Thoughts on Man: His Nature, Productions, and Discoveries | ||
SECTION I.
It can scarcely be imputed to me as profane, if I venture to put down a few sceptical doubts on the science of astronomy. All branches of knowledge are to be considered as fair subjects of enquiry: and he that has never doubted, may be said, in the highest and strictest sense of the word, never to have believed.
The first volume that furnished to me the groundwork of the following doubts, was the book commonly known by the name of Guthrie's Geographical Grammar, many parts and passages of which engaged my attention in my own study, in the house of a rural schoolmaster, in the year 1772. I cannot therefore proceed more fairly than by giving here an extract of certain passages in that book, which have relation to the present subject. I know not how far they have been altered in the edition of Guthrie which now lies before me, from the language of the book then in my possession; but I feel confident that in the main particulars they continue the same[1].
"In passing rapidly over the heavens with his new telescope, the universe increased under the eye of Herschel; 44,000 stars, seen in the space of a few degrees, seemed to indicate that there were seventy-five millions in the heavens. But what are all these, when compared with those that fill the whole expanse, the boundless field of æther?
"The immense distance of the fixed stars from our earth, and from each other, is of all considerations the most proper for raising our ideas of the works of God. Modern discoveries make it probable that each of these stars is a sun, having planets and comets revolving round it, as our sun has the earth and other planets revolving round him.—A ray of light, though its motion is so quick as to be commonly thought instantaneous, takes up more time in travelling from the stars to us, than we do in making a West-India voyage. A sound, which, next to light, is considered as the quickest body we are acquainted with, would not arrive to us from thence in 50,000 years. And a cannon-ball, flying at the rate of 480 miles an hour, would not reach us in 700,000 years.
"From what we know of our own system, it may be reasonably concluded, that all the rest are with equal wisdom contrived, situated, and provided with accommodations for rational inhabitants.
"What a sublime idea does this suggest to the human imagination, limited as are its powers, of the works of the Creator! Thousands and thousands
The thought that would immediately occur to a dispassionate man in listening to this statement, would be, What a vast deal am I here called on to believe!
Now the first rule of sound and sober judgment, in encountering any story, is that, in proportion to the magnitude and seemingly incredible nature of the propositions tendered to our belief, should be the strength and impregnable nature of the evidence by which those propositions are supported.
It is not here, as in matters of religion, that we are called upon by authority from on high to believe in mysteries, in things above our reason, or, as it may be, contrary to our reason. No man pretends to a revelation from heaven of the truths of astronomy. They have been brought to light by the faculties of the human mind, exercised upon such facts and circumstances as our industry has set before us.
To persons not initiated in the rudiments of astronomical science, they rest upon the great and high-sounding names of Galileo, Kepler, Halley
The modest enquirer therefore, without pretending to put himself on an equality with these illustrious men, may be forgiven, when he permits himself to suggest a few doubts, and presumes to examine the grounds upon which he is called upon to believe all that is contained in the above passages.
Now the foundations upon which astronomy, as here delivered, is built, are, first, the evidence of our senses, secondly, the calculations of the mathematician, and, in the third place, moral considerations. These have been denominated respectively, practical astronomy, scientific, and theoretical.
As to the first of these, it is impossible for us on this occasion not to recollect what has so often occurred as to have grown into an every-day observation, of the fallibility of our senses.
It may be doubted however whether this is a just statement. We are not deceived by our senses, but deceived in the inference we make from our sensations. Our sensations respecting what we call the external world, are chiefly those of length, breadth and solidity, hardness and softness, heat and cold, colour, smell, sound and taste. The inference which the generality of mankind make in relation to these
Modern philosophy has taught us, in certain cases, to controvert the position, that the causes of our sensations are like to the sensations themselves. Locke in particular has called the attention of the reasoning part of mankind to the consideration, that heat and cold, sweet and bitter, and odour offensive or otherwise, are perceptions, which imply a percipient being, and cannot exist in inanimate substances. We might with equal propriety ascribe pain to the whip that beats us, or pleasure to the slight alternation of contact in the person or thing that tickles us, as suppose that heat and cold, or taste, or smell are any thing but sensations.
The same philosophers who have called our attention to these remarks, have proceeded to shew that the causes of our sensations of sound and colour have no precise correspondence, do not tally with the sensations we receive. Sound is the result of a percussion of the air. Colour is produced by the reflection of the rays of light; so that
It follows that, if there were no percipient being to receive these sensations, there would be no heat or cold, no taste, no smell, no sound, and no colour.
Aware of this difference between our sensations in certain cases and the causes of these sensations, Locke has divided the qualities of substances in the material universe into primary and secondary, the sensations we receive of the primary representing the actual qualities of material substances, but the sensations we receive of what he calls the secondary having no proper resemblance to the causes that produce them.
Now, if we proceed in the spirit of severe analysis to examine the primary qualities of matter, we shall not perhaps find so marked a distinction between those and the secondary, as the statement of Locke would have led us to imagine.
The Optics of Newton were published fourteen years later than Locke's Essay concerning Human Understanding.
In endeavouring to account for the uninterrupted transmission of rays of light through transparent substances, however hard they may be found to be, Newton has these observations.
"Bodies are much more rare and porous, than is commonly believed. Water is nineteen times lighter, and by consequence nineteen times rarer, than gold; and gold is so rare, as very readily, and without the least opposition, to transmit the magnetic effluvia, and easily to admit quicksilver into its pores, and to let water pass through it. From all which we may conclude, that gold has more pores than solid parts, and by consequence that water has above forty times more pores than parts. And he that shall find out an hypothesis, by which water may be so rare, and yet not capable of compression by force, may doubtless, by the same hypothesis, make gold, and water, and all other bodies, as much rarer as he pleases, so that light may find a ready passage through transparent substances[2]."
Again:
In the Queries annexed to the Optics, Newton further suggests an opinion, that the rays of light are repelled by bodies without immediate contact. He observes that:
"Where attraction ceases, there a repulsive virtue ought to succeed. And that there is such a virtue, seems to follow from the reflexions and inflexions of the rays of light. For the rays are repelled by bodies, in both these cases, without the immediate contact of the reflecting or inflecting body. It seems also to follow from the emission of light; the ray, so soon as it is shaken off from a shining body by the vibrating motion of the parts of the body, and gets beyond the reach of attraction, being driven away with exceeding great velocity. For that force, which is sufficient to turn it back in reflexion, may be sufficient to emit it. It
Newton was of opinion that matter was made up, in the last resort, of exceedingly small solid particles, having no pores, or empty spaces within them. Priestley, in his Disquisitions relating to Matter and Spirit, carries the theory one step farther; and, as Newton surrounds his exceedingly small particles with spheres of attraction and repulsion, precluding in all cases their actual contact, Priestley is disposed to regard the centre of these spheres as mathematical points only. If there is no actual contact, then by the very terms no two particles of matter were ever so near to each other, but that they might be brought nearer, if a sufficient force could be applied for that purpose. You had only another sphere of repulsion to conquer; and, as there never is actual contact, the whole world is made up of one sphere of repulsion after another, without the possibility of ever arriving at an end.
"The principles of the Newtonian philosophy," says our author, "were no sooner known, than it
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 incumbent 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 compass 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
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
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
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 pronounced impossible, it is then chiefly that we are seen to participate 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
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 illustrious 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 space.
Thoughts on Man: His Nature, Productions, and Discoveries | ||