hile the ratio between
the weights would not be sensibly changed by the additional weight
of the bags. I keep little bags for this purpose, inside the box
that holds the weights.

_Arrangement of the Weights_.--The weights are placed in sets of
threes, each set in a separate shallow tray, and the trays lie in
two rows in a box. Each tray bears the register-marks of each of the
weights it contains. It is also marked boldly with a Roman numeral
showing the difference between the register-marks of the adjacent
weights. This difference indicates the grade of sensitivity that the
weights in the tray are designed to test. Thus the tray containing
the weights _WR0_, _WR3_, _WR6_ is marked as in Fig. 1, and that
which contains _WR2_, _WR7_, _WR12_ is marked as in Fig. 2.

[Illustration: Fig. 1.]

[Illustration: Fig. 2.]

The following is the arrangement of the trays in the box. The
triplets they contain suffice for ordinary purposes.

|=========================================|
| Just | | |
| perceptible | Grade of | Sequences |
| Ratio. | Sensitivity | of Weights |
|-------------+-------------+-------------|
| 1.020 | I. | 1, 2, 3 |
| 1.030 | I.1/2 | 2, 3-1/2, 5 |
| 1.040 | II. | 3, 5, 7 |
| 1.050 | II.1/2 | 2, 4-1/2, 7 |
| 1.061 | III. | 0, 3, 6 |
| 1.071 | III.1/2 | 0, 3-1/2, 7 |
| 1.082 | IV. | 1, 5, 9 |
| 1.082 | IV.1/2 | 0, 4-1/2, 9 |
| 1.104 | V. | 2, 5, 7 |
| 1.127 | VI. | 0, 6, 12 |
|=========================================|

But it will be observed that sequences of 1/2 can also be obtained,
and again, that it is easy to select doublets of weights for coarser
tests, up to a maximum difference of XII., which may be useful in
cases of morbidly diminished sensitivity.

_Manipulation_.--A tray is taken out, the three weights that it
contains is shuffled by the operator who then passes them on to the
experimenter. The latter sits at ease with his hand in an
unconstrained position, and lifts the weights in turn between his
finger and thumb, the finger pressing against the top, the thumb
against the bottom of the cartridge. Guided by the touch alone, he
arranges them in the tray in what he conceives to be their proper
sequence; he then returns the tray to the operator, who notes the
result, the operator then reshuffl