Popular Science Monthly/Volume 9/August 1876/On the Backwardness of the Ancients in Natural Science
By CARL VON LITTROW.
I CAN hardly be mistaken in holding that the ceremonies attending the installation of a rector of our university chiefly concern the students. Thus only can I account for the fact that on the one hand the newly-installed officer is burdened with the unpleasant duty of listening to a history of his own life, and, on the other, that he is required to deliver an address whose sole purpose is to make known the ground he occupies in science and in his teaching. His colleagues, to whom he is indebted for his election, of course have no need to be informed where he stands, while the students oftentimes have but scant opportunity of knowing what manner of opinions are held by him. Hence it is that my words are addressed first of all to you, my young friends.
Those nations of antiquity which so long freely and unchallenged have borne the title of "classical," owe to their mastery of form whatever right they have to that honorable epithet. While we must regard our predecessors in culture as being the best patterns in all that regards form, we may nevertheless of ourselves assert that in the investigation of matter, and in the arts of making it subservient to man, we in turn equally or even to a greater degree surpass the ancients. This condition of things is indeed nothing but one phase of the strife between the real and the ideal—a strife which, fortunately for mankind, is never altogether allayed. That in nearly every department of art—taking this terra in its widest sense—we are on the whole the miserable Epigoni of the ancients, is universally admitted, and the causes of our inferiority are well enough understood. On the contrary, the reasons of our own preëminence in the exact sciences are by no means so generally known. Schiller, who, had he not been a profound philosopher, would never have been the prince of poets that he was, describes the realist as being characterized by a spirit of "sober observation," and the idealist by a spirit of "restless speculation." "When we presume," says he, "by the mere force of reason to determine anything about the outer world, we do but trifle." However obvious the meaning of this remark may at first appear, we shall find, on closer consideration, that in fact the author not only ascribes to the idealistic mind of antiquity an undue bent toward speculation, but that furthermore he plainly denies to it the faculty of correct observation. The entire justice of Schiller's remark, whether as taken in its literal or in its implicative sense, is perhaps nowhere so patent as in the province of astronomy.
Every one knows of the clear skies which canopy the homes of the early civilizations—Italy, Greece, Spain, Egypt, Arabia. The purity of the atmosphere enjoyed by these regions is shown by the importance attached by the ancients to the knowledge of the rising and setting of certain stars. In our countries astronomy must have been precluded from taking the same direction by the fact that but rarely do we see the stars near the horizon, to say nothing of seeing them on the horizon, owing to the presence of haze, which in these regions nearly always narrows the field of view. For this reason, had we not the telescope, we should have been unable to attain to the comparatively accurate knowledge possessed by the ancients with regard to the movements of Mercury, a planet which is hardly visible from our latitudes We inhabitants of Central Europe might easily, in point of cloudy skies, be the rivals of the dwellers on the shores of the Sea of Azof—the Cimmerians of the ancients. It might therefore be supposed that the starry heavens, as these ancestors would describe them to us, must be in great part invisible to us, and far richer than we have been able to see them in later times. We must the more expect them to describe things hardly visible to us as our present division of the northern heavens into constellations dates, as far as its main features are concerned, from at least 2,000 years ago, and the firmament formed an object of studious contemplation even then. Add to this the fact that, as early as the year 130 b. c., Hipparchus began to draw up a complete catalogue of all the fixed stars; and Claudius Ptolemæus, 150 years later, took up this task anew. Now the "Almagest," as Ptolemy's work is called by the Arabs, who handed it down to us, includes 1,028 stars; and even if, on the strength of a remark made by the elder Pliny, who speaks of 1,600 observed stars, we with faint probability grant that the "Almagest" does not represent the complete labors of Hipparchus and Ptolemy, still even the second figure is far less than we should have expected. Argelander, at Bonn, sets down in his charts no less than 3,256 stars visible to the naked eye; and Heis, whose eye indeed was possessed of an abnormal power, seeing stars as points without rays, increased Argelander's list by 2,000 stars visible at Münster. Thus, not taking into the account the no less than twenty more degrees of the heavens visible from Alexandria than from Germany, the ancients noted hardly one-half of the stars which were visible to them! The defectiveness of their observations can be more easily understood from the fact that for instance they reckoned 474 stars of the fourth magnitude, only 271 of the fifth, and finally only 49 of the sixth magnitude; whereas the fact is, that the number of stars increases so rapidly in the order of magnitudes that each succeeding class embraces a much larger number than all the classes that precede it. In our latitudes Argelander makes out with the naked eye nineteen nebulæ and star-clusters, while Hipparchus mentions only two, and Ptolemy five, neither of them noting such prominent objects as the nebula in Orion and that in Andromeda. And such defective knowledge as this of the open-lying heavens persisted long after the invention of the telescope—for full 1,500 years. Among the old astronomers the Persian, Abdalrahman-Al-Sûfi, who lived in the tenth century, forms a notable exception; but he did not inspire his contemporaries or his successors with his own ardor, or prompt them to add to his labors.
The same is to be said of the southern heavens. The Arabians, surely, did not lack opportunity for acquiring a knowledge of many of its constellations. Ever since the days of Bartolomeo Diaz, it was a necessity for Europeans, on sea-voyages, to determine places by southern constellations. Ptolemy was acquainted with only a few of the principal stars of the antarctic hemisphere, and it was not till the beginning of the seventeenth century that Theodor von Emden regularly divided these regions of the heavens into constellations. It remained for Herschel, in recent times, to determine a number of open questions with regard to these southern constellations.
To account for this backwardness in the investigation of a subject which certainly possessed at least as much interest for the ancients as for ourselves, by declaring it to be the result of their superficiality, were an injustice to the olden time, seeing that in other respects it commands our unconditional admiration for its arduous achievements. That what they needed was to have their senses trained to this kind of work, and that, although they had keen appreciation of art, they never learned to look at things with the eye of the investigator of Nature, will be better understood from a statement of what they knew about individual celestial objects than of what they knew about the entire firmament.
That well-known group of stars, the Pleiades, which in the Fall adorns our eastern sky by night, serves well to show that in observing the stars something else is required besides a clear atmosphere and good eyesight. In a didactic poem by Aratus, written 270 years b. c., we have our earliest trustworthy account of Grecian astronomy. There the Pleiades are called "έπταπόροι"—stars traveling in seven paths—though according to Aratus only six stars were visible. Some 300 years later Ovid writes—
"Quæ septem dici, sex tamen esse solent;"
while Hipparchus, in his critique of Aratus, about 150 years before Ovid, expressly says that in clear, moonless nights seven stars can be actually made out. Now, Aratus lived in Macedonia, and Ovid apparently wrote his "Fasti" at Rome, giving the finishing touches to the work on the southern shore of the Black Sea: thus both writers lived beneath a very clear sky. The fact that Hipparchus labored at Rhodes, a few degrees farther south, must not be supposed to account for his having seen one more star than the others, though the discrepancy between the observers is all the more surprising as the group about which they differed was of great importance for navigators in the then state of nautical science, and was constantly under observation. This circumstance, in fact, attracted the attention of the astronomers of the time, but for centuries they sought in vain for the seventh star, and offered all manner of curious explanations for its supposed disappearance, one of which is worthy of special mention, viz.: that this seventh star had moved over to the position of the middle star in the tail of Ursa Major, called by the Arabians Mizar, and that it was the little star now commonly known as the Postilion and which stands close to Mizar. The scholia to Homer cling to this idea of the disappearance of the seventh star. Not until the thirteenth century do we find a correct description of the Pleiades, in a work by the Persian astronomer Kazvini, who apparently borrowed it from Sûfi. "There are," says Kazvini, "six stars (in the Pleiades) and in the midst of them a number of dark (i. e., faint) stars;" but his observations received no attention from subsequent astronomers. In vain, too, was the observation even of such a man as Maestlin, Kepler's preceptor, who distinguished no less than fourteen stars in the Pleiades group. Not till after the invention of the telescope could Sir Christopher Heyden, in 1610, write as follows, showing the power of the new instrument: "I see with my telescope eleven stars in the Pleiades, though never before were more than seven distinguished." But how stands the case to-day? At present they who discern these eleven stars with the naked eye are considered anything but prodigies; indeed, I am acquainted with persons—not professional astronomers, but laymen—who can make out from fourteen to sixteen stars in this group. But then we are the descendants of generations of men who from infancy were taught to put their organs of sense to the sternest test, and to take note even of the faintest sense-impressions; our eyes have been schooled, and in this special instance of the Pleiades they are not so much dazzled by the brighter stars as guided by them to the stars in their neighborhood, for, in fact, more than one half of the fourteen stars are of a magnitude far below the commonly-accepted limit of vision for the naked eye. We have learned to observe, to choose favorable conditions, to know what is a really clear atmosphere; we know that small stars in the vicinity of bright ones are far more readily descried in twilight than in the depth of night, the brightness of the larger stars in the latter case obscuring the smaller. Hipparchus errs in saying that moonlight is a hinderance to such observation: keen eyes may, with a bright full moon shining, count as many as fifteen stars in the Pleiades.
Another point of considerable interest we note in this instructive example. The fact that the Postilion, the Alcor of the Arabians, was taken to be the lost seventh star of the Pleiades, further shows that Alcor, though a star of the fifth magnitude, and easily discernible, had not been noted by previous astronomers, else it could never have passed, at the beginning of our era, as a new star, then first registered. And indeed the Arabian astronomers, one thousand years later, call this star "The Forgotten," plainly because it had not been noticed previously.
We have a like instance in the star Alpha in Capricorn. Mankind had to observe this star for thousands of years before they saw, what any child may see when its attention is directed to the object, that here are two stars (one of the third and one of the fourth magnitude) so close together as to coalesce into one when hastily viewed. Again, it was the Arabians who noted this circumstance. Still, this did not avail to establish the true nature of a Capricorni. Ulugh Beigh, in the fifteenth century, and Tycho Brahe, in the beginning of the seventeenth, in their famous "Catalogues of the Stars," take no notice of it, and it was not till one hundred years later that Hevelius formally entered the companion-star in his list. We cite two or three further instances to show how the idealistic bias of the ancients, which culminated in Aristotelism, has almost down to our own times diverted men from simple but correct views of the world of sense.
The amazing progress of observational astronomy during the last two centuries is in great measure due to the hippy accident of our hemisphere containing a bright polar star. Sundry investigations can be made only with regard to stars near the pole, and all the more easily, of course, and with smaller instruments, the larger the star happens to be. The importance of this star impressed itself upon men in former times, it being employed for correcting the compass. And yet even Columbus was not clear whether Polaris is situated at the north-pole, or only near to it, though it must be observed that in his day its distance from the pole not altogether escape his means of observation. "It appears," he cautiously observes, "as if the pole-star had a motion [round the pole] like the rest of the stars."to more than three degrees, i. e., about six diameters of the full moon, and that hence it could
Again, is it not amazing that for thousands of years mankind should have been in presence of so frequent a phenomenon as the zodiacal light—a phenomenon which in southern latitudes is specially impressive—without considering it to be worthy of mention, or rather, let us say, without seeing it, until Childrey, in the middle of the seventeenth century, discovered it, if we may so speak? So, too, may it excite our wonder, to think that the earliest definite mention of the noteworthy phenomena (easily visible with the naked eye) attending a total eclipse of the sun dates only from the year 1706, that is to say, a period of time full one hundred years subsequent to the invention of the telescope.
Thus the ancients were deficient in even the most elementary powers of observation. The simple but truthful noting of what is perceived by the senses is the prerogative of our time. But what of the restless spirit of speculation with which Schiller taxes the ancients?
Here permit me to recall anew to your memories, by an instance taken from the history of astronomy, thoughts which oftentimes, perhaps, have occurred to us all. Plutarch's dialogue on "The Visage that is seen in the Moon's Disk" has ever been regarded as containing the sum and substance of all man's notions and knowledge of our satellite down to the period when it was written. The very title is provocative of mirth to us, the children of the modern time. The Visage in the Moon! Nowadays it only suggests to the poet and the artist satirical ideas: in olden times it was the starting-point of profound meditations, which were held not to be unworthy of being attributed to the most famous philosophers and mathematicians of the day. The author first in all earnestness demonstrates the absurdity of the opinion which asserts the figure appearing in the moon to be nothing else but an optical illusion arising from the visual sense being dazzled by the brightness of the moon's disk. Next we have a lengthy refutation of another opinion, which says that the visage in the moon is the reflection of our ocean. Among other reasons given to show the erroneousness of this opinion is this, that there is only one ocean, and that, if the visage in the moon were a reflection of it, then the ocean must be made up of parts separated from one another by isthmuses and continents! The third opinion combated by Plutarch is to the effect that the moon is a mixture of air and of a mild kind of fire; as sometimes during a perfect calm the surface of a body of water becomes ruffled—a thing itself to be demonstrated—so too does the air assume a blackish color: thus is explained the appearance as of a human face in the moon. The hypothesis of the Stoics, who affirmed the moon to be a globe of fire, on the surface of which rests the atmosphere, is rejected on the ground that in that case the moon would need some matter whereon to rest, and from which it might derive fuel for its fire. We are informed that, according to Pindar, the earth is propped up all round by pillars with bases of adamant, whereas, according to the Stoics, she has no need of supports, being situate in the centre of the universe toward which all things tend. This last opinion is declared to be untenable, because the earth, whose surface is so broken with elevations and depressions, must then be considered as spherical, and that would imply the existence of antipodes clambering up and down the earth's sides like lizards. Coming back to the principal question under discussion, the solitary interlocutor in this dialogue maintains that, even granting the impossibility of ponderous, earth-like bodies moving in the heavens, it does not follow thence that the moon is not another earth, but only that it happens to be in a region to which it does not by its nature belong. Man, for example, in like manner has his ponderous, earth-like parts in the upper region of his body, in the head, and the warm, fire-like parts in the lower; of his teeth some are directed downward, others upward, but in neither is there anything contrary to Nature. The moon, situate between the sun and the earth, as the liver or other soft viscus lies between the heart and the stomach, transmits heat from the upper regions to us, at the same time dissipating the mists which rise from the earth, purifying and attenuating them by the action of her own heat. Considered as an earth, the moon is a splendid body; as a star it would be a shame to its class; for of all the innumerable heavenly bodies—to quote the author literally—she is the only one that needs another's light! When the sun goes down he is hidden from us by the earth; in an eclipse, on the contrary, by the moon. Hence the earth, owing to its great size, covers the sun entirely, as long as the night endures, while the moon sometimes conceals him totally, but only for a short time. The moon, therefore, is a body like our earth; and inasmuch as it contains nothing that is foul, and enjoys the purest light of heaven, and is filled with genial fires which do not consume like the fires of earth, the moon must contain the most delightful savannas, flames like mountains of light, empurpled zones, and abundance of gold and silver; all this—accounts for the visage in the moon's disk! The objection that the spots on the moon are too large to be thus accounted for is met with the noteworthy proposition that it is the remoteness of the light from the body casting the shadow, and not the size of the body, that makes a shadow large; and if Mount Athos casts a shadow 700 stadia in length, that is a consequence not of its height, but of the sun's great distance. The discussion here is diverted to the question of the habitability of the moon and the fate of our souls after death; of this argument I need only quote the comforting assurance that the devout and the virtuous migrate to the moon, and that from the ether in which they float they acquire an elasticity and a strength, for the maintenance of which the most attenuated vapor affords sufficient nourishment.
However incomplete this summary of Plutarch's voluminous tractate, it will serve to convey some idea of the state of astronomy and physics among the Greeks. In it we look in vain for simple recognition of the facts, or for any just apprehension even of the most elementary principles. Approaching their inquiries with foregone conclusions, they had decided the causes of phenomena long before they came fairly within range of them.
The point therefore is, not merely what we see, but also how we see; we must be able to critically examine what we have seen, and, above all, we must be able to recognize those features of the object which are of importance. And, as in the foregoing examples we have shown that in the domain of science mere seeing was not the strong point of the ancients, so it can be proved that they were even less distinguished for reflex seeing. By way of antithesis to a generally-received proverb, we may with more justice, though less poetry, declare that the simplicity of the child's understanding dwells on what is unimportant, but commonly passes by unnoticed what is really of moment. The senses, it is true, supply the material—the conscious, or mediate substructure—for the grandest systems of thought; but yet in their further development they must be subject to the action of the culture to which they themselves gave rise. Though at first they were our preceptors, now they are oftentimes our pupils. In seeing we have, perhaps, more need of the understanding than of the eye, just as in walking we could better dispense with strong legs than with sound lungs. The disciplined eye, though of feeble power, descries more objects difficult to be discerned than the strong but unpractised organ. This is true of the microscope and telescope as well as of the naked eye; and the student of Nature to-day, even with the imperfect instruments of his predecessors, sees much more than they. Who is there that has not innumerable times had experience of the dependence of the senses on the understanding, in the fact that, when he is intent on seeing a definite object, his eye becomes almost insensible to all other objects? Thus, one who is searching in a garden for red berries is quite unconscious of the blue berries which stand side by side with the red.
We have in German a term which very happily expresses the faculty, possessed by the most eminent of scientific geniuses, of discovering the important phases of ordinary phenomena: such men are said to have "Blick." Have we not an instance of a higher visual faculty, exalted not only by genius, but also by comprehensive knowledge, when a Gauss was led by the glistening of the windows of a church-tower which he was observing with his telescope to the idea of his heliotrope—an instrument without which no accurate triangulation is nowadays ever thought of; or when a Rittenhouse, in the pretty images seen in a reversed telescope, discovered a means—ever since universally employed—of producing artificial signals which have precisely the same properties as though they stood in infinite distance; or when a Newton made of the spectrum, a thing that had been gaped at as a mere curiosity a thousand times before, the foundation of modern optics?
The sudden arrival at a truth from all sides—a thing so frequent in the history of the sciences, which often makes it hard to decide to whom the honor of new discoveries properly belongs—of itself shows that cultivated minds in general have grasped the idea. The human race might be compared to a traveler in unexplored countries. As the booty he brings home is rich in proportion to the extent of his own intellectual acquirements, which enable him to distinguish what is new from what is hackneyed, so mankind has need of schooling in order to understand what is of importance in the events occurring round about. In short, one must be impressible in order to be impressed.
Ever since the fourth century of our era, the Chinese have used the magnetic needle as a nautical instrument, and thus were enabled to extend their voyages as far as India and Eastern Africa. The Arabians brought us into relations with India in the eighth century, and the Crusaders with the Orient in the tenth, and yet the mariner's compass was not introduced into Europe till the twelfth century.
Does it not seem wellnigh incredible that we cannot trace the use of the free-hanging plummet, as a means of observation, farther back than the period when the Arabians were our teachers in astronomy; nay, that only in the fifteenth century it found general acceptance by the exertions of our renowned countryman Georg von Peuerbach?
When, at the beginning of the last century, Amontons worked with entire success an optical telegraph; and Franklin, fifty years later, robbed the clouds of their lightning; and when both of these men were dismissed even by a learned body like the Paris Academy with stale witticisms; if for thousands of years countless aërolites have been seen to fall to the earth without ever giving rise to an inquiry as to the nature of meteors—the reason is always to be found in the self-same indisposition to receive what is new, which caused mediæval Europe to pass by unnoticed the golden teachings of a Roger Bacon or of a Leonardo da Vinci. Both of these stood high above Francis Bacon as inductive philosophers; but he had for his contemporaries men who had been taught by Copernicus, Galileo, Kepler, and others, some of the mighty consequences of that principle which Francis Bacon had now simply to formulate in order to have it universally accepted. Here and there other eminent men had, long before Roger Bacon himself, hit on the right way of investigating Nature. This assertion, too, rests on unquestionable evidence, which, however, is perhaps not so familiar to you. The visibility of the crescent moon after new moon is of ritual significance to the Jews, the ecclesiastical commencement of their months depending upon it. Their great philosopher, Maimonides, who wrote in the twelfth century, informs us of the process whereby they for a long time noted the moments wherein the lunula became visible; hence they deduced a formula by the aid of which the time of the visibility of the crescent may be calculated. This is induction pure and simple; but not till long afterward was the soil fitted to receive such seed, or the significance of this process recognized.
For only a little over a hundred years have we been following the right path. We have enlarged the capacities of our organs to an extraordinary degree; we have learned to warn our senses of the veils with which preconceived philosophical ideas were wont to blindfold them; we prize the good-fortune which places in our hands any important clew to the working of Nature; disdainful skepticism, of which Alexander von Humboldt says that, in individual instances, it is almost more harmful than unquestioning credulousness, is like the latter disappearing from among us. But we must guard against the error of supposing that herein is our entire salvation. "The educated man is more than a virtuoso, than a specialist; his power does not lie in the exercise of one faculty alone. . . . The man who harmoniously combines within himself the largest number of diverse faculties is a leader of men, though he be surpassed by others in the development of individual faculties. Here we have the fruits of true humanism, of true culture, which is ever aiming at the establishing of an inward equilibrium in the individual as in the state." These words of a renowned poet of the present age foreshadow the counsel I would offer to you for your guidance through life. While, on the one hand, the principle of the division of labor, without which human progress is inconceivable, restricts the functions of the individual within a comparatively narrow province: on the other hand, he only can wisely elect to labor in such a province, and can work the field profitably, who does not lack comprehensiveness. There is no science which has not its æsthetic side, as there is no study of form which may not be advanced by having a basis in fact. Philologists and historians of late have been desirous of having their studies classed among inductive sciences; the investigator of Nature feels more and more every day that he has, perhaps, too long neglected the deductive method. And philosophy itself, the science of sciences, can it subsist without a fundamental knowledge of the grounds of all the sciences? Without philosophy any high degree of intellectual development, in any direction whatever, is inconceivable. Even they who turn away with contempt from Philosophy are, in spite of themselves, compelled to have recourse to her. She alone brings clearness in thoughts upon the nature of one's chosen pursuit—thoughts from which there is no escape for whoever thinks!
Let it then he your firm resolve, students of the high-school par excellence, not to attend the lectures simply of one faculty, or of one branch of a faculty. Be true to the principles of universitas literarum. Over and above the studies special to your future calling, do not fail to acquire as liberal an education as possible. Postpone purely specialist studies to the time when you will not only have to receive, but also to give—to produce. Hold in high esteem the ancients in all things wherein they were and still are our teachers. Despise not your less remote predecessors and your contemporaries the world over in matters wherein they alone are the authorities.