Everybody agrees that all the energy utilized on this planet of ours,
with the single exception of that supplied by the tides, comes from
the sun. We are all familiar with the changes due to the earth’s daily
rotation bringing us now on the side of our planet illuminated by
the sun, then plunging us into darkness; that changes of season must
necessarily follow from the earth’s yearly journey round the sun is
universally recognized.
On the other hand, it is a modern idea that those solar phenomena which
prove to us considerable changes of temperature in the sun itself,
may, and indeed should, be echoed by changes on our planet, giving us
thereby an eleven-year period to be considered, as well as a year and a
day.
This response of the earth to solar changes was first observed in the
continuous records of those instruments which register for us the
earth’s magnetism at any one place. The magnetic effects were strongest
when there were more spots, taking them as indicators of solar changes.
Lamont first (without knowing it) made this out, at the beginning of
the latter half of the century (1851), from the Göttingen observations
of the daily range of the declination needle. Sabine the next year not
only announced the same cycle in the violence of the “magnetic storms”
observed at Toronto, but at once attributed them to solar influence,
the two cycles running concurrently. It is now universally recognized
that terrestrial magnetic effects, including auroræ, minutely echo the
solar changes.
The eleven-year period is not one to be neglected.
Next comes the inquiry in relation to meteorology. Sir William
Herschel, in the first year of the century, when there were practically
neither sun-spot nor rainfall observations available, did not hesitate
to attack the question whether the price of wheat was affected by the
many-or-few-spot solar condition. He found the price to be high when
the sun was spotless, and _vice versa_.
By 1872, however, we had both rainfall and sun-spot observations,
and the cycle of the latter had been made out. Meldrum, the most
distinguished meteorologist living at the time, and others, pronounced
that the rainfall was greatest at sun-spot maximum, and, further, that
the greatest number of cyclones occurred in the East and West Indies at
such times.
This result with regard to rainfall was not generally accepted, but
Chambers showed shortly afterwards an undoubted connection between the
cycles of solar spots and barometric pressure in the Indian area.
By means of a study of the widened lines observed in sun spots an
attempt has been recently made to study the temperature, history of the
sun since about 1877, and the years of mean temperature and when the
heat was in excess (+) and defect (-) made out, have been as follows:
Heat
condition mean + mean − mean + mean − mean
Years 1869 1876 1881 1886–87 1891–92
1870–75 1877–80 1882–86 1881–91 1892
Having these solar data, the next thing to do was to study the Indian
rainfall during the southwest monsoon for the years 1877–1886, the
object being to endeavor to ascertain if the + and − temperature pulses
in the sun were echoed by + and − pulses of rainfall. The Indian
rainfall was taken first because in the tropics the phenomena are
known to be the simplest. It was found that in many parts of India the
+ and − conditions of solar temperature were accompanied by + and −
pulses, producing pressure changes and heavy rains in the Indian Ocean
and the surrounding land. These occurred generally in the first year
following the mean condition, that is, in 1877–78 and 1882–83.
The rainfalls at Mauritius, Cape Town, and Batavia were next collated
to see if the pulses felt in India were traceable in other regions
surrounding the Indian Ocean to the south and east. This was found to
be the case.
A wider inquiry was followed, we are told, with equal success, so that
we are justified in hoping that the question of the dependence of
terrestrial upon solar weather has made a step in advance.
But just as the general public and practical men took little heed of
the connection between sun spots and magnetism until experience taught
them that telegraphic messages often could not “get through” when
there were many sun spots, so the same public will not consider the
connection in regard to meteorology unless the forecasting of droughts
and famines be possible.
The recent work suggests that, if the recent advances in solar physics
be considered, the inquiries regarding rainfall may be placed on a
firmer basis than they could possibly have had in 1872, and that such
forecastings may become possible.
What was looked for in 1872 was a change in the quantity of rain at
maximum sun spots only, the idea being that there might be an effective
change of solar temperature, either in excess or defect, at such times
and that there would be a gradual and continuous variation from maximum
to maximum.
We see that the rainfalls referred to above justify the conclusions
derived from the recent work that two effects ought to be expected in a
sun-spot cycle instead of one. There was excess of rainfall, not only
near the sun-spot maximum, but near the minimum.
If the authors of this communication to which I refer are right, then
droughts and famines occur in India because the rain pulses, which are
associated with the solar-heat pulses, are of short duration. When
they cease the quantity of rain which falls in the Indian area is not
sufficient, without water storage, for the purposes of agriculture;
they are followed, therefore, by droughts, and at times subsequently by
famines. They divide the period 1877—89 as under:
{ 1877.
Rain from − pulse { 1878.
{ 1879 (part).
{ 1879 (part).
No rain pulse { 1880 (central year).
{ 1881 (part).
{ 1881 (part).
{ 1882.
Rain from + pulse { 1883.
{ 1884 (part).
{ 1884 (part).
{ 1885 }
No rain pulse { 1886 } (central year).
{ 1887 (part).
{ 1887 (part).
Rain from − pulse { 1888.
{ 1889.
Their statement is based on the fact that all the famines which have
devastated India for the last seventy years have occurred at intervals
of eleven years, or thereabouts, working backward and forward from the
central years 1880 and 1885–86 in the above table, the middle years,
that is, between the pulses.
Mr. Willcocks, in a paper read at the Meteorological Congress at
Chicago, remarked that “famines in India are generally years of low
flood in Egypt.”
It is now pointed out that the highest Niles follow the years of the +
and − pulses, as does the highest rainfall in the Indian area.
Even if these results, which were communicated to the Royal Society
of London five weeks before the end of the century, be confirmed, it
may be pointed out that Sir William Herschel’s suggestion of 1801 will
have required a whole century for its fulfilment, so slowly do those
branches of science move which have not already led to some practical
development.