thoughts on man-第71章
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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
