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28 stronger standard. The subject was always warned of a change in the standard.

Two grounds of objection to the method of just noticeable differences are mentioned by Wundt. They are the haphazard choice of the more intensive stimulus, which may light upon a stimulus unnecessarily large, and thus weary the subject’s attention and sense-organ unnecessarily, and the irregularity and immeasurability of the moving back and forth in the vicinity of the difference-limen,—the “Tatonnieren.” It should be noted, however, that as exhaustion increases during the act of determination, A Δro would always be too large and Δru too small, were it not that adhesion has a precisely opposite effect, which is increased by the time-error. Thus, there is really a rude double cancelling of errors.

The true method of minimal changes involves great practical difficulties if applied to difference-determinations with Zwaardemaker’s olfactometer. On account of the adhesion in the inhaling-tube, either two olfactometers must be used, and both inhaling-tubes cleaned after every comparison of two stimuli, or only such substances must be used as are insoluble in water and do not condense on the inner surface of the inhaling-tube. Zwaardemaker tried the method with vulcanized India-rubber, and believes it to be practicable for this substance. We, too, tried it with the tube of red vulcanized India-rubber sent from Holland, and obtained very satisfactory results. (See Table VIII.)

We also tried a combination of the two methods mentioned. Giving the subject a variable stimulus objectively equal to the standard, we bade him make it subjectively equal,—for it would tend to seem subjectively less from the effect of exhaustion,—and then after pausing to let us take the reading, to make it subjectively just greater than the standard, Then he was directed to make a variable stimulus very appreciably greater, just equal subjectively, Next, after making an objectively equal stimulus subjectively equal, he made it subjectively less, Lastly, he made an appreciably weaker stimulus subjectively equal to the standard. Some of the results obtained by this method are given in Table VII. They are arranged in connection with results obtained for the same subject, substance and standard by the method of just noticeable differences. The uncertainty of a method in which the subject exhausts an already wearied organ by hunting for subjective equality before proceeding to the determination proper, is obvious. Therefore, the two sets of results tally surprisingly well.