Popular Science Monthly/Volume 40/March 1892/Sketch of William Ferrel
WILLIAM FERREL.
| SKETCH OF WILLIAM FERREL. |
By Prof. WILLIAM M. DAVIS.
SIXTY years ago, the study of meteorology gained a notable impetus from the discoveries then recently made concerning the phenomena of storms. The tempestuous winds had been called to order by the investigations of Dové and Redfield, followed by those of Reid, Piddington, and others in the succeeding decades, and even the literary quarterlies contained reviews of books treating revolving gales. But at that time the understanding of the general circulation of the atmosphere about the earth had hardly advanced from its position early in the eighteenth century, when Hadley first and incompletely explained the oblique course of the trade-winds, as a consequence of their motion upon a rotating globe. In the middle of our century, Dové, then the leader of European meteorologists, taught that all our northeast winds were portions of the return current from the poles, whose battling with the equatorial current gave us our alternations of wind and weather in the temperate zone. In this country, the most commonly accepted explanation of atmospheric circulation was derived from Maury's fascinating Physical Geography of the Sea—a book whose erroneous teachings concerning the source of our rains in evaporation from the South Pacific Ocean, and concerning the northeast-southwest course of the return polar current at great altitudes, still find recent advocacy by those who would persuade us that cannonading will cause rainfall.
The meteorology of to-day is another science from that of those earlier decades. The store of facts has increased wonderfully, both from the observations made at sea, in good part as a result of the incentive given by Maury, and from the establishment of weather services in many countries following the suggestions of Espy, Henry, Leverrier, and others. The hydrographic offices of various governments have charted the winds of the oceans; Buchan has determined the distribution of barometric pressure over the world, Loomis has discussed more fully than any one else the features of the cyclonic storms whose action is so well indicated on the weather maps.
But from whom has the finer spirit of understanding of all these facts been received? From whom have we now gained an insight into the wonderful correlations that exist among the varied motions of the atmosphere? We would not belittle the ingenious theories of Espy, to whom greater honor is given with the passing years; we would not forget the many contributions made by earnest students at home and abroad; but the fuller appreciation of the system of the winds, both great and small, both in the full sweep of the terrestrial circulation and in the constricted whirl of the tornado, comes from one man—a man lately described by the leading meteorologist of Europe as one "who had contributed more to the advance of the physics of the atmosphere than any other living physicist or meteorologist—a man of whom Americans are justly proud."[1] Alas that this man is no longer living, and that so few Americans know how proud they may be for having had him for a countryman!
William Ferrel died on September 18, 1891, at May wood, Kansas, in his seventy-fifth year. The first half of his life was a struggle against adverse circumstances in uncongenial surroundings. His later years saw him on the staff of the Nautical Almanac, in charge of tidal computations in the Coast Survey, Professor of Meteorology in the Signal Service, member of the National Academy of Sciences, and our recognized leader in scientific meteorology. Let those of us whose paths of life have been opened by the labors of our fathers marvel at the innate powers of such a man as this, who made his own way through heavy discouragements.
Ferrel was born in Bedford (now Fulton) County, Pa., on January 29, 1817. We are fortunate in having from his own hands a record of his early years. At the request of Mr. A. McAdie, of the Signal Service, Prof. Ferrel wrote, in 1887, an account of his life, and from this Mr. McAdie prepared a biographical sketch that was published in the American Meteorological Journal for February, 1888. The same journal for December, 1891, contains several notices of Ferrel's works by Newcomb, Abbe, and others, read at the October meeting of the New England Meteorological Society. A list of his published writings is given in the Journal for October of the same year. The manuscript autobiography has been presented by Mr. McAdie to the Library of Harvard College, and the following account of Ferrel's youth is prepared from it. Although never widely known, even among our scientific men, his work since his fortieth year gives a record of the latter part of his life; and for that reason the narrative of his earlier years is here given more fully. It is one that may certainly inspire young men who labor under discouragement; and perchance it may also lead the more generous of our readers to seek out and lend a helping hand to those whose lines are hard and who are working earnestly to help themselves; not that all such shall become Academicians, but that well-timed help extended in such directions is the best investment that a man can make for himself and for his country.
Ferrel's father was of Irish and English descent; his mother came from a German family. They lived in a simple way in the country, and the boy went to a common district school. In 1829 the family moved across the narrow western arm of Maryland into Berkeley County, Virginia (now West Virginia). There the son was kept closely at work, except while at school for two winters, the school-house being a rude log cabin, in which he went "through the arithmetic and the English grammar," and then remained out of school till 1839. Having mastered his school-books, he had nothing further to study except a weekly newspaper, the Virginia Republican, published at Martinsburg; this he waited for eagerly, to read its occasional scientific items.
While thus engaged on the farm young Ferrel saw somewhere a copy of Park's Arithmetic, with a sketch of mensuration at its close. Of this he writes: "At the sight of the diagrams I was at once fired with an intense desire to have the book. But I had no money, and at this time I was too diffident to ask my father for even a half-dollar, or to let him know that I wanted the book. Soon afterward I earned fifty cents in the harvest-field of one of the neighbors, and with this I determined to buy the book. The first time I had a chance to go to Martinsburg I inquired for it at a store, but learned that its price was sixty-two cents. I told the store-keejDer I had only fifty cents, and so he let me have it at that price. It was a light task to learn all that was in it." One can not forbear to moralize over this intense desire for knowledge, for what would not such a boy have learned with proper encouragement and opportunity! It must be to these and the succeeding years of hampered effort that Ferrel refers in a few sad words at the close of his narrative: "Much of my time has been wasted, especially the earlier part of it, because, not having scientific books and scientific associations, I often had nothing on hand in which I was specially interested."
It may be said that Ferrel began his career as an investigator in 1832, when on going out one day to work he noticed that the sun was eclipsed. He had not known that such an event was to occur, but it set him to thinking. He had somewhere learned the cause of solar and lunar eclipses, but his materials for further study were only a German calendar, such as farmers use, and a copy of Adams's Geography, with an appendix giving problems on the use of the globes. From these he found that the sun and moon moved with unequal velocities in different parts of their orbits, and that the fastest and slowest motions were at opposite points. Of this he writes: "My theory was that the earth and the moon moved with uniform velocity in circular orbits, and that these orbits were eccentrically situated with regard to the sun and earth. With regard to the moon's path, I knew that it crossed the ecliptic, but I did not know at what angle, and I also at first supposed that the node was fixed. At the beginning of the next year, when the next calendar came to hand, I discovered from the predicted eclipses that the node must recede. I saw from the calendars that there was some cycle of nineteen years, and suspected that this had something to do with the moon's node. This would make the node recede about 19° in a year, as the next year's eclipses seemed to require." Then, with the aid of some older calendars, Ferrel, about at the age of sixteen, proceeded to make out tables of the dates of eclipses in an empirical fashion, but he unfortunately assumed that the diameter of the earth's shadow was constant. "Upon this assumption I spent a vast amount of time, but could get no positions of the nodes or inclination of the orbit which would satisfy the eclipses. The amount of study I gave to the subject both day and night was very great, but I at last gave the matter up in despair. Some time after I was at work one day toward evening on the thrashing-floor, and saw the shadow of a distant vertical plank against the wall; I observed that it was much smaller than the width of the plank, and the reason for it occurred to me at once. I then saw the error of my assumptions with regard to the earth's shadow in my eclipse investigations and was now very anxious to go over again all my computations with the true diameter of the earth's shadow, for, knowing the distance of the moon and the angular diameter of the sun, I was able to determine this. As soon as I could find time I went over the whole work, and everything came out as satisfactory as could reasonably be expected with my methods. . . . This was in the winter of the first part of 1834. I now ventured to predict by my method the eclipses for the next year, 1835. I determined that there would be three eclipses—two of the moon and one of the sun. . . . I made a record of the whole in a book and awaited for the next calendar for comparison with its predictions. All the circumstances of the lunar eclipses agreed remarkably well, and the greatest error in the predicted times was only nine minutes.'* And this was the work of a farmer's boy, without help, without encouragement, in the time that he could spare from daily work!
His next book seems to have been Gummere's Surveying, which he mastered in the spring of 1834, with the exception of the miscellaneous examples at the end of the volume, for which no rules had been given and which required a knowledge of geometry. "During the summer, as I had a little time to spare, I dwelt upon these, giving weeks sometimes to a single proposition. It happened that during the summer I was engaged a good part of my time on the thrashing-floor, which had large doors at both ends with wide and soft poplar planks. Upon these I made diagrams, describing circles with the prongs of large pitchforks, and drawing lines with one of the prongs and a piece of board. One by one I mastered all the problems in this way except three. For more than a quarter of a century these diagrams were visible on the doors, and, in returning occasionally to the old homestead, I always went to take a look at them."
This kind of home study continued until 1839, when Ferrel went to Marshall College, at Mercersburg, Pa. Here he learned algebra, geometry, and trigonometry, and gave some time also to Latin and Greek. The next winter he taught near home; but in 1840 he returned to Marshall It was in this year that one of his professors assigned original problems in mathematics to the class. "On one occasion he gave the problem: Given the distances of a well from the three angles of an isosceles triangle, to determine the triangle. . . . This was easy to me at the time, for it was one of the problems which I had solved while at work on the thrashing-floor, with the use of diagrams on the barn doors, before I had seen a college or a treatise on algebra or geometry."
His money was exhausted in the latter part of 1841, and he went home to teach for two years. Bethany College was then opened in Virginia, and he was admitted to the senior class, and graduated in 1844. It is curious to notice that during all these years there is no mention of apparatus, experiments, or systematic observations; the boy's work, like that of the man afterward, was almost entirely internal and mental. Thus, at the age of twenty-seven, his schooling was ended, and he left his home and went to Missouri to teach. Failing health compelled him to stop work for a time, and his next engagement was at a small school in Kentucky, where he remained for seven years, until 1854.
While in Missouri he had happened on a copy of Newton's Principia, ordered but never called for by an earlier teacher; he bought it for five dollars, making little advance then on account of poor health, but later returned to it in Kentucky. "I now became first interested in the tides, and conceived the idea that the action of the moon and sun must have a tendency to retard the earth's rotation on its axis. Knowing that Laplace had treated the subject extensively in the Mécanique Céleste, I was very desirous of obtaining a copy, mostly to see what he had in that subject. I accordingly instructed a village merchant, on going to Philadelphia for a supply of goods, to procure me the work, having little idea of the magnitude of the work or the cost. On learning the cost at Philadelphia, he did not procure it for me until after writing and hearing further from me. I had now plenty to study in connection with my teaching for several years." From this followed Ferrel's first scientific paper. On the Effect of the Sun and Moon on the Rotary Motion of the Earth, a subject to which he returned with success in later years.
In the spring of 1854 Ferrel went to Nashville, Tenn., and opened a private school; here Prof. W. K. Bowling, of the Medical College, became his warm friend, and here he first turned his attention to meteorology, from meeting with Maury's Physical Geography of the Sea. "From this book I first learned that the atmospheric pressure was greatest near the parallels of 30°, and less at the equator and in the polar regions; and I at once commenced to study the cause of it. . . . In conversation one day with my friend Dr. Bowling, I told him I had read Maury's book, and he was at once desirous of knowing what I thought of it. I told him that I did not agree with Maury in many things. He then desired me to 'pitch into him,' as he expressed it, and furnish a review for his Journal of Medicine. This I declined to do, but at length consented to furnish an essay on certain subjects treated in the book, and notice Maury's views a little in an incidental way." This was the beginning of the studies in meteorology, which gave a new aspect to the science. The promised article was his Essay on the Winds and Currents of the Ocean. It has since been republished by the Signal Service in Professional Paper No. XII.
In the spring of 1857 the third period of Ferrel's life began on his accepting an offer from Prof. Winlock, transmitted through Dr. B. A. Gould, to take part in the computations for the Nautical Almanac, then prepared in Cambridge, Mass., and thus opened the happier situation of his later years; but it was not until the spring of 1858 that he finally left Nashville. From this time on he did not lack opportunity for study and acquaintance with scientific men. In 1867 he joined the Coast Survey, then under the superintendence of Prof. Benjamin Peirce, and remained in that service until 1883. The chief results of his work during this period were his Tidal Researches, Meteorological Researches, and his Tide-predicting Machine, all of which contribute to his well earned reputation.
Ferrel's researches on the tides were in both theoretical and practical directions. His theoretical discussions began in his days of teaching in Kentucky, and in 1853 had led him to conclude that the action of the tides would very slightly retard the rotation of the earth, but at that time no indication of such retardation had been found by astronomers. In 1860, however, it was found that the position of the moon was somewhat in advance of its calculated position; all the known effects of external perturbations having been allowed for, its advance still was unexplained. Ferrel, then living in Cambridge, returned to this problem and showed that the moon's unexplained advance might be accounted for as only an apparent result, the real fact being a retardation of the earth's rotation by tidal action. The essay on this subject was published in the Proceedings of the American Academy of Arts and Sciences in Boston in 1864. An incident in this connection illustrates the diffidence that Ferrel felt in coming in contact with strangers. He carried his essay on The Influence of the Tides in causing an Apparent Secular Acceleration of the Moon's Mean Motion in manuscript to the meetings of the Academy time after time, with the intention of reading it, but his courage always failed, until at last the paper was presented in 1864. Had its presentation been deferred over one more meeting, its appearance would not have antedated a similar essay by the French astronomer, Delaunay, on the same subject.
This was before Ferrel was a member of the Coast Survey; it was naturally followed by his engagement as expert in tidal studies in that office; and when afterward in Washington, he discussed and reduced many tidal observations made at various points on our coast. To lighten the labor of such computations he invented a tide-predicting machine, by means of which the time and value of high and low tides can be mechanically determined for various ports with sufficient accuracy for publication in the official tables, after the constants for the ports are worked out. This machine is now in regular use in Washington, where it is regarded as doing the work of thirty or forty computers. A general work on tides and their theory was among the latest studies that Ferrel undertook, to be stopped only by the illness that caused his death.
In 1882 Ferrel accepted a professorship in the Signal Service, producing while there several special reports of high value, among which his Recent Advances in Meteorology should have first mention. He also lectured to the officers of the Signal Corps at Washington, and it is from these lectures that he subsequently prepared his Popular Treatise on the Winds, the most comprehensive statement of theoretical meteorology in the English language. He resigned this professorship in 1886, in his seventieth year. He had before this accumulated a competence from judicious investments of the small earnings of earlier years.
Ferrel's name is chiefly connected with his original investigations in meteorology. The first of these was made at Nashville, as stated above, but a more serious study was made in his Motions of Fluids and Solids relative to the Earth's Surface, prepared shortly after going to Cambridge, and published in Runkle's Mathematical Monthly. This is regarded by a most competent critic as "the starting-point of our knowledge of the mechanics of the atmosphere." It is here that he first clearly states the important law that "in whatever direction a body moves on the earth's surface there is a force arising from the earth's rotation which tends to deflect it to the right in the northern hemisphere, but to the left in the southern." This was published in May, 1858, six months before it was discussed, with the same result, in the French Academy of Sciences. Space can not be given here to show the great importance of this principle in meteorology, but if the reader desires to follow it to its applications he should consult the Treatise on the Winds, named above. As to the importance of the principle, let any one attempt to explain the motions of the wind and the distribution of atmospheric pressures without it, and he will soon see the service rendered to meteorology by Ferrel in its introduction. The essential quality of this principle may perhaps be briefly stated.
The general conception of the theory of the winds refers them to convectional movements, arising from the action of gravity on parts of the atmosphere of different temperatures. According to this, the poles, where the temperatures are low, should have high pressures, and the occurrence of low pressures there has been a stumbling-block to more than one writer on the subject; indeed, hardly an English text-book can be named that will lead the student around this difficulty. The consideration introduced by Ferrel is to the effect that the actual distribution of pressure does not depend only on differences of temperature, but also on the motions excited by reason of the pressure differences. The condition of steady motion, under which the winds are impelled by an acceleration just sufficient to overcome their resistances, requires that the acceleration should be not only the small component of gravity acting on the barometric gradient, but the much smaller resultant of this component acting with the deflective force arising from the motion of the wind itself. The course adopted by the established interchanging circulation between the equator and the poles consists for the most part of a great circumpolar whirl from west to east; and the deflective forces here in play reduce the polar high pressures to low pressures. A reactionary relation therefore exists between the winds and the pressures, by which the distribution of pressures according to temperature alone is greatly modified. Instead of finding high pressure at the cold poles, a low pressure is produced there by the great circumpolar whirl of the general winds, and the air thus held away from the poles accumulates around the tropical belts of high pressure, of which Ferrel had first learned from Maury's book. The absence of northeast return currents (in this hemisphere), except in the trade-wind belt, is as important a feature of Ferrel's theory as the reversal of polar high pressure into low pressure. Maury's erroneous explanation of the winds gained great acceptance from the attractive style in which his book was written; but it is time that his explanation should be abandoned even in elementary teaching, and replaced by more serious views, less easily acquired but of more permanent value.
Ferrel's theory of the winds not only explains the general distribution of atmospheric pressure over the world, as no other theory can do; it introduces broad correlations among many phenomena in meteorology, greatly to the advance of the science. The legitimate analogies that may be drawn between the great circumpolar whirl of the terrestrial winds, the smaller whirls of tropical cyclones, and the concentrated whirling of tornadoes show the unity of action of the convectional processes in the moist atmosphere of a rotating planet. In earlier years, meteorology consisted chiefly of rules for observation and statistical study. The broad generalizations taught by Ferrel raise the science from this simple inductive condition and complete the philosophical rounding of its parts.
Ferrel was not an observer, but he carefully based his studies on well-ascertained facts. He was not an experimenter, but he followed the results obtained by the best physicists. He was a reasoner, able to employ the stronger methods of mathematical analysis. He was sincere and judicial, single-minded and simple-hearted. No one criticised his results more carefully or deliberately than he did himself. He was indifferent to popularity, and took little trouble to enforce his views on the world. He lived a quiet life, more with books than with men, although the few to whom his closer friendship was given prized it highly. From his isolation as a boy and young man, he was diffident, even to his own embarrassment, in going out to meet others; but to those who came to him he was generous and sympathetic in giving assistance. He never pushed himself forward, and all his official positions came unsought. His earlier essays were inconspicuously published, and never had a wide circulation, even in separate pamphlet form. Many who have received them must have passed them by hardly noticed. The attention of scientific men turned slowly to his work; only in later years than 1870 is his name often mentioned abroad. His preference was always for original methods, in his college demonstrations as well as in later investigations. He did little in the way of restatement of the conclusions of others, but liked better to give his time to original researches in which there was a prospect of discovering something new or of explaining facts that had not been explained before. When his interest was aroused in such work, he devoured everything that he could find about it, "studying almost day and night," and never giving up a problem until it was solved, or until he was satisfied that his labors could not solve it. His conquest of physical problems was not the result of intuitive perceptions alone, but followed patient and persevering work. This appears in his boyhood when he pondered over geometrical problems in the barn, and in later years when his meteorological theories gradually developed.
Ferrel was a man whose teachings reach slowly through the world. Many of the problems that he solved bear only remotely on the lives of the millions of unmarked men from among whom he won his way to eminence; but all who read of him may understand the lesson of his courageous perseverance, of his earnest work and of his simple life. They will do well if, even without adding much to the world's store, they can say as he did at the close of life, "I regret to leave my friends, but that is all I regret."
- ↑ Dr. Julius Hann, Director of the Austrian Meteorological Observatory, in the Proceedings of the Vienna Academy of Sciences, April 9, 1891.