Thoughts on Man, His Nature, Productions and Discoveries Part 23

(45) Priestley, Disquisitions, Section II. I know not by whom this ill.u.s.tration was first employed. Among other authors, I find, in Fielding (Joseph Andrews, Book II, Chap. II), a sect of philosophers spoken of, who "can reduce all the matter of the world into a nutsh.e.l.l."

It is then with senses, from the impressions upon which we are impelled to draw such false conclusions, and that present us with images altogether unlike any thing that exists out of ourselves, that we come to observe the phenomena of what we call the universe. The first observation that it is here inc.u.mbent on us to make, and which we ought to keep ever at hand, to be applied as occasion may offer, is the well known aphorism of Socrates, that "we know only this, that we know nothing." We have no compa.s.s to guide us through the pathless waters of science; we have no revelation, at least on the subject of astronomy, and of the unnumbered inhabitable worlds that float in the ocean of ether; and we are bound therefore to sail, as the mariners of ancient times sailed, always within sight of land. One of the earliest maxims of ordinary prudence, is that we ought ever to correct the reports of one sense by the a.s.sistance of another sense. The things we here speak of are not matters of faith; and in them therefore it is but reason, that we should imitate the conduct of Didymus the apostle, who said, "Except I put my fingers into the prints of the nails, and thrust my hand into his side, I will not believe." My eyes report to me an object, as having a certain magnitude, texture, and roughness or smoothness; but I require that my hands should confirm to me the evidence of my eyes. I see something that appears to be an island at an uncertain distance from the sh.o.r.e; but, if I am actuated by a laudable curiosity, and wish to possess a real knowledge, I take a boat, and proceed to ascertain by nearer inspection, whether that which I imagined to be an island is an island or no.

There are indeed many objects with which we are conversant, that are in so various ways similar to each other, that, after having carefully examined a few, we are satisfied upon slighter investigation to admit the dimensions and character of others. Thus, having measured with a quadrant the height of a tower, and found on the narrowest search and comparison that the report of my instrument was right, I yield credit to this process in another instance, without being at the trouble to verify its results in any more elaborate method.

The reason why we admit the inference flowing from our examination in the second instance, and so onward, with less scrupulosity and scepticism than in the first, is that there is a strict resemblance and a.n.a.logy in the two cases. Experience is the basis of our conclusions and our conduct. I strike against a given object, a nail for example, with a certain degree of force, because I have remarked in myself and others the effect of such a stroke. I take food and masticate it, because I have found that this process contributes to the sound condition of my body and mind. I scatter certain seeds in my field, and discharge the other functions of an agriculturist, because I have observed that in due time the result of this industry is a crop. All the propriety of these proceedings depends upon the exact a.n.a.logy between the old case and the new one. The state of the affair is still the same, when my business is merely that of an observer and a traveller. I know water from earth, land from sea, and mountains from vallies, because I have had experience of these objects, and confidently infer that, when certain appearances present themselves to my organs of sight, I shall find the same results to all my other senses, as I found when such appearances occurred to me before.

But the interval that divides the objects which occur upon and under the earth, and are accessible in all ways to our examination, on the one hand, and the lights which are suspended over our heads in the heavens on the other, is of the broadest and most memorable nature. Human beings, in the infancy of the world, were contented reverently to behold these in their calmness and beauty, perhaps to wors.h.i.+p them, and to remark the effects that they produced, or seemed to produce, upon man and the subjects of his industry. But they did not aspire to measure their dimensions, to enquire into their internal frame, or to explain the uses, far removed from our sphere of existence, which they might be intended to serve.

It is however one of the effects of the improvement of our intellect, to enlarge our curiosity. The daringness of human enterprise is one of the prime glories of our nature. It is our boast that we undertake to "measure earth, weigh air, and state the tides." And, when success crowns the boldness of our aspirations after what vulgar and timorous prudence had p.r.o.nounced impossible, it is then chiefly that we are seen to partic.i.p.ate of an essence divine.

What has not man effected by the boldness of his conceptions and the adventurousness of his spirit? The achievements of human genius have appeared so incredible, till they were thoroughly examined, and slowly established their right to general acceptance, that the great heroes of intellect were universally regarded by their contemporaries as dealers in magic, and implements of the devil. The inventor of the art of printing, that glorious instrument for advancing the march of human improvement, and the discoverer of the more questionable art of making gunpowder, alike suffered under this imputation. We have rendered the seas and the winds instruments of our pleasure, "exhausted the old world, and then discovered a new one," have drawn down lightning from heaven, and exhibited equal rights and independence to mankind. Still however it is inc.u.mbent on us to be no less wary and suspicious than we are bold, and not to imagine, because we have done much, that we are therefore able to effect every thing.

As was stated in the commencement of this Essay, we know our own sensations, and we know little more. Matter, whether in its primary or secondary qualities, is certainly not the sort of thing the vulgar imagine it to be. The ill.u.s.trious Berkeley has taught many to doubt of its existence altogether; and later theorists have gone farther than this, and endeavoured to shew, that each man, himself while he speaks on the subject, and you and I while we hear, have no conclusive evidence to convince us, that we may not, each of us, for aught we know, be the only thing that exists, an entire universe to ourselves.

We will not however follow these ingenious persons to the startling extreme to which their speculations would lead us. But, without doing so, it will not misbecome us to be cautious, and to reflect what we do, before we take a leap into illimitable s.p.a.ce.

SECTION II.

"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 a.n.a.logy, 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 a.n.a.logy 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 circ.u.mstances, which are calculated to induce a circ.u.mspect 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 const.i.tute 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 undistinguis.h.i.+ng 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 ent.i.tled to boast, so long as we remained inclosed in the sanctuary of unmingled truth. As has already been said, we know what pa.s.ses 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 a.s.sist 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 pa.s.sion 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 fas.h.i.+on 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 a.n.a.lyst.

(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 s.p.a.ce, 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 ill.u.s.trious names of Copernicus, Galileo, Ga.s.sendi, 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 fas.h.i.+on 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 ill.u.s.tration 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. .h.i.therto 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 pa.s.sing 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.