Further details will be treated as they come up in the consideration of the work by groups, into which the experiment naturally falls.

II.  EXPERIMENTAL RESULTS.

1.  The first group of experiments was undertaken to find the direction of the constant error for the 5.0 sec. standard, the extent to which different subjects agree and the effects of practice.  The tests were therefore made with three taps of equal intensity on a single dermal area.  The subject sat in a comfortable position before a table upon which his arm rested.  His hand lay palm down on a felt cushion and the tapping instrument was adjusted immediately over it, in position to stimulate a spot on the back of the finger, just above the nail.  A few tests were given on the first finger and a few on the second alternately throughout the experiments, in order to avoid the numbing effect of continual tapping on one spot.  The records for each of the two fingers were however kept separately and showed no disagreement.

The detailed results for one subject (Mr,) are given in Table I. The first column, under CT, gives the values of the different compared intervals employed.  The next three columns, under S, E and L, give the number of judgments of shorter, equal and longer, respectively.  The fifth column, under W, gives the number of errors for each compared interval, the judgments of equal being divided equally between the categories of longer and shorter.

In all the succeeding discussion the standard interval will be represented by ST, the compared interval by CT. ET is that CT which the subject judges equal to ST.

TABLE I.

      ST=5.0 SEC.  SUBJECT Mr. 60 SERIES.

CT S E L W 4. 58 1 1 1.5 4.5 45 11 4 9.5 5. 32 13 15 21.5 5.5 19 16 25 27 6. 5 4 51 7 6.5 1 2 57 2

We can calculate the value of the average ET if we assume that the distribution of wrong judgments is in general in accordance with the law of error curve.  We see by inspection of the first three columns that this value lies between 5.0 and 5.5, and hence the 32 cases of S for CT 5.0 must be considered correct, or the principle of the error curve will not apply.

The method of computation may be derived in the following way:  If we take the origin so that the maximum of the error curve falls on the Y axis, the equation of the curve becomes

y = ke^{-[gamma] squaredx squared}

and, assuming two points (x_{1} y_{1}) and (x_{2} y_{2}) on the curve, we deduce the formula