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n there is a window opposite the key…hole。 A dark object of the size of a key…hole will not be visible at one hundredth of the distance at which the key…hole is perceived。 Moreover； the difference in intensity is not alone in consideration； the intensity of the object _*with regard to its background_ has yet to be considered。 Aubert has shown that the accuracy of the distinction is the same when a square of white paper is looked at from an angle of 18''； and when conversely a square of black paper on white background is looked at from an angle of 85''。 ‘‘When we put a gray paper in the sunshine； it may become objectively brighter than white paper in shadow。 But this does not prevent us from knowing one as gray and the other as pure white。 We separate the color of the object from the intensity of the incident light。'' But this is not always so simple； inasmuch as we know in the case in hand which paper is gray and which white； which is in the sunlight and which in the shadow。 But if these facts are not known mistakes often occur so that a man dressed in dark clothes but in full light will be described as wearing lighter clothes than one who wears light clothes in the shadow。
Differences of illumination reveal a number of phenomena difficult to explain。 Fechner calls attention to the appearance of stars： ‘‘At night everybody sees the stars； in daylight not even Sirius or Jupiter is seen。 Yet the absolute difference between those places in the heavens where the stars are and the environing places is just as great as in the nightthere is only an increase in illumination。'' Of still greater importance to us is the circumstance noted but not explained by Bernstein。 If； in daylight； we look into a basement room from outside； we can perceive nothing； almost； everything is dark； even the windows appear black。 But in the evening； if the room is ever so slightly illuminated； and we look into it from outside； we can see even small articles distinctly。 Yet there was much intenser light in the room in question during the day than the single illumination of the night could have provided。 Hence； it is asserted； the difference in this case is a standard one。 In open day the eye is accustomed to the dominating brightness of daylight； beside which the subdued illumination of the room seems relatively dark。 But in the evening one is in the dark； and hence even the little light of a single candle is enough to enable one to see。 That this explanation is untrue is shown by the fact that the phenomenon is not regulated even when the circumstances in question are made identical。 If； for example； you approach the window in daylight with your eyes shut； lean your forehead against the pane and shut out the light on the sides with your hands； and then open your eyes； you see as little in the room as when you looked into it without performing this ceremony。 So again； if during the night you gazed at some near…by gas lamp and then glanced into the room； there is only a few moments' indistinctness at most； after that the single candle is enough。 The reason； then； must be different from the assigned onebut whatever it is； we need only to maintain that immediate judgment concerning numerous cases involving situations of this kind would be overhasty。 It is often said that a witness was able to see this or that under such and such illumination； or that he was unable to see it； although he denies his ability or inability。 The only solution of such contradictions is an experiment。 The attempt must be made either by the judge or some reliable third person； to discover whether； under the same conditions of illumination； anything could be seen at the place in question or not。
As to _*what_ may be seen in the distance； experiment again； is the best judge。 The human eye is so very different in each man that even the acute examination into what is known of the visual image of the Pleiades shows that the _*average_ visual capacity of classic periods is no different from our own； but still that there was great variety in visual capacity。 What enormous visual power is attributed to half…civilized and barbarous peoples； especially Indians； Esquimos； etc。！ Likewise among our own people there are hunters； mountain guides； etc。； who can see so clearly in the distance that mere stories about it might be fables。 In the Bosnian campaign of 1878 we had a soldier who in numerous cases of our great need to know the enemy's position in the distance could distinguish it with greater accuracy than we with our good field…glasses。 He was the son of a coal…miner in the Styrian mountains； and rather a fool。 Incidentally it may be added that he had an incredible； almost animal power of orientation。
As we know little concerning far…sightedness； so also we are unable to define what near…sighted people can see。 Inasmuch as their vision does not carry； they are compelled to make intellectual supplementations。 They observe the form； action； and clothes of people more accurately than sharp…eyed persons； and hence recognize acquaintances at a greater distance than the latter。 Therefore； before an assertion of a short…sighted man is doubted an experiment should be made； or at least another trustworthy short…sighted person should be asked for his opinion。
The background of objects； their movement and form have decided effects on the difference in visual perception。 It is an ancient observation that lengthy objects like poles； wires； etc。； are visible at incomparably greater distances than； e。 g。； squares of the same length。 In examination it has been shown that the boundary of accurate perception can hardly be determined。 I know a place where under favorable illumination taut； white and very thin telephone wires may be seen at a distance of more than a kilometer。 And this demands a very small angle of vision。
Humboldt calls attention to the large number of ‘‘optical fables。'' He assures us that it is certainly untrue that the stars may be seen in daylight from a deep well； from mines； or high mountains； although this has been repeatedly affirmed since Aristotle。
The explanation of our power to see very thin； long objects at a very great distance； is not our affair； but is of importance because it serves to explain a number of similar phenomena spoken of by witnesses。 We have either incorrectly to deny things we do not understand； or we have to accept a good deal that is deniable。 We will start； therefore； with the well…known fact that a point seen for a considerable time may easily disappear from perception。 This has been studied by Helmholtz and others； and he has shown how difficult it is to keep a point within the field of vision for only ten or twenty minutes。 Aubert examines older studies of the matter and concludes that this disappearance or confusion of an object is peripheral； but that fixation of a small object is always difficult。 If we fix a distant point it is disappearing at every instant so that an accurate perception is not possible； if however we fix upon a long； thin body； e。 g。； a wire； it is unnecessary to fix a single point and we may see the object with a wandering eye； hence more clearly。
Helmholtz adds that weakly objective images disap