Evening star., 1912-07-07

of rainfall recorded at more than nfty
stations in all parts of the earth, cover
ing all the available data for period ol
more than forty years, and as result o.
his studies he finds the average rainfall
for the earth to be about 3S12 inches an.
nually, with a variation of four inches
the maximum rainfall occurring generally
about year after the Sun-Spot maximum
Lit is generally conceded that any cause
which would induce such variations In
weather conditions as these must ineVi-
tably have it's effect upon the crops, ana
in consequence upon industry and general
prosperity, as we'll as upon the living
conditions of the race.
Other scientists. including Lord Kelvin.
hold to the theory that the sun spots do
not cause these weather changes. with
their consequent alterations of human
adversely and good times. but rather that
both the spots and the terrestrial weather
disturbances may be due to the same
great cause. Nevertheless. 1t is not denied
that IL the sun spots can be proved to
presage coming events that make for the
veal or woe OF humanity. then their study
with a view to finding out what they fore
shadow is a matter of untold Importance.
1t is in this connection that the great
cycle Of sun-spot photographs, just COM
pleted at the Naval Observatory. is re-
garded as a matter Of widespread popular
concern.
4
The process Of taking these photographs
is one Of the triumphs of civilization The
instrument with which the major part OF
the work was done is called the pnoto-
heliograph. The sun is caught In the
telescope, which reflects the image from
a tilted mirror to the camera lens
whence it is carried a distance OF forty
feet by means Of the long shediike struc-
ture called the photo-heliograph gallery
to a sensitized plate in darkroom. Ine
photograph is registered on the plate with
an exposure of one five-hundredth of q
second.
So delicate is the adjustment OF TINS
great apparatus, which photographs ar
object $1,000 900 miles away. that even
relatively slight change OF temperatur'
will make the lens infinitesimaily small
er. necessitating painful calculation or
the mart Of Prof Peters to redeter
mine the true focus. once tnls Is Iouno
Reimbursement is made by means OF ta'
micrometer screw wnich inca adsdmces 'ha nboto =,
heliograph pier on which rests the camera
nlate In the darkroom. Then the blt
photo heliograph camera Is ready 10 TAX
further sun spots. Until another change o.
Temperature necessitates still another re
adjustment.
In view of the fact that the first sun
snots discovered by Europeans were notec
, in 1910. and that they have been subject
ed to almost constant study since then
S,,rnrise has been expressed that astrono
. mers do not seem to know more abou
than-their origin, causes and develop
. ment. AS yet very little Of our knowl
, edge concerning these remarkable solal
disturbances has advanced peyond th'
stage of theory.
The most commonly accepted account o.
|, them is based on the conception OF thu
sun as a vast. seething, hubbling caul
: dron Of gaseous matter, heated TO tenn
. nerature OF 14,4OO degrees Fahrenheit
. and reduced to the consistency OF pitcf
by inconceivabie solar pressure. Som'
, idea Of this pressure is given by scien