standards, and thus to conceal the operation of Weber's law. If we look now at the values of Δr⁄r in Table II, we shall see at a glance that this variation exists. It should be noted that no variation in the order of the standards will eliminate the movement-error, If the smaller standard is given first and a certain habit of movement acquired, this habit will make Δr⁄r for the larger standard too small. If the habit is acquired in connection with the larger standard, it will make Δr⁄r for the smaller too large. It is true that if the standards were alternated by single determinations, rather than by short series, a habit of movement would be less likely to establish itself, but such a procedure is excessively confusing to the subject in the case of smell, and, moreover, all work done with the smaller standard after the organ is blunted with the larger is more or less unsatisfactory. If the distance between the standards and the stimuli offered as decidedly greater or less were kept not absolutely but relatively equal, the movement-error would be concealed. The fact that these distances cannot be kept absolutely equal, if the stimulus of comparison is to be accepted as such by the subject, is in itself no small confirmation of Weber's law. As a matter of fact, they were kept as pearly equal as possible, both to avoid concealing the movement-error and to minimize exhaustion by strong stimuli. They often varied in the same series as the subject's organ became blunted to all differences and then recovered itself, but in general for a standard of 10 or 15 mm., the difference was made 10 mm. ; for a standard of 20 or 30, 15 ; for a standard of 40 or 50, 20, and for a standard of 60 or 70, 25.
The moving back and forth at the limen is some safeguard against the error, yet the tendency of Δr⁄r to be smaller for the larger standards is apparent in the results of subjects whose attention was good and whose movements were careful. Thus, it is particularly well-marked in the work of Se., who was certainly not inferior to any of our subjects. Moreover, the same tendency showed itself when the different standards were used on different days, and a habit in such nice adjustments could scarcely persist from day to day or week to week with so little practice. If (1) the movement-error is one explanation of the variation, (2) the escape of odorous vapor is in some cases another. The equal though unmeasured increment is a larger fraction of the smaller standard than of the larger. If our standards are 20 and 40 and the increment is 4, while
