criminal psychology-第60节
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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 disappear like a wet spot on warm tin； at the moment a single point is fixed； as does e。 g。； a landscape seen at night。 This last acute observation is the basis of many a testimony concerning the sudden disappearance of an object at night。 It has helped me in many an examination； and always to advantage。
In this connection the over…estimation of the moon's illuminating power is not to be forgotten。 According to Helmholtz the power of the full moon is not more than that of a candle twelve feet away。 And how much people claim to have seen by moonlight！ Dr。 Vincent＇1＇ says that a man may be recognized during the first quarter at from two to six meters； at full moon at from seven to ten meters； and at the brightest full moon； an intimate may be recognized at from fifteen to sixteen meters。 This is approximately correct and indicates how much moonlight is over…estimated。
＇1＇ Vincent： Traitdecine lgrand du Saule。
In addition to the natural differences of sight there are also those artificially created。 How much we may help ourselves by skilful distinctions； we can recognize in the well…known and frequently… mentioned business of reading a confused handwriting。 We aim to weaken our sense…perception in favor of our imagination； i。 e。 so to reduce the clearness of the former as to be able to test upon it in some degree a larger number of images。 We hold the MS。 away from us； look at it askant； with contracted eyebrows； in different lights； and finally we read it。 Again； the converse occurs。 If we have seen something with a magnifying glass we later recognize details without its help。 Definite conditions may bring to light very great distinctions。 A body close to the face or in the middle distance looks different according as one eye or both be used in examining it。 This is an old story and explains the queer descriptions we receive of such objects as weapons and the like； which were suddenly held before the face of the deponent。 In cases of murderous assault it is certain that most uncanny stories are told； later explained by fear or total confusion or intentional dishonesty； but really to be explained by nothing more than actual optical processes。
I do not believe that binocular vision is of much importance in the law； I know of no case in ordinary vision where it matters whether one or both eyes have been used。 It is correct to assert that one side or the other of a vertically held hand will be clearer if； before looking at it with both eyes； you look at it with one or the other； but this makes little difference to our purpose。 It must be maintained that a part of what we see is seen with one eye only；if； e。 g。； I look at the sky and cover one eye with my hand； a certain portion of the heaven disappears； but I observe no alteration in the remaining portion。 When I cover the other eye； other stars disappear。 Therefore； in binocular vision certain things are seen with one eye only。 This may be of importance when an effect has been observed first with both eyes； then with one； raising the question of the difference in observationbut such a question is rare。
There are two additional things to consider。 The first is the problem of the influence of custom on increasing visual power in darkness。 This power is as a rule undervalued。 No animal； naturally； can see anything in complete darkness。 But it is almost unbelievable how much can be seen with a very little light。 Here again； prisoners tell numerous stories concerning their vision in subterranean prisons。 One saw so well as to be able to throw seven needles about the cell and then to find them again。 Another； the naturalist Quatremologie。'' Aubert tells of his having had to stay in a room so dark as to make it necessary for others to feel their way； but nevertheless being able to read books without detection because the others could not see the books。
How quickly we get used to darkness and how much more we see after a while； is well known。 It is also certain that the longer you are in darkness the more you see。 You see more at the end of a day than after a few hours； and at the end of a year； still more。 The eye； perhaps； changes in some degree for just this purpose。 But a prolonged use of the visual mechanism tends to hypertrophy or atrophy； as the eyes of deep…sea fishes show。 It is well； in any event； to be careful about contradicting the testimonies of patients who have long lived in the dark； concerning what they have seen。 The power to see in the dark is so various that without examination； much injustice may be done。 Some people see almost nothing at twilight； others see at night as well as cats。 And in court these differences must be established and experimentally verified。
The second important element is the innervation of the muscles in consequence of movement merely seen。 So Stricker points out； that the sight of a man carrying a heavy load made him feel tension in the muscles involved； and again； when he saw soldiers exercising； he almost was compelled openly to act as they。 In every case the muscular innervation followed the visual stimulus。
This may sound improbable but； nevertheless； everybody to some degree does the identical things。 And at law the fact may be of importance in cases of assault and battery。 Since I learned it； I have repeatedly observed in such cases； from harmless assault to murder； that people； although they had not been seen to deal any blows； were often accused of complicity simply because they were making suspicious movements that led to the following inference： ‘‘They stuck their hands into their trousers pocket looking for a knife； clenched their fists； looked as if they were about to jump； swung their hands。'' In many such cases it appeared that the suspects were harmless spectators who were simply more obvious in their innervation of the muscles involved in the assault they were eagerly witnessing。 This fact should be well kept in mind； it may relieve many an innocent。
Section 38。 （2） _Color Vision_。
Concerning color vision only a few facts will be mentioned： 1。 It will be worth while； first of all； to consider whether color exists。 Liebmann holds that if all the people were blind to red； red would not exist； red； i。 e。； is some cervical phantasy。 So are light； sound； warmth； taste； etc。 With other senses we have another world。 According to Helmholtz； it is senseless to ask whether cinnabar is red as we see it or is only so as an optical illusion。 ‘‘The sensation of red is the normal reaction of normally constructed eyes to light reflected from cinnabar。 A person blind to red； will see cinnabar as black； or a dark grayish yellow； and this is the correct reaction for these abnormal eyes。 But he needs to know that his eyes are different from those of other people。 In itself the sensation is neither more correct nor less correct than any other even though those who can see red are in the great majority。 The red color of cinnabar exists as such only in so far as there are eyes which are similar to those of the majority of mankind。 As such light reflected from cinnabar may not properly be called red； it is red only for especial kinds of eyes。'' This is so unconditionally incorrect that an impartial judge of photography says＇1＇ that everything that normal eyes call violet and blue； is very bright； and everything they call green and red is very dark。 The red…blind person will see as equal certain natural reds； greens and gray…yellows； both in intensity and shadow。 But on the photograph he will be able to distinguish the differences in brightness caused by these three otherwise identical colors。 We may； therefore； assume that colors possess _*objective_ differences； and that these objective differences are perceived even by persons of normal vision。 But whether I am able to sense the same effect in red that another senses； and whether I should not call red blue； if I had the color…vision of another； is as impossible to discover as it is
