Popular Science Monthly/Volume 78/January 1911/The Meteorology of the Future
|THE METEOROLOGY OF THE FUTURE|
By Professor CLEVELAND ABBE
U. S. WEATHER BUREAU
AFTER some introductory remarks by Dr. Finley, president of the College of the City of New York, Professor Abbe said:
I think myself specially honored by these kindly words from the president of the College of the City of New York. You all know how thoroughly that noble institution has, during the past sixty years, entrenched itself in the hearts of our citizens, and you know what Dr. Finley is doing to carry its work forward. To it many of us owe those youthful inspirations that have determined our careers in maturer life. It is always a delight to me to recall the years 1851–1857 when at that college I studied the foundations of modern physical science; mathematics under Docharty, descriptive geometry under Koerner, mechanics under Nichols, physics and chemistry under Gibbs. Not to speak of those other revered instructors, Owen in Latin and Greek, Anthon in history, Duggan in architecture, Roemer in French. Each one of these is still to me a living inspiration. Such men do not die so long as their words and lives continue vividly before us. It was worth living in those days to have listened to the brilliant diction and witnessed the successful experiments of Robert Ogden Doremus in his lectures on the Nebular Hypothesis. These admirable educators dealt with questions that I have gradually come to see are intimately associated with our atmospheric problems, though they themselves probably did not think of such connection at that time. It may be said that every course of study then pursued at that college has proved useful in the modern development of meteorology. Of course this is equally true of the studies now pursued at Columbia University. May both that college and this university in the future send forth many meteorologists and others to benefit our city, our nation and our science.
My task to-night is to be as difficult as the problem proposed of old byto Joseph. I am to tell you a dream of the future of science and also the interpretation thereof.
In the preceding nine lectures, my colleagues have given you some idea of the present state of our knowledge of the atmosphere. Possibly you may have already suspected that we know very little about the air in which we live. You must not think less of the honest scholar when he assures you that what we really know beyond all peradventure is as nothing compared to the unknown ocean of truth still to be explored. I trust that you will sympathize with my enthusiasm over the study of the atmosphere. Does not the wonderful glory of a sunset sky stimulate one to study its causes and to discover what its clouds and colors have to do with the weather of to-morrow? Who can watch the approach or recession of a thunder-storm and not be impressed with the dreadful majesty of its appearance? We may dream of the immensity of space as we contemplate the star-lit sky at night, for the stars are far, far away and men are always dreaming of them—but we can not merely dream of the clouds, the weather and the storms; the atmosphere is too near at hand for mere dreams; it forces us to action; it is close to us; we are in it and of it. It rouses us to both study and do; we must know its moods and also its motive forces; we must conquer it in our struggle for existence. Now that our aeronauts Orville and Wilbur Wright have learned to fly, we must learn to utilize the air just as the mariners have learned to utilize the winds and avoid the storms.
In the days of Columbus (1437-1514), Drake (1540-1596), Dampier (1652-1715) and Halley (1656-1742) the mariner long ago knew of the trade winds and the seasonal monsoons and the prevailing westerlies, and took advantage of them. It took two more centuries to acquire a knowledge of whirlwinds as they advance over the globe; and only the present living generation of men has seen the growth of national and local weather bureaus in every part of the civilized globe established to forewarn mariners of storms, or landsmen of rain and wind, frosts and blizzards. We are not yet able to speak of such weather forecasts as anything more than probabilities or indications, they have not yet become certainties, but surely you are all convinced that already, even in the present imperfect state of our knowledge, the meteorologist is worthy to be recognized as a benefactor of mankind.
Has any community in this country or in the whole world profited by the steady daily watchfulness of such a weather bureau more than this very city of New York? Thousands of your law cases are decided annually on the testimony of official weather records. Your business men are forewarned of every storm. Whenever current weather conditions threaten misfortune to any special branch of industry you make a hundred inquiries by telephone, telegraph or personally, asking for details as to what is going on overhead. Your morning papers and your evening papers are consulted by every one for the weather forecasts; your business matters are arranged in accordance with the conviction that one can not afford to neglect this little item of information, any more than he can afford to neglect ordinary insurance, even though he knows that there is a chance for an occasional mistake. The daily weather map is distributed as widely as possible for the benefit of all and is a splendid educator. This map gives us the facts, even though the best of us often fail to perceive what they mean and what they foretell.
And right here I must remind you that this system of daily telegrams, with its maps and forecasts owes its origin and subsequent perfection almost entirely to the citizens of the city and the state of New York. New York City has always been the home of meteorologists, just as our bay with its sailing vessels and steamships has always been filled with the bravest of sailors and navigators. Others besides Hudson and Fulton, Stevens and Ericsson, Cyrus Field and Wm. H. Webb have helped to make the fame of New York and the Hudson.
Here lived W. C. Bedfield, whose busy life as a merchant did not prevent him from collecting the logs of ships and studying all the characteristics of storms at sea. For forty years he devoted his leisure hours to this work, publishing one research after another from New York City, until the whole world understood that hurricanes, cyclones and typhoons are whirlwinds, revolving and progressing as a whole, moving slowly along paths that carry them from equatorial toward polar regions; that our own hurricanes move westward and northward over the West Indies into our south Atlantic and gulf states and thence north and east along our coasts to northern Europe.
Here lived Elias Loomis, teaching meteorology and astronomy for many years as a professor at the New York University, and studying the storms of the land.
Here lectured James P. Espy, a native of Pennsylvania, who, with inimitable eloquence and enthusiasm defended his great discoveries that a cloud must contain the heat that was originally consumed in the evaporation of the water; that the moist air by rising had cooled by expansion down to its dew point; that the condensation into cloud caused latent heat to be set free.
Here, and in the northern part of our state, we had B. F. Hough at Lowville, who gave us our best studies of the New York climate and our first stimulating reports on the importance of forestry.
Our dear New York, the youthful city of a century ago, was the home of Professor Samuel F. B. Morse, artist and inventor, whose enthusiasm triumphed over the difficulties in the way of perfecting the electro-magnetic telegraph, and made it possible for our great national weather bureau to carry on its work expeditiously and economically.
At Albany Professor Joseph Henry, the father of the electromagnetic telegraph, maintained the importance of the study of the atmosphere. In 1847, when he was called from Princeton to become the secretary and brains of the Smithsonian Institution in Washington, he immediately arranged with the telegraph companies for telegrams, displayed them on daily weather maps and demonstrated the possibility of forecasting storms and weather.
Greater New York, that is to say the Brooklyn of sixty years ago, was honored as the residence of Ebenezer Meriam, "the sage of Brooklyn Heights," a manufacturer, but also special correspondent and associate editor of the New York City Commercial, in whose columns, about 1850, he began to publish his weather forecasts compiled by using all the information at his disposal, especially the telegrams of weather conditions in distant places. His forecasts of "heated terms" and "cold terms" not only prepared the general public to believe that weather could be predicted, but had a special influence on one young student just entering your City College, whose scrap book of 1850 still contains the history of early events that stimulated his boyish imagination and aspiration. Meriam was but carrying out single-handed the ideas urged by Redfield and Loomis, Espy and Henry, looking to the formation of a government weather bureau. The rule that weather changes move eastwardly for several days in succession was utilized by New York business men even before Professor Joseph Henry announced from Washington the general result of the labors of James H. Coffin, of Ogdensburg, N. Y. It was Professor Coffin who during the years 1838-1840 published our first American meteorological magazine and eventually compiled a great work on the winds of the globe, demonstrating that in these latitudes (between 30 and 60 degrees north) there always is a strong west wind high above the ordinary layers of clouds, that apparently explains the eastward drift of our storms.
The complete mechanism of the atmosphere was clearly explained by William Ferrel in 1858, so that finally, in May, 1868, when our country was rapidly recovering from its terrible internal dissensions, a young astronomer from New York, a graduate of your City College, who had been revolving in his mind all these teachings of his elders, and had from boyhood been observing the clouds and winds and weather, submitted to the Chamber of Commerce of Cincinnati his project of weather forecasts for the benefit of that city. He was ably supported by the officers of the famous astronomical observatory, by the citizens of the "queen city of the west," by her newspapers and her telegraph authorities. You will agree with me that he was within bounds when he wrote from Cincinnati to his parents in New York: "I have started a work that the country will not willingly let die." This was the work that in the hands of General Albert J Myer, of Buffalo, has brought such fame to our country and city.
Although the study of science and the pursuit of research is most fascinating and elevating, yet no man should be satisfied therewith. It is right to be content from day to day, but never satisfied. The highest type of man is he who seeks to be most useful to his fellow men. It is the duty of every citizen of this republic to attain the highest usefulness that he is capable of. He may temporarily devote himself to acquiring knowledge or money; to perfecting art or inventing machinery; he may apparently devote his whole life to some mercantile pursuit, but if he be true to his own conscience, his ultimate hope must be to benefit his country and mankind. Anything else less than this dies; just as he himself must die; it dies with him. Patriotic philanthropy can alone afford a man the comfortable assurance that his life has been well spent. No one founds a hospital, a library, a museum, a park or a university, for purely selfish ends; he knows, and he takes pleasure in knowing, that the whole community will be benefited, and that future thousands will thank him for that which otherwise would have been unattainable to them. He has given to his money and his life their maximum power for good.
At this moment Columbia University surrounds us with this group of noble buildings, testifying to the wisdom of many wealthy men. The names of the best of New York are inscribed above these portals. There is room for other temples and why should not one of these be devoted to the science and the art that I represent, to the study of the atmosphere, and the utilization of that knowledge for the benefit of man? Give meteorology a home of its own among these temples of science, and its students will build a noble intellectual structure. Provide generous fellowships, stimulate able physicists to devote their lives to this study, and thus assure the development of usefulby future generations of men.
But is there a future for meteorology? Can we to-night lift the curtain and look forward? What are the problems that now seem to be pressing for solution? The great problems of the past were vital to the progress of science and to the welfare of mankind. Some of these problems still await our careful attention, and other newer ones have become prominent. This present generation of men must provide for this future study. "We understand the general nature of the work that remains to be done, but a future generation must do it. It is our first duty to provide for the education of the young men that are to carry the work a few steps further forward. Progress in knowledge is always slow. How slowly Africa has been opened up. How hard it was to find the North Pole. How long the world waited for Christopher Columbus to cross the Atlantic.
With the kind assistance of Professor Wm. Hallock and his colleagues I have prepared a few experiments to illustrate the points to which I would draw your attention. But first I must emphasize my statement that as soon as one generation of men arrives at a simple law or generalization, then another generation calls attention to the fact that there are exceptions to these laws and that obscure influences are at work preventing the operation of any one single, simple law. Thus a new series of researches opens up; we descend to the study of details and try to unravel all the complexities of natural phenomena. To enforce this point we may say that in our atmosphere every local weather phenomenon results from the interaction of the following seven forces:
1. The diurnal rotation of the earth on its axis.
2. The annual revolution of the earth in its orbit.
3. The attraction of gravitation holding the atmosphere to the earth.
4. The centrifugal force resulting from the rotation of the earth on its axis, and due to the inertia of the moving masses of air.
5. The molecular forces known as heat, light, chemism, electricity and radiant energy received by radiation from the sun with all the variations depending upon latitude, diurnal rotation and annual revolution.
6. The loss of heat by radiation from the earth and atmosphere.
7. The irregular expansions due to the irregular distribution of heat in the atmosphere which depends on the distribution of continents and oceans, and the presence of an easily condensable vapor like steam mixed with the permanent gases, nitrogen and oxygen that form the great mass of the atmosphere.
You will see from this brief and partial enumeration that we have to do with very complex combinations of phenomena, and that the results must vary with every slight variation in any one of these forces. Worse than this, we have not yet been able to observe or investigate the boundary between our atmosphere and the illimitable planetary space beyond. We know not whether gaseous particles are being added to and removed from this outer boundary. We know not whether our outer layer of atmosphere experiences any resistance from the cosmic ether as the earth rushes along in space. There are many speculations as to the origin of the earth's atmosphere; not only do these belong to geology, cosmic physics or cosmology, but they also lie at the foundation of meteorology. In the present state of our knowledge these are merely speculations; dynamic meteorology passes them by in silence and assumes that the atmosphere is now unchangeable as to its composition and mass. But who knows how soon the day will come when we shall have to recognize that a change has taken place! From this point of view I should say that in logical order the first problem for future study bears on the condition of the outer layer of our atmosphere, and in fact, my predecessors in this course of lectures, Professor R. S. Woodward, of Washington, and Professor J. H. Jeans, of Princeton, have already touched upon this question. More than that. Dr. C. C. Trowbridge, of Columbia University, has brought together many interesting facts relating to the trains left behind by meteors or shooting stars as they rush through the upper air. These meteors become visible at altitudes as high as 120 miles, showing that at that elevation there are obstacles of a nature analogous to that of a resisting gas. In fact, as the meteors are burned up, we must acknowledge that the debris are perpetually making new additions to our atmosphere. So important is this question, both to astronomy and to meteorology, that the Astronomical and Astrophysical Society of America has lately started an inquiry as to what methods are available for photographing meteors and meteor trains, or what studies can give us any facts about the highest air. I understand Professor Woodward to state that there is a mechanical possibility of the existence of another atmosphere above that which affects our barometer, which therefore may revolve about the globe, like the rings of Saturn, in equilibrium within itself.
The most interesting definite problem bearing on the highest atmosphere relates to the cause and nature of the aurora borealis. These beautiful northern lights have been carefully studied by Swedes and Norwegians. Twenty years ago, all the nations of the globe united in a series of expeditions to both the arctic and antarctic regions for the study of magnetism, auroras and meteorology. Since that date four special expeditions have been sent northward by Norwegians, and the leader of these. Professor Birkeland, of Christiania, has developed some new views as to the aurora, that have been confirmed by the mathematical investigations of his colleague. Professor Stoermer. They have devised remarkable ways of continuous photography and accurate calculation of altitudes. The publication of the details of their work has begun, and I think we may safely anticipate that future generations will busy themselves developing the ideas that are now being presented by these physicists. All that we need say at the present moment is that particles which we call ions (or, when they are electrified, electrons), pass with the velocity of light from the sun to the earth. If this be incredible, we must at least say that some influence passes from the sun to the earth, with the speed of gravity or the speed of light, causing electrons from space or from the celestial bodies to approach the earth's atmosphere with great speed. But no sooner do these come within the influence of the earth's magnetism (and that influence extends to great distances beyond the atmosphere), no sooner do the electrons feel this influence, than they are diverted from their straight-line courses and begin to describe curves surrounding the earth like spiral corkscrews. Whenever such particles enter certain gases (such as krypton), the gas becomes luminescent or phosphorescent, and gives us the auroral light. This hypothesis is sufficiently complex to allow of many uncertainties as to details. It is at present in its formative stage, but there is good reason to believe that we have here a solid base on which to build a structure that will carry us from the firm ground of experimental laboratory physics over into the equally firm, but unexplored region of mathematical cosmical physics.
Let us come down from the highest atmosphere to some of the phenomena nearer the earth's surface. Possibly you may think that to the agriculturists the vital question is how to make it rain or how to stop the rain, according to the needs of the farmer. You may ask what are the ultimate causes of calamitous droughts, such as those of Syria, India and Australia, or the less injurious dry periods in Europe and America. These usually result from several successive years of deficient rainfall, as in the famous Biblical story of seven years of high water and seven years of low water, in the river Nile, in the days of Joseph. We have now many years of continuous record of the fluctuations of this great river and we know something of its irregularities. In order to understand why and when these droughts should occur, we must first understand how rain and snow are formed in the clouds and why rain does not always fall from the clouds. I have here on this laboratory table a small globe filled with the vapor of water mixed with air as it ordinarily occurs in the atmosphere. Now we know that when moist air rises up to the level of the clouds, it has expanded and by pushing aside the adjacent air has done work in its expansion. That work has used up some of the internal energy of the air which we call heat energy, so that the air has become cooler, just as steam expands and pushes the piston of a steam engine. When by this cooling the temperature of the moist air has been so reduced that it is near the dew-point, then the air is saturated with moisture and a cloudy condensation begins. This invisible vapor in the air begins to condense around every little particle of dust and every invisible electron. You have seen an ice pitcher covered with moisture on a warm summer day. In the same way these atmospheric dust particles are covered with moisture. I will now allow the air in this globe to expand by opening this lower stopcock leading to a low pressure chamber and you will notice the formation of a slight cloud of haze. The cloud is, however, not very dense because there is not much dust in the air. I will now repeat the experiment. First I will exhaust the air already in the globe, then close the lower stopcock. I wish to introduce into the globe more dust than is in the ordinary air of the room. To do so I light a match and hold it so that the smoke from the flame is near the upper end of the tube. When I turn the upper stopcock so that the vacuous space may become fllled with air, the inrushing air carries the smoke in with it. I close the upper stopcock and now the globe is full of dusty moist air. I open the lower stopcock, this dusty air expands downward into the lower pressure chamber and you see a dense cloud of fog is formed. These successive steps illustrate the ordinary method of the formation of clouds, but not of rain. To understand that, we must go a step further. Thus far I have allowed the dusty moist air expanding downward to increase its volume in the ratio of 600 or 650 to 760, i. e., 1 to 1.2 or 1.3. I will now enlarge the lower chamber so that the expansion may be in ratio of 500 to 760 or 1 to 1.5. Moreover, I will not allow any dust to enter the upper globe, but will draw into that globe dustless air filtered through this bit of cotton wool. If now I allow moist or saturated dustless air to expand into the lower chamber from the pressure 760 to that of 500 or an expansion of about 1.5 in volume then I shall form not a cloud of small particles, but a few larger drops of water. This is the process that must be going on within the thunder-cloud, or in fact inside any raincloud. Out of the great mass of moist air that makes up the whole cloud only a small proportion is free from dust and of that only a small portion expands rapidly enough to form drops of rain-water.
I think you will see that the firing of cannon or dynamite in order to make a great noise is not likely to form rain and in fact can not possibly bring it down. Neither can it prevent the formation of hail or rain. If we wish to avert heavy rain or hail we must either cut off the supply of moisture, or else prevent the rapid expansion, or else throw dust upward into the air to cause cloudy condensation instead of rain. Apparently this latter process is carried out for us in nature when great forest fires afford enough particles of smoke to provide for the cloudy condensation of the free moisture. From the great clouds of smoke that attend these forest fires we get no rain until after a long time the heat that is in the cloud is lost by radiation, or until larger drops are formed by further expansion.
Even the bombardment of a cloud by the explosion of dynamite within it is inefficient to produce rain, in part because no violent concussion can drive the cloud-particles together into large drops of rain, and in part because the explosive itself furnishes more dust particles and more nuclei of condensation and therefore produces clouds instead of rain. In the same way the bombardment of the clouds by means of vortex rings is inefficient.
I have here an apparatus for making vortex rings of air; you notice that a slight stroke on the rear side of this box drives forward a vortex ring of smoky air. It is a beautiful sight and very instructive in many ways, but the special form of cannon devised in Italy to send such rings of gunpowder smoke up into the clouds and break up the formation of hail does not usually send them higher than 1,000 feet; they break up long before they reach the clouds. We have no evidence that they ever reach them, or that they could have any effect if they did so. If they carry up much dust they ought to have a slight effect in producing cloudy condensation, and thus cutting off the formation of rain or hail. But this effect is certainly too slight to be appreciable in our statistics. I regret to think of so many thousands of farmers wasting time and money on this delusion. You know that De Morgan after spending much time in combating analogous delusions wrote an interesting volume classifying as "paradoxers" all those who believed in squaring the circle, or in perpetual motion, or that the world is flat, or that the sun do move. They can believe the impossible. It is the same way with those who expect great mechanical work to be done without the expenditure of a corresponding amount of force or energy. The law of the conservation of energy runs all through meteorology as it does through the mechanics of nature everywhere. Energy and work may be transformed to and fro, but never destroyed nor created by man.
I have no doubt that we shall some day long years hence acquire some control of the atmosphere, but at the present time we are not ready for it, neither scientifically nor socially. I say socially because if A could make it rain when his neighbor B wants dry pleasant weather, we should have grumbles and lawsuits and socialistic eruptions far worse than now.
I dare say that if ever we are to follow in the footsteps of Franklin who deprived lightning of its terror, or of Eedfield who taught the mariner how to avoid the dangers of the storm-center, we must adhere closely to nature: when once we know the details of her methods, then we may hope to learn how to make or to prevent the weather. To this particular study of the formation of rain, John Aitken, of Scotland, Carl Barus, of Brown University, and C. T. E. Wilson, of Cambridge, England, have especially contributed by their laboratory experiments. It is a question on which meteorological observers and laboratory physicists must labor together.
In India the prediction of great droughts has long been held to be one of the most important questions that can be attacked by the weather bureau of that country, and eminent men have worked upon it for twenty years past. The progress of their studies has gradually led us to see that the moist air of the southwest monsoon from which the rain falls has come from an unexpectedly great distance, namely, from the southern Indian Ocean. As you see on this globe before you, during the Asiatic winter season we have northeast trade winds here, and southeast trade winds there, south of the equator; but in the Asiatic summer season the heated air of the great continent of Europe, Asia and Africa, produces such an immense disturbance that over a large portion of the Indian Ocean the southeast trade wind disappears, or rather is turned about and flows northward over the equator to the region of the northeast trade, which is also turned about, and both combine to feed the great southwest monsoon of Asia. Knowing the origin of this moist monsoon, we shall be able to determine the probability of droughts or rains in India when we know whether the supply of air is sufficient and whether it will flow over the right region, or whether it will be deflected away from India. But to settle this question is at present very difficult.
The flow of any current of air is determined largely by the pressure of other air on each side of it, and it is quite possible that the flow of the southwest monsoon, at any place and time, may be affected by something that occurred long before in a very distant part of the globe. At first it was thought that the condition of the snow lying on the ground in the Himalaya Mountains would determine the movement of the monsoon and the amount of rain in the lowlands, but, as I have elsewhere stated, the supply of air to the southern Indian Ocean must ultimately come from the great westerly winds of the roaring forties, and therefore the Asiatic circulation must be affected by the condition of affairs in south Africa and the south Pacific and even the south Atlantic oceans.
On November 14, 1896, simultaneous balloon ascensions were made from St. Petersburg and Munich and from intermediate cities, in the midst of an area of high pressure that was moving slowly eastward over Europe. My study of these observations in the light of my maps of high-level isobars for the northern hemisphere gave occasion for the following long range forecast which was made early in December, and, of course, long before we received any reports from India, "As a result it is quite possible that this area may have brought to upper India light snow followed by cold dry weather about the first of December, 1896."
As this prediction was abundantly verified, as shown by the reports which we received a year later, it may be worth saying that the study of these upper isobars explains why the areas of high pressure over North America usually move at first from the northwest; subsequently their velocity diminishes while the path turns more nearly eastward; on the other hand, similar areas of high pressure and cold air in Europe are apt to come from the northeast before they turn southeastward.
It seems certain that the atmosphere is so mobile that whatever happens on one side of the globe will soon be known by its results on the opposite side. Whatever happens in the atmosphere fifteen miles above the earth will soon produce results at the earth's surface far away. Meteorology must embrace the whole atmosphere above and below, north and south, east and west.
I suppose that the most important problem of the present time is to attain a clear idea of the mechanics of the earth's atmosphere as a whole. We separate this problem into three closely related divisions. First we treat the atmosphere as we would a liquid of very rare but uniform density. Next we introduce the idea of a gas which enlarges or contracts in volume with every change of pressure or temperature.
Finally we pass from simple dry air and moisture to study the changes of volume and pressure and corresponding changes of temperature, moisture and cloud. These studies are comprised under the technical terms hydro-mechanics, aero-dynamics and thermo-dynamics. The atmospheric problems of to-day and of all future time will undoubtedly be concerned principally with these three classes of questions, and another century may elapse before men can solve them all.
I have here at hand a circular table which represents a small portion of our globe within the polar circle, while the center of the table represents the north pole itself. I will set the table in rotation; of course it revolves much more rapidly than the earth does. It is now revolving from left to right as the earth itself does when we stand facing the north and see the sun rising in the east. If I shoot this ball so that it rolls straight across the revolving table, it will not trace a straight line on that table but a curved line. If the track lie on the right-hand side of the pole the curvature will be toward the equator, but if on the left-hand side then the curve will be away from the equator. In both cases the curvature is toward the right hand as the ball progresses. This sentence corresponds to the two cases of a body moving, respectively, eastward or westward on the earth. When it moves eastward it has a greater centrifugal force than the corresponding point on the globe and pushes toward the equator. When it moves westward it has a less centrifugal force and retreats toward the pole. Corresponding phenomena occur when a pendulum is swung to and fro as in the Foucault pendulum experiment; or when a gyroscope is rapidly spun, as was also done by Foucault. We were long since taught by Poisson, Tracy and Ferrel that any mass, whether solid, liquid or gaseous, moving on the surface of the rotating earth in the northern hemisphere experiences a deflection to the right, and this is true under ordinary circumstances. Perhaps you will not be surprised to learn that our distinguished mathematical colleague. Professor Chessin, of Washington University, St. Louis, has lately reopened this question and even yesterday in this very lecture room showed that under some circumstances the deflection may be to the left, so that questions which have been considered settled for many years are now deemed worthy of a new investigation. Thus in meteorology we must expect to be frequently called upon to revise our old ideas in the light of the newest researches.
The study of hurricanes and typhoons long ago led to the general conclusion that they consist of comparatively thin layers of air revolving horizontally in nearly circular orbits, and therefore analogous to the revolving horizontal wheel of a gyroscope whose axis is vertical. On the other hand the phenomena of the waterspout at sea and the tornado on land had led to the idea that in these cases we have to do with nearly vertical ascending currents of air. Redfield's careful construction of numerous weather maps made him certain that in a hurricane the winds trend inward toward the center to such an extent that the hurricane can not be considered as a system of circular rotations, but of spiral inflowing ascending and overflowing currents of air, or the ideal cyclonic vortex movement. The same conclusion was soon formed with regard to the waterspout and tornado, the only differences being as to the question what are the angles of inflow, ascent and overflow? Since 1871 a still more careful analysis of the United States daily weather maps has shown that it is necessary to consider the fact that the winds on the west side are colder and drier than those on the east side of the storm center. Thus it follows that in the northern hemisphere we have cold dry northwest winds swirling around the central low pressure and running under the more moist southerly winds, sometimes even going so fast as to overflow these for short distances while pushing them aside. In this respect a hurricane storm lies intermediate as to its mechanism between the thunder-storm and the waterspout. In the waterspout we have a relatively small mass of air, no great differences of temperature, a rapid ascension with a rapid horizontal rotation. In the thunderstorm we have a simple horizontal overturning; cooler or drier air descends from overhead and warmer or moister air ascends from below. In every style of storm and in every form of atmospheric circulation there is and must be overturning with overflow and underflow.
The problems of simple overturning have been studied by Margules from the thermo-dynamic point of view. Perhaps I can illustrate these problems by means of this glass box with vertical divisions. I will place this dividing blanket in the middle. On the left-hand side we have a mass of air cooled by this adjacent ice; on the other side is an equal volume of air at the temperature of the room. If I quickly remove the blanket the cold air settles down, flowing beneath the warm moist air and covering the bottom, while the warm air is raised to the top. The differences of density have caused an interchange of energy due to the action of the force of gravity quite independent of radiation or conduction of heat. The descending cold air has expended some of the potential energy of its position in elevating the warm air. If the warm air was anywhere near the point of saturation, then its small loss of temperature due to its rising and expanding may have produced a haze in our little experiment, but in nature it often produces a great thunder cloud, and every gradation of cloud from that form down to the thinnest stratum.
These overturnings are perpetually going on in every room of our buildings and of course in the atmosphere. If a cloudy mass descends it is warmed by compression as it descends; evaporates all its cloudy particles, and in its further descent eventually has its own temperature raised. In general we have very low temperatures at great altitudes in the atmosphere, but if such air were brought down rapidly to the earth's surface it would be wanned up by compression so as to be insufferably hot and dry. This is the method of the formation of the hot, dry southwest winds of Kansas, Arkansas and Oklahoma where "corn is roasted on the stalk." Our North American cold winds from the northwest represent one step in the general condition of the whole atmosphere; they are undoubtedly descending winds, but descending so slowly and rolling along the earth to such great distances toward the equator that the air has time to cool by radiation before it reaches us. This is the formation of our areas of "high pressure" and cool, dry, clear weather.
In close analogy to the steam engine driven by heat that is derived from fire but is lost in the condenser, so the motive power in the atmosphere is the heat received from the sun, but lost by radiation from the earth. As to quantity and quality of this solar heat we are still at the beginning of our knowledge. Eminent authorities adopt figures ranging between two and four calories per minute per square centimeter. Every effort must be put forth to determine more accurately this fundamental datum.
Very many insist on searching our climatological records for periodic phenomena such as solar rotation periods and sunspot periods and lunar periods. Brückner's period of 35 years is quite famous. We have as yet very little data on which to base satisfactory researches into these questions, but the trend of our present knowledge is to show that in so far as these periods depend upon external or cosmical influences they are too feeble to be of importance; in fact, too feeble to be clearly recognized.
On the other hand, in so far as they depend on the internal mechanism of the atmosphere, they die out in a short time after they have been started, and are not permanent or steady periods in the proper sense of the word, but are driven and imposed on the atmosphere by conditions outside of it. Just as we see ripples standing in the rear of a stone in a shallow stream of water, so we have waves and clouds in the atmosphere on the leeward side of every obstacle. The annual periodic changes in the declination of the sun and in the resulting monsoons are undoubtedly accompanied by great reactions in our atmosphere extending like waves around the whole globe; but these again die out in a few years. Almost the only periodic phenomenon due to the internal mechanism of the atmosphere, one that is permanent and appreciable, is the semi-diurnal change of pressure which appears likely to be an internal phenomenon of resonance maintained by the regular diurnal change of temperature. But these questions are not settled and remain for further investigation.
I think the great climatic changes that seem to have taken place during geological history must be explained in connection with the corresponding changes that have taken place in the orography of the continents, and the changes in the distribution of land and water. The great gorges that extend from the Hudson through New York Bay toward the Middle Atlantic and from the Congo on the western coast of Africa also into the mid-Atlantic prove beyond controversy that there was a time when the ocean level was 5,000 feet lower than now, relative to the land on either side. Of course we know that mountain ranges have risen gradually by successive slight earthquake rifts; that the surface of the globe has always been cracking and bending, rising here and falling there. When we are able to demonstrate clearly the connection between our present climates and our present surface orography, then we shall be able to show what geological climate must have prevailed in any other age if the geologists can tell us what were then the characteristics of the surface. I consider this to be the ultimate end of meteorology, namely, the logical deduction of the climate and the weather for any time and any given configuration of continents and oceans. When we have attained this goal; when meteorology has become more truly deductive, then we can pass to the satisfactory discussion of the great problems that we now can merely toy with like children. Then we shall know whether Mars is inhabitable, and whether man could possibly have existed and evolved anywhere on this earth during geological ages preceding the present.
I am safe in saying that it is impossible to foresee in detail the problems of the future meteorology. I have by a few special cases illustrated the general conclusion that a long array of unsettled problems confronts those who would understand the operations of our earth's atmosphere. The fundamental problem of to-day is to educate men for the work that we see is at hand. Friends of science and humanity must be found who will provide for the expenses of men able to work on these problems. We need laboratories, physicists and sympathetic supporters. Perhaps the very first step is to provide generous fellowships, securing a support for enthusiastic men who are adapted to these researches. Atmospheric phenomena are not too difficult for us, nor is there any known natural limit to our steady intellectual progress. Those who are attentive to the voice of nature hear a command like that given to Joshua, "Go up into the land and possess it." But we also hear the voice that said unto Adam, "In the sweat of thy brow shall the earth bring forth its fruit." Whatever is worth doing involves hard work both physical and intellectual. We have many years of work before us, many abstruse and difficult problems, but what we ask first and last is your kindly sympathy and hearty support until success crowns the end.
- A public lecture, illustrated with experiments, at Columbia University, March 16, 1909.
- One hundred and ninety miles were recorded on March 14, 1910.
- See Monthly Weather Review, November, 1896, p. 415.
- Published as chart VII. in that number of the Review.
- See p. 420 of that same number of the Review.