34. Of Telescopes.
MAny Ingenious and Industrious Artists take much labour and pains in studying the natures and figures of Celestial objects, and endeavour to dis∣cover the causes of their appearances by Telescopes, and such like Optick Instruments; but if Art be not able to inform us truly of the natures of those Creatures that are near us, How may it delude us in the scarch and enquiry we make of those things that are so far from us? We see how Multiplying-glasses do present nu∣merous pictures of one object, which he that has not Page 153 the experience of the deceitfulness of such Glasses, would really think to be so many objects. The like de∣ceits may be in other optick Instruments for ought man knows. 'Tis true, we may perhaps through a Te∣lescope see a Steeple a matter of 20 or 30 miles off; but the same can a natural Eye do, if it be not defective, nor the medium obstructed, without the help of any such Instrument; especially if one stand upon a high place: But put the case, a man should be upon the Alps, he would hardly see the City of Paris from thence, although he looked through a Telescope ne∣ver so perfect, and had no obstruction to hinder his sight: and truly the Stars and Planets are far more di∣stant from us then Paris from the Alps. It is well known, that the sense of sight requires a certain pro∣portion of distance betwixt the Eye and the Object; which being exceeded, it cannot perform its office; for if the object be either too near, or too far off, the sight cannot discern it: and as I have made mention in my Philosophical Letters of the nature of those Guns, that according to the proportion of the length of the barrel, shoot either further or shorter; for the Barrel must have its proportioned length; which be∣ing exceeded, the Gun will shoot so much shorter as the barrel is made longer; so may Prospective-glasses perhaps direct the sense of seeing within a certain com∣pass of distance; which distance, surely the Stars and Planets do far exceed; I mean so, as to discern their Page 154 figures as we do of other objects that are near us; for concerning their exterior progressive motions, we may observe them with our natural eyes as well as through Artificial Tubes: We can see the Suns rising and set∣ting, and the progressive motion of the Moon, and other Planets; but yet we cannot see their natural fi∣gures, what they are, nor what makes them move; for we cannot perceive progressive local Motion otherwise, then by change of distance, that is, by composition and division of Parts, which is commonly, (though improperly) called change of Place, and no glasses or tubes can do more. Some affirm, they have discovered many new Stars, never seen before, by the help of Telescopes; but whether this be true, or not, or whether it be onely a delusion of the glasses, I will not dispute; for I having no skill, neither in the art of Opticks, nor in Astronomy, may chance to err, and therefore I will not eagerly affirm what I do not cer∣tainly know; I onely endeavour to deliver my judg∣ment as reason directs me, and not as sense informs, or rather deludes me; and I chose rather to follow the guidance of regular Reason, then of deluding Art.