respond in greater or less degree to the sun’s changes of condition
with respect to spots. We cannot doubt that the emission both of light
and of heat is affected by the presence of spots. It is not altogether
clear in what way the emission is affected. We cannot at once assume
that because the spots are dark the quantity of sunlight must be less
when the spots are numerous; for it may well be that the rest of the
sun’s surface may at such times be notably brighter than usual, and the
total emission of light may be greater on the whole instead of less.
Similarly of the emission of heat. It is certain that when there are
many spots the surface of the sun is far less uniform in brightness
than at other times. The increase of brightness all round the spots is
obvious to the eye when the sun’s image, duly enlarged, is received
upon a screen in a darkened room. Whether the total emission of light
is increased or diminished has not yet been put to the test. Professor
Langley, of the Alleghany Observatory, near Pittsburg, U.S., has
carefully measured the diminution of the sun’s emission of light and
heat on the assumption that the portion of the surface not marked by
spots remains unchanged in lustre. But until the total emission of
light and heat at the times of maximum and minimum has been measured,
without any assumption of the kind, we cannot decide the question.
More satisfactory would seem to be the measurements which have been
made by Professor Piazzi Smyth, at Edinburgh, and later by the
Astronomer Royal at Greenwich, into the underground temperature of
the earth. By examining the temperature deep down below the surface,
all local and temporary causes of change are eliminated, and causes
external to the earth can alone be regarded as effective in producing
systematic changes. “The effect is very slight,” I wrote a few years
ago, “indeed barely recognizable. I have before me as I write Professor
Smyth’s sheet of the quarterly temperatures from 1837 to 1869 at
depths of 3, 6, 12, and 24 French feet. Of course the most remarkable
feature, even at the depth of 24 feet, is the alternate rise and fall
with the seasons. But it is seen that, while the range of rise and fall
remains very nearly constant, the crests and troughs of the waves lie
at varying levels.” After describing in the essay above referred to,
which appears in my “Science Byways,” the actual configuration of the
curves of temperature both for seasons and for years, and the chart in
which the sun-spot waves and the temperature waves are brought into
comparison, I was obliged to admit that the alleged association between
the sun-spot period and the changes of underground temperature did
not seem to me very clearly made out. It appears, however, there is a
slight increase of temperature at the time when the sun-spots are least
numerous.
That the earth’s magnetism is affected by the sun’s condition with
respect to spots, seems to have been more clearly made out, though
it must be noted that the Astronomer Royal considers the Greenwich
magnetic observations inconsistent with this theory. It seems to have
been rendered at least extremely probable that the daily oscillation
of the magnetic needle is greater when spots are numerous than when
there are few spots or none. Magnetic storms are also more numerous at
the time of maximum spot-frequency, and auroras are then more common.
(The reader will not fall into the mistake of supposing that magnetic
storms have the remotest resemblance to hurricanes, or rainstorms, or
hailstorms, or even to thunderstorms, though the thunderstorm is an
electrical phenomenon. What is meant by a magnetic storm is simply such
a condition of the earth’s frame that the magnetic currents traversing
it are unusually strong.)
Thus far, however, we have merely considered relations which we might
fairly expect to find affected by the sun’s condition as to spots.
A slight change in his total brightness and in the total amount of
heat emitted by him may naturally be looked for under circumstances
which visibly affect the emission of light, and presumably affect the
emission of heat also, from portions of his surface. Nor can we wonder
if terrestrial magnetism, which is directly dependent on the sun’s
emission of heat, should be affected by the existence of spots upon his
surface.
It is otherwise with the effects which have recently been associated
with the sun’s condition. It may or may not prove actually to be the
case that wind and rain vary in quantity as the sun-spots vary in
number (at least when we take in both cases the average for a year, or
for two or three years), but it cannot be said that any such relation
was antecedently to be expected. When we consider what the sun actually
does for our earth, it seems unlikely that special effects such as
these should depend on relatively minute peculiarities of the sun’s
surface. There is our earth, with her oceans and continents, turning
around swiftly on her axis, and exposed to his rays as a whole. Or,
inverting the way of viewing matters, there is the sun riding high in
the heavens of any region of the earth, pouring down his rays upon that
region. We can understand how in the one case that rotating orb of the
earth may receive rather more or rather less heat from the sun when
he is spotted than when he is not, or how in the other way of viewing
matters, that orb of the sun may give to any region rather more or
rather less heat according as his surface is more or less spotted.
But that in special regions of that rotating earth storms should be
more or less frequent or rainfall heavier or lighter, as the sun’s
condition changes through the exceedingly small range of variation due
to the formation of spots, seems antecedently altogether unlikely; and
equally unlikely the idea that peculiarities affecting limited regions
of the sun’s surface should affect appreciably the general condition
of the earth. If a somewhat homely comparison may be permitted, we
can well understand how a piece of meat roasting before a fire may
receive a greater or less supply of heat on the whole as the fire
undergoes slight local changes (very slight indeed they must be, that
the illustration may be accurate); but it would be extremely surprising
if, in consequence of such slight changes in the fire, the roasting of
particular portions of the joint were markedly accelerated or delayed,
or affected in any other special manner.
But of course all such considerations as to antecedent probabilities
must give way before the actual evidence of observed facts. Utterly
inconsistent with all that is yet known of the sun’s physical action,
as it may seem, on _à priori_ grounds, to suppose that spots, currents,
or other local disturbances of the sun’s surface could produce any but
general effects on the earth as a whole, yet if we shall find that
particular effects are produced in special regions of the earth’s
surface in cycles unmistakably synchronizing with the solar-spot-cycle,
we must accept the fact, whether we can explain it or not. Only let it
be remembered at the outset that the earth is a large place, and the
variations of wind and calm, rain and drought, are many and various in
different regions. Whatever place we select for examining the rainfall,
for example, we are likely to find, in running over the records of the
last thirty years or so, some seemingly oscillatory changes; in the
records of the winds, again, we are likely to find other seemingly
oscillatory changes; if none of these records provide anything which
seems in any way to correspond with the solar spot-cycle, we may
perchance find some such cycle in the relative rainfall of particular
months, or in the varying wetness or dryness of particular winds, and
so forth. Or, if we utterly fail to find any such relation in one
place we may find it in another, or not improbably in half-a-dozen
places among the hundreds which are available for the search. If we
are content with imperfect correspondence between some meteorological
process or another and the solar-spot cycle, we shall be exceedingly
unfortunate indeed if we fail to find a score of illustrative
instances. And if we only record these, without noticing any of the
cases where we fail to find any association whatever—in other words,
as Bacon puts it, if “we note when we hit and never note when we
miss,” we shall be able to make what will seem a very strong case
indeed. But this is not exactly the scientific method in such cases.
By following such a course, indeed, we might prove almost anything. If
we take, for instance, a pack of cards, and regard the cards in order
as corresponding to the years 1825 to 1877, and note their colours as
dealt _once_, we shall find it very difficult to show that there is any
connection whatever between the colours of the cards corresponding to
particular years and the number of spots on the sun’s face. But if we
repeat the process a thousand times, we shall find certain instances
among the number, in which red suits correspond to all the years when
there are many spots on the sun, and black suits to all the years
when there are few spots on the sun. If now we were to publish all
such deals, without mentioning anything at all about the others which
showed no such association, we should go far to convince a certain
section of the public that the condition of the sun as to spots might
hereafter be foretold by the cards; whence, if the public were already
satisfied that the condition of the sun specially affects the weather
of particular places, it would follow that the future weather of these
places might also be foretold by the cards.
I mention this matter at the outset, because many who are anxious to
find some such cycle of seasons as Sir John Herschel thought might be
discovered, have somewhat overlooked the fact that we must not hunt
down such a cycle _per fas et nefas_. “Surely in meteorology as in
astronomy,” Mr. Lockyer writes, for instance, “the thing to hunt down
is a cycle, and if that is not to be found in the temperate zone, then
go to the frigid zones or the torrid zone to look for it; and if found,
then above all things and in whatever manner, lay hold of, study, and
read it, and see what it means.” There can be no doubt that this is the
way to find a cycle, or at least to find what looks like a cycle, but
the worth of a cycle found in this way will be very questionable.[7]
I would not have it understood, however, that I consider all the cycles
now to be referred to as unreal, or even that the supposed connection
between them and the solar cycle has no existence. I only note that
there are thousands, if not tens of thousands, of relations among
which cycles may be looked for, and that there are perhaps twenty or
thirty cases in which some sort of cyclic association between certain
meteorological relations and the period of the solar spots presents
itself. According to the recognized laws of probability, some at least
amongst these cases must be regarded as accidental. Some, however, may
still remain which are not accidental.
Among the earliest published instances may be mentioned Mr. Baxendell’s
recognition of the fact that during a certain series of years, about
thirty, I think, the amount of rainfall at Oxford was greater under
west and south-west winds than under south and south-east winds when
sun-spots were most numerous, whereas the reverse held in years when
there were no spots or few. Examining the meteorological records of
St. Petersburg, he found that a contrary state of things prevailed
there.
The Rev. Mr. Main, Director of the Radcliffe Observatory at Oxford,
found that westerly winds were slightly more common (as compared with
other winds) when sun-spots were numerous than when they were few.
Mr. Meldrum, of Mauritius, has made a series of statistical inquiries
into the records of cyclones which have traversed the Indian Ocean
between the equator and 34 degrees south latitude, in each year from
1856 to 1877, noting the total distances traversed by each, the sums
of their radii and areas, their duration in days, the sums of their
total areas, and their relative areas. His researches, be it marked
in passing, are of extreme interest and value, whether the suggested
connection between sun-spots and cyclones (in the region specified)
be eventually found to be a real one or not. The following are his
results, as described in _Nature_ by a writer who manifestly favours
very strongly the doctrine that an intimate association exists between
solar maculation (or spottiness) and terrestrial meteorological
phenomena:—
“The period embraces two complete, or all but complete, sun-spot
periods, the former beginning with 1856 and ending in 1867, and the
latter extending from 1867 to about the present time [1877]. The broad
result is that the number of cyclones, the length and duration of
their courses, and the extent of the earth’s surface covered by them
all, reach the maximum in each sun-spot period during the years of
maximum maculation, and fall to the minimum during the years of minimum
maculation. The peculiar value of these results lies in the fact that
the portion of the earth’s surface over which this investigation
extends, is, from its geographical position and what may be termed
its meteorological homogeneity, singularly well fitted to bring out
prominently any connection that may exist between the condition of the
sun’s surface and atmospheric phenomena.”
The writer proceeds to describe an instance in which Mr. Meldrum
predicted future meteorological phenomena, though without specifying
the exact extent to which Mr. Meldrum’s anticipations were fulfilled or
the reverse. “A drought commenced in Mauritius early in November,” he
says, “and Mr. Meldrum ventured (on December 21) to express publicly
his opinion that probably the drought would not break up till towards
the end of January, and that it might last till the middle of February,
adding that up to these dates the rainfall of the island would probably
not exceed 50 per cent. of the mean fall. This opinion was an inference
grounded on past observations, which show that former droughts have
lasted from about three to three and a half months, and that these
droughts have occurred in the years of minimum sun-spots, or, at all
events, in years when the spots were far below the average, such as
1842, 1843, 1855, 1856, 1864, 1866, and 1867, and that now we are
near the minimum epoch of sun-spots. It was further stated that the
probability of rains being brought earlier by a cyclone was but slight,
seeing that the season for cyclones is not till February or March, and
that no cyclone whatever visited Mauritius during 1853–56 and 1864–67,
the years of minimum sun-spots. From the immense practical importance
of this application of the connection between sun-spots and weather
to the prediction of the character of the weather of the ensuing
season, we shall look forward with the liveliest interest to a detailed
statement of the weather which actually occurred in that part of the
Indian Ocean from November to March last [1876].”
It was natural that the great Indian famine, occurring at a time
when sun-spots were nearly at a minimum, should by some be directly
associated with a deficiency of sun-spots. In this country, indeed,
we have had little reason, during the last two or three years of few
sun-spots, to consider that drought is one of the special consequences
to be attributed to deficient solar maculation. But in India it may
be different, or at least it may be different in Madras, for it has
been satisfactorily proved that in some parts of India the rainfall
increases in inverse, not in direct proportion, to the extent of
solar maculation. Dr. Hunter has shown to the satisfaction of many
that at Madras there is “a cycle of rainfall corresponding with the
period of solar maculation.” But Mr. E. D. Archibald, who is also
thoroughly satisfied that the sun-spots affect the weather, remarks
that Dr. Hunter has been somewhat hasty in arguing that the same
conditions apply throughout the whole of Southern India. “This hasty
generalization from the results of one station situated in a vast
continent, the rainfall of which varies completely, both in amount and
the season in which it falls, according to locality, has been strongly
contested by Mr. Blanford, the Government Meteorologist, who, in making
a careful comparison of the rainfalls of seven stations, three of which
(Madras, Bangalore, and Mysore) are in Southern India, the others
being Bombay, Najpore, Jubbulpore, and Calcutta, finds that, with the
exception of Najpore in Central India, which shows some slight approach
to the same cyclical variation which is so distinctly marked in the
Madras registers, the rest of the stations form complete exceptions
to the rule adduced for Madras, in many of them the hypothetical
order of relation being reversed. Mr. Blanford, however, shows that,
underlying the above irregularities, a certain cyclical variation
exists on the average at all the stations, the amount, nevertheless,
being so insignificant (not more than 9 per cent. of the total falls)
that it could not be considered of sufficient magnitude to become a
direct factor in the production of famine. It thus appears that the
cycle of rainfall which is considered to be the most important element
in causing periodic famines has only been proved satisfactorily for
the town of Madras. It may perhaps hold for the Carnatic and Northern
Siccars, the country immediately surrounding Madras, though perhaps,
owing to the want of rainfall registers in these districts, evidence
with regard to this part is still wanting.” On this Mr. Archibald
proceeds to remark that, though Dr. Hunter has been only partially
successful, the value of his able pamphlet is not diminished in any
way, “an indirect effect of which has been to stimulate meteorological
inquiry and research in the same direction throughout India. The
meteorology of this country (India), from its peculiar and tropical
position, is in such complete unison with any changes that may
arise from oscillations in the amount of solar radiation, and their
effects upon the velocity and direction of the vapour-bearing winds,
that a careful study of it cannot fail to discover meteorological
periodicities in close connection with corresponding periods of solar
disturbance.” So, indeed, it would seem.
The hope that famines may be abated, or, at least, some of their most
grievous consequences forestalled by means of solar observatories, does
not appear very clearly made out. Rather it would seem that the proper
thing to do is to investigate the meteorological records of different
Indian regions, and consider the resulting evidence of cyclic changes
without any special reference to sun-spots; for if sun-spots may cause
drought in one place, heavy rainfall in another, winds here and calms
there, it seems conceivable that the effects of sun-spots may differ at
different times, as they manifestly do in different places.
Let us turn, however, from famines to shipwrecks. Perhaps, if we admit
that cyclones are more numerous, and blow more fiercely, and range
more widely, even though it be over one large oceanic region only, in
the sun-spot seasons than at other times, we may be assured, without
further research, that shipwrecks will, on the whole, be more numerous
near the time of sun-spot maxima than near the time of sun-spot minima.
The idea that this may be so was vaguely shadowed forth in a poem of
many stanzas, called “The Meteorology of the Future: a Vision,” which
appeared in _Nature_ for July 5, 1877. I do not profess to understand
precisely what the object of this poem may have been-—I mean, whether
it is intended to support or not the theory that sun-spots influence
the weather. Several stanzas are very humorous, but the object of the
humour is not manifest. The part referred to above is as follows:—Poor
Jack lies at the bottom of the sea in 1881, and is asked in a spiritual
way various questions as to the cause of his thus coming to grief. This
he attributed to the rottenness of the ship in which he sailed, to
the jobbery of the inspector, to the failure of the system of weather
telegraphing, and so forth. But, says the questioner, there was one
“In fame to none will yield,
He led the band who reaped renown
On India’s famine field.
“Was he the man to see thee die?
Thou wilt not tax him—come?
The dead man groaned—‘_I met my death
Through a sun-spot maximum_.’”
The first definite enunciation, however, of a relation between
sun-spots and shipwrecks appeared in September, 1876. Mr. Henry
Jeula, in the _Times_ for September 19, stated that Dr. Hunter’s
researches into the Madras rainfall had led him to throw together the
scanty materials available relating to losses posted on Lloyd’s loss
book, to ascertain if any coincidences existed between the varying
number of such losses and Dr. Hunter’s results. “For,” he proceeds,
“since the cycle of rainfall at Madras coincides, I am informed, with
the periodicity of the cyclones in the adjoining Bay of Bengal” (a
relation which is more than doubtful) “as worked out by the Government
Astronomer at Mauritius” (whose researches, however, as we have seen,
related to a region remote from the Bay of Bengal), “some coincidence
between maritime casualties, rainfalls, and sun-spots appeared at
least possible.” In passing, I may note that if any such relation were
established, it would be only an extension of the significance of
the cycle of cyclones, and could have no independent value. It would
certainly follow, if the cycle of cyclones is made out, that shipwrecks
being more numerous, merchants would suffer, and we should have the
influence of the solar spots asserting itself in the _Gazette_. From
the cyclic derangement of monetary and mercantile matters, again,
other relations also cyclic in character would arise. But as all these
may be inferred from the cycle of cyclones once this is established,
we could scarcely find in their occurrence fresh evidence of the
necessity of that much begged-for solar observatory. The last great
monetary panic in this country, by the way, occurred in 1866, at a
time of minimum solar maculation. Have we here a decisive proof that
the sun rules the money market, the bank rate of discount rising to a
maximum as the sun-spots sink to a minimum, and _vice versâ_? The idea
is strengthened by the fact that the American panic in 1873 occurred
when spots were very numerous, and its effects have steadily subsided
as the spots have diminished in number; for this shows that the sun
rules the money market in America on a principle diametrically opposed
to that on which he (manifestly) rules the money market in England,
precisely as the spots cause drought in Calcutta and plenteous rainfall
at Madras, wet south-westers and dry south-westers at Oxford, and wet
south-easters and dry south-easters at St. Petersburg. Surely it would
be unreasonable to refuse to recognize the weight of evidence which
thus tells on both sides at once.
To return, however, to the sun’s influence upon shipwrecks.
Mr. Jeula was “only able to obtain data for two complete cycles of
eleven years, namely, from 1855 to 1876 inclusive, while the period
investigated by Dr. Hunter extended from 1813 to 1876, and his
observations related to Madras and its neighbourhood only, while the
losses posted at Lloyd’s occurred to vessels of various countries, and
happened in different parts of the world. It was necessary to bring
these losses to some common basis of comparison, and the only available
one was the number of ‘British registered vessels of the United Kingdom
and Channel Islands’—manifestly an arbitrary one. I consequently
cast out the percentage of losses posted each year upon the number of
registered vessels for the same year, and also the percentage of losses
posted in each of the eleven years of the two cycles upon the total
posted in each complete cycle, thus obtaining two bases of comparison
independent of each other.”
The results may be thus presented:—