There are two theoretical approaches to the development of manflight: the natural, birdflight approach and the mechanical, brute force approach. The first relies on close observation of birds to obtain insight into Nature’s way of converting organically generated power into flight. The second relies on sheer force of machine power, primarily that to be supplied by the steam engine. In the second approach, the main problem to be solved is to determine a structural framework strong enough to support the stresses caused by a power source–typically a steam engine–at full operation. This train of thought can be traced in the work of Cayley through Stringfellow and Henson, to Maxim, and finally to Langley. The second approach begins once again with Cayley but proceeds to Lilienthal, Pilcher, Chanute, and finally the Wright brothers. We are more familiar with the brute force approach–the application of power to achieve flight, but the natural approach, studying the flight of birds, contributed to the advent of human flight as well.

One of the clearest contemporary statements of the significance of the close observation of birdflight as the basis of aeronautical development is provided by Victor Lougheed, in his 1909 summary of aeronautical achievement, Vehicles of the Air:

“Besides constituting the most conclusive evidence imaginable of the perfect practicability of flight, as well as serving as the original and a constant stimulus to man in his efforts to achieve navigation of the air, the birds and other animals that fly afford models that naturally merit the most thorough and profound consideration of all students of aerodynamics. For in nature’s mechanisms of flight must exist answers to all the problems of flying, awaiting for their discovery only the analyses and applications of sufficiently persevering and painstaking investigators.” (159)

That birds should have provided the inspiration for powered flight comes as no surprise. When we investigate the history of the interrelationship between the observations of birdflight and the development of manflight, we can notice some interesting correspondences. The most active time of the development of manflight occurs during a 20-year period from 1885 through 1905. During this relatively brief period, studies of bird flight provide two interesting kinds of input into the invention process. One shapes the theory and becomes the basis for the modern science of aerodynamics, the fundamental science of flight. The other impulse, closely associated with the first, is of a more thematic or even spiritual nature rather than technical; it can be described as the inspirational component of the purpose of flight. Birdflight provides two necessary impulses to the achievement of flight. One, the technical, is absolutely essential to its success; the other, the inspirational, is also important, but its effect, towards the end of the period is, interestingly, to work against the accomplishment of technical mastery.
The idea of birdflight gains its strongest inspirational force from the theory behind much of the writings of the romantic poets of the 19th century, beginning with Coleridge, Wordsworth, and Goethe, and continuing through the transitional poetry into the Victorian and early modern eras. The Romantic movement invested the idea of birdflight with its greatest symbolic and thematic effect. The romantic movement saw the advancements of science through a perspective that mixed skepticism with admiration.

Douglas Bush has suggested that the “one main impulse in romanticism” was its “conscious and subconscious revolt against the Newtonian universe and spirit of science” (82). But, as Bush points out, in preferring an “animistic” to a “mechanistic” universe, Blake, Coleridge and Wordsworth “were much closer to Newton himself than they realized” (83). The romantic vision sought to blend the careful observation of nature with a sense of the meaning of the forces that lay behind the shapes that appeared in nature. In studying nature, observant men would, according to Wordsworth, “see, hear, perceive, And cannot choose but feel”

The power, which all
Acknowledge when thus moved, which Nature thus
To bodily sense exhibits, is the express
Resemblance of that glorious faculty
That higher minds bear with them as their own. (227)

This credo might have been taken straight from the thoughts of Francis Bacon himself, who suggested that scientific study should originate in the observation of natural events, and not in the memorization of the writings of Aristotle (Shuler 36).

The image of the bird was one of the most prominent natural images to appear in romantic poetry. There was scarcely a poem written with a bird as its central image that did not have complex spiritual imagery associated with it. If Wordsworth failed to write much poetry specifically incorporating images of birds, others in the romantic movement did not fail to do so. Coleridge made the image of the Albatross one of the iconic symbolic objects in literature:

At length did cross an Albatross:
Through the fog it came;
As if it had been a Christian soul,
We hailed it in God’s name.

After Coleridge’s mariner shoots the albatross in an unexplained impulse (romantic rebellion? scientific curiosity?), it is hung around the Mariner’s neck “instead of a cross.” When he finally gains release from his afflictions, the mariner’s message to those who listen is that

He prayeth well, who loveth well
Both man and bird and beast.

–an encomium to a spiritual view of the supernatural powers represented by wildlife.
The image of the bird as a link to divine power appears repeatedly, in poetry following Coleridge, from Shelley’s Sky-lark:

Bird thou never wert,
That from Heaven, or near it,
Pourest thy full heart

or Keats’ Nightingale:

Thou wast not born for death, immortal bird!

or John Clare’s “Birds’ Lament”:

Oh, says the sparrow, my love is gone,
She so much that I doted on . . . .

The American contributions provided ample examples as well, including Thoreau’s Marsh Hawk:

In each heaving of thy wing,
Thou dost health and leisure bring . . .

Or William Cullen Bryant’s Waterfowl:

There is a Power whose care
Teaches thy way along that pathless coast–
The desert and illimitable air–
Lone wandering, but not lost.

Poe’s Raven matches Coleridge’s Albatross for pervasive symbolic significance.

The aeronautical pioneers of the 1800s demonstrated repeatedly that the study of nature–in particular, birdflight, was essential for success. The pioneer of aeronautical theory, Sir George Cayley, was an inspired and determined scientist of his era. Cayley’s first writings on aeronautical schemes date from 1804; these unpublished writings describe a design for airships well in advance of their actual appearance. This first fragment proposing a method of powered flight was written within five years of the publication of both Wordsworth’s Lyrical Ballads and the Prelude. The second of Cayley’s aeronautical writings described a gunpowder engine, which appeared in Nicholson’s Journal in 1807.

Cayley’s most important contribution to aeronautical theory was a three-part paper on “aerial navigation,” published in Nicholson’s Journal in 1809 and 1810, which described a flying machine incorporating wings for lift. The design of the wing is described in some detail; Cayley draws on natural observation of bird flight to develop his scientific ideas:

“For the sake of perspicuity I shall . . . analyse the simple action of the wing in birds . . . . When large birds, that have a considerable extent of wing compared with their weight, have acquired their full velocity, it may frequently be observed that they extend their wings, and without moving them continue to skim for some time in a horizontal path. Fig I . . . represents a bird in this act. Let ab be a section of the plane of both wings opposing the horizontal current of air (created by its own motion), which may be represented by the line cd and is the measure of the velocity of the bird. The angle bdc can be increased at the will of the bird, and to preserve a perfectly horizontal path, without the wing being waved [moved downward or upward to gain propulsion], must continually be increased in a complete ratio . . . till the motion is stopped altogether; but at one given time the position of the wings may be truly represented by the angle bdc [diagram].” (Pritchard 228)

Thus from the observation of the bird in flight Cayley moves rapidly to the representation of the flight in the language of geometry and physics, a Newtonian language of scientific precision. Cayley states that he has “measured the surface of a great many birds,” finally basing his computations on the measurements of a rook, or crow, because, he says, “its surface and weight are as nearly as possible in the ratio of a superficial foot to a pound” (231). In concluding, Cayley observes that “the whole of this subject is of so dark [unknown] a nature,” that the “only way” to gain further knowledge is to “copy Nature” (251).

However Cayley might have wished to solve the problem of flight, he was unable to do so, finishing his research in the area with a letter to the Bulletin of the Societe Aerostatique and Meterologique de France in 1853, describing a design for a man-powered flying machine. To the end, Cayley believed strict imitation of birdflight held the secret. Cayley’s awkward 1853 device was based on an approximation of birdwing design:

“When the surfaces are hinged to look like the wings of a bird, as with the framework, shewn in Fig 5, that portion nearest the hinge will give support in both the ascending and descending movement, on the principle of the inclined plane, and in the same manner as birds are thus supported during both these movements. . . .

This is a complicated action depending upon a nice adjustment of all the parts of the wing, and the degree of force applied, and to effect this purpose as in the wings of birds, we must adapt the same mechanic construction that Nature uses in the long feathered quills of their extreme wing.” (257)

While the connection with the romantic urge is evident, it is interesting to note that the only poet, apparently, who appealed to Cayley’s taste was Charles Darwin’s grandfather Erasmus Darwin, who Douglas Bush says sought to “raise the scientific level of poetry” (114). Cayley approvingly quoted Erasmus Darwin’s poetry in a letter written in the 1840s:

Soon shall thy arm, unconquered steam! afar
Drag the slow barge or drive the rapid car;
Or on the wide waving wings expanded bear
The flying chariot through the fields of air. (93)

Cayley is the acknowledged father of the theory of manflight. Because Cayley’s writings appeared in lesser-known journals of his day, awareness of his achievement was limited. In America, Cayley’s work was largely unknown until James Means discovered Cayley’s writings and reprinted them in his 1895 Aeronautical Annual (James Howard Means 37).

The one individual who was the most influential in the birdflight approach to the development of manflight was the German Otto Lilienthal, who built a series of functional gliders and developed more refined theoretical data pertaining to lift and drag. Otto Lilienthal, helped by his brother Gustav, began his experiments with gliders in the 1860s and 1870s. After a brief interruption, they returned to their experiments in the late 1880s and early 1890s, building more maneuverable gliders and even building a hill, with a storage shed in the interior and a launching platform at the top, from which to conduct their experiments. Otto Lilienthal was killed on 9 August 1896, when he lost control of a glider.

That Lilienthal knew of Cayley’s work can be intuited from the fact that a copy of Cayley’s ground-breaking 1909-1910 paper on aerial navigation (reprinted in 1875) was found in Lilienthal’s library (Gibbs-Smith 210). A further link is suggested in the fact that one of Lilienthal’s first experimental devices was a man-powered flying machine (based on the flapping motion of bird wings) described in Cayley’s 1853 publication (Lilienthal 30).

Lilienthal’s book, Birdflight as the Basis of Aviation, was in press at the time of his death. As its title suggests, birdflight characteristics provide the basis for the theoretical insights the book contains. Of its 94 illustrations, 20 are drawings or photographs of birds, and an additional 15 are diagrams describing wind forces acting on a wing. But even more indicative of the significance of birdmotion are the comments emphasizing the spiritual value of interpreting birdflight found throughout Lilienthal’s book. His opening comments, for instance, challenge the reader to consider the liberating capabilities of birdflight:

“Who is there who . . . does not deplore the inability of man to indulge in voluntary flight and to unfold wings as effectively as birds do, in order to give the highest expression to his desire for migration? . . . . Are we still to be debarred from calling this art our own, and are we only to look up longingly to inferior creatures who describe their beautiful paths in the blue of the sky?” (Lilienthal 1)

Flying creatures, and especially birds, demonstrate that transit through the air is far more perfect than all other modes of locomotion to be found in the animal kingdom as well as any method of artificial locomotion devised by man.

Lilienthal understands that the two primary problems to be solved are wing design and propulsion, the two problems linked through the operation of the bird’s wing. “How,” he asks, “are those wings to be constructed, and how are they to be moved when we wish to imitate that which nature shows us in so masterly a fashion, when we desire to effect that rapid, voluntary flight which requires so small an expenditure of energy?” (22). Lilienthal concludes his opening section with the following statement (the emphases are his):

“Although this [discussion] will not give us an exhaustive explanation the various phenomena of birdflight, yet we may see that natural birdflight utilizes the properties of air in such perfect manner, and contains such valuable mechanical features, that any departure from these advantages is equivalent to giving up every practical method of flight.” (23)

This statement is the Newtonian equivalent of Wordsworth’s injunction to his readers to observe the powers of nature; however, Lilienthal translates Wordsworth’s recommendation to a scientific principle by suggesting that only observation of nature will lead to the technical mastery of flight. Lilienthal’s message is repeated with, if possible, even greater force in the concluding section of his book:

“We are, therefore, forced to the conclusion that the only possibility of attaining efficient human flight lies in the exact imitation of birdflight with regard to the aerodynamic conditions, because this is probably the sole method which permits of free, rapid flight, with a minimum of effort.” [Lilienthal’s emphases] (128)

Before he concludes his discussion, Lilienthal mentions the only poet included in his otherwise completely scientific treatise. That poet is, not surprisingly, the German romantic poet Goethe, and the passage is from Faust:

Aye, ’twill not be so easy,
To mate the wings of mind with material wings.

Lilienthal had many reasons to quote Goethe; the least important, perhaps, was Goethe’s reputation as a poet. Goethe was known, in Germany, if not elsewhere, for his scientific research as well as his literary achievements. As Rudolph Magnus has observed, Goethe’s scientific theories strongly influenced German theoretical research during the late 1700s and early 1800s. Goethe believed, for instance, that animal forms are determined by the forces that constitute their environment (Magnus 108-9). For Goethe, perception of nature was most important: “In science, all depends . . . on growing aware of what lies at the bottom of the [natural] phenomena, and such awareness is infinitely fruitful” (quoted in Magnus 228).

Lilienthal concludes with a passage that phrases his scientific impulse in a rhetorical grace:

“It will, indeed, be no easy matter to construct a useful wing for man, built upon the lines of the natural wing and endowed with all the dynamically economical properties of the latter; and it will be even a more difficult task to master the wind, that erratic force which so often destroys our handiwork, with those material wings which nature has not made part of our own body. But we must admit the possibility that continued investigation and experience will bring us ever nearer to that solemn moment, when the first man will rise from earth by means of wings, if only for a few seconds, and marks that historical moment which heralds the inauguration of a new era in our civilization.” (129)

In this passage we can see clearly the manner in which scientific knowledge and idealism associated with scientific effort are combined; Lilienthal saw the achievement of manflight as “inaugurating” a “new era in civilization.” The “historical moment” that Lilienthal anticipated lasted only a few seconds. It occurred on December 17, 1903, when the Wright brothers flew successfully at Kitty Hawk, North Carolina, less than seven years following Lilienthal’s death. In the meantime, another aerial pioneer, Percy Pilcher, died flying his glider in much the same manner as Lilienthal had. Like Lilienthal, Pilcher used birdflight as the basis for his glider design (Jarrett 66). But to achieve success, the Wright brothers had to break free not only from the weight of the earth, but from the traditional birdflight-bound view of the successful route to the mastery of flight. Neither accomplishment was easy.

The Wright brothers repeatedly acknowledged the influence of Cayley and Lilienthal on their efforts to achieve powered flight; they were inspired to begin their study of flight at least partly by the death of Lilienthal in 1896 (McFarland 103). Like Lilienthal and Cayley, they believed the effort to fly depended on the careful study of birdflight. Initially their thoughts “pertained more particularly to gliding flight and soaring. If the bird’s wings would sustain it in the air without the use of any muscular effort, we did not see why man could not be sustained by the same means” (McFarland 4).

The Wright brothers corresponded frequently with Octave Chanute, their chief mentor, supporter and technical resource. Like Lilienthal and Pilcher, Chanute had built several gliders and used birdflight as the basis for his designs (Crouch Dream 176). Chanute encouraged the Wright brothers to match technical care with safety as they undertook to craft their own gliders, which they did in 1900, 1901, and 1902. The influence of the birdflight tradition of Cayley and Lilienthal is evident in notes Wilbur made while he and Orville were at Kitty Hawk for the first time in September and October of 1900:

“The buzzard which uses the dihedral angle [upward V sketch] finds greater difficulty to maintain equilibrium in strong winds than eagles and hawks which hold their wings level [sketch of flat V]. . . .

“All soarers, but especially the buzzard, seem to keep their fore-and-aft balance more by shifting the center of resistance than by shifting the center of lift. Thus a buzzard soaring in the normal position [upward V sketch] will be turned upward by a sudden gust. It immediately lowers its wings, much below its body [flat V sketch]. The momentum of its body now acting above the center of resistance turns the bird downward very quickly.” (McFarland 34-5)

The emphasis in Wilbur Wright’s description of birdflight differs noticeably from that of Cayley or Lilienthal, who used bird wing observation to determine the best shape of the wing and to estimate the forces of lift and drag. The Wright brothers (but especially Wilbur, who seems to have been the most knowledgeable aeronautical engineer of the two) were more interested in controllability of the machine. Wilbur studied how the birds adjusted themselves to maintain their stability in changing wind forces. Because he knew of the hazards of the inappropriate control of gliders, he was most interested in determining how birds adjusted to the vagaries of sudden wind shifts or gusts. The issue of wing design had pretty much been determined, at least at its most basic level, and Wilbur was more concerned with glider stability and responsiveness to control movements.

In his report to the Chicago branch of the Western Society of Engineers, in June of 1903, six months before the successful first flight, Wilbur Wright described the nature of his
observation of birdflight at Kitty Hawk in the fall of the previous year (1902). Wilbur reported that he and Orville observed buzzards and eagles gaining height with little to no effort on calm days; he deduced from this observation that this seemed to indicate the existence of “rising columns of air,” and that these rising columns of air “do not exist everywhere, but that the birds must find them” (328). He also reported seeing a feather from one of the birds rising above them rather than falling to the ground. Thus for the Wright brothers, and especially for Wilbur, the behavior of the birds and of the air in which they flew was most important. Controllability was at least as important as design.

After the Wright brothers flew successfully at Kitty Hawk in December of 1903, Octave Chanute asked Wilbur if he had any “final conclusions” about the power required for artificial flight, stating that he was “under the impression that birds use less power than you have found necessary” (468).

Wilbur responded that

“your suggestion regarding the power expended by birds found us considering that very point, having been led to consider the subject by the very ingenious calculations of Sir George Cayley as published [reprinted] in the Aeronautical Annual for 1895. He attempts to compute the power expended by a consideration of the thrust possible to be obtained by a crow in its flight. . . . I can see no hope, based on any information at present accessible, for any considerable advance on what we have already done in the matter of dynamic efficiency. I think the great room for improvement will be . . . in mechanical details and methods, and especially in the skill of the operators. If it could be definitely proved that the birds do very much better [than the Wright brothers’ efficiency], it would lead to a revision of our present views . . . .” (475)

In his own polite, tactful, and rather clever fashion, Wilbur Wright suggests to Chanute that the continued observation of birdflight will produce little in the way of meaningful results, and that the most fruitful research should be devoted to machine design and improvements in controllability. To base his conclusions on reality rather than theory, two months later, after he “secured and measured” a crow, Wilbur reported to Chanute that “after considering its structure and its flight, I am far from believing that it [the crow] expends less power, in proportion to weight and speed, than is readily attainable in a dynamic flying machine of large size” (479). Whether intentional or not, Wilbur Wright’s choice of a crow as the basis of his experiments brought symbolic closure to the movement begun by Cayley, who also chose a crow (or “rook”) as the bird upon which he based his initial theories in 1804.

It is likely that Wilbur Wright’s skepticism about the value of too close a study of birdflight as the basis for aviation can be traced to his familiarity with James Means’ 1884 pamphlet, Manflight, which suggested that European experimenters, especially the English, had gone to illogical extremes in following this principle:

“Some of the most eminent designers of flying-machines have spent years of labor in trying to construct an apparatus which should follow the bird model and accomplish artificial flight by the same means that are used in natural flight. Some English scientists have gone into the most tedious and useless analyses of bird-flight with a view to its mechanical reproduction. It will not be difficult to show why these endeavors are useless. Nature is a good teacher, and the models which she furnishes have helped many an inventor to accomplish his task. But too close an imitation of nature is in many cases more of a hindrance than an aid.” (9)

Means illustrated his view by suggesting the folly of basing the design of a locomotive upon the motive forces employed by an elephant or by designing a powered boat on the same principles of motion employed by a duck. Means concludes by suggesting that only rotary motion–a “screw,” as he terms it–will provide an efficient method of propelling a flying machine through the air (15). An “airscrew” is exactly what the Wright brothers devised to propel their flying machine.

Two other features of their writings during the period from 1899 to 1904 demonstrate Wilbur Wright’s totally different use of birdflight from those of his predecessors: one is the noticeable absence of diagrams of birds or even of discussion of birdflight characteristics. The last mention of birdflight in the Wright brothers’ writings, discussed above, was initiated by Chanute, who, like his other European predecessors, was conditioned to place that concern as primary in his aeronautical investigations. The Wright brothers were able to think through the situation for themselves. The second item of evidence is the Wright brothers’ reliance on a device that had been used by few before them: the wind tunnel. While some, like Hiram Maxim, had used the wind tunnel, the Wright brothers’ wind tunnel was the first wind tunnel “in which measurements of any accuracy” could be obtained (McFarland 549n).

The Wright brothers, in other words, were successful not only because they were good theorists, good craftsmen, and good experimenters, but also because they also saw the problem of flight as one which was to be solved by the traditional principles of physics, of applied forces to fixed shapes, and not resulting from intuitive empathy with the forces of nature. The Wordsworthian-Goethian impulse was set aside in favor of the language of science: mathematics.

It would be convenient to say that Wilbur and Orville were led to their results because they preferred reading Victorian poets like Tennyson and Arnold to Shelley and Keats. But there is no evidence that they read Victorian poetry, or much poetry at all, for that matter. But it would be erroneous to suggest that they were not well-educated members of their society, for though neither one completed high school, education was strongly emphasized in their household. Their father, Bishop Milton Wright, was heavily involved in editing and printing religious education materials, and there was a “large and varied library” in the house, which included classics of history and biography like Plutarch’s Lives, Gibbon’s Decline and Fall of the Roman Empire, Boswell’s Life of Johnson, and sets of the writings of Nathaniel Hawthorne and Walter Scott (Crouch Bishop’s Boys 77-78).

In addition, the Wright brothers were instrumental in the publication of some of the poetry of one of the first black American poets, Paul Laurence Dunbar, a classmate of Orville’s at Dayton’s Central High School (Crouch Bishop’s Boys 101). Every biography of the Wright brothers includes Dunbar’s salute to Orville Wright’s printing skills:

Orville Wright is out of sight
In the printing business.
No other mind is half as bright
As his’n is.

It is not unlikely that the Wright brothers read many of Dunbar’s other poems, which describe the daily activities of the working world familiar to many whites as well as blacks. The style of Dunbar’s tribute to Orville Wright was not unlike that of much of the popular poetry of the day, such as Trowbridge’s poem on “Darius Green,” who built an unsuccessful flying machine.

But even if Wilbur Wright had read the poetry of Gerard Manley Hopkins, he would have seen in “The Windhover,” for instance, the same mystical interpretation of birdflight; in Hopkins’ case, the style and mysticism, though more complex, perhaps, than that of the romantics, still shared the Blakean vision.

While the Wright brothers set aside reliance on the study of birdflight as essential to the development of the theory of flight, other students of flight did not. Even after the Wrights and others in Europe and America developed flying machines of various designs, the reliance on birdflight as an essential element of design continued for several years. Because the influence of Lilienthal was so great, that tendency was nearly impossible to overcome. The following standard texts, for instance, published between 1908 and 1911, included discussions and diagrams of birdflight:

F. W. Lanchester, Aerodonetics (London, 1908, reprinted 1917); Paul Renard, L’Aviation: Conferences Faites en 1909 (Paris, 1909); Victor Lougheed, Vehicles of the Air, 1909, quoted at the opening of the paper; W. J. Jackman, T. H. Russell, and O. Chanute, Flying Machines: Construction and Operation (Chicago, 1910); Paul Schiemann, Vogelflug und Kunstflug (Rostock, 1910); and Albert F. Zahm, Aerial Navigation (New York, 1911).

But by 1915, when the Great War moved into its second year, and military experts on both sides realized the potential of the airplane to profoundly affect the outcome of ground battles, reference to birdflight disappeared from the texts, as the romantic vision of the mystery of flight was replaced by descriptions of the mechanisms of gunfire, bombing, and reconnaissance.

 

Works Cited

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Bush, Douglas. Science and English Poetry: A Historical Sketch, 1590-1950. New York: Oxford Univ Press, 1950.

Chanute, Octave. Progress in Flying Machines. M. N. Forney: New York, 1891, 1899.

Crouch, Tom D. A Dream of Wings: Americans and the Airplane, 1875-1905. New York: Norton, 1981.

Crouch, Tom D. The Bishop’s Boys: A Life of Wilbur and Orville Wright. New York: Norton, 1989.

Gibbs-Smith, C. H. Sir George Cayley’s Aeronautics, 1796-1855. London: HSMO, 1962.

Hartner, Willy. “Goethe and the Natural Sciences.” Goethe: A Collection of Critical Essays. Ed. Victor Lange. Englewood Cliffs NJ: Prentice-Hall, 1968. 145-160.

Jarrett, Philip. Another Icarus: Percy Pilcher and the Quest for Flight. Washington: Smithsonian, 1987.

Lilienthal, Otto. Birdflight as the Basis of Aviation. Tr. A. W. Isenthal. London: Longmans Green, 1911.

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Magnus, Rudolph. Goethe as Scientist. Henry Schuman: New York, 1949.

McFarland, Marvin W., ed. The Papers of Wilbur and Orville Wright: Including the Chanute-Wright Letters and Other Papers of Octave Chanute. 2 Vols. 1953; rpt Arno, 1972.

Means, James. Manflight. J. Means: Boston, 1884, 1891.

Means, James Howard. James Means and the Problem of Manflight During the Period 1882-1920. Washington: Smithsonian, 1964.

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Schuler, Robert M. Francis Bacon and Scientific Poetry. Transactions of the American Philosophical Society (82:2) 1992.