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Predict Next Year's Weather
By John Elfreth Watkins
CIENTISTS at Wash- forecasts is being developed. This long
ington feel almost con- range weather forecast possibility will fident of being able to appear more clear to you if I first predict, before long repeat, as nearly as I can recall, what perhaps in a year was told me, by way of introduction whether an approaching to a description of the full modus operseason will be abnormal- andi, by Mr. C. G. Abbott, now in charge ly hot or cold, wet or of the Astrophysical Observatory, where
dry. Ability to forecast he has been Professor Langley's aid for weather several months ahead, has been the past ten years. claimed by no end of mystics and char- The earth is a body hanging out in latans; and the term "long-range fore- space and receiving rays from the suncasting" had in consequence fallen into
some visible and some invisible, the latter disrepute long before that distinguished approaching in wave-length our electric physicist, Prof. S. P. Langley, late Sec- rays used in wireless telegraphy. Now, retary of the Smithsonian Institution, the earth not only receives this energy commenced work upon the problem by from the sun, but radiates it back into methods which are the purest of pure space. If the sun should grow hotter, science.
the earth would have to grow hotter also In the shadow of the Smithsonian
to keep a balance between radiation retowers, in Washington, is a group of white ceived and sent out. If the sun's radiaframe buildings known as the United tion of this energy, or heat, upon earth States Astrophysical Observatory. This is measured from day to day, and is found unique institution, conceived, developed, to fall off 10 per cent, say to-day, a week and directed by Professor Langley, is or more will be required before the conwhere the new system of long-range sequent fall of temperature will be felt in
our climate. Then would follow what we should call a "cold September.” The sun and earth being such tremendous bodies, the observers of the phenomena feel justified in supposing that the cold spell is likely to continue for some time. In fact, a variation in the sun's radiation has been found thus far to occur only two or three times a year. Hence, when such a change is definitely established, it will be pos
sible for those cognizant PYRHELIOMETER HOUSE, MOUNT WILSON OBSERVATORY,
of the conditions to pre
dict whether the approaching season will sorbed at the earth's surface or in the be hot or cold, wet or dry.
screen of air above it, alter climate and The instrument playing the chief rôle vegetation, Mr. Abbott considers it imin this work is the "bolometer”—a won- portant to determine how much of this derful electric thermometer invented by radiation is thus lost in the air. This Professor Langley, and so delicately amount is found to vary greatly at difwrought that it registers variations of the ferent times, because of clouds, invisible sun's radiation in millionths of a degree. moisture, dust, or smoke in the air. In The bolometer stands in a dark room, autumn the air is generally more transand the sunbeams are thrown into it after parent than in spring and summer; but it being first caught outside the building by sometimes happens that whole years are a traveling mirror which follows the sun found by these delicate measurements to by clockwork and is always in a posi- differ from others in the transparency of tion to reflect the beam through a prism the air. It was discovered at the Observain the dark room and then from one re- tory that during 1901 and 1902 the air flector to another, into the bolometer. allowed much more heat to pass through This instrument registers the sunbeam's it than during the first eight months of changes in radiation by means of a mag- 1903, after which the transparency innetic needle swinging somewhat like that creased to about its former state. It is of a compass.
thought that this change was caused by Another delicate instrument—the "pyr- the great volcanic eruption of Mont Peheliometer”-is employed for measuring lée, which sent thousands of tons of dust the rate at which the sun's heat is re- into the air. ceived at the earth's surface. You may Speaking generally, it is found that the have heard that a bucket of water would sun's beam, in passing entirely through be warmed by the sun much faster on a our atmosphere, to sea-level, loses about mountain top than at the brink of the half its heat in the air ; but most of this sea, because upon the mountain there is loss is made up to us on a clear day by less air between the bucket and the sun the light coming from all parts of the to screen off the latter's rays from the sky. Clouds, on the other hand, reflect bucket. Since all sun rays, whether ab- away about three-fourths of the sunlight
U. S. ASTROPHYSICAL OBSERVATORY, WASHINGTON, D. C.
Building at extreme right is the Smithsonian Institution.
that reaches them; and the earth is 60 our earth placed in the center, our moon per cent covered with clouds. If the might continue revolving in its orearth did not have this protecting cloudy bit about us, all within the hollow sun envelope, it would get nearly twice as itself without approaching to the outside. much heat from the sun, and the tempera- The instruments at the Astrophysical Obture upon its surface would be fully 50 servatory indicate that the temperature of degrees warmer than it is at present. this enormous orb is over 10,000 de
By measuring the total amount of sun- grees F. The greatest heat ever genlight reaching the surface of the earth, erated on earth is only about half as and adding to it the amount estimated great. Looking at the sun through a as lost in coming through the envelope telescope, you see that its disc it not quite
of air, Mr. Abbott finds the rate at which equally bright all over, but is slightly the sun is actually throwing off heat. darker toward the edges. This is beThis rate varies independently of the cause the great orb has a gaseous envelchange in our atmosphere, and its varia- ope or atmosphere which at the edges tions—which are more or less irregular acts like our own atmosphere at sunrise -are probably caused by a greater or or sunset, when the latter intercepts more less permeability of the sun's own atmos- light than at noon. This envelope is of phere. These variations generally occur the greatest consequence to us, and reguonly two or three times a year, as already lates for our use the heat of the sun, upon said ; and once this change is definitely which is dependent every earthly thing noted, it may be as safe to predict a radi- that has life. Were this gaseous solar cal change in an entire season—whether covering removed, our sphere would be it will be unusually cold or wet—as it unfit for habitation. We should all friznow is to forecast a change of local weather for a mere day.
At times this envelope of atmosphere Few of us realize the enormous bulk about the sun becomes hazy, much as of the sun. If it were hollowed out and does our own atmosphere. When it is
pecially near the edges, little bright spots system as soon as it shall have been percalled facule. They are brighter than fected. At its new research observatory the sun itself, and are supposed to be on the summit of Mount Weather, Vircaused by metals glowing as they melt ginia, it is preparing for the installation and boil. At other places on the great of apparatus similar to that used by Mr. orb are seen spots darker than the re- Abbott. A Weather Bureau man has been mainder of the surface and moving in training for some months at the Astroamong themselves like clouds. These physical Observatory, in order to master "sun spots,” supposed to be holes in the the methods exactly. solar surface, are often of enormous size The Mount Weather Observatory is an —so large, in fact, that the whole earth institution unique in the western hemimight be dropped into the center of one sphere. It occupies a high crest of the "like a pea into a thimble," as Professor Blue Ridge mountains, in the upper corLangley used to put it. In 1903, when ner of Virginia, very near the West Virthe Astrophysical Observatory estimated ginia line, and overlooks not only the a fall of from 10 to 13 per cent of the beautiful Loudoun valley on the east, but