criminal psychology-第140章
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rtant fact that the size of the orifice influences considerably the estimation of the size of objects seen through it。 Observations through key…holes are not rarely of importance in criminal cases。 The underestimations of sizes are astonishing。
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Arial perspective has a great influence on the determination of these phenomena； particularly such as occur in the open and at great distances。 The influence is to be recognized through the various appearances of distant objects； the various colors of distant mountains； the size of the moon on the horizon； and the difficulties which arial perspective offers painters。 Many a picture owes its success or failure to the use of arial perspective。 If its influence is significant in the small space of a painting； the illusions in nature can easily become of enormous significance； particularly when extremes are brought together in the observations of objects in unknown regions。 The condition of the air； sometimes foggy and not pellucid； at another time particularly clear； makes an enormous difference； and statements whether about distance； size； colors； etc。； are completely unreliable。 A witness who has several times observed an unknown region in murky weather and has made his important observation under very clear skies； is not to be trusted。
An explanation of many sensory illusions may be found in the so…called illusory lines。 They have been much studied； but Zllner＇1＇ has been the first to show their character。 Thus； really quite parallel lines are made to appear unparallel by the juxtaposition of inclined or crossing lines。 In figures 1 and 2 both the horizontal lines are actually parallel； as may be determined in various ways。
＇1＇ Poggendorf's Annelen der Physik； Vol。 110； p。 500； 114； 587； 117； 477。
The same lines looked at directly or backwards seem； in Fig。 1； convex； in Fig。 2 concave。
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Still more significant is the illusion in Fig。 3； in which the convexity is very clear。 The length； etc。； of the lines makes no difference in the illusion。
On the other hand； in Fig。 4 the diagonals must be definitely thicker than the parallel horizontal lines； if those are to appear not parallel。 That the inclination is what destroys the appearance of parallels is shown by the simple case given in Fig。 5； where the distance from A to B is as great as from B to C； and yet where the first seems definitely smaller than the second。
Still more deceptive is Fig。 6 where the first line with the angle inclined inwards seems incomparably smaller than the second with the angle inclined outwards。
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All who have described this remarkable subject have attempted to explain it。 The possession of such an explanation might put
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us in a position to account for a large number of practical difficulties。 But certain as the facts are； we are still far from their _*why_ and _*how_。 We may believe that the phenomenon shown in Figs。 1 and 2 appears when the boundaries of a field come straight up to a street with parallel sides； with the result that at the point of meeting the street seems to be bent in。 Probably we have observed this frequently without being aware of it； and have laid no particular stress on it； first of all； because it was really unimportant； and secondly； because we thought that the street was really not straight at that point。
In a like manner we may have seen the effect of angles as shown in Figs。 5 and 6 on streets where houses or house…fronts were built cornerwise。 Then the line between the corners seemed longer or shorter； and as we had no reason for seeking an accurate judgment we paid no attention to its status。 We simply should have made a false estimate of length if we had been required to judge it。 It is also likely that we may have supposed an actual or suppository line on the side of the gables of a house enclosed by angles of the gables； to be short；but until now the knowledge of this supposition has had no practical value。 Nevertheless； the significance of these illusions should not be underestimated。 They mean most of all the fact that we really can be much deceived； even to the degree of swearing to the size of a simple thing and yet being quite innocently mistaken。 This possibility shows； moreover； that the certainty of our judgment according to sensible standards is inadequate and we have no way of determining how great this inadequacy is。 We have already indicated that we know only the examples cited by Zllner； Delboeuf and others。 It is probable that they were hit upon by accident and that similar ones can not be discovered empirically or intentionally。 Hence； it may be assumed that such illusions occur in great number and even in large dimensions。 For example； it is known that Thompson discovered his familiar ‘‘optical circle illusion'' （six circles arranged in a circle； another in the middle。 Each possesses bent radii which turn individually if the whole drawing is itself turned in a circle） by the accident of having seen the geometrical ornament drawn by a pupil。 Whoever deals with such optical illusions may see very remarkable ones in almost every sample of ladies' clothes； particularly percale； and also in types of carpets and furniture。 And these are too complicated to be described。 In the course of time another collection of such illusions will be discovered and an explanation of them will be forthcoming； and then it may be possible to determine how our knowledge of their existence can be turned to practical use。
Practical application is easier in the so…called inversion of the visual object。 Fig。 7 shows the simplest case of itthe possibility of seeing the middle vertical line as either deeper or higher than the others。 In the first instance you have before you a gutter；
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in the second a room。 Similar relations are to be observed in the case of a cube in which the corner a may be seen as either convex or concave according as you think it behind or before the background of the angles from which _a_ proceeds。 It is still clearer when； in a rhomboid； the line _XY_ is drawn。 Then _x_ or _y_ may be seen alternately as nearer or further and the figure can thereby be brought into a different position。 （Fig。 9。） Done once it may be repeated voluntarily。
There are many practical examples of these illusions。 Sinsteden saw one evening the silhouette of a windmill against a luminous background。 The arms seemed now
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to go to the right； now to the leftclearly because he did not make out the body of the mill and might equally assume that he saw it from the front or from the rear； the wheels going toward the right in the first； and toward the left in the other case。 An analogous case is cited by Bernstein。 If （Fig。 10） the cross made of the thin lines stand for the bars of a weather vane and the heavy lines represent the weather vane itself； it may be impossible under the conditions of illumination for an eye looking from N to distinguish whether the weather vane points NE or SW； there is no way of determining the starting point of motion。 All that can certainly be said is that the weather vane lies between NE and SW and that
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its angle is at the crossing of the two lines； but the direction in which its heads point can not be determined at even a slight distance。 Both forms of this illusion may occur in a criminal trial。 If once a definite idea of some form of order has been gained； it is not abandoned or doubted； and is even sworn to。 If asked； for example； whether the mill…wheel moved right or left； the observer will consider hardly one time in a hundred whether there might not have been an optical illusion。 He will simply assure us that the thing was as he thinks he saw it； and whether he saw it correctly is purely a matter of luck。
To all these illusions may be added those which are connected with movement or are exposed by movement。 During the movement of certain
