March i, 1889.] 



SCIENCE. 



165 



mal world. The physicist, he observes, before deducing any re- 

 sult, takes into account the errors of his instruments. The scien- 

 tist is always working with one certain instrument, the human 

 mind. The errors of this ever-present factor in all work form a 

 most important field of study. 



In the study of instincts, such as those that direct birds in the 

 building of their nests, insects in the formation of their communi- 

 ties, we often admire the wonderful resemblance of these complex 

 acts to the results of reason. And yet we recognize an important 

 distinction between them : their sphere is limited, their power of 

 adaptation to new conditions is small. It is a remarkable mechan- 

 ism, but has application to a limited number of movements. A 

 bird shows remarkable skill in weaving the threads with which it 

 builds its nest, fastening it to the limb of a tree, and adapting it to 

 the shape of the twig. But tie the foot of a bird in a cage, and it 

 cannot make use of its skill in weaving to untie the fastening, but 

 struggles and flutters until it kills itself or is accidentally freed. 

 Teleologically speaking, certain adjustments are ingrained in its 

 nervous system ; but these adjustments are special, not general. 

 The more perfect the instinct, the more stable and invariable is it ; 

 the less rigidly the adjustments are ingrained, the more does the 

 act resemble what we term " reason." Diversity and adaptability 

 are the marks of rational development. The weakness of animal 

 intelligence is always in the lack of ability to break away from 

 routine associations ; to proceed from two facts to a third. A dog 

 will defend himself if you tease him, but he will not bite. He 

 knows how to use his teeth well enough with his fellows, but to- 

 wards man he has acquired an attitude of deference. 



Animal instincts result from the environment, and must be 

 judged in the environment. When looked at from a human stand- 

 point, these actions seem foolish and irrelevant. We, too, have 

 our rigid instincts, our reflex actions. The closure of the eyelids 

 when an object threatens the eye is a useful protective mechanism ; 

 but when we are to undergo an operation, it may be harmful. 

 None the less all the strength of the will is incompetent to keep 

 the eye open. It acts according to its acquired habits. It is true 

 that we are conscious of our error, which animals are probably 

 not ; but this is not an essential point. It is proposed to show 

 that the typical kinds of error arise, as do these misapplications of 

 instincts, from the unwarranted application of a general rule to a 

 particular case. 



The majority of sense-deceptions support this view. Irritation 

 of any part of the retina arouses a sensation localized in space 

 where an object causing such an irritation would ordinarily be 

 found. In some cases we are freed from illusion by the remem- 

 brance of former experiences. Savages are apt to mistake an 

 image in a mirror for a real object behind it : repeated experience 

 allows us to see the image as an image in the plane of the mirror. 



Here it is easy to distinguish between the sensory and the mem- 

 ory factors, but in some cases this may be difficult. If you draw a 

 Une on a sheet of paper, and cover it up with a second sheet so as 

 just to conceal the end of the line, and show it to some one ignorant 

 of the arrangement, he will be greatly surprised not to find the en- 

 tire Une longer than it is when you remove the second sheet. He 

 does this because it is an uncommon experience to have so little of 

 a line covered up. He cannot help forming a prejudgment on the 

 basis of what is most probable. Is this an error of sensation, or 

 of memory ? 



There are a host of similar deceptions. One need only refer to 

 the tricks of the conjurer. He takes care to appeal to something 

 true as a rule, but false in this particular case. Again : he directs 

 his gaze towards his right hand, infallibly carrying the eyes of the 

 observers to the same spot, while he is performing the trick with 

 the unobserved left hand. Ordinarily we direct our attention to 

 the point of the field of vision in which an action is going on, and 

 we erroneously follow this rule vifhen we should not. We as 

 mechanically obey the general rule as we close our eyelids when an 

 object threatens us. 



The illusion consists in the observation of the general to the ex- 

 clusion of the special. A high intelligence consists in the command 

 of a wealth of associations, and thus a power of distinguishing be- 

 tween the two. A typical instance is that of the host of persons 

 who religiously record the numbers drawn at the lottery, reasoning, 



that, inasmuch as all numbers have an equal chance of being 

 drawn, numbers not drawn now must have a greater chance of 

 being drawn later on. In all games of chance one hears the same 

 argument. The luck must change : good fortune must be followed 

 by bad, and vice versa. This common error, again, consists in 

 overlooking the particular case ; for while, in many cases, such 

 reasoning would be entirely correct, in the case of the lottery and of 

 games of chance it does not hold, because the numbers are all 

 replaced, the cards newly dealt after each issue, thus making the 

 chances of every lucky event just the same as before. It is a con- 

 fusion of the case in which the ball is returned to the urn with the 

 more frequent cases in which it cannot be returned. Of the same 

 character is the belief in the luckiness or unluckiness of certain 

 players ; in the argument, that, because a person has happened to 

 receive more than a normal share of lucky turns, he has a right to 

 expect the continuance of such luck ; or, again, the fancied relations 

 between the weather and terrestrial events, etc. : in short, in many 

 kinds of superstition. 



More refined examples of the same kind of error can be found in 

 the fields of art and science. When an architect supports a bal- 

 cony upon two slender iron pillars, it does not appear pretty, be- 

 cause of the disproportion between the supports and the object 

 supported. The origin of this judgment is to be traced to the fact 

 that we have comparatively little experience with the strength of 

 iron, and much experience with the weight of stone. In general, 

 the impression of solidity carries with it the sentiment of beauty ; 

 while the use of iron, however convincing the calculations of the 

 architect, does not carry with it this impression. In various forms 

 of art we see the same association between the form and the 

 material used. Our traditions and the experiences of the race thus 

 play a role in our sentiments, and are a factor in the genesis of 

 error. The Greeks built temples of marble in a style derived from 

 times when wood was the building-material. Returning to science, 

 we may examine the famous argument of Zeno for illustration of 

 our main thesis. Achilles cannot overtake the tortoise if the latter 

 is at all ahead of him, because, while Achilles makes up the dis- 

 tance, the turtle has advanced beyond it ; and so on. We get 

 the impression of infinite space by the infinite aggregation of finite 

 spaces, because ordinarily such a sum would be infinite ; but here 

 the spaces tend to the infinitely small, and so their sum to a finite 

 quantity. In spite of the ages of discussion spent over this prob- 

 lem, it still remains a real source of error ; and from this puzzle of 

 Zeno, down to the blind action of a humble animal, one can trace 

 the genesis of error as a faulty application of a general law to a 

 special case ; as the instinctive action of an ingrained nervous ad- 

 justment to an environment different from the normal. 



Abnormal Sense-Associations. — Increased attention has- 

 recently been given to a class of sensory associations of rare occur- 

 rence but extremely interesting. When a certain part of the body 

 is hurt, some persons snnultaneously feel a pain in a distant and 

 disconnected part of the body : to these the name of " synalgia " 

 has been applied. They are idiosyncrasies, and are of various 

 kinds. So, too, there are " synEesthesias," or cases of an irritation 

 in one place causing a sensation in another. Dr. Fromentel brings 

 these into line with the common experience of sneezing in response 

 to a glaring light stimulation. He does not regard this as reflex, 

 but thinks it psychic in character, and due to the irradiation of a 

 disturbance in the cortex of the brain. The explanation ascribing 

 the connection to an anastomosis between various nerves is also re- 

 jected. The peculiar case of hearing colored sounds would also be 

 susceptible to the same explanation. They would be more or less 

 present in all persons, but would only be striking in peculiarly 

 nervous individuals. 



BOOK-REVIEWS. 

 Physical Realism. By THOMAS Case. New York, Longmans, 

 Green, & Co. 8°. 

 This work contains a criticism of philosophical idealism, or sub- 

 jectivism, together with the presentation of a new theory which the 

 author offers in its stead. According to the view of Berkeley and 

 his followers, the external world of material things has no real ex- 

 istence, what we call a body being in fact nothing but a cluster of 



