Δro and Δru. If two figures stand on a line in the fourth column, the first refers to Δro and the second to Δru. One figure refers not to both together but to each alike. The numbers in parentheses are all mean variations. A dash in parentheses means that the number by which it stands is not an average. In the column headed Δr⁄r, for the sake of brevity values greater than 1⁄2 are indicated by the letter A; values equal to 1⁄2 or less, but nearer to 1⁄2 than to 1⁄3, are indicated by the figure 2; values equal to 1⁄3 or nearer to 1⁄3 than to 1⁄2 or to 1⁄4, by the figure 3; values equal to 1⁄4 or nearer to 1⁄4 than to 1⁄3 or to 1⁄5, by the figure 4; values equal to 1⁄5 or nearer to 1⁄5 than to 1⁄4 or to 1⁄6 by the figure 5; values equal to 1⁄6 or greater, but nearer to 1⁄6 than to 1⁄8, by the figure 6; and values less than 1⁄8, by the letter&bnsp;Z. Every subject sometimes moved the cylinder beyond the standard, and the reading, if taken at all, could be written only as a minus quantity. This crossing of the standard almost never occurred with the fluid-mantle olfactometer, and when it did the error was so easily explained that the reading was not taken. Between November 9 and the time when the liquids were first used, two sets of averages were obtained, the first by excluding and the second by including these negative quantities when they occurred. In Tables IV, V and VI only values representing no negative quantities and differing from averages of the same series with the addition of such quantities by less than 1⁄4 are included in the enumeration. The averages enclosed in square brackets in Table II were found by including minus quantities in the average values of Δro and Δru . From all unbracketed averages, negative quantities are excluded. A dash in square brackets indicates that the corresponding value of Δr is itself a negative quantity.
The effect of some of the disturbing factors which are constant can best be illustrated in connection with this Table. Besides exhaustion, adhesion, and the tendency to judge in terms of hand-movement, which we call for short “the movement-error,” some obstruction of the nasal passages, some slight compensating-smells, such as that of the absorbent cotton used to wipe the inhaling-tube, and some distraction of the attention in manipulating the large instrument, must be taken for granted with all the subjects. Only marked exhaustion is expressly noted in Table II. Another source of error which comes into operation with asafœtida, oil of mace, Russian leather, and all the liquids except coumarine, heliotropine and musk is the escape of odor between the cylinder and the tube. The effect of this circumstance, which was mentioned in Section 2 of Chapter 2, must be to make the value of Δr⁄r too large, because it makes the standard larger than the instrument indicates. If, for example, r on the instrument is 207nbsp;mm., but really is 25 mm., and Δr is found to be 5 mm., then Δr⁄r will be nominally 1⁄4 while really it is really 1⁄5.
As we explained in discussing the disadvantages of the method of just noticeable' differences, the effect of the movement-error is to make the value of Δr⁄r smaller for the larger
