"The sun," we are told, "is a solid body, ninety-five millions of miles
distant from the earth we inhabit, one million times larger in cubic
measurement, and to such a degree impregnated with heat, that a comet,
approaching to it within a certain distance, was by that approximation
raised to a heat two thousand times greater than that of red-hot iron."
It will be acknowledged, that there is in this statement much to
believe; and we shall not be exposed to reasonable blame, if we refuse
to subscribe to it, till we have received irresistible evidence of its
truth.
It has already been observed, that, for the greater part of what we
imagine we know on the surface or in the bowels of the earth, we have,
or may have if we please, the evidence of more than one of our senses,
combining to lead to the same conclusion. For the propositions of
astronomy we have no sensible evidence, but that of sight, and an
imperfect analogy, leading from those visible impressions which we can
verify, to a reliance upon those which we cannot.
The first cardinal particular we meet with in the above statement
concerning the sun, is the term, distance. Now, all that, strictly
speaking, we can affirm respecting the sun and other heavenly bodies,
is that we have the same series of impressions respecting them, that we
have respecting terrestrial objects near or remote, and that there is an
imperfect analogy between the one case and the other.
Before we affirm any thing, as of our own knowledge and competence,
respecting heavenly bodies which are said to be millions of millions
of miles removed from us, it would not perhaps be amiss that we should
possess ourselves of a certain degree of incontestible information, as
to the things which exist on the earth we inhabit. Among these, one of
the subjects attended with a great degree of doubt and obscurity, is the
height of the mountains with which the surface of the globe we inhabit
is diversified. It is affirmed in the received books of elementary
geography, that the Andes are the highest mountains in the world. Morse,
in his American Gazetteer, third edition, printed at Boston in 1810(46),
says, "The height of Chimborazzo, the most elevated point of the vast
chain of the Andes, is 20,280 feet above the level of the sea, which
is 7102 feet higher than any other mountain in the known world:" thus
making the elevation of the mountains of Thibet, or whatever other
rising ground the compiler had in his thought, precisely 13,178 feet
above the level of the sea, and no more. This decision however has
lately been contradicted. Mr. Hugh Murray, in an Account of Discoveries
and Travels in Asia, published in 1820, has collated the reports of
various recent travellers in central Asia; and he states the height
of Chumularee, which he speaks of as the most elevated point of the
mountains of Thibet, as nearly 30,000 feet above the level of the sea.
(46) Article, Andes.
The elevation of mountains, till lately, was in no way attempted to
be ascertained but by the use of the quadrant, and their height was
so generally exaggerated, that Riccioli, one of the most eminent
astronomers of the seventeenth century, gives it as his opinion that
mountains, like the Caucasus, may have a perpendicular elevation of
fifty Italian miles(47). Later observers have undertaken to correct the
inaccuracy of these results through the application of the barometer,
and thus, by informing themselves of the weight of the air at a certain
elevation, proceeding to infer the height of the situation.
(47) Rees, Encyclopedia; article, Mountains.
There are many circumstances, which are calculated to induce a
circumspect enquirer to regard the affirmative positions of astronomy,
as they are delivered by the most approved modern writers, with
considerable diffidence.
They are founded, as has already been said, next to the evidence of our
senses, upon the deductions of mathematical knowledge.
Mathematics are either pure or mixed.
Pure mathematics are concerned only with abstract propositions, and have
nothing to do with the realities of nature. There is no such thing in
actual existence as a mathematical point, line or surface. There is no
such thing as a circle or square. But that is of no consequence. We can
define them in words, and reason about them. We can draw a diagram, and
suppose that line to be straight which is not really straight, and that
figure to be a circle which is not strictly a circle. It is conceived
therefore by the generality of observers, that mathematics is the
science of certainty.
But this is not strictly the case. Mathematics are like those abstract
and imaginary existences about which they are conversant. They may
constitute in themselves, and in the apprehension of an infallible
being, a science of certainty. But they come to us mixed and
incorporated with our imperfections. Our faculties are limited; and we
may be easily deceived, as to what it is that we see with transparent
and unerring clearness, and what it is that comes to us through a
crooked medium, refracting and distorting the rays of primitive truth.
We often seem clear, when in reality the twilight of undistinguishing
night has crept fast and far upon us. In a train of deductions, as
in the steps of an arithmetical process, an error may have insinuated
itself imperceptibly at a very early stage, rendering all the subsequent
steps a wandering farther and farther from the unadulterated truth.
Human mathematics, so to speak, like the length of life, are subject to
the doctrine of chances. Mathematics may be the science of certainty to
celestial natures, but not to man.
But, if in the case of pure mathematics, we are exposed to the chances
of error and delusion, it is much worse with mixed mathematics.
The moment we step out of the high region of abstraction, and apply
ourselves to what we call external nature, we have forfeited that sacred
character and immunity, which we seemed entitled to boast, so long as
we remained inclosed in the sanctuary of unmingled truth. As has already
been said, we know what passes in the theatre of the mind; but we cannot
be said absolutely to know any thing more. In our speculations upon
actual existences we are not only subject to the disadvantages which
arise from the limited nature of our faculties, and the errors which may
insensibly creep upon us in the process. We are further exposed to the
operation of the unevennesses and irregularities that perpetually
occur in external nature, the imperfection of our senses, and of the
instruments we construct to assist our observations, and the discrepancy
which we frequently detect between the actual nature of the things about
us and our impressions respecting them.
This is obvious, whenever we undertake to apply the processes of
arithmetic to the realities of life. Arithmetic, unsubjected to the
impulses of passion and the accidents of created nature, holds on its
course; but, in the phenomena of the actual world, "time and chance
happeneth to them all."
Thus it is, for example, in the arithmetical and geometrical ratios, set
up in political economy by the celebrated Mr. Malthus. His numbers will
go on smoothly enough, 1, 2, 4, 8, 16, 32, as representing the principle
of population among mankind, and 1, 2, 3, 4, 5, 6, the means of
subsistence; but restiff and uncomplying nature refuses to conform
herself to his dicta.
Dr. Price has calculated the produce of one penny, put out at the
commencement of the Christian era to five per cent. compound interest,
and finds that in the year 1791 it would have increased to a greater sum
than would be contained in three hundred millions of earths, all solid
gold. But what has this to do with the world in which we live? Did
ever any one put out his penny to interest in this fashion for eighteen
hundred years? And, if he did, where was the gold to be found, to
satisfy his demand?
Morse, in his American Gazetteer, proceeding on the principles of
Malthus, tells us that, if the city of New York goes on increasing for
a century in a certain ratio, it will by that time contain 5,257,493
inhabitants. But does any one, for himself or his posterity, expect to
see this realised?
Blackstone, in his Commentaries on the Laws of England, has observed
that, as every man has two ancestors in the first ascending degree,
and four in the second, so in the twentieth degree he has more than a
million, and in the fortieth the square of that number, or upwards of a
million millions. This statement therefore would have a greater tendency
to prove that mankind in remote ages were numerous, almost beyond the
power of figures to represent, than the opposite doctrine of Malthus,
that they have a perpetual tendency to such increase as would infallibly
bring down the most tremendous calamities on our posterity.
Berkeley, whom I have already referred to on another subject, and who
is admitted to be one of our profoundest philosophers, has written
a treatise(48) to prove, that the mathematicians, who object to the
mysteries supposed to exist in revealed religion, "admit much greater
mysteries, and even falshoods in science, of which he alleges the
doctrine of fluxions as an eminent example(49)." He observes, that their
conclusions are established by virtue of a twofold error, and that these
errors, being in contrary directions, are supposed to compensate each
other, the expounders of the doctrine thus arriving at what they call
truth, without being able to shew how, or by what means they have
arrived at it.
(48) The Analyst.
(49) Life of Berkeley, prefixed to his Works.
It is a memorable and a curious speculation to reflect, upon how slight
grounds the doctrine of "thousands and thousands of suns, multiplied
without end, and ranged all around us, at immense distances from
each other, and attended by ten thousand times ten thousand worlds,"
mentioned in the beginning of this Essay, is built. It may be all true.
But, true or false, it cannot be without its use to us, carefully
to survey the road upon which we are advancing, the pier which human
enterprise has dared to throw out into the vast ocean of Cimmerian
darkness. We have constructed a pyramid, which throws into unspeakable
contempt the vestiges of ancient Egyptian industry: but it stands upon
its apex; it trembles with every breeze; and momentarily threatens to
overwhelm in its ruins the fearless undertakers that have set it up.
It gives us a mighty and sublime idea of the nature of man, to think
with what composure and confidence a succession of persons of the
greatest genius have launched themselves in illimitable space, with
what invincible industry they have proceeded, wasting the midnight oil,
racking their faculties, and almost wearing their organs to dust, in
measuring the distance of Sirius and the other fixed stars, the velocity
of light, and "the myriads of intelligent beings formed for endless
progression in perfection and felicity," that people the numberless
worlds of which they discourse. The illustrious names of Copernicus,
Galileo, Gassendi, Kepler, Halley and Newton impress us with awe; and,
if the astronomy they have opened before us is a romance, it is at least
a romance more seriously and perseveringly handled than any other in the
annals of literature.
A vulgar and a plain man would unavoidably ask the astronomers, How came
you so familiarly acquainted with the magnitude and qualities of the
heavenly bodies, a great portion of which, by your own account, are
millions of millions of miles removed from us? But, I believe, it is not
the fashion of the present day to start so rude a question. I have just
turned over an article on Astronomy in the Encyclopaedia Londinensis,
consisting of one hundred and thirty-three very closely printed quarto
pages, and in no corner of this article is any evidence so much as
hinted at. Is it not enough? Newton and his compeers have said it.
The whole doctrine of astronomy rests upon trigonometry, a branch of the
science of mathematics which teaches us, having two sides and one angle,
or two angles and one side, of a triangle given us, to construct the
whole. To apply this principle therefore to the heavenly bodies, it is
necessary for us to take two stations, the more remote from each other
the better, from which our observations should be made. For the sake
of illustration we will suppose them to be taken at the extremes of the
earth's diameter, in other words, nearly eight thousand miles apart from
each other, the thing itself having never been realised to that
extent. From each of these stations we will imagine a line to be drawn,
terminating in the sun. Now it seems easy, by means of a quadrant, to
find the arch of a circle (in other words, the angle) included between
these lines terminating in the sun, and the base formed by a right line
drawn from one of these stations to the other, which in this case is
the length of the earth's diameter. I have therefore now the three
particulars required to enable me to construct my triangle. And,
according to the most approved astronomical observations hitherto made,
I have an isosceles triangle, eight thousand miles broad at its base,
and ninety-five millions of miles in the length of each of the sides
reaching from the base to the apex.
It is however obvious to the most indifferent observer, that the more
any triangle, or other mathematical diagram, falls within the limits
which our senses can conveniently embrace, the more securely, when our
business is practical, and our purpose to apply the result to external
objects, can we rely on the accuracy of our results. In a case therefore
like the present, where the base of our isosceles triangle is to the
other two sides as eight units to twelve thousand, it is impossible
not to perceive that it behoves us to be singularly diffident as to the
conclusion at which we have arrived, or rather it behoves us to take for
granted that we are not unlikely to fall into the most important error.
We have satisfied ourselves that the sides of the triangle including
the apex, do not form an angle, till they have arrived at the extent of
ninety-five millions of miles. How are we sure that they do then? May
not lines which have reached to so amazing a length without meeting, be
in reality parallel lines? If an angle is never formed, there can be no
result. The whole question seems to be incommensurate to our faculties.
It being obvious that this was a very unsatisfactory scheme for arriving
at the knowledge desired, the celebrated Halley suggested another
method, in the year 1716, by an observation to be taken at the time of
the transit of Venus over the sun(50).
(50) Philosophical Transactions, Vol. XXIX, p. 454.
It was supposed that we were already pretty accurately acquainted with
the distance of the moon from the earth, it being so much nearer to us,
by observing its parallax, or the difference of its place in the heavens
as seen from the surface of the earth, from that in which it would
appear if seen from its centre(51). But the parallax of the sun is so
exceedingly small, as scarcely to afford the basis of a mathematical
calculation(52). The parallax of Venus is however almost four times as
great as that of the sun; and there must therefore be a very sensible
difference between the times in which Venus may be seen passing over
the sun from different parts of the earth. It was on this account
apprehended, that the parallax of the sun, by means of observations
taken from different places at the time of the transit of Venus in 1761
and 1769, might be ascertained with a great degree of precision(53).
(51) Bonnycastle, Astronomy, 7th edition, p. 262, et seq.
(52) Ibid, p. 268.
(53) Phil. Transactions, Vol. XXIX, p. 457.
But the imperfectness of our instruments and means of observation
have no small tendency to baffle the ambition of man in these curious
investigations.
"The true quantity of the moon's parallax," says Bonnycastle, "cannot be
accurately determined by the methods ordinarily resorted to, on account
of the varying declination of the moon, and the inconstancy of the
horizontal refractions, which are perpetually changing according to the
state the atmosphere is in at the time. For the moon continues but for
a short time in the equinoctial, and the refraction at a mean rate
elevates her apparent place near the horizon, half as much as her
parallax depresses it(54)."
(54) Astronomy, p. 265.
"It is well known that the parallax of the sun can never exceed nine
seconds, or the four-hundredth part of a degree(55)." "Observations,"
says Halley, "made upon the vibrations of a pendulum, to determine these
exceedingly small angles, are not sufficiently accurate to be depended
upon; for by this method of ascertaining the parallax, it will sometimes
come out to be nothing, or even negative; that is, the distance will
either be infinite, or greater than infinite, which is absurd. And, to
confess the truth, it is hardly possible for a person to distinguish
seconds with certainty by any instruments, however skilfully they may
be made; and therefore it is not to be wondered at, that the excessive
nicety of this matter should have eluded the many ingenious endeavours
of the most able opetators."(56).
(55) Ibid, p. 268.
(56) Phil. Transactions, Vol. XXIX, p. 456.
Such are the difficulties that beset the subject on every side. It is
for the impartial and dispassionate observers who have mastered all the
subtleties of the science, if such can be found, to determine
whether the remedies that have been resorted to to obviate the above
inaccuracies and their causes, have fulfilled their end, and are not
exposed to similar errors. But it would be vain to expect the persons,
who have "scorned delights, and lived laborious days" to possess
themselves of the mysteries of astronomy, should be impartial and
dispassionate, or be disposed to confess, even to their own minds, that
their researches were useless, and their labours ended in nothing.
It is further worthy of our attention, that the instruments with which
we measure the distance of the earth from the sun and the planets, are
the very instruments which have been pronounced upon as incompetent in
measuring the heights of mountains(57). In the latter case therefore we
have substituted a different mode for arriving at the truth, which
is supposed to be attended with greater precision: but we have no
substitute to which we can resort, to correct the mistakes into which we
may fall respecting the heavenly bodies.
(57) See above, Essay XXI.
The result of the uncertainty which adheres to all astronomical
observations is such as might have been expected. Common readers
are only informed of the latest adjustment of the question, and are
therefore unavoidably led to believe that the distance of the sun
from the earth, ever since astronomy became entitled to the name of
a science, has by universal consent been recognised as ninety-five
millions of miles, or, as near as may be, twenty-four thousand
semi-diameters of the earth. But how does the case really stand?
Copernicus and Tycho Brahe held the distance to be twelve hundred
semi-diameters; Kepler, who is received to have been perhaps the
greatest astronomer that any age has produced, puts it down as three
thousand five hundred semi-diameters; since his time, Riccioli as seven
thousand; Hevelius as five thousand two hundred and fifty(58); some
later astronomers, mentioned by Halley, as fourteen thousand; and Halley
himself as sixteen thousand five hundred(59).
(58) They were about thirty and forty years younger than Kepler
respectively.
(59) Halley, apud Philosophical Transactions, Vol. XXIX, p. 455.
The doctrine of fluxions is likewise called in by the astronomers in
their attempts to ascertain the distance and magnitude of the different
celestial bodies which compose the solar system; and in this way their
conclusions become subject to all the difficulties which Berkeley has
alleged against that doctrine.
Kepler has also supplied us with another mode of arriving at the
distance and size of the sun and the planets: he has hazarded a
conjecture, that the squares of the times of the revolution of the earth
and the other planets are in proportion to the cubes of their distances
from the sun, their common centre; and, as by observation we can
arrive with tolerable certainty at a knowledge of the times of their
revolutions, we may from hence proceed to the other matters we are
desirous to ascertain. And that which Kepler seemed, as by a divine
inspiration, to hazard in the way of conjecture, Newton professes to
have demonstratively established. But the demonstration of Newton has
not been considered as satisfactory by all men of science since his
time.
Thus far however we proceed as we may, respecting our propositions on
the subject of the solar system. But, beyond this, all science, real or
pretended, deserts us. We have no method for measuring angles, which can
be applied to the fixed stars; and we know nothing of any revolutions
they perform. All here therefore seems gratuitous: we reason from
certain alleged analogies; and we can do no more.
Huygens endeavoured to ascertain something on the subject, by making the
aperture of a telescope so small, that the sun should appear through it
no larger than Sirius, which he found to be only in the proportion of 1
to 27,664 times his diameter, as seen by the naked eye. Hence, supposing
Sirius to be a globe of the same magnitude as the sun, it must be 27,664
times as distant from us as the sun, in other words, at a distance so
considerable as to equal 345 million diameters of the earth(60). Every
one must feel on how slender a thread this conclusion is suspended.
(60) Encyclopaedia Londinensis, Vol. 11, p. 407.
And yet, from this small postulate, the astronomers proceed to deduce
the most astounding conclusions. They tell us, that the distance of the
nearest fixed star from the earth is at least 7,600,000,000,000 miles,
and of another they name, not less than 38 millions of millions of
miles. A cannon-ball therefore, proceeding at the rate of about twenty
miles in a minute would be 760,000 years in passing from us to the
nearest fixed star, and 3,800,000 in passing to the second star of which
we speak. Huygens accordingly concluded, that it was not impossible,
that there might be stars at such inconceivable distances from us, that
their light has not yet reached the earth since its creation(61).
(61) Ibid, p. 408.
The received system of the universe, founded upon these so called
discoveries, is that each of the stars is a sun, having planets and
comets revolving round it, as our sun has the earth and other
planets revolving round him. It has been found also by the successive
observations of astronomers, that a star now and then is totally lost,
and that a new star makes its appearance which had never been remarked
before: and this they explain into the creation of a new system from
time to time by the Almighty author of the universe, and the destruction
of an old system worn out with age(62). We must also remember the power
of attraction every where diffused through infinite space, by means
of which, as Herschel assures us, in great length of time a nebula,
or cluster of stars, may be formed, while the projectile force they
received in the beginning may prevent them from all coming together, at
least for millions of ages. Some of these nebulae, he adds, cannot well
be supposed to be at a less distance from us than six or eight thousand
times the distance of Sirius(63). Kepler however denies that each star,
of those which distinctly present themselves to our sight, can have its
system of planets as our sun has, and considers them as all fixed in the
same surface or sphere; since, if one of them were twice or thrice
as remote as another, it would, supposing their real magnitudes to be
equal, appear to be twice or thrice as small, whereas there is not in
their apparent magnitudes the slightest difference(64).
(62) Encycl. Lond. Vol. II, p. 411.
(63) Ibid, p. 348.
(64) Ibid, p. 411.
Certainly the astronomers are a very fortunate and privileged race of
men, who talk to us in this oracular way of "the unseen things of God
from the creation of the world," hanging up their conclusions upon
invisible hooks, while the rest of mankind sit listening gravely to
their responses, and unreservedly "acknowledging that their science is
the most sublime, the most interesting, and the most useful of all the
sciences cultivated by man(65)."
(65) Ferguson, Astronomy, Section 1.
We have a sensation, which we call the sensation of distance. It comes
to us from our sight and our other senses. It does not come immediately
by the organ of sight. It has been proved, that the objects we see,
previously to the comparison and correction of the reports of the organ
of sight with those of the other senses, do not suggest to us the idea
of distance, but that on the contrary whatever we see seems to touch the
eye, even as the objects of the sense of feeling touch the skin.
But, in proportion as we compare the impressions made upon our organs of
sight with the impressions made on the other senses, we come gradually
to connect with the objects we see the idea of distance. I put out
my hand, and find at first that an object of my sense of sight is not
within the reach of my hand. I put out my hand farther, or by walking
advance my body in the direction of the object, and I am enabled to
reach it. From smaller experiments I proceed to greater. I walk towards
a tree or a building, the figure of which presents itself to my eye,
but which I find upon trial to have been far from me. I travel towards
a place that I cannot see, but which I am told lies in a certain
direction. I arrive at the place. It is thus, that by repeated
experiments I acquire the idea of remote distances.
To confine ourselves however to the question of objects, which without
change of place I can discover by the sense of sight. I can see a town,
a tower, a mountain at a considerable distance. Let us suppose that the
limit of my sight, so far as relates to objects on the earth, is one
hundred miles. I can travel towards such an object, and thus ascertain
by means of my other senses what is its real distance. I can also employ
certain instruments, invented by man, to measure heights, suppose of
a tower, and, by experiments made in ways independent of these
instruments, verify or otherwise the report of these instruments.
The height of the Monument of London is something more than two hundred
feet. Other elevations, the produce of human labour, are considerably
higher. It is in the nature of the mind, that we conclude from the
observation that we have verified, to the accuracy of another, bearing
a striking analogy to the former, that we have not verified. But analogy
has its limits. Is it of irresistible certainty, or is it in fact to
be considered as approaching to certainty, because we have verified
an observation extending to several hundred feet, that an observation
extending to ninety-five millions of miles, or to the incredible
distances of which Herschel so familiarly talks, is to be treated as
a fact, or laid down as a principle in science? Is it reasonable to
consider two propositions as analogous, when the thing affirmed in the
one is in dimension many million times as great as the thing affirmed
in the other? The experience we have had as to the truth of the smaller,
does it authorise us to consider the larger as unquestionable? That
which I see with a bay of the sea or a wide river between, though it
may appear very like something with which I am familiar at home, do I
immediately affirm it to be of the same species and nature, or do I not
regard it with a certain degree of scepticism, especially if, along with
the resemblance in some points, it differs essentially, as for example
in magnitude, in other points? We have a sensation, and we enquire into
its cause. This is always a question of some uncertainty. Is its cause
something of absolute and substantive existence without me, or is it
not? Is its cause something of the very same nature, as the thing that
gave me a similar sensation in a matter of comparatively a pigmy and
diminutive extension?
All these questions an untrained and inquisitive mind will ask itself
in the propositions of astronomy. We must believe or not, as we think
proper or reasonable. We have no way of verifying the propositions by
the trial of our senses. There they lie, to be received by us in
the construction that first suggests itself to us, or not. They
are something like an agreeable imagination or fiction: and a sober
observer, in cold blood, will be disposed deliberately to weigh both
sides of the question, and to judge whether the probability lies in
favour of the actual affirmation of the millions of millions of miles,
and the other incredible propositions of the travelling of light, and
the rest, which even the most cautious and sceptical of the retainers of
modern astronomy, find themselves compelled to receive.
But I shall be told, that the results of our observations of the
distances of the heavenly bodies are unvaried. We have measured the
distances and other phenomena of the sun, the moon, Mercury, Venus,
Mars, Jupiter, Saturn, and their satellites, and they all fall into a
grand system, so as to convey to every unprejudiced mind the conviction
that this system is the truth itself. If we look at them day after day,
and year after year, we see them for ever the same, and performing
the same divine harmony. Successive astronomers in different ages and
countries have observed the celestial orbs, and swept the heavens, and
for ever bring us back the same story of the number, the dimensions,
the distances, and the arrangement of the heavenly bodies which form the
subject of astronomical science.
This we have seen indeed not to be exactly the case. But, if it were, it
would go a very little way towards proving the point it was brought to
prove. It would shew that, the sensations and results being similar, the
causes of those results must be similar to each other, but it would not
shew that the causes were similar to the sensations produced. Thus, in
the sensations which belong to taste, smell, sound, colour, and to those
of heat and cold, there is all the uniformity which would arise,
when the real external causes bore the most exact similitude to the
perceptions they generate; and yet it is now universally confessed that
tastes, scents, sounds, colours, and heat and cold do not exist out
of ourselves. All that we are entitled therefore to conclude as to the
magnitudes and distances of the heavenly bodies, is, that the causes of
our sensations and perceptions, whatever they are, are not less uniform
than the sensations and perceptions themselves.
It is further alleged, that we calculate eclipses, and register the
various phenomena of the heavenly bodies. Thales predicted an eclipse of
the sun, which took place nearly six hundred years before the Christian
era. The Babylonians, the Persians, the Hindoos, and the Chinese early
turned their attention to astronomy. Many of their observations were
accurately recorded; and their tables extend to a period of three
thousand years before the birth of Christ. Does not all this strongly
argue the solidity of the science to which they belong? Who, after
this, will have the presumption to question, that the men who profess
astronomy proceed on real grounds, and have a profound knowledge of
these things, which at first sight might appear to be set at a distance
so far removed from our ken?
The answer to this is easy. I believe in all the astronomy that was
believed by Thales. I do not question the statements relative to the
heavenly bodies that were delivered by the wise men of the East. But the
supposed discoveries that were made in the eighteenth, and even in the
latter part of the seventeenth century, purporting to ascertain the
precise distance of the sun, the planets, and even of the fixed stars,
are matters entirely distinct from this.
Among the earliest astronomers of Greece were Thales, Anaximander,
Anaximenes and Anaxagoras. Thales, we are told, held that the earth is
a sphere or globe, Anaximenes that it is like a round, flat table;
Anaximander that the sun is like a chariot-wheel, and is twenty-eight
times larger than the earth. Anaxagoras was put in prison for affirming
that the sun was by many degrees larger than the whole Peloponnesus(66).
Kepler is of opinion that all the stars are at an equal distance from
us, and are fixed in the same surface or sphere.
(66) Plutarch, De Placitis Philosophorum. Diogenes Laertius.
In reality the observations and the facts of astronomy do not depend
either upon the magnitudes or the distances of the heavenly bodies. They
proceed in the first place upon what may lie seen with the naked eye.
They require an accurate and persevering attention. They may be assisted
by telescopes. But they relate only to the sun and the planets. We are
bound to ascertain, as nearly as possible, the orbits described by the
different bodies in the solar system: but this has still nothing to do,
strictly speaking, with their magnitudes or distances. It is required
that we should know them in their relations to each other; but it is no
preliminary of just, of practical, it might almost be said, of liberal
science, that we should know any thing of them absolutely.
The unlimited ambition of the nature of man has discovered itself in
nothing more than this, the amazing superstructure which the votaries
of contemplation within the last two hundred years have built upon the
simple astronomy of the ancients. Having begun to compute the distances
of miles by millions, it appears clearly that nothing can arrest the
more than eagle-flight of the human mind. The distance of the
nearest fixed star from the earth, we are informed, is at least
7,000,000,000,000 miles, and of another which the astronomers name, not
less than 38 millions of millions of miles. The particles of light are
said to travel 193,940 miles in every second, which is above a million
times swifter than the progress of a cannon-ball(67). And Herschel
has concluded, that the light issuing from the faintest nebulae he
has discovered, must have been at this rate two millions of years in
reaching the Barth(68).
(67) Ferguson, Section 216. "Light moves," says Brewster, Optics, p. 2,
"from one pole of the earth to the other in the 24th part of a second: a
velocity which surpasses all comprehension."
(68) Brinkley, Astronomy, p. 130.