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through them distinctly with one eye only, and will still distort the other. The true method of cure, I take to be this, When the child is arrived at such an age as to be capable of observing directions, place him directly before you, and let him close the undistorted eye, and look at you with the other. When you find the axis of this eye fixed directly upon you, bid him endeavour to keep it in that situation, and open his other eye, you will now immediately see the distorted eye turn away from you towards his nose, and the axis of the other will be pointed at you. But with patience and repeated trials, he will learn by this effort to keep the distorted eye fixed upon you, and thus effect a cure.”
Of Deceptions of the Senses.
That our senses sometimes deceive us, furnishes no argument against the truth of those informations which they give in their sound and natural state, and respecting those things concerning which their testimony ought to be trusted. Besides, admitting the veracity of their testimony as the reporters of matters of fact, the errors into which they lead may all be accounted for upon the strictest principles of philosophy. Nothing can be more idle and unworthy of the serious and sober spirit of philosophy, than a sceptical turn of mind. Our powers of understanding, although no doubt competent to every useful and important purpose of life, and exactly accommodated to our state of being, it is not to be denied, are extremely limited, and our investigations neces. sarily circumscribed by very narrow bounds. But, because our faculties are not able to penetrate into all mysteries, and all knowledge, to deny ourselves the advantage and enjoyment of that portion which we can attain, and arrest nur footsteps at our first approach into the dominions of nature, because we are not able by a single effort to tear off the veil in which she shrouds her secret operations, and disclose to view her mighty plan; discovers not only an irreverence for the Creator, who hath bestowed upon us our rational powers, bordering upon impiety, but the utmost levity and wantonness of mind,
We have before illustrated the justness of the observation, that in all our acquired perceptions we proceed according to
the interpretation of signs, and whenever the sign of any thing is presented, the mind naturally concludes that the thing signified is present. A gentleman passing along the streets of Philadelphia, imagines that he perceives a steamboat in the Delaware at a distance, but upon approaching it, finds that he was deceived, for that the object he saw was a sign post before an inn, upon which the representation of a steain-boat was rudely painted. Here the same sign was presented to his eye as if a steam-boat had been really moving upon the river. In the same manner are effected all deceptions of sight, touch, taste, or hearing.
In the month of January, of the present year, 1821, three suns were distinctly seen in the heavens, at Montreal, in Lower Canada, and we know that in Europe two, three, five, and even seven, have been seen at one time. These phenomena are occasioned by the refraction and reflection of rays of light during a very condensed state of the atmosphere. Now, what should we think of that man who, because two, three, or even six suns, besides the real sun, are sometimes perceived, should maintain that there is no such thing as a real sun? And yet this man would have much better ground for his conclusion than the sceptick who denies the evidence of the senses, since he, in this case, distrusts only the evi. dence of his eyes. In the very common experiment of crossing the fingers, and placing a pea or marble between them, so that it shall touch two sides of the fingers which do not correspond, there appear to be two peas or marbles. Here also there is presented the sign by which we have been accustomed to distinguish two objects of this nature, and of course, two appear to be present. It is for want of a knowledge of this kind, and irequent observation of such signs, that children and ignorant persons are so apt to be mistaken in the perception of objects at a distance, or of those whose appearances are not clearly discerned. And even, with persons the most intelligent, the nicest observation becomes ne.
cessary in order rightly to distinguish objects by these signs, and from the earliest period of life, we are acting the philosophers in this respect, although unconsciously to ourselves, in the prosecution of this kind of study. The force of reflection and habit in these matters is rendered very evident by the consideration, that whenever we are taken off our guard, and unprepared to form a judgment, we discover all the imbecility and incapacity of children. A strong reason in such cases is of little or no avail. He who has been accustomed to determine magnitude and distances only upon a horizontal plain, finds himself greatly at a loss in determining them when he looks up to a height, or down from some elevation. The men, who according to Shakspeare's representation, when beheld upon the strand from the heights of Dover, appeared like rooks or crows, if beheld upon a level surface, would have assumed their natural dimensions. A man seen through a mist appears much larger than he really is, because to the circumstance of his usual size in nature, and the image upon the retina, there is added also the other part of the sign of great bulk, to which we become familiarized, that of great distance, in the dimness with which he is viewed. A tree when beheld over a wall, however large or remote it may be, appears to be a small shrub or twig, resting upon the wall; until we become sensible of the interjacent space, and then the delusion vanishes. Bishop Berkeley remarked that when passing through Italy, on account of the uncommon clearness of the Italian sky, objects which were remote appeared much nearer to him than they did in other climates. Oblique distances appear longer in proportion as the eye is raised higher, to view them more distinctly, and long walks with a rising mount or ascent at the end, appear longer than they really are, especially if they be artfully contracted at the ascent so as to present the natural appearance of a long level walk with parallel sides. Animals and houses, and all objects of this nature appear smaller upon the sides of mountains than in any other positions, because mountains always appear nearer to us than they are. Dechales tells us, says Dr. Smith in his opticks, from whom I have taken several of these fallacies of vision, that while he stood at the bottom of a mountain, he once observed a parcel of crows going to fly over it, which, at first, he thought were higher than the mountain, but he found they spent half an hour in ascending before they got to the top. Aguilonius, continues the Doctor, mentions a fallacy in distance, which he had frequently observed and admired. In a warm summer's morning when fogs are exhaled from moist ground, we frequently see them very near us in some known place; but so soon as they are separated from the ground and are going to ascend, they appear so remote, that he could never have believed that they hung over that place, had he not seen them there but the moment before. The reason is, that they, then, appear in the manner and direction of other remote clouds in the horizon, whose dif. ference and distance cannot be discerned for want of some visible surface extended between them, like the surface of the ground while the rising cloud lay upon it. It is said to be a common observation of travellers that small objects, as houses and trees, seen in the dusk of the evening, appear remote, and larger than they naturally are. The same view of this subject will serve to account for the following facts mentioned by Mr. Jefferson in his notes upon Virginia, page 122. “Having had occasion,” says he,“ to mention the particular situation of Monticello for other purposes, I will just take notice that its elevation affords an opportunity of seeing a phenomenon which is rare at land, though frequent at sea. The seamen call it looming. Philosophy is as yet in the rear of the seamen, for so far from having accounted for it, she has not given it a name.