weights, instead of the 119 that were originally
supposed. These are--

12354 13245 13254
21345 21354 21435

But exception might be taken to two even of these, namely, those
that appear in the third column, where 5 is found in juxtaposition
with 2 in the first case, and 4 with 1 in the second. So great a
difference between two adjacent weights would be almost sure to
attract the notice of the person who was being tested, and make him
dissatisfied with the arrangement. Considering all this, together
with the convenience of carriage and manipulation, I prefer to use
trays, each containing only three weights, the trials being made
three or four times in succession. In each trial there are three
possibilities and only one success, therefore in three trials the
probabilities against uniform success are as 27 to 1, and in four
trials at 81 to 1.

_Values of the Weights_.--After preparatory trials, I adopted 1000
grains as the value of _W_ and 1020 as that of _R_, but I am now
inclined to think that 1010 would have been better. I made the
weights by filling blank cartridges with shot, wool, and wads, so as
to distribute the weight equally, and I closed the cartridges with a
wad, turning the edges over it with the instrument well known to
sportsmen. I wrote the corresponding value of the index of _R_ on
the wad by which each of them was closed, to serve as a register
number. Thus the cartridge whose weight was _WR4_ was marked 4'. The
values were so selected that there should be as few varieties as
possible. There are thirty weights in all, but only ten varieties,
whose Register Numbers are respectively 0, 1, 2, 3, 3-1/2, 4-1/2, 5,
6, 7, 9, 12. The reason of this limitation of varieties was to
enable the weights to be interchanged whenever there became reason
to suspect that the eye had begun to recognise the appearance of any
one of them, and that the judgment might be influenced by that
recognition, and cease to be wholly guided by the sense of weight.

We are so accustomed to deal with concurrent impressions that it is
exceedingly difficult, even with the best intention of good faith,
to ignore the influence of any corroborative impression that may be
present. It is therefore right to take precautions against this
possible cause of inaccuracy. The most perfect way would be to drop
the weights, each in a little bag or sheath of light material, so
that the operatee could not see the weights, w