of light, such as a fired star, and notices that i t is
apparently wobbling in all directions irregularly. This is un-
doubtedly due to the irregular refractions of the my of light,
which is bent out of its course by having to pass through so
many curved surfaces separating the masses of warm air from
those of cold air. In addition to refract.ion, the ray of light
is also subject to prismatic dispersion, and the star is seen to
oscillate in color from blue, through green and yellow, to red,
especially when it is low down in the horizon. The existence
of this mixture of small masses of air having different degrees
of refracting power is also very prettily shown when we look
at a white surface illuminated by a bright point, such as the
electric light. In this case we see the white surface, not of a
uniform tint, but spotted all over with dark and bright patches,
which are in comtant motion corresponding to the movements
of the nlised cold and warm currents.
During the progress of a total eclipse the sun's disk ie for
a few minutes before and after the totality reduced to an es-
ceedingly thin, bright circular arc, whose light throws iipon
a bright wall, or a white sheet laid upon the ground, visible
shadows perfectly analogous to those just referred to as cast by
the electric light; the principal differences arise from the fact
that the eclipse happens during the warmer daytime and that
the sunlight comes from a considerable angular altitude, whereas
in the electric light we observe during the cooler night-time,
and the bean1 of light is nearly horizontal and passes through
only a small thicknesu of the lower air. I f there were minute
waves on a horizontal surface separating two strata. of air at
some distance above us, then the sunlight refracted at this
wave surface would produce simple bands of shadow on the
ground analogous to the shadows of the ascending warm air.
This is a possible phenomenon, but not one that is likely to
occur without being combined with the more importaut phe-
nomena due to ascending currents analogous to waves in B
vertical plane. To these combined horizontal and vertical
waves we owe the phenomena of scintillation that have been
most patiently observed by Montigny, in the hope of deriv-
ing therefrom some additional knowledge of the conditions
prevailing in the upper air. But the investigations made, by
means of t,he scintillometer, and especially the complete espla-
mtioii by Esner and Pernter, of the origin and nature of
scintillation have shown that but little of any value to dynamic
nieteorology can be espected to be derived from this study,
although i t is important to astronomy. The eclipse of May,
1900, added considerably to the observational data on the
shadow bands or the dark fringes, as tliep are sometimes
called. Among the articles written on the subject we note
one by G. Johnst.one Stoney in the Monthly NoticeR of the
Royal Astronomical Society, vol. GO, p. 586. A memoir by
Beiior V. Ventosn. Astronomer at the Madrid Observatory, is
sumiiixrized on page S6, vol. G2, 1900, of the English journal
Nature, as follows:
The examination of the obserwd facts uppears t.1, support the view
t.liat t,liese shadow phenointma are not diffraction fringes bordering the actual sliadow of the n~uon, but are produced in t.he body of our own atinospliere and are affected by the direction of the wind. FSefiur Ventom has been occupied for some tinie in studying the cur-
rents in the higher regions of our atmosphere by observing the undula-
tions mind the sun and stars with a telescope, and thinks that these upper atmospheric current,s may possil:dy have some bearing on the ques- tiun of t,he eclipse shadow bands: the movement of these higher portions
showing tlirough the quieter lower strata. and being rendered visible on account of different refractive powers. He thinks it would be useful to determine the velocity of these currents by auenionieters at various alti-
tudes. and also tc) observe the undulations round the limb of the sun at tlie tinie ut eclipse. comparing them with the shadow bands in direction
and reiocity of movement. To ascertain if any experimental illustration
of this hypothesis could be presented, he states that bands may be pro-
duced by passing diffused light reflected from a sheet of corrugated glass through a circular aperture repwsenting the sun. over which an opaque
disk. representing the moon, is made to slide. When tlie segment left uiiimvereil is about 5 nim. in width, alternate bright and dark bands can
be obscrved on tt white screen held near, if the length of the segmental
opening is approximately parallel to the undulations of the glass: but if a t right angles they entirely disappear. * * * This hypothesis shows the advisability of recording the direction and velocity o f tho wind during
eclipses.
The subject of the shadow bands has been especially con-
sidered l.ry Prof. F. H. Bigelow in the third chapter of his
Eclipse Meteorology and Allied Problems. On page 57, after
tlie collation of observations at many stations, he says:
The direction of the cusps of the visible arc of the sun and the direc- tion o f t.he shadow bands are generally parallel to ea.ch other, and this
direction varies distinctly between the center of the path of totality and
the edge of the path, yet, keeping up the same parallelism. These two geonietric facts are practically decisive in regard to the origin of the bands * * *. We. therefore, dismiss the dwraction theory from
further consideration. We are, therefore, brought to conceive of the
umbra [or central blackest portion of the moon's shadow] as surrounded by s~iiiiopaque rings * * * of such a character that the crescents
of the siiii's disk will cast clown images upon the ground through a flick-
wing and wavy medium. The widt,li of the bands was found to be on the
average 1.37 inches before totality, and 1.21 inches after totality; the widths of the bright spaces were 8.15 Inches before and 9.24 inches after
tohlity.
Owing to the irregular refractions of sunIight passing
through a iiiisture of small masses of warm and cold or dry
and moist air, the air must contain an immense number of small
beams of light slightly inclined to each other and some of
t,hese produce what are known as optical interference. This
subject is esplained fully in all treatise on physical optics (see
also Watson'a test-liook of physics). Interference is the cause
of numerous well-known phenomena, such as the colors seen on
irridescent mother of pearl and the magnificent ruled gratings
of Rowlrtnd; also the so-called colors of thin plates seen in