Chapter XVIII: Part 18

From a careful attendance to those newly discovered celestial travellers, and their various motions, direct and retrograde, the great discovery arose, that the sun is the centre of their motions; and that by attributing a similar motion to the earth, and supposing the sun to be at rest, all the phænomena will be solved. Hence a hint was taken that opened a new and surprizing scene. The earth might be similar to them in other respects. The planets too might be habitable worlds. One cannot help greatly admiring the sagacity of minds, that first formed conclusions so very far from being obvious; as well as the indefatigable industry of astronomers, who originally framed rules for predicting eclipses of sun and moon, which is said to have been done as early as the time of Thales;[A14] and must have proved of singular service to emancipate mankind from a thousand superstitious fears and notions, which juggling impostors (the growth of all ages and countries) would not fail to turn to their own advantage.

For two or three centuries before and after the beginning of the Christian era, astronomy appears to have been held in considerable repute; yet very few discoveries of any consequence were made, during that period and many ages following.

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Footnote A14:

Thales, who died about five centuries and an half before the Christian
era, in the ninety-sixth year of his age,[A14a] first taught the
Greeks the cause of eclipses, He knew the spherical form of the earth;
he distinguished the zones of the earth by the mean of the tropicks
and the polar circles; and he treated of an oblique circle or zodiac,
of a meridian which intersects all these circles in extending north
and south, and of the magnitude of the apparent diameter of the sun.

Herodotus, Cicero, and Pliny, assert, as is noticed by Mr. Lalande,
that Thales had predicted, to the Ionians a total eclipse of the sun,
which took place during the war between the Lydians and the Medes, But
the manner in which Herodotus (who lived about one century, only,
after the time of Thales) speaks of this prediction, is so vague, that
one finds some difficulty in believing that it was fact, If it were
true, says Lalande, that Thales had actually foretold an eclipse of
the sun, it could be no otherwise, than by means of the general period
of eighteen years, of which he would have acquired a knowledge from
the Egyptians or the Chaldeans: for the period had not yet arrived,
when eclipses could be prognosticated by an exact calculation of the
motion of the moon. W. B.

Footnote A14a:

But, according to Dufresnoy, he was born in the first year of the 35th
Olympiad, and died the first year of the 52d, those periods
corresponding, respectively, with the years 640 and 572, B. C.: and if
so, he lived only sixty-eight years.

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The ancients were not wanting in their endeavours to find out the true dimensions of the planetary system. They invented several very ingenious methods for the purpose; but none of them were at all equal, in point of accuracy, to the difficulty of the problem. They were therefore obliged to rest satisfied with supposing the heavenly bodies much nearer to the earth than in fact they are, and consequently much less in proportion to it. Add to this, that having found the earth honoured with an attendant, while they could discover none belonging to any of the other planets, _they_ supposed it of far greater importance in the Solar System than it appears to _us_ to be: And the more praise is due to those few, who nevertheless conceived rightly of its relation to the whole.

Tycho took incredible pains to discover the parallax of Mars in opposition; the very best thing he could have attempted in order to determine the distances and magnitudes of the sun and planets. But telescopes and micrometers were not yet invented! so that not being able to conclude any thing satisfactory from his own observations, he left the sun’s parallax as he found it settled by Ptolemy, about twenty times too great. And even after he had reduced to rule the refraction of the atmosphere, and applied it to astronomical observations, rather than shock his imagination by increasing the sun’s distance, already too great for _his_ hypothesis, he chose to attribute a greater refraction to the sun’s light, than that of the stars, altogether contrary to reason; that so an excess of parallax might be balanced by an excess of refraction. Thus when we willingly give room to one error, we run the risk of having a whole troop of its relations quartered upon us. But Kepler afterwards, on looking over Tycho’s observations, found that he might safely reduce the sun’s parallax to one minute; which was no inconsiderable approach to the truth. Alhazen,[A15] an Arabian, had some time before, discovered the refraction of light in passing through air; of which the ancients seem to have been entirely ignorant. They were indeed very sensible of the errors it occasioned in their celestial measures; but they, with great modesty, attributed them to the imperfections of their instruments or observations.

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Footnote A15:

Alhazen was one of the greatest of the Arabian astronomers. He went,
about the year 1100, to Spain, where many of his nation had
established themselves in the eighth century, and carried thither
their knowledge of astronomy; yet, from the year 800 down to about
1300, science remained shrowded with the darkest ignorance, throughout
Europe.

Mr. Lalande observes, that the theory of Refractions is an important
one, in astronomy; although it was considered of little consequence
until the time of Alhazen. W. B.

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I must not omit, in honour of Tycho, to observe that he first proved, by accurate observations, that the comets are not meteors floating in our atmosphere, as Aristotle,[A16] that tyrant in Philosophy, had determined them to be, but prodigious bodies at a vast distance from us in the planetary regions; a discovery the lateness of which we must regret, for if it had been made by the ancients, that part of Astronomy (and perhaps every other, in consequence of the superior attention paid to it), would have been in far greater perfection than it is at this day.

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Footnote A16:

Aristotle, as though he had been of the race of the Ottomans, thought
he could not reign except he first killed all his brethren. Insomuch
as he never nameth or mentioneth an ancient author or opinion, but to
confute or reprove. _Bacon. Advancement._

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I had almost forgot to take notice of one important discovery made in the early times of Astronomy, the precession of the equinoxes. An ancient astronomer, called Timocharis, observed an appulse of the Moon to the Virgin’s Spike, about 280 years before the birth of Christ. He thence took occasion to determine the place of this star, as accurately as possible; probably with a view of perfecting the lunar theory. About four hundred years afterwards, Ptolemy, comparing the place of the same star, as he then found it, with its situation determined by Timocharis,[A17] concluded the precession to be at the rate of one degree in an hundred years; but later astronomers have found it swifter.

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Footnote A17:

Timocharis of Alexandria endeavoured, with Aristillus, a philosopher
of the same school, to determine the places of the different stars in
the heavens, and to trace the course of the planets. Dr. Lempriere
places him 294 years before Christ; and the Abbé Barthelemy has
inserted his name in the list of illustrious men, who flourished in
the fourth century before the Christian era: he probably lived some
time after the commencement of that century. W. B.

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Whatever other purposes this great law may answer, it will produce an amazing change in the appearance of the heavens; and so contribute to that endless variety which obtains throughout the works of Nature. The seven stars that now adorn our winter skies, will take their turn to shine in summer. Sirius, that now shines with unrivalled lustre, amongst the gems of heaven, will sink below our horizon, and rise no more for very many ages! Orion too, will disappear, and no longer afford our posterity a glimpse of glories beyond the skies! glittering Capella, that now passes to the north of our zenith, will nearly describe the equator:[A18] And Lyra, one of the brightest in the heavens, will become our Polar Star: Whilst the present Pole Star, on account of its humble appearance, shall pass unheeded; and all its long continued faithful services shall be forgotten! All these changes, and many others, will certainly follow from the precession of the equinoxes; the cause of which motion was so happily discovered and demonstrated by the immortal Newton: A portion of whose honors was nevertheless intercepted by the prior sagacity of Kepler, to whom I return.

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Footnote A18:

By its peculiar situation it will continue to do so for a long time.

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Kepler’s love of harmony encouraged him to continue his pursuits, in spite of the most mortifying disappointments, until he discovered that admirable relation which subsists between the periodic times of the primary planets, and their distances from the sun; the squares of the former being as the cubes of the latter. This discovery was of great importance to the perfection of Astronomy; because the periods of the planets are more easily found by observation, and from them their several relative distances may be determined with great accuracy by this rule. He likewise found from observation, that the planets do not move in circles; but in elipses, having the sun in one focus. But the causes lay hid from him, and it was left as the glory of Sir Isaac, to demonstrate that both these things must necessarily follow from one simple principle, which almost every thing in this science tends to prove does really obtain in Nature: I mean, that the planets are retained in their orbits by forces directed to the sun; which forces decrease as the squares of their distances encrease.

Kepler also discovered that the planets do not move equally in their orbits, but sometimes swifter, sometimes slower; and that not irregularly, but according to this certain rule; That in equal times, the areas described by lines drawn from the planet to the sun’s centre, are equal. This, Sir Isaac likewise demonstrated must follow, if the planet be retained in its orbit by forces directed to the sun, and varying with the distance in any manner whatsoever. These three discoveries of Kepler, afterwards demonstrated by Newton, are the foundation of all accuracy in astronomical calculations.[A19]

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Footnote A19:

According to Lalande, Kepler was as celebrated in astronomy by the
consequences he drew from the observations of Tycho Brahé, as the
latter was for the immense mass of materials which he had prepared for
him: and the Abbé Delaporte (in his _Voyageur François_) represents
him as precursor of Descartes in opticks, of Newton in physicks, and
as a law-giver (“_legislateur_”) in astronomy.

John Kepler, for this was the name of that famous mathematician, was
born at Wiel, in the duchy of Wirtemberg, in the year 1571; and the
Abbé Delaporte says, his family was illustrious. He died at Ratisbon,
in 1630. W. B.

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We now come to that great discovery, which lay concealed from the most subtle and penetrating geniuses amongst mankind, until these latter ages; which so prodigiously enlarged the fields of astronomy, and with such rapidity handed down one curiosity after another, from the heavens to astonished mortals, that no one capable of raising his eyes and thoughts from the ground he trod on, could forbear turning his attention, in some degree, to the subject that engages us this evening.

Galileo, as he himself acknowledges, was not the first inventor of the telescope, but he was the first that knew how to make a proper use of it.[A20] If we consider that convex and concave lenses had been in use for some centuries, we shall think it probable that several persons might have chanced to combine them together, so as to magnify _distant_ objects; but that the small advantage apparently resulting from such a discovery, either on account of the badness of the glasses or the unskilfulness of the person in whose hands they were, occasioned it to be neglected.

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Footnote A20:

The true invention of the telescope cannot be carried back to an
earlier date than the beginning of the seventeenth century. Johannes
Baptista Porta, a Neapolitan, in his _Natural Magic_, which was
published in the year 1589, says, “_Si utramque (lentem concavam et
convexam) recté componere noveris, et longinqua et proxima majora et
clara videbis_:” and he is said to have made a telescope, accordingly,
about the year 1594. But Porta is represented as having made this
discovery such as it was, by accident; and, as not well understanding
the proper use of his own invention.

According to Baron Bielfeld,[A20a] however, telescopes were first
constructed a long time after, in Holland; some say, by John
Lippersheim, a spectacle-maker at Middelbourg in Zealand; others, by
James Metius, brother to the celebrated professor Adrian Metius, of
Franeker. Although the invention of this instrument, of indispensable
use in astronomy, is sometimes attributed to the great Galileo, he has
himself acknowledged, in his treatise, entitled _Nuncius Siderius_,
that he took the hint from a report of a German having invented an
instrument, by means of which, and with the assistance of certain
glasses, distant objects might be distinguished as clearly as those
that were near. This is precisely what Porta had mentioned in his
book, in 1589; and therefore, if Galileo had not referred to a German,
he might be supposed to have had in his view the Neapolitan’s
conception of a telescope, announced long before such an instrument
was properly constructed.

Whatever may have been the merit of Porta’s discovery, or the
pretensions of Lippersheim, the spectacle-maker, and Metius, Peter
Borel (in his treatise _De vero Telescopii Inventore_) is of the
opinion that Zachariah Johnson, who, like Lippersheim, was a
spectacle-maker, and in the same city, made this discovery by chance,
about the year 1500; that Lippersheim imitated him, after making
numerous experiments; and that he instructed Metius. There are others,
who have been considered as having had some sort of claim to this
important invention; among whom were a Mr. Digges, of England, and a
M. Hardy, of France, both towards the commencement of the seventeenth
century.

It is certain, however, that Galileo in Italy, (who died in 1642, aged
seventy-eight years,) and, according to Bielfeld, Simon Marius in
Germany, were the first that applied the telescope to the
contemplation of celestial objects. W. B.

Footnote A20a:

_Elem. of Univ. Erud._ b. i. ch. 49.

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But Galileo, by great care in perfecting his telescope, and by applying a judicious eye, happily succeeded; and with a telescope magnifying but thirty times, discovered the moon to be a solid globe, diversified with prodigious mountains and vallies, like our earth; but without seas or atmosphere. The sun’s bright disk, he found frequently shaded with spots, and by their apparent motions proved it to be the surface of a globe, revolving on its axis in about five and twenty days. This it seems was a mortifying discovery to the followers of Aristotle; who held the sun to be perfect without spot or blemish.[A21] Some of them, it is said, insisted that it was but an illusion of the telescope and absolutely refused to look through one, lest the testimony of their senses should prove too powerful for their prejudices.

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Footnote A21:

In treating of the astronomy of the Greeks, Lalande contents himself
with barely introducing the name of Aristotle, among their
philosophers; seeming to consider him as one who had done very little
for astronomical science. This philosopher (who died in the
sixty-third year of his age, and only 322 years B. C.) among his other
doctrines, not only maintained the eternity of the world; but, that
Providence did not extend itself to sublunary beings: and as to the
immortality of the soul, it is uncertain whether he believed it or
not. Bayle calls his logic and his natural philosophy, “the weakest of
his works:” and says, further; “It will be an everlasting subject of
wonder to persons who know what philosophy is, to find that
Aristotle’s authority was so much respected in the schools, for
several ages, that, when a disputant quoted a passage from this
philosopher, he who maintained the thesis durst not say, _Transeat_;
but must either deny the passage or explain it in his own way.” W. B.

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Galileo likewise discovered the four attendants of Jupiter, commonly called his satellites:[A22] Which at first did not much please that great ornament of his age, the sagacious Kepler. For by this addition to the number of the planets, he found their Creator had not paid that veneration to certain mystical numbers and proportions, which he had imagined. Let us not blush at this remarkable instance of philosophical weakness, but admire the candour of the man who confessed it.

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Footnote A22:

This discovery was made on the 8th of January, 1610. It was, as Mr.
Vince observes, a very important one in its consequences; as it
furnished a ready method of finding the longitude of places, by means
of their eclipses. W. B.

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Galileo not only discovered these moons of Jupiter, but suggested their use in determining the longitude of places on the earth; which has since been so happily put in practice, that Fontenelle does not hesitate to affirm, that they are of more use to Geography and Navigation,[A23] than our own moon. He discovered the phases of Mars and Venus; that the former appears sometimes round and sometimes gibbous, and that the latter puts on the shapes of our moon: And from this discovery, he proved to a demonstration, the truth of the Copernican System.[A24] Nor did that wonderful ring, which surrounds Saturn’s body, without touching it, and which we know nothing in nature similar to, escape his notice; though his telescope did not magnify sufficiently to give him a true idea of its figure.

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Footnote A23:

Although both Geography and Navigation have been wonderfully improved
by the important discoveries made by the moderns in astronomy, they
have nevertheless, derived the most essential aid from the application
of the Compass to their purposes.

The invention of this instrument, which is of indispensible utility,
is almost universally ascribed to Flavio Gioia, a native of Amalfi in
the kingdom of Naples. He is called, by some writers, Flavio de Melfi,
(by which is meant, Flavio of Amalfi, this town being the place of his
nativity;) and his invention of the Compass is placed in the year
1302. But it is affirmed by others, that Paulus Venetus brought the
Compass first into Italy from China, in the year 1260. The Chinese
Compass, however, whatever may be its antiquity, appears to have been
a very imperfect instrument, compared with the modern Mariner’s
Compass; and, more especially, with the Azimuth Compass, as improved
by Dr. Knight and Mr. Smeaton. The Chinese Compass, now used, is
represented as being nothing more than a magnetic needle kept
floating, by means of a piece of cork, on the surface of water, in a
white china ware vessel, divided at bottom into twenty-four points.

It is worthy of observation, that the French have laid claim to the
invention of the Compass, upon no better foundation than the
circumstance of a _fleur de lys_ being always placed at the north
point of the chard; although it is known, that Gioia decorated the
north end of the needle with that flower in compliment to his own
sovereign, who bore it in his arms, as being descended from the royal
house of France. “It hath been often,” says Dr. Robertson,[A23a] “the
fate of those illustrious benefactors of mankind, who have enriched
science and improved the arts by their inventions, to derive more
reputation than benefit from the happy efforts of their genius. But,”
continues this eminent historian, “the lot of Gioia has been still
more cruel; through the inattention or ignorance of contemporary
historians, he has been defrauded even of the fame to which he had
such a just title. We receive from them no information with respect to
his profession, his character, the precise time when he made this
important discovery, and the accidents and enquiries which led to it:
the knowledge of this event, though productive of greater effects than
any recorded in the annals of the human race, is transmitted to us
without any of those circumstances which can gratify the curiosity
that it naturally awakens.” W. B.

Footnote A23a:

Hist. of America, vol. i, b. i.

Footnote A24:

Galileo Galilei was a strenuous defender of the system of Copernicus;
for which he was condemned by the inquisition, in the year 1635, under
Pope Urban VIII. This extraordinary man was a native of Florence, and
born in 1564. He died in 1642, aged seventy-eight years.

W. B.

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Amongst the fixed stars too, Galileo pursued his enquiries. The Milky-Way, which had so greatly puzzled the ancient Philosophers, and which Aristotle imagined to be vapours risen to an extraordinary height, he found to consist of an innumerable multitude of small stars; whose light appears indistinct and confounded together to the naked eye. And in every part of the heavens, his telescope shewed him abundance of stars, not visible without it. In short, with such unabated ardour did this great man range through the fields of Astronomy, that he seemed to leave nothing for others to glean after him.

Nevertheless, by prodigiously encreasing the magnifying powers of their telescopes, his followers made several great discoveries; some of which I shall briefly mention. Mercury was found to become bisected, and horned near its inferior conjunction, as well as Venus. Spots were discovered in Mars, and from their apparent motion, the time of his revolution on an axis nearly perpendicular to its orbit, was determined. A sort of belts or girdles, of a variable or fluctuating nature, were found to surround Jupiter, and likewise certain spots on his surface, whence he was concluded to make one revolution in about ten hours on his axis; which is likewise nearly perpendicular to his orbit. Five[A25] moons or satellites were found to attend Saturn, which Galileo’s telescope; on account of their prodigious distance, could not reach:[A26] And the form of his ring was found to be a thin circular plane, so situated as not to be far from parallel to the plane of our equator; and always remaining parallel to itself. This ring, as well as Saturn, evidently derives its light from the sun, as appears by the shadows they mutually cast on each other.

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Footnote A25:

It has been since ascertained that Saturn has seven satellites, as is
more particularly mentioned in the subsequent note. W. B.

Footnote A26:

It was about six years after the delivery of this oration, (viz. on
the 13th of March, 1781,) that Herschel discovered the Georgium Sidus.
And nearly eight years and an half after this first discovery, he made
two others: on the 28th of August, 1789, he was enabled to ascertain,
by means of his telescope of forty feet focal length, that Saturn has
a sixth satellite; and, on the 17th of September following, he found
that he has a seventh. The same celebrated astronomer has since made
several important discoveries. Thus, under the liberal patronage of
his sovereign, has the great Herschel succeeded, by his extraordinary
skill and industry in the making of very large _specula_, in
constructing telescopes, which, in the words of the learned Mr. Vince,
“have opened new views of the heavens, and penetrated into the depths
of the universe; unfolding scenes which excite no less our wonder than
our admiration.”

Many important discoveries (some of which are noticed in the foregoing
pages of these memoirs) have been made by other eminent astronomers,
since the date of Dr. Rittenhouse’s Oration; some of them, indeed,
since his decease; among which are the discoveries of three new
planets. W. B.

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Besides several other remarkable appearances, which Hugenius[A27] discovered amongst the fixed stars, there is one in Orion’s Sword, which, I will venture to say, whoever shall attentively view, with a good telescope and experienced eye, will not find his curiosity disappointed. “Seven small stars, (says he,) of which three are very close together, seemed to shine through a cloud, so that a space round them appeared much brighter than any other part of heaven, which being very serene and black looked here as if there was an opening, through which one had a prospect into a much brighter region.” Here some have supposed old night to be entirely dispossessed, and that perpetual daylight shines amongst numberless worlds without interruption.

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Footnote A27:

The celebrated Huygens, who, in his Latin works, is styled _Hugenius_.
W. B.

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This is a short account of the discoveries made with the telescope. Well might Hugenius congratulate the age he lived in, on such a great acquisition of knowledge: And recollecting those great men, Copernicus, Regiomontanus, and Tycho, so lately excluded from it by death, what an immense treasure, says he, would they have given for it. Those ancient philosophers too, Pythagoras, Democritus, Anaxagoras, Philolaus, Plato, Hipparchus; would they not have travelled over all the countries of the world, for the sake of knowing such secrets of nature, and of enjoying such sights as these?

Thus have we seen the materials collected, which were to compose the magnificent edifice of astronomical Philosophy; collected, indeed, with infinite labour and industry, by a few volunteers in the service of human knowledge, and with an ardour not to be abated by the weaknesses of human nature, or the threatened loss of sight, one of the greatest of bodily misfortunes! It was now time for the great master-builder to appear, who was to rear up this whole splendid group of materials into due order and proportion. And it was, I make no doubt, by a particular appointment of Providence, that at this time the immortal Newton appeared. Much had been done preparatory to this great work by others, without which if he had succeeded, we should have been ready to pronounce him something more than human. The doctrine of atoms had been taught by some of the ancients. Kepler had suspected that the planets gravitated towards each other, particularly the earth and moon; and that their motion prevented their falling together: and Galileo first of all applied geometrical reasoning to the motion of projectiles. But the solid spheres of the ancients, or the vortices of Des Cartes,[A28] were still found necessary to explain the planetary motions; or if Kepler had discarded them, it was only to substitute something else in their stead, by no means sufficient to account for those grand movements of nature. It was Newton alone that extended the simple principle of gravity, under certain just regulations, and the laws of motion, whether rectilinear or circular, which constantly take place on the surface of this globe, throughout every part of the solar system; and from thence, by the assistance of a sublime geometry, deduced the planetary motions, with the strictest conformity to nature and observation.

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Footnote A28:

Among the many eminent astronomers in the sixteenth and seventeenth
centuries, mentioned by Mr. Lalande, in his _Astronomie_, with
interesting particulars concerning most of them, the only notice he
there takes of his ingenious countryman, who endeavoured to establish
the theory of Vortices which he had projected, is in these words:
“Descartes (René,) né en Touraine en 1596, mort à Stockholm en 1650.
Sa vie a été écrite fort au long par Baillet, à Paris, 1691, in 4^o.”
W. B.

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Other systems of Philosophy have been spun out of the fertile brain of some great genius or other; and for want of a foundation in nature, have had their rise and fall, succeeding each other by turns. But this will be durable as science, and can never sink into neglect, until “universal darkness buries all.”

Other systems of Philosophy have ever found it necessary to conceal their weakness, and inconsistency, under the veil of unintelligible terms[A29] and phrases, to which no two mortals perhaps ever affixed the same meaning: But the Philosophy of Newton disdains to make use of such subterfuges; it is not reduced to the necessity of using them, because it pretends not to be of nature’s privy council, or to have free access to her most inscrutable mysteries; but to attend carefully to her works, to discover the immediate causes of visible effects, to trace those causes to others more general and simple, advancing by slow and sure steps towards the great First Cause of all things.

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Footnote A29:

The philosophy of Aristotle retained terms so very obscure, that it
seems the Devil himself did not understand, or at least could not
explain them; otherwise we can hardly suppose, that, when the good
patriarch of Venice had summoned his attendance for this very purpose,
he would have been so rude as to put him off with an answer not only
unintelligible but inarticulate. See _Bayle, in Art. Barbaro._

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And now the Astronomy of our planetary system seemed compleated. The telescope had discovered all the globes whereof it is composed, at least as far as we yet know. Newton with more than mortal sagacity had discovered those laws by which all their various, yet regular, motions are governed, and reduced them to the most beautiful simplicity: laws to which not only their great and obvious variety of motions are conformable, but even their minute irregularities; and not only planets but comets likewise. The busy mind of man, never satiated with knowledge, now extended its views further, and made use of every expedient that suggested itself, to find the relation that this system of worlds bears to the whole visible creation. Instruments were made with all possible accuracy, and the most skilful observers applied themselves with great diligence to discover an annual parallax, from which the distances of the fixed stars would be known. They found unexpected irregularities, and might have been long perplexed with them to little purpose, had not Dr. Bradley happily accounted for them, by shewing that light from the heavenly bodies strikes the eye with a velocity and direction, compounded of the proper velocity and direction of _light_, and of the _eye_, as carried about with the earth in its orbit; compared to which, the diurnal motion and all other accidental motions of the eye, are quite inconsiderable. Thus, instead of what he aimed at, he discovered something still more curious, the real velocity of light, in a way entirely new and unthought of.

All Astronomical knowledge being conveyed to us from the remotest distances, by that subtle, swift and universal messenger of intelligence, LIGHT; it was natural for the curious to enquire into its properties, and particularly to endeavour to know with what velocity it proceeds, in its immeasurable journeys. Experimental Philosophy, accustomed to conquer every difficulty, undertook the arduous problem; but confessed herself unequal to the task.[A30] Here, Astronomy itself revealed the secret; first in the discovery of Roemer, who found that the farther Jupiter is distant from us, the later the light of his satellites always reaches us; and afterwards in this of Dr. Bradley, informed us, that light proceeds from the sun to us in about eight minutes of time.[A31]

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Footnote A30:

Alluding to the experiments made in France, for determining the
velocity of light; which, though unsuccessful, discovered a noble
philosophical spirit.

Footnote A31:

This prodigious velocity of light can be no argument against its
materiality, as will appear from the following considerations. The
greatest velocity which we can communicate to any body, is that of a
cannon-ball, impelled by gun-powder; this may be at the rate of about
20 miles in a minute of time. The planet Saturn moves about 360 miles
in a minute, that is 18 times swifter than a cannon-ball; and the
comet of 1680, in its perihelion, moved near 56.66 times swifter than
Saturn, or 990.5 times swifter than a cannon-ball. Now these are
material bodies, moving with very various, and all of them exceedingly
great velocities; and no reason appears why the last mentioned
velocity should be the utmost limit, beyond which nature cannot
proceed; or that some other body may not move 7 or 8 hundred times
swifter than a comet, as light is found to do.

That the different refrangibility of the rays of light, on which their
colours depend, arises from their different velocities, seems so
natural a conjecture, that it has perhaps occurred to every one who
has thought on this subject. To this there are three principal
objections. The first is, that, according to this hypothesis, when the
satellites of Jupiter are eclipsed, their colour ought to change,
first to a green and then to a blue, before their light becomes
extinct; which is contrary to experience. But this objection appears
to me of no weight; for we do not lose sight of the satellite because
there is no light coming from thence to the eye, but because there is
not light enough to render it visible. Therefore at the time a
satellite disappears, there is still light of all colours arriving at
the eye: and though the blue light should predominate on account of
its slower progress, yet the red may predominate on another account;
for along the edge of Jupiter’s shadow, as it passes over the
satellite, a greater proportion of red light, than of blue, will be
thrown by the refraction of Jupiter’s atmosphere. The second objection
is, that since the velocity of the earth in its orbit, causes an
aberration of about 20 seconds in the place of a star, if the
different colours of light depended on different velocities, the
aberration of blue light ought proportionably to exceed that of red
light, which would give such an oblong form to a fixed star as might
be discovered with a good telescope. This objection is of no more
force than the former. The effect ought indeed to follow, but not in a
sensible quantity; for at the altitude of 70 degrees, the apparent
place of a fixed star is likewise removed 20 seconds by refraction,
and the very same separation of the rays must take place; yet this I
think is not discoverable with the best telescope. Perhaps by uniting
these two equal causes, which may be readily done, and thereby
doubling the effect, it may become sensible.

The third objection arises from that curious discovery of Dollond, by
which we are enabled so greatly to improve refracting telescopes. And
this objection I shall for the present leave in its full force; as
well against the above hypothesis, as against every other which I have
seen for the same purpose.

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As the apparent motion of the fixed stars, arising from this cause, was observed to complete the intire circle of its changes in the space of a year, it was for some time supposed to arise from an annual parallax, notwithstanding its inconsistency in other respects with such a supposition. But this obstacle being removed, there followed the discovery of another apparent motion in the heavens, arising from the nutation of the earth’s axis; the period whereof is about nineteen years. Had it not been so very different from the period of the former, the causes of both must have been almost inexplicable. This latter discovery is an instance of the superior advantages of accurate observation: For it was well known that such a nutation must take place from the principles of the Newtonian Philosophy; yet a celebrated astronomer had concluded from hypothetical reasoning, that its quantity must be perfectly insensible.

The way being cleared thus far, Dr. Bradley assures us, from his most accurate observations, that the annual parallax cannot exceed two seconds, he thinks not one; and we have the best reason to confide in his judgment and accuracy. From hence then we draw this amazing conclusion; that the diameter of the earth’s orb bears no greater proportion to the distance of the stars which Bradley observed, than one second does to the radius; which is less than as one to 200,000. Prodigiously great as the distance of the fixed stars from our sun appears to be, and probably their distances from each other are no less, the Newtonian Philosophy will furnish us with a reason for it: That the several systems may be sufficiently removed from each other’s attraction, which we are very certain must require an immense distance; especially if we consider that the cometic part, of our system at least, appears to be the most considerable though so little known to us. The dimensions of the several parts of the planetary system, had been determined near the truth by the astronomers of the last age, from the parallax of Mars. But from that rare phenomenon the transit of Venus over the sun’s disk, which has twice happened within a few years past, the sun’s parallax is now known beyond dispute to be 8 seconds and an half, nearly; and consequently, the sun’s distance almost 12,000 diameters of the earth.

If from the distances of the several planets, and their apparent diameters taken with that excellent instrument, the micrometer, we compare their several magnitudes, we shall find the Moon, Mercury, and Mars, to be much less than our Earth, Venus a little less, but Saturn many hundred times greater, and Jupiter above one thousand times. This prodigious globe, placed at such a vast distance from the other planets, that the force of its attraction might the less disturb their motions, is far more bulky and ponderous than all the other planets taken together. But even Jupiter, with all his fellows of our system, are as nothing compared to that amazing mass of matter the Sun. How much are we then indebted to Astronomy, for correcting our ideas of the visible creation! Wanting its instruction, we should infallibly have supposed the earth by far the most important body in the universe, both for magnitude and use. The sun and moon would have been thought two little bodies nearly equal in size, though different in lustre, created solely for the purpose of enlightening the earth; and the fixed stars, so many sparks of fire, placed in the concave vault of heaven, to adorn it, and afford us a glimmering light in the absence of the sun and moon.

But how does Astronomy change the scene!—Take the miser from the earth, if it be possible to disengage him; he whose nightly rest has been long broken by the loss of a single foot of it, useless perhaps to him; and remove him to the planet Mars, one of the least distant from us: Persuade the ambitious monarch to accompany him, who has sacrificed the lives of thousands of his subjects to an imaginary property in certain small portions of the earth; and now point it out to them, with all its kingdoms and wealth, a glittering star “close by the moon,” the latter scarce visible and the former less bright than our Evening Star:—Would they not turn away their disgusted sight from it, as not thinking it worth their smallest attention, and look for consolation in the gloomy regions of Mars?[A32]

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Footnote A32:

Mars appears to be surrounded by a very great and dense atmosphere.

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But dropping the company of all those, whether kings or misers, whose minds and bodies are equally affected by gravitation, let us proceed to the orb of Jupiter; the Earth and all the inferior planets will vanish, lost in the sun’s bright rays, and Saturn only remain; He too sometimes so diminished in lustre, as not to be easily discovered. But a new and beautiful system will arise. The four moons of Jupiter will become very conspicuous; some of them perhaps appearing larger, others smaller than our moon; and all of them performing their revolutions with incredible swiftness, and the most beautiful regularity:—varying their phases from full to new and from new to full, and frequently eclipsing the sun and each other, at least to the equatorial parts of Jupiter; and almost in every revolution suffering eclipses themselves by falling into Jupiter’s shadow; excepting that the outermost will seem, like a traveller fond of the sun-beams, cautiously to avoid the shadow for whole years together. Since we are advanced so far, if not tired of the journey, let us proceed a step further; it is but 400 millions of miles to the globe of Saturn. Here again all will be lost, but Jupiter itself. The Sun will put on something of a starlike appearance, but with excessive brightness. The five[A33] satellites of Saturn will exhibit appearances similar to those of Jupiter, but they will very rarely eclipse the Sun, or suffer eclipses themselves. The particular phænomena of Saturn’s ring, we cannot explain, unless we knew the time and plane of Saturn’s revolution on his axis. But this we know, that it must sometimes appear, by night, like a prodigious luminous arch, almost equal to one quarter of the heavens; and at other times, dark, so as to afford no light itself, but to intercept the light of every star beyond it, by night, and of the sun itself by day. And to conclude, if borne on the wings of a comet we should travel with it to the remotest part of its orbit; our whole planetary system would disappear, and the sun become a star, only more refulgent than Sirius perhaps, because less distant.

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Footnote A33:

Dr. Herschel discovered, in the year 1789, (fourteen years after the
delivery of this Oration,) two other satellites of Saturn. These are
the innermost of his (now) seven secondary planets.

W. B.

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The opinion of the earth’s rotation on its axis was once violently opposed, from a notion of its dangerous tendency with respect to the interests of religion:[A34] But, as truth is always consistent with itself, so many new proofs were furnished from time to time by new discoveries, that a mistaken interpretation of some passages in the bible was compelled to give way to the force of astronomical evidence. The doctrine of a plurality of worlds, is inseparable from the principles of Astronomy; but this doctrine is still thought, by some pious persons, and by many more I fear, who do not deserve that title, to militate against the truths asserted by the Christian religion. If I may be allowed to give my opinion on a matter of such importance, I must confess that I think upon a proper examination the apparent inconsistency will vanish. Our religion teaches us what philosophy could not have taught; and we ought to admire with reverence the great things it has pleased divine Providence to perform, _beyond the ordinary course of Nature_, for man, who is undoubtedly the most noble inhabitant of this globe. But neither religion nor philosophy forbids us to believe that infinite wisdom and power, prompted by infinite goodness, may throughout the vast extent of creation and duration, have frequently interposed in a manner quite incomprehensible to us, when it became necessary to the happiness of created beings of some other rank or degree.

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Footnote A34:

In 745, Virgilus, bishop of Saltzburg, having publicly asserted in
some of his sermons, that there were antipodes, he was charged with
heresy, by Boniface, bishop of Mentz, and cited to appear before the
Pope, who recommended the hearing of the cause to Utilo, King of
Bohemia, and at the same time wrote to him in favour of Boniface. The
event was, the bishop of Saltzburg lost his cause, and was condemned
for heresy.

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How far indeed the inhabitants of the other planets may resemble man, we cannot pretend to say. If like him they were created liable to fall, yet some, if not all of them, may still retain their original rectitude. We will hope they do: the thought is comfortable.—Cease, Galileo, to improve thy optic tube: and thou, great Newton, forbear thy ardent search into the distant mysteries of nature: lest ye make unwelcome discoveries. Deprive us not of the pleasure of believing that yonder radiant orbs, traversing in silent majesty the etherial regions, are the peaceful seats of innocence and bliss: where neither natural nor moral evil has ever yet intruded; where to enjoy with gratitude and adoration the creator’s bounty, is the business of existence. If their inhabitants resemble man in their faculties and affections, let us suppose that they are wise enough to govern themselves according to the dictates of that reason their creator has given them, in such manner as to consult their own and each other’s true happiness, on all occasions. But if, on the contrary, they have found it necessary to erect artificial fabrics of government, let us not suppose that they have done it with so little skill, and at such an enormous expence, as must render them a misfortune instead of a blessing. We will hope that their statesmen are patriots, and that their kings, if that order of beings has found admittance there, have the feelings of humanity.—Happy people! and perhaps more happy still, that all communication with us is denied. We have neither corrupted you with our vices, nor injured you by violence. None of your sons and daughters, degraded from their native dignity, have been doomed to endless slavery by us in America, merely because _their_ bodies may be disposed to reflect or absorb the rays of light, in a way different from _ours_. Even you, inhabitants of the moon, situated in our very neighbourhood, are effectually secured, alike from the rapacious hand of the haughty Spaniard, and of the unfeeling British nabob. Even British thunder impelled by British thirst of gain, cannot reach you: And the utmost efforts of the mighty Frederick, that tyrant of the north and scourge of mankind, if aimed to disturb _your_ peace, becomes inconceivably ridiculous and impotent.

Pardon these reflections; they rise not from the gloomy spirit of misanthropy. That being, before whose piercing eye all the intricate foldings and dark recesses of the human heart become expanded and illuminated, is my witness with what sincerity, with what ardor, I wish for the happiness of the whole race of mankind: how much I admire that disposition of lands and seas, which affords a communication between distant regions, and a mutual exchange of benefits:[A35] how sincerely I approve of those social refinements which really add to our happiness, and induce us with gratitude to acknowledge our great Creator’s goodness:—how I delight in a participation of the discoveries made from time to time in nature’s works, by our Philosophic brethren in Europe.

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Footnote A35:

It has been shewn, in a preceding note, how much the means of
communicating between distant regions, separated by seas, ware
facilitated by the discovery and use of the Compass: but those means
have been still further and very greatly improved, since the
introduction of the use of the Quadrant at sea, especially that called
Hadley’s Quadrant.

The true inventor of the reflecting Quadrant was Dr. Robert Hook, a
very ingenious English mathematician and philosopher, who died in the
year 1702, at the age of sixty-seven years. This instrument, now
commonly styled Hadley’s, was afterwards rendered much more complete
than Dr. Hook’s invention had made it, by Sir Isaac Newton: but our
modern artists, more skilful than those of former times, as Mr.
Lalande has observed, have profited of the ideas of the great Newton
himself, on the subject; and among the later improvers of the Sea
Quadrant, or Octant, is Mr. Hadley, whose name the instrument usually
bears.

It would, however, be doing an act of injustice to the memory of an
American who possessed an extraordinary genius, to omit, in the course
of these memoirs, some notice of his merits in relation to this
matter. Mr. Thomas Godfrey, a native of Pennsylvania, is said to have
turned his attention to this subject, so early as the year 1730; and
in the Transactions of the Royal Society of London, No. 435, will be
found, an “_Account of Mr. Thomas Godfrey’s Improvement of Davis’s
Quadrant transferred to the Mariner’s Bow_,” drawn up by James Logan,
Esq. formerly of Philadelphia, a gentleman of extensive learning, and
a very eminent mathematician, Mr. Godfrey is stated to have “sent the
instrument (which he had constructed) to be tried at sea by an
acquaintance of his, an ingenious navigator, in a voyage to Jamaica,
who shewed it to a captain of a ship there, just going for England; by
which means, it came to the knowledge of Mr. Hadley, though perhaps
without his being told the name of the real inventor.” [See _The
American Magazine_, for July 1758.] In a letter, dated at Philadelphia
the 25th of May, 1732, Mr. Logan, who very ably as well as
meritoriously patronized Godfrey, communicated to the celebrated Dr.
Edmund Halley a detailed account and description of the _improved_
Sea-Quadrant constructed by that ingenious citizen of America, of
which his patron confidently believed him to be the original inventor.
On the 28th of June, 1734, a further account of Godfrey’s invention
was drawn up by Mr. Logan, and subscribed with his name; which, it is
presumed, was also communicated to the Royal Society: and on the 9th
of November, in the same year, Mr. Godfrey transmitted an account of
it, draughted and signed by himself, to the same learned body. The
whole of these interesting letters, with some accompanying
observations on the subject, are published in the valuable _Magazine_
just referred to, and in the one for the succeeding month.

In the Transactions of the Royal Society, for the months of October,
November and December, 1731, No. 421, is contained a Proposal, by Dr.
Edmund Halley, for finding the longitude at sea, within a degree or
twenty leagues, &c. In the conclusion of this paper, Dr, Halley, in
speaking of John Hadley, Esq. VP.R.S, (“to whom,” as he observes, “we
are highly obliged for his having perfected and brought into common
use the reflecting telescope,”) says—He “has been pleased to
communicate _his_ most ingenious instrument for taking the angles _by
reflection_,” (referring, here, to the Philos. Trans. No. 420;) “it is
more than probable that the same may be applied to taking angles _at
sea_, with the desired accuracy.”

In Mr. Logan’s account of Mr. Godfrey’s invention, dated June 28,
1734, he says: “Tis now four years since Thomas Godfrey hit on this
improvement; for, his account of it, laid before the (Royal) Society
last winter, in which he mentioned two years, was wrote in 1732; and
in the same year, 1730, after he was satisfied in this, he applied
himself to think of the other, viz. _the reflecting instrument, by
speculums for a help in the case of longitude_, though ’tis also
useful in taking altitudes: and one of these, as has been abundantly
proved by the maker, and those who had it with them, was taken to sea
and there used in observing the latitudes the winter of that year, and
brought back again to Philadelphia before the end of February 1730–1,
and was in my keeping some months immediately after.”

In Mr, Logan’s prior letter to Dr. Halley (dated May 25, 1732,) he
says, that about eighteen months before, Godfrey told him, “he had for
some time before been thinking of an instrument for taking the
distances of stars by reflecting speculums, which he believed might be
of service “at sea;” and that, soon after, Godfrey shewed him an
instrument, which he had procured to be made, for the purpose. Thus,
the time to which Mr. Logan refers Godfrey’s communication of his
improvement to him, would make its date to be about the month of
November, 1730.