CHAPTER I.
HISTORY OF THE INVENTION OF TELESCOPES.
The telescope is an optical instrument for viewing objects at a distance. Its name is compounded of two Greek words,—τηλε, which signifies, at a distance, or far off, and σχοπειν, to view, or to contemplate. By means of telescopes, remote objects are represented as if they were near, small apparent magnitudes are enlarged, confused objects are rendered distinct, and the invisible and obscure parts of very distant scenes are rendered perceptible and clear to the organ of vision. The telescope is justly considered as a grand and noble instrument. It is not a little surprising that it should be in the power of man to invent and construct an instrument by which objects, too remote for the unassisted eye to distinguish, should be brought within the range of distinct vision, as if they were only a few yards from our eye, and that thousands of august objects in the heavens, which had been concealed from mortals for numerous ages, should be brought within the limits of our contemplation, and be as distinctly perceived, as if we had been transported many millions of miles from the space we occupy, through the celestial regions. The celebrated Huygens remarks, in reference to this instrument, that, in his opinion, ‘the wit and industry of man has not produced any thing so noble and so worthy of his faculties as this sort of knowledge; (namely of the telescope) insomuch that if any particular person had been so diligent and sagacious as to invent this instrument from the principles of nature and geometry,—for my part, I should have thought his abilities were more than human; but the case is so far from this, that the most learned men have not yet been able sufficiently to explain the reason of the effects of this casual invention.’
The persons who constructed the first telescopes, and the exact period when they were first invented, are involved in some degree of obscurity. It does not certainly appear that such instruments were known to the ancients, although we ought not to be perfectly decisive on this point. The cabinets of the curious contain some very ancient gems, of admirable workmanship, the figures on which are so small, that they appear beautiful through a magnifying glass, but altogether confused and indistinct to the naked eye: and, therefore, it may be asked, if they cannot be viewed, how could they be wrought, without the assistance of glasses? And as some of the ancients have declared that the moon has a form like that of the earth, and has plains, hills, and valleys in it,—how could they know this—unless by mere conjecture, without the use of a telescope? And how could they have known that the Milky Way is formed by the combined rays of an infinite number of stars? For Ovid states, in reference to this zone, ‘its ground-work is of stars.’ But whatever knowledge the ancients may have possessed of the telescope or other optical glasses, it is quite evident that they never had telescopes of such size and power as those which we now possess; and that no discoveries in the heavens, such as are now brought to light, were made by any of the ancient astronomers; otherwise some allusions to them must have been found in their writings.
Among the moderns, the illustrious Friar Bacon appears to have acquired some rude ideas respecting the construction of telescopes. ‘Lenses and specula’ says he, ‘may be so figured that one object may be multiplied into many, that those which are situated at a great distance may be made to appear very near, that those which are small may be made to appear very large, and those which are obscure very plain; and we can make stars to appear wherever we will.’ From these expressions, it appears highly probable, that this philosopher was acquainted with the general principle both of telescopes and microscopes, and that he may have constructed telescopes of small magnifying power, for his own observation and amusement, although they never came into general use. He was a man of extensive learning, and made so rapid a progress in the sciences, when attending the university of Paris, that he was esteemed the glory of that seat of learning. He prosecuted his favourite study of experimental philosophy with unremitting ardour; and in this pursuit, in the course of twenty years, he expended no less than £2000 in experiments, instruments, and in procuring scarce books. In consequence of such extraordinary talents, and such astonishing progress in the sciences, in that ignorant age, he was represented, by the envy of his illiterate fraternity, as having dealings with the devil; and, under this pretence, he was restrained from reading lectures, and at length, in 1278, when sixty-four years of age, he was imprisoned in his cell, where he remained in confinement for ten years. He shone like a single bright star in a dark hemisphere—the glory of our country—and died at Oxford, in the year 1294, in the eightieth year of his age. ‘Friar Bacon,’ says the Rev. Mr. Jones, ‘may be considered as the first of English philosophers; his profound skill in mechanics, optics, astronomy, and chemistry, would make an honourable figure in the present age. But he is entitled to further praise, as he made all his studies subservient to theology, and directed all his writings, as much as could be, to the glory of God. He had the highest regard for the sacred scriptures, and was persuaded they contain the principles of all true science.’
The next person who is supposed to have acquired a knowledge of telescopes, was Joannes Baptista Porta, of Naples, who flourished in the sixteenth century. He discovered the Camera Obscura—the knowledge of which might naturally have led to the invention of the telescope; but it does not appear that he ever constructed such an instrument. Des Cartes considers James Metius, a Dutchman, as the first constructor of a telescope, and says, that ‘as he was amusing himself with making mirrors and burning-glasses, he casually thought of looking through two of his lenses at a time, and found that distant objects appeared very large and distinct.’ Others say that this great discovery was first made by John Lippersheim, a maker of spectacles at Middleburg, or rather by his children, who were diverting themselves with looking through two glasses at a time, and placing them at different distances from each other. But Borellus, who wrote a book ‘on the invention of the telescope,’ gives this honour to Zacharias Jansen, another spectacle-maker in the same town, who, he says, made the first telescope in 1590. Jansen was a diligent inquirer into nature, and, being engaged in such pursuits, he was trying what use could be made of lenses for those purposes, when he fortunately hit upon the construction. Having found the arrangement of glasses which produced the effect desired, he enclosed them in a tube, and ran with his instrument to prince Maurice, who, immediately conceiving that it might be of use to him in his wars, desired the author to keep it a secret. Such are the rude conceptions and selfish views of princely warriors, who would apply every invention in their power for the destruction of mankind. But the telescope was soon destined to more noble and honourable achievements. Jansen, it is said, directed his instrument towards celestial objects, and distinctly saw the spots on the surface of the moon, and discovered many new stars, particularly seven pretty considerable ones in the Great Bear. His son Joannes is said to have noted the lucid circle near the lower limb of the moon, now named Tycho, from whence several bright rays seem to dart in different directions. In viewing Jupiter, he perceived two, sometimes three, and at the most four small stars, a little above or below him, and thought that they performed revolutions around him. This was, probably, the first observation of the satellites of Jupiter, though the person who made it was not aware of the importance of his discovery.[17]
It is not improbable that different persons about Middleburgh hit upon the invention, in different modes, about the same time. Lippersheim seems to have made his first rude telescope by adjusting two glasses on a board, and supporting them on brass circles.[18] Other workmen, particularly Metius and Jansen, in emulation of each other, seem to have made use of that discovery, and by the new form they gave it, made all the honour of it their own. One of them, considering the effects of light as injurious to distinctness, placed the glasses in a tube blackened within. The other, still more cautious, placed the same glasses within tubes capable of sliding one in another, both to vary the prospects, by lengthening the instrument, according to the pleasure of the observer, and to render it portable and commodious. Thus, it is probable that different persons had a share in the invention, and jointly contributed to its improvement. At any rate, it is undoubtedly to the Dutch that we owe the original invention. The first telescope made by Jansen, did not exceed fifteen or sixteen inches in length, and therefore its magnifying power could not have been very great.
The famous Galileo has frequently been supposed to have been the inventor of the telescope, but he acknowledges that he had not the honour of being the original inventor, having first learned from a German, that such an instrument had already been made; although, from his own account, it appears that he had actually re-invented this instrument. The following is the account, in his own words, of the circumstances which led him to construct a telescope. ‘Nearly ten months ago (namely in April or May 1609) it was reported that a certain Dutchman had made a perspective through which many distant objects appeared distinct as if they were near: several effects of this wonderful instrument were reported, which some believed and others denied: but, having it confirmed to me a few days after by a letter from the noble John Badoverie, at Paris, I applied myself to consider the reason of it, and by what means I might contrive a similar instrument, which I afterwards attained to by the doctrine of refractions. And, first, I prepared a leaden tube, to whose extremities I fitted two spectacle-glasses, both of them plain on one side, and on the other side, one of them was spherically convex, and the other concave. Then applying my eye to the concave, I saw objects appear pretty large and pretty near me. They appeared three times nearer and nine times larger in surface than to the naked eye: and soon after I made another, which represented objects about sixty times larger, and eight times nearer; and, at last, having spared no labour nor expense, I made an instrument so excellent, as to show things almost a thousand times larger, and above thirty times nearer, than to the naked eye.’ In another part of his writings, Galileo informs us that ‘he was at Venice when he heard of Prince Maurice’s instrument, but nothing of its construction; that the first night, after he returned to Padua, he solved the problem, and made his instrument the next day; and soon after, presented it to the Doge at Venice, who, to do him honour for his grand invention, gave him the ducal letters which settled him for life in his lectureship at Padua; and the Republic, on the twenty-fifth of August in the same year (1610) more than tripled his salary as professor.’
The following is the account which this philosopher gives of the process of reasoning, which led him to the construction of a telescope:—‘I argued in the following manner. The contrivance consists either of one glass or more—one is not sufficient, since it must be either convex, concave, or plane; the last does not produce any sensible alteration in objects, the concave diminishes them; it is true that the convex magnifies, but it renders them confused and indistinct; consequently one glass is insufficient to produce the desired effect. Proceeding to consider two glasses, and bearing in mind that the plane glass causes no change, I determined that the instrument could not consist of the combination of a plane glass with either of the other two. I therefore applied myself to make experiments on combinations of the two other kinds; and thus obtained that of which I was in search.’ If the true inventor is the person who makes the discovery by reasoning and reflection, by tracing facts and principles to their consequences, and by applying his invention to important purposes, then, Galileo may be considered as the real inventor of the telescope. No sooner had he constructed this instrument—before he had seen any similar one—than he directed his tube to the celestial regions, and his unwearied diligence and ardour were soon rewarded by a series of new and splendid discoveries. He descried the four satellites of Jupiter, and marked the periods of their revolutions; he discovered the phases of Venus, and thus was enabled to adduce a new proof of the Copernican system, and to remove an objection that had been brought against it. He traced on the lunar orb, a resemblance to the structure of the earth, and plainly perceived the outlines of mountains and vales, casting their shadows over different parts of its surface. He observed, that when Mars was in quadrature, his figure varied slightly from a perfect circle; and that Saturn consisted of a triple body, having a small globe on each side—which deception was owing to the imperfect power of his telescope, which was insufficient to show him that the phenomenon was in reality a ring. In viewing the sun, he discovered large dark spots on the surface of that luminary, by which he ascertained that that mighty orb performed a revolution round its axis. He brought to view multitudes of stars imperceptible to the naked eye, and ascertained that those nebulous appearances in the heavens which constitute the Milky Way, consist of a vast collection of minute stars, too closely compacted together to produce an impression on our unassisted vision.
The results of Galileo’s observations were given to the world in a small work, entitled ‘Nuncius Sidereus,’ or, ‘News from the starry regions,’ which produced an extraordinary sensation among the learned. These discoveries soon spread throughout Europe, and were incessantly talked of, and were the cause of much speculation and debate among the circles of philosophers. Many doubted; many positively refused to believe so novel and unlooked-for announcements, because they ran counter to the philosophy of Aristotle, and all the preconceived notions which then prevailed in the learned world. It is curious, and may be instructive, to consider to what a length of absurdity, ignorance and prejudice carried many of those who made pretensions to learning and science. Some tried to reason against the facts alleged to be discovered, others contented themselves, and endeavoured to satisfy others, with the simple assertion that such things were not, and could not possibly be; and the manner in which they supported themselves in their incredulity was truly ridiculous. ‘O my dear Kepler,’ says Galileo in a letter to that astronomer, ‘how I wish we could have one hearty laugh together. Here at Padua is the principal professor of philosophy, whom I have repeatedly and urgently requested to look at the moon and planets through my glass, which he pertinaciously refuses to do, lest his opinions should be overturned. Why are you not here? what shouts of laughter we should have at this glorious folly! and to hear the professor of philosophy at Pisa labouring with the Grand Duke with logical arguments, as if with magical incantations, to charm the new planets out of the sky.’ Another opponent of Galileo, one Christmann, says in a book he published, ‘We are not to think that Jupiter has four satellites given him by nature, in order, by revolving round him, to immortalize the Medici who first had notice of the observation. These are the dreams of idle men, who love ludicrous ideas better than our laborious and industrious correction of the heavens. Nature abhors so horrible a chaos; and to the truly wise, such vanity is detestable.’ One Martin Horky, a would-be philosopher, declared to Kepler, ‘I will never concede his four new planets to that Italian from Padua, though I should die for it;’ and he followed up this declaration, by publishing a book against Galileo, in which he examines four principal questions respecting the alleged planets; 1. Whether they exist? 2. What they are? 3. What they are like? 4. Why they are? The first question is soon disposed of by declaring positively that he has examined the heavens with Galileo’s own glass, and that no such thing as a satellite about Jupiter exists. To the second, he declares solemnly that he does not more surely know, that he has a soul in his body than that reflected rays are the sole cause of Galileo’s erroneous observations. In regard to the third question, he says, that these planets are like the smallest fly compared to an elephant; and finally, concludes on the fourth, that the only use of them is to gratify Galileo’s ‘thirst of gold,’ and to afford himself a subject of discussion. Kepler, in a letter to Galileo, when alluding to Horky, says, ‘He begged so hard to be forgiven, that I have taken him again into favour upon this preliminary condition—that I am to show him Jupiter’s satellites, AND HE IS TO SEE THEM, and own that they are there.’
The following is a specimen of the reasoning of certain pretended philosophers of that age against the discoveries of Galileo. Sizzi, a Florentine astronomer, reasons in this strain: ‘There are seven windows given to animals in the domicile of the head, through which the air is admitted to the rest of the tabernacle of the body to enlighten, to warm and to nourish it; two nostrils, two eyes, two ears, and a mouth; so in the heavens, or the great world, there are two favourable stars, two unpropitious, two luminaries, and Mercury alone undecided and indifferent. From which and many other similar phenomena in nature, such as the seven metals, &c., we gather that the number of planets is necessarily seven. Moreover, the satellites are invisible to the naked eye, and therefore can exert no influence on the earth, and therefore would be useless, and therefore do not exist. Besides, as well the Jews as other ancient nations have adopted the division of the week into seven days, and have named them from the seven planets. Now, if we increase the number of the planets, this whole system falls to the ground.’ The opinions which then prevailed in regard to Galileo’s observations on the moon, were such as the following:—Some thought that the dark shades on the moon’s surface arose from the interposition of opaque bodies floating between her and the sun, which prevent his light from reaching those parts; others imagined that, on account of her vicinity to the earth, she was partly tainted with the imperfections of our terrestrial and elementary nature, and was not of that entirely pure and refined substance of which the more remote heavens consist: and a third party looked on her as a vast mirror, and maintained that the dark parts of her surface were the reflected images of our earthly forests and mountains.
Such learned nonsense is a disgrace to our species, and to the rational faculties with which man is endowed, and exhibits, in a most ludicrous manner, the imbecility and prejudice of those who made bold pretensions to erudition and philosophy. The statement of such facts, however, may be instructive, if they tend to guard us against those prejudices and pre-conceived opinions, which prevent the mind from the cordial reception of truth, and from the admission of improvements in society which run counter to long-established customs. For the same principles and prejudices, though in a different form, still operate in society and retard the improvement of the social state, the march of science, and the progress of Christianity. How ridiculous is it for a man, calling himself a philosopher, to be afraid to look through a glass to an existing object in the heavens, lest it should endanger his previous opinions! And how foolish is it to resist any improvement or reformation in society, because it does not exactly accord with existing opinions, and with ‘the wisdom of our ancestors.’
It is not a little surprising, that Galileo should have first hit on that construction of a telescope which goes by his name, and which was formed with a concave glass next the eye. This construction of a telescope is more difficult to be understood, in theory, than one which is composed solely of convex glasses; and its field of view is comparatively very small, so that it is almost useless when attempted to be made of a great length. In the present day, we cannot help wondering that Galileo and other astronomers, should have made such discoveries as they did with such an instrument, the use of which must have required a great degree of patience and address. Galileo’s best telescope, which he constructed ‘with great trouble and expense,’ magnified the diameters of objects only thirty-three times; but its length is not stated—which would depend upon the focal distance of the concave eye-glass. If the eye-glass was two inches focus, the length of the instrument would be five feet four inches; if it was only one inch, the length would be two feet eight inches, which is the least we can allow to it—the object-glass being thirty-three inches focus, and the eye-glass placed an inch within this focus. With this telescope, Galileo discovered the satellites of Jupiter, the crescent of Venus, and the other celestial objects to which we have already alluded. The telescopes made in Holland, are supposed to have been constructed solely of convex glasses, on the principle of the astronomical telescope; and, if so, Galileo’s telescope was in reality a new invention.
Certain other claimants of the invention of the telescope, have appeared, besides those already mentioned. Francis Fontana, in his ‘celestial observations,’ says, that he was assured by a Mr. Hardy, advocate of the parliament of Paris, a person of great learning and undoubted integrity, that on the death of his father, there was found among his things an old tube, by which distant objects were distinctly seen, and that it was of a date long prior to the telescope lately invented, and had been kept by him as a secret. Mr. Leonard Digges, a gentleman who lived near Bristol, in the seventeenth century, and was possessed of great and various knowledge, positively asserts in his ‘Stratoticos,’ and in another work, that his father, a military gentleman, had an instrument which he used in the field, by which he could bring distant objects near, and could know a man at the distance of three miles. Mr. Thomas Digges, in the preface to his ‘Pantometria,’ published in 1591, declares, “My father, by his continual painful practices, assisted by demonstrations mathematical, was able, and sundry times hath by proportional glasses, duly situate in convenient angles, not only discovered things far off, read letters, numbered pieces of money, with the very coin and superscription thereof, cast by some of his friends of purpose, upon downs in open fields, but also, seven miles off, declared what hath been done that instant, in private places. He hath also, sundry times, by the sun-beams, fired powder and discharged ordnance half a mile and more distant, and many other matters far more strange and rare, of which there are yet living divers witnesses.”
It is by no means unlikely, that persons accustomed to reflection, and imbued with a certain degree of curiosity, when handling spectacle-glasses, and amusing themselves with their magnifying powers and other properties, might sometimes hit upon the construction of a telescope; as it only requires two lenses of different focal distances to be held at a certain distance from each other, in order to show distant objects magnified. Nay, even one lens, of a long focal distance, is sufficient to constitute a telescope of a moderate magnifying power, as I shall show in the sequel. But such instruments, when they happened to be constructed accidentally, appear to have been kept as secrets, and confined to the cabinets of the curious, so that they never came into general use; and as their magnifying power would probably be comparatively small, the appearance of the heavenly bodies would not be much enlarged by such instruments—nor is it likely that they would be often directed to the heavens. On the whole, therefore, we may conclude that the period when instruments of this description came into general use, and were applied to useful purposes, was when Galileo constructed his first telescopes.