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moved from the light. He concluded that starch results from the decomposition of carbon-dioxide in chlorophyl under the influence of light. (Adapted from Creighton.)

(d) During the months of October and November, 1907, there was great stringency in the American money market, leading to a general retrenchment in business. It was noticed that the outgoing steamers that left the port of New York in late November and early December had unusually large bookings for steerage passage to Europe.

(e) Tyndall opened twenty-seven sterilized flasks in pure Alpine air and found no signs of putrefaction. He later opened twenty-three in a hay-loft and only two showed no signs of putrefaction after three days. (Adapted from Creighton.)

(f) During a recent trial intended to place responsibility for a railroad wreck, the following facts were submitted in evidence: At the time of the wreck a train of (say) seven cars was drawn by two electrical engines. The controller was set at "series-parallel" (implying about three-quarters full speed). The train left the track in rounding a curve. Later a test was made over the same track by State officials, with a duplicate of the wrecked train, with the controller at series-parallel, and the train did not jump the track. Testimony was introduced proving that the outside rail was double-spiked at the curve during the time intervening between the accident and the official tour of inspection.

(g) Goldscheider showed that perception of movement is mainly due to pressure-sensations from the inner surface of the joints. He had his arm held so that the surfaces of the joints were pressed more together, and found that he could distinguish a smaller movement. (Adapted from Creighton.)

(h) The deeper a person descends into a mine the higher rises the column of mercury in the thermometer. The higher a person ascends a mountain the lower falls the column of mercury in the barometer.

(i) "The bull-frog just from the mud, or from some place of concealment in deep water, is so dark-colored that he is nearly black. Experiments prove that light has much to do with these changes of color; at least, that these changes in color take place with changes in light, when temperature

and moisture conditions remain the same." (Dickerson, The Frog Book, p. 230.)

(j) (Description of the exposure of a spiritualistic séance.) The two females were then seated upon two chairs placed near together, their heels resting on cushions, their lower limbs extended, with the toes elevated and the feet separated from each other. The object in this experiment was to secure a position in which the ligaments of the knee-joints should be made tense and no opportunity offered to make pressure with the foot. We were pretty well satisfied that the displacement of the bones requisite for the sounds could not be effected unless a fulcrum were obtained by resting one foot upon the other or on some resisting body. The company, seated in a semicircle, quietly waited for the 'manifestations' for more than half an hour, but the 'spirits,' generally so noisy, were now dumb. On resuming the usual position on the sofa, the feet resting on the floor, knockings very soon began to be heard. The conclusion seemed clear that the Rochester knockings emanate from the knee-joint." (Quoted by Podmore, Modern Spiritualism, Vol. I, p. 184.)

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(k) "In 1893 Lord Rayleigh undertook to determine the density of nitrogen with all the accuracy of present-day science. To his astonishment, he discovered that nitrogen from the air and nitrogen from chemical compounds did not weigh the same. The difference was small but exasperatingly constant. Out of this curious anomaly arose the discovery of a new and hitherto unsuspected element of the air which had been weighed as nitrogen and considered as nitrogen by all preceding chemists. This new element was named argon and it constituted nearly one per cent. of the air we breathe. Subsequently this 'argon' was discovered to be itself impure, and from it were isolated four other elements: helium, neon, krypton, and xenon." (Duncan, New Knowledge, p. 36.)

CHAPTER XVIII.-THE FALLACIES OF

INDUCTION

115. CHARACTER OF THE FALLACIES OF INDUCTION -We are liable to certain habitual forms of error in pursuing inductive investigations. These forms of error are known as the inductive fallacies. Some of the common errors already met with in deduction will meet us again here. Others are peculiar to induction. They are all psychological in their nature. They are ways in which the human mind is likely to err when it is especially striving to get at the truth. They are incident to the several kinds of functioning of the mind. Some occur in perception, some in the use of the imagination; others in forming judgments of experience, and still others in conception. Accepting the usual classification of the mind's functioning, we may readily distinguish the following great categories of inductive fallacies. I. Errors of perception.

II. Errors of memory.
III. Errors of imagination.
IV. Errors of apperception.
V. Errors of conception.
VI. Errors of judgment.

116. ERRORS OF PERCEPTION.-We are here considering perception employed in the service of science. Perception involves the use of the various senses, especially

those of sight and hearing, and the interpretation of the sense-facts introduced by the senses into the forms of the various objects that make up the material universe. We shall assume that the sense-organs are capable of doing their work of furnishing the sense-data. Then errors of perception will be limited to the use we choose to make of the senses, and particularly of sight, which is most prominent in observation.

The first error of perception arises from failure to take in the entire field of observation. In this way some fact having a vital bearing upon the investigator's problem may be overlooked. It not infrequently happens that some obscure part of the object is ignored, when this part, if noticed, would have caused an entirely different interpretation of the phenomena. Even skilled scientists are sometimes guilty of this error. The only way to guard against it is to cultivate the virtue of patience. It is usually the overhaste of the observer that is responsible for carelessness in this regard. A scientist, eager in the search for facts confirming a theory, is prone to select favorable aspects from the field of observation. If they are found, he hastens on without careful observation of other parts of the field. Among such neglected parts may lie facts that would upset his theory. But the most careful scientists will look over the entire field without slighting any part, making truth, and not the establishment of a pet theory, the goal of their endeavor.

The second error of perception to be noticed is the tendency of the investigator to thrust his own mental states into the objective field. In general one sees what he wants or expects to see. What the psychologists call

expectant attention accounts for many of the strange experiences to which people of undeniable veracity bear witness. Let the mind be charged with an interesting and absorbing idea, and the tendency is to find in our sensations an object corresponding. The fear-haunted lad who has to pass a graveyard late at night is already far on his way to seeing ghosts before he reaches the dreaded spot. This tendency often amounts to an actual sensing of the thing corresponding to the idea. In some cases of mental disease the subjective states take the form of hallucinations that have for their unfortunate victim a veritable sensuous reality. Even under normal conditions we tend to perceive in accordance with the dominant group of ideas lying within the field of consciousness. Now the scientist always brings an organized group of dominant ideas to his problem. Added to this are numerous habits of thought that influence his perceiving. These ideas and habits are essential to all fruitful use of the senses, and yet they may be also a pregnant source of danger. They are necessary because they give his work initiative, energy, and direction. They are dangerous because unless he be constantly on his guard they will bias his observations and vitiate the scientific accuracy of his results. If he comes to his field of observation surcharged with such a group of ideas, he may project them as sense-data into the objective field and take for objective reality what is merely a subjective prepossession. The only way to prevent this kind of error is to test by repeated examinations of the field under investigation whether the supposed facts are really there. The scientist who puts

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